I have a friend who put a mid 70s XR500 motor in a 89` 250R frame. It has 12 to 1 comp, big cam, ported & polished and custom header with a Supertrapp.

When he rides in first gear it ratchets like the chain is skiping but it`s not. He put a new chain and sprockets on just to be sure. If he pulls a wheelie it will come up then all of a sudden it will slip and the front comes down but before the tires ever get to the ground it catches again. It doesn`t do it in any other gear or make noise in first when riding under partial throttle.

Is it popping in and out of gear or is the gear stripped? If something like that is the problem is it possible the tranny is too weak for a quad?

Thanks

98 Scrambler 500
00 Trailblazer 250

 

sounds to me like frist gear is stripped or..your buddy has a bent shift fork you can have a bent fork and only have it mess with one or 2 gear's
if thats the case a new set is only around 50 to 60 bucks im dealing with this now on my project 86 atc 250r
hope i helped
monica

 

Sounds more like the rear axle hubs to me.... A stripped 1st gear would be terminal.

Check the rear wheel hubs, they are probably worn and jumping on the splines.

 

OK here a question do you think an xr500 motor will fit in a 300ex frame? How much work was it to get in the r frame???

 

Thanks for the reply`s but it`s not the axle or hubs brand new Durablues. The guy is an mechanical engineer and a nit picky one at that so everything is new or in good condition. I know what your thinking and I`ve seen some not so good conversions but this is top notch. He even made a jig to hold the frame before he cut it apart to keep it from springing with no lower frame rails.

He`s got only about 25 to 30 hrs of ride time it just working out the bugs. He did take it to Silver lake, Mich. for the first ride without a problem but he didn`t use first gear at all. Now this past summer trail riding around here and using first gear is when he noticed it.

If it`s a bent shift fork, which I think it might be could this be a weak link?
Thanks

98 Scrambler 500
00 Trailblazer 250

 

Very possible... If that's the case, fix it immediately or severe transmission damage will probably result.

 

ex_master
Putting the 500 in your 300 could be easier, could be worse hard to say I`ll tell you some of the the things he had to do and you decide. It was a pain to do the R.

1)The engine is taller than the 250 2 stroke which meant he needed to cut out the lower frame rails and lower them 2 inches. You may not need to do this on your`s since the 300 4 stroke is taller but tall enough, I do not know.

2)The routing of the tube from the airbox to the carb was difficult because a cross piece in the frame which happens to be the upper shock support was in the path. A custom and I mean custom fiberglass one was made. It started out round at both ends and flattened out to go over the cross piece but be low enough to fit under the seat. This took a few tries to get right. He did all this because it was to be a trail machine.

3)The XR500 motor being from a bike kicks rearward which means it arc`s to the rear this caused the most engineering and work. The engine is also narrow which meant that the kick starter was inside the frame by about an inch. So the upper rear part of the frame where the master cylinder mounts needed to be moved in. It also meant that he needed to remove his seat & fenders every time to start it. There were easier ways around these extend the kick starter out and cut the right rear fenderbut he didn`t want to do these.

4) Relocating the master cylinder for the rear brakes now that you modified the frame in that area. He came up with a pretty ingenius idea to over come this. Have the brake pedal extend forward and mount the master cylinder in front of the engine and run metal lines to the rear.

These are some of the major things you will encounter obviously the smaller ones will be easier to deal with such as throttle cable, foot pegs, shifter and exhaust to name a few.

Hope I haven`t discouraged you but if you like 4 strokes it will hall a$$. There are many after market hop up parts for it also since it used to be popular with the flat trackers back in the late 70`s early 80`s.

98 Scrambler 500
00 Trailblazer 250

 

It could be a bent shift fork or the shift fork and gear are wore where they ride together. I had an old Yamaha DT250 that would jump in and out of third gear. Took it apart and had to replace both the fork and gear.