Engine not running right with choke disengaged

[meri]

Please excuse my description, as I am not very technically sound. This is my first bike.

I purchased a previous gstwin members bike, and it has never been able to run with the choke off. When the choke is off, the bike kind of sputters at certain RPMs and occasionally backfires. When the choke is on, it seems to sound and run fine (to me).

The idle was set for the choke on, so I tried to adjust it for the choke being off. I did this after a 40 minute ride or so. The idle seemed to jump around a bit, but I'm not sure what is normal.

I am hoping to get some input on where to start. I was thinking of starting with the carb air mixture screws, but I'm not sure if that is the right place to look for the problem.

Any help would be greatly appreciated. Thanks.





Pertinent bike information:

All I know about the jet upgrades he did is what he told me: "If I had to guess they are probably 142.5 or 145 mains, more likely the 142.5 because I know I went back down one size after I initially put the pod filter on because it was too rich.  There was a table floating around on the gstwin site that had suggested jet sizes based on what mods you have.  I know the pilots are one size up from stock, which is whatever size the factory pilots were in Canada.  Pretty sure I just set the mixture screw to whatever the table suggested."

it also has the K&N lunch box and wileyco slip on.

[BaltimoreGS]

Are your sure the idle jets are not clogged?

-Jessie

[meri]

I am not. I have not gone into the carbs yet. That could cause high rpm sputtering and backfires?

[BaltimoreGS]

it has never been able to run with the choke off. When the choke is off, the bike kind of sputters at certain RPMs and occasionally backfires. When the choke is on, it seems to sound and run fine (to me).

I took that to mean the bike has an issue at idle too.  If so, That would be my starting point for repair.  Once the idle is sorted out I'd see how it runs.  Clean out the main jets while you are in there too.  Let me know if you need help.  Good luck   

-Jessie

[black and silver twin]

your main jets are way too small. with a lunch box and exhaust you need at least 145s. mine needed 155 mains (verified by wide band O2 sensor on dyno) and I have lunch box and V&H exhaust. runs perfect. if you need choke to run then the jets are to small, the choke increases the fuel ratio. if he gave you the 145s try them if not buy some bigger jets.

Note: the info above is for the 04+ f models with the 3 circuit carbs. I dont know what year you have, so if its older 2 circuit carbs the sizes may be different, but IF YOU NEED CHOKE TO RUN THEN JETS ARE TOO SMALL.

[meri]

Oh, sorry. It's a 90.

[RichDesmond]

Needing the choke on to run/idle is a classic symptom of a carb with clogged idle/pilot circuits. Pull the carbs and clean them before messing with jet sizes.

[The Buddha]

K&N and slip on you should be running 147.5 mains.
But Idle issues are pilot jet, so yes like Richdesmond said, clean them, heck clean everything while you're in there.
Make sure you're not reading 147.5 as 142.5 and try it.
Cool.
Buddha.