slow to accelerate until 5000 rpm - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 6 (permalink) Old 02-15-2012, 04:54 PM Thread Starter
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slow to accelerate until 5000 rpm

Im pretty sure i know whats wrong but id like to get some opinions before hand. Ive got a 91 vn750 with cobra pipes and ear shave. Currently im using size 38 pilots and 140 main jets. The carbs are synched and there are 2 washers under the needles. Carbs are completely rebuilt with all new parts. Ive had air screws anywhere from 1.5 to 4 turns out. When taking off from a stop the bike is slow to accelerate and it feels like quite a load on the engine. When the bike reaches about 4k rpm it stutters for a little bit and when hitting 5k it takes off like normal. This happens in all gears and even while not moving. I think I need to go up a size or 2 on my pilots jets but I just want a second opinion before ordering. Is it possible that I am still lean in fuel. My house sits at 500ft above sea level. Any suggestions.
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post #2 of 6 (permalink) Old 02-15-2012, 06:04 PM
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I know this sounds weird, but I swear Pick had the same problem and after he put the washers on top of the needles all was fine.

If the bike idles fine, you can try going bigger on the main and see if that helps....this based on that you are too lean.

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post #3 of 6 (permalink) Old 02-15-2012, 07:12 PM Thread Starter
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It's my understanding that by putting the washers above the needle you won't be changing anything with the fuel. It will only push against the spring and diaphram more. Are you sure?

As for the jets I was thinking up a size on the pilots to 40. The main doesn't kick in till later and all my problems seem to be below half throttle and below 4500 rpm. Did you mean to say main jets?
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post #4 of 6 (permalink) Old 02-15-2012, 08:42 PM
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Quote:
Originally Posted by yukonjon View Post
It's my understanding that by putting the washers above the needle you won't be changing anything with the fuel. It will only push against the spring and diaphram more. Are you sure?

As for the jets I was thinking up a size on the pilots to 40. The main doesn't kick in till later and all my problems seem to be below half throttle and below 4500 rpm. Did you mean to say main jets?
Sorry, meant to say pilot jet actually....was wrapped up with the needle thing and forgot to read my post before I hit send.

I'm not sure either about why the washer thing worked... It's just what a remember reading...

I'd put the air/fuel screws at 2 1/2 out and leave them there till you get the jets right.

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post #5 of 6 (permalink) Old 02-15-2012, 08:53 PM
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As for the jets I was thinking up a size on the pilots to 40. The main doesn't kick in till later and all my problems seem to be below half throttle and below 4500 rpm. Did you mean to say main jets?
Jon....check the link below. I think you're starving it w/38s. Pilot 42 Main 142
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post #6 of 6 (permalink) Old 02-15-2012, 10:30 PM Thread Starter
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Well i just ordered bigger jets so we will see what happens when they get here. Hopefully it fixes my problem. Thanks for the help guys
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