Visit The Dirt Forum for More Information

Author Topic:   motor runs poor under 2800 rpm's
BK19
Member
posted August 24, 2003 01:39 PM
355 chev 12 to 1 domes rochester 2 barrel dui ignition, runs great at high rpm's but when there is a caution it seems to be loading up (the carb has been completely redone) when we are stopped to relign up i have it in neutrel and when i put it in gear (auto trans) it will die i have to start it in gear while holding it to the floor to get going any ideas


Earl Parker II
Member
posted August 24, 2003 06:29 PM
What brand of carburetor are you using and how much fuel pressure do you have at idle?

------------------
Earl Parker II
www.parkercarburetion.com
704.482.7588


BK19
Member
posted August 24, 2003 07:36 PM
rochester 2 barrel dont know the pressure yet i have to get a gage and it has been only doing scince i have been useing these 291 heads and on 2 different motors coul it be the heads although they were all redone also before i started useing them
i should ay it runs ok cold but when warm is when t starts to cut out and run poor
[This message has been edited by BK19 (edited August 24, 2003).]

[This message has been edited by BK19 (edited August 24, 2003).]

Donnie Ross
Member
posted August 24, 2003 08:53 PM
sounds to rich if runs good cold and messes up when hot, could e jets, float -especially if it just started happening, float could be fuel soaked and raising bowl level, I think the 2gc uses a power piston wich could be sticking, or when you changed heads if some thing caused a lower vacuum signal to the carb this would activate the power circuit mentioned this because of what you said about the heads,have also seen where a piece of rubber flakes off the fuel line during instalation gets caught in the needle and seat causing this,hope this helps but i'm sure earl or kp will get ya straightened out.


BK19
Member
posted August 24, 2003 10:02 PM
brad new brass float, power valve is working right, i m going to put my buddies carb on tomorrow and see if it does the same thing so i can rule the carb out or not, thanks


tilley88
Member
posted August 25, 2003 12:34 AM
I have the same problem. Too much fuel pressure at idle. Drop your idle to 700-800 rpm's, then re-set your air/fuel mixture by the vacuum gage(should raise your idle).


BK19
Member
posted August 25, 2003 09:06 PM
8 pounds of fuel pressure at idle, switched carbs it ran better but still not right could the valve train or plug gap have anything to do with it? or the intake


norightturn
Member
posted August 26, 2003 07:36 AM
BK19, 8lbs fuel pressure is too high for a Rochester 2G carb. That little float is more finicky about idle fuel pressure than in the typical Holley carb.
Adjust your idle fuel pressure down to 6lbs (use an inline fuel pressure regulator), and then re-adjust your idle circuit, and the carb will behave much better for you.
Hope that helps,
KP.


FastEddy
Member
posted August 26, 2003 05:23 PM
What do your spark plugs look like? They should have a sand color. If not, what color are they?


BK19
Member
posted August 26, 2003 07:39 PM
after racing they are a greyish tan but after running it today and yesterday trying different things mosly while idleing they are now pitch black,i wil try and get a regulator tomorrow thanks


FastEddy
Member
posted August 27, 2003 12:00 AM
Yip, to rich. I will have to go with reducing your fuel pressure as others stated. Will you please let us know that works?


ss#4
Member
posted August 27, 2003 12:22 PM
I had the same problem as far as chugging during cautions. I found it was too far advanced.


BK19
Member
posted August 27, 2003 08:38 PM
i have the timeing at 34 degrees, i got a presure regulator but didnt get it on yet, hopefully tomorrow night,another question what should the float (brass) be set at?


BK19
Member
posted August 28, 2003 08:36 PM
i put the reg. in but can really tell until a get in racing conditions so i ill let you know if it cured it after sat night! should there be any fuel dripping out o the booter venturiasembly?


KPLugnut
Member
posted August 29, 2003 08:09 AM
No, there should not be any fuel dribbling out of the venturi booster assembly at idle. What that means is you do not have the idle circuit set properly. Your butterflies could open too far at idle (exposing too much of the idle transfer slots in the baseplate) and you'll need to enlarge (or drill) holes in the butterflies to allow air in at idle and be able to close down the butterflies some. Probably about a .100"-.125" hole will be sufficient to start with. Once that's done and the butterflies are only exposing about .030" of the slot (viewed from underneath) then you'll be able to properly reset your idle mixture screws and the dribbling boosters should be gone.
Another thing that can cause booster pullover is a float level that is set significantly too high (or high fuel pressure, which I'll assume you've just corrected).
Set the 2G float to 21/32" by holding the carb top upside down and measure from the gasket surface up to the casting seam of the leading edge of the float (the part furthest away from the needle/seat). Then turn the carb top right side up and let the float drop and adjust the float drop to 1 3/8".
This will get ya in the ballpark.

Hope that helps and let us know how it goes.

Dayton Umholtz, owner
Kinetic Performance

[This message has been edited by KPLugnut (edited August 29, 2003).]

BK19
Member
posted August 31, 2003 01:05 AM
well not good it ran worse then ever! i just cant figure it out it alays happens when it gets warmed up to racing conditons, now it seems to not get enough fuel,sputtering out of the turns big time and when i got a flat i could hardly keep the thing running while they were changeing the tire


dirtracer7
Member
posted August 31, 2003 09:32 AM
sounds like high float level and fuel expanding when it gets hot.Just a thought.


BK19
Member
posted August 31, 2003 11:39 AM
yeah i dont now the fuel lines dont go anywhre near anything hot and the carb is cool to luke warm at most when the motor is warmed up


BK19
Member
posted August 31, 2003 08:43 PM
i checked the idle screws one is a little longer then the other (the tapered part) the butterflies have a hole in them ,the rod that goes from the throttle lever to the accelerator pump was too short so it wasnt allowing the butterflies to close all the way,i fixed that,i replaced the idle screw and the driver side booster just has 1 or 2 drips coming out of it, the right side is just pouring out at idle could it be just a bad cab or ?


dirtracer7
Member
posted September 01, 2003 08:41 AM
If you can get ahold of another carb it would be a easyto try, most of this stuff we run has been used many years already.


dirtracer7
Member
posted September 01, 2003 08:44 AM
Hey bk earl parker II helped me getting my holley straightened out give him a call.


KPLugnut
Member
posted September 01, 2003 01:29 PM
If you've got boosters dribbling fuel, then you've got way too high of a float level.
Your idle mixture screws need to match both each other AND the holes they are being used in, as there are different styles and different diameter idle circuit feed holes.
We can help further, but I'll need to see the carb to do it.

KPLugnut


BK19
Member
posted September 01, 2003 04:54 PM
thanks for all the help so far it is just getting frustrating as i set the float lower and the it is not gettng enough fuel,and that it is only dribbleing out of 1 booster baffles me


BK19
Member
posted September 01, 2003 06:54 PM
put a different base and another float in it and still no change with fuel dribbleing out of the right booster if i adjust the float any lower it wont hardly run then hestitates just when i start to rev it from idle


Back to the Archives