Just wondered if others had encountered this issue.  I rode a fairly tough two day trial this weekend and every time I re-fueled I noticed a lot of pressure built up in the tank when I removed the cap.  A look inside revealed the half tank or so of remaining fuel was actually boiling.  It was warm weather around 28°C (82F) but it will get a lot hotter than that in summer.  I've only owned the bike during the winter months so this is the first time I've seen it.

 

It appeared to have no impact on engine performance - it ran fine all weekend. The engine is not overheating but there's clearly plenty of heat getting into the tank especially when parked even with the engine off.  At least I know the one way valve in the vent pipe is working!

 

I am curious as to any potential damage this might be causing (and I'd hate for it to blow up while I'm riding).

 

Chris.

Have experienced the same excessive venting, on only hot days. Not many in the UK though! Have used stick on heat insulation and covered underneath of tank and fuel pump. Not had any venting since.

The tank shouldn't build pressure, the breather on the filler cap should allow the gasses to escape. Check the valve is working correctly, by blowing back through the cap while its upright.

Edited October 5, 201510 yr by jrsunt

Just wondered if others had encountered this issue.  I rode a fairly tough two day trial this weekend and every time I re-fueled I noticed a lot of pressure built up in the tank when I removed the cap.  A look inside revealed the half tank or so of remaining fuel was actually boiling.  It was warm weather around 28°C (82F) but it will get a lot hotter than that in summer.  I've only owned the bike during the winter months so this is the first time I've seen it.

 

It appeared to have no impact on engine performance - it ran fine all weekend. The engine is not overheating but there's clearly plenty of heat getting into the tank especially when parked even with the engine off.  At least I know the one way valve in the vent pipe is working!

 

I am curious as to any potential damage this might be causing (and I'd hate for it to blow up while I'm riding).

 

Chris.

HI Chris,

I have had 4RT,s since 2005 without any issue in hot weather of which we also get plenty in W.A. John is right the tank should not pressurise, make sure the std one way valve in the breather tube is the correct way round and clear.

Yes the fuel does get hot, I noticed this early on and always try to refuel regularly to keep the pump covered with fuel and increase the volume of fuel taking up the heat. I don't know if this has a major effect all I can tell you is two others over here that tended to refuel only when empty developed pump problems, I have never had any pump problem in the last ten years. I also run 91 octane fuel as recommended by Tarp, not the premium grades.

Hope this helps

HI Chris,

I have had 4RT,s since 2005 without any issue in hot weather of which we also get plenty in W.A. John is right the tank should not pressurise, make sure the std one way valve in the breather tube is the correct way round and clear.

Yes the fuel does get hot, I noticed this early on and always try to refuel regularly to keep the pump covered with fuel and increase the volume of fuel taking up the heat. I don't know if this has a major effect all I can tell you is two others over here that tended to refuel only when empty developed pump problems, I have never had any pump problem in the last ten years. I also run 91 octane fuel as recommended by Tarp, not the premium grades.

Hope this helps

 

First I've heard of not using premium fuel! Always use the good stuff on bikes. What's the issue? (2015 260)

 

My bike has always been a pain (IMO) to start. Needs a good kick. If I turn off the motor and re-start within 30 seconds it fires easily. If I stop for a chat for 2 minutes or more it's a female dog to start again - needs a really good kick. I'm pretty sure this is because of the heat building up some place.

 

Interesting about potential fuel pump issues if you run the tank dry. It happens all the time to me as I use mine for lanes mostly. I'll adjust my thinking on this now so thanks for the advice.

 

Maybe this will help? Linky:   http://www.ebay.co.uk/itm/Reflect-A-Gold-Exhaust-Manifold-Heat-Wrap-Reflective-Sheet-12x24-DEI-Performance-/301750372936?hash=item4641b94a48

http://www.ebay.co.uk/itm/Reflect-A-Gold-Exhaust-Manifold-Heat-Wrap-Reflective-Sheet-12x24-DEI-Performance-/301750372936?hash=item4641b94a48

 

Just bought some of this. It can't hurt can it. Let you know how it goes.

Thanks guys. That's all good information.

 

I agree that some insulation will be the answer but I don't want anything stuck to the bottom of the pump that will hold moisture and cause rust.  But I am very interested how that material goes ChrisA.

 

Certainly, keeping the fuel topped up will help.

 

The question of what fuel to run is an interesting one.  I've been running 95 for no particular reason.  The bike can be a bit frustrating on warm or hot starts often taking two to four kicks.  I just thought it was poor technique as I also ride a Gas Gas.  The gasser needs throttle and a sharp kick while the Monty is the opposite.  But the Montesa starts 1st kick from cold every time.  I checked the valve clearances today and they were spot on.  Same for plug gap.  So I will try running 91 octane fuel next time.

 

Again, thanks.

Chris.

As has been said the tank should not pressurise so there's a venting issue.As for premium fuel unless an engine really needs it and I doubt a 4rt in it's low state of tune does you'll get no benefit.

Premium fuels like Shell V-Power contain less crap like Ethanol so they do have benefits for normal engines.

In my road racing days we've done a fair bit of testing of fuels,inappropriate octane ratings for an engine have a negative benefit although they might be better for polar bears.