Need help

[jungleboy213]

I am having a problem with our Cobra getting out of the gate. Here's my setup. Stock RM 85, Cobra 70 pipe,14/49 gearing, DWT rears, stock ignition, br9ex plug,. I have changed front sprocket to a 13 and a 15 tooth. I have changed tires to the little Carlisles and to big Hoosiers. I have changed the carb from a 28mm flat slide to a 24mm round slide to try to get more bottom end. Nothing seems to help. Out of the gate he will be around 3/4 throttle and when the gate drops he'll go to full throttle but the quad will just roll out of the gate, go about 7 feet and the it'll kick in. Top end wise, this thing is fast. It is just a dog out of the gate. Any suggestions would be appreciated.

[nastynotchback1]

The stock cobra pipe would be my guess.I would pick up a good aftermarket pipe for a rm motor.

[jungleboy213]

I kind of figured that. It's already on my list of things to order. I was just trying to figure if the gearing is close, too. After dealing with DRR's for 3 years, this is a new venture for me.

[nastynotchback1]

Yes your gearing is about what must people run with an rm85.I am running a 12-40 right now but the final ration comes out almost the same as a 14-50.

[heathmxracing]

I would agree that the pipe is your problem. Trackside makes a good pipe that will bolt right into the Cobra chassis with that engine combination..

[neveready]

I have that pipe for sale

[fish-d-fish]

We ran the stock cobra pipe on our fully built rm 85. Same numbers on the Dyno as the trackside. The pipe is not the problem. Check reeds? What year rm? When was the carb cleaned last? The 24 mm is way too small to get an accurate read too. What fuel? Lots could be wrong but it's not the pipe unless the head pipe was not designed properly..

[chris p.]

clutch slipping ???

[neveready]

powervalve spring or adjustment

[stevo7706]

I agree with fish, the pipe isn't the problem.I would put the 28mm back on and look closely at your jetting.Try not to change too many things at once.Establish a baseline of what works i.e; stock, and go from there.

[jungleboy213]

That's what I do. I'll change one thing and if it doesn't work, I'll change back and try something else. I am also running Sunoco112 mixed 40:1. I clean the carb eveery race. The 24mm carb was new out of the box. It is an '07 RM Motor.

[bigdaddy77]

You guys coming up to Crossroads for any moto X outcast races? First one is feb 17. We would love to have you guys back and any one else you might bring with you. Shoot me a text if you want. 618-975-7303 thanks Brian

[TeamNeilson]

We run a bone stock internals 2004 RM85 in my boys bike and he was never further than 3-4th at the first corner in the 90 mod class... granted it didn't take long for that little motor to cap out, but the thing came out of the hole super strong.

Even with me on it, the thing would pull super hard for me.

We had the stock 70 pipe on there, and upgraded to the Trackside 90cc pipe and on the dyno, the HP numbers were the same (19) but the torque numbers jumped up dramatically (like 20%).

Sprocket choice is 14/48 (428 chain).

The only other thing the motor had, and I don't know if they all have it, is the VForce3 Reed cage.

Carb is 28mm D-Slide (factory) carb..

I did notice that in the quads, with the open air filter that jetting was SUPER temperamental and I have notes galore on changes I'd have to make even day to day. You can check the powervalve engagement by taking off the little l shaped side cover and revving it up a little.. ours kicks out of the way just over 1/4 throttle in neutral.. Also make sure its not dirty and covered in carbon.. and the front plate should be removed and the sludge cleaned out once and again, as the hoses don't always get it all out.

I found that if I got the bike just a hair lean it ran the best and smoothest across the entire RPM range.. Never smoked unless the temperature changed and it was an easy fix.. I found that one jet size change caused the motor to act funny.. The 2 motors I have behave the exact same way when incorrectly jetted.. I liked hair lean on idle, slightly normal-rich on the needle and then lean again on the main. (When I say lean, not grey/white plug lean, but I found the plug to be a dry coffee with a lot of cream color to work the best for us). I could get you the exact jet numbers we used, but they are in the trailer and not accessible right now due to snow hahah. Just let me know if you are interested, and when it melts i'll get them for you.

I run Shell 94 non-ethanol fuel with 40:1 castor oil.

When I sent my main motor to our engine builder (its time to upgrade her), she had just over 60 hours on it racing and practice with 120lb compression and I never put a dollar into it. It just kept running and running.


As far as gate launch.. My son does the 1/2 throttle blip just before the 5 second board to clear it out and when the 5 second board comes up he just does the 3/4 throttle hold and when the gate drops, he lets the clutch out fast and smooth and it just goes...

I hope that helps you as I know we spent lots and lots and lots of hours getting ours to run happy.