radiateu2

I am running a 600cfm holley on a 305 I have 66 primary jets and have a little surge or miss at cruise should I jet up or down The plugs are neither lean or rich.

xpndbl3

iTrader: (5)

i'd say jet up, especially if it's a surge. but i'm not where near a carb expert by any means....so take this advice with a grain of salt.

F-BIRD'88

Is the miss or surge at steady cruise or while you roll into the throttle?

Blow out the airbleeds first before adjusting jetting.

If nessessary go up 1 or 2 jets and see how it reacts.

A surge at cruise can be caused by too much vacuum advance too. may need an adjustable vacuum can.

radiateu2

The miss is mostly when rolling into the throttle. Funny you mentioned vacuum advance. The engine seems to like a lot of initial advance off the scale. There isnt much in the way of mechanical advance. If i try to retard the timing it will miss really bad. so maybe an adjustable vac advance would be a good thing. I will nuy an advance timing light this week to find out what total advance is. It does not ping on hard acceleration the way it is now. What air bleeds are you refering to? What are you suggesting to blow out with air.

F-BIRD'88

Here's a pic. May respond to a power valve change.
Try a 10.5 power valve to have the power circuit kick in a little sooner.
Sounds like you need to go through the igition advance curve. It should not be off the scale at idle with a mild cam like the one you have.
Should be 12-16 deg initial at idle 700rpm or less advanceing to 32-36 total at 3000-3500 rpm.
Check it with the vacuum advance disconnected.
Then plug vacuum advance into Ported vacuum.
should add 15-20 deg vacuum advance at high cruise.

A set of the lightest springs in an advance curve kit will result in a unstable idle advance as they are too light to control the advance weights. Select one light and one medium spring.

radiateu2

F-BIRD I think the reason why I have so much or require so much initial advance is that it maybe possible that the rotor may be coming into contact with the weights. Since mechanical advance is non existing or very little. Another possibility is the advance mechanism maybe a little sticky. What would you recommend tolube this? I was thinking a little w-d40 would clean it and give it a little lube and then a few drops of 30 weight. At idle in drive I am at 12", would a 10.5 powervalve be to much to soon? All in all I have a few things to check. On the pump shot should it be .015 of travel or clearance between the pump arm and screw? Could you clarify that for me?

Thanks,
Ed

F-BIRD'88

There should be no clearance between the acelerator pump linkage when the throttle is closed. The spring should not be fully compressed.
Sometimes the pump arm lever gets bent.

Usually from haveing the spring adjusted to tight at idle.
Fuel does not compress so when the throttle is slammed open the spring has to compress or the pump linkage will bend.
When the throttle is opened all the way there should be an additional .015" of travel left on the pump diaphram.
(slide a feeler guage between the pump arm and the bottom of the screw with the spring around it.

Try a 10.5" powervalve and see what happens.

Remove the rotor, weights and springs and make sure the advance mechanism is able to turn. The shaft may be bent or seized. The weights may be worn.
The bottom of the rotor may be out of spec and allowing the weights to hit or rub.

White grease is a good lube for this.