Carb 308 builds up idle, by itself?!?

Really od thing...
I have just rebuild carburators with Eurospares "rebuild package", did synchronization by Birdman's Web-page (THANKS for excellent information!) and set timing right, with my "computer" from year 1970 (still going strong...)

Everything should be ok...

Only problem is I can't get air flow to 3,5-4kg/hr at 900rpm, instead air flow is around 5-6kg/hr??? airflow is even to all carburators


Engine behaves like this:
At idle car idles for 5min and then by itself buils by up idle to 3000-4000rpm and wont get down untill turn of by key. When start up again car runs fine.
Car is -77 US car and all parts as original.

Here are pictures from it:
http://s166.photobucket.com/albums/u84/unknow82/projekti/?start=all

What is wrong with this car? Any ideas? (I am running out of ideas) Please help!

 

Does this problem repeat itself again after you turn it off? Does it take 5 minutes for the RPM to climb the second time, or is it faster?

Is this only on a cold engine, or only hot start, or any condition?

My initial thought is a vacuum leak somewhere, that is engine temperature sensitive. You are probably also getting mechanical distrib advance kicking in over 1500 RPM which compounds the problem.

Is your fuel delivery adequate? Over lean can raise RPM.

Or, your high airflow may act as a vacuum leak by itself, but i don't know why it would idle at normal RPM then decide to rise with no other inputs, other than engine temp rise.

Doug

 

You may have a vacuum leak at the throttle bearings . As the engine heats up the leak will get greater and may be the cause of the increase in idle. Next I would check the fast idle cam and make sure that it is either disconnected (screw backed out ) or that it is working. If it gets stuck the idle seems to increase as the engine warms up. Also do we assume that the chokes are either disconnected or all of the way closed. As to the air bypass measurement do you not see a difference with ALL of them closed? Maybe you should just walk back through Birdmans tune up procedure again just to make sure. Good luck

 

I have also heard of the fast idle cam spring being installed backwards, raising the idle as it warms.

 

A possibility.

Disconnect the linkage from the carbs and try it.
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I know you said you rebuilt the carbs, but did you replace the needle valves on all 4 carbs?

 

Yes it repeats itself cold and warm. I can't say if it gets faster or not.

Yes, Thought that, but it builds up speed so fast like suddenly, could one leaking bearing make that?

Yes I got four point system now on. I did try it without the first set of point. It could be advance but high airflow is not explain by ignition.

Yes, have to check fuel pump delivery, thought this one also, I took out all US-model fuel system stuff and now it is like European. All new fuel lines, and even took filter out. (going back of course.)

I don't know either.

 

Idle gets faster sudenly and as it gets faster and stay there, airflow is even with all sylinders.

Disconected and have not been used.

Chokes are closed, but i'll check CO% as idle gets fast.

Tune up procedure!?!! for fourth time... oh no, not again!
Flow is even and at 1500rpm 8kg2/hr and it is even at 900rpm.

 

Yes I did all four are new. I did open needels again to clean them up IF there was debree.
I did mesure float height adjustment. One float was at 47mm and other three are 48mm could this be answer?

All carburator base spacers are new, (btw: I did wrote wrong it was Superformance "rebuild package", too tired last night.) All tubes and jets are correct as they where. last week car did run fine.

 

Today I got new jets:
Air corector 200
Main Jets: 135
idle jet 50



Now it has not done "run up." We have to see what it does. It seems, there was something wrong with jets...

Now I'll synchronize or check it if I'll get airflow down.

 

Good luck and I hope this gets you happily motoring........

 

No... can't get airflow down.

Fuel pump is ok

Timing is ok, rews all the way up and only att very top, some misfireing as car is stasionary.

Carburator balance is ok, but too high airflow

Carburator are check, no debree.

New blugs, New leads...

Now what?

It seems front side of engine is somehow off, as front carburator spit up now, all four, but they where fine...

Could I have timing off from front inlet cam? or timing belt jumped? How it behaves then?

 

I would check timing front bank vs rear bank first, sticky centrifugal advance plates can cause issues like this. Only applies to a double dizzy car, of course. Much easier to do than check valve timing.

Doug

 

Good point! How easy should this centrifugal-mechanicha advance move, Can I twist it from rotor arm? (I can't, I did try it...)

 

are you sure the butterflies are closed shut at idle? you should be running off the progression holes at idle!!!!
all idle stop screws are turned all the way out amd not topuching any linkage arms? disconnect all the the linkage and see if the idle drops.

 

Partial answer to your question.

Known fact:

I can take a 1960's Chev V8 dizzy and simply twist the rotor around to full centrifugal advance and release it and it will snap back to unadvanced position.

Hazy memory of 20 years gone by:

I had a sticky advance plate on one of my 308 dizzies,and as I recall, the good dizzy did the same thing the Chev dizzy did, but the bad Fcar dizzy wouldn't move until I took the dizzy out and rebuilt it, which mostly consisted of removing old sticky grease and re lubing. I think I changed bearings at the same time, but not totally sure about the bearings.

Doug

 

No, the rotor arm does not twist. On the 308 design, the distributor rotor arm is mounted on a shaft that is rigidly attached to the camshaft end, and the distributor cam is mounted on a concentric hollow shaft that rotates around the distributor rotor arm shaft -- i.e., it's the spring-loaded distributor cam that rotates to change the timing. The second photo shows a couple of different examples of the 308 hollow distributor cam that rotates independent of the (fixed) distributor rotor arm shaft:
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Thank you for refreshing my memory on this.

As I recall, the grease that was under the pivot arms of those weights on the lower plate had thickened to the point the weights were stuck in the outermost position.

Doug

 

My euro 308 did the same and it was the servo pipe leaking.

 

Aha! plot tightens...

I took compresson from cold engine and rough numbers are; front 10:1 and rear 8(and something):1. And there was awnser front side had falty valve timing.

Just took valve covers out and there it was, jumped one tooth from crank axel. This error have been for sometime as rear distributor has numeros "timing"marks to indicate, this problem had been search for long time... (not by previous owners)