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Old 03-02-2010, 06:04 PM   #1
Jammin OP
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HELP: DR650 Running Too Hot At High Speeds

I was supposed to leave on my South America trip yesterday but didn't get a chance to do any test runs until the night before leaving and that was the first time riding the bike after rebuilding the engine and installing the GSX-R exhaust. What to do; I know it's not the proper way but it's been snowing like crazy and I'm trying to beat the rains in Central America by leaving now.

I have a Vaportech dash with an engine temp sensor on the spark plug and the bike usually runs around 170-180 F. Now, it's running around 200F and shoots up past 220F when I go above 50 mph. When I slow down, the temp drops and when I speed up past 50 again, it shoots up. Running at 45 mph or slower, the temps stay between 190-210.

This means that it's lean, right? The bike was running great at the end of last season and the only major change has been installing the GSX-R exhaust and bad on me, but I didnt know I had to tune the jets for this exhaust. I read that it wasn't necessary.

The bike is a 98, with a Mikuni TM40 Flat Slide (non pumper), K&N filter with foam pre-filter and airbox mod (top cut) and now GSX-R exhaust. It starts easily and idles nicely at 1500 rpm.

I had a 270 main jet in there before the exhaust mod and if it's running lean at higher rpms, I was told by a mechanic to put in a larger main jet. So I ran a 300 and noticed no difference. It was still heating up and going past 220F above 50 mph. I then put in a 340 main jet and no difference again.

Spark plug with 270 main jet was lightly coated in black. Spark plug with 300 was white-ish. Does that mean it's running leaner with a bigger main jet? I'm confused on what to do now.

I checked the connection between the carb and the engine and the carb and the airbox and it looks tight with no air leaks. Sprayed WD40 on it to see if it would get sucked in while running and nothing there. I dont see any damage, holes in the airbox besides the cut in the top of the airbox.

The next thing I'm going to try is putting the stock exhaust back on and returning it to the spec it was in at the end of last season where it ran great on a 2 week trip with no issues.

Any other ideas on how I can reduce the lean condition at higher rpms?
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Old 03-02-2010, 06:14 PM   #2
tbirdsp
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Not a DR650 guy, and just my guess - I don't think there's necessarily anything wrong. I'm not familiar with this temp sensor, where is it exactly?

With my old XL600R I used to routinely see *oil temps* in the 250 f range, even as high as 290 (as indicated by a thermometer dipstick in the frame oil tank).

Usually a lean 4-stroke will run like crap long before the mixture is lean enough to hurt anything.
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Old 03-02-2010, 07:12 PM   #3
Jammin OP
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Quote:
Originally Posted by tbirdsp
Not a DR650 guy, and just my guess - I don't think there's necessarily anything wrong. I'm not familiar with this temp sensor, where is it exactly?

With my old XL600R I used to routinely see *oil temps* in the 250 f range, even as high as 290 (as indicated by a thermometer dipstick in the frame oil tank).

Usually a lean 4-stroke will run like crap long before the mixture is lean enough to hurt anything.
I'd like to think that too and hope that's it. It's just that previously the temps were lower so now with the exhaust, is there a reason the temps should be higher? It's a freer flowing one and all that's doing is scavenging more exhaust gases from the chamber, so that shouldn't affect chamber temperatures, right?

This temp sensor is a metal ring that gets placed between a spark plug and the head. Would it matter which spark plug I have the sensor on? (DR is dual spark)
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Old 03-02-2010, 07:58 PM   #4
Ron Seida
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I honestly don't know if tour bike is running in the danger zone, but if its lean, the plug will show white. The Mikuni book i have states that the jet sise is only relevant in the last quarter turn of thottle. Tour needle dictares fuel measurement from 1/16th to 3/4 throttle. I would start with raising your needle And your previous size jet And go from there. Document your adjustments And only adjust one thing at a time. Maybe the problem isnt fuel?did you check the oil pressure? Any Parts left over
Btw, please excuse my fat fingers, I'm typing on my IPhone.
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Old 03-02-2010, 08:26 PM   #5
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What exactly does "after rebuilding the engine" mean?

What's new in there?

Is there a possibility you've blocked or obstructed a cooling oil port or line?




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Old 03-02-2010, 08:27 PM   #6
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Those numbers don't sound hot to me at all.

My 2003 dr 650 with vapor dash and the same temp setup as yours.

