High idle

[Sam Danenberger IV]

Hello all-

New problem - Very frusrtating because the car is running so well otherwise.
Throttle was sticking a couple of weeks ago, at the end of a long hot drive(s).
Lubrictated linkages and cables and problem was/is pretty much gone.
Now after warm up, it idles high - 1500-1600 rpm at stoplights, drops down normal after selecting first and pulling away. Air temp 90 degrees F
Stop again and the rpms go right back up to 1500-1600.
Very strange.
Ideas? Opinions? Theories?

[tim]

couple of thoughts.


Maybe you altered the balance accidentally when lubing which can give a higher and variable throttle at idle. Had same with mine after taking carbs off. What also happens is as engine comes of idle revs the advance increases which makes the engine run a bit faster.

Alternatively you may have a gotten an air leak on the manifold check carefully using a thin rubber hose as a stethascope.....

Tim

[Sam Danenberger IV]

Thanks Tim-
I will check these out.
I read about the air leak in the Fulvia Tech Q&A section.
Is this a common problem?
Sam

[tim]

If your rubber joining piece is old it could cuase leak problems. I get by by using superglue to control/seal any cracking. Your carbs should have the support strap to prvent loading this spacer. I have also had problems with the very thin gaskets either side of this piece on my HF which i solved with (again) a drop of super glue. Suggest you check for leaks but go through a carb tune which will take about half an hour of paitent twiddling using an under bonnet electronic rev counter and a rubber tube to listen at the venturies for a balance.

[John Simister]

My HF currently idles at 1800rpm, which is clearly hopeless. And that's with correct ignition timing, new advance springs, no manifold or servo leaks, correct carb balance, the fine-adjustment air-bleed calibration screws fully shut and the idle screw adjusted right out. The spindle bushes in the Solex 42 DDHFs were worn, which was what I originally thought was causing the problem. Rebushing didn't cure it. What has happened, I think, is that the worn bushes caused the throttle plates to rub against the carburettor barrels, wearing both plate and barrel and causing an air gap which is clearly visible if I look through the barrels while holding the carbs up to the light. I tried loosening the throttle plates' fixing screws and repositioning the plates so they seal as well as possible (snap the throttles shut and retighten in that position), but that didn't help much.

What I need to do is have the barrels fractionally rebored (maybe 0.2mm or so) and rebuild the carbs with oversize throttle plates to suit. With a single carb an air gap like this isn't too much of a problem, but when there are four barrels there's four times the problem.

I hope this is possible. Has anyone reading this tried it?

John Simister

[Ed Levin]

Sam

Air leaks in the carb gasket usually causes the idle speed to 'hunt' rather than to consistently stay high. It's possible that your problem is an air leak, but it doesn't sound like it.

Further, I'm not a big believer in coincidence. If this started only after you lubricated some cables and linkages, I'd bet that those lubricating efforts caused this, and it's unlikely that you caused an air leak.

I'd suspect the choke lever (you may have lubricated things so much that the choke won't stay off), or the throttle synchronizing lever between the two carbs, or the idle adjustment screws. I'd check these long before I pulled the carbs the check the gaskets.

Regards, Ed

[andrea]

Hi John,

If barrels and flaps are worn, your reboring solution is a good one. Furthermore, have you checked the CO emission at your high idle? Are you sure that both needle valves in the carbs are the same (check the type which is etched on them), are the correct ones and do work properly?

[Geoffrey Goldberg]

Sam -

There is an issue with older Webers with the shafts wearing in the carb housings. Turns out Mr. Weber ran the shafts directly on the casting. Solution is to pull the carbs, rebore and bush. Painful, due to accuracy issues. Pierce Manifold does this very nicely.

Not sure if this is also true on Fulvias.

Geoff

[Sam Danenberger IV]

Geoff-

Carbs, Solexes not Webers, were completely rebuilt/rebored/rebushed when the engine was done.
So I doubt they have worn out with the 900 miles I have on the car since.
Could be an air leak somewher too , but everyting is relatively new rubber and gasket wise.
I have a suspiscion it is in the throttle linkages/cables or pedal hinge points, somewhere throttle in the system.
I'm trying to diagnos and rectify it myself, but Giovanni might find it faster than I.
Thank to all of you for your input.
I will report the nature of the problem and its cure later.
Sam

[Huib]

If you have a new carb rubber the lever may touch the steel plate. Originally your car had two seperate rubbers and the carb has a straight lever. For the newer one piece rubbers you would need a bent lever or grind some away from the steel plate.