Poor Idle question.

[fingersnfumbs]

I have my YB N/A running very nicely but the idle is not a smooth as I would expect even after recent RR set-up.

Cams are fairly mild 288 duration and 410 lift. Solid lifters, 45's etc.

Engine wasnt balanced on rebuild but all parts where new, pistons rods etc.

Before it was set-up I had some issues with plugs fouling so changed to 4 electrode plugs which completely eliminated the problem.

It has never in my view been particularly smooth at 900rpm.

I have 'played' with the mixture screws but it doesnt really help, I always end up with same settings as it was set-up with.

Anybody got any ideas? Should I put standard plugs in?

[Graham]

asking for a smooth 900 rpm idle might be a bit optimistic on a 288 degree duration cam, it isnt that mild, and depending how the cams are timed it could be far from mild. getting the carb balance right plays a massive effect on idle.

[Miniliteman]

Ignition timing?

[fingersnfumbs]

Um, I dont think the cam timing was adjusted. If it was its ended up in the same position I set it at initially.

Ignition timing is 11 Deg. Any more and it pinks on part throttle.

I have loads of piston to valve clearence, could I move the cam timing about myself to see if it makes any difference? Advance inlet a bit and retard Exhaust to improve things?

[fingersnfumbs]

asking for a smooth 900 rpm idle might be a bit optimistic on a 288 degree duration cam, it isnt that mild, and depending how the cams are timed it could be far from mild. getting the carb balance right plays a massive effect on idle.

Carb balancing seems optimal. Any more or less on any screws makes it idle worse.

[Miniliteman]

So what did the RR operator do? Jetting and ignition timing?
Do not overdo changing the timing of the cams; you might have enough piston to valve clearance at TDC but the valves open fast on the ramp of the cam whilst the piston almost stays at the top.

[onecamohv]

Carb balancing seems optimal. Any more or less on any screws makes it idle worse.

You sure you're not talking about idle mixture when you say 'screws' ?? There's only one screw that adjusts the balance and as Graham rightly said id be going there first. It will make the biggest difference to idle quality. If you don't have a syncrometer, you can do the same job with a piece of hose and listen to balance the hiss a tiny adjustment on the screw will knock it out of balance on idle

[Enea]

maybe cleaning idle jets could help?

[fingersnfumbs]

Thanks guys, I do have a syncrometer and have checked. Both carbs are the same on all four barels.
I have noticed the idle screws are over 2 turns out when it runs best though.
Possibly change to Idle ritcher jets?

[fingersnfumbs]

Also carbs as most of the engine and components are new.
Weber DCOE 152G. With 4 progression holes.

[Graham]

Thanks guys, I do have a syncrometer and have checked. Both carbs are the same on all four barels.
I have noticed the idle screws are over 2 turns out when it runs best though.
Possibly change to Idle ritcher jets?

your problem if you have one isn't idle jets, your probably expecting too much from it wanting a smooth 900 rpm idle, whats it like at 950 or 1000? how accurate is the rev counter? i remember years ago spending ages trying to get a smooth idle at low rpm, only to find the rev counter was reading fast

[fingersnfumbs]

your problem if you have one isn't idle jets, your probably expecting too much from it wanting a smooth 900 rpm idle, whats it like at 950 or 1000? how accurate is the rev counter? i remember years ago spending ages trying to get a smooth idle at low rpm, only to find the rev counter was reading fast

Now that is something I never thought of.

I will check it with my timing light.