07' 300 overheating...I think(4 stroking, and coolant on engine)?

[CDBiker220]

Hi, just bought an gasgas 300. And after riding hard for about 15 min. it started to 4 stroke when coming back from idle (jumpy idle but higher than usual) also i noticed a few specks of coolant over the left side of the motor, and think it came from the coolant overflow hose. I checked the waterpump impeller and it looked fine to me(plastic one). And then checked the sparkplug and it was a nice light brown color. So any ideas were to go from here. I know nothing about the jetting but it seams to run great. I thought i heard it detonate though a few times when on WOT but could have just been chain slapping or something.

[noobi]

Radiator cap may have worn out, or been damaged. Replace it with a KTM rad cap, its a higher pressure rating, and see if its makes a difference.

[GMP]

If its surging with a hanging idle your lean for some reason. Plug color is unreliable to diagnose a 2stroke across all the ranges. Look at your jettting and rule out any air leaks. Agree on the cap though, go with a 1.8 bar, and ditch the expansion tank just run a crossover hose. These bikes do not run hot, even in extreme conditions like slow steep climbs and tight sand woods they rarely burp the cap when setup right.

[CDBiker220]

How should I go about checking to see if jetting is correct or too lean? I thought the plug would be white if the jetting was off. I will check everything over tonight after work to confirm no air leaks or anything. My buddies dad had similiar behavior on a 07 KTM, ended up being bad crank seal. Hoping thats not the case.

[GMP]

You don't jet a 2stroke by plug color unless you really control the conditions and isolate the throttle positions. Even so there are too many variables in fuel, oil. You can be too lean in some areas and too rich in others and have a plug with color. For example my bike is jetted close to perfect IMO and produces a dark brown plug overall after an average ride, perhaps a bit lighter after a high speed ride, still what you would consider rich by textbook or 4stroke standards.

Pull the carb and record your jetting, then report back and consult the jetting database to see if your at reasonable settings. Check the rubber coupler between the manifold and the carb for cracks and distortion from overtightening. I bond mine to the manifold with grip glue and dont go crazy tight with the clamp. These are cheap and a good idea to change when you do reeds or top end work. You can do a quick and dirty air leak test before any disassembly by carefully spraying starting fluid near the manifold and crank seal, revs will increase if drawn in. If it is a crank seal (not likely) its simple on this bike, done from the outside in minutes.

[CDBiker220]

Jetting specs

Main - 178
Pilot - 42
Needle - N1EF 2nd clip down


Im at 1200 ft. and it has been about 45F out while testing. Looks like reasonable jetting to me. Could those settings still be lean causing it to run hot and 4 stroke? Also thought i heard some detonation at WOT. has a gnarly pipe if that makes any difference, also overflow tank is gone and just has a tube coming out where i believe coolant was leaking from, picking up 1.4 bar KTM cap today(didnt have 1.8 in stock, just giving me one off a new bike). Ive heard of a chop test to see WOT mixture, just kill the engine and pull in clutch at WOT and then check plug?

[stainlesscycle]

Originally Posted by CDBiker220

Ive heard of a chop test to see WOT mixture, just kill the engine and pull in clutch at WOT and then check plug?

yes, but: you need to be at wot and under load... i ride a big long uphill, at wot, then kill engine/pull clutch. read plug right there...

to me, your jetting does not look lean at all.

[lankydoug]

Check for an air leak, if it doesn't have one give it what it want's an go rich a step on the main. Too rich wont kill your engine like to lean will and you will have feedback to compare to.

[CDBiker220]

Put in 180 main and rode in yard some pretty hard, no 4 stroking but still ended up with coolant splattered on engine, Didnt come from overflow tube as I put a paper towel on it while riding to see if anything came out and it didnt. Need to find the source of the coolant..maybe a loose hose connection. Ran the bike in neutral sitting still till pretty hot and found no leaking anywhere but after hard riding you can smell coolant and see dropplets all over the motor. Not sure if i trust the clip type hose clamps. may try normal hose clamps.

[kendunn]

Originally Posted by CDBiker220

Put in 180 main and rode in yard some pretty hard, no 4 stroking but still ended up with coolant splattered on engine, Didnt come from overflow tube as I put a paper towel on it while riding to see if anything came out and it didnt. Need to find the source of the coolant..maybe a loose hose connection. Ran the bike in neutral sitting still till pretty hot and found no leaking anywhere but after hard riding you can smell coolant and see dropplets all over the motor. Not sure if i trust the clip type hose clamps. may try normal hose clamps.

I had this happen and it was indeed one of those clip on clamps when the motor got a bit hot. Lose them, especially the lower right one on the water pump, it is easy to get knocked around down there and leak.