Running on

[Mad4slalom]

Does anyone suffer from occasional running on upon switching off ignition. Rebuilt motor so not coked up ,
I read too high an idle speed can cause it , any thoughts? Tia

 

[Alben78]

According to the US sites most C3s were fitted with idle stop solenoids which either increased the curb idle for a/ c use or prevented dieseling by shutting off the throttle blades and effectively preventing a hot engine pulling fuel from the float chamber via the idle circuits. I do remember some adjustment info in the Haynes manual but that’s now long gone.

 

[Chuffer]

Does anyone suffer from occasional running on upon switching off ignition. Rebuilt motor so not coked up ,
I read too high an idle speed can cause it , any thoughts? Tia

What rpm does it tick over at ? It could be that as you say , or the timing could be out .

 

[Mad4slalom]

What rpm does it tick over at ? It could be that as you say , or the timing could be out .

About 700 but will double check in a bit

 

[Mad4slalom]

According to the US sites most C3s were fitted with idle stop solenoids which either increased the curb idle for a/ c use or prevented dieseling by shutting off the throttle blades and effectively preventing a hot engine pulling fuel from the float chamber via the idle circuits. I do remember some adjustment info in the Haynes manual but that’s now long gone.

Thanks alben I will look into that, it is an after market holley 650 dp.

 

[Roscobbc]

Whilst too weak an idle mixture can cause 'running-on' also if idle mixture is too rich carbon build-up on spark plug (and perhaps piston) can retain heat from combusion cycle and ignite mixture (potentially causing 'running-on'). Retarded ignition at idle speeds can cause higher combustion chamber temperatures and the same thing (or combination) - The fact that you have a Holley DP could mean its running a richer idle mixture. A sometimes useful exercise is (if a mid/late 70's car) is to re-curve the distributor and advance the initial timing. This will make the engine run cooler and make it a little more 'perky' off the line. Needs to be done carefully in case of potential 'pinging'.......what colour are spark plugs?

 

[Chuffer]

About 700 but will double check in a bit

It`s not tick over too fast then as 700 rpm is about right and what mine is happiest at for tick over , especially when cold . Hope you get it sorted .

 

[Chuffer]

By the way , I have a Holley 750 cfm.

 

[Mad4slalom]

It`s not tick over too fast then as 700 rpm is about right and what mine is happiest at for tick over , especially when cold . Hope you get it sorted .

Went out for a test and tickover is 800. Spoke to local tuner who will look at it in two weeks time, he said to run millers esp octane boost And V power super unleaded. So will swap to that, topped up but only took 22 quid so cant tell any difference yet.

 

[Chuffer]

I used to run mine on V Power and made no difference to the engine running or performance . I now always use Branded 95 RON for about two years and even local supermarket petrol occasionally when I am desperate and running on fumes . Performance doesn`t seem to change . I do now use Millers additive to combat the dreaded ethanol though .

 

[Mad4slalom]

Whilst too weak an idle mixture can cause 'running-on' also if idle mixture is too rich carbon build-up on spark plug (and perhaps piston) can retain heat from combusion cycle and ignite mixture (potentially causing 'running-on'). Retarded ignition at idle speeds can cause higher combustion chamber temperatures and the same thing (or combination) - The fact that you have a Holley DP could mean its running a richer idle mixture. A sometimes useful exercise is (if a mid/late 70's car) is to re-curve the distributor and advance the initial timing. This will make the engine run cooler and make it a little more 'perky' off the line. Needs to be done carefully in case of potential 'pinging'.......what colour are spark plugs?

I replaced plugs ten days ago they were not nice mid brown , a little sooty but far from oily or fouled

 

[Mad4slalom]

I used to run mine on V Power and made no difference to the engine running or performance . I now always use Branded 95 RON for about two years and even local supermarket petrol occasionally when I am desperate and running on fumes . Performance doesn`t seem to change . I do now use Millers additive to combat the dreaded ethanol though .

I wondered about that as usa gas i thought was a lower ron than ours so normal unleaded should be fine..

 

[Chuffer]

Yeah , USA gas was virtually cooking oil + paraffin grade when your car was built compared to our higher octane petrol
As for your plugs being a bit sooty after only ten days and I guess very little mileage , my guess is running too rich . But all you have done is a few cold starts and short trips that will fowl up the plugs . Maybe it just needs a good old Italian Tune Up .

 

[Forrest Gump]

Was it running on before you changed the plugs?

 

[Mad4slalom]

Yeah , USA gas was virtually cooking oil + paraffin grade when your car was built compared to our higher octane petrol
As for your plugs being a bit sooty after only ten days and I guess very little mileage , my guess is running too rich . But all you have done is a few cold starts and short trips that will fowl up the plugs . Maybe it just needs a good old Italian Tune Up .

No , the plugs i took out were only very mildly sooty and that was i think only because of 10 weeks backing in and out of garage and not getting it warm, it was on seven at one stage, soon as i changed the plugs she ran smoothly ever since.
think the carb needs a tweek for uk atmosphere, as po in buffalo was at 650 ft asl.

 

[Chuffer]

I doubt 650 feet ASL would make much difference to atmospheric pressure , not exactly top of Everest is it ? I live at 440 feet ASL and don`t have to tweek the carb every time I drive down to the coast .

 

[Roscobbc]

Perhaps the OP can give us a run-down of the car spec' - what year, auto/manual - any mods to engine (other than carb) if the plugs are generally a coffee colour with a bit of soot on the tip of the earth electrode and on the visible metal part of the plug then its probably not too far off. To determine whether primary jetting is correct you need to use a set of new or cleaned plugs, do a 4 or 5 mile 50mph steady cruise - cut the engine - coast to a stop and pull the plugs for an evaluation.

 

[stealthyflatfish]

I'd go for timing retarded, Chevy will take up to 36deg of timing all in at 3000 rpm, and it's a free fix so good place to start.

 

[Mad4slalom]

I doubt 650 feet ASL would make much difference to atmospheric pressure , not exactly top of Everest is it ? I live at 440 feet ASL and don`t have to tweek the carb every time I drive down to the coast .

I did wonder as we are about 400ft. Whether humidity etc would be different to buffalo ny.
my diesel vans run with noticeably mor power on a damp misty day

 

[Mad4slalom]

I did wonder as we are about 400ft. Whether humidity etc would be different to buffalo ny.
my diesel vans run with noticeably mor power on a damp misty day

440 feet That must be a nightmare getting back from town chuffs when its the wrong type of leaves on the line !!