Holley carb issues

junkyardjeff · September 03, 2008, 10:44:02 PM

I have a 600 or 650 on a 351-W in my 55 Ford and it has always idled like there is a vacumn leak,I have replaced carb gaskets and the power valve thinking I could of blow it during break in of the motor but still acts the same. The motor has a mid 80s cast iron 4 bbl intake with aftermarket one inch spacer and I was thinking one of the two might be cracked so I finally checked the vacumn with a gauge and its at 21 so there must not be a leak. I was told to drill a 1/8 hole in the primary throttle plates but what would that do,I checked the vacumn at the port where the trans modulator and wiper motor hook up to so they are not the cause so any ideas onwhat to chek or could I got a bad carb out of the box. Jeff

wayne petty · September 04, 2008, 12:51:55 AM

what i would like to know... is when you had it apart ... did you take the base plate off the main body and check the gasket in there...

did you also hold the base plate up to the light and see if any of the throttle blades is off center... this happens a lot... loosen the screw not more than half a turn... (more than that and it may break off as the end of the threads is mashed over to prevent it falling in)

does that manifold have a blocked off egr passage??? that might be leaking somehow??

before you take it off make sure the secondarys are totally closed.. not held open.. there is a secondary stop set screw on many holleys..

drilling the primary plates allows the carb primarys to be adjusted so the edge of the blade is in the lower half of the idle transition passage... ( the little slot next to the idle passage hole)

when a high idling motor is built.. if the engine won't idle as the adjustment puts the edge of the plate past the transition passage... so no fuel can be pulled out after it leaves idle... this transition port is necessary as there is not enough air speed through the booster venturi to pull the fuel over yet...

PS... i love people who know so much about the tuning of the idle transition circuit.. that when they modify it... they test their work at WOT... they are people that i know... nothing to do with the rrt... or any body on it...

wayne

junkyardjeff · September 04, 2008, 08:38:28 AM

All I had apart was the fuel bowl and primary metering block and I did not check anything else,the EGR passage should be blocked off with the carb spacer. Fords have the EGR on the carb spacer and should I find a factory spacer and block off the EGr from it. Jeff

Mikej · September 04, 2008, 01:38:36 PM

Is it surging or idleing to fast? If you have 21" of vacuum, you don't have a big cam, so you should be able to make adjusts to the carb without drilling a hole in the throttle plates. A lot of times the throttle plates are open to much so you are running on the transition slots. You should able to close the throttle plate and adjust with the idle screws.

junkyardjeff · September 04, 2008, 05:32:40 PM

No surging just idling like it has a vacumn leak. Jeff

EMSjunkie · September 04, 2008, 06:18:42 PM

Quote from: "junkyardjeff"No surging just idling like it has a vacumn leak. Jeff

I agree with Mike
sounds like it is idling on the primary circuit instead of the idle circuit.

but what do I know :oops:

Vance

phat46 · September 04, 2008, 06:55:17 PM

I put too much cam in a basically stock SBC and the idle was terrible with a Holley 600, I did drill the holes in the throttle blades and it helped smooth it out. However i was pulling only around 12" of vacumn and it was really bouncey. I don't feel that drilling the holes will fix yours; with as much vacumn as you have I would think it's elsewhere.

enjenjo · September 04, 2008, 08:46:15 PM

If you are not using the factory spacer, I think you will find a passage that is covered by the gasket, but the base of the carb doesn't match close enough to seal it. I have run into this before. I used an aluminum plate from Summit, with two gaskets, and cured it.

reborn55 · September 04, 2008, 09:05:49 PM

Do the idle mixture screws have any effect on the idle when you try to adjust them. Might have a little spec of dirt in an idle passage and may need to shoot a little compressed air into the passages. Holleys do not like the tiniest spec of dirt

junkyardjeff · September 04, 2008, 10:40:10 PM

The idle screws do make a difference but I cant get it to idle smooth,I am planning on changing the cam this winter so I will put on a aftermarket aluminum intake and get rid of the factory stuff. The guy I had build this motor put in a 302 cam instead of a RV grind for a 351 like I was expecting and could that effect anything. Jeff

393Bird · September 10, 2008, 10:39:26 AM

I have had good luck setting the front throttle blades to expose about .020 of the transition slot, so the hole looks square, then adjusting the idle speed on the rears. On older Holleys, this may require you to reposition the rear stop screw to the top. I even painted the front idle speed red to remind me to not change it. With it set this way, you can adjust the idle air like is should be, and prevent a stumble as you start to accelerate, since the Tslot is ready to feed as you open the throttle blades.

I am running .600 lift and about half the vacuum you have, and it idles great.