Please help---V8 running problems..
Discussion
Hi have posted before but still causing problems.......right, MGB V8 3.5 edelbrock carb. Starts beautifully,ticksover beautifully, but when under load a massive flatspot, engine sounds like it has cut out for 1-2 seconds then picks up and dies again....
I have changed plugs leads coil,float level fine, using a lot of fuel, plugs sooty.
I think either distributor ( anyone else think this) or carb jets too big, although have been assured by a carb expert that this is not the case.
Oil pressure excellent uses no oil or water.
Any other suggestions please........
I have changed plugs leads coil,float level fine, using a lot of fuel, plugs sooty.
I think either distributor ( anyone else think this) or carb jets too big, although have been assured by a carb expert that this is not the case.
Oil pressure excellent uses no oil or water.
Any other suggestions please........
Timing? You might need to play with it a bit because of the carbs etc.
First check the dynamic advance. Set up a timing light and remove the vacuum hose to the dizzy. Rev the engine, the timing should move. If not the centrifugal advance is not working. Now reconnect the hose, and do the same again, the timing should move more then before...also it'll move lots as the engine picks up revs, and then settle back if the engine is held at constant revs, if not the vacuum advance is broken.
(if you can, safely) With the engine running, rotate the dizzy very slowly....the revs will fall, then rise, then fall. You want to aim for the middle of this, i.e. where engine revs are greatest. Now retard the engine a bit. Now check the static timing, if it's miles out (I don't know what's normal for these engine) then you might have an issue, if not drive it very gently and see how it is. The risk here is that the timing is massively advanced and you risk detonation, so you need to be careful to not labour the engine or put it under too much load at first.
These symptoms also sound like they could be caused by a post-carburettor air leak...i.e. a leak in an inlet manifold or a dodgy inlet manifold gasket.
I'm assuming the carbs are in good condition (could it be that when you floor it the carbs don't respond properly? they should richen the mixture significantly, there's a mechanism that does this, it's name escapes me at the moment).
If you still struggle my next step would be to fit a standard carb. to it and see what happens.
First check the dynamic advance. Set up a timing light and remove the vacuum hose to the dizzy. Rev the engine, the timing should move. If not the centrifugal advance is not working. Now reconnect the hose, and do the same again, the timing should move more then before...also it'll move lots as the engine picks up revs, and then settle back if the engine is held at constant revs, if not the vacuum advance is broken.
(if you can, safely) With the engine running, rotate the dizzy very slowly....the revs will fall, then rise, then fall. You want to aim for the middle of this, i.e. where engine revs are greatest. Now retard the engine a bit. Now check the static timing, if it's miles out (I don't know what's normal for these engine) then you might have an issue, if not drive it very gently and see how it is. The risk here is that the timing is massively advanced and you risk detonation, so you need to be careful to not labour the engine or put it under too much load at first.
These symptoms also sound like they could be caused by a post-carburettor air leak...i.e. a leak in an inlet manifold or a dodgy inlet manifold gasket.
I'm assuming the carbs are in good condition (could it be that when you floor it the carbs don't respond properly? they should richen the mixture significantly, there's a mechanism that does this, it's name escapes me at the moment).
If you still struggle my next step would be to fit a standard carb. to it and see what happens.
Edited by varsas on Saturday 11th August 14:13
Sooty plugs mean too much fuel or not burning properly to me.
Try new points and condensor if it has them, condensor problems show up under engine load.
Ignition timing? advance till it pinks under load on the road and then back it off a bit till it doesn't, thats yer best setting as long as the mechanical advance is working ok.
hope that helps
Try new points and condensor if it has them, condensor problems show up under engine load.
Ignition timing? advance till it pinks under load on the road and then back it off a bit till it doesn't, thats yer best setting as long as the mechanical advance is working ok.
hope that helps
Given the choice I would have used a Holley in preference to an Edelbrock carb (which in itself is a re-hashed Carter AFB of the late 60s early 70s) It not that the Holley is better than the Edelbrock ('cos it isn't) its just that the Holley is simpler to tune - the jets etc are easier to source fro people like Real Steel at Uxbridge. Post your problem on Rods'N'Sods - I'm sure someone local to you will help out.
