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I had my carb apart and decided to drill the main jet to .027" it seems to have helped my engine power at high rpm but at low speed I picked up a surge or hunt. I thought this was caused by a lean condition? can a rich condition cause this as well? I am replacing the oil seals this weekend also. should I put a stock jet back in or is it likely that the richening didn't cause it? this is a silver model 10304....

I don't make modifications to the carb. They are precise fuel metering assemblies, and I figure the engineers that design them know way more than me about carbs. I just clean them, replace the needle and seat and they run fine.

Jeff

I agree with Jeff and do the same. Do I punch jets, yes. Only when it is the last resort, when I feel that I have nothing to lose. I also did it as a teaching tool for my students, to show them the purpose of a jet and what can happen, good and bad, when people try it. We've destroyed a few carbs doing it, and lots of jets.

Here's an interesting side story regarding carburetors. My dad owned a machine shop in Warren MI. Holley carburetors was having a problem with their two barrel carbs that were factory installed on Chrysler slant six engines (mid 70's, the car would stall when making turns). Holley came to my dad and wanted him to machine a Holley two barrel out of clear Lucite. They wanted to dye the fuel and film it while the car was running. They ran an ad in the Detroit News asking to 'rent' your Dodge Dart or Plymouth Duster for two weeks while this test was performed. The body of the carb was totally clear, all machining was done with automatic transmission fluid, so the machined hole would remain somewhat clear. This carb my dad built was a work of art for being non CNC'd. Not sure if this clear carb ever solved their problem, but I figure if a team of engineers couldn't get it right, my chances of successfully tickering with a carb are slim to none,,,LOL.

Jeff Pittel

jp1961 said:

Here's an interesting side story regarding carburetors. My dad owned a machine shop in Warren MI. Holley carburetors was having a problem with their two barrel carbs that were factory installed on Chrysler slant six engines (mid 70's, the car would stall when making turns). Holley came to my dad and wanted him to machine a Holley two barrel out of clear Lucite. They wanted to dye the fuel and film it while the car was running. They ran an ad in the Detroit News asking to 'rent' your Dodge Dart or Plymouth Duster for two weeks while this test was performed. The body of the carb was totally clear, all machining was done with automatic transmission fluid, so the machined hole would remain somewhat clear. This carb my dad build was a work of art for being non CNC'd. Not sure if this clear carb ever solved their problem, but I figure if a team of engineers couldn't get it right, my chances of tinkering with a carb are slim to none,,,LOL.

Jeff Pittel

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Great story... I've read about how hard it is to mathematically model fluids and gasses moving through passageways. I know they still build physical wind tunnels instead of just modeling with a computer.

Thanks for posting.

I drill out my jets main 69 and pilot 79 for best results as a rule on all duraforce engines to acheive maximum performence and reliability.my physicical formula is l=h=$$$.In comon terms LEAN carbs make more HEAT which warps the carb body and costs MONEY to replace

beg said:

I drill out my jets main 69 and pilot 79 for best results as a rule on all duraforce engines to acheive maximum performence and reliability.my physicical formula is l=h=$$$.In comon terms LEAN carbs make more HEAT which warps the carb body and costs MONEY to replace

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That's a good formula -- I agree.

I'm still looking for the right duraforce mower so I can try out the carb modifications that I've read about on this forum. :thumbsup:

I got it ironed out. I replaced the jet with a stock one and found my gov setting was too low. when I would run it on the slow side it would surge.