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MG Midget and Sprite Technical - newly built 1380cc tuning dilema

Dear Community;

I’m two years+ into a full restoration on a ‘74 (U.S. Market) chrome bumper MG midget. The project is very near completion, looking great, drawing many a wave and smile while on the road (just over 900 miles on the engine) but suffering from a lack of power when attempting to accelerate from a stop on even a mild hill, or goosing it in second from around 10 to 15 mph after slowing for traffic. On a hill from a stop, I’ll e-brake on, clutch in, slip it into first and goose it to 4000+. As soon as I release the e-brake and clutch out at high RPMs, the engine will loose power. I have to keep clutching in, revving gas and nursing the car on as the clutch heats up and traffic builds behind me. Once I’m moving at sustained speed at 3500+ RPMs It seems fine. On a local freeway grade, the car will not pull over 60MPH at 3500RPMs. The engine was represented as the shop’s best build, and said to deliver 116 HP and 135ft lbs of torque. I’m I expecting too much from the this 7k+ USD build?

The engine was built by an experienced Mini specialist in Costa Mesa, California, taken up to a 1380cc with a Calver ST performance head (35.7 X 29.5), and what I was told would be a fast street cam (listed as a MIN003 254/266-.358 lift). The carbs are stock SU HS2 1 1/4” rebuilt by the shop that did the engine. The needles are identified as N6 #6. The rear end is a 3.7 from a later model, the exhaust is maniflow LCB header into a free flo 1 5/8" straight pipe and can.

I’ve calibrated the jets, lifting of the dashpots to zero the jets flush with the chamber floor, then dropping the front jet 11 flats (just under two full turns) and the rear 10 for a slightly rich tune. The engine starts well, idles with a few hiccups but fairly smooth at around 800RPMs, and seems to take the gas well with a typical SU acceleration curve. The plugs are NGK BPR8ES (colder than the 6ES plugs initially in the build) gapped at .035. The distributor is an Aldon performance Yellow with a mechanical advance. I’ve done nothing to the timing, but suspect the problem may lie there. The mechanic has set the TDC with strobe at 6 degrees before, down from 10 on the initial (very rich) break-in tune.

The number two and three plugs are sooty black, the one and four are relatively clean.

I’m about take the car back to the shop that built the engine (sixty+ miles each way) for a second attempt at a final tune. The mechanic is difficult at best. What could the problem be? Some have suggested the timing gears may be off a tooth or more. How would I determine that without pulling the cover? Suggestions?

Thanks,
Christopher


C.L. Howell

well...a 1380 is a big engine,

It makes me wonder if the cam didnt get timed correctly, according to vizard you cant just throw the cam in and line up the marks as that can lead to as much as 24 degrees out, Unfortantly I loaned my vizard book out just 2 hours ago, but the A-series has got to to be dead on when it comes to timing the came ...on a pure stock there is like 4 degrees of play, but on high performance its like 1 degree, and thats to the retard side to account for chain and sproket wear....the problem with this theroy is this was built by an expericed shop, so they "should" know better, but I once had a so caled BMC mechanic put in all new gaskets as I was working none stop and was trying to get the car ready for paint and they "forgot to tighten BEYOND finger tighten the whole engine" plenty in the archives, so the fact that they adjusted on factory marks instead of with Dial indicator at top dead center dosnt surprise me.

the other issue,,,,and this is just a guess but Im wondering if yuo need to upgrade to duel HS4 carbs, After all increasing the displacement to 1380 is alot, 107cc or a 13% increase in engine volume is alot esp. for these little engine

definatly keep us posted

Prop
Prop

Before you take that 120 mile drive Id call the engine builder and ask how he "timed the cam" and ask for a detailed account in how he did it, ask what type of timeing chain set up...is it set up with off set keys (if so what degrees used) or did you have a fully adjustable venier chain and sproket set, installed....before you call him get visards book, and read up on that chapter, if not avialable, you might be able to get a book on high performance 4 bangers engines from your local barns and noble and they will no doulbt explain the procedure for "timing a cam" with a dial indictaor at TDC beyound factory marks, and you will get a good idea of whats involved...remember as vizard makes note the cam marks cant be trusted, vary few are correct. and you dont have any leeway, they must be dead on.

