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MG MGB Technical - She doesn't like 60 plus

Had the first run out yesterday,even though the garden is still covered in snow. I had the engine rebuilt about this time last year and spent the summer, what there was of it, running it in and basically keeping around 3500 rpm (60mph).
Towards the end of the season I started to wind her up a bit and noticed she really didn't like accelerating beyond 60. She would start hesitating slightly until I eased off on the throttle and then it seemed to slowly pick up. Up to 60 she's fine. So yesterday I tried hoofing it a bit and she was up to 65 mph with a struggle but that's as fast as I could go due to the local speed limit. I haven't been on the local motorway yet, but wondered if anybody has any ideas. All new electrics last year.
Thanks
Ken
Ken Martin

Fuel starvation (pull the pipe off and check the flow, probably 1 pint in a minute would be OK, you'd need to check pump specs but a problem might be obvious)and retarded timing (is the centrifugal advance working freely?) would be my first checks Ken. The spark plugs might give a clue. Rich.
Rich

Ken, it sounds like you have a timing issue. The further advanced your timing is, the less high-rpm power you will have. If your cam was not degreed in, it could be retarded 5 degrees, causing half of the problem. Adjusting the ignition timing is the other half of the equation. What is your timing set at, and at what idle rpm?

Jeff Schlemmer

Ken; Two SU's? Is engine built to stock specifications or is it modified? Ignition timing? Was the camshaft dialed in when the engine was rebuilt? If two SU's, engine is modified and you have stock metering needles you may need to use different needles with a richer/thinner mid section. AAA needles are used by some of us in place of OE spring loaded needles.

Clifton
Clifton Gordon

Ok, I had a new fuel pump installed last year due to fuel starvation, so I don't think it's that. Also installed a new see through fuel filter so there's no dirt and new NGK plugs yesterday. I also had the carbs cleaned and rebuilt while the engine was out with a basic rebuild package which I assume had standard needles. Twin SU's with K&N filters by the way. They were then set up by the same guy when fitted back on the engine. There were no modifications done in the rebuild which was done by a machine shop, except to bore out +30. new pots etc. However, the engineer did say he had reground the cam. Could he have ground too much off the lobes? My engine knowledge is limited to a degree, so I'm not sure what you mean by "was the cam dialed in". Timing wise, I believe it would be set up as per the book for an 18GK engine i.e. 14 deg before TDC. So if the cam wasn't "dialed in" how do I determine what the correct timing should be?
Thanks
Ken
Ken Martin

Ok, so here's another one for you all. When I was out yesterday, I thought I could smell hot rubber, execpt I couldn't smell anything when I got back home. However, the rear RHS wheel was feeling warm. So I've just jacked it up and the RHS wheel doesn't rotate as freely as the LHS, plus, whereas when I rotate the RHS, the LHS rotates in the opposite direction, as it should right, but when I rotate the LHS wheel the RHS stays still. I thought initialy that a brake cylinder may have seized over the winter, but now I'm leaning towards a partialy seized wheel bearing. Any offers?
Ken Martin

Ken I should have asked if the camshaft was degreed with a degree wheel and dial indicator or set by the timing marks. I suppose you would have to get that information from the engine builder. A reground cam is ok but it could be off a little from the factory marks. It shouldn't be off enough to keep it from turning at high speeds, but could hurt overall performance. The reground cam would have the correct lobe dimensions so that shouldn't be the problem. The K&N filters may require that you adjust the SU's richer or change needles. The next time you take it out pull the choke out a little when you want to increase speed and see if that helps. If the choke helps, turn the jet adjusting nuts down 2 flats if you have HS4's, if you have HIF4's turn each jet adjusting screw in clockwise about a half turn. Try another test run to see if the results are better.

I would think your RHS brake has rust in the drum or the cylinder is binding, it could also be adjusted too tight.

Clifton
Clifton Gordon

Yes, sounds like the RH brake is adjusted a little tight Ken. If you have the spanner jack up the wheel, release the handbrake and tighten the adjuster til the wheel locks then back it off 2 clicks = 1/2 turn and check the wheel rotates without binding - it may touch a little but that's not a problem. Rich.
Rich

Hi,

If you had a new fuel pump installed last year and you have not driven the car much since, I would check to see if the holes in the banjo bolts are lined up with the holes in the fuel line. I had this problem once, the car would lean out as the rpms increased. Poor fuel delivery caused by banjo bolts misalignment at the fuel pump union. FWIW Alyn
Alyn

Thanks Clifton, I was starting to wonder if I would have to replace the cam, not a nice thought. I have the HS4 carbs, '71 B, so I'll try pulling the choke a little over 60 and see if that helps and then try adjusting the carbs a bit richer, although the plug tips are a nice sandy colour.
As a matter of interest, where can I get richer needles and assuming I have standard at the moment, what would be the reference? Moss only seem to show standard in their catalogue.
Re the rear brakes, I will be having them checked shortly, so we'll see what the problem is. Your probably right with the rust though.

