In my effort to try and return a once great bike to glory come the following questions. The bike, a 79 KTM 420 is a beast to kickover, so I dont think compression is the problem here. Upon getting the bike to fire off it appears that it is running extremely rich. Copius amounts of white smoke out the exhaust along with the oily residue of fuel blowing thru the exhaust flange joint lead me to believe more fuels going in than what can be used. I pulled the carb and cleaned it thoroughly and the jetting and settings for the air fuel mixture are correct per the manual for this bike. I am not sure what carb problems are causing this though? The bike definitely seems as if its running fat. It will rpm or rev up to a point, but the response is very sluggish, not clean and crisp. I set the timing at 78 thousandths BTDC or 2.0 mm. Now I know this bike calls for 2.2-2.4 mm advance,but I felt it better to be conservative till I got it sorted out. Could this be a worn slide or bad needle and seat in the carb? Or should I go ahead and advance the ignition a little more? Please, everyone weigh in here as I know there is a wide range of expertise among the group.
Thanks but frustrated,
Bob
Make sure there are no obstructions in your exhaust system. This can cause many a difficulty that are had to detect.
Tony
Bob,
Since that bike was a very complete original bike, and most likely untouched in the engine area, I would guess that the crank seals might be part of the problem. My MX-6 with the new Circle F pipe blows out a lot of oil in the flange area, so I suspect that crank seals are in order. I have never done it, but I am sure that a crankcase pressure check might shed some light on part of the problem. I would adjust the float level down some to see if it would help also. How much trans fluid are you running? My 1980 manual calls for 1.6 litres or almost 1.7 quarts for the 125-400 engines and my earlier manuals only call for 1 quart. Depending on the crank seal condition you might try less fluid (1 QUART) and see if it runs better just for a trial period with new a B8HS NGK plug. Mike
Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 250'S
Mike and Tony,
Thanks for weighing in. The exhaust is new and silencer just recently repacked, so I know I am good there. The crankcase seals you brought up Mike are one of the areas I was suspicious of. The 420 takes a B9ES plug that is a long reach plug, of which I had a new one in place to fire this monster off. If the crankcase seals are bad, then the engine is pulling fluid from the crankcase? and contaminating the air/fuel mix from the carb? Your saying to try and lower the amount of ATF I have in the crankcase to see if this eliminates or lessens the problem? I dont recall the exact amount, but there is a screw in he left clutch case cover that you fill your crankcase till it overflows out this screw. I can drain the crankcase a little and try that and then that will determine if I am dealing with bad crankcase seals?
Thanks for the help, Bob
Bob.. I to think it is the oil side crank seal or the center gasket is not there. Pull your plug and look to see what it looks like. If it was mine I would pull it apart and install new one's. Hope this will help Gary Ellis
Bob, Hasen't anybody told you what the abbreviation for KTM stands for? All kidding aside, All the big bore KTM's need to be laid down on their side till the fuel runs out of them, then try to "Kick Ten Minutes" :D
Raymond
Down East Pentons
Ray and Gary,
Thanks for the replies. Ray, I use that procedure for starting your refering to on all my bikes and yes this thing is a @$#^%& to kick over and start.
Gary, if crankcase seals are my problem,then this motor may find its way to your shop, as replacement of these is beyond my expertise.
Thanks again, Bob
Bob you have maul. Later Gary
I have learnt a rather easy way of checking if the crankcase leaking, (as long as you are able to start the engine). Take the transmission vent hose and run it into a glass of water. Rew the engine, then if it blows bubbles into the water the crankcase is leaking.
Mats from Sweden
Mats...that is a great tip!
Thanks and welcome to POG
Steve Minor
Wilmington, NC
Thank you Steve! I find that leaking crank´s are not unusual on this type of bikes, and trying to tune if the crank´s leaking is not worth the effort! If you have a bike that you dont use over long period´s the seals get hard and start to leak. If you are lucky they can "heal" after running the engine a while.
Mats from Sweden
i too had a suspected seal leak on my 400 mint. i made a blank 1/4 thick plate to cover both the inlet side and the exhaust side of the cylinder. the exhaust side cover plate was tapped with a 1/4 pipe thread so i could put a tee with a gauge and a schaeder valve on it. make sure that you have good gaskets and bolted down correctly and then test it with about 50 lbs of air. of course you have to leave the sparkplug in to seal it. it worked great and i found that there was a small crack in the gasket for the intake manifold. air leak solved and its been running right ever since. chi jer