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Old 07-07-2010, 03:04 PM
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350 SBC woes

I have a problem with an engine that i just rebuilt. I am having trouble with getting the engine tuned and I need some advice. I searched and have not come up with a good solution. I am only getting 5-7" of manifold vacuum. When I rev the engine it picks up to 15-18". It also backfires thru the carb. I have the intial timing set at 12* btdc. Here are the engine specs;

SBC 350 .030 over
Cam: comp 12-210-2
heads: iron eagle 165cc 72cc chambers
carb: 625 road demon
stock deck
Pistons: flat top sealed pro np345; probably rebuilders spec.
head gasket is a steel shim
good oil psi 60 ish

I also get gas spitting out the vent tube of the carb and when I hook the vacuum gage up it gets gas in the line. I have exhausted all my ideas. I think it might have wiped a lobe. Any advice would be appricated. Thanks in Advance.

Eric
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Old 07-07-2010, 03:28 PM
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Quote:
Originally Posted by ericb350

I also get gas spitting out the vent tube of the carb and when I hook the vacuum gage up it gets gas in the line.

Eric
start with a fuel pressure regulator. the problem with the gas spitting out is because of too high of fuel pressure. get the literature for your carb and set it accordingly. most likely it will be around 5-6psi
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Old 07-07-2010, 05:04 PM
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You are off 1 or 2 teeth on the distributor gear advanced or retarded, move the dizzy to find out which way its off.
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Old 07-07-2010, 05:39 PM
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Quote:
Originally Posted by ericb350
I have a problem with an engine that i just rebuilt. I am having trouble with getting the engine tuned and I need some advice. I searched and have not come up with a good solution. I am only getting 5-7" of manifold vacuum. When I rev the engine it picks up to 15-18". It also backfires thru the carb. I have the intial timing set at 12* btdc. Here are the engine specs;

SBC 350 .030 over
Cam: comp 12-210-2
heads: iron eagle 165cc 72cc chambers
carb: 625 road demon
stock deck
Pistons: flat top sealed pro np345; probably rebuilders spec.
head gasket is a steel shim
good oil psi 60 ish

I also get gas spitting out the vent tube of the carb and when I hook the vacuum gage up it gets gas in the line. I have exhausted all my ideas. I think it might have wiped a lobe. Any advice would be appricated. Thanks in Advance.

Eric
from what i read here, youve got one or so rockers too tight on the intake side (and possibly exhaust as well). the poor vacuum to me also is an indicator as well as the backfiring through the carb.
as far as fuel getting into line of the vacuum gauge, that also is tied in with the backfiring through the carb. with an intake valve being too tight, the engine is not just pulling vacuum out of some cylinders while its getting air pushed back from another.
just a thought
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Old 07-07-2010, 07:22 PM
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Thanks for the replies. I will adjust the valves with the motor running and see what that does... The guy from Barry Grant told me my carb was too small whats you guys opinion? Again thanks for the help.
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Old 07-07-2010, 07:31 PM
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If you have never adjusted valves get a good book or do a search on here on the proper way, Or find someone you know that knows engine to help you. If you go to tight you will get the problems you have described and your timing is more then likely is off like already stated also re-check these things, And remember if you go to tight on the valve you will pop a valve and then it gets even worse. JMO


Cole
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Old 07-07-2010, 08:36 PM
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I have read many post on here adjusted as Tech and many recommend. The timing could be off but i thought it was on if not close. I fired it up earlier and gave it some revs for a friend so he can listen and the headers started to glow ever so slightly. Mind you it was running for less then five mins and no higher then 2500 revs. Just thought this might give some more insight. Thanks.

Eric
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Old 07-07-2010, 08:48 PM
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Glowing headers in that case is retarded ignition timing and/or overly rich fuel mixture. I'd look at the timing first, that cam will require 12-18 inital timing.
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Old 07-09-2010, 11:29 AM
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Well a little update to the status of my engine. I went out and bought a fuel pressure gauge that screws into my fuel line. It was bouncing very erratic between 6-13psi. So I bought a regulator and installed that. Then I readjusted my timing btw it was way off. (Thanks eric72nova). The header glowing because of retarded timing made sense. Now the engine runs better and has between 14-16" of vacuum at idle with about 12*initial timing. I still have to adjust the carb and find out why the vacuum fluctuates a little, but that might be fine tuning issues. I just wanted to say thanks to everyone who gave me insight to my problems. I will keep the major updates coming.

Eric
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