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MG MGB Technical - Accelerator

Hi,

I have a problem whereby I can start the engine, it runs ok ish..but when I depress the accelerator the engine dies. If I was to depress very very lightly (as in feather light!) I can make the revs rise.
Could this be the distributor?


Thanks,

Andrew
Andrew

Just a stab in the dark, but do you have any oil in your dashpots?

Otherwise, I'd check all the tune-up things: Dwell, timing, valve clearance and fuel mixture. I'd also check for vacuum leaks, as this is a common symptom of really lean mixture.

Matt Kulka

Matt,

Thanks for the quick reply, I have recently stripped down the carbs and reset the timing as best I can as the car hasn't moved for 10 years. The vavle clearances are fine and I believe the dwell is ok as well. What is the best starting point for carbs - is it screw them fully clockwise then undo 2 full turns? (HIF as the MGB is 1980 model).

Thanks,

Andrew
Andrew

With the HIF's I think it's to get them level with the top of the carb and then two turns. If it's the mixture adjustment. What kind of choke are you using?
J Arthurs

If you don’t know where to start tuning your motor I would suggest you look in the archives there is plenty of info in there. One thread that is going on at present, which may be of use to you is the one called white smoke, and a few more Qs. I have detailed two web pages that gives details on how to start a car that has been sitting for some time. If a car has been stood for as long as 10 years have you checked things like piston rings, they could be rusted in position, what about the oil have you changed that?
J. Arthur’s answer is correct.
I would suggest you do a stating timing rather than look at the dwell given that the car does not seem to run correctly yet.
Cecil Kimber

I am using a manual choke which I believe is standard.

Cecil, I have looked through the 'White smoke pages...'
I have been through a similar process to get my engine to run ....stripped and cleaned the carbs, new fuel pump, new battery, new points, new plugs, new plug leads, new coil, and new oil....it now starts but I am having trouble getting my head round adjusting the carbs ( I have a haynes manual but it seems to jump between the earlier model carbs abnd the later). I belive my timing is roughly there (6 degrees BTC) and the points gap (dwell?) is 13 thou.
The engine runs fine with the choke out...does this mean the carbs mixture is too lean? also when I when I depress the accelerator the engine dies. If I was to depress very very lightly (as in feather light!) I can make the revs rise. - I was wondering whether this could be the vacuum advance on the dizzy?

Does this make sense?

any help greatly aprreciated

thanks,

Andrew
Andrew

Andrew,
I would agree with you that the Haynes manual seems to be left wanting at times. I have a few web sites I can suggests as a good back up, the first one is:
http://www.mgbexperience.com/
Loads of information on this one.
This page may also help… http://www.mgbexperience.com/service/tips/fuel.html
This one has a very good description on how to set up twin SU’s
http://www.mgbexperience.com/service/su-tune.html
This next site is also good, sometimes the site owner help answers queries posted here. http://www.mgbexperience.com/service/su-tune.html
You have to click on spanners, on the left hand side then SU_carbs at the top. Again another full explanation on how to undertake the set-up of the carbs.

Moving on to timing of the ignition; it does vary between 5 and 10 deg, depending on the engine. I would assume you have a later engine, unless it has been changed. The timing marks are not that precise so setting it up exactly can be a little hard. The dwell should be 60 deg and the gap is 0.014 to 0.016 “. The dwell is measured with a tool that measures the total time the points are open during a revolution of the distributor.
I doubt if your problem extends from the failure of the vacuum advance. I have a car, which does not have a vacuum unit.
Cecil Kimber

Cecil,

Thanks for that, I will look through the web pages and see if I can work from them and I will let you know what occurs.
I am correct in thinking that the timing marks on the later models are ..as you look down onto the makrs the top mark is TDC then the next one down is 5 degrees then 10 then 15?

Thanks

Andrew
Andrew

Andrew
Your correct with the markings, like I said it is a little hard to set up at 7 deg.
I may be teaching you to suck eggs but someone will benefit from this bit of information. Paint the timing marks and the area around the mark on the pulley with Tipex or white paint. You can see the marks easily.
I have added many web page printouts to my Haynes manual!
Let us know how you get on.
Cecil Kimber

This thread was discussed between 21/06/2002 and 22/06/2002

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.