Rebuilt a list 4412 2v Holley, it had never been cracked open. This is more of a circle track carb and what I should have done is bought a remanufactured Autolite. Way too rich out of the box, with #74 jets.

Engine is stock 292 and pulls 20 in. of vac at 500, it's running great. The power valve included in the rebuild kit was a 4.5 and the info am reading on this is contradictory. At least, Holley says if an engine pulls more than 13 in Hg, the stock power valve is OK. But their other docs say divide idle vacuum in half, this would mean a 9 or 10 power valve.

 

No idea, huh? Just about everything on the forums and webpages is geared for people trying to make maximum power or mph. The stock PV that came with the carb was a 5.0, going to try a 9.5 that should be closer. In hindsight a careful carb selection would have avoided a lot of hassle.

 

Hi Ted
For a stockish engine I'm thinking the stock pv would be fine.
Since a pv is for WOT enrichment it prolly won't effect to much since a WOT situation drops the Hg to around zero.
Though you're right to try for half of your idle Hg. Seems like a "try it and see if it runs better" deal. Maybe the pv opening a hair sooner will help but I keep going back to it being a stock engine.
Have you tried 68 jets yet?
Edit
I went back and saw it has 74 jets so I would mean 70s not 68s to start.

 

Right, from what I'm reading the PV doesn't change the amount of fuel, just when the fuel kicks in. All this mucking around shows I shouldn't have grabbed a carb off the shelf. A 350 cfm would have been a better choice. This carb wasn't necessarily designed for a low compression low output engine, so "stock" PV doesn't apply, is what I'm thinking.

Yeah, the #68 jets run fine, no surging at steady cruise and just sounds better: it almost seems like the RPMs are lower for a given speed, or maybe it's just quieter. Here's some before after with 74 vs. 68:

 

Well the plug certainly looks better.
Yeah by "stock" I meant the 5.5 that came with it.
I'm kinda going through the same thing right now with my FE trying to figure out what the engine likes with an off the shelf old carb that I grabbed and rebuilt.
About to do the same with my Y.
Enjoy this stuff though.
Good luck with it.

 

Your 500 cfm is probably a little more then you need but it won't hurt as long as your jetting is close. What size venturi does it have, larger then the intake holes? My 292 just has a mild Isky cam, stock G heads. I'm running a 390cfm 4V, had to go up 2 sizes on jets and 2 sizes on the squirter to get it dialed in. Now it runs like a Swiss Watch..

 

Hell, I dunno. It's the standard 500 cfm 2300 that everybody sells. It is running good. Better take a look at the other plugs just to see. In the pics, the #5 plug was completely fouled, upper rightmost. So I'm thinking these jets are close now.

Maybe, should even try jetting down some more, until it surges and then go back up one number. What I'm anticipating with a 9.5 PV and proper jetting is both better acceleration and better economy, so long as I keep my foot out of it. Prior to tuning, it was bad all the time.

 

Swap the plugs, put a clean burning one in #5 and see what happens. If the jetting is off too much it will be the same on all plugs. When only one or two foul you probably have a different problem..

 

Pro-tip - put the #5 plug back in before starting engine! Yeesh.

 

Nice to know we're all the same

 

Tightened up the float level and idle mixture and it's 21 inches of vac with a nice idle. Steady but has a little lope that I like. Leaned out good. Idle spec is 500 tho closer to 600 just sounds a lot better.

A 9.5 PV should improve acceleration a little bit, no? We'll see.

 

Give 'er a shot.
Looks good on paper.

 

PV should be here today. Do they react fast enough to affect crispness of throttle, or just when really stepping on it? Have never been satisfied with that. Could be the squirters are actually too big, figuring that changing the PV first makes more sense, as well as one thing at a time. It doesn't stumble but it's slow to get up to power.

 

Ted I'm not that familiar with 4412s but I believe they are like 4150 and 60s only 2 bbl and have the same adjustments.
If that is the case then throat blade adjustment should be at the very bottom of the transfer slot so that just a little is showing. It makes a perfect square when it's right. This greatly affects throttle response on a 4160.
I would pay attention to the pump circuit from the actuator arm (and its cam) to the squirter.
If you think you have to big a squirt I might try that first since it's easy.
How's your float bowl adjustment? Bottom of sight window?
Almost forgot PV has not much if any effect on throttle response.
Good luck.

 

Yes, float level is correct, and the T slot barely exposed just reset idle mixture, etc. The accelerator pump is adjusted correctly, it does its thing as soon as throttle is moved. It's a 50cc with the cam set on the 1 slot. It just doesn't have a snappy response when throttle is goosed quickly. It's not bad, just a little slow. Pulling 19 in. vac at 500 or so. Took it for a short spin and the transition is better, so we'll run with the 9.5 PV

So to be clear, too big of an accelerator pump squirt will affect the crispness of throttle response?