2012+ WRs: fuel "percolating" when hot ?

Hi guys.

 

When I shut my bike off when its hot, it makes a percolating sound for 20 minutes or so.  It sounds like something is gently boiling within the engine.

 

At first I thought it was the cooling system, but came to realize its actually the fuel system making the noise.  If I remove my gas cap the noise goes away entirely.   Furthermore, if my tank is half full and I look into the tank, I can see bubbles coming up from the bottom of the tank. 

 

This can go on for quite a while.  On one ride the fuel was still making this noise after I had undressed, packed up and we had loaded 2 bikes onto my truck.  At least 15 minutes. 

 

At first I thought (and was told) that this is fuel leaking back from the high pressure side of the injection system (ie between the pump and the fuel injector) into the tank.   But the more I think of it, the volume of fuel to release that pressure should be pretty small and it shouldn't take anywhere near 10 minutes to do so.

 

I'm wondering if others are seeing and hearing the same thing or if its just my bike.

 

I'm wondering if the fuel percolation is caused by boiling fuel in the fuel line between the fuel pump and the injector.  

 

This season my bike stopped starting on the first kick.  I also installed a higher pressure rad cap (2.1 bar, 30 PSI) at the start of the season.  I'm wondering if the two are related.

 

An interesting tidbit of information possibly related to this issue is that factory KTM race bikes have their fuel injection line insulated and wrapped with a metal foil to keep the heat out.

 

Observations, comments and advice ?

 

NORMAL

 

All bikes can do this in the summer months  if you run them slow, or bikes that still have stock exhaust and jetting/mapping, cause they run extremely hot.

 

If you run slow, you need a fan for the hot months.

 

If you race, you will need to insulate the bottom of the tank with reflective tape, and re-pipe and re-map

 

If you race professionally, then you wrap everything, add an oil  cooler, a fan, and VP fuel that boils at a much higher temp.

Interesting.  But none of my riding friends, that own a variety of 2 stroke and 4 stroke bikes, have seen it before ?  Only happens on the fuel injected bikes ? 

 

Is it boiling off the bottom of the tank ?  Or in the fuel line ?

 

If it boils in the fuel line and forces some liquid fuel back past the pump, is the fuel line partially empty when I go to kick start it ?

The grizzly 700s have the same percolating problem and it is because the tank vent was not working and did not vent, them it builds up pressure causing the percolating and if you take the cap off gas shoots out all over the bike. So you may want to check your vent hose to make sure its open.

The grizzly 700s have the same percolating problem and it is because the tank vent was not working and did not vent, them it builds up pressure causing the percolating and if you take the cap off gas shoots out all over the bike. So you may want to check your vent hose to make sure its open.

 

Tomerb: so your WR isn't doing this ?

Edited by MidlifeCrisisGuy

Your WR runs hot , ESPECIALLY if you have not  installed the GYTR kit necessary to make it run reasonably.

 

Interesting.  But none of my riding friends, that own a variety of 2 stroke and 4 stroke bikes, have seen it before ?  Only happens on the fuel injected bikes ? 

 

Is it boiling off the bottom of the tank ?  Or in the fuel line ?

 

If it boils in the fuel line and forces some liquid fuel back past the pump, is the fuel line partially empty when I go to kick start it ?

 

It happens on bikes that are poorly set up, and running hot.

 

Have you done the GYTR kit yet?  If not, it's going to continue to run poorly and hot.

Your WR runs hot , ESPECIALLY if you have not  installed the GYTR kit necessary to make it run reasonably.

 

 

It happens on bikes that are poorly set up, and running hot.

 

Have you done the GYTR kit yet?  If not, it's going to continue to run poorly and hot.

 

 

I'm running the comp ECM, an FMF muffler and I've bumped the idle A/F mixture from "0" to "8".  I wouldn't say my bike runs hot.  But after a long, tough hill climb on a hot day with lots of clutch work, it will be hot. 

 

It certainly doesn't run poorly.  On the contrary, it runs really well.  Crisp throttle response , no hesitation, good power and its virtually stall proof now.   Doesn't burn any oil.

 

The only thing it doesn't do is start on the first kick, like it did last year.   And it makes the percolating noise when shut off.  I'm trying to figure out if the two are related.

Just curious if you know but is it percolating from heat or air? Next time you turn it and it percolates shove a meat thermometer under the tank or use one of those electronic temp guns. Just a thought. 

