YFZ Central banner
1 - 20 of 37 Posts

·
Registered
Joined
·
15 Posts
Discussion Starter · #1 · (Edited)
Yamaha YFZ 450 2008 - Major issue !!!! I need your advice !!!!

Team,

My apologies that its my fist post and I'm already looking for help. But I came-up with extremely frustrating issues with my YFZ 450. I've been reading this forum for some time, and got many great ideas - for which I'm great full, so please let me know if you can help me out:

I bought 2008 yfz 450 atv. From that day the bike demonstrates the effect of premature cut-off point, while keeping it at full throttle at any gear. Initially, we replaced the module or magneto. After replacing these items a symptom persisted, therefore we replaced the following from another yfz450 without any success:

- Voltage regulator
- Ignition Coil
- We fitted New spark
- Head (cleaned, measured etc... and adjusting valves)
- We replaced the wiring
- We replaced magneto
- We replaced alternator cover, along with pulse output
- We replaced carburettor
- We replaced the CDI to stock


Engine is stock other than Vortex and Leo Vince exhaust. We also connected the quad to the oscilloscope and it shown no issues whatsoever.

I appreciate your input.


Thanks,
 

·
Registered
Joined
·
546 Posts
When you say "Cut off point" do you mean it sounds like its hitting the rev limiter? If so, i think i can help
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #5 · (Edited)
you didnt mention anything about jetting. is this bike modded. it kinda sounds like the main jet could be lean.

Yeah we've tried that too :cry. We've even replaced the carburettor from another yfz. Tried different jets etc...

EDIT: the engine is stock, other than Vortex and after market exhaust
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #6 ·
When you say "Cut off point" do you mean it sounds like its hitting the rev limiter? If so, i think i can help
Yeah, that would be that kind of sound. Whenever I accelerate it would go good up to 3/4 of full throttle. But when getting into higher revs full throttle bike would cut out. Please let me know what you reckon.
 

·
Registered
Joined
·
378 Posts
could it be the boot from the carb to the engine cracked and sucking air if so then you will never get the jetting right
 

·
Registered
Joined
·
1,819 Posts
What is the jetting your running now?
 

·
Registered
Joined
·
824 Posts
Your pilot jet is lower then stock...are you running a kick start? Try messing with you fuel screw. Have you eliminated the TORS? And is the bike dieing at full throttle or is it just back firing?
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #12 · (Edited)
Your pilot jet is lower then stock...are you running a kick start? Try messing with you fuel screw. Have you eliminated the TORS? And is the bike dieing at full throttle or is it just back firing?

No its electric. There are no issues with starting the bike. Yeap we got TORS on the bike. Yeah, we've tried playing with fuel screw and different jets as I said before, but that didn't help - I also had someone with really good knowledge to look at jetting, thinking there was something wrong with what I did - but he said it was good. Its back firing at full throttle - starting from 3/4 of throttle. Similar sound, to if it was limited by something. Thanks for your input.
 

·
Registered
Joined
·
824 Posts
Try removing your TORS system all together and try un plugging the tps sensor I don't run any of those on my bike. If none of that fixes it then it has to be a jetting issue but I'm pretty sure its either your TORS system or the tps.
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #15 ·
Try removing your TORS system all together and try un plugging the tps sensor I don't run any of those on my bike. If none of that fixes it then it has to be a jetting issue but I'm pretty sure its either your TORS system or the tps.

Yeap, we tried both ways with TPS plugged and removed. Same result.

What jetting would you recommend for this set up ?
 

·
Registered
Joined
·
1,819 Posts
I think your way lean. I'd run a 45 pilot, 3rd clip on needle, 168-172 main and 2.5 on fuel screw n see how that goes. N adjust smaller from there.
Are you using kehihn jets or dynojet kits? Use only kehihn dynojets use different numbering system
 

·
Registered
Joined
·
1,463 Posts
Try the jetting suggestions first.

I thought there was a thread about the carb's fuel float not being set right. 9mm is the height. That fixed his issue which sounds like this issue.

Not sure how to test it, but maybe the valves are worn out? It is 3 years old.

Just thinking out loud.
 

·
Registered
Joined
·
546 Posts
Mine did the same thing. Its a lack of fuel getting to the bowl. Check and adjust the carb floats!
 

·
Registered
Joined
·
546 Posts
To measure them, get a set of good dial calipers and measure from the lip of the bowl to the top of the floats while the float is resting on the needle valve but NOT compressing it. Feel free to ask anymore questions if your still not sure
 
1 - 20 of 37 Posts
Top