van revving on full load, no stuck cable, butterfly or rod

[xpress]

hi there. in Sw country. van revving up to full load without pressing pedal. no stuck cable, spring is fine. all at idle position so maybe something stuck in carb, float valve? please can anyone advise?

[kevtherev]

Have you lifted the lid to see if the throttle is stuck?

[xpress]

checked that. no joy. could it be a broken vac advance pipe but i would have thought it wouldn't rev to full load would just affect timing. I suspect stuck float valve?

[kevtherev]

Well if it were on choke then it would rev out with an air leak

An air leak should be looked for first.
If an engine over fuels it just stalls.

Air makes engines go faster.
Make sure all the throttle connections are good and the butterfly isn't detached

[California Dreamin]

As Kevs says...the engine speed is controlled by the amount of air you allow through the throttle body ie: throttle pedal/butteryfly valve.
So...this is either sticking or there is another air leak allowing the engine revs to rise.

Martin

[xpress]

today not revving as bad but feels like choke is stuck on. still higher than normal. whipped carb lid off. strings to right of carb, both seem ok either side the cams rock ok. the lifter in the middle doesn't seem to be spring loaded but feels heavier than the springs either side, this seems to set the butterfly, it feels greased. the butterfly has no obstructions. I disconnected the choke mech wire, no difference. I don't know this pieberg carb too well. its a 2e3. anyone near st ives. lol. any ideas? ps I checked the pull down its not stuck notes freely.

what could the options be for faults, how to sort it. what to check for? thank you.

[kevtherev]

Im sorry but Im having dificulty understanding your description
whats a choke mech wire?
Where are the strings?
How have you decided the choke is on?
Have all the vac lines been checked for cracks and splits?
Is the engine running rough now.?

You have two replies saying the same thing virtualy. so I would say thats as good as it gets from your description for a diagnosis.

Is the choke flap open when the engine is warm?

[xpress]

now the revs are high and its making a bit of a whooshy thrashy sound.

[xpress]

hi revs if you have a number I can call you pm me or I can send you mine. my recovery is pants will only take me to nearest garage and will tow back if its more serious. it seems more serious than a service or minor problem.

[BOXY]

Have you checked to see if the carb is bolted securely to the manifold and there are no leaks around the gasket if a Pieberg has one?

[toomanytoys]

Only way an engine can rev is with more air and more fuel.. an air leak on the manifold will produce odd run ning and missfires and backfires,.

Main throttle valve HAS to be open, doesnt need to be far when no load on engine.. make sure the throttle IS returning to its stop on the carb.. and choke stepped cam is not round too far and jaming the throttle open..

Have you/anyone been buggering about in the engine bay since it was last run?

My fave would be throttle cable has either frayed..
return spring could be at fault..
choke return springs fault..
throttle pedal mech worn and stuck

Got your haynes manual with you??? get it out and read it.. the carb is covered very well in there....

[xpress]

after a heat and cool cycle and a good run after wiggling the butterfly valve and it has righted itself. I was careful not to start with the auto choke ie a pedal press and after a run Its returning back to normal position. toomanytoys this is what i was thinking, if there was air leak and suction of air, it would be running leaner, air doesn't always equate to higher idle unless it's with more petrol. that's why i thought carb

re haynes, i have got it, i had a good read of it but it's not an exhaustive and thorough primer on carbs, just a few tests and then refer to a specialist as per haynes, quite a few things not covered in haynes, waxstat, tests for voltage, details on auto choke etc, that I have picked up elsewhere.

there seems to be a set of springs together, but the middle rocker on this rod is not spring loaded and can be moved by hand, is this right i wonder, and this appears to be controlled by the auto choke mechanism. i am thinking the butterfly valve was a bit stiff, and the waxstat, and the auto choke mechanism was a bit stiff, maybe it didn't have enough time to release itself or it's becoming slow to release itself, this is why i thought wax stat, or should there be some kind of return spring. if it's going to start sticking and being a pain, i will undo the three screws, turn it so the choke valve is completely open and then nip them up and just wait for her to warm up in future before setting off, anyway could anyone answer my questions and i will maybe have a few more things to think about, thanks all.

Only way an engine can rev is with more air and more fuel.. an air leak on the manifold will produce odd run ning and missfires and backfires,.

Main throttle valve HAS to be open, doesnt need to be far when no load on engine.. make sure the throttle IS returning to its stop on the carb.. and choke stepped cam is not round too far and jaming the throttle open..

Have you/anyone been buggering about in the engine bay since it was last run?

My fave would be throttle cable has either frayed..
return spring could be at fault..
choke return springs fault..
throttle pedal mech worn and stuck

Got your haynes manual with you??? get it out and read it.. the carb is covered very well in there....

[kevtherev]

, if there was air leak and suction of air, it would be running leaner, air doesn't always equate to higher idle unless it's with more petrol.

nearly ...
if you get air leaking in.. then it will suck more fuel from the carb.. so not always leaner.
I think you are talking about the fast idle cam?
This is controlled by the bi-metal spring in the autochoke housing
The spring will try to return it to the cold start position but the bi-metal spring will over ride it when warm
Pressing the pedal once will lift the throttle stop to allow the cam to rotate to the best position for starting the engine. (for it's temp)
The bi-metal spring will rotate the cam as the engine warms.
It does not take long for the engine to come off the choke (5 mins) at 30 deg C flap should be fully open.

[xpress]

thanks for the info. it would be good to put all the tests and service elements into the Wikipedia. I have found a lot out trawling the net.

[mblake4u]

Another thing you can check is your vacuum advance by sucking on the tube that connects it to the carb. If you can suck air through the tube (with the vacuum advance connected of course) then there's a leak in the vacuum advance diaphragm which will mean the engine can suck in extra air.

I've also seen a vacuum advance that moves to easily which means you're getting an advance when you shouldn't get one. It also wouldn't return to it's normal position when there's no vacuum meaning you'd still get the advance - this caused my engine to rev higher than it should have.