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Idle problems

P

pruyter

Donation Time
A few days ago the idea was to collect my Tiger from the shop where it has been nearly 11 months. All the work I had ordered was done and I was satisfied with the result. However after a test drive I noticed that the idle r.p.m. was far to high. When the mecanic tried to adjust the carburettor the idle mix scew adjusting had no result i.e. there was no effect on changing the position of the screw. Besides that the idle was not smooth as I was used to.
This all is very strange because all the jobs I had told them to do had nothing to do with the engine, in fact the engine has never given me any troulbe before.
It amazed me however that the cold start now did not need my special treatment to get the car to start: this procedure was waiting until the pump did not making any noise and then switch of the contact and wait of a minute and after 3 or 4 pumps of the accellerator pedal it started immediately. I have done this for more than 28 years and it always worked. But now no procedure is needed it starts right away, very ver strange.
So how is it possible that this idle problem occured while there was no work done to the engine?
All I know is that the shop removed enigen plus gearbox from the top (now from below after removing the fron suspension). So I guessed that while removing the engine the engine is tilted backover and perhaps some dirt in the carburettor has moved and disturbed the float needle in the carburettor. But after inspection of the carburettor is showed that the carburettor was very clean, no dirt what so ever.
The brake servo was removed and sent to a specialist for inspection and in order to remover the engine the waterpump was removed. Other than that the shop did not touch the engine no other than placing new spark plugs (which I had not ordered) to my disappointment they had placed Bosch spark plugs which I don't like but anyhow this can't be the cause of the strange idling i.e. to high when warm and not smooth and not responding on the idle screw.
So I am very curious if somebody has an idea what could be the cause of this.
Thanks in advance!

Regards,

Peter
 
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Peter you don't mention what type of carb you have.. you just say the idle has now increased...
The carbs with the electric cold start could cause that kind of problem... If they moved it, knocked it.. that would increase the idle speed separate and not be impacted by the idle mixture.
 
Hi Michael,

I have the standard Autolite Tiger carburettor. Could an air leak be the cause? I was thinking on the brake servo which was removed in order to inspect it on faults and maybe the rubber hose from the servo to the intake manifold has some minor cracks?
The irritating thing is that this engine has always had a very smooth idle and now suddely after having been in the workshop I have this problem while nothing has been done to the engine or the carburettor. They have changed the timing from 2 degrees befor TDC to 6 degrees before TDC but that should not have any influence on the idling isn't?

 
If you have vaccun leak the car will run roigh and be ok when you open the throttle.

A stock carb has a power valve.. they can get stuck and would make the idle bad
 
High idle that you cannot bring down by unscrewing the idle speed (not mixture) screw says vacuum leak.
Most likely it is the carb to spacer or spacer to manifold gasket.
 
Easy check for the vac leak.. spray some carb clean around the base of the carb and manifold and see if the idle changes ...of ifle picks up . Vac leak
 
Reading this comments I start to doubt with which screw the mechanic was trying to get the idle speed down.
I understand that when it regards the screw that changes the throtle position then an air leak causes that there is no change in the idle speed.
But if it regards the mixture screw which does not change the idle speed what is in this case the probable cause?
 
Based on memory, ford carb has two mixture needles under front of carb base, pointing to rear of car. They should be under the fuel inlet pipe. Beginning setting for those would be screw them in gently seating them and then screw them out counting turns.....say one and three quarter turns out. Now for vacuum leaks, I like to listen for the hiss of a hose that has fallen off or broken. Use one of these without the probe, just an open hose: https://www.harborfreight.com/mechanics-stethoscope-63691.html?_br_psugg_q=stethoscope Or, three feet of hose with a funnel held against your ear. You can hear most vacuum leaks, confirm by spraying ether, brakleen, propane or such fuel; engine RPM will respond when you find a leak.
1720457419503.jpeg
 
Oh, and the secondary throttle valve can stick open, giving similar symptoms. . Spray inside and out with lubricant, actuate linkage (with engine off). Reach down secondary bores with long skinny screwdriver and tap on throttle blades, using a pool cue action, to ensure the throttles are closed.
 
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