holley 800 cfm

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plumcrazeman

plumcrazeman

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got my 340 running idles fine at 1000-rpm when i put it in to drive it stalls.has a high lift cam. (524 lift ) 340 torker 2 intake a 800 cfm double pumper mech. secondarys.Dont no much about tuning carbs, or is the carb my problem?
(solid lifter valvetrain)
 
i don't know the duration. It's a schooler cam no. 349-8 , I cant find any info. on it. I have the cam card it gives me intake & exhaust size & clearance.
 
What's your initial and total timing set at? Total should be 34 to 36 degrees BTDC with the vacuum advance dissconected. Once that's set and your idle speed is set, you can set your idle mixture to highest vacuum.
 
initial and total timing set at 33* . changed the springs on dist. full advance.have not set the idle mixture to highest vacuum yet.
 
I'm assuming this carb still has a power valve. If so, check to see what it is, and then check your vacuum. Could be you're running richer than Bill Gates
 
i just took the carb out of the box today & installed ,whatever power valve came w/ it is what it has. I need to purchase a vacuum gauge. if i hold the rpm @ 1900 it does not stall.
 
A backfire on the old style Holleys will burst the power valve diaphram, IIRC, the new style Holleys have backfire protection (a check valve). The old style Holleys can be retrofitted with this.

Since this is a new Holley, I wouldn't think that this is a problem. Set your idle mixture and get back to us. Vacuum gauges are relatively inexpensive. I suggest a good quality one though rather than the parts store stuff. Snap-on, Matco, etc. A little more total advance probably wouldn't hurt either. Are you running open chamber heads?

Also, if your power valve is rated at or above the vacuum you're pulling in gear at idle it'll open and run rich.
 
my last new holley came with 7.5 power valves, and were open at idle . it was so rich it would burn your eyes..... i put in 3.5 s and it runs much better....if they are open you should be able to tell just be the smell and the burn to your eyes......also make sure the secondarys are fully closed.
 
As suggested I would check the power valves,also with big cams you generally have to adjust the idle to far open to get enough air to idle which uncovers the primary circut and causes it to run too rich and stumble.You can fix this by either adjusting the secondaries open slightly (theres a screw/allen head at the base plate for that adjustment) or drill two holes in the primary throttle blades,I use a 3/32nds bit.I actually drill 90% of my carbs this way,also if set up correctly your carb should run best at idle with the idle mixture srews at 1 1/2 to 2 turns out to be right,otherwise theres more tuning needed.
 
I put a vacuum gauge on my carb today the best vacuum i could get is 6" , witch would mean i need a 2.5 power valve.what is the difference between a standard and a high flow power valve? witch should i get?
 
well here is my 2 cents/others might disagree but that carb is a bit much 800cfm double pump.if you use the formula for computing cfm by rpm based on engine size you will be in the 600-650 range/for me i like to go 100 cfm above to keep the cylinders charged at full throttle. if you have a street driven ocasional strip car especially with an automatic run a vac seconday carb then tune it with the spring kit for the secondarys with a vac secondary carb you can run a little more cfm as the back barrels only open when the engine pulls enough vacuumn to open them.a book with a really good section devoted speciffically to tuning holley carbs is how to hotrod bigblock chevys. (really sometimes you gotta go outside the box to be efficent)/only reason i have read it. it explains how to select the proper power valve based on engine vacummn /jetting /reading spark plugs the whole 9 yards from experience my carbs have run best with 750 vac secondary/#31 extended shooters #68 jets and tall yellow secondary spring however every engine is different and you just have to work with it hope this helps for a starting point
 
Man, 6 inches is all? That's got to be a pretty big cam.

Stick with the standard flow power valve.
 
That does sound like a pretty big cam but if it's not running right it may pull some more vacuum when you finally get it tuned in so I'd go with a 3.5 PV to start.

