2008 RM85 bog

ck float height and make sure the vent tubes on the carb are not clogged with dirt or mud

Check the needle (needle & seat) and make sure it hasn't swelled up (I have seen this happen with fuel with ethanol added to it) or has any blockage or wear.

Check the fuel for water contamination.
Make sure the gas cap is venting.
If it is bogging below 1/8 throttle, a richer pilot jet ,not leaner , would be the way to go.

It sounds like you have tested most everything... The only thing I see you didn't check was disconnecting the kill button. You might have to talk more with the customer and see exactly if he changed anything before he started with the problem (maybe ran out of race fuel and put pump gas in it or borrowed some gas with different oil?) the final thing to check would be a air leak at the crankseal or head gasket leak.

Hello, the "customer" here.

Here's the issue:
2008 RM 85 with stock motor. Pro Circuit exhaust and VForce reeds. Maybe I can save some time here and get right to it. I don't think the specs play into this issue so much.
Racing last weekend. Bike ran great all day Saturday during practice. Didn't do anything to the bike (no adjustments, no washing, etc) that night. Sunday practice the bike was running crisp and strong, then on the fourth lap it began to bog. Little guy comes off the track.
From idle it will bog in the first 1/8th twist of throttle, then run fine through the rest of the range up to WOT. However, if at idle I quickly twist the throttle 1/2 or more it also bogs. It did not do this before. Always a crisp running bike.
My question is: With all the track conditions and bike settings the same, what could cause a great running bike to suddenly have this issue?
I replaced the air filter (though it was fairly clean), cleaned the jets (twice now), checked the reeds, reed block gaskets replaced, reed boot replaced. Performed the starting fluid air leak test and didn't notice a change in RPM. Fuel IS getting to the carb just fine, all the vent tubes clear.
What am I missing? Again, everything identical, it ran great then suddenly had this issue. Seems to me that that's an important clue in all this.

Also,
To bring the above post up to date, I'll include what we've checked and what I've done to date (that wasn't already mentioned).

We ruled out the carb by swapping with another RM85. His carb still produced the same bog issue on my bike, my carb ran perfect on his bike.

I replaced both crankshaft seals (right & left). New plug, new gas. Checked connecting rod, cylinder, piston and ring. Replaced ring (it was about due anyway). New cylinder base gasket and head O rings. Removed and cleaned out airbox (sparkly clean!).

I've gone through two cans of starting fluid testing for air leaks.

Please can someone help me out with this one. It's his only bike and we can no longer afford a backup bike. He's doing quite well in a race series, though will now miss another (or more) race.

Thank you

I know this sounds crazy but do you have one of those fancy colored vent caps on the gas cap? I had on of those get clogged up with dust and etc and it did similar results as to what you are describing. Also if you don't have one of those make sure the gas cap is venting. If it is not venting properly it will cause the carb to be starved of fuel as it is a gravity feed system.

Not crazy at all. When my boy first moved to 65's I chased a bogging issue that turned out to be a clogged stubby vent tube. For two months!!

ALL vent tubes on the 85 have been checked. I even ran it with the gas cap off.

I don't think it was mentioned yet, but it's smoking excessively now as well. It didn't do this before the bog issue. It's whitish in color.

It's not losing coolant and as far as I know it's not losing motor oil either. I change the motor oil every, or every other ride and I certainly don't measure what comes out.If it is sucking oil in, I confident it's not coming through the crankshaft oil seal. I replaced it.

Thanks for the suggestion.

I would check the compression next. Then since it doesn't seem to be a mechanical problem it almost has to be in the electrical's if you have another bike try swapping out the CDI, and then the stator, and even coil.

Low speed coil on the stator.

Compression is over 150psi.

We've already swapped out the CDI with no luck. I'll try the rest of the electrical sys.

Would the electrical sys cause excessive smoking? Again, that only started after this issue began.

Bike was running perfect, he lands off a jump and there's the bog!

One suggestion I heard was I may need to reseal the cases. That it could be drawing motor oil and air into the crankshaft chamber. That's a bit beyond my motor understanding, but does that sound like a possibility?

Thank you

Sounds like the clutch side crank seal is leaking.

If you had a leak it should show up on a compression test and you would also use gearbox oil. If the stator was bad it is possible that there is a point where you lose spark and when you regain it you have a rich mixture. Besides swapping the stator double check all the wires in the electrical circuits including the kill button ands wires leading to it.

I replaced both crank seals. Still bogging.

Sounds like the stator's my next check. Just to be clear though, the mechanic did test the stator and the rest of the electrical sys. Says the readings were fine.

