Stumped Again

[MikeH]

Hi All, I've been fighting an acceleration problem. I feel my timing is right, fuel a little to rich, and I can't get her to rev above 3,000 on the road. It's like it hits a wall and no more go. Probably something I've overlooked, normally it's something simple that you know is right, but its not. For what its worth, I kinda know my way around LBC engines; just rebuilt my TR, and have always been able to get her dialed in.Thanks for any hints, Mike

71 MGB OD and Wires
63 TR4 Surrey Top

 

[jackq]

Ate lunch with a buddy today..he has a 77 B with o/d. Sonedays he takes it out and the rpms build and the thing screams..90mph+...shut it off, come back ten minutes later and it will do 3100 rpm max??? Acts like it has a rev limiter. next week we're tearing into it but maybe someone can shed some light...for both of us.

 

[tony barnhill]

What type distributors/ignition do both of them have?

 

[Banjo]

Check the mechanical advance mechanism in the dizzy.
any chance there is a blockage in the exhaust?
vacuume leak?

 

[MikeH]

Tony and Banjo, I've got a 25D distributor and points. Dizzy advance is ok, maybe a little weak. As for exhaust blockage, seems to have good pressure at exhaust tips (Monza Free Flow). Mike

71 MGB OD & Wires
63 TR4 Surrey Top

 

[tony barnhill]

I'm guessing its in the dizzy itself.

 

[piman]

Hello Mike,

if the ignition side is OK, yoiu could have a fuel restriction, partially blocked filter etc. Does the gear you are in change anything, e.g. will it rev higher in first?
It might be worth doing a colour check on the plugs, run the car onload as fast as possible, cut the engine then check.

Alec

 

[Guinn]

If it runs smoothly at 3000 it is probably not a fuel problem. Better to check the dizzy first.

Guinn

 

[MikeH]

OK, I've changed distributors, readjusted carbs, same problem. Should mention that it revs fine with no load, just setting in the carport, but as sone as you drive no go. Thanks, Mike

71 MGB OD & Wires
63 TR4 Surrey Top

 

[tony barnhill]

Do you get a lot of change when you turn the distributor as far forward as possible? Or is it basically the same but idling rough?

 

[MikeH]

Here's where I'm at, done for the day before I do something really stupid, like run her into a tree. Tony dizzy doesn't change things, gone as far advanced as I can and have the engine still run. Now it's set at 20 degress before TDC at 1000 RPM as per the general data for a GH engine. Carbs are rich. Pulled the exhaust apart, and no obstructions. I can get a nice idle, but engine hesitates and stumbles when I accelerate. Tops out at 3000 and will do no more. Thanks for all the suggestions, I've tried to check them all. Mike

71 MGB OD & Wires ( May be looking for a new home. )
63 TR4 Sutrrey Top

 

[tony barnhill]

If its doing it at any dizzy 'location' from real retarded to advanced, then its in the dizzy...

...however, your "carbs are rich" statement is puzzling - are they only rich when dizzy is advanced?

 

[David_DuBois]

Mike - Take a look at my fuel delivery troubleshooting guide at: https://www.custompistols.com/cars/dave/ddFuelDeliveryTroubleshooting.htm
particularly the portion on volume of fuel being pumped. You should be getting right around 2 pints per minute of fuel being delivered tot he crburetors.
Good luck,