Base Idle problem Griffith 500

[Loubaruch]

Although the car is now running OK I continue to have problems setting the base idle.
Initially the car would not idle at all until the air bleed hole in the Plenum was given a thourough cleaning. With the feed to the idle motor blanked off the maximum revs/minute only reaches 300 even with the adjuster fully out.

The timing has been checked and is spot on at 12 BTDC. Thinking the air flow maybe impeded by the filter (new) or elephants trunk I disconected the filter but it made no difference the maximimum revs still 300 rpm. Any thoughts? I did wonder if the plenum casting was maybe faulty and the air bleed passage is a bit restricted, not an easy thing to check!

[Johno]

Did you try to check the air bleed passage? Maybe with fluid, water or thin oil.

Also, have you checked the other pipes/air sources to the plenum/trumpet base, carbon can, servo and oil breather? All of them are in the system, so it should balance across all of them. With the throttle closed it’s quite a vacuum and should be able to get air from all of these sources. One way valves etc. which can all cause issues.

Probably simpleton thinking, I’d want to check all of those before worrying about the filter and induction hose.

[Belle427]

I can't think of anything else apart from the throttle disc blanking the air bleed hole but I cannot see that personally.

[blaze_away]

I agree with johno, go check all the crank case ventilation (CCV) hoses that run into the plenum, especially the short small bore hose passenger side that tees off the main CCV hose. This I beleive has a Non-return valve in it, maybe fitted wrong way round or blocked. Check the other hoses are clear eg carbon cannister hose, brake servo hose.

Also check/clean the rocker cover flame trap, I believe this is also a oneway valve.

Edited by blaze_away on Sunday 13th July 15:46

[Loubaruch]

Thanks for all the suggestions. I perhaps misunderstand the air flow but if either the Brake servo, the crank case breather or the charcoal cylinder feeds are leaking air would that not introduce more air into the plenum and increase the revs. The Charcoal cylinder valve I believe only opens at higher revs not at idling so that should be shut, similarily the brake servo should be sealed not allowing air but the crankcase breather is a mystery maybe that does need to be free to allow some air in.

Cheers

[blaze_away]

Loubaruch said:

Thanks for all the suggestions. I perhaps misunderstand the air flow but if either the Brake servo, the crank case breather or the charcoal cylinder feeds are leaking air would that not introduce more air into the plenum and increase the revs. The Charcoal cylinder valve I believe only opens at higher revs not at idling so that should be shut, similarily the brake servo should be sealed not allowing air but the crankcase breather is a mystery maybe that does need to be free to allow some air in.

Cheers

Thats correct but if any of those hoses are blocked then it may indicate others getting crap and potentially blocked.

[Johno]

blaze_away said:

Loubaruch said:

Thanks for all the suggestions. I perhaps misunderstand the air flow but if either the Brake servo, the crank case breather or the charcoal cylinder feeds are leaking air would that not introduce more air into the plenum and increase the revs. The Charcoal cylinder valve I believe only opens at higher revs not at idling so that should be shut, similarily the brake servo should be sealed not allowing air but the crankcase breather is a mystery maybe that does need to be free to allow some air in.

Cheers

Thats correct but if any of those hoses are blocked then it may indicate others getting crap and potentially blocked.

This . The servo and carbon can are one way valves, or at least carbon canister is operated under certain conditions. There also a restrictor I think in the CCV system.

It’s about making sure everything is operating as it should, then retracing your steps. It becomes all about 1 issue until you realise it’s nothing to do with it.

I chased an air leak on my old S for weeks and weeks and weeks, Turned out the servo had rotted and it had a small hole at the bottom, which you couldn’t see, bingo…. All sorts of shenanigans with AFM s and all sorts. It was a basic element of the system.

Edited by Johno on Sunday 13th July 21:20