250r overheating

xtracrispy

xtracrispy

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Picked up an 85 ATC250r couple months back. Been running 32:1 Super Techniplate or Castor 927 with premium gas. Stock intake and carb, UNI filter, Dg pipe, FMF silencer, Stock bore, Boyeson 2 stage power reeds. 

Took it out last trip with no significant issues. Seemed like it was loading up and running real rich while cruising 1/4-1/2 throttle. Poor throttle response, pulled ok in the powerband, seemed like it signed off kinda early. But you couldn't clutch it to keep the power if it fell out of the powerband, once it fell out it was gone, even downshifting and clutching. Smoked a bit, breaking up wile cruising 1/4-1/2 throttle, plug was black and wet. Stock jetting, 52 pilot, 152 main, needle in second clip from top(second from lowest needle position). Dropped the needle all the way with maybe a little improvement. 

Second trip(last weekend), rejetted with 48 Pilot, 154 main, needle in middle clip(hoping to lean the bottom for better throttle response with richer mid-top for cooling and hopefully better pull on hills), no other changes(except a twist throttle conversion). First run to Olds from washes: better throttle response, less breaking up. Thought I heard some pinging pulling Olds but seemed to run better overall. Next ride at moderate pace, missed a shift and got stuck on a hill. While turning around smelled coolant, overflow tank was higher than normal, looked at my temp strips and they were high (226F or so). Decided to head back to camp, while cruising back temp strips indicated similar temps, higher than I was used to seeing, blew the upper crossover coolant hose about half way back to camp and had to be towed. 

Plug looked good, water pump still spins, not seized.

What should I check next? Pressure test the coolant system? I don't think I'm running lean enough to cause it to get that hot. 

 
My first thought, not too many people run 32:1 anymore, I would run 40:1.  32:1 actually makes the bike run more lean than 40:1.  Lean conditions could cause over heating. At 32:1 there is less fuel, thus making the bike run more lean. 

 
Aw the two stroke shuffle...... Seals, reeds, rings......mixture...go to 40... get some non ethanol 94... 

 
32:1 all the time with 91/93 octane with no issues ever. Crank seals or time for a top end rebuild ? 

 
Cookie said:
My first thought, not too many people run 32:1 anymore, I would run 40:1.  32:1 actually makes the bike run more lean than 40:1.  Lean conditions could cause over heating. At 32:1 there is less fuel, thus making the bike run more lean. 
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me too, 12 oz golden spectro to 5 gal. prem. 

I did replace rings about 20 years ago, base gasket was leaking

 
Sandkist said:
32:1 all the time with 91/93 octane with no issues ever. Crank seals or time for a top end rebuild ? 
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Haven't done a test but compression feels strong when kicking, top end was supposedly done somewhat recently. 

I suppose it could be a left crank seal, wasn't smoking like they reportedly do when the right seal goes out. 

 
xtracrispy said:
Picked up an 85 ATC250r couple months back. Been running 32:1 Super Techniplate or Castor 927 with premium gas. Stock intake and carb, UNI filter, Dg pipe, FMF silencer, Stock bore, Boyeson 2 stage power reeds. 

Took it out last trip with no significant issues. Seemed like it was loading up and running real rich while cruising 1/4-1/2 throttle. Poor throttle response, pulled ok in the powerband, seemed like it signed off kinda early. But you couldn't clutch it to keep the power if it fell out of the powerband, once it fell out it was gone, even downshifting and clutching. Smoked a bit, breaking up wile cruising 1/4-1/2 throttle, plug was black and wet. Stock jetting, 52 pilot, 152 main, needle in second clip from top(second from lowest needle position). Dropped the needle all the way with maybe a little improvement. 

Second trip(last weekend), rejetted with 48 Pilot, 154 main, needle in middle clip(hoping to lean the bottom for better throttle response with richer mid-top for cooling and hopefully better pull on hills), no other changes(except a twist throttle conversion). First run to Olds from washes: better throttle response, less breaking up. Thought I heard some pinging pulling Olds but seemed to run better overall. Next ride at moderate pace, missed a shift and got stuck on a hill. While turning around smelled coolant, overflow tank was higher than normal, looked at my temp strips and they were high (226F or so). Decided to head back to camp, while cruising back temp strips indicated similar temps, higher than I was used to seeing, blew the upper crossover coolant hose about half way back to camp and had to be towed. 

