Holey 390 vac secondery Idel problems.

stagcar · Post by **stagcar** » Mon Mar 29, 2010 8:23 pm

Hi all.

I have got a Holey 390 and i have just done a full service on it.

It seems to be fine apart from the idle is to high

I have wound the Idle stop screw out so the primary flaps are shut and also i have wound the screew out the botem of the carb so the secondarys are shut but it still idles at about 1200 RPM.

Apart from this it seems to go nice with plenty of power. i would think i have an air leak or somthing what do you think?

Not sure if this is right but i have conected the large vac port on the botem of the carb to the right hand rocker box via a flame trap and the other rocker box is free to air via a fuel filter?

any help would be apriciated

Cheers
Derek

JP. · Post by **JP.** » Tue Mar 30, 2010 3:14 pm

stagcar wrote:Hi all.

......... i have just done a full service on it...........

Did you put the correct gasket between the throttleplate and carbbase ??
(not the one between your engine & carb). There are several throttle plate gaskets in the service kit for the Holley just be shure you use the correct one cause not all the vacuum hole's are the same.

Did you only serviced it or did you fully cleaned it to. I normaly put a stripped carb in a bath of paint thinner for 24hrs and blow it through with compressed air after it. This normaly cures all the problems.

I assume you have all the vacuum hoses connected correct. Meaning ignition on the primary meteringplate and PCV on the big one on the throttle plate. The small vacuum pipe on the throttle plate under the primary fuelbowl should be plugged.

stagcar · Post by **stagcar** » Tue Mar 30, 2010 3:33 pm

Hi,

yep all looks good on the gaskit front I was very carfull to use the correct ones.

As for the cleaning I used a can of carb cleaner and scrubbed it up with that and it looks nice and shiney now then I blew it all out with an air line.

looks like I got all the pipes in the right place to and yes the little full vac port is plugged.

If the idle mixture is wrong would it cause this to happen?

When I set it up I just started at 2 turns out on both screws then screwed them both in until it stalled and wound them out about quater of a turn is this right?

I have got a vac gauge on it's way so I should be able to set this up a bit better.

Somthing is not right some where just not sure where to look.

Cheers
derek

Boosted LS1 · Post by **Boosted LS1** » Tue Mar 30, 2010 4:16 pm

The vacuum port is drawing in loads of unrestricted air from the rocker cover. That's why it's idling high. Try blanking off the port and see if the idle drops.

mgbv8 · Post by **mgbv8** » Tue Mar 30, 2010 5:22 pm

JP. · Post by **JP.** » Tue Mar 30, 2010 7:09 pm

Boosted LS1 wrote:The vacuum port is drawing in loads of unrestricted air from the rocker cover.......

Holley 390cfm & most others are callibrated for this to happen from factory, blanking this port will result in power loss as the carb needs to be re-callibrated.( its more than main jets only).
Did a test sesion on this matter on the dyno.

Had my idle jets about ½ turn out on each side.

Boosted LS1 · Post by **Boosted LS1** » Tue Mar 30, 2010 7:30 pm

^ I don't accept that at all. The carbs are often supplied with bungs over those ports. They expect the pcv circuit to have a restriction in it, not be open to atmosphere. Or if he's using the brake vacuum port it would go to a sealed brake canister so once again, extra air wouldn't be drawn into the engine. Likewise the dizzy port can be blocked or it goes to the vac cannister on the dizzy. You had something wrong with your set up. Main jets aren't active at idle anyway!

The OP is sucking air in even with the throttle blades closed. It's obvious where it's getting in.

stagcar · Post by **stagcar** » Tue Mar 30, 2010 7:50 pm

Thanks for the responses chaps.

I have just been through the guide on holley carbs on the net

Got a feeling i may have pluged the wrong hole on the manul choke bit.
Aparentley they have a small hole that sucks some of the heat out the bimetalic housing on a auto choke setup. I think i may have left this open so will check this first

After that i will plug the PCV and see what happens.

I wil give it a go tomorrow and post an update

i am not to clued up with the holley at the moment but i am getting there slowley cheers for the help
Thanks
Derek

jefferybond · Post by **jefferybond** » Wed Mar 31, 2010 12:32 pm

Possibly a simple thing like the throttle cable being too tight?

As for the breathers, have you got a restrictor in the line sucking the fumes out of the rocker cover? If you let the carb suck in too much air/fumes, it can affect the idle.

Jeff

stagcar · Post by **stagcar** » Fri Apr 02, 2010 4:16 pm

Hi,

Good news it looks like it is a problem with the breather system.

as it was sugested i pluged the pcv and the idle dropped right down and it stalled. not suprising as the idle screw was wound all the way out.

so i will be making up a restricter and resticting the air into the other rocker cover or maybe i will stick it in the carb side just before the flame trap what ever works tbh.

Thanks again for the help

Cheers
Derek

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Holey 390 vac secondery Idel problems.

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