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Old 08-11-2003, 08:52 AM
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Need help -- SBC running rich all of a sudden

Good day to all of you. I have a problem with my SBC race motor that I can't seem to figure out. I have discussed this with many people and nobody seems to have any answers.

We had the motor built last year for road racing. It's a 350, 4 bolt, with all the normal goodies, but nothing really fancy. We built it to have around 370hp and around 400tq, and that's right about where it was. And we built it to be durable. It ran great all last year and for the first 2 races this year, but the it all of a sudden developed a problem.

The best was to describe it is that it's running very rich, but we're running the same carb and jets as last year. We had the carb rebuilt 3 times and it didn't help so we ruled that out. We've replaced and tested the entire ignition system, new gaskets everywhere, check vacuum leaks, checked lifters, valve springs, etc etc. We basically checked everything you could check without pulling the motor and tearing it apart.

So it must be something that has changed somehow internally, and nobody can figure it out. The conditions we're seeing are basically that it runs rich at all rpms. When we fire the motor up cold, it starts right away as if the choke is on (there is no choke), and you can smell raw gas coming out the exhaust. When I'm on the track it pops and bangs, and actually sometimes chokes itself with gas. I have to dump the clutch, coast, and rev the engine repeatedly until it blows the excess gas out.

So, with all that being said, does anyone have any opinions on what the heck could have changed? The only viable idea that I've heard is that something has caused the mechanical timing to go out, so that even though electrical timing is accurate, the valve timing is way off causing it to run rich. We checked the timing chain and there is very little slack.

Any ideas? We are going to pull the motor eventually, but would like to know what to look for first.

Thanks in advance.

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Old 08-11-2003, 09:55 AM
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have you checked the fuel pressure?
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Old 08-11-2003, 10:04 AM
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Yes, at first glance, I would think it would be the carb you are running. But you said that you worked on it numerous times. I would take a look at your fuel pump. Other than that, I don't really have any ideas on what could be your problem(s).

Good luck with it.

78SilverShark
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Old 08-12-2003, 06:41 PM
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How is the float level? Why did you rebuild the carb so many times before, and were new gaskets used?
I'll agree with 78SilverShark on this one check the fuel pump.
If its running rich, look at the parts on the carb that can cause the problem, fuel pump, float/jets, metering jets.
I bought some rebuild kits from EBAY and the fuel jets would NOT SHUT OFF no matter what I done, flooding just turning the key.
I ended up putting in the old one's after a few hours.
Put on a good fuel filter, sounds like a fuel management problem.
If the motor is kinda new put in some Marvel Mystery Oil in the gas to help clean the deposits in the motor and fuel system.
Watch and listen for a fouled spark plug, once fouled don't use the plug again.
How do the spark plugs look? Please I have to ask so I get the answer: Why did you rebuild the carb so many times before?
And what was done each time or new part put on.
If you prefer you can send me a private email.
George
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Old 08-12-2003, 07:10 PM
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Knowing what carb you are running would help. After all the rebuilds you have done, you are overlooking something. One thing I would look for is a crack or casting flaw in the float bowl that is letting raw gasoline flow into the throat of the carb. Next, I would turn the engine over with the top of the carb off to ensure the float is floating as advertised and shutting the fuel off when reaching advertised level. Still have not found the problem, then I would take the carb off and put on stand and fill the bowl and try to find out how the fuel is getting into the throat. I have seen brass floats develope pin holes and slowly sink enought to flood the carb as well as the black closed foam will also develope a leak and become fuel logged.

Trees
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Old 09-05-2003, 06:15 AM
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I forgot to mention that we had tried 2 other carbs as well. We didn't actually rebuild our carb 3 times, but made adjustments to it. First time was all new seals, second time was new power valve and metering block, last time was just adjustments.

Since I first posted this problem, we've tried even more solutions and nothing has worked.
-3 different sets of plugs
-new cap, rotor, wires
-different distributor
-tested MSD box
-tested chassis ground
-multiple carbs and jetting
-checked vacuum leaks
-tested valve springs and lifters
-played with fuel pressure from 3 psi up to 9 psi
-etc etc etc

Nothing has worked so the engine is over at the builders being torn down, inspected and rebuilt. Will let you know what I find.

Thanks for the inputs.
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Old 09-05-2003, 08:59 AM
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There is nothing in the engine to cause a rich condition.
It has to be fuel delivery. Bad float, crack,warp,pressure,nettle and seat. Has to be there someplace. HTH

Good Luck
Troy
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