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MG MGB Technical - '76 MGB GT rolling resto lacking poke+only 20MPG!!

Hi everyone,

I've had my B for about six months as a rolling resto, she had a full years ticket when I bought her so mechanically she's fine really, however I get 20 or less to the gallon (UK), which when you pay 1.249 a litre it ain't funny.

The Lumenition ignition that was there when I bought her failed somewhat so I went to a Lucas 45D, cured some emmisions problems (Have a friend with a garage and analyser), but the MPG is still 20 at best, average for the time I've had her is 15. Just coming up 100k so is it worth a top end rebuild and clean up? The ignition is as good as it will get, points, cap, leads etc all as good as can be, the plugs foul up some but do get hot enough to self clean, still sooty though, so again does this point to general engine wear and bad combustion? I've even poured water through the carbs when hot etc to try and help decoke as the chambers and piston face are quite oily and grubby (Checked using a probe through the spark plug hole) Carbs set up okay, both sucking the same, both lifting pins allow some increase in rpm followed by a fall and they both are actuated at the same time by the throttle linkage. Would a grade hotter plug help with the carbon build up? Currently on Denso w20ep-u plugs.

Despite all these changes, ignition system being the biggest, there still seems to be a lack of grunt, even allowing for 33 years of outdating (Which doesn't concern me) I still feel there is more life to be had from her.

Any and all suggestions welcome.

Regards,

Will
W Harrison

Perhaps your ignition timing needs advancing - that can make quite a difference to MPG. Somehow my timing was "off" last year ... I was able to advance it by 6 degrees and got an extra 5mpg.
Geoff Everitt

Further to what Geoff has said: My 1970 GT seemed to be down on power with lack lustre throttle response. The vacuum advance fittings had gone hard and brittle and had cracked = no vac advance.

Bought some new rubber end fittings for the vac advance line and now she's running beautifully.

John
J Tait

Greater London - 20 mpg-sooty plugs...what sort of runs are you doing?

You could try V Power (whats it called now?) @ , if you are convinced that the ign advance is ok. I find this helps
Michael Beswick

octane booster responses Gents,

The Vac advance is new bioth ends so it is working and the diapraghm moves freely in the unit as well, though I know it can make a big difference. The timing was re-done at the garage I believe, I could only static time it when I put the new dizzy in, I wil check it though. Runs are mostly 5-15 miles ata timne, either pleasure driving on a and b roads or some in town around traffic.

I've read others experience with plugs fouling when idling alot or in traffic, which makes sense, but even on longer runs I still get low mpgs, I've looked for leaks too, nothing doing, though the SU's could probably do with a service, there may be a leaking gasket in there somewhere.

As for the higher octane fuels, yes its
W Harrison

I get mid to high 30s (and not pussy-footing around) so yours is well down, although 5 mile runs are pretty short, I can imagine you spend half of that with the choke partially out (apart from the last few days).

These days timing can really only be set (on high compression cars at least) by seeing just how high you can get without pinking at any combination of throttle, revs or load, and on some eras of engine that is going to be less than the manufacturers original specs, despite the use of 97/99/99 octane fuel. Personally I found no improvement with the boosted Castrol Valvemaster, so only use the unboosted.

Parts being new is no guarantee of them working correctly, they must be tested. As far as vacuum advance goes remove the vacuum pipe from the carb or inlet manifold (in this latter case seal the manifold port) and suck hard on the end of the pipe. Not only should you see the points plate turn clockwise, but sealing the end of the pipe with your tongue it should stay there, only springing back when you break the seal. With the engine running there should be a noticeable increase in idle revs when sucking on the pipe. Note that with manifold vacuum the idle will slow with the vacuum disconnected and the port sealed, and may even stall.

For centrifugal advance with the cap off you should be able to twist the rotor arm anti-clockwise, against spring pressure, which should be felt initially as a light spring then a heavy spring, and released slowly it should go all the way back with no loose slop. That's ideally, in practice older distributors will have a little slop as the springs lose tension.

