Overheating on high load and revs only, what could it be ?

[poelinca]

Changed the reeds, PV rocker arm and the air filter, went out for a ride and it looks like the bike is overheating only on high load and high revs.

I tried riding with low revs and it doesn't seam to overheat, nor does it overheat with high revs on flat ground, strictly only when pinning it on hill climbs (takes about 5-15 minutes to overheat, depending on the climb). The engine pulls really strong in all conditions, especially on high revs.

Strange thing is that the bike didn't smoked at all, so i had to top off with some oil to get a little bit of smoke out the pipe. Engine ran good but it didn't last too long, soon enough i had to put more oil as the pipe wasn't smoking again and had that lean kind of sound. Ended up using double the amount of oil that i usually premix.

Jetting is JD red needle #4, 180 main and 40 pilot (should be on the rich side, never had problems with this setup under the same weather conditions and trail).

I highly doubt it's only bad gas/oil.

Maybe sucking air witch leans out the already rich mixture ? If it does suck air thru somewhere, doesn't that mean it should also affect low revs ?

Maybe radiators have tiny small pores ? Last time when the engine overheated it was fixed by welding the tiny pores on the radiators, but then again it used to over heat on low revs too back then.

Maybe piston rings ? I think i have roughly 35-40 hours on the top end.

Maybe crank seals ?

Thanks

 

[Powerhouse]

What does the spark plug look like ? If the water pump and other cooling system components are working like they should I would suspect it's lean, and by adding more premix oil your running it even leaner. Go up on your main jet if it's only doing it at wot and reassess.

 

[Zman]

Do your radiator shrouds fit tight to the sides of the radiators? If you have a gap the air will flow around the radiator instead of through the radiator. You can use some foam rubber to seal the sides if you have a gap.

 

[poelinca]

What does the spark plug look like ? If the water pump and other cooling system components are working like they should I would suspect it's lean, and by adding more premix oil your running it even leaner. Go up on your main jet if it's only doing it at wot and reassess.

I'll check the spark plug when i get back home.
Re: adding more premix will make it run even leaner, does it also explain why when i added the premix oil the bike ran a lot better and it didn't sound leaner anymore, for about 30 minutes until the next climb ... The 180 is the largest main jet JD recommends, should be rich enough so if i need to go one step larger makes me think the problem is elsewhere.

Do your radiator shrouds fit tight to the sides of the radiators? If you have a gap the air will flow around the radiator instead of through the radiator. You can use some foam rubber to seal the sides if you have a gap.

Nope, i have a 2-3mm gap between them and they are pretty bent and in poor shape (radiators). I know new radiators would work wonders, but i've used them like this for close to 1 year without issues so i'm planning to keep them for another 2-3 months. And it wouldn't explain the "sudden change" in overheating the engine from one ride to another.

 

[Lincolnlock]

By adding more oil you are effectively leaning the fuel mixture out. More oil= less gas= lean mixture. That is why the bike seems lean. Take out the gas/oil mix that you have in there with the extra oil and go back to the original mix. Then I would either move the needle to the 3rd clip and try it, or install one size larger main jet and see if this solves the issue. Also try turning the air screw in a bit to make the bike a bit more rich on the bottom.

 

[Powerhouse]

Any time the premix ratio is changed it will slightly affect jetting. Say If the bike is jetted for a 40:1 mix it will run leaner if you run it at 32:1 because there's less gas getting into the engine because there's more oil mixed in the gas. It's not a huge difference it does make a difference. Pull your stator cover and see if there's alot play in the crank. The seals usually don't go bad unless the bearings are going away or if you get a bunch of dirt or junk up into the stator and it finds its way into the seal. Have you pulled the bowl off the carb ? Maybe there's some junk partially blocking the main jet.... Could be lots of things, you just need to check stuff out until you find something.

 

[Jakobi]

I very much doubt a 1% change in oil ratio has any significant effect on jetting. Loads of info online that it does, but really.. it's a small change in the grand scheme of things. A carb can't tell what the liquid it's atomising is made of, and the 2T oil still burns as well.

Water pump impellors? Could be not circulating enough? Have you popped the rad cap and had a look? Again, you'd expect there to be more circulation at high revs though and as such notice the boiling at lower revs.

How's airflow in general? Are you revving the tits off it in 1st and 2nd? or is it faster? I'd be inclined to try some fresh fuel and a new spark plug and work from there. Haven't changed the ignition from sun to rain or anything accidently which could be impacting? Isn't a blocked tank breather (or inline filter) slowing fuel flow to the carb and causing it to lean out on sustained load? Or even float level?

 

[poelinca]

I very much doubt a 1% change in oil ratio has any significant effect on jetting. Loads of info online that it does, but really.. it's a small change in the grand scheme of things. A carb can't tell what the liquid it's atomising is made of, and the 2T oil still burns as well.

Water pump impellors? Could be not circulating enough? Have you popped the rad cap and had a look? Again, you'd expect there to be more circulation at high revs though and as such notice the boiling at lower revs.

How's airflow in general? Are you revving the tits off it in 1st and 2nd? or is it faster? I'd be inclined to try some fresh fuel and a new spark plug and work from there. Haven't changed the ignition from sun to rain or anything accidently which could be impacting? Isn't a blocked tank breather (or inline filter) slowing fuel flow to the carb and causing it to lean out on sustained load? Or even float level?

I did notice some some hissing coming from the tank cap, didn't payed attention to it and that's why i forgot to mention it. May be just as simple as that a blocked tank cap breeder ?

