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OMC GM 305 Holly Carburetor problems

otto

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"Hi, I have a OMC 225 (305

"Hi, I have a OMC 225 (305) small block from GM. The guy who owned the boat before me did put a Carburetor for a 454 big block on the small block. The problem is that the carb floods the engine and it tops out at 3500 rpm with a top speed at 17 Mph. It is a stringer 800 with a 21/16 upper in a 24' 1974 Sea Ray. The boat does not go on plane at all due to the low speed. If any one has a idea on either how to adjust the big block carb to the small block or where to get a small block carb. I would be happy to get some ideas."
 
"The two carbs are either simi

"The two carbs are either similar or close to it, and that's NOT the problem. What you have is a carb in need of rebuilding.

Jeff"
 
If the carb was not rejetted f

If the carb was not rejetted for the 305 from the 454 calibration the jetting is way to much.
Best to call a dealer and find what size main jets were used in the 305 and what number needles were used in the secondaries.
If you have the 750 cfm carb you may need to change these jets a few times until you find the size that works the best.
The 305 came with a 650 cfm carb if it did have a 4 barrel carb from the factory.
This is why the size of the needles and main jets the dealer tells you to use may not be correct if being used in the larger carburetor.
 
"So sorry, I didn't notice

"So sorry, I didn't notice it was a holly carb. In this case you would not have needles in the secondaries.
The carb may need new metering plates as well as rejetting in main and secondaries.
The holly is a breed of it's own and can be alot of fun to get a correct calibration with.

If this is a spread bore carb you are going to have a problem making it work. The spread bore was used most on high preformance / high fuel use engines."
 
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