What's the condition of the plugs, leads, cap, rotor and points? If these are rough economy and performance will suffer. What's the dwell i.e. gap? What's the timing?

When all ignition aspects are correct have you correctly set up the carbs for air-flow and mixture balance?

Is the choke functioning correctly? Are the needles or jets worn?

With all that correct, different driving styles can have a huge effect on economy.
Paul Hunt 2010

Thanks Paul,

I checked the vac already as it was a used unit and it appears sound, the centrifugal advance seems to also be in order with little wear in the dizzy, the cap is good with no hairlines, the rotor is new which solved a previous problem when the plugs fouled so much it wouldn't even fire let alone run (Now resolved to the point stated in the first post), leads were renewed just before I bought the car and have good connections all round, points look almost new, no pitting and the spark at the points with the cap off and cranked is not massive so condenser failure isn't a problem by the look of it. Dwell was set as per the manual, timing was adjusted at the garage I believe but I will check and see what it was set to.

Moving over to the fuel side after all other aspects seemed okay: I checked and adjusted both carbs for flow rate and balanced them by ear, throttle linkage correct and mixture set using lifting pins. K&N filters of the same size as the originals (i.e. not pancakes) with plate mounted on top not in the saucepans. There's oil in the dashpots and the floats will raise and lower freely when the engine is running or not, which is the closest to checking the needles I can get. The choke only comes on when you tell it and I haven't used the choke at all for probably four or five of the six months I've owned the car, operating temp comes up okay and I drive like the proverbial granny (No offence to any reading) - overdrive where appropriate, coasting everywhere, gauging traffic up to where the horizon is so I don't break too much and avoiding using much gas unless needing to clear junction etc, on countryside runs I'll push it more but then there is the lack of response and the knowledge I'm still only getting 20 mpg...

Just as a side point when the timing was advanced as much as it would go with the Lumenition system before performance did go up but the economy went down to 15...not sure exactly what this indicates though.

Many thanks for all the replies, many hands...

Will
W Harrison

Will,

Really only a guess, but I do need choke in our winters here, so wondering about the need in yours. You say you haven't used choke in months - can you be running rich? Really rich? Has me wondering about the state of the combustion chambers you described and the degree of carbon fouling of your plugs. Possibly and/also plug gap and temperature rating.

Regards
Roger
Roger T

Thanks Roger,

I'm assuming its running rich or not burning correctly, however setting the carbs up as described in all manuals/forums/university motors etc and checking the mixture with the lifting pins indicates a correct if slightly lean mixture. If I back out the HIF screws to lean it out any more then the performance will go and in my previous experience the economy will still be similarly low.

I wondered about the grade of plug as mentioned in the first post, they are getting hot enough to self clean but still sooty around the rest of the plug.

Thanks for the input!

Will
W Harrison

Yes, sooty, if you mean on the flat of the thread end, is probably the norm with modern fuel. What is the gap set to?

With NGK BP6ES plugs I opened mine out to 0.030 from the manual 0.025 with noticable improvement in running and soot depositing. They showed a littlt 'too' white on the porcelan for my liking however, so I have taken them back to 0.028 - expected colouring, a little soot but still running better than at the start. the slightly longer (higher charge) spark seems to burn the fuel more completely. to the extent that a burble in the exhaust has ceased - must have been burning fuel in the exhaust to an extent.

I'm still fiddling to the extent that I have less clean burn in cylinder 2, which I know to have some wear. I'll run a few hundred miles more and check again - if the same signs my plan is to try a hotter plug in that spot.

Paul mentioned needle and seat wear above?