I've heard of guys drilling the primary plates to get more air in. Even read it in a Holley book but I tried it on my 750 and it didn't work out good. It idled fine but then ran rich off idle. I replaced the primary plates with new ones and opened the secondary idle stop adjustment a half turn and re-adjusted the idle mixture with the trans. in gear and parking brake set and it ran great all the way through the range. Vacuum now runs about 7 to 7-1/2 inches at idle. (pretty big cam in mine too).

I agree with 6pkmopar about the carb being too big. And being a double pumper with a tight converter like you have will probably make it pretty hard to tune. A 750 vacuum sec. in my opinion will work alot better for your application. I'm running one on my car and have a fairly large cam so I have the 3.5 pv in it and one size bigger jets than it came with and it runs great.

A buddy of mine bought a new Holley 4150 HP series 750 double pumper and he let me try it on my car just to see how it would run and it bogged bad when I mashed the loud pedal real fast and I had a 2800 converter and 4:11 gears. I even went up one size in the jets all the way around and it still bogged pretty bad and then it ran a little rich on the top end. I'm sure I could've tuned it better but since it wasn't mine I didn't worry about it. I doubt it would have ran better than the 750 vac. secondary but that's JMHO.
 
Is the distributor locked out. I see 33* initial and total. I'm confused because there is mention of springs in the distributor... I suspect it's not locked.

Is that 6" of vacuum in gear? Need to be the in gear reading for an auto car. Take whatever you get and either split it or go 1.5-2" below for a PV.
 
crackedback said:
Is the distributor locked out. I see 33* initial and total. I'm confused because there is mention of springs in the distributor... I suspect it's not locked.

Is that 6" of vacuum in gear? Need to be the in gear reading for an auto car. Take whatever you get and either split it or go 1.5-2" below for a PV.
Click to expand...

Good catch Rob. I just re-read that post and am wondering if he installed both the light springs that come with the kit cause if he did it might go to full advance anything above 1000 rpm cause those springs are so light. One is all that should be used along with one of the stock springs.
 
If there is advance in the distributor and it hasn't been restricted, then the engine will have anywhere from 5-9* of initial advance... NO WAY NEAR ENOUGH for this set up.

My two cents if it does have any mechanical advance in the distributor.

Get the car running, set the initial timing to 5 btdc, then run the engine up in RPM until it no longer advances, to find how much advance is in the distributor. You'll need a marked balancer or timing tape. Whatever it say -5 is total mechanical in the distributor.

Use a vacuum gauge to set you initial timing. dial in advance until it stops increasing, then dial it back 1". Read were it's set using a timing light. I'm going to guess it's going to want about 18-22* initial. Subtract that from the 32-34 and that number is advance needed be in the distributor mechanical. You have to JB weld or weld the slots to restrict the advance weight from moving.

Good luck
 
the distributor is full advance (locked out).It idles at 1100 rpm when i put it in drive it stalls.so i cannot get a vacuum reading in gear.
 
I would really take a look at the cam and convertor,you really need to have the cam specs and is the convertor off the shelf or custom built?-also what are the actual stall rpms in the car-both foot brake and flash?.From the sounds of it you are building a pretty nasty combo and more info would really be helpful since they are much more sensitive to the tune and the whole combo-but you probaly know that:-D
 
plumcrazeman said:
the distributor is full advance (locked out).It idles at 1100 rpm when i put it in drive it stalls.so i cannot get a vacuum reading in gear.
Click to expand...

What distributor are you using and how did you lock it out?
 
Just picked up 488 gears & a 4000 stall fairbanks convertor. These will replace the 323 gears & 2500 stall. I think the convertor is locking up.I will let you know tomorrow how it goes. The 2500 stall i had built. mopar performance distributor w/ spring kit installed.
 
Have you put a timing light on it to see what happens when it's pulled into gear? What does it read when you have it at idle?

If the mechanical advance weights have springs hooked up to them it's not likely to be locked out. To lock it out you have to put limiters into the slots the weight run in. If those weights move at all, you have mechanical advance.
 
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