Prop
Prop

Check the basics and don't make any changes without noting what you did carefully, and change in performance.

In order, I'd:

- check compressions to make sure there's no problem with rings, valves, gasket

- set plugs to 25 thou to make sure HT voltage isn't too high to cause breakdown other than plugs

- note current static ign timimg and set to 7 deg static

- check dashpots rise smoothly, and drop fully down when let go

... and so on; keep it simple and methodical.

A
Anthony Cutler

Chris your English leaves a little to be desired but hopefully we can almost understand what you mean.

Fiurst things first, as you rightly say what should you realistically expect from this engine?

Looking at your spec, like every other engine builder they have exagerated what its power should be, I think with a relatively mild cam as that 116 BHP is a little optomistic, perhaps with a 286 that kind of figure would be achieved but hey 100BHP should occur easily.

The engine should idle at 8 or 900 relatively smoothly and should work well from low revs.

As stated above (not by Prop) simply set the basics correctly first. Not knowing the characteristics of the dissy it is foolish to try and set it at low revs. You must set it up at 4.5KRPM with vac disconnected and an advance figure of no more than 34 degrees BTDC

The SUs should be tuned as per thousands of books on the subject and then you can report the following.

Does the car accelerate easily in 3rd gear to 6000RPM plus?
Driving along at 1500 RPM in 4th gear push the throttle down hard and does the car pick up speed, slowly at first is normal then accelerating agressively from 2500 RPM onwards?

Prop for your information The bigger the engine capacity the less effect timing the cam will have. Indeed the use of offset keys to alter the cam timing a degree or 2 is vague to say the least. 2 degrees of cam timing either way would have very little effect and would be almost unmeasurable.
Robert (Bob) Midget Turbo

Christopher,

That torque figure of 135ft-lbs has to be incorrect for a normally aspirated engine. The standard 1275 HC is quoted as 72 ft-lbs, a quick look at Vizard shows a 1400 at around 88ft-lbs peak, 135 would be typical of a 1.8 - 2 litre engine.
David Billington

but to conclude

there is something wrong your engine is not producing near the power that was promised.

if you have waranty on it go back and let them solve it
if you don't have waranty the don't go to the punters who screwed up the first time!

to put it in perspective my engine made a RR proven 84 BHP and it pulled in al gears way over 6000rpm even in the hils
so there definitifly is something wrong
Onno Könemann

Robert (Bob) Midget Turbo, England,

I think your idea the basics are alittle out ...I think is a stretch, if they are...they are at at polar oppisites to, none the less I agree it should be looked at 1st just to concel that part out, but the issues he is decribing is ALOT more then a dissy being 2-3 degree out

as to camshaft timing, Im simply relaying what vizard was describing, yes the bigger the engine the less it accuracy is needed, but, if it is a camshaft timing issue, Im guessing its going to be out way more then 3-4 degrees based on what desribing, also, My personal opinion on the idle If he is running at 8- 900 Rpms, that may well be where his problem is, as the lobes on the camshaft Id think would be well worn off,,,Id think 1200 to 1300 rpm would be a better idle with a performance cam and roller rockers

My personal hope is that its a broad range of many things needing massive adjustment, I just cant imagine how badly it would have to be set-up to have the car run as chris is decribing

I do take issue with your opening statmeent as to chris grasp of english, I for one love the attenion I get from my grammer and spelling inconsistancys, and incourage it, as it gives me a scence of brotherhood in our BBS family, just like arie and his fasination with sheep. but I cant see a problem with chris grasph of english personally (granted Its me saying that,,lol) but I havnt seen chris here on our BBS before. and dont know anything about him. Attacking him for a core part of his being Is ... Well I personally think its over the top, even if I was aware of his grammer faux-paws, I wouldnt call him out on it. At least until I had some scence that he would enjoy the chiding...then its gloves off, lets have some fun.