I get temps over 300 deg f at extended highway speeds all the time and at least 230-250 at the coolest once fully warmed up.

just jet it correctly and as long as it runs good don't worry about the trailtec temp
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Old 03-02-2010, 08:36 PM   #7
Jammin OP
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Quote:
Originally Posted by Ron Seida
I honestly don't know if tour bike is running in the danger zone, but if its lean, the plug will show white. The Mikuni book i have states that the jet sise is only relevant in the last quarter turn of thottle. Tour needle dictares fuel measurement from 1/16th to 3/4 throttle. I would start with raising your needle And your previous size jet And go from there. Document your adjustments And only adjust one thing at a time. Maybe the problem isnt fuel?did you check the oil pressure? Any Parts left over
Btw, please excuse my fat fingers, I'm typing on my IPhone.
With the 270 main jet and running hot, plug is black. When I put in the 300 main jet, plug went white.
Yup, know that jet size relevant more towards full throttle.

Yeah, oil seems to be flowing nicely, dont know how else to check that.

When I got it rebuilt, made sure with mechanic that no extra parts left over. Everything went smoothly.

Quote:
Originally Posted by Lornce
What exactly does "after rebuilding the engine" mean?

What's new in there?

Is there a possibility you've blocked or obstructed a cooling oil port or line?

I got the engine rebuilt to take a look at the insides and replaced a suspect 3rd drive gear (known to fail occasionally on the DR) and installed new Wossner forged pistion (stock compression) along with fresh gaskets all around, no leaks notices.

That's what I thought right away and checked oil lines and filter - everything looks good there. How can I check oil pressure?



If it's something to do with oil pressure would that also only affect higher rpms? or is that effect felt throughout the throttle range?
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Old 03-02-2010, 08:45 PM   #8
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Quote:
Originally Posted by rallyhound
Those numbers don't sound hot to me at all.

My 2003 dr 650 with vapor dash and the same temp setup as yours.

I get temps over 300 deg f at extended highway speeds all the time and at least 230-250 at the coolest once fully warmed up.

just jet it correctly and as long as it runs good don't worry about the trailtec temp
Wow. Ok, that makes me feel better :)

Should I be concerned that previously on extended highway runs (before gsxr exhaust), I never saw temps near 220F?

I thought 260F was a danger zone for the chamber? But yeah, what exactly the temp sensor is touching would affect what the numbers I'm seeing mean.
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Old 03-02-2010, 09:53 PM   #9
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Wait a minute - let's backtrack:

First ride after a new piston/rings installed? Is it even broken in yet? Increased friction could easily result is the temp rise you noticed. Perfectly normal.

So are you comparing head temps before and after the rebuild?
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Old 03-02-2010, 10:49 PM   #10
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the motor is breaking in which is friction/heat
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Old 03-03-2010, 06:32 AM   #11
Jammin OP
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Yes, these are the first rides with new piston. Ah ok, so the rings are getting seated and this initial friction is causing raised temps, makes sense. Sorry, I don't have too much experience in rebuilds and break-ins, I'm learning :)

After about how many miles would it be broken in and temps return to before rebuild numbers? 1000?
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Old 03-03-2010, 08:39 AM   #12
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I certainly wouldn't delay your trip trying to get 1000 miles on it.

If it was me - I'd ride it around for a few hundred miles (maybe 500 max), varying rpm and load. Put it through a few heat cycles. Don't baby it too much, but don't bounce it off the rev limiter or lug it in high gear/low rpm either. Change the oil and filter and go ride.

IMHO - you are overly concerned with the head temp.
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Old 03-03-2010, 09:20 AM   #13
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You were planning on leaving for South America after modifying and rebuilding your engine without taking the time to properly break it in and make sure everything is working properly? I guess the adventure really starts when you have to change your plans...
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Old 03-03-2010, 11:57 AM   #14
Ron Seida
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Yesterday I rode into Cuernavaca and was looking for a hotel. My temprature registered 140 celcius, whick equates to 284 degrees f. No problems. I think your fine. Reguarding your carb jetting, you should just call Jesse keintz at 541-472-0835, he'll tell you what's going on with your jetting and how to fix it as it sounds way off the chart to me, but it not being a pumper model I could be wrong.
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Old 03-03-2010, 09:36 PM   #15
Jammin OP
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Yeah I know, bad on me for letting it come to this, didn't plan it this way but circumstances lead me to only running the new motor now.

I did a 100 miles today and temps were hovering near 250 when I was cruising at 60. Bike's running fine, changed oil twice already since rebuild and checked after ride and things look clean. I think I'm good to go.

Yeah I know the jets sound huge but it works well. Previous owner setup the bike with this carb and he said he tuned it on a dyno to get the right jetting. It's a non standard carb for the DR but seems to work fine.

Thanx Ron. I guess I got worried cause I didn't see temps this high before the rebuild, but sounds like it's running just fine.

I've been in touch with Jesse and he's said the same kind of things here.

Thanks for all the help everyone. Feeling good about engine now. Leaving on my trip Friday morning :)
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