MGB No power

[Simon Hughes]

Hi guys, making progress with my 77 MGB such that she's driveable but it feels like she's got no power. Unfortunately I've never driven an MGB before so have no reference point but it doesn't feel right. Assuming I am correct, what should I be checking for first? I have a single zenith carb, damper oil is good but I've heard these can be an issue. She starts well but won't hold idle. Any suggestions? Thanks. Simon

 

[drooartz]

Take a look for vacuum leaks.

Otherwise, make sure you've gone through the normal tune-up process: ignition, timing, valves, fuel delivery, maybe a compression test.

 

[Simon Hughes]

The car has had the emission systems removed by a previous owner e.g. no air pump, but I have no idea if it was done correctly. Is there anywhere on this site where I could find a description of what it should look like e.g. which hoses go where, which ones blocked, etc? Thanks.

 

[Blackjokr]

uh you relaize the HP is very little... hehehehe <|;^P

 

[Stewart]

check the diaphragm on the carb for holes, make sure it has the stock air filter setup if not it will not run right and if you do need to adjust the needle make sure you have the right tool or you will tear the diaphragm in the carb. The zs carb really kills the horse power however it should feel ok around town and rather anemic at speed though the car should go well into the 90's

 

[aeronca65t]

I'd agree with Drew that vacuum leaks may be the cause. Also, check ignition timing at idle (you may need a second person to hold the engine running while you do this). And then rev the engine and make sure the timing marks "move" (indicating the timing advance is working). An MGB isn't a rocket, but it's fairly light and should feel somewhat peppy, especially in the lower gears.

 

[billspohn]

Single carb MGB engines and power don't go together.

Make sure you don't have any of the issues mentioned and then just enjoy what you have.

 

[CZ_Dave]

How to find a vacuum leak. 1, get a bottle of propane with a burner valve mounted. 2, turn on burner without igniting and with the engine running, wave around the carb and vacuum hoses. when you hear a change in the tone of the motor as it is running, that is where your vacuum leak is.

 

[PAUL161]

The car has had the emission systems removed by a previous owner e.g. no air pump, but I have no idea if it was done correctly. Is there anywhere on this site where I could find a description of what it should look like e.g. which hoses go where, which ones blocked, etc? Thanks.

Simon, here's what the system looks like, basically the same on all models with slight variations. In place and working, to many's disbelief, it takes nothing away from the performance of the engine as it merely blows air into the exhaust system starting at the head. Removal does no harm to the engine and performance is not affected. Plugs are installed in the head where the air distribution manifold connected and a shorter fan belt is incorporated. The Zeneth carb is a decent carb if working correctly but requires a little more maintenance that an SU. The diaphragm in them can get pin holes in them and create problems due to age. Rebuild it if that's the problem. To change over to SUs can get expensive as it usually leads to other modifications. My suggestion, fix what you have, except the lower horse power and enjoy the car as others have done in the past. Happy motoring! PJ

 

[ecurie_ecosse]

I agree with Paul. Find the fault (vacuum leak?) and keep driving. I am driving with a Zenith carb and find it runs okay. Of course, all the emission stuff has been removed,and that is an improvement. Stuart.