MGB & GT Forum

I commented earlier how I replaced the incorrect resonator on my B with a straight pipe and how much more power it has. Problem now is that It's much harder to start, especially when warm. I can shut it off and try and restart it in 30 min and it's cranking like hasn't been started in months. Cold starts harder too, but they always took a bit more time. It used to fire right up when warm, but not anymore.

I rebuilt and adjusted the carb under the old system and now I'm wondering if I need to revisit the basic adjustments?

Difficulty in starting can be attributed to several possibilities, While I cannot think of any exhaust-related causes there are other checks you could consider to eliminate the problem.
Here are several areas that could be causing your car to be difficult to start. It’s worth examining each of them in the quest to find your problem:

Out of Fuel, or a fuel restriction caused by heat-related issues - Carburettors could be the problem

Fuel Pressure - MG's are renowned for fuel pump issues

Dead or Dying Battery - Sounds unlikely but certainly worth checking

Electrical System - All sorts of gremlins cause oddball problems, not always easy to find

Sensors - If you have electronic ignition for example

Spark Plugs - Always a good thing to check as these look perfect but fail under heat-related issues

Faulty Starter - Probably not in your case, but still worth eliminating

Charging issues - A weak battery is always worth considering

Cold Temperatures - This speaks for itself, but again worth considering

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What year MGB? What carburetor are you using? Do you still have the charcoal canisters?
Pictures of the engine bay would help.

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1978 MGB
When diagnosing issues related to running and stalling, always check to see if you have gas in the tank first.

If that old resonator was partially plugged up it could very well affect fuel mixture. Pieces from defective catalytic converter ending up in the resonator? Just a possibility.

Looking at your older posts, you have the Zenith Stromberg carb.
For grins, the next time it won’t restart after it’s been running, disconnect the line from the carb to the charcoal canisters and try starting again. If it starts you need to refresh the charcoal canisters.

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1978 MGB
When diagnosing issues related to running and stalling, always check to see if you have gas in the tank first.

I would start by "going back to where you previously were" when there is a problem after maintenance.

All interesting avenues to explore, but none explains why changing the exhaust would change things. That's what has me scratching my head. The old resonator appeared to create significant back pressure and I adjusted the mixture as best I could under those conditions. I'm wondering if mixture being off would create a warm hard to start issue.

Sometimes things aren’t related at all. Chance circumstances.

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1978 MGB
When diagnosing issues related to running and stalling, always check to see if you have gas in the tank first.

Occam's razor I get it, but it's still suspicious the coincidental change.

I'd try resetting the carb since you state that you had difficulty setting the mixture with the old exhaust causing so much back pressure. Shouldn't take but a few minutes, won't cost anything, and even if it doesn't solve the issue you can at least rule that out.

I'd also yank the plugs and clean them in case an overly rich mixture has fouled them. Again, costs nothing and quick and easy.

I always like to check the easiest stuff first. Often times, that's where the problem lies anyway.



Edited 1 time(s). Last edit at 2024-04-20 06:35 PM by JoeReed.

To add to the confusion just discovered that my heater valve is badly leaking. And I tried blocking the hose from the charcoal canister and was surprised to find car was extremely hard to start, backfiring and wouldn't idle or keep running. I guess I need to figure out how that system works, as it won't run without it.

If your heater valve is leaking, check your distributor.


GMc

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2008 - 2022

If you were following my advise, I never said to block it, just disconnect and see if it will start.
It’s a diagnostic procedure.

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1978 MGB
When diagnosing issues related to running and stalling, always check to see if you have gas in the tank first.

I misread it of forgot that point. Still, I'm surprised as usually out put from a canister goes into intake manifold somewhere via vacuum and Plugging the inlet would work. As I said I'll have to figure out that system. After I replace the heater valve.

Nathaniel The leaking heater valve might very well damaged or shorted your distributor cap and wires and is possibly what is causing all of the hard starting problems.