Jump to content
Sign in to follow this  

1/8 to 1/2 steady throttle miss

Recommended Posts

1)07 Yamaha YZ450F

2)1100-1600ft, 65F-90F, motocross

3)FMF 4.1 with Megabomb, stock air box, twin air filter, rebuilt motor with stock piston and adjusted valves

4)current jetting 42 Pilot, stock needle at stock height (clip 4)(will get needle code if needed), 170 Main, wired accelerator pump, pilot circuit set as per guidelines.

5)Pops and stumbles very badly at small and steady throttle openings maybe from 1/8 to 1/2. Does not have a bog when cracking throttle open quickly it is just impossible to ride at steady throttle opening.

6) the running issue does not change with motor temp or air temp

Share this post


Link to post
Share on other sites

Has it always been this way or is it a new issue? How many hours on the bike?

Try the bike with the TPS unplugged. If it is better, then the TPS needs attention, if it is the same, then it is is the straight diameter of the needle (or a worn needle jet emulsion tube). Being you state temp does not affect it, my money is on the TPS.

Share this post


Link to post
Share on other sites

Can i run the bike with the TPS unplugged and not be down on power? Doesn't the TPS change the ignition curve for better low end power? IT doesn't really matter if it's missing like it is currently, but for future reference if disconnecting it seems to fix my problem, should i buy a new TPS to bring my performance back up to the full potential.

Share this post


Link to post
Share on other sites

No, you will loose a little power with the TPS unplugged. Unplugging is a quick and simple way to see if your issue is the TPS or actually the jetting. If the problem improves, your TPS is at fault and either needs adjusting or replacement. If the problem remains, it is 99.9% probable that it is the jetting.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×