Help! I've been trying everything to tune this carb from jets to pump cams and squirters... but I can't seem to fix it! I upgraded to a .037" squirter from the stock .031" and to the green cam on position 1, and the carb liked it.. it eliminated the off idle stumble in park... however it is still present in gear below 2,000 rpm, and also if I mash the gas from a dead stop the carb takes a while to catch up (about 3 seconds) and give it all it has (almost like the secondaries are taking too long to open). Anyway the carb tuning has been improving when I do things that give it more gas, such as larger jets and a bigger squirter/different pump cam. Could this hesitation from a stop be a power valve issue?? The cam is pulling just north of 14" at idle.. and I haven't pulled the power valve, but I'm pretty sure it came from Holley with the 6.5 valve. Should I upgrade to an 8.5 valve? Or maybe even go to a larger squirter like maybe a .042"?? ,
What are your engine specs? After all you've done, I'm also reminded of the old adage that 90% of carb problems are ignition problems... You running vacuum advance? Have you tried kicking the advance up a couple degrees?
First off What carb are you tuning What motor are you using it on What cam is in the motor What intake is on the motor What is the initial timing set at What is the total timing set at All the above questions need to be answered to get an accurate answer to your question!!
Well unfortunately I don't have an adjustable vacuum canister, but here's the motor: Holley 670 street avenger (71/78 jets, .037 squirter, green cam on 1) Delco HEI dizzy w/ MSD weights and springs (medium springs used) 18° initial at 1000rpm in park 38° total 350 small block Edelbrock performer rpm heads 9.6:1CR Comp cams 12-223-4 with 1.6 roller rockers (.528/.528 w/ 236° @ .050 Performer rpm intake w/ 2 inch carb spacer
Is your 18* initial with our without the vacuum advance hooked up? From your description, it sounds like you need more timing, but from your numbers listed, it seems like you've got enough timing already? What car is this in? I would think the .031" squirter would be fine, but I guess it depends on the car. What transmission? If auto, are you running a stall? What gearing?
18 vacuum disconnected, same with the 38.. and I don't hear any pinging. The car is a 50 fleetline with a th400 and 2500 stall, 373 gears.
It really seems to like as I give more and more gas.. whether it's jets or squirters.. and my plugs are a nice coacoa brown, so it doesn't look like I'm running too rich.
I would check the vacuum at ilde in gear if possible. I have 13 inches of vacuum at idle in park, and I needed to go to a 4.5 PV. Also check your accelrator pump adjustment, as soon as the throttle is moved you should get a good steady stream from the squirter
That all sounds decent. I would try to get a little more initial advance (like 2*) if you can, just because it seems like that's what it wants. What fuel are you running? The 10% ethanol in most gasoline today will need a little more timing than what you would think. Just keep checking those plugs and listening for pinging. Good luck and have fun.
Yeah I haven't checked vacuum in park. Why such a low power valve?? Hahaha I need that luck! This timing and carb tuning has been driving me nuts. I run premium, but it is that 10% ethanol ****.
Maybe I'll change to a medium/light spring combo on the dizzy and see if I can't squeak 2 more degrees in on the initial. I feel like I need a larger squirter and a medium pump cam with a long gradual increase, like orange on 2. But then again I'm new to this carb/ignition tuning game.
You're going about it the right way. Just be patient and like I said, have fun. The 10% ethanol isn't all bad, and we can't do anything about it anyway lol. I think the distributor springs and maybe the orange cam would be a good idea. One change at a time and you'll eventually find your solution.
Yeah I agree with you. I've about exhausted the whole pump cam idea with my current squirter, and when I went back to the 31 it hated it... stumbled all over the place and backfired through the air cleaner. So i suppose it's time to try thr next size up and tinker with pump cams there! If that doesn't do the trick I'll tinker with timing. I appreciate all the help guys. Once I get the chance to put in the new squirter and play with the cams, I'll report back and let y'all know what I come up with.
