Carb or Ignition adjustment?

[Dm1pfoy1]

So I have barry grant 750 dp carb and I have a issue im not able to figure out.

So under throttle 50% or better rpms can be as low as 1k there will be a flash/pop (much quieter than carb or engine backfire) almost like a cough on cold start.It will cut power for moment and recover without dying (typically i let off throttle).

I think im over fueling or not enough timing but its rich to point it will gas me out of garage so not leaning out and there is no ping that would lead to believe its lean either.

Does anyone have reliable info on how to 4 post tune carb and tune ignition?Really need help this is first 4 post I have had.

Running 4* static/idle timing i dont have dial light to test high end of timing
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[pwdcougar]

What motor are you running? 750 is a lot of carb. What is your initial advance set at?

Paul

[Dm1pfoy1]

Originally Posted by pwdcougar

What motor are you running? 750 is a lot of carb. What is your initial advance set at?

Paul

Its very mild 383 487x heads and "rv" cam specs unknown for sure think similar to 1102 summit cam. Its more carb then whats prolly recommended but until i can get heads and cam that take advantage of it im stuck.If by initial you mean set at idle im running 4* before. Sorry can never remember my timing terms.
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[Fldawg]

check your float level and the o rings on your needle and seat, had the same probelm with my 650 dp

[Dm1pfoy1]

I also feel I should add I did spring swap on dizzy which helped hugely. Was running heaviest springs now running middle set not black super lights but next step up. I know im running low on timing but want to make sure I set things on safe side because I had a ping between 10* and 12* before on the old set springs and with these being lighter im trying to be conservative.
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[Dm1pfoy1]

Originally Posted by Fldawg

check your float level and the o rings on your needle and seat, had the same probelm with my 650 dp

I thought sticky float might be issue hadn't checked it yet and because I was unsure I wanted to check here first but will now. Thank you
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[GASoline71]

Only 4 degrees initial timing is running less timing than a stock 350. Bump that up to 12 to even 16 degrees initial and see what you get.

What jets are in that carb? front and rear.

Gary

[Dm1pfoy1]

Originally Posted by GASoline71

Only 4 degrees initial timing is running less timing than a stock 350. Bump that up to 12 to even 16 degrees initial and see what you get.

What jets are in that carb? front and rear.

Gary

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Sorry had to edit phone messed up.
I dont remember jet #'s without looking.

So I guess my inexperience lies in where do I set carb so that I can run that much timing because I do not know these carbs well. I know carbs but these are bit different. Where should I set carb so that its not too lean causing need for low timing? Like i said was having ping at 10* so I must have set carb too lean making whole setup run lean at 10* right?

[ol'blu72]

Set timing first then adjust carb. You will be running around in circles if you dont. Also what dist. are you running? Vacuum advance hooked up?

[Dm1pfoy1]

Originally Posted by ol'blu72

Set timing first then adjust carb. You will be running around in circles if you dont. Also what dist. are you running? Vacuum advance hooked up?

HEI it is hooked up for Vac but pull it to time
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[geezer#99]

Originally Posted by Dm1pfoy1

I also feel I should add I did spring swap on dizzy which helped hugely. Was running heaviest springs now running middle set not black super lights but next step up. I know im running low on timing but want to make sure I set things on safe side because I had a ping between 10* and 12* before on the old set springs and with these being lighter im trying to be conservative.
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If you only get 10 to 12 before pinging it's possible your timing tab/balancer isn't accurate.
You'll need to check that.
Look here.
http://www.crankshaftcoalition.com/w...op_dead_center

Also your running rich is because you're idling on the power circuit.

[pwdcougar]

Pinging at 10 is way too soon. Is it possible that the cam wasn't installed straight up?

Paul

[Dm1pfoy1]

Originally Posted by pwdcougar

Pinging at 10 is way too soon. Is it possible that the cam wasn't installed straight up?

Paul

So there is 4* timing advance on cam install. I am presently at 10* inital time with static timing that would be 14* I was able to start from 0 turns and at 2 1/4 turns now there is no pinging. So both were wrong. So once i found timing and got that set I counted turns backwards on each post then added 50% put me at 3 turns was running really rich and used 1/4 increments and finally got to 2 1/4.
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[geezer#99]

Cam timing has nothing to do with dizzy timing.
You can't add them togethor.
Advancing or retarding cam timing moves the torque curve up or down the rpm scale.
What are you talking about when you say you started at 0 turns and at 2 1/4 turns there is no pinging?
Have you proved #1 tdc is accurate yet on your timing tab?

[ol'blu72]

When you are talking turns are you talking about tuning the carb?

[mike16]

not alot to go by but ...here goes

because th lean condition occurs under throttle I would guesse that your little plasic accelorator cam on the side of the carb pumps too much fuel in the first part of its travel and the acceloratore system reservoir runs out as it , the cam, tries to pump whats suppose to be left in the reservoir during the second part of its travel. but because the cam is too radical for the application it pumps too much fuel at the geginning and runs dry befor the main jets catch up. quite common when people set up a carb that is too radical for the engine.

if somebody is standing behind the truck while it is acceloratig and sees black smoke comming from your exhuaste as you accelorate. thats probably what it is. Aslo maybe you may be hearing a mild or soft popping noise from your tail pipe, thats an indication of an overly rich setting causing raw fuel to ignight in the muffler. This would occur at the beginning od excelloration

and then at the accellorator resivoir runs dry you then get the symtoms of a lean condition with the popping up through the carb.

Its an easy fix. I think there are 5 to 7 of thos accelorator cams available. each with two mounting holes so you have about ten possible setting, some cames actuly have three holes with settings. so you can explore tose various settings.

if you experience a rich mixture indication in the first half of ecceloration I wouls fix that and see if the lean condition goes away too. if it does not than select another cam that extends the time period that the accelorator pumps fuel up to and beyond the point where the lean condition occurs.

I dont kno alot about the four corner carbs but witha four corner idle system you dont need a 50 cc pump but again I dontknow alot about your engin parameters and specs.

if you cant solve it with pump cams then I would look at fuel starvation.

Timing is easy to diagnose, check with a timing light and check for vacuum leaks and be sure your advance is working. not rusted if not get a quality adjustable advance, or for a points system get one from a year compatable with your engine. My '72 c 10 307 used a 74 corvette advance when it was points, when I converted to an HEI i went to a 75 corvette HEI advance. NOS cost more but quality is consistant. Replacements adjustables are easier to find and can be adjusted. Some advance kits come with springs and bushings in the kit. Still years later the quality of the return spings are iffy. I would recomend springs from MSD

A lean condition will continue to exist, symptoms and all, no matter what your timing is set at

I hpe I have not confused you nd I have not made any mistakes here. I dont know the 4 corner sytstem. but its a Holley by another name.

I think there Is abook By SA on the 4 corner pumps written by David Vizard.Well written by an incredable and gifted engineer.



so you may be getting rich mixture signals at the beginning of acceloration but when the