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Enduro Engine - 2 stroke Cylinder, Piston, Tranny, Bearings, Clutch, Pipes & Silencers, etc.


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Old 06-06-2017, 03:39 AM
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poelinca poelinca is offline
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Default Overheating on high load and revs only, what could it be ?

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


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Old 06-06-2017, 05:31 AM
Powerhouse Powerhouse is offline
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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.
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Old 06-06-2017, 07:27 AM
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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.
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Old 06-06-2017, 09:54 AM
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Quote:
Originally Posted by Powerhouse View Post
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.

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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.
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Old 06-06-2017, 10:31 AM
Lincolnlock Lincolnlock is offline
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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.
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Old 06-06-2017, 10:33 AM
Powerhouse Powerhouse is offline
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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.
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Old 06-06-2017, 04:53 PM
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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?
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Old 06-07-2017, 04:15 AM
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Quote:
Originally Posted by Jakobi View Post
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
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Old 06-07-2017, 07:57 AM
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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.
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Old 06-07-2017, 09:09 AM
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Quote:
Originally Posted by Jakobi View Post
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?
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