does .5mm really make a difference

fred /
fred_rva
Mar 25, 2009 12:12PM

I really need some opinions here. I swapped down to a 19mm from a 19.5mm, kept the same jetting but now at WOT with load i get a sputtering. Before anyone asks, the reason i swapped was that through all of the learning, jetting, screwing, and unscrewing, i stripped a couple of the screws that hold the float bowl on which lead to a nice little fuel/air leak. I haven't got to take it out for a good test run, just rode it around the yard for a few minutes.

So this brings me to the question, which i asked before but didn't get very many responses, is .5mm going to make a huge difference?

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Re: does .5mm really make a difference

Jesse -B /
jtbechtold
Mar 25, 2009 12:15PM

no. your other carb was just not properly jetted.

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Re: does .5mm really make a difference

fred /
fred_rva
Mar 25, 2009 12:31PM

With the same jetting the other carb didn't have the same problem, it ran fairly well throughout the throttle range.

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Re: does .5mm really make a difference

Chris Rice /
chrisr
Mar 25, 2009 12:43PM

Idle jet too? Air mixture screw? Same size needle? What carb?

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Re: does .5mm really make a difference

fred /
fred_rva
Mar 25, 2009 04:49PM

19.5 mm phbg to 19mm phbg both dellorto, the only thing that's different is the needle, 19.5 has w9 on 3rd clip, 19 has w7 on 2nd clip. I'm fine in the idle, mid range positions, it's the WOT that's acting weird.

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Re: does .5mm really make a difference

Chris Rice /
chrisr
Mar 25, 2009 05:47PM

Throw your old needle back in it and match the air mixture screw settings and see what happens. Worth a shot right?

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Re: does .5mm really make a difference

fred /
fred_rva
Mar 25, 2009 06:54PM

i'll give it a shot tonight and see what happens. My only concern with that is at the throttle position where it starts acting up it's all main jet. But i'll give it a shot.

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Re: does .5mm really make a difference

R . /
jasonf
Mar 25, 2009 07:00PM

And you can't have an air leak through your float bowl.

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Re: does .5mm really make a difference

fred /
fred_rva
Mar 25, 2009 07:36PM

Sorry fuel leak, you knew what i was getting at.

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Re: does .5mm really make a difference

finny /
Mar 25, 2009 08:15PM

Just put some hondabond or yamabond or your fav sealant on the float bowl of the 19.5mm carb, let it set for a day and run leak free!

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Re: does .5mm really make a difference

fred /
fred_rva
Mar 25, 2009 08:50PM

I'll try that when i get ready to upgrade the carb on one of my other bikes but as for now i have the 19mm on there and learned the difference .5mm makes. Jetting on the 19.5 was 109 when i stripped the screws, jetting on the 19mm 93 and it's just a hair on the rich side.

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