Today I installed a Holley 4160 (1850) 600 CFM with vacuum secondaries and 66 primary jets and 70 secondariesin the metering plate. The power valve is a 8.5". The carb was completely dissasembled, cleaned and rebuilt with everything inside new. I originally was running a 750 Q-jet on the 69' 331(327+0.030) with Lunati 216/228 with 454/480 lift. The cam has a 107 ICL and 112 LSA.

With the q-jet, the idle at 800 RPM was smooth and I was pulling 16 steady inches of vacuum. With the Holley, the idle is fairly rough at 800 RPM and the vacuum at idle causes the vac gauge to continuously bounce from 14 to 16 inches. The engine seems quicker to rev with the Holley but I hav not had a chance to try it out on the road yet. The floats are set right and the idle valves are set to obtain the smoothest idle and best rpm.

The Lunati cam (06109) was listed as a "decent" idle. It was always really smooth with the Q-jet and now it is a little shaky/rough with the Holley. So now my question is, "Is it right now or was it right with the Q-jet? Every vehicle that i have ever had used a q-jet, so i don't know how the Holley is supposed to act.

Clyde,

You don't mention what manifold you're using. If it's an Edelbrock Performer with the universal Q-jet/Holley/Carter AFB/Edelbrock AFB mounting flange you probably have a vacuum leak. Edelbrock sells a flat steel plate that fixes this. They saved aluminum and weight by leaving out some material on the drivers side of the mounting flange towards the rear. Q-jets are OK on this manifold, but square bore carbs need the plate. Use a paper-thin gasket under the plate and over too, if the bottom of your Holley is still flat. Often, guys have over-tightened them on thick or stacked gaskets, leading to the bottom being bowed. If yours is like this you'll need a thicker gasket under the carb.

Clear as mud?

Tom

I guess the obvious question would be why did you switch carbs?

Tom,

I am using the performer manifold with a spacer designed to make holley carbs fit GM intakes. It looks like a holley on the top and a q-jet on the bottom. Its about 3/4" thick. Its possible that i have a leak. I will check tommorow.

Oneofakind,
I switched to a holley because my friend gave it to me with a bunch of spare parts and I was fed up with the Quadrajet. The q-jet ran rich and flooded at idle and ran lean at speed. I couldn't get any performance out of it. I tried the modifications for performance and it still acted the same.

Sounds like a vacum leak. Spray around the carb with carb cleaner.

Later
Steve

Is the idle clean,or does it burn your eyes?
Some fluctuation in the vacuum signal is normal, especially with a performance cam.
Where is you vacuum advance connected?
Ported vacuum, or Manifold?
Do the idle mixture screws seem to make much difference, or does it seem like they don't do much?
First, if the idle seems rich, and has that Burn your eyes stink, then you need to lower the value of the power valve. Generally, the power valve should be half of what your MANIFOLD vacuum reading. For example: if you have 14" of maniflod vacuum, you should run a 7.5 power valve.
Most Holleys come stock with a 6.5 This is probably the single most important piece of the puzzle. The power valves are cheap...may $3.00 at any local parts store.
Also, most engines will run better with the vacuum advance connected to manifold vacuum rather than ported.
Fianlly, once you have determined you have the correct power valve, adjust the idle to a reasonable RPM, the connect a vacuum gauge to manifold vacuum, and adjust the idle mixture screws to achieve the higset vacuum reading.(both should be about the same)
If it idled smooth with the quadarjet, it should idle smooth with the Holley. graemlins/thumbsup.gif

Clyde,

Lose the adapter, all you need is the thin steel plate, not a regular thick carb adapter. You've got a vacuum leak.

Tom

Power valve is an 8.5???? I think there is the problem right there.You will probably need a 5.5 or 6.5 depending on your vaccuum reading..

I checked all around the carb tonight with propane and i couldn't find a leak. I even listened all around the base with the old garden hose and couldn't pick up any hiss. After the wife got back, i took it for a spin.