Thanks

Ken
Ken Martin

Joe Curto, http://www.joecurtoinc.com has every needle you could want, and will be able to help you figure out about what needle you need based on the engine build specs.


Paul K

If you had your cam reground to a different profile to stock, you might need to change the ignition timing.
dave

The fuel pump should deliver 2.4 pints/minute (US pints), although anything around 2 pints /minute will work fine. see my article SU fuel pumps 101 at: http://www.custompistols.com/cars/articles/dd_su_fuel_pumps_101.htm
Even though the fuel pump is new, you could still have something else in the fuel system that is causing a problem. Any flexible hoses can develop a split on the inside, creating a flap that will shut off fuel flow above a certain level. Another possible problem could be a fuel tank that is not venting properly. You don't indicate the year of your car, but the early MGBs vented through the filler cap and the later ones through the charcoal canister. Try driving the car without the fuel filler cap on and see if the problem goes away.

Alyn - If your banjo bolts have to be lined up with holes in line with the hose outlet, there is something wrong with the banjo fittings you are using. The banjo fitting should have a grove around the inside perimeter to form a channel for the fuel to flow to the outlet hole without having to line up the hole in the bolt. If this is not the case, you may have a fitting that has been packed full of dirt or the fitting was manufactured incorrectly.
Good luck - Dave
David DuBois

Ken, if you have a 25D distributor, which should have been paired with the 18GK engine, your timing should be more like 8 degrees before TDC, not 14. Although like dave said if you had a reground cam you might want to check with your engine builder to see what your ignition timing should be.
Mark

Ken,

Let's try some basics on timing. You're quoting numbers that don't mean a whole lot. Timing is stated in two ways--static or dynamic. Static is for initial set-up. Dynamic is what we should be dealing with here. Dynamic is always stated in TWO terms--degrees of advance AND engine rpm. If you could give us the dynamic timing setting on your fairly stock engine, the fault could be found or timing eliminated as an issue. It should be 20 BTDC @ 900 rpm. If you look at the third post from the top, this is what Jeff S. is asking for.

Now don't think that because a "professional" shop did the work, all is correct. A friend's car just received a professional tune-up and I found timing out 15 degrees! One thing you could do is simply slacken the distributor retaining clamp and move the distributor about 3/4 inch clockwise. Retighen and go for a test drive. Do this only if you don't own a timing gun. If you do own a gun, is it the dial/adjustable type or a standard one and in general, are you familiar with its usage? hth

Paul
Paul Hanley

Ok, I increased the mixture on each carb about ½ flat. She definately ticked over better and I didn't have to hold the choke out for so long. Then I took her out on the motorway/highway and booted it. Came up to 60 in fairly quick time, slowed off but kept climbing and seemed to go through a barrier around 65. After that she climbed up to 70 and sat there quite nicely for about 5 miles. Only thing I found was the vacuum gauge that I fitted was showing max vacuum, even though I was cruising. Could have been a lead foot though.
I didn't set the original timing by the way. I left that to the guy that set up the carbs. I just quoted the figure from Haynes.
Also the RHS rear wheel didn't seem warm anymore so maybe it was a bit of rust on the drum as Clifton said. So I will take it back on the motorway/Highway when the weather is warmer, it was a bit cool with the top down and see how it runs on a longer trip.
Thanks every one, you were a great help as always.
Ken
Ken Martin

Ken,

From Haynes manual--misfire at high speeds, point gap too small. One other thing to double check.

And again, don't go with the "guy that set up the carbs". Consider a recheck of the timing to eliminate it as posibility. When I said to rotate distributor 3/4 inch, I meant move the tip of the vacuum advance unit by that amount. This will increase your idle speed, so you may need to then back off the idle screws to get to 900 rpm for timing gun check and final slow idle. Is you vacuum advance unit hooked up and working. To check, remove hose from rear carb, suck on the end and verify continuous suction-holding with the tip of your tongue.

Cheers,

Paul
Paul Hanley

Hi DAve,
Looking back I don't think that the connections that were in my car were stock. The fuel pump certainly wasn't. As is my habit with things that don't work as advertised, I remove them and chuck them into the trash bin. Got a lot of old parts in there now. I replaced the connections from the fuel pump to the hoses with brass fittings and hose clamps. God why do they persist in using pre WW1 technology on these little pots. I really don't think that you could call my MGB an MG anymore. Looks like a stock MGB but so much has been discarded in the interests of reliability .... Runs great now and I do not have any of the same old recurring problems that are mentioned on this bbs everyday. Almost every post I read, brings to mind the phrase "been there -done that" Now if I can get that 3.4 efi v6,new front suspension -Hoyle style, and some sort of irs....
Alyn

Thanks Paul, I do intend to check everything that has been suggested. I'm just glad it doesn't seem to be too serious, as in a new cam or whatever.
Thanks again guys. Incidentally, you can see the beast in question on:
http://photos.yahoo.com/wildejokers
Ken
Ken Martin

This thread was discussed between 27/03/2005 and 28/03/2005

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