1/4-28. Due to the angle of the hole and interference with the edge of the fuel bowl.

Do not discard that float bowl! It can be fixed.

Remember, jets have no effect on idle.

Sorry, I've been there. You'll get through it.

I have same displacement as you, stump puller cam, and '65 tri-power. I modified the idle circuit same as you, and my jetting is 74-64-74. It all works good. Warm idle at 14.5 AFR. Cruise at 14 AFR. WOT at 12.5-13 AFR. I needed a stiffer torsion spring on the rear carb as it wasn't closing fulling after actuating them. Good luck!

Thanks wb. Seems I’m going in wrong direction. See here: https://m.youtube.com/watch?v=1Q3nMs...ature=youtu.be

Car won’t start now. This is similar behavior to that bigger Venturi carb I put on the shelf I mentioned earlier. This is original base plate, original carb top and replaced carb bowl. All the mods already discussed. What would cause this? Air bubble in gas line?

When I drop gas in carb bowl or down carb it starts up for a couple seconds and then dies

Here is with 3 turkey baster full of gas in carb bowl

https://m.youtube.com/watch?v=YPBukW...ature=youtu.be

Is there gas in the float bowl? You can tell by opterating the throttle to see if gas squirts from the accelerator pump holes.

This stuff is hard to troubleshoot online.

Do you have the block off plates for the end carbs installed? I'd block them off to eliminate the chance of a vacuum leak on the outboard carbs.

Then, run a fuel line from pump up to carb. Unhooked, have it run into a bucket and have a helper start the car. Is fuel coming out? Consistently? This is after the inline filter, so we will know that the carb is getting fuel and the pump works.

Then, with fuel in the bowl, install the airhorn and actuated the accelerator pump and visual confirm it's squirting.

I have to ask, any chance on ignition issues?

This is almost comical. Had to exercise the walk-away earlier.

Yes , the carb was squirting. I took the top off and low and behold the powerpiston is sitting in bowl, and after inspecting it’s kind of bent and no longer works. It’s jammed. So somehow it got wrecked when I put the top on. I triple checked the size of the new power valve, same as the old one, so was not a clearance issue. Who the hell knows.

I took the top of my bigger Venturi carb that had a fresh power piston staked in it and threw it on the carb on the motor. Car started up and idled. Af was actually worse. 10.5. Now mind you Ive got the ultimate Frankenstein going at this point, my original base throttle body, center bowl from another carb off the shelf with my original cluster that is mod’d and a top air horn off the 500 cfm carb (that did not work). It’s insanity. And I’m at 10.5 idle.

Dick if you happen to have a one of these carbs available for sale, I might be ready to cut bait over here. Winter is coming and I want to make sure to get some time in with my new rebuild before salt hits the road.

Wb just saw your note. See my last. Also appreciate the feedback on comparison to your ride, happy to hear jets are in the ballpark.

because I got the air horn off the 500 cfm carb to work, I am going to go back and give that 500 cfm unmolested whole carb set up another try tomorrow. I am not enthusiastic, but I’ve got nothing to lose at this point.

If someone had a carb set up for this, I could just drop on, I’d buy it tomorrow.

I've had to walk away numerous times from various projects. It really helps.

Did you adjust your idle screws on this go around? 10.5 is too rich IMO. I have the identical idle circuit modifications that you have and mine are only ½ turn out. that gets me to 14+ AFR.

Any chance the float is mis adjusted on this airhorn?

well Wb hit it. Occam's razor often prevails and it did here, partially. With the frankenstein carb set up, i was able to adjust the screws to fluctuating between 13.5 - 15. its constantly moving between those numbers, hitting 14.7ish maybe 1/3 of the time. so feels like its good enough. plugs look cleaner. Thanks for all the help guys.

Why I say partial - i got a 5 minute cruise before the rain started and cruise was dropping down to 9.9 some of the time, but more of the time was around 10.5 or 11. So my biggest problem still continues to be cruise...

The idle circuit is out of play.

You're running a 64 center jet? If yes, try a 63 or 62. On this one, you are confident your power valve is good and the power piston is installed and the spring correct?

Power valve is brand new, power piston is new too.. I cut about 3 coils off this spring but don’t know how to determine if that is enough. Would you cut more coils, or drop to 62 jet? I have a 64 in their right now

At this point, try lowering the jetting. If too rich, maybe some fuel is leaking into the venturi.

As for piston spring coils, that's beyond my expertise.

Of interest, this gentleman has a lot of interesting Rochester 2 videos: https://www.youtube.com/user/MikesCarburetor/videos

If I was in your shoes, I'd send the center carb to a pro, and for fun tinker with another to learn while you wait on getting that one back in your hands.

Carb issues are really tough on a forum.

Wow he does have a lot of videos. Ty.

I have an idea I am going to investigate - plugging the power valve and seeing where cruise comes in on meter. That should isolate power valve from jets

Fixed orifices wouldn't be on my list of things to change while dealing with fluctuating AFR numbers.

(1) Fuel level in the bowl at the trickle over point. I'd lower float level at the toe 1/8th to 1/4 inch and go for a drive.

(2) Check ignition timing at the cruise RPM where things are acting up. Could be weights, springs, or vaccum advance kicking in and out.

(3) Engine mis or skip at cruise RPM will skew AFR numbers. Dirty plug, plug wire, lean condition, rich condition can all cause a mis/skip. That's along with ignition timing being too high or too low for said cruise RPM.

(4) Fuel pressure going up with RPM could make the carb load up to the trickle over point.

(5) The AFR meter itself and wire connections.

Shoot for stable numbers and then fine tune
Clay

Thanks qs. I will go through that list.

Waiting on plug for pv. In the interim I did cur a couple more coils off pp spring, and it did not seem to have much impact. I then dropped the center jets down to 62 and that raised af to run in the mid 12’s at cruise. I felt like I might have a hesitation now when I am at hgwy speed and I mat the pedal. Need to get back on road and confirm that

I mentioned a while ago, you really need to be sure your ignition is dialed in before assuming the carb is the issue. I assume it is.

As for trimming that power piston spring, that is related to the vacuum / cam. I would just follow Pontiac Tri-Power or Dick's advice on that one.

Also, I went for a cruise last night, and there is a lot of fluctuation on the 02 meter both at idle and different cruise RPMs. That is normal. My warm idle fluctuates 1 whole point sometimes.

Maybe the 62s are the right size for you?

Another side note, I have a regulator and gauge on my fuel. I set it at 3.25psi. I also have a 5/16" dead end feed line from my tank to the pump. I can WOT through all 4 gears and never run out of fuel.
This a 455/469 with stump puller.

Ok thanks for all the comparisons. For kicks I took the vacuum advance off to see if that would change anything. Not really. My initial is at 23 right now and all in at 35 on timing.

After car warms up idle usually moves 1 to 1.5 points on 02. My cruise does seem to get better as the car warms up, but it fluctuates from 11-13.5 depending on rpm.

I am going to put an ask out on a new thread to see if anyone near me is mechanic near me good at Pontiac tripower tuning to have them take a look as another set of live eyes. As u say, hard to do online. Let’s see. Appreciate all the help guys. And yes maybe the 62 are right.