Regards
Roger
Roger T

Get to basics. Do a compression check. 20 mpg is so bad, something is really wrong.
Art Pearse

No choke in the UK? Mine need choke all year round, but obviously for less time in summer. Given everything you have said there is something very wrong somewhere. You haven't got someone siphoning fuel out at night, have you?
Paul Hunt 2010

Yes I agree, a compression test is overdue here. This car has covered 100k miles and may well be due for a head job if not more. So I think this would be a very good place to start then at least we know what we are working with.
Iain MacKintosh

Thanks for the replies,

I don't need choke to start or smooth out the idle unless its been very cold, as when I first bought her. Checked the plug gap and all at .6 to .7 mm, now all .7 (Manual suggests up to .09 for a 45d4), points at .04 mm as I remember (Manual - up to .43).

I'll try and get some compression readings this week, I've suspected more than ignition and fuel delivery for some time, hopefully the readings will give a better indication as to what's happening. She's coming off the road next Monday night so I'll try and get as much info up as possible before then.

Just a side point, may be related, when the weather gets hot like today, and underbonnet temps soar too, the temp gauge reads a little under mid way between C and H, but the revs go right up at idle between 1300 and even 1500 by the end of the run, normally 8-900. Any connection or just worn SU's? Only happens when it gets HOT (Rare in the UK I know)

If there is anyone half inching the fuel I'll be linking the HT circuit to the fuel tank via a tremble switch, there's normally only fumes left in the tank at the best of times anyway...goodbye blue sky.

Any further insights much appreciated gents, she's a tired old lady at the moment but I don't want to quit just because of the running costs, she deserves a bit better I think.

W Harrison

Regarding Above: points were at .40 mm and manual says up to .40, and spark plug suggests up to 0.9 mm. My eyes and typing need improving...
W Harrison

I'd love to get a reliable 20 mpg. And my 72B starts perfectly, idles after warm at 500-600 rpm, no weak spots on acceleration in any gear at any rpm range. Can race up hills, etc. But I'm in the teens for mileage.

I've been slowly going up 1 flat at a time to lean things out, up 3-4 flats so far with little if any affect to performance or mileage.

I haven't done the test yet, where I suck and hold pressure on the vacuum advance hose to see how plate is moving and/or holding.

At one time I did the 4000+ rpm and 30+ degree setting of timing, but cannot recall if I'm still utilizing that approach or if I returned to setting timing at idle.

I've heard others say they gave up trying to improve their mileage and I've heard others in the mid-30s and up for mileage.

Maybe there are a ton of bricks in the trunk I'm not aware of.
R.W Anderson

Rememeber when we talk about MPG there is quite a big difference between UK MPG and US MPG. I see Will did specify UK in his origial message.

http://en.wikipedia.org/wiki/Miles_per_gallon

20 UK MPG is about 16.7 US MPG.

We should all use litres per 100km :)

Out of interest is it US or UK gallons in Canada?

Simon

Simon Jansen

It MUST be extremely rich. Any MGB I've had experience of would not start from cold, summer or winter, without full choke. OK in summer the control is pushed in pretty quickly, but cold start without it? Never - you would flatten the battery first. And your plugs should be a chocolate colour, not all black and sooty. I have no experience of the HIF carb, but they must be set much too rich. Paul does get very good mpg with his car - I would expect high twenties (UK gallons) round town, with mid thirties on a motorway trip.
Mike Howlett

HIF have tiny O rings in the cold start mechanism; when they die, the "choke" is effectively ON, and you get all the symptoms described. Since the choke effect diminishes with RPM, leaning out will help a bit at/near idle but kill performance and eventually the engine at higher throttle openings.
Rebuild the carbs, with special attention to the cold start.

FRM
Fletcher R Millmore

Further to my above:
There are two holes in the floor of the HIF carb bore, just engine side from the jet. One is a vent to the float bowl, the other is the cold start discharge port. Start the engine and run it up to 3-4000 rpm, while looking down the throat with a good light. If fuel can be seen issuing from the port, then the O rings are perished or omitted; or the cold start is ON or wrongly assembled.

I first discovered this on a car that unaccountably had little screws installed in the discharge ports, couldn't be started cold. When I took them out I got just what all of you with rich HIFs are reporting.