Back to what chris wrote that gives me Pause to Thought...

>>>>suffering from a lack of power when attempting to accelerate from a stop on even a mild hill, or goosing it in second from around 10 to 15 mph after slowing for traffic. On a hill from a stop, I’ll e-brake on, clutch in, slip it into first and goose it to 4000+. As soon as I release the e-brake and clutch out at high RPMs, the engine will loose power. I have to keep clutching in, revving gas and nursing the car on as the clutch heats up and traffic builds behind me. Once I’m moving at sustained speed at 3500+ RPMs It seems fine. <<<<<<


Prop
Prop

Sorry some clarification needed

I wrote >>>>>>My personal hope is that its a broad range of many things needing massive adjustment, I just cant imagine how badly it would have to be set-up to have the car run as chris is decribing<<<<<<<<<


Meaning a bunch of little things, like dissy, points, carb A/F, choke, valve clearances... things that are easy and inexpensive to sort....And Not something like a mis-alined camshaft (engine out or almost out fix)
Prop

The cam sounds really mild.

Having had an engine with a cam mistimed by a full 10 degrees I can't remember how well it peformed but it certainly did close to 100mph and would rev to 5000rpm plus (car has a 5 speed).

I don't think your problem really sounds like cam timing though of course you haven't checked it.

I'd go with Bob and say it sounds like the ign timing is way off the mark (although that wasn't exactly what he said).

For anyone interested have a look at Tom Colby's Speedwell web site (forget the URL) where he has a modified front timing cover that allows a section to be removed so the cam timing can be varied (assuming vernier gear fitted) without having to pull the engine.

Daniel Thirteen-Twelve

Don't know about the rest of the stuff, but i would think that the carbs are to small and the inlet manifold needs to be of a larger diameter.
A weber 45 DCOE perhaps or an 1.75"su.
brian s

Prop I was not comparing Chris' use of english grammar to yours!! I was saying that using terminology like ""goosing it"" means absolutely nothing to me and I suspect many others on these boards. Perhaps it is cool language in CAL but on an international BBS just does not convey meaning!
Secondly Here we have someone who has spent an arm and a leg on an engine and it is not right. The last thing he needs is for you to tell him about the need for offset keys and vernier timing gear. I tried in vain to explain to you that it is simply not necesary to time a cam with offset keys or a vernier.

As to whether you agree with my assessment of basics is neither here nor there to me I suppose it is a judgement that Chris will need to make. Whether he checks the basics as I described or whether he buys a copy of Visard and retimes his cam with an offset key!

Daniel and others I am unsure of how well the engine is performing at present so I was merely suggesting as is common practice that the basics should be set and then tested in the manner described.
Robert (Bob) Midget Turbo

I think I'd check the TDC mark that this "Mini Mechanic" is timing against.
Trevor Jessie

Robert (Bob) Midget Turbo, England


Your last posting makes valid common scence, I can live with that. COOL.

Prop
Prop

My opinion on this engine is it sounds like a total mismatch of parts and has been built with a magor lack of comunication between engine 'builder'??? and client. A Calver Head with Cooper S valves is maybe a bit restrictive for a 1380, and a pair of 1 1/4" SUs won't help the power output either. After saying all that, I would hope that the engine would perform far better than you describe....!

I too agree with the above, Ignition timing and perhaps the distributor would be a good starting point.

Is it possible Christopher, that you could give us the FULL spec of your $7k engine.....? Is it an all steel bottom end?

Mark.
M T Boldry

Our 1380 had a Kent 266 initially and on Aldon's rolling road produced exactly 100 bhp at the flyhweel, (84 bhp wheels) and >=100 lbf ft torque from 2,500 to 5,000 rpm.

