University Motors Limited, Ada, Michigan

University Motors Limited

Goldstar Products

Technical Assistance

6490 East Fulton
Ada, Michigan 49301
616.682.0800

MGB Tuning

I don't know if you remember but during the B Maintenance symposium I mentioned I was about to tune an engine I rebuilt for my 72 GT. Weather has improved to where I can run it with the garage door open so I am trying to get it done.
I have set the ignition pretty well but here is the problem. The engine rebuild included a new VP-11 APT cam, I had to overbore to .060, and a ported and polished standard late head, opening up the ports a good deal. I have needed ether to start it initially when cold so far. Once warm it runs way too fast, about 2100 rpm at idle with the choke off and throttle screws backed out full. If I lift a carb (standard HIFs) piston it dies out nearly all the way. That tells me the carbs are too lean. Looking in the throat of the carbs the jets are maybe 1/16ths or less down from the shoulder in the carb intake. If I richen the carbs, it should speed up more. I'm guessing that with the increased volume flowing through the vacuum in the intake is lifting the carb pistons too much and drawing more fuel. It seems to me that the only solution is to change needles to something that allows less fuel at idle. Is my logic wrong?

I've driven it around the block and it seems strong, no hesitation or pinging on acceleration. Thanks for any recommendations you can give.

You've probably already worked through this (despite the turn in the weather -- there's still snow on the ground here) -- but here are some hints.

I always open the initial cam specs for run in -- better too loose than too tight.

Rev the engine right up to 4000 or so and set the timing at 32 BTDC at max advance with the vacuum disconnected. By 4000 the distributor has usually opened all the way. Then let it idle down and re-connect the vacuum -- if you check it again at idle, it wouldn't be uncommon to find it at 25-40 BTDC because of the vacuum.

Get that idle DOWN -- there is either a mechanical reason the idle is too high, or there is an air leak. You can find the air leaks with spray carb cleaner -- or you can listen to the carbs to discover which one is draughting more than the other. If the engine doesn't have enough air, it will slow down and kill. Timing and mixture will not cause a fast idle.

The jets are probably close to being in the right spot -- but after you get it idling at 800-1000, then lift the pistons, just as the workshop manual suggests, and judge the change in rpm. The engine idles rich, so when you lift the piston the rpm will rise about 50, then fall off.

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