Engine revvs high, overheats-whats going on?

[djg42]

Hello,
Thanks in advance for any pointers!
I have a 1980 GS450. When I pull the throttle and let go, the revvs stay high. It seems like im riding with the choke way up. Also, if im in neutral or have the clutch in the bike will revv high. It then overheats. Also, it dies sometimes when i have the clutch in. Im not sure whats going on, the performance is bad too. The throttle is returning normally, the slides and diaphragms seem to be normal, i have new intake boots+O Rings, tightened as tight as i could get them on. The jetting was good up till now so I dont think that its a lean jetting. I recently had to take the camshaft tensioner off, could I have put it back in wrong? It has pods, the enigine breather hose was spitting exhaust-although i supposed that mighjt have been the oily residue being burnt by the high engine temp.

Where do I go from here? Thanks!!
DG

[Nessism]

Did you rejet for the pods? If not, you need to. You also need to set the pilot screws to somewhere in the range of 3 turns from lightly seated. A vacuum sync is also necessary as well as spotlessly clean carbs and fresh O-rings (not 30 year old ones).

Hope this helps and good luck.

[djg42]

Thanks! Yes, I did rejet-its a little rich if anything.

[Nessism]

Thanks! Yes, I did rejet-its a little rich if anything.

Did you move up one size on the pilot jet? Did you shim or change the needles? Where are the pilot screws set?

[djg42]

went up on the pilot and shimmed the needle. i never adjusted the pilot screws, the factory cap is still over them. I used a color tune to choose the best pilot and it had been fine up till now. When I first start the bike it will idle, but after riding when i come to a red light i will hear my engine revving way high, it eventually comes back down to the regular idle if i sit for a while. I took the carbs apart and everything seemed ok so im really baffled.

[Nessism]

went up on the pilot and shimmed the needle. i never adjusted the pilot screws, the factory cap is still over them. I used a color tune to choose the best pilot and it had been fine up till now. When I first start the bike it will idle, but after riding when i come to a red light i will hear my engine revving way high, it eventually comes back down to the regular idle if i sit for a while. I took the carbs apart and everything seemed ok so im really baffled.

If the factory cap is still on there you never properly cleaned the carbs. Time to do the job right. cycleorings sells O-ring kits for the 450.

[djg42]

Thanks! This happened all of the sudden, do you still think it could just be clogged carbs? Im not even sure where the pilot screw is on these carbs... Ill defintily give them a thorough cleaning in anycase.

Could the camshaft tensioner be the cause of this?

[BassCliff]

Hi,

The "pilot screw" you refer to is actually the "idle mixture screw" and is located under the factory caps on the top front of the carbs (CV type Mikuni BS series).



As Mr. Nessism mentioned, these must be removed to properly clean and rebuild your carbs. It sounds like you need to:

A) Properly clean and rebuild your carbs with an O-ring kit from cycleorings.com. See: The Carb Cleanup Series. Follow the directions and dip each carb body in Berryman's chem dip for 24 hours.

B) Make sure your air intake system has no air leaks. Since you have pod filters this will mean new intake boots and intake boot O-rings. You can read about this procedure on my website article "Air Intake Repair".

C) Make sure your carbs are properly jetted. This will take some experimentation. The plug chop method is explained on my website. There are also links to other carb tuning procedures.

D) Make sure your cables are lubed and functioning properly. Make sure they are routed properly so that the engine doesn't race when you turn the handlebars. There's a manual on my website that might help.

I encourage you to do the proper maintenance correctly the first time. If you don't, you may be plagued the with erratic, continuing symptoms that you are now experiencing. Keep us informed.


Thank you for your indulgence,

BassCliff

[Nessism]

The 450 mixture screws are in a different place, they come in from the side I believe. Basscliff's photo is in the general area.

A hanging idle is not going to be cam chain tensioner related, but if the mechanical spark advance unit is binding that can cause a similar issue. Take off the ignition cover and grab the rotor and make sure you can twist it a little - against spring pressure. Turn the rotor until it stops, about 20 degrees, and then let go - it should snap back. If not, remove the rotor and figure out what's binding.

Good luck

[djg42]

Thanks for the great advice! I loosened the lock nut on the cam chain tensioner a tiny bit and now the problem is resolved, i have no idea why