The Stovebolt Site Forums The Shop Area The HiPo Shop Holley carb issue

My 59 apache has a 69 327 in it. It had a q-jet which had burned in it's past life and was literally disintegrating, so i swapped it for a new Holley spread bore with elec. choke and vac secondaries. When I start it up the idle is fine, it will drop correctly when i blip the throttle. Once I start driving when i come to a light it will not drop down to the correct idle but will race a bit. When I blip it again it drops back down to a nice purr. Any suggestions? it's disappointing as the truck runs a thousand time better. Very responsive with lots more pep. I've checked the linkage it's not binding, it has all new linkage bushings and springs.
Thanks in advance,
Greg

Your problem has 6 letters- - - - -"H O L L E Y". Buy another Q jet, with the correct part number for your engine. There are several hundred variations of Quadrajet carbs, and Holley sells a few "One size fits nothing" replacements. You could try loosening the screws that hold the primary throttle plates to the shaft and letting them close fully with the idle speed screw backed all the way out, then retighten the screws. The throttle plates are possibly misaligned and dragging on the casting a little, or more likely, the casting is a little out of round.
Jerry

Try adjusting the choke a little leaner. It may be not releasing all the way leaving the fast idle on. You might try backing the fat idle screw out a little.

I'll check these issues out. Am I right to assume that a vac leak wouldn't act this way? ie calm down with a throttle blip. it would keep on racing?

The problem you're describing is almost always caused by dragging throttle plates, especially on a new carburetor. You made a big mistake going with a Holley- - - - -now about all you can do is make the best of a bad situation. No, a vacuum leak would not respond to tapping the throttle.
Jerry

Greg,

On the Chevy Talk High Performance forum http://www.chevytalk.org/fusionbb/showforum.php?fid/72/keyword/Chevy_Performance/ there is a Holley guru with the handle "Ignition Man". He has actually worked for Holley in R & D and could probably help in this matter.

I'll check the throttle plates first. I went with Holley b/c the q-jets are all rebuilt at this point and did not want to risk the $$$ they cost on a pig in a poke. Also while maybe an irrational fear, this manifold in combination with a q-jet was a recall in 69 due to engine fire risk, which my carb had already experienced sometime in it's past. It released tiny bits of metal which would clog it shutting down the engine-not fun in a construction zone late at night with no shoulder and the engine is dying on you. Restart, madly hitting the flashers gun it, die, restart etc...luckily the semi behind me stayed there till I was off the road. Opened it up for a rebuild and found the fire damage. The Holley btw runs great otherwise.

I had a Holley model 4165 650 cfm spread bore on both my '63 C10 and '77 Blazer. No trouble with either of them.

I currently have a Holley model 4175 650 cfm on my '62 C10 and the only trouble I had with it was flooding from the rear vent tube on hard deceleration. I built a connector tube out of solid fuel line and connected the front and rear vents, then drilled a couple of vent holes in the top of the connector and that solved the problem.

I've been using Holley carbs since the late 70's with no major issues.

I Went with the 4175. How did you deal with gasketing re the hot slot on the 63" Did it have one? I used the original Q-jet with the holley gasket on top of the stainless gasket to protect it from the heat. Still ahven't had time to sort it.

Never had a heat problem. I don't run the heat riser valve so it doesn't shove the hot exhaust through the intake and under the carb.

I had headers on both the '63 C10 and the '77 Blazer. On my '62 C10 I have the Ram Horns, but eliminated the heat riser valve when I had the exhaust built.

You need to be able to jump out and look at the carburetor and see if it is really open or if the timing is advanced, from there you can decide what the fix might be. So next time it sticks, pull over without blipping the throttle and take a look.

If the timing is slightly advanced, you will see this problem. Light springs in the distributor may not be pulling the mechanical advance back 100% which will cause the higher rpm. The blip of the throttle is just enough of a jolt to get them moving again. It takes trial and error to get the right springs and weights to come in and advance to the right point. I rebuilt dad's old 1950's Allen distributor machine to run 12volt distributors.so setting them is a breeze.

As a quick test, run around with the vacuum unit unplugged at the distributor, plug the hose. It may not tell you anything other then it's not the problem.
Try and duplicate the problem by slowly raising the rpm in the driveway and letting off the throttle. If you can get it to "stick", throw a timing light on and check it.

It will be difficult, if not impossible to see a difference in the position of the throttle linkage when the engine doesn't return to normal idle- - - -we're talking about a difference of a few thousandths of an inch- - - - -at the throttle plates deep inside the carb. Bite the bullet, pull the carb, and adjust the centering of the throttle plates!
Jerry

Update, I thought maybe it is a vac leak? Snugged up the mounting nuts just in case.

Now for the public service announcement.
Be very careful with the front right mounting nut. Right above it upside down is a mounting screw for the accelerator pump. You can turn that screw with your wrench just enough for gas to gush out when you start the engine. All it takes is about a third of a turn or less. in less than 30 seconds of running there is a half a cup of gas on the manifold. The wrench acts like a gear against the side of the screw. BTW the idiot who designed that mounting flange didn't plan on anyone tightening the nut, you have to have someone stand on the throttle, tighten 1/8th a turn, flip the wrench over sneak under another part of the throttle tighten 1/8th a turn, flip the wrench another 1/8th go back to the other position, curse a lot, repeat.
anyway, waiting for new gaskets to get back to it.

Also, I think I found the problem. I had stupidly left the little arm for the original choke connection to the manifold heat sensor coil in place.(like an idiot) It was up into the choke/fast idle mechanism, maybe catching the mechanism? The engine heats up, the coil moves the wire bingo it's in the way to goober it up.

Anyway, I'll know soon, gaskets should be here Monday.

btw the throttle plates look ok, no binding, seating good etc..

Yet even more...So I was wrong about the cause of the gas leak. it was not because i'd accidentally loosened the cover. It was because the darn thing was defective. It leaked again so I took it off again and lifted the accelerator pump cover and discovered that the face that the cover mates to had a big grinder defect - i.e. an arc left behind from manufacturing. The arc was about 1/64th deep? Maybe more. So, no chance for the seal to last. Very aggravating. They're making it right but the time this has taken and the risk....

so the "pig in a poke" was new, rather than rebuilt?

Joking aside, glad you found it with no fire!

Jon.