be very careful about changing things like condensors as the old part may be fine and the new part rubbish, rotor arms can also be rubbish too - buy both from somewhere like the Distributor Doctor - http://www.distributordoctor.com/
better still get rid of an old probably well worn but not well maintained (lubed and oiled regularly) dissy for a new fully electronic 123 - this is the guy and if you want he can tune on his rolling road at excellent value - http://www.mgcars.org.uk/peterburgess/
and these people do good quailty HT lead sets - performanceleads - http://www.performanceleads.co.uk/
having said all that it might not be ignition related - I had a B V8 with a Holly and Offy and it used to drop in power and then clear itself as if a turbo was cutting, I took the car to a American carb 'expert', he had the car for a week at his insistance and couldn't find the problem and still wanted paying for some of his time - I then took it to a tuning chap and he was embarassed to take 20 minutes to find the problem and didn't want to charge me a penny
turned out to be a vacuum pipe connected that shouldn't have been, plugged it off and the car run fine
moral of all this get the right parts and go to the right people - going to the right people can be a lot cheaper than changing parts willy-nilly (changing service parts or replacing worn parts is a good idea thouugh, just because a part looks ok and works doesn't mean it's at it's best)
better still get rid of an old probably well worn but not well maintained (lubed and oiled regularly) dissy for a new fully electronic 123 - this is the guy and if you want he can tune on his rolling road at excellent value - http://www.mgcars.org.uk/peterburgess/
and these people do good quailty HT lead sets - performanceleads - http://www.performanceleads.co.uk/
having said all that it might not be ignition related - I had a B V8 with a Holly and Offy and it used to drop in power and then clear itself as if a turbo was cutting, I took the car to a American carb 'expert', he had the car for a week at his insistance and couldn't find the problem and still wanted paying for some of his time - I then took it to a tuning chap and he was embarassed to take 20 minutes to find the problem and didn't want to charge me a penny
turned out to be a vacuum pipe connected that shouldn't have been, plugged it off and the car run fine
moral of all this get the right parts and go to the right people - going to the right people can be a lot cheaper than changing parts willy-nilly (changing service parts or replacing worn parts is a good idea thouugh, just because a part looks ok and works doesn't mean it's at it's best)
roscobbc said:
Given the choice I would have used a Holley in preference to an Edelbrock carb (which in itself is a re-hashed Carter AFB of the late 60s early 70s) It not that the Holley is better than the Edelbrock ('cos it isn't) its just that the Holley is simpler to tune - the jets etc are easier to source fro people like Real Steel at Uxbridge. Post your problem on Rods'N'Sods - I'm sure someone local to you will help out.
I strongly disagree -you can tune Holley main jets easily enough (once you've removed the float bowls), but to change the part throttle fueling you have to start drilling and tapping the body for screw-in air jets, transfer slot restrictors, idle jets etc. With an edelbrock you can change the needle and spring that controls part throttle fueling from the top of the carb without even removing the float bowls. And you can buy a complete kit of needles, springs and jets for $40.00.V10Mike said:
I strongly disagree -you can tune Holley main jets easily enough (once you've removed the float bowls), but to change the part throttle fueling you have to start drilling and tapping the body for screw-in air jets, transfer slot restrictors, idle jets etc. With an edelbrock you can change the needle and spring that controls part throttle fueling from the top of the carb without even removing the float bowls. And you can buy a complete kit of needles, springs and jets for $40.00.
Sorry what I should have said was - theoretically Edelbrock carbs are simpler to tune than Holleys, but oddly there seem to be very few people out there able to do it! - and yes bog stock cheapo Holley carbs will not have replaceable metering blocks, jets and idle bleeds (purchase the higher spec' and generic 'clones' for that!) BUT a Holley is a very simple carb with a very broad operating range and will work more or less straight out of the box.There is an awful lot of information out there on Edelbrock, Holley and even Barry Grant Demon (my preference) carbs and time spent reading up on 'your' carb is never wasted. Personally I found the Edelbrock easier than the Holley but both were put to shame by the Barry Grant Speed Demon, for ease of reading up and for putting the information into practice. But thats just me, the American forums do battle regularly on which carb is best, the main thing is to get your carb working properly.
Getting back to the OP's problems... I am assuming that his ignition system has been checked through and that has narrowed the problem to the carb, as a previous poster alluded to 90% of bad running problems are down to ignition. On the Edelbrock website there are volumes of guidance on setting up and problem solving your carb you will find some excellent articles here, http://www.corvetteclub.org.uk/kb.php?mode=cat&...
By a guy called Lars, he was GM's carb and ignition guru, he has a way with words and makes tuning clear and simple to understand, hope this helps.
G
Getting back to the OP's problems... I am assuming that his ignition system has been checked through and that has narrowed the problem to the carb, as a previous poster alluded to 90% of bad running problems are down to ignition. On the Edelbrock website there are volumes of guidance on setting up and problem solving your carb you will find some excellent articles here, http://www.corvetteclub.org.uk/kb.php?mode=cat&...
By a guy called Lars, he was GM's carb and ignition guru, he has a way with words and makes tuning clear and simple to understand, hope this helps.
G
Edited by VetteG on Monday 13th August 12:07
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