Man was there a big difference. The engine responded faster and really pulled good when I gave it the gas. I couldn't open it up as i don't have a good place to wind it out but it sure feels alot better than the quadrajet. It feels like I picked up 40 horses. Now when I nail it, i can hear it squal. Thats pretty good for a 3600 pound car with 3.31 gears and positraction turning P235/75 R15 radial tires. I'll trade the good idle and poor performance for the poor idle and good performance any day. Its amazing the difference in sound also, its louder with the Holley and has a much deeper rumble than the Q-jet. I think the q-jet was starving it.

I know the idle problem is going to drive me nuts though so I'm not givin' up. As for the power valve, the vacuum never drops below 14" at idle so i don't think the power valve could be causing the problem. I haven't checked the vacuum under load so I don't know what power valve to put in it yet. Everything that I've read says to shoot for about 2" below the cruise vacuum.

Clyde

Originally posted by Clyde_Maston:
The q-jet ran rich and flooded at idle This says alot right here. A rich idle is a smoother idle most of the time. If it was idling too rich, chances are that the engine had an "artificially" smooth idle due to being too rich. If teh idle is not fluctuating, Id bet you DONT have a vacuum leak.

Check your plugs with the Holley- how do they look? Did you set the idle up with a vacuum gauge? If so, and its best where you have it, then yea, the idle is more than likely lopier because thats what it should have been like in the first place.

As others have said, dial in teh timing first. Maybe advance it a few degrees and see what happens. Afterall, you need to tune it for a carb that is running right.

Originally posted by Clyde_Maston:
I know the idle problem is going to drive me nuts though so I'm not givin' up. As for the power valve, the vacuum never drops below 14" at idle so i don't think the power valve could be causing the problem. I haven't checked the vacuum under load so I don't know what power valve to put in it yet. Everything that I've read says to shoot for about 2" below the cruise vacuum.

Clyde Yeah, even the Holley tech site recomends about 2" below cruising vac., but they're also making that recomendation based on ported vacuum advance!
I'm telling you...use a power valve rated at half of your manifold vacuum at idle! graemlins/thumbsup.gif
You never said anything about your timing...
What is the initial timing set at?
What is your total advance?
Where is the vac. advance. connected?
Again, manifold vacuum will produce a smoother idle. The only reason ported vacuum advance is used, is for smog purposes. It helps richen the mixture under partial throttle.(thus the 2" less recomendation you keep reading about)When you're crusing along at say 30 mph, and then accelerate,
(even a slightly with the 2" less power valve) the vacuum drops, the power valve opens, and richens the mixture. Does that make more sense now?
Manifold vacuum will give you more advance at idle speeds, and will give better off idle throttle response. graemlins/beers.gif

Originally posted by Clyde_Maston:
I checked all around the carb tonight with propane and i couldn't find a leak. I even listened all around the base with the old garden hose and couldn't pick up any hiss. After the wife got back, i took it for a spin.

Man was there a big difference. The engine responded faster and really pulled good when I gave it the gas. I couldn't open it up as i don't have a good place to wind it out but it sure feels alot better than the quadrajet. It feels like I picked up 40 horses. Now when I nail it, i can hear it squal. Thats pretty good for a 3600 pound car with 3.31 gears and positraction turning P235/75 R15 radial tires. I'll trade the good idle and poor performance for the poor idle and good performance any day. Its amazing the difference in sound also, its louder with the Holley and has a much deeper rumble than the Q-jet. I think the q-jet was starving it.

I know the idle problem is going to drive me nuts though so I'm not givin' up. As for the power valve, the vacuum never drops below 14" at idle so i don't think the power valve could be causing the problem. I haven't checked the vacuum under load so I don't know what power valve to put in it yet. Everything that I've read says to shoot for about 2" below the cruise vacuum.

Clyde Clyde,

The Qj that you had likely was a poor match for your 327. I ran several Qj's back to back with my Holley. Performance was pretty close, maybe better with the Qj.

Anyway, glad to hear it's running good! graemlins/thumbsup.gif

As far as the power valve issues goes I agree with Zman.The power valve is a low vacuum fuel in richment circuit....and should open at lower manifold vacuum/Hi load situitions.

