91 xr 600 HELP!!!!

hello, i am new to your thumper room and looking for help!I bought a 91 600 and i rebuilt the head and new timing chain few other odds and ends and as i was cleaning the carb realized that this had a mukuni flat slide carb, in my manual it shows a kehein carb!.Did this bike ever come with this carb?i found some info that honda offered a 660 big bore kit that came with a different cyl ,piston and carb? is this what happened somewhere down the line before i got it? I am having problems starting.It has a fmf mega max and the carb has a 250 main jet and i cant read the pilot jet size.when i did have the bike running for just a couple of minutes it idled good but when i reved it up it bogged for second and then it reved up good, it back fired and shut down.I have only had it fired up 2 times after that and it has'nt stayed running long enough to get a good idea to start from.I was going to check my valve clearances again and try to find out more on this carb and why its on this bike, any info would be great! I worked mostly on 2 strokers the last four stroke i rebuilt was a 75 sl350 and my last bike was a yz490 . i want to feel what this big dog can do , thanks highdrive6

No, it's not the stock carb. The stock carb, which I have, kind of sucks. A different carb is a commom mod. I'd say the first thing to do is clean that carb out real good. If the bike was sitting long, it's likely all clogged up.

If the timing chain is off by one tooth, it's very hard to start and it will not run right if it runs at all.

thanks cleonard for your response, I made a few calls to honda dealers and they said the same thing, one old timer said he remembers a big bore kit that honda offered and it come with a jug ,piston and different carb. I spent alot of time looking at the at the cam shaft gear and moving it one tooth at a time to make sure that the lines on the sprocket lined up perfectly flat with the head while having the t lined up with the notch on the flywheel.I actually had the bike running after about 10 to 15 kicks.I had to open the throttle wide open before it fired,It run for a couple of seconds and quit,It acted like it wasnt getting enough gas, i checked plug ,I put the old plug back in and kicked another 10 or 15 times and it fired up.I had to work the throttle a little to keep it going and it seem to smooth out a little and than i had it idling, I actually wheeled it outside while it was running and let it sit and run for a couple of minutes. I went up to it and gas it couple of times and it boged a little at low end and then it reved up good.Not alot of smoke or anything out the exhuast ,then she back fired a little after being reved up and it quit.I tried starting again a half hour later (stress break) and it would'nt fire at all. The next day i tore the tank and seat off and checked my valve clearences again, the right exhaust valve (decompression side) did not have any play at all so i reset 0.05mm.When i put it back together it seem to have alot more compression!.I took apart the carb and cleaned the @#$% out of it.did not find anything ,its the 3rd time i have cleaned the carb.I have got the pilot jet out 2 turns.I think i am going to loosen up the valves all over again and rscheck it one more time by the manual.open to any suggestions that someone might have !thanks highdrive6

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