[skeezer541]

I dont know if you guys have this prob. or not but when i sit in traffic and my bike warms up it runs like crap until you ride for a bit and cool it off.What happens is the rubber fuel lines get hot and vapor lock the fuel system...I went to a drag race shop and went through a catalog and bought 6ft of fuel line insulation...13 bucks and it rejects 95% of the heat.....bike runs awesome all the time....

 

[tye1138]

Hmm... Never had that problem with my bike.

 

[yellow blur]

Usually fuel injection isn’t prone to vapor lock due to the constant flow of fuel through the lines. Glad that fixed your problem. Thanks for the post.

 

[skeezer541]

I know its not vapor lock per say I just thought that would be easier to understand...The heat from the rear cylinder was "Super Heating" the fuel.....

 

[tye1138]

Ehh, I'm gonna say your bike is running lean and its causing the problem...

 

[jerry5]

I have not had this problem on my ST4s while running but have had a few incidents when shutting it off when hot and restarting a few minutes later, it is not common but the bike will stumble until I hit the road. When I did my first service and seen the length and route of the fuel lines I believed that there was a fuel vapor issue causing these random moments. You are on the right track with your cure.

Jerry
04 ST4s

 

[LAN]

that's neat..

 

[nine16]

Hmmm. Wondering if this could be the cause of my "dificult starting when hot" problem in another post. Once going, my bike runs fine and I've already swapped the coils and solenoid.

Gonna try it. Can't hurt and a lot cheaper than a new starter, which is about all I have left.

 

[ZDM]

When I installed my magnesium valve cover, I re-routed my gas line hoses. Originally they ran on top outside edge of the cover. As per the service manual I ran them inboard and let them bow up into the recess in the gas tank. I believe I did loose that little cough after sitting at idle for a while, but didn't think about till this post....Hmmmm.
Tell you one thing those magnesium cam covers let the heat out, compared to the stock ones which seem to contain the heat better.

 

[pjonte]

Ehh, I'm gonna say your bike is running lean and its causing the problem...

Thermal insulation is a great idea but I'm inclined to agree with Tye. The fuel pump normally circulates fuel through hoses. Plus the normal fuel pressure ~45psi would prevent the fuel from vaporizing at that pressure. I'd guess your fuel pump is on the way out and as Tye says its probably "running lean". Might be worthwhile to have the fuel pressure checked.

2c

 

[tye1138]

Its running lean because the stupid ECU's are tuned that way. Its just the way things are and ya can't do really much about it besides adjust the CO level.

Why the bike works better when you put the shielding on the hoses is just coincidence. Perhaps when you put the tank back on the bike, it was re-assembled better then the previous time... Now thats something I've had happen before.

 

[LAN]

^
seen that before like a rat's nest..

 

[skeezer541]

The Hoses were always in the same spot,plus I have a Power Commander with a custom Map....The reason Im trying this is because most of the factory motocross bikes have had this problem with the fuel line becoming hot and the bikes running poorly...and yes they are fuel injected now....think about it you have rubber hoses sitting on 200 something degrees,how can you think this has no effect on the fuel? All I know is the bike started hard when hot and ran crapy at low speeds in traffic when hot and now it doesnt, so it helped...

 

[tye1138]

Ya know, the PC doesn't effect anything below 3k right?

Every bike is different, they all have small issues. As I said earlier, your bike has a fueling issue and throwing on some shielding has only patched the issue, not resolved it. The bike should run fine without it, just like everyone else's bike.