The other possibility is that the floats have gas in them, causing high fuel levels in the bowls - common on HIF.

FRM
Fletcher R Millmore

Simon - in Canada, 1 gallon = 4.54 litres, so UK gallon.

I have a 73B with rebuilt carbs, rebuilt engine with cam reground to fast road profile, CR about 9:1, Head ported and polished, pertronix with distributor rebuilt by Jeff Schlemmer. My city MPG is about 17 mpg, which is about 16.6 litres per 100 km.

I have advanced the timing to the point where I start to get some pinging, then backed it off about a degree. I think I hit about 30 degrees advance at about 3000 rpm. I use mid-grade gas to further avoid pinging.

I need to use the choke every time I start the car, and need to leave it out longer in the cooler months.

I am not sure if my poor mileage is due to the modifications I made to the engine when it was rebuilt, or if the carbs are set a bit rich. I have tried leaning mine out but performance starts to suffer. As it is right now, my car runs great and has plenty of power.

A frustrating observation I have had with all 3 MGBS I have owned (2 72's and a 73, so all HIFs) is that when the engine gets real warm, the idle speed wants to drop off while sitting at a light, to the point where it will stall if I don't blip the throttle to keep it from stalling. This has happened before and after my carb rebuild. Anyone know a fix for this?

Will, do you have a 76? The photo posted looks like a late-sixties B at the latest to me.
Erick Vesterback

Hmm, thanks Fletcher I'll do the tests you described, not heard about that before.

Hi Erick, yes she's a '76 (R plate), PO did the CB conversion, ride height is the same as the '76 though (For now anyway.)

Doing some work on the car today so will report back on what I find.

Thanks Gents for the continuing replies and suggestions, much appreciated.
W Harrison

Urban driving, 20 to 25 is not bad. My journeys are shared almost 50 50 between stage two engined 76 MGB and an audi tt. The audi pod tells me I average 23, and I put about the same amount of fuel each month in both.
The previous audi owner according to the pod managed 8.8mpg: commuting between salons no doubt.
c cummins

Quick update,

I've advanced the ignition by "ear" (road testing) to the point that performance is quite reasonable, not snappy but not bad, (Probably now a question of fuel/air as much as timing), the plugs are more chocolate than black and for more of their area. MPG still low though. I've ordered a compression tester and am considering a colortune as the lifting pins method doesn't seem to be overly accurate, especially if there is wear int eh engine.

CT should be here Monday so I'll post the figures then.

I was wondering about putting a DLB 105 on at some point (either ballasted 6v or unballasted 12v and appropriate wiring modifications) to see if this helped with the burn, anyone any experience with these? Some say it helped with economy, others say only helped with starting (after plug re-gap/grading).

Between salons ey? At least you know what crossed our minds... ;)

W Harrison

Plugs should be paler than that. Lifting pin method should work, once you have dialled your ear in, as it is as much a dynamic method as colourtune or timing light i.e. taking into account real world factors.

You've never said what year your car is apart from a reference to 33 years, 1977?. If so it should already have a 6v coil and ballast resistance in the harness as all rubber bumper cars did. The reason for the change was to give improved starting in marginal conditions aka poorly maintained car. Ordinarily a 12v coil will only be getting 10v at best during cranking, and it can easily be 9v and lower. The ballasted system puts up to 10v on a 6v coil during cranking, so giving a spark *boost* instead of a reduction, and theoretically the battery could drop to 6v and you would still be getting a 'normal' spark ... if the engine was still capable of being turned over at that battery voltage. Changing to a 12v coil and bypassing the ballast on a rubber bumper car is obviously a retrograde step. Going the other way on an originally chrome bumper car would theoretically be an improvement, but would need the later starter or a wiring modification to get the cranking boost. Whatever, this only affects starting, it will have no effect on running as 12v on a 12v coil produces the same spark as 6v on a 6v coil, and it certainly won't affect mpg on a car where everything is operating as it should. There is a theory that 6v coils need less reflux time as they have lower inductance, which may be relevant on a multi-cylinder high-revving engine, which doesn't include out 5200rpm plodders.

