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spudder under 2000rpm...

stockk5

stockk5

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i just put a new 350 in my rig with some goodies to boost it to 400hp,it has vortec heads and 9.5 comp.etc. with a new 770 truck avenger, i didnt do it at first but after a week or so, anytime i give it more then 8th throttle under 2000rpm it spudders,if i really get on it, and hold it, it will shut off, but anything above 2000rpm it will run perfect...(well at least i think perfect)...i set the bowl levels, idle mixture,timed it(or close to). its odd that at just 2000 rpm its like a switch is hit and turns into a normal engine....i cant figure it out:doah:
 
sounds like too much carb to me. Try playing with the timing some, advance it a little more. If that doesn't work, time for a rejet in the carb.
 
Cowboy_80 said:
sounds like too much carb to me. Try playing with the timing some, advance it a little more. If that doesn't work, time for a rejet in the carb.
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ya thats what i was thinking of, some people say its over carbed, but the company i bought it from dynoed it with a 750...so maybe a little less fuel will do it some good?
 
I think less would be best.

You could just stick a blower on it and call it good... :D
 
How did you time it?

Vortec heads need less timing than standard heads, it shouldn't be like a light switch, but try backing initial timing off by a few degrees, see if it's any different. At least it's free and easy. You really want high idle advance and low vacuum/mechanical advance all other times with these heads, but kind of tough to do without a lot of effort.
 
What happens if you just drop the hammer from a dead stop? Does it just fall on its face and die or come very close to dieing?

I'm guessing like the 670 TA's, the 770's require richening the accelerator pump circuit. You can try different discharge nozzles and pump cams.
 
way to not use your own name... shaun89...... (my bro posted on this name which is mine)
 
dyeager535 said:
How did you time it?

Vortec heads need less timing than standard heads, it shouldn't be like a light switch, but try backing initial timing off by a few degrees, see if it's any different. At least it's free and easy. You really want high idle advance and low vacuum/mechanical advance all other times with these heads, but kind of tough to do without a lot of effort.
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sorry guys, didnt no my bro was signed in....i called the company that made my engine and they said 8-12degrees of initial timing,so i put it to ten...i was going to try the old spin it til it started stalling and turn it back a bit, but then my timing is WAAAY off the timing tab.
 
mrk5 said:
What happens if you just drop the hammer from a dead stop? Does it just fall on its face and die or come very close to dieing?

I'm guessing like the 670 TA's, the 770's require richening the accelerator pump circuit. You can try different discharge nozzles and pump cams.
Click to expand...

ya from an idle i have to be east on it, until 2000rpm, if i get on it under 2000 it will fall on its face...pretty fast too, if i just pound it at say, 1500rpm, it will act like i turned the key, but if i let off it will catch again....im so confused...:doah:
 
shaun89 said:
sorry guys, didnt no my bro was signed in....i called the company that made my engine and they said 8-12degrees of initial timing,so i put it to ten...i was going to try the old spin it til it started stalling and turn it back a bit, but then my timing is WAAAY off the timing tab.
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Odd thing about that timing tab. My '79 had a 400 in it, but the timing was about 60* off the tab. Wouldn't run where it was supposed to be. I went through that thing forwards and backwards for two weekends thinking I had something wrong somewhere. Then I took it on a 900 mile road trip. Never had a problem. My buddy was just as confused as I was, then he bought a '82 and had the same problem. We chalked it up to the wrong timing cover on the right engine.
 
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If the carb being used tends to need some adjusting, I'd go that route first. If it didn't do it initially, and you didn't change anything, then carb is probably a likely bet.
 
dyeager535 said:
If the carb being used tends to need some adjusting, I'd go that route first. If it didn't do it initially, and you didn't change anything, then carb is probably a likely bet.
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ya, im starting to think its that, theres a hotrod shop near me with some old timers that know too much for their own good. maybe ill give it to a carb expert...thanks for all the help guys:bow: u keep me sane.
 
I thought that was the big advantage to all these aftermarket carbs, you can do all the adjustments yourself?
 
dyeager535 said:
I thought that was the big advantage to all these aftermarket carbs, you can do all the adjustments yourself?
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ya, me too, but all i could do without ripping into it, is the bowl levels,idle mixture,fast idle, and actual idle speed....i think thats it...pretty lame...i only know my bikes' carb....this is my first truck carb, i want to do the work my self but i dont no what adjustments would be good or bad for it.:rolleyes:
 
Not true. As I was saying you need to tune the accelerator pump circuit. You can do most all of that with the carb on the truck; squirters and pump cam are the biggies. You can also change the secondary spring, but you've gotta fix the problem you have now.

shaun89 said:
ya from an idle i have to be east on it, until 2000rpm, if i get on it under 2000 it will fall on its face...pretty fast too, if i just pound it at say, 1500rpm, it will act like i turned the key, but if i let off it will catch again....im so confused...
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If I'm understanding you correctly, you're describing a lean accelerator pump circuit.

This post might help: http://coloradok5.com/forums/showthread.php?t=174116

If you don't know much about the holley carbs, get this book:
 
mrk5 said:
Not true. As I was saying you need to tune the accelerator pump circuit. You can do most all of that with the carb on the truck; squirters and pump cam are the biggies. You can also change the secondary spring, but you've gotta fix the problem you have now.


If I'm understanding you correctly, you're describing a lean accelerator pump circuit.

This post might help: http://coloradok5.com/forums/showthread.php?t=174116

If you don't know much about the holley carbs, get this book:
Click to expand...

o ya! i forgot about those, i think ill take a look at that book, thanks for the help!
 
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