Power Valve Selection
Postmaster
Joined: Oct 2010
Posts: 4,656
Likes: 4
From: Northern and Southern Cal
Try adjusting the pump actuator bolt in the spring.
Making it longer can cut down the amount of fuel the pump can take in thus cutting down the shot.
Go slow and remember what you do for obvious reasons.
Good luck.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
OK. I never had a good handle on that. .015 clearance is specified at WOT to avoid tearing the diaphragm, but it's important that fuel shot is dispensed as soon as throttle is moved as well. Will give that a try!
Postmaster
Joined: Oct 2010
Posts: 4,656
Likes: 4
From: Northern and Southern Cal
It's all about how much the spring and diaphragm pulls back in on release as well as the cam on the shot.
The less the arm moves the less fuel it takes in.
I went for a long time thinking it was the squirter size, come to find out it's pump volume.
Hope it helps.
The less the arm moves the less fuel it takes in.
I went for a long time thinking it was the squirter size, come to find out it's pump volume.
Hope it helps.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Well it is a little better maybe, not what I think it should be though. Juuust a slight hesitation/hiss when snapping the linkage before it spools up? Maybe expecting too much.
The pump squirters. These look like an accident waiting to happen. Stuff a rag down the carb in case (when) I drop the phillips screw down the intake? I think 28 is stock maybe try 25s? Of course didn't think to check during rebuild.
The pump squirters. These look like an accident waiting to happen. Stuff a rag down the carb in case (when) I drop the phillips screw down the intake? I think 28 is stock maybe try 25s? Of course didn't think to check during rebuild.
Postmaster
Joined: Oct 2010
Posts: 4,656
Likes: 4
From: Northern and Southern Cal
That's where I would go next.
Let's assume the amount of fuel in the shot is now optimized.
The squirter is a time release controller.
The smaller the hole the longer it takes that now optimized shot to disperse.
The total shot stays the same yet with a smaller squirter it takes longer to use it all. So you get a smaller initial shot which lasts a bit longer.
And yes it scares me changing them also.
Have a magnet and flashlight handy.
How's your timing?
Let's assume the amount of fuel in the shot is now optimized.
The squirter is a time release controller.
The smaller the hole the longer it takes that now optimized shot to disperse.
The total shot stays the same yet with a smaller squirter it takes longer to use it all. So you get a smaller initial shot which lasts a bit longer.
And yes it scares me changing them also.
Have a magnet and flashlight handy.
How's your timing?
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Well I backed off the initial and vacuum advance timing a bit last night based on a couple observations. Steady highway cruise @ 50 to 60 had some light ping. Not Good. None at part throttle or, heavy acceleration. Just when vacuum comes back up at cruise. Could be, a lot of carbon buildup burning off. But.. A hole in piston is guaranteed otherwise?
So I backed off the vacuum advance some. The plugs show a bit too much timing, so now running about 10. This should fatten up the mixture some as well, as well as leave some cushion for a bad tank of fuel. Maybe can dial the vac advance back up some as well.
So I backed off the vacuum advance some. The plugs show a bit too much timing, so now running about 10. This should fatten up the mixture some as well, as well as leave some cushion for a bad tank of fuel. Maybe can dial the vac advance back up some as well.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
It had a total rebuild maybe 20k miles since then. it's a strong motor and runs well. It was never tuned well at all till relatively recently. Like new.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Not sure exactly how the replacement vacuum cans work pretty sure it's sensitivity alone. 12 turns lock to lock, I backed off three. Leaner jetting, but no surging. Should be close. 10 BTDC too, leaves a little room to play with yet. A pair of .025 nozzles should be here tomorrow and try them out.
Cargo Master
Joined: Apr 2003
Posts: 2,389
Likes: 58
Does it really have the 50cc pump? That's potentially a very big shot of fuel. You can get a pump cam kit. I think all of the pump cams will work with the 50cc pump. Not sure, though. I know there are a couple cams you do not use with the smaller pump.
https://www.holley.com/products/fuel...ts/parts/20-12
My Holley 570 has .028 squirters and the orange cam, I don't recall in which position, with the smaller pump. I don't know if that translates directly to 2 barrel, though. Might be a good place to start.
https://www.holley.com/products/fuel...ts/parts/20-12
My Holley 570 has .028 squirters and the orange cam, I don't recall in which position, with the smaller pump. I don't know if that translates directly to 2 barrel, though. Might be a good place to start.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Pretty sure list 4412 comes stock with 74 jets, 5.0 PV .028 nozzles and a 50cc acc pump. It's WAY too big for a 292 out of the box. One of my dumber stunts and had plenty.
I can tune it down so it will be OK, but.
I can tune it down so it will be OK, but.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
For some reason the .025 pump nozzles haven't shipped yet. Did look down the carb throat, and don't see any phillips screws. Guess I thought they were more easily replaced. Does the carb have to be removed and inverted or something?
Logistics Pro
Joined: Mar 2005
Posts: 3,771
Likes: 80
From: tujunga, calif
I had to do just the opposite on my 390 cfm 4V, it came with 25's and I had to go to 28's to get rid of the off idle hesitation. I've dropped the screw many times on Holleys and it can't go past the throttle plates unless you crack them open..