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Discussion Starter #1
I have a old 88' KSF250 that I just cant get to run right. I bought this machine a couple years ago with a engine that had trashed camshafts and kick/ reverse idler gears. Fast forward.... bought a used engine off Facebook that has been cut from a home made go cart and its condition was unknown for $80. Turns out kick start is good and camshafts are mint! After mounting and connecting engine with a rebuilt carburetor, new plug, engine oil etc it starts very easy and idles like a boss with no noise or smoke but it wont rev up at all, falls on its face if the throttle is opened to fast and if rode using easy throttle it has no power at all. So naturally I went through the carb again and again and again.... even tried different carburator with no change in results. So I tried other things. I have duplicate parts for everything and I've swapped carbs, coils, CDI (even bought a brand new one to the tune of $300) stator, plug cap etc. You name it, I've tried it more than once all with the same results. Now I was thinking maybe a engine mechanical issue. Compression in range at 85 PSI (book say this is good due to comp release) performed cylinder leak down and had 0% loss. I've check camshaft timing several times including valve lash. I've checked the rotor for a sheared key, ok. I've checked CDI power and pickup coil output both by DVOM and even went as far to put these signals on my lab scope looking for anything to no avail. I've tried running both with airbox on and off, exhaust silencer on and off.
I've tried one up and one down with main jet (I have stock non adjustable needle) I've checked several times if I had main and pilot switched. I've checked and replaced choke plunger and cap, doesnt run better with choke on other than faster idle... and its needed for cold start, works good. Starts good hot. I've checked wiring connections, pin tensions and resistance of wiring.
I'm just not sure what to check or replace now. Part of me thinks it's a carburetor issue but I somehow feel even if I bought a brand new carb from Kawasaki it wouldn't change anything. It seems like its lean but when you snap throttle (and its bogging) you can physically see fuel being sucked in..... lots! I even tried shutting off fuel and get the same results thinking maybe too much fuel like high float level etc, no change. I'm at a loss and have over $1k and Probably 50 hrs into this thing so I really dont want to throw it out. I'm open to any suggestions and nothing at this point is a stupid idea.
There are a couple things I've not checked is ignition timing, the book shows the curve through RPM range so I should probably check it. I also dont know if these are stock grind camshafts or aftermarket such as a stage 1 or 2 etc. Its running stock air box but has a supertrap exhaust system. Part of me thinks it acts like fuel but also seems like a timing issue but never pops or misfires.
Here is the funny thing, I've read in various posts and forums of the exact same symptom from several other Mojave owners but no one ever mentioned a solution.
And once, one time only it ran perfect! Excellent throttle response and power, tried next day.... back to the same ole issues.
I myself am a master certified technician and have run this issue by many other professional ATV/ bike and automotive techs with no good idea to what's going on.
Any ideas or help will be greatly appreciated ?
 

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Discussion Starter #3
You know I want to say I've checked that but at this point I cant remember. I will dig the bike out, fire it up and check for vacuum leaks.
 

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1987 KSF250 Mojave
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We had a similar issue with another one of our quads, my son's DS90. Turns out there was an exhaust issue and it was essentially acting like a banana in the tailpipe. Started up, idled great, but when you hit the throttle it just bogged down. We cleaned the exhaust screen and spark arrestor and completely pulled it apart to make sure that there was nothing else. Ran like a champ right after. Found a clogged screen and spark arrestor. Good luck.
 

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Discussion Starter #5
I've speculated possible exhaust issue but to the possibility of to much flow and not enough back pressure? The bike has a DG pipe and spark arrestor, I've run both without the silencer and with diffusers removed with no change.... I've wondered if it needs its stock muffler, I've had bikes in the past loose power with aftermarket exhaust due to carb and airbox tuning not being matched. I've thought about getting a stock pipe and muffler off Ebay and giving that a try
 

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If it’s the exhaust yammed full of crap you’d be hearing the air leaking out after kicking it. Unless it has a leak at the header or joint. If one of those leaks that eliminates any clog. Pull the end cap off the silencer and look. Probably needs repacked anyway. ?
 
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