85 250R Overheating Causes

[oscarmayer]

I do not agree. Logic dictates if you can burn a hole into a piston you then you will significantly increase temps. I have experienced and witnessed this a few times. More than I would like. The whole engine will be hotter.
My guess is your lean ( doubt your doing a plug check correctly, no offense) and or air leak.
To properly check a your tune.
You need 2 new plugs.
Put in new plugs. Start and out around in with no more the 1/4 throttle used and ride for about 5 min. Take plug out. This shows you the pilot/idle jet circuit tune.

Install new plug. Start but take off to at least 1/2 throttle and run for 1/2 throttle non stop. You can even blip to WOT. Shut down by NOT idling or sowing engine speed. You want to kill it right off the bad at mid throttle. Take plug out and check. This shows your mail jet circuit.

I would venture to guess if no air leak, the idle is fine and your main is light tan. Not good. Needs to be dark tan. Your probably rich. Again this depends on you NOT having an air leak like the boot or reed gaskets or something.


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[The_Steve_Man]

He is saying that the internal temp in increased not the coolant temp.

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[Flyingw]

As far as I know the gasket is in correctly. Tab to the rear. I can't say its lean causing the engine to run hot but I will offer this up. The plug has always been in the brown to tan range. The motor has always ran very well. When I tore the engine down a year and a half a go to refresh it, the piston was still pristine meaning no signs of scorching and very minimal carbon on top of the piston. No scratches or gouging on the skirt. It was in excellent condition considering the many times it overheated. when I say overheated, it would boil the coolant out the overflow bottle cap. Once I got air moving through the radiators it would cool right down. It has done this with two different sets of radiators (stock and over-sized). I originally thought the OE radiators were obstructed so I went with the aluminum over-sized radiators on the refresh. I have beat the hell out of that motor and it usually runs and cools just fine except when the weather is hot and humid running slow moving high rev trails but Lee said this past weekend they were not running trails when it overheated but it was very hot and humid.

[arlaunch]

As far as I know the gasket is in correctly. Tab to the rear. I can't say its lean causing the engine to run hot but I will offer this up. The plug has always been in the brown to tan range. The motor has always ran very well. When I tore the engine down a year and a half a go to refresh it, the piston was still pristine meaning no signs of scorching and very minimal carbon on top of the piston. No scratches or gouging on the skirt. It was in excellent condition considering the many times it overheated. when I say overheated, it would boil the coolant out the overflow bottle cap. Once I got air moving through the radiators it would cool right down. It has done this with two different sets of radiators (stock and over-sized). I originally thought the OE radiators were obstructed so I went with the aluminum over-sized radiators on the refresh. I have beat the hell out of that motor and it usually runs and cools just fine except when the weather is hot and humid running slow moving high rev trails but Lee said this past weekend they were not running trails when it overheated but it was very hot and humid.

Looking forward to hearing about the change over to the stock head gasket.

It will likely be awhile until the results come in.

I am not going anywhere though, also i think it will be interesting if and when the solution is found.

Thanks for starting the post and engraving this into the web forever.

[oscarmayer]

Possible the HG or the radiators are slightly plugged from old buildup in them. Have you tried changing. The radiators? eBay has some nice larger better cooling alloy ones with silicone hose sets for $110 shipped.


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[BOB MARLIN]

My ESR 330 hits 245 on my digital trail pro gage in about 15 min. and doesn't boil over. The only time I had a boil over is when I had a head gasket leak that was pumping exhaust gas into the cooling jacket. And yes 245 is hot enough to make sieze because that's what it did the last time out.

[Flyingw]

Possible the HG or the radiators are slightly plugged from old buildup in them. Have you tried changing. The radiators? eBay has some nice larger better cooling alloy ones with silicone hose sets for $110 shipped.


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That's what I bought Oscar.

[arlaunch]

My ESR 330 hits 245 on my digital trail pro gage in about 15 min. and doesn't boil over. The only time I had a boil over is when I had a head gasket leak that was pumping exhaust gas into the cooling jacket. And yes 245 is hot enough to make sieze because that's what it did the last time out.

Race Gasoline?

[*ATC*]

I ran the CR head gasket way back when, and currently on pump gas with no issue. I ride trails in 2nd gear and open area. Just putting it out there

[BOB MARLIN]

No, 91 .......

Race Gasoline?

[arlaunch]

After a bit of thought in this department, i have come to the conclusion that this could be an electrical issue due to the plug not firing at full strength at all times. Likely not to the point of detonation but kinda close to it. This could make a warm engine under certain conditions.

It seems you have jetted to match the current ignition system perfectly while the electronics have slowly deteriorated. Kind of masking the latent problem?

These CDI's etc. are long in the tooth.

Is the machine really easy to start?

Also whenever cylinders get bored it seems to increase compression. This is if the head is not re chambered i suppose? Some builders used to cut the top of pistons for this purpose at the bore shop.

I am curious if what the bore is on that fine machine and if anything has been done to the head to compensate?



Its the only thing that makes sense. This would be a complex problem if you posted for help on this board, as you are one of the best and most experienced fellas out there.

IMO