Jump to content
Sign in to follow this  

Clutch Slipping and Bike Bogging

Recommended Posts

Hey guys, I have a 2008 RMZ250 with 90 hours on it. The valves haven't moved since I bought it and are still in spec. Recently my bike began bogging (about the time it started getting into the 90's) and it's gotten worse lately. Whenever I'm hard on the gas around 1/2 to wide open my bike seems "bubbly" sometimes.

I tried fiddling with the fuel screw and it seemed to help a bit. I turned it all the way in, then out 2 turns. My friends said it sounds cleaner and I didn't notice it bogging. But I thought the fuel screw was just for idling. I'm hoping it's the jetting and not the motor going out.

Also, I noticed that my bike doesn't seem to pull like it used to. And today I thought it could be my clutch plates. So we took them off and the smooth ones (drive plates?) are blue/black along the outer edges of them. I put it back together and it seemed to get much worse as the day went on, in fact I cased several jumps because the bike just wouldn't pull like it normally does.

I have a race this weekend, and the dealer said that they could get some in by Friday. But I was looking online and all but the Tusk plates which are only $60 costs like $180 dollars. I was wondering if I could get by with just the drive plates(?) and/or some stiffer springs. If not, would there be anything I can do such as sand them down to get me through this weekend?

Thanks!

Share this post


Link to post
Share on other sites
Hey guys, I have a 2008 RMZ250 with 90 hours on it. The valves haven't moved since I bought it and are still in spec. Recently my bike began bogging (about the time it started getting into the 90's) and it's gotten worse lately. Whenever I'm hard on the gas around 1/2 to wide open my bike seems "bubbly" sometimes.

I tried fiddling with the fuel screw and it seemed to help a bit. I turned it all the way in, then out 2 turns. My friends said it sounds cleaner and I didn't notice it bogging. But I thought the fuel screw was just for idling. I'm hoping it's the jetting and not the motor going out.

Also, I noticed that my bike doesn't seem to pull like it used to. And today I thought it could be my clutch plates. So we took them off and the smooth ones (drive plates?) are blue/black along the outer edges of them. I put it back together and it seemed to get much worse as the day went on, in fact I cased several jumps because the bike just wouldn't pull like it normally does.

I have a race this weekend, and the dealer said that they could get some in by Friday. But I was looking online and all but the Tusk plates which are only $60 costs like $180 dollars. I was wondering if I could get by with just the drive plates(?) and/or some stiffer springs. If not, would there be anything I can do such as sand them down to get me through this weekend?

Thanks!

#!... It is your jetting. We have the same bike and there is an air screew under the bowl (front) of the carb. I loosen the strap bolts and twist the carb up. You may have to lay down to see the screew but it's there. About one turn at a time and if you go over 3 turns you'll need to raise the needle which means move the clip down.....

#2... I've used Tusk clutches with good results in my 300 but my son (RMZ290) can burn them out in three off road races. But he rides expert classs. Yes they will get you through. Be sure to get both fiber and steel plats....

Share this post


Link to post
Share on other sites

the keihin fcr carbs need to be between 1 and 2 turns on the pilot screw, takes more than 2, the pilot jet needs to be bigger, less than 1 turn, smaller. The idle circuit is ALWAYS on, so it's always dumping fuel, raising the needle clip does in no way affect the idle circuit. Sounds like your too rich up top, but what do you mean by "bubbly".

Share this post


Link to post
Share on other sites

Thanks for the responses guys. The local shop wanted $200 for a clutch. So I bought a Tusk clutch with over night shipping for $65! I didn't want to take a chance this weekend.

As far as the jetting I think the bike was better at 2 turns out. But you are saying I may need to lean out the pilot jet? Why not the main jet if it's too rich up top?

But as far as describing it as bubbly, if was almost like the bike would bog for a second then pull for a second then bog for a second and so forth. I noticed this on a semi whooped-out straight where I shifted early to 5th and was rolling on the throttle. It started the bogging thing when I was over half throttle and was really getting on it hard. But where it was "bubbly" was normally a section where I'm topped out in 5th so the bike does have the power to pull it.

Another time I noticed this "bubbly" thing, was I was at a new track and practicing starts and I was in 5th before the first turn (long start) and the dirt was so sweet that I was able to hold it on and never let off through the turn so I was 5th gear pinned for a while (but still accelerating, not on the limiter) through the first turn and on up this hill where it seemed to have the "bubbly" sensation where it would kind stutter and quickly alternate between pulling and bogging. Some of that could have been my clutch going out though :smirk:

One a side note, do you motocross guys find yourselves in 5th gear a lot? I'm running stock gearing and I can't see how it works for faster riders.

Share this post


Link to post
Share on other sites

if you're at 2 turns, you can leave it be, or you can try the next size larger pilot jet. As far as the bogging in the whoops, it could be

-Float too low

-Splash shield not installed on main jet

-vent tubes blocked

-float too high--->gas trapped in vent tubes

i pulled this off of 4strokes.com in techinical section for non-model specific stuff, has a fair list of stuff that can help diagnose a ton of carb issue, and how to tune them, i.e. fuel screw (turns out) and sizing the pilot jet. Check it out, actually a pretty useful article. Here's a link;

http://www.4strokes.com/tech/4sjetting.asp

good luck!

Share this post


Link to post
Share on other sites

Thanks for that reply. That's really helpful for jetting issues. But I believe it was my motor, as it seized yesterday..

Share this post


Link to post
Share on other sites

90 hours...did you ever do a complete rebuild, or just a top end? how often did you do oil changes? what oil did you use? a motor seizes because there is a lack of lubrication or if you never rebuilt the bottom end then your rod and main bearings are worn out.

Share this post


Link to post
Share on other sites

The bearings wore out. Never did any engine work on it. It started first or second kick every time, valves never moved. I used motul 5100 and changed it every 6 hours or sooner.

Share this post


Link to post
Share on other sites

Ya thats what did it, thats amazing that the valves never moved! well don't cheap out on the rebuild (if thats your plan) do every thing, bearings, piston and rings, and the valve train (valves, springs, cams, lifters, timing chain) and get the head machined, heck why not a big bore kit and get the head some serious work done to it with some stage 2 cams, the total cost wouldn't be much more and that bike would really rip!

Share this post


Link to post
Share on other sites

Well I'm going to keep it stock for better reliability and so I can qualify in the stock class next year. I was going to read up on porting the head though.

Share this post


Link to post
Share on other sites

I see, I hear these 250's really wake up with head work, so definately worth looking into

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×