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Old 08-19-2013, 06:59 AM
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ruff running sbc350

I have a newly built sbc350 with a 700r tans. Installed a Holley 750 double pumper. Probably too much carb but it seems to be working just fine for now. engine starts right up and idles great. The engine actually runs real smooth until about a 45-50 mph cruise. Then I sense a slight sluggishness, or stuttering. If I accelerate it goes away. If I take my foot off the gas it goes away. Is my timing off? It doesn't really seem to be. Is my carb out of adjustment. I did mess with one of the pump adjustment screw on the carb, but not too much. Could it be a spark plug or crappy wires? I have never ran a sbc350 before so I am not real sure what the power band should feel like. I do not sense a huge amount of power. It seems to me that a sbf302 produces more power, but I guess i could be wrong.

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Old 08-19-2013, 07:13 AM
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Originally Posted by JOHNSHENOUDA View Post
I have a newly built sbc350 with a 700r tans. Installed a Holley 750 double pumper. Probably too much carb but it seems to be working just fine for now. engine starts right up and idles great. The engine actually runs real smooth until about a 45-50 mph cruise. Then I sense a slight sluggishness, or stuttering. If I accelerate it goes away. If I take my foot off the gas it goes away. Is my timing off? It doesn't really seem to be. Is my carb out of adjustment. I did mess with one of the pump adjustment screw on the carb, but not too much. Could it be a spark plug or crappy wires? I have never ran a sbc350 before so I am not real sure what the power band should feel like. I do not sense a huge amount of power. It seems to me that a sbf302 produces more power, but I guess i could be wrong.
More info pls, tell us about the motor, cam, heads, compression. What converter and gear, what's your timing at, what are you using for dist etc.
Could be anything from a lean surge, misfire, converter problem, so any more info would be help full.
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Old 08-19-2013, 07:20 AM
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bygddy,

I am sorry I was not trying to be vague, I bought the motor with a fresh build and do not know a whole lot about it. I am running a HEI distributor. The timing I set by ear. Seems to be smooth, any slight movement forward or back and it gets rough.
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Old 08-19-2013, 01:42 PM
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bygddy,

I am sorry I was not trying to be vague, I bought the motor with a fresh build and do not know a whole lot about it. I am running a HEI distributor. The timing I set by ear. Seems to be smooth, any slight movement forward or back and it gets rough.
No worries, had lots of "unknown" sbc's myself.
Whatever info you do have would help, gear, converter, what's the model number on the Carb. Are you using vacuum advance, is it a lockup converter....

Best guess without having enough info, lean surge, or converter locking and unlocking.
Check all tune up parts first.
Plugs, wires, cap, rotor. The usual
Then get a timing light, start conservitive given the unknown cam.
Start at 16* initial, this with a stock HEI should give you 36*total
Now the Carb, get your transfer slot square, turn your mixture screws all the way in until lightly seated. Then come out 1.5 turns each. Buy a vacuum guage, they are cheap
Once the car is running, and up to temp, plug your vacuum guage into the base of your Carb at a full manifold port. Car in gear, park brake set, tires blocked, start turning your mixture screws out, your aiming for your highest steady vacuum reading. Once this is done, unplug your guage, plug your vacuum advance into the same port you were just using. Now go drive it.
This is a generic basic starting point that will need tweaking depending on cam, compression, gear etc etc. But should hopefully eliminate your stumble.
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Old 08-19-2013, 03:31 PM
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Your trans will shift into OD,or,4th gear @ approx 45 mph.Sounds like that's what may be happening.You could also be having lockup issues with the convertor.Put your gear selector in 3rd,(drive),instead of 4th,(OD) & see if the problem still exists.Cruising 45 in OD will feel sluggish,especially if you have a higher geared rearend.If so,you may just need to drive in 3rd until you can reach a higher speed for cruising.There is a world of difference between a stock 350 & a stock 302.
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