85 250R Overheating Causes

[Flyingw]

Guys,

when I built Whiskey Bent back in 09, it had a problem of overheating on slow moving high rev trails. When I got it up to open ground and got air moving through the radiators, it would cool down. Stock radiators and rebuilt water pump.

I refreshed it a couple years ago and sold it. I just found out it still has the overheating problem but now it does it on open ground. When I refreshed it, I put oversized radiators on it and rebuilt the water pump again.

My question is, what can cause the motor to overheat? I know the head is not obstructed nor are the water jackets in the cylinder. I'm at a loss as to what can be causing it to overheat.

[Flyingw]

I also know the pipe does have a good seal at the head. Perhaps the main jet is too lean?

[Flyingw]

Its running a Woods type 6 pipe

[Flyingw]

This is Whiskey Bent

[El Camexican]

Have you done a leak down on it? I don't know your cooling system first hand, but some require the non-cap side to be bled. If it's jetting it is more likely your pilot or needle is lean unless your riding pined out most of the time.

[atc007]

What head gasket? It doesn't take much to throw things off. Knowing how impeccable your work is, this is tougher. I'm sure you cleaned the rads thoroughly,what did you use? You are SURE they are open and flowing? My bet is a tad lean,not much, and slight restrictons inside the rads or head gasket
.

[El Camexican]

Do those trikes use a thermostate?

[82 250r]

You are describing my 250r perfectly on tight trails. Riding on trails in 1st or 2nd gear will overheat...just not enough airflow...i have to take breaks and let it cool down.
Define overheating on open ground. Boiling over after 10 min.? I have a temp guage on mine and it wont boil until somewhere above 245*.
I suspect there is nothing wrong with it.

[yaegerb]

What does your plug look like?

What makes you think it's running hot? Is your radiator puking?

[Flyingw]

Its had this problem from day one. I have done leak down tests and all passed. The plug was always a golden brown. I fitted it with an 86 TRX carb jetted stock and its always ran very well so I always left the jetting alone because of that. I sold it to Lisa Dugeon and they have it out at the dunes this weekend. The weather is hot and humid so that may have something to do with it.

[Flyingw]

and yes, the radiator is puking out the overflow bottle. To answer atc007, I've always run the metal head gasket.

[yaegerb]

Head gasket leak is my bet. I never had luck with the three piece metal gaskets unless you apply copper gasket. I stocked up on the OEM fiber gaskets. They seal 10x better.

[Flyingw]

its not the three piece gasket. Its a single CR250 metal gasket. I will have the owner install a stock fiber gasket and see how it does

[muthey]

what coolant is it running? I myself use strictly engine ice, just because all I ride is trails

[Flyingw]

nothing but ice.

[just ben]

Sounds lean to me plug should be a chocalate color

[bkm]

its not the three piece gasket. Its a single CR250 metal gasket. I will have the owner install a stock fiber gasket and see how it does
This headgasket borderlines on having to run race gas. I'd switch it back to the oem fiber gasket.

[bkm]

Also since 90 percent of trail riding is on the needle, lower the clip one position and raise the needle.

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[The_Steve_Man]

Are you using the same head? You know a lot of us run 250r's out there and in the trails without problems. I wonder if there is a problem with the head restricting flow.

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[Flyingw]

Hi King, this has happened with two configurations of the cooling system. Stock radiators, hoses, and cap as well as oversized radiators, silicone hoses, and aftermarket cap that came with the radiators so there is something else common to those two configuration that's causing it. I suggested to Lee to install a stock head gasket and fatten up the jetting a little on the main.

I have scoped the head Steve and there are no obstructions and it's a stock head.

[The_Steve_Man]

Ok. That would be the only thing common that I could think of. I ran a cr head gasket with different carbs in trails and dunes without any problems. The time mine ever overheated was last year at Rampage and the cap I got from you fixed it. The head or cylinder being restricted in some way by a casting flaw would be the only thing I could think of. I would think being too lean to hot like that would burn up the piston on a 2 stroke.

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[NETRA3]

I would have also suggested replacing the radiator cap......Same thing happened on a bike I owned and sure enough it was the cap.

[RIDE-RED 250r]

The CR head gasket does bump the compression up, which in turn raises combustion chamber temps some as well, particularly if you leave jetting where it ran well with a standard thickness gasket.. If you swap in a standard thickness gasket in and the problem goes away, there is your smoking gun.

Or leave the CR gasket in and try richening the slide needle one step and the pilot jet one size and see of that helps.

Also another thought: Do you have a CB carrier with adjustable timing mount?? If so, try backing off the ignition timing a smidge.

I am doubting it is an actual cooling system problem given all the info you provided.

[82 250r]

Before you change the head gasket, run a tank of VP110 fuel through it. The higher compression may need better fuel and a cleaner burn to bring temps down.

[arlaunch]

I have never heard of radiator fluid blowing out due to carb jetting.

The first thing that comes to my mind as stated above is compression.

The thinner head gasket coupled with ever growing carbon deposits could be just the ticket.

But after reading NETRA 3's post about the same thing happening to him and swapping radiator caps was the ticket... Well......

I suppose the carbon deposits get worse over time and so do radiator caps.

[Flyingw]

I always run 91 pump gas at 32:1 Castrol 927. Like I said, two different radiator sets with 2 different radiator caps so I can only conclude that whatever is causing the problem is common between the 2 configurations such as the metal head gasket and jetting. Oh and when I tore the motor down last refresh, there was barely any carbon on the piston. The skirt was still pristine. Its always run like a raped ape.

[RIDE-RED 250r]

91 octane should be good for standard compression. But the CR head gasket and the compression increase it yields might not play well there... Curious as to what you are getting for compression... I'm still thinking you may be pushing the limit on your fuel and jetting with that gasket mod... Maybe not detonating, but can certainly run hotter.

Apologies if this was answered earlier in this thread, but are you certain that it's overheating and not a leaking head gasket causing over pressure of the cooling system?? You can have a head gasket fail in such a way that engine compression/combustion leaks from the combustion chamber into a coolant jacket and over pressurizes the cooling system...

[Flyingw]

Ok guys. For troubleshooting purposes, I have asked the owner to install a stock head gasket and see what we get.

[atc300r]

Are the holes in the head gasket lined up correctly between head and cylinder.I have ran a cr head gasket for years on 91 octane no issues.Trail riding and racing.

[The_Steve_Man]

Jerry Hall posted this another site. He a very reputable builder.
http://uploads.tapatalk-cdn.com/20160708/bdcf0404c0eced6ab7efaf40b280022d.jpg

[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.


Sent from my iPhone using TapatalkThat'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