The bottom line is that these cars should start and run very well with the original equipment ... *if* they are correctly maintained with no actual defects.
Paul Hunt 2010

Hi, thanks paul, I was refering to the ballasted 6v verion of the dlb105 and the neccesity to change the wiring should I get the normal dlb 105 at 12v. In terms of spark it is supposed to produce up to 40kv compared with the 102 coil I have at the momment. Mind you if it 'aint broke don't fix it...

W Harrison

And she's a '76, August 18th, as it says in the title of this thread. At least this year has more of the mods that makes some things easier - front chasis member ready for v8, 6v coil system and associated starting benefits as you say, anti roll bars changes etc, hence why I'm intrested in getting better things, its just getting them out of the rust and low mileage.
W Harrison

Fair enough on the title, I don't read it every time, just click on it.

The actual spark is governed by the plug gap, you won't get any more HT *voltage* from one over another, and the ballasted system is better for starting. A DLB105 is a 12v sport coil, but if there were a 6v version then you wouldn't need to change the wiring, it would be 'plug compatible', but I'm not aware of one. If there were one I'm pretty sure it would have a different number. Whilst a sports coil might deliver a bit more spark energy it's not going to make any difference on the road, over a correctly working standard coil, they are for high-performance applications and the unwary. It's not going to make one jot of difference to your mpg, unless the existing coil is faulty. If you mean *internal* ballast that's irrelevant and just causes confusion, a coil is either a 12v coil or a 6v. If a 12v coil is made up of 3 ohms (for example) of primary winding or just 1.5 ohms plus 1.5 ohms of resistance makes no difference to how you use it. Your real problem is not needing choke to start it. Forgive the implied but not intended insult but have you owned cars of this era before? I can imagine younger drivers would never have come across point ignition, carbs and choke before. As one who has owned many cars of this era over 40+ years I have *never* had one that would start without choke even in summer, when everything was working as it should.
Paul Hunt 2010

Hi Paul, sorry mate, no insult intended or received, forums don't communicate intentions very well do they? I am young but I try and read a lot and am even more grateful when people such as yourself are willing to pass on their valuable experience, trying to find ANYone who knows what a set of points are is increasingly difficult!

The fact there isn't a computer anywhere in sight confuses most mechanics who look under the bonnet. On thoughts about the choke, currently the revs have gone up at idle to 2000...no changes have I made to anything, still drives fine but obviously something has gone wrong, and previous comments about the cold start mechanism inside the carbs may be spot on. Perhaps a carb rebuild? Is it worth doing the throttle shaft and butterfly valves at the same time? I've come across two kits, one with the above and one without, the difference in price is about 20, the throttle shaft t the moment doesn't have any endfloat etc so appears okay for leaks etc.

I once found a dlb105 that was sold in 12v and 6v, I was surprised as I thought they only did the 12v, again, limited difference in performance, just compatibility with wiring, trying to find the site again is proving difficult though. Never mind, I'll post the compression figures when the tester arrives, hopefully Tuesday night.

Many thanks for your replies, genuinely appreciated.

Regards,

Will
W Harrison

Here's the site, how I forgot it was MOSS I don't know. It could be the part number IS different to a 105, but that is what they sell...mind you I hear the website isn't always as accurate as it could be.

http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=12627
W Harrison

Boy they do like to confuse, don't they! The 12v version is numbered TT2981, and the 6v TT29812 i.e. with a '12' on the end! It should be made clear that an external ballast resistance is required with the 6v item. With only one coil listed but two different types available the part number on the actual item, if visible, isn't going to apply to both. Searches indicate that DLB110 is the 6v version. This is just one of the reasons why when fitting a new coil one should *always* measure the primary resistance and make sure it is suitable for your ignition system by measuring that as well, regardless of any labelling on coil or box, let alone what the supplier might say. Standard 12v coils are about 3 ohms, 12v Sport about 2.4 ohms. Standard 6v coils are about 1.5 ohms, so I'm guessing the 6v Sport will be about 1.2 ohms.