 

I see several people referring to kick starting these bikes when they have electric start. Just guessing but do  you take the battery out to save weight?

I'm running the comp ECM, an FMF muffler and I've bumped the idle A/F mixture from "0" to "8".  I wouldn't say my bike runs hot.   But after a long, tough hill climb on a hot day with lots of clutch work, it will be hot. 

 

It certainly doesn't run poorly.  On the contrary, it runs really well.  Crisp throttle response , no hesitation, good power and its virtually stall proof now.   Doesn't burn any oil.

 

The only thing it doesn't do is start on the first kick, like it did last year.   And it makes the percolating noise when shut off.  I'm trying to figure out if the two are related.

 I assumed that since you've never experienced gas boiling in the summer, you had no experience or tuning prowess.

 

My bad.

Not sure but it could be the fuel pump. The fuel pump is a motor that is running all the time. As such the fuel could be boiling off the pump. Some of the Raptor 700R's had this problem. But would also vapor lock as well. Have you ever touched a RC car motor after running for 10 mins?

Not sure but it could be the fuel pump. The fuel pump is a motor that is running all the time. As such the fuel could be boiling off the pump. Some of the Raptor 700R's had this problem. But would also vapor lock as well. Have you ever touched a RC car motor after running for 10 mins?

 

Does your bike do this, vlxjim ? 

 

If it is the pump, I wonder if my fuel filter is dirty ?  My bike has been ridden in a lot of nasty stuff in the last year.

Thanks, DonnieD. I have exactly the same symptoms. Good find.

 Good luck and I'm certainly curious on the outcome of yours. 

You're still running the 'base' map in the comp ECU. It's still a lean map. Lean = hot. Seriously, get the GYTR tuner already. You're obviously a tinkerer, and this is one tool that you can play around with to greatly change the personality of your bike's motor/power delivery. You're willing to spend the time and money etc to put YZF cams in your bike, yet you seem unwilling to simply tune your FI... why? Would  you also refuse to rejet a carb'ed bike?? I don't get it...

deleted

Edited by woods-rider

 

This season my bike stopped starting on the first kick.  I also installed a higher pressure rad cap (2.1 bar, 30 PSI) at the start of the season.  I'm wondering if the two are related.

 

 

I don't know why anyone would think that increasing the pressure in their coolant system would be a good idea. The manufacturers design the system to run at a certain max pressure and put on the appropriate rad cap to keep it under that pressure. By replacing the cap with a higher release pressure you are putting extra strain on parts that were not designed to take it (gaskets, etc.). In addition, just because you don't boil as often now, doesn't mean that you aren't still running hot. You most likely are running hot but just don't know it because you aren't boiling so you keep pushing it and could damage your motor. I would bet that your starting issue and fuel noise are related to the high pressure cap.

 

Just my $.02

I don't know why anyone would think that increasing the pressure in their coolant system would be a good idea. The manufacturers design the system to run at a certain max pressure and put on the appropriate rad cap to keep it under that pressure. By replacing the cap with a higher release pressure you are putting extra strain on parts that were not designed to take it (gaskets, etc.). In addition, just because you don't boil as often now, doesn't mean that you aren't still running hot. You most likely are running hot but just don't know it because you aren't boiling so you keep pushing it and could damage your motor. I would bet that your starting issue and fuel noise are related to the high pressure cap.

 

Just my $.02

 

Most coolant systems are designed for 3x the cap rating.

So going from 1.1 to 1.6 is not an issue.

A defective cap is way more prevelent than overstressing the entire cooling system; a cap that doesn't open soon enough, or not at all.  

 I've had this happen on my WR, and it caused a split in the radiator!

 

It's really about getting back to the truck having not spewed all your coolant on a tough ride.

Yeah my WR's cap was stuck to the bottom of the fill neck. The cap was loose but the seal on the bottom was stuck. I had to peal it off and clean the rubber that was on the bottom of the fill neck. Dont think it was working right.

Does your bike do this, vlxjim ? 

 

If it is the pump, I wonder if my fuel filter is dirty ?  My bike has been ridden in a lot of nasty stuff in the last year.

You know I think is has. Once we came back to camp and I was sitting next to it and heard a bubbling air venting sounds. I didnt think much about it. Now that I think about it I bet it was. The bike nevered boiled over or seemed to be hotter than normal. It was a 98F day but mostly open desert riding.

 

If your fuel is clean and your careful your tank should be clean as well. I wash my fuel cans out every now a then.

Edited by vlxjim

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