This sounds like a vacuum leak to me. I also have a 670 CFM Street Avenger on a 350 ZZ4. It came from Holley new with .65 and .68 jets that proved to be too lean. I've gradually increased the jet sizes to .67 and .69 and have just a little hesitation while the engine is running cold. Plugs are still white. I plan to go to .68 and .70 but I'll be surprised if I need to go above .70 on the jets. I'm running an MSD ignition and 10 degrees BTC initial at 700 rpm, vacuum advance disconnected. You've got a lot more cam though. I want to follow your posts and see what you find out.
Your power valve is to make the transition from primary circuit(jets) to secondary circuit!Is your power valve good? turn your idle mixture all the way in it should stall,if not the valve is letting fuel in! If its good get a vacuum gauge that you can read while you are driving,take a drive on the highway and hold 55mph or steady speed,what the vacuum at?if its below what your power valve is its dumping fuel in,not good! If your vacuum is above that then step on the gas and watch the vacuum drop to you power valve number,thats when it lets fuel in as your secondarys start to open(spring in diaphram) Pete
Oh it's good, the motor damn near kills itself if i turn just one of the idle mixture screws all the way in. I wish I could just use my hand held vacuum gauge, but the hose isnt long enough... maybe i should get more from advance and make my own in car gauge with this handheld one haha. Just to see what my motor is doing vacuum wise in situations other than idling in park.
Do a few things first With the engine off, car in park, air cleaner off. move the throttle just a bit - do you see any squirt out of the squirters ?? If no then adjust the spring on the pump until any movement of the throttle will give you a squirt. You may have to start the car once or twice to fill the fuel bowls while doing this. The power valve you want is just a touch below where your car is idling, warmed up and in gear. If the vacuum is 10 then a 9.5 power valve Mine is 8 and I run 7.5 valves - runs 14/15 down the road
Oh trust me. This 670 has proven to give me hell. Way lean out of the box. Even when i was runninv 68/71 jets I still had white plugs. Now i'm up to 71/78 and just about on the money.. but still have an off idle stumble. I hope it isnt a vacuum leak, I didnt over torque any if the fasteners around the intake/spacer/carb due to the fact they're all aluminum.. and I even used the top of the line fel pro intake gaskets with the blue permatorque stripes around each port.
The squirters do squirt, I checked that last night and adjusted the spring to a .015" lash on the pump arm like holley suggests. I really need to set up the vacuum gauge so I can really know how much vacuum I have in gear at idle and during c4uise. I think I'll just rig my hand held gauge into the cabin and do some testing around the neighborhood haha.
There's nothing wrong with that. Just buy like 6' of vacuum tubing, run the line inside your car, and monitor what it's doing.
OKAY, update: So I recurved my distributor. I did a little internal trickery and took my mechanical advance from 20* to 14*, and the motor likes it A LOT. I used the light springs and a total timing of 38* with a snappy curve. It still stumbles down below 1500 because my initial is about 4* higher than the motor likes (it likes around 18* - 20* initial), but other than that this really helped. I'll probably tear the dizzy apart again and try and adjust it a little more so I can back my initial down to around 20* - 22*.. in terms of carburetor tuning, it seems to be pretty solid. I have my idle screws backed out about 5/8 of a turn, and the primary jetting seems to be money. The only thing is it would seem that I'm still running a little rich in the secondaries with my 78 jets, but if I jet back to about 75 or 76 it would be money. The .037" squirter seems to suit me well, however I may change from the more aggressive #2 position on the green cam to the #1 position to go ahead and even out the pump shot. Once I try the pump cam on #1 and get the timing tweaked how I want I'll report back. Thanks for the help fellas, an outside perspective always helps. I tend to get a little too focused on one problem and overlook others.. but I think we're all guilty of that at some point or another
I'll more than likely do that once I get this distributor curve right. It would be nice to know how my motor is performing in terms of vacuum at other loads than just parked and idling.
You know, I was thinking the same thing.. but I don't feel like readjusting all my throttle cable brackets and linkages lol. So I'm gonna frustrate myself and tune around this spacer. The spacer is the one with the 4 separate barrels, which supposedly is aimed towards mid range torque rather than the open spacer which is for top end power... but then again I do already run the Performer RPM air gap, which is somewhat of a high rise intake for being a dual plane. I may just rip it off some day and see how the motor likes it.
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