Oddly they have two pages entitled Lucas Sports Coils, one with just the 12v item and the other with both. Doesn't give one much confidence.

That's the 2nd 'mythical' thing from Moss Europe that has come to my attention in the last few days, the other is what I thought were the long NLA quick-release static seat-belt fastenings to the tonneau panel.
Paul Hunt 2010

Well gents I've run the compression tests,not good news!!

1 - 75 psi
2 - 95 psi
3 - 95 psi
4 - 100 psi

I'm surprised it even runs!! I also found that the choke operating linkage was binding, loosened it off and now need some choke to start...figures, why neither I nor the PO saw this I don't know. Carbs need some attention again now, still considering the rebuild kit.

Any suggestions on the compression figures? I've checked the gauge and it read correctly against a known air source, however I can't believe they are this low.

All thoughts appreciated!

Will

W Harrison

Were all plugs out? Was the throttle wedged wide open? Should be in both cases. Compression should be 160 psi or better for a UK high-compression engine, those figures are so low I suspect an error somewhere, otherwise it wouldn't pull the skin off a rice-pudding. Even low-compression was 130 psi.
Paul Hunt 2010

My thoughts too so I tried again after my last post and did a wet test with choke all the way out and throttle wide open, all plugs out, engine warmed up prior, wet they were 1 - 90, 2 - 120, 3 - 120, - 4 125. Dry even with the throttle open etc they were still low, the oil helped (only a table spoon) but would diagnose rings?

I'll try and borrow another tester and see what those figures are like.

Also found the rear carb is venting fuel like BP from the overflow, which I think is a recent thing so I'll investigate as I get time.

Thanks for the reply Paul,

Regards,

Will
W Harrison

That disparity between dry and wet does indicate rings, but the consistent disparity between cylinders indicates other issues as well such as valves.

For the carb overflow I assume HIFs which is a shame as they have to be removed to get at the float and valve, and then the bottom cover O-ring has to be replaced. Worth a try is to disconnect the fuel pump (white wires where the main harness joins the rear harness near the fusebox) and run the engine till the carbs empty, then reconnect the pump. The resulting rush of fuel through the now wide-open float valve may dislodge any debris. If that doesn't work then it's carbs off.
Paul Hunt 2010

I tested the compression on my roadster last year and got a reading of around 140 to 120. On removing and stripping the engine, I was surprised to see how worn the bores were and had a broken piston ring even though it seemed to use no oil and performed quite reasonably.
Your figures are lower than mine were, so I would suspect an engine that needed some serious attention.
All the best.
Trevor Harvey

Hi,

Finally got the compression tester, here's the new readings:

1 - 125 psi
2 - 165 psi
3 - 165 psi
4 - 175 psi

Introducing a little oil into number 1 didn't bring the figures up which I believe refers to a problem with the valves not the rings. Any thoughts?

Inbetween times I have pulled the carbs, the throttle shafts have worn, or the bushes,so I'm investigating parts at the moment, and an engineer friend of mine can assist with the reaming if necessary.

Thanks for any and all replies!

Regards,

Will
W Harrison

No increase with oil does indeed indicate a valve problem, but you should be able to hear this as a regular additional beat in either the exhaust or the intake. First spannering check would be to check the valve clearances. I'm surprised it runs that badly in performance and economy terms if 'all' that is wrong is that one cylinder down.
PaulH Solihull

Thanks Paul!

I did the valves clearances as well a few weeks ago, all were a little too big. I went over them again today after the new readings and they appear to have stayed put , though I did tweak one or two. It may be nothing but I thought that #1 inlet and exhaust valves didn't seem to move or compress rather as much as the others, especially compared to #4 cylinders (Rule of nines: 1 closed adjust 8), is this worn pushrods or the camshaft on its way out would you think? I haven't the space to pull the engine down at the moment to find out so any diagnostics you can think of would be much appreciated.