Plug looked good, water pump still spins, not seized.

What should I check next? Pressure test the coolant system? I don't think I'm running lean enough to cause it to get that hot. 
Click to expand...
Lean kills!  Lean will get really hot too. What size carb? Come get my compression tester, i’ll put it in the tray of the stand up ski

 
My 85 ATC started to overheat last year and I believe it was from running too lean.  Had Selvy tune the bike when I put the pipe on back in 1993 and haven't had to touch it since.  Literally, haven't pulled the carb apart...ever.

Any detonation? My 85, which I recently pulled the top end off of showed detonation even though I did not feel it.  I run about 50:1 with Golden Spectro and premium gas and have since 1993.  I know people talk sh%t on GS but this is the first time I have had the top end off since 1993 and it showed very little wear.  It doesn't "smell good" and looks like tar but it works!  Stock round slide carb with hand coned Selvy pipe. 

New engine with be ported stock head, CR ignition, NOS Honda piston & rings, same pipe, and oval slide off an 86 (possibly a 38mm).  Still up in the air about stock air box.

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A leak down test will tell you if you have a bad seal.  32:1 is not your problem for sure.

 
xtracrispy said:
But you couldn't clutch it to keep the power if it fell out of the powerband, once it fell out it was gone, even downshifting and clutching. Smoked a bit, breaking up wile cruising 1/4-1/2 throttle, plug was black and wet. 
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If youre still searching for answers you could test the resistance of the coils. Maybe you are getting weak spark at times? Could pull the stator cover and look for obvious frayed wires. 

You might have multiple problems. Maybe the jetting is rich in spots causing the wet plug. Got to think the main seals are somewhat old if the previous owner didnt mention doing the bottom end. I guess you could take the Boyeson reeds out and make sure theyre sealing. Give them a flip if needed. 

Sounds like the bike overheated during your fastest ride. Was it a new spark plug and was it again black and wet? I wonder if a weak spark could cause overheating. First thought is the explosion is weaker, so that should be less hot. But if the motor is struggling due to a weak spark, maybe that could cause it to run hot. Losing efficiency and developing heat. 

Another reason to overheat could be from a very slight brake pad drag. Sand could get wedged in there and not get cleaned out quickly because we dont really use the brakes aggressively in the sand. Air in the brake fluid. (although that goes against us not using the brakes much, its not likely to overheat)

Just to knock off possibilities could borrow a CDI from a buddy with older bikes? Do they use the rectifier? My 1989 bike uses it. Not sure if they go bad and completely fail. Or if they can act funny and cause loss of power.

 
Thanks for the input, it gives me a few things to start looking at. All I’ve had time to do is pop the water pump cover, it still spins and the impeller looks good. 
 

I’ll probably do a compression test and cooing system pressure test once I replace that coolant hose and see how they turn out. Then I can start looking into some other things. Take the head off while the coolant is drained, etc. 

 
Did a compression test yesterday. Got around 70psi first kick maxing out around 150psi after 5 or 6 kicks, cold motor, 60* ambient, 3,700ft elevation give or take. 

 
Not enough timing also leads to hot engines. Not sure how that’s set on a water cooler job though. 

 
Timing is not adjustable on 85/86 250Rs. Go or no go system if it is stock.

 
Sprayed carb cleaner around the intake, carb, cylinder base and head with no change.
Popped the head and reeds off. Holy RTV. No obvious signs of head gasket failure but someone was really sloppy when they were in there last. 
Intake was quite wet, as were the reeds  

Some light scoring on the exhaust you can feel with your fingernail. Piston seems to have some excess play but I don’t have to means to measure. 
Does the porting look weird to anyone else. Almost looks like someone has messed with it. 

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Looks like you discovered the cause of your overheating issues. What’s your plan? Bore and hone and new piston or a big bore kit? LOL

 
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Its defiantly been ported. 

Don't use any silicone with new gaskets when you put it back together. 

 
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