Same head (36/29 valves, ~10:1 CR), same dizzy (Aldon yellow), but with BPR7ES plugs, 1.5 rockers, HIF6 on Titan manifold and 2" exhaust.

The timing was around 15° BTDC @ 1,000 rpm (vac disconnected) to give the usual 33/34° maximum advance.

The 8ES plugs seem to too 'cold', the carbs too small and assuming the TDC mark is correct, the timing very retarded. I would get the TDC mark checked and reset the timing as Bob/Daniel have suggested, then set the carbs to give the correct idle mixture (which is all you can do without a rolling road). I think before spending money on a rolling road session, I would replace the carbs with either an HIF6/44 or 2 x HS4 (1.5") - either should be on a decent manifold.

Finally what air filters are you using?

Having spent $7k I would have hoped that the builder would take more interest, which is a bit of a worry?
Richard Wale

Christopher,

I will echo the advice to check the TDC mark.

Also, I would consider marking the current distributor location and try a bit of timing by ear. I bought an MGB one time, and found that the ignition timing was about 20 degrees off of where it was supposed to be. When I corrected it, it barely ran at all. I found that a custom grind cam had been installed using the standard timing marks. I suppose the off ignition timing helped to compensate for the bad cam timing. Another symptom of the cam being off was that the cranking compression was 105 psi on a fresh rebuild from a supposedly reputable shop. I moved the cam two teeth and the compression came up to 145. So, running a compression test may be worthwhile.

In the pic, I can't quite make out what is going on with the crankcase ventilation. I don't see a PCV valve at the intake manifold end, and the hose looks misaligned where it attaches. Maybe you have a large vacuum leak. It's been a while since I looked, but I thought that it normally attached on the other side of the heat shield.

Was anything done to alter the balance tube in the intake manifold? On mine, which uses a cut down MGB manifold, someone told me it would run better if I blocked the balance tube. I tried it and the result was similar to removing one of the spark plug wires.

Regarding the comments about the small carburetors, wouldn't it run just fine with those until the RPMs got to the point where the engine was limited by air flow?

Charley
C R Huff

Chris - my 1380 is very sensitive to timing. I have recently rebuilt mine, and at the moment I am struggling a little with the timing. Mine pinks very slightly at 3500rpm, or if I retard it a smidge, it is flat as a fart off the line. I am going to try a different brand of super unleaded, if that doesn't work, the dizzy will have to come off for interal mods.
Shawn

Christopher

Sounds like a fuel distribution problem, does the engine sound the same if you pull off 1 or try 4 plug lead, conversly does it sound the same with 2 or 3 off at idle? Siamesed port heads are notorious for causing distribution problems, usually associated with weber carbs. If the manifold has been polished or if the bridge where the brass fuel jet supplies fuel via the needle and piston has been smoothed you could exhibit the problems you mention. I have spent hours trying to make a series run 'right' only to fail cos someone has been at the carb or manifold.

Peter
peter burgess

Chris, apart from the perfomance problem which is very well adressed sofar and will be I saw this: " I’ll e-brake on, clutch in, slip it into first and goose it to 4000+. "

If the original Midget or Sprite Gearbox is in it wont like this. First gear is a bit weak compared to the other gears. Also the playing with the clutch to adress the power isnt realy the way to go.

Eventually the power problem will be solved and I guess the engine rebuilder is responsible for that, at 7k$ for the job he has to. But even when the engine is ok be carefull with the first gear and only apply the power the car can put on the street. Otherwise you will be rebuilding your gearbox soon and changing halfshafts earlier.

If you want big power and release it with a bang then consider the 5 speed conversions.
That way you can go back to a 3.9 diff and have a much smoother release of power but also a bullit proof box.

Bas
Bas Timmermans

This thread was discussed between 02/05/2009 and 03/05/2009

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