The largest number PV that Holley makes is a 10.5.My BBC idles at 18 in of manifold vac and cruises at 22 in of vac.I'm running a 9.5 PV.Since most street driven engines have manifold vac higher than 12 in of vac why doesnt Holley produce PV's in larger vac ratings ? The main system by itself can supply most of the off idle / cruise / part throttle / roll into the throttle type engine demands... It normally only needs the extra fuel in the Hi Demand low vacuum situitions. graemlins/beers.gif

I'm running manifold vac with the holley and the timing is set at 12 initial 36 total and the vac advance adds in 11 inches. When vacuum advance is hooked up its pulling about 46-48 degrees. With the 93 octane, I have no detonation that i can tell.

The plugs were just beginning to clean up after the flooding that occurred when i first installed the Holley. The metering block gasked was leaking around the accelerator pump hole above the power valve and the manifold vac was sucking raw fuel right out of the fuel bowl. Man it blacked the plugs quick and they wouldn't clean up until I drove it. The plugs are a light tam where they have burnt off. It might still be running a little lean at speed. I currently have 66 jets in there but i have a set of 68's and 70's to try after I run it a while.

Clyde

Try pulling the vacumm line from the distributor and plugging it and see if you can clean up the idle without it. If that helps, hook up to ported. Contrary to a popular belief, many engines run rough, or surge, on manifold vacumm.

http://www.chevelles.com/forum/ultimatebb.php?ubb=get_topic;f=9;t=015266

The largest number PV that Holley makes is a 10.5.My BBC idles at 18 in of manifold vac and cruises at 22 in of vac.I'm running a 9.5 PV.Since most street driven engines have manifold vac higher than 12 in of vac why doesnt Holley produce PV's in larger vac ratings ? I often wondered this myself. the powervalve is a simple device with spring tension provided by a simple coil spring. I would think it would be possible to test the opening vacume with a hand held mityvac vacume pump, maybe the spring tension could be shimmed to provide a higher opening vacume. Or the valve could also be made adjustable with spring selections?

I really doubt that the powervalve is causing trouble in this case. Most of the reading that I've done recommends getting a PV that opens 2"h.g. below what your idle vacuum is. Clyde's powervalve shouldn't even be close to open at idle.

His Qj idled fine he said, and the PV on most of those open at 8-9"h.g.

Mike

Guys thats my point.I am aware what most of the print says but I tend to think that it's a " CYA " sort of thing.Probably figuring it's better to be a little rich than too lean.But for a typical street driven car that sees part throttle 95% of the time one rarely if ever needs to have a PV opening so close to manifold idle vac.The main system is perfectly capable of supplying enough fuel for nearly all part throttle needs...They may need help at full throttle high demand situations to my thinking thats where the PV should be doing it's thing.

I do agree that I dont think thats his problem unless the PV has some sort of small leak.I simply wanted to add to the already mentioned PV part of the discussion. graemlins/beers.gif

Greybeard- I think i'll give your suggestion a chance tomorrow night and see what happens and I'll drive it a while with the vacuum gauge hooked up so i can see what my vac is doing at driving conditions.

As for the power valves, there is a lot of error in them. I had a 5.5, three 6.5's and a 10.5 PV to use. I tested them all with a vacuum gauge and determined the point when they just started to open. The 5.5 opened around 6". The three 6.5's opened from 7.0 to 8.5" and the 10.5 opened around 11.0 inches. 11" was a little too close and I thought that would be a problem so I went with the 6.5 PV that actually measured 8.5". They were all aftermarket PV's, not Holley originals.

Now< I have a theory about the unsteady vacuum. The carb gasket that i was using on the Q'jet was the compressed paper type about 1/4" thick. The gasket did not have a divider ridge running down the center of it to match up with the divider on the performer intake. It kind of mimicked the "air gap" designed intakes. The gaskets that i used with the holly had a divider built into the gasket, therby completely separating the the two sides of the intake. I'm thinking that the open gap under the carb may have been contributing to my smoother idle and vacuum. What do you think? how would this effect the performance?

Clyde

I sent you an e-mail last night--if it has an attachment--DON'T OPEN---I woke up this AM with a bug and don't know if it had attached to my mailbox. Am running fix

It would be nice if all the creative energy used creating worms and other difficulties for us were channeled into something useful.