I'll have a look around different areas as you guys mentioned, hopefully it's something that is quick and easy to fix. Thanks all for the input, i'll get back with the results.

p.s. i was in 2nd gear, 1st was to slow for the trail we did felt like it didn't have enough speed

 

[pscook]

I had a similar issue and it was the rad cap. I had "upgraded" to the 1.8 bar KTM cap, but I was having overheating issues on long climbs. I then went back to the "original" 1.6 bar cap and haven't had any issues. Apparently my 1.8 bar cap went bad somehow, and the 1.6 "fixed" the issue.

 

[shawbagga]

I very much doubt a 1% change in oil ratio has any significant effect on jetting. Loads of info online that it does, but really.. it's a small change in the grand scheme of things. A carb can't tell what the liquid it's atomising is made of, and the 2T oil still burns as well.

Pete getting royalties from you jake?

 

[Jacob 'Berg]

Changed the reeds, PV rocker arm and the air filter, went out for a ride and it looks like the bike is overheating only on high load and high revs.

Was it overheating before or after you did the reeds, pv, and air filter?

Only reason I ask, is I am not a big believer in coincidences...

 

[Jakobi]

Pete getting royalties from you jake?

Should be eh!

 

[poelinca]

Was it overheating before or after you did the reeds, pv, and air filter?

Only reason I ask, is I am not a big believer in coincidences...

It was overheating after i've changed all those.

Anyways, tried to remove the vent hose from the fuel cap to check the cap out ... i've used muscle instead of brains that's for sure and i tore the little lip that the hose attaches to. It does have some white gunk of some sort in it, i can blow thru it but it's difficult (definitely not as it should be).

Ordered new tank cap and vent hose, meanwhile i'll check the carb see if everything is ok in there clean it up and then ride again see how it goes with a new spark plug (i didn't had the time to take the old one off and see how it looks like, but i will this weekend).

Unfortunately i don't think i'll have the time to go out and ride soon, maybe in a couple of weeks ...

 

[poelinca]

Should be eh!

Went to ride once more, same symptoms but overheating a lot more. Basically i could only ride 1/4 throttle or less.

Took the carb out today, it was way richer than i remembered and float height was way way off.

What i did till now:
- adjusted the float height to 7.5 mm
- the jet was in good position (red #4, the position i like the most during the summer)
- changed the pilot from 40 to 38 (since the summer is in full swing, 37 celsius today)

Now on to the main jet, i would put a 175 instead of 180 BUT i don't have one. I only have a 172 that i used a couple of years ago in the summer with the NEDJ needle. Unfortunately i don't have time to order a 175 to go with the JD red needle, as i'm leaving in 3 days to my first ever hard enduro race (C class).
Am i safe with the 172 ?

Things i'll also do before the race that will impact the overheating:
- new piston rings + top end gaskets (i'm getting really close or already have passed the 40 hour mark on the piston)
- radiators (they are bent pretty bad, ordered some chinese ones, if they fit they go in for the race, if not i'll use the old ones)
- aluminium water pump mod (if it arrives on time, ordered but i don't have a tracking number for it)
- new fluids

I still have a ton to do for the bike and not all parts arrived, i won't have time to test the bike out before the race ... maybe stop on my way there, but it will be dark, hope it will work out just fine. If needed, i can stop on the track to fiddle with the jets/needles, but everything else needs to be in tip top condition.

 

[pscook]

Replace the radiator cap before you do anything else. Cheap and simple to prove right or not. And it's good to have a spare.

 

[poelinca]

Replace the radiator cap before you do anything else. Cheap and simple to prove right or not. And it's good to have a spare.

It will only work if it's sucking air thru the cap, otherwise the coolant will still boil inside the rad, right ?

Unfortunately i don't have the time to wait for a new one, any other crossover cap (from kato for example) that fits ?

 

[pscook]

It will only work if it's sucking air thru the cap, otherwise the coolant will still boil inside the rad, right ?

Unfortunately i don't have the time to wait for a new one, any other crossover cap (from kato for example) that fits ?

If the radiator is unable to pressurize, the water will boil over and vent out of the cap, allowing the bike to overheat. it is a very common problem, and I had this happen on two of my bikes recently. If the system can't contain pressure, it can't contain water, and it overheats and burps and spits. The radiator cap has exactly one job- to control the pressure in the cooling system. If it can't control the pressure, the system fails to operate at the right pressure and temperature, and the water pushes past the cap.

Purpose of the radiator cap

Another example

 

[VilluEST]

First, just try to bend the ears on the cap a bit more so it's really snug and clean the inner seal and inner radiator lip to see if it makes it better. My GasGas had quite a lot of coolant crystals/aluminium oxide built up and wasn't sealing good enough.

 

[poelinca]

The top piston ring was pretty worn out, i removed it with bare hands + left hand side radiator hose that goes into the frame to connect to the right radiator was pinched + carb float was way off.

Now with new radiators, new piston rings, new water pump and re-jet, everything is back to normal. Kind of ripped my arms off till the piston rings seated tough, but we're back in business.

Had a blast last week, unfortunately fell off on my right shoulder again and with the broken collar bone i had 2 months ago i had to cut the vacation short. Now i'm on "standby" again, for who knows how long the only good thing is that the bike is running amazing, starts first kick and didn't overheat once, not even on upstream rivers in 1'st.

Thanks all for the suggestions!!!