Author Topic: Need help tuning carbs... (Read 3267 times)

coreytrevortpb · « **on:** April 26, 2007, 09:15:52 PM »

Hi,
I recently installed a Yosh RS3 that I cut down to 10". I also installed a factory pro jet kit. The recommended baseline was 97.5 main jet, middle clip position. I have ridden with this config for the last week or so and it seems like it has a bit less top end grunt than when it was stock. (BTW, bike is a 91 B4, with K&N,stock airbox, yosh slip on, and jet kit). The lower/middle rpm range (4-7K) is peppier than stock but it no longer has that hard pull from 8K to redline that it used to. It does still pull decently well but I think it can/should be better. I was thinking about going bigger on the main jets and putting the 102.5's (stock) back in, and seeing if that helps or hurts. How do I know if I need bigger or smaller main jets? Also, i've read some of you guys are using mains as big as 130+; where do you get jets that big, and how much do they cost? Thanks.

gsxr400 racer · « **Reply #1 on:** April 26, 2007, 09:18:07 PM »

central ohio as in where?

gsxr400 racer · « **Reply #2 on:** April 26, 2007, 09:19:41 PM »

yank your air filter out did the top end get worse or better most people on here i think have holes in the air box that was the way to go awhile ago

coreytrevortpb · « **Reply #3 on:** April 26, 2007, 10:03:40 PM »

I will give it a try and let you know how it goes. I live in Hilliard OH. Thanks.

interfuse · « **Reply #4 on:** April 26, 2007, 10:50:57 PM »

You probably need to go up on the MJ. I'd try the 102.5's. I've tried tons of different settings... I think I settled on 102.5 mains, middle clip, 2.5 turns out, 15mm float height. I have to crack open the carbs this weekend. I'll check...

duane · « **Reply #5 on:** April 27, 2007, 01:43:02 AM »

I hate to complicate things here but I have nearly the same set up you have except I have the old school Yosh can. Stock air box, 97 mains etc etc. Mine pulls hard for a 400. What was difficlut for me was getting the air fuel idle screws right. I believe I'm at 3 1/4 turns out. The Factory Pro kit comes with both 95 and 97 mains, I'd be reluctant to go larger. When I purchased my bike someone had put 105's in it. It had good top end power but a big midrange flat spot. Yuk. The guys at Factory Pro do this all day long and that little sheet that came with your jet kit had settings that worked for at least three other GSF400's. If you get stuck, Marc from Factory Pro will talk to you on the phone, he's friendly and very helpful. I vote for trying to stay with their settings.

coreytrevortpb · « **Reply #6 on:** April 27, 2007, 09:24:01 PM »

Thanks for all of your replies. I put the 102.5 mains in tonight and it is noticably better on the top end. I hear quite a bit of muffled sputtering when I'm not giving it throttle, and it was doing this with the smaller jets as well. Would that be and indictator that I should try a different needle clip position? Its on the middle position now. Anybody know where I can get bigger main jets like 105 or 110 and how much $$? I kind of want to see if I can get even more out of the top end. Thanks.

gsxr400 racer · « **Reply #7 on:** April 27, 2007, 10:23:23 PM »

PM me your addy if i have any i will send them your way
cheers
Jay

duane · « **Reply #8 on:** April 28, 2007, 02:44:23 PM »

Main jets are relativley common. Every motorcycle parts counter I've been to has kept a stock of them behind the counter. Secondly, they're not that expensive, maybe a few bucks each. Call some dealers and ask.

Quote

Would that be and indictator that I should try a different needle clip position?

No it would not be. The needle takes care of the midrange while under throttle. When Idling, that is the area of the air/fuel idle screws and idle jets. Take a look...

Have you read this? Clicky here

interfuse · « **Reply #9 on:** April 29, 2007, 06:15:16 PM »

As it turns out I wasn't using 102.5s. I had 97.5s in...