Carb question
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Carb question Ok I have a 750 holley double pumper with no choke on a 355 sbc with a com cam 282 extreme energy cam and a 3000 stall. I had the idle set at 800rpms and it would bog then take off when I floor it below 2500rpms. The carb came with a .28 squirters and moved up to a .35 and the problem got back and now does it around 1500rpms. I went up to a .37 in front and .35 in the rear and no improvement so I switch it back to .35 front and .28 rear.
The operating range on the cams starts around 2200rpms so I turned the idle up to 1k rpms and thing are alittle better when I crack the throttle it revs better but the bog is still there.
I checked my timing and it set to 34degrees and 14 at idle, the carb cam to 1 for a light automoblie, next I plan to swap out the springs in my distrubtor so the advance can kick in sooner after that I am out of idea's.
I called holley and they said the 37 squirter should have solved the problem and think there is either a clog, problem with the vac advance or the accel pump arm is not set right. I check the timing and will check the arm but there is no clogs cause I can see the fuel. I spoke with a local shop and they are saying to bump the idle to 1200 but I really did not want to go that high and feel that I shouldn't to solve the problem
I am going to weld in a O2 bung this week and install a wideband sensor and gauge this weekend.
Any tips guys this is my 1st carb project and still learning
The operating range on the cams starts around 2200rpms so I turned the idle up to 1k rpms and thing are alittle better when I crack the throttle it revs better but the bog is still there.
I checked my timing and it set to 34degrees and 14 at idle, the carb cam to 1 for a light automoblie, next I plan to swap out the springs in my distrubtor so the advance can kick in sooner after that I am out of idea's.
I called holley and they said the 37 squirter should have solved the problem and think there is either a clog, problem with the vac advance or the accel pump arm is not set right. I check the timing and will check the arm but there is no clogs cause I can see the fuel. I spoke with a local shop and they are saying to bump the idle to 1200 but I really did not want to go that high and feel that I shouldn't to solve the problem
I am going to weld in a O2 bung this week and install a wideband sensor and gauge this weekend.
Any tips guys this is my 1st carb project and still learning
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That is a decent sized cam for a 355. What is the compression? 14 Degrees base seems a little low...may need to be up around 18 (watch for detonation!).
I would bring the timing in real fast (all in by 2000-2400RPM). You may even experiment with the timing locked out at full (just to see if it helps).
Try the blue pump cam (pretty aggressive). I don't think you need to put the idle over 1000RPM. With the bigger squirter, you may need to go with the hollow screw to get enough FUEL FLOW. Are both pumps on the double pumper working?
How does the car run under normal driving? I also suspect that the cam would like a little more stall speed (3600). Stick with it though, you'll get it sorted out.
I would bring the timing in real fast (all in by 2000-2400RPM). You may even experiment with the timing locked out at full (just to see if it helps).
Try the blue pump cam (pretty aggressive). I don't think you need to put the idle over 1000RPM. With the bigger squirter, you may need to go with the hollow screw to get enough FUEL FLOW. Are both pumps on the double pumper working?
How does the car run under normal driving? I also suspect that the cam would like a little more stall speed (3600). Stick with it though, you'll get it sorted out.
Last edited by pancherj; Apr 6, 2010 at 09:53 AM. Reason: wording
Pull the power valves out of it and put in bigger jets. Like panch said, go with a more aggresive accel pump cams (both front and rear) and put the 37 squirter in the rear. Your air bleed screws should be about 1 1/4 to 1 1/2 turns out.
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I am running 10.3-1 C/R and brodix ik200 heads. I had the timing alittle low cause I also run nitrous 200shot.
I will play with the timing since I have a new msd box with nitrous retard. And try another pump cam, think mine is red and see at what rpm I am getting full timing.
Could please explain alittle about timing lockout. And what turning the bleed screws will do.
I will play with the timing since I have a new msd box with nitrous retard. And try another pump cam, think mine is red and see at what rpm I am getting full timing.
Could please explain alittle about timing lockout. And what turning the bleed screws will do.
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Forgot to add this motor is in a 91 S10 shortbed so it's kinda light and comp cam said with the intake I have my vac will be arould 12-15 at idle
update: I called holley again to get another techs opinion and he does not think I will be able to get bog to go away completely. He feels because the operating range of the intake is 1500 and the cam is 2200rpms.
He said to to try a brown pump cam and bigger squirter but it will only make it better. I feels that if I dump too much fuel that I will have problems with the carb loading up and having a rich condition at the launch
update: I called holley again to get another techs opinion and he does not think I will be able to get bog to go away completely. He feels because the operating range of the intake is 1500 and the cam is 2200rpms.
He said to to try a brown pump cam and bigger squirter but it will only make it better. I feels that if I dump too much fuel that I will have problems with the carb loading up and having a rich condition at the launch
Last edited by t6378tp; Apr 6, 2010 at 11:02 AM.
It can be tuned out, just need to keep playing with the tune of the carb, start backing out your idle mix till the big starts to clear up, if it does then you need to go back up with the squirters maybe, keep tinkering with it.
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Ok, I did some reading up on the timing lock out. I daily drive the truck sometimes and will try lighter springs 1st to bring the advance in faster
Going to pickup some pump cams and springs this weekend and play with this and the mixture alittle more.
Going to pickup some pump cams and springs this weekend and play with this and the mixture alittle more.
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Another thing I thought of...make sure the springs that goes under the pump arm adjusting nut and bolt isn't worn out (primary or secondary). Instead of the pump arm motion activating the pump, it may be compressing the spring. If it looks like the spring is compressing as the arm moves, shim the spring.
I checked this on a recent carb rebuild and sure enough, the spring was compressing. A guy over on Chevelles.com recommended it.
I checked this on a recent carb rebuild and sure enough, the spring was compressing. A guy over on Chevelles.com recommended it.
Thread Starter
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Another thing I thought of...make sure the springs that goes under the pump arm adjusting nut and bolt isn't worn out (primary or secondary). Instead of the pump arm motion activating the pump, it may be compressing the spring. If it looks like the spring is compressing as the arm moves, shim the spring.
I checked this on a recent carb rebuild and sure enough, the spring was compressing. A guy over on Chevelles.com recommended it.
I checked this on a recent carb rebuild and sure enough, the spring was compressing. A guy over on Chevelles.com recommended it.
Last edited by t6378tp; Apr 6, 2010 at 06:32 PM.