Ok, thanks guys!

My money is on stator breaking down under heat

Wow, Once you find the problem post what it was. I am anxious too know because I have a kx100.

I have basically no mechanical experience on bikes so I cant help, sorry.


Good Luck!

Did the new seal on the clutch side get knackered during installation? If it was drawing a significant amount of oil from the gearbox, the smokescreen would be huge, light grey / blue in color, and it would never run "clean", anywhere in the rev range.
As I mentioned in my prior post, going to a leaner pilot may be worsening the condition. Lower the clip (raising the needle) a couple of notches and see what happens.

It will be (or should be) very fat from zero to about 1/3 throttle.


Where is the airscrew setting adjusted to?


Has the weather cooled off significantly in your area ,then the bog started occuring?

You are not using fuel from a contaminated container / source, are you ? (water).

Petcock flowing properly?

Project racer,
I was also concerned that maybe I wasn't careful enough when I replaced the oil seal. Yesterday I re-replaced the oil seal to be sure. Then went ahead and replaced the stator side (left) seal as well. I used extreme caution when doing this and can confidently state I don't believe the crankshaft oil seal is the culprit.

However..... When I removed the cylinder yesterday I noticed a small amount of oil in the crankcase chamber. About 2cc/ml resting on sort of a ledge towards the front of the chamber. It was dark like motor oil.

I don't know how many oil seals separate the oil from the crankcase chamber, but I feel the crankshaft seal isn't the one leaking. Any other seals I could replace to rule out?

I'm frustrated as hell, but very thankful to all of you who have taken the time to share your thoughts on this. Please keep 'em coming!

If the seals are good and not leaking the only other way to have a leakage is by the main case gasket (between the left & right main cases), if that has failed you might look under the engine and see if there is any drool or signs of fuel. I would swap the stator before splitting the main cases. Also if this is the problem you should surface the mating surfaces of the cases.

Davis224 and mxnational wrench got you covered. You have attacked the mechanical side without success. I'm convinced you have an intermittent electrical problem. First thing to do is to take off the coil and sand down the the coil itself and the spot on the frame where it screws to,to insure a proper ground. Then clean all electrical connections. Next ,grab the stator out of the other bike and see what happens. As 224 suggested,I suspect that is the problem. We ran suzuki 85's for 3 years, and had a similar problem which turned out to be the stator. Suzuki actually replaced it for us free of charge. Heat is the problem,but they can be funny when they fail and expensive to replace,and cause intermittent crazy problems. If you swap stators,be careful of the position, which determines the timing of the spark. Good luck.

mx5471,
Thanks for the response. A friend of mine had recommended the same thing on the coil. I took care of that pretty early on in this wild goose chase!

Worth mentioning: A (difficult to notice) hairline crack was spotted on the frame near where the coil mounts. Though I'm aware of the RM's frame cracking issue and check it often enough, I just can't be sure this happened on that landing that caused the issues. I may have simply missed that crack before. It's not easy to spot. Mechanic caught it. Anyway, I had that welded.

Ok, sounds like I need to swap out some electrical components starting with the stator.

Thanks all

This might be dumb but I didn't see in the previous comments but have you tried a new plug wire and cap.

Plug wire is most likely epoxied into the coil and not replacable.

With everything else they've done, I doubt they missed trying a plug cap, but if not, why not?

Make sure that base is covered before swapping stators. Most often (not always) primary coil failures only show up once the engine temp is up. This is happening hot or cold.

I can see where your mind is going, Upnflamz. It really does sound like it may have breeched the seal at the cases (usually the Three-Bond type product) and may be inhaling tranny oil. Since it's not being ridden, you may not notice the gearbox fluid going down, but it does look more like steam than motor oil when it starts burning in the engine.

I vote for stator. We have had them test good and be bad. We will replace 15 stators to 1 CDI box or coil.

^ x2. There are only a couple bench tests that can be done on a stator, it can be hard to replicate the conditions that would make it fail. The best electrical part test hands down is replace with known good part. I'm kinda going through the same thing with my bike, I'm pretty sure it's the stator, but I don't have a stator to rob and don't have the money to purchase one blindly and have it not be the problem.

STATOR!!!!!

That did it!

Thanks everyone!

Why is my Rm85 bogging out when i give it more than 1/2 throttle in 3rd gear.......please help..A.S.A.P

Plus i fergot to mention it is a new bike to me-got it a week ago But back to the subject its a 2003 RM85 And it runs perflectly fine in 1st and 2nd its all the other gears that the bike "BOOGS-OUT" on me with a little less than 1/2 throttle ...PLEASE HELP
!!!!!