Thanks for the quick response, really appreciated.

Regards,

Will
W Harrison

Before I decided 100% to go down the V8 route I had a 'lame' straight 4 much as yours was. No power, poor MPG and trying to tune to problem away never really worked.

When I took my car off the road (which it still is...) I naturally opened the engine up to see what was going on.

The exhaust valves in 2 and 3 leaked, and almost all the valves had nearly 1/4 inch of carbon buildup, sometimes on both sides! The already marignal flow rate of the standard head must have been next to nothing...

My HIFs leaked and ran 'funny'. All bushings and shafts worn, a float ruptured and full of fuel and the needles worn to a strange shape in the bowls. One of the choke orings was a bit tatty, so I suspect leakage through there too.

My piston rings seemed ok, if well used, and the bores were all servicable. Cam was worn but not badly and the timing chain wasn't too slack.

My GT was a 77 and had done 95k or so, so it's in every way possible similar things are happening with yours.

If you have access to a cylinder leak tester, then that will save you some spannering diagnosis by confirming exactly where the leaks are.
Rebuild your carbs. They're easy to work on as long as you're clean and methodical, do one at a time so you don't mix parts up! Get the biggest rebuild kit you can, no matter the cost it's cheaper than new carbs and then you're sure they'll be really good when finished.
Clean and put some petrolium jelly on all electrical connections pertaining to the ignition, even before I took mine off the road, doing this helped a lot to get over some of the lack of performance (I had a high resistance on the live to coil, so it wasn't even getting 6v...)

Lastly, since I didn't see anyone else answer this (maybe I missed it) someone asked why the HIFs change idle speed under differing weather conditions. The jets are mounted on a flexable bi-mettalic strip that distorts accoring to temperature to try and compensate the mixture somewhat automatically. It's perhaps more annoying than it is good...
RoadWarrior

Will,

Chances are it's nothing more problematical that a sticking valve. This may be caused by a bent valve stem or valve guide damage, but the most probably cause will be carbon build-up. I would try using an upper-head cleaner that you can buy in a local car accessory store. If that doesn't work then you'll need to strip the head down, which is not a hugely complex job on the B. Wear in the pushrod or cam will be taken up by the valve adjustment screw.

If you try the de-coking additive take the car out into the wilds where you will not upset the neighbours - it will smoke like a good-un as it burns off!
Mike

If you have a sticking valve you should be able to see this by clipping an adjustable timing light onto a plug lead, then pointing the light at each valve in turn and twiddling the adjuster. In a dark garage when on the appropriate valve you can 'freeze' the valve in any position from fully up to fully down. But a sticking valve, like a burnt valve, should be audible in the exhaust or intake. Removing each plug lead in turn will also tell you the cylinder, and hence the actual valve.
PaulH Solihull

Hi gents, thanks for the responses!!

A sticking valve would explain the poor compression on #1, if I can get hold of a timing light again I'll check the valve with it, thanks Peter, after I rebuild the carbs, hopefully next week, I'll try the engine with some valve cleaner and see if there's any difference, if not as you say they aren't too big a job to take apart. As for the exhaust note, there is a regular blip, not sure how best to describe it but could be a valve, I'll check it out though.

Thanks for the info about your engine strip too, could well be the case here, as I said before I'll spend a tenner on valve cleaner and see if it helps and consider a head rebuild, maybe some port and polishing too - although there's lots of information around I know it isn't easy to do a good port and polish yourself first time without wrecking your head, if its good in the first place. Has anyone any thoughts or experience of DIY P+P's? I guess you pay your money to have it done correctly for a reason, never mind the work, just being accurate.

Thanks again gents,

Will
W Harrison

This thread was discussed between 24/05/2010 and 31/07/2010

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