The 'E' Type Forum

4.2 E Type
Could anyone help an engine acceleration problem.
Engine has had a complete rebuild since last run.
The first time starting engine starts and runs about 300 to 400rpm.
The problem I have is when the throttle is pressed there is zero pick up of engine rpm.
Checked butterfly valves on carburettors which are opening fine
Also checked the dampers on the carburettors are moving freely and that there is fuel to them.
Have checked ignition timing on cylinder 1 nearest screen and rotor arm points to correct ht lead.
Distributer has been renewed as I thought this may be the issue
Initial thoughts are this could be a vacuum problem so disconnected brake vacuum pipe and blocked off vacuum outlet but still zero response to rpm pick up
All valves have been reground and have checked the position of cam shafts and timing tool fits perfectly

Not sure where to look next

Trev

Dumb thought but is the exhaust blocked?
Otherwise you seem to have covered the obvious bases...fuel, sparks,
Only other thing I can think is the carbs are set very VERY lean...but I would have though it would not start...300 to 400 rpm sounds a bit low too...

Exhaust pipes are full new system and smoke exits on start-up.
Carbs are set 2.5 turns down after being set level to bridge.

Hi,

I think you must to re-check your SU as it is explained into the Service Manual. Follow exactly the instructions. It's very important to disconnect the SU. Do all the operations as it was the first time.
An other thing
Your engine run, too low, ok but it run. Locate the fast idle screw and screw the third a little. you must to have around 700 rpm when the last one is screw. So go slowly
After that, with a screwdriver, push up slowly a damper on one SU and look at if the 2 others "answer". Normaly your engine is going to have it's rpm goes up.
If it works, you are on the good way, the SU are in question. Re check them.
Use a balance suction at last.
Good work
Mich

Hmmmm. The exhaust pipe was a very long shot!!!

Am guessing you have tried opening the throttle from the shaft above the carbs while the engine is running? As Michael has said, check the carb set up but it sounds like you have. 2.5 turns should be fine. If there is absolutely no increase in rpm when the throttle is opened I would begin to suspect the ignition timing or plug lead order or points etc. Providing all six pots are firing correctly it is almost impossible for the speed not to rise if you allow more fuel/air mix in.
Hope you get to the bottom of the issue.

Recheck the needles. Are they the correct type (UM) and fitted correctly. If you do find it Trev, please report back! And good luck!

Is the throttle linkage actually connected.......are you trying to rev it from the pedal or the linkage on the carbs

Yes...I wondered the same...hence my gentle suggestion to operate the carbs from the engine.... : :D

Have been through the su carb setup and the next step is to run the engine!
Needles are original and correctly stamped um.
Have operated the throttle linkage from the carb end and can see butterfly valves opening and closing but there is no change at all.

trev_car wrote:Have operated the throttle linkage from the carb end and can see butterfly valves opening and closing but there is no change at all.

This is close to impossible.

Even at 400 rpm the engine is pumping air and under the light load of generating a partial vacuum. Reduce the load by opening the throttles and the rngine must speed up or weak stall. Try blocking the manifold vacuum take-off, or put a vacuum gauge in line and see what happens.

Fuel pump?

Cactusman: this is a 4.2 so does not have a shaft above the carbs. However, the principle of your suggestion was good . In addition to the various things suggested, I would also check

1. Float levels

2. That valve timing is not significantly out

3.That pistons in carbs are moving freely and that bellchambers are securely screwed down

4.Checking that the bronze choke actuators are actually moving the jets when the choke lever is operated

4.Blocking with a rag the intake to 1 or 2 carbs as the throttle is opened i.e. choking it

being simplistic, to me it means there's no fuel getting through other than a trickle to support a low tickover. Fuel pump or floats? Have you disconnected the fuel line from the carbs, then turned ignition on to see how much fuel comes out?

Ah...mine is a 3.8....did not appreciate the 4.2 carb up nkage is different.

As others have said...maybe fuel but then if there was barely enough to run and then you open the butterfly I would have though the engine would die.

Thinking vaguely logically...presuming spark is OK and timing is OK and exhaust is OK and fuel supply is OK and throttle works then it seems almost impossible for the engine speed not to rise.....unless it is pulling air from elsewhere than through the carbs.or the air/fuel mix can't get in

I recall you saying you blocked the outlet to the vacuum for the brakes. Any hiss from elsewhere? Missing gaskets somewhere between the carbs and head? Something loose? Clutching at straws here....Really really dumb thought....you did not put rags in the inlets at some point to stop dust ingress and forgot them...no....thought not.

You could carefully spray some carb cleaner into the Venturi and see whether it increases in revs indicating fuel in some way. Have a fire extinguisher near by not sure how flammable it is but I have used this to detect vacuum leaks on manifolds before. Comes with a health warning and if you are not confident DONT DO IT