Im trying to get my new Holley 1000 HP carb dialed in. This is on my 71 455. The cam is a 308S The car idles just fine in neutral at 1000 rpm. Floats are set so that they just trickle out as the engine shakes. All 4 mixture screws are out 1 1/2 turns. I first thought that the transfer slots were too exposed on the primary side. So I adjusted the secondary butterflies. As the idle came up, I adjusted the primary down. So now the idle screw is maybe one turn out. But when I put it in drive, the car just dies out. Almost feels like the engine drowns. Now I only have about 4" of vacuum at an idle. The old 850 I had idled fine in drive, but as I recall, I had a 3.5 in that one. Did I just answer my own question? The new carb setup is: Primary jets- 84 Secondary jets- 92 Primary power valve- 4.5 No secondary power valve Primary/ secondary nozzles 32
4" of vacuum with a 4.5 power valve sounds like the problem to me. If there isn't enough vacuum to hold that valve shut, wouldn't it just dump fuel?
I think you did. Below 4" vacuum the power valve is opening, putting the mixture over the deep end. That little trickle of fuel from the boosters is an indication of this. There should be no fuel flow from the booster discharge tubes at idle...if so, you should look at float level, fuel pressure, power valve(s) or all of the above. If you're trying to run vac advance you may be having a timing problem if the vac is too weak to keep the diaphragm pulled in all the way, causing you to lose some advance. I run the 308S as well and run power valves about 1 number lower than the vacuum reading I get in drive. It's still so close to the ragged edge that if it weren't for high stall on the switch pitch, the engine would die. Devon
Jason, I have a very similar combo and had the same problem. The key for my idle was to lock the timing @34* BTDC and set all 4 idle screws @2.25 turns out, a little on the rich side. It now idles around 1200-1400 in neutral and around 900 in gear with no stalling whatsoever. I always shut it down in gear to prevent dieseling. I have the same power valves and vac in gear I think was around 4.5". As the idle speed goes down, the vac goes down. Are you reading the 4" as it's about to stall or at 1000 RPM?
We'll give a 3.5 a try and see what's what after that. I got the 850 to idle nice, Im sure I can this one to do the same. The vacuum reading was when it was idling at around 1000 rpm. Im sure its a bit lower in gear. I hope the 1000 is going to be as streetable as the 850 wasray: You guys think Im in the ball park as far as jet sizes go?o No: Dave- how do you have yours setup? On a side note- How do you guys test your power valves? I bought the coolest power valve tester from Moroso. Works with a mity-vac. No more guessing.
I had 12-15 inches of vacuum so the 6.5 that came in it worked fine.. Plugged the rear one and 84-94 front and rear jets. Idle screws are out 1 1/2 turns.. Brown accelerator cam which is the biggest. Remember accelerator pump shot relative to cam color from lightest to heaviest are as follows. White, Blue, Red, Orange, Black, Green, Pink and Brown One thing you may have to do is tighten up the accelerator spring a bit and bend the tab down so it's tight against the cam. When I mashed the gas the spring would squish to much and I'd get a stumble.. Not enough gas in the shot. That fixed it. I'm going to have to start over with the new motor..:rant:
The secret to taming a big cam on the street is to run as much initial timing as you can. That gives you the most vacuum and best idle. 20* + is best. locked out timing with a start retard is even better.
I run the same cam with a Proform 950. With that cam you definately need a lot of initial advance. Lately I've run 28 degrees initial with a total of 34. Did this by reducing the slot size on the HEI. Your Vac readings shoud be a tad higher at 5-7 inches. I get around 6". I can also idle at 900 in gear in high stall mode. An MSD starter saver module cuts it back 20 deg during cranking. Tom
Just wanted to follow up on this. I managed to get the car out of the garage over the weekend and replace the 4.5 PV wit ha 3.5. No change. Now, I have a PV plug and #92 jets in the rear. What advantage is there to a PV plug as opposed to just putting a PV back in? Im thinking of replacing the PV plug with another 3.5, then bringing the jet sizes down. Any suggestion on what size jets I should put in? I was thinking on 84s
I would definetly lock the timing out! Fixed the same prob on two separate cars by locking out the timing. If you dont want to lock it out to see if that fixes it at least pop a couple of STIFF advance springs on there and see if it goes away. Im guessing you have fairly weak advance springs in there. What happens is when you are in neutral the rpms are up a little and the weights are actually starting to advance the timing already. Advanced ign timing equals higher idle rpms. When you put it in gear your rpms drop a little, causing the distributor to slow down and the weights retract. This then retards the ignition timing and retarding timing slows down you idle speed, and in your case causing it to go too low and stalling the engine. Even if this doesnt fix you prob keep this advice in the back of your head for a rainy day. Good LUCK!! :TU:
I agree that the power valve and timing should be worked on. I am surprised at how many turns you guys are running on the idle screws. With the 4 corner system you usually start at 1 turn out and work from there. Johnny Angel had a thread on idle with the 1000HP. He found out he had a defective carb. http://www.v8buick.com/showthread.php?t=144491&highlight=1000+holley
The car had an 850 DP on it previously and it idled fine in drive. Idled at about 1000 rpm in neutral and about 800 or so in drive. No other changes were made with the rebuild So there's no reason for me to think at this point that the problem is somewhere other than the carb. Distributor and timing are the same. I'm planning on tearing the carb back apart this weekend and make the changes. The 3.5 PV and 84s ought to do it. From what Ive read, the PV plug is more for drag racing. it tends to give an excessive rich mixture at low idle conditions. Stay tuned!
Hey Jason,what happened with this? Did you figure it out.I found this on power valves. http://www.youtube.com/watch?v=6vKlAnKdcB4
Chris, Im sorry I didnt see this post until now. Im not sure of the number. I assume its on the throttle body? Tom- Thats a neat video. I never thought to look to Youtube for tuning tipsou: I havent had a chance to take the car back out. Its either been too cold, raining or Ive been too busy to do anything. But Im pretty confident removing the plug will fix the stupid thing. I'll get to it soon. Its on the list....the never ending list of stuff I have to take care of
Success!!! It was a gorgeous day today. Good carb tuning weather. I took the carb off, and installed a 3.5 PV in the rear and 85 jets. Re installed carb and did a bit of fine tuning on the mixture screws. Just swapping in the PV, the car ran leaner at idle. Now idles in neutral at 900-1000 and it will idle in gear at 700. I think thats as good as it gets folks. Chris- the list is 80514. Stamped HP. I bought the carb from a Allstate Carb & Fuel Injection. They custom built as per my specs from parts
Jason, Yours now idles better than mine :TU: I'd like to get mine to idle lower like yours. I don't understand how installing a PV in the secondary side leans out the idle. I googled it and read a bunch of stuff but nothing on that. Can you explain the logic or point me to where you read about this?
