Jump to content
Sign in to follow this  

rm85 sputter/surging at low rpm

Recommended Posts

hi guys

new here and looing for advice..

my sons 2006-2007 rm85 is sputttering or surging whatever you guys cal it at low/mid rpm but when the powerband kicks in it runs fine, i have cleaned the carb 3 times to be sure it not clogged but the problem is still there i have also noticed from time to time that oil will come out of the exhaust valve overflow and on the most recent ride a little also came out of the exhaust, could this have anything to do with wrong air/fuel screw being set incorrectly ? i am running at the manuals oil/fuel ratio of 30:1 (166mil oil per 5 litres of fuel) according to an oil/fuel ratio calculator, if any of you guys can shed a little advice it would be much appreciated...

thanks

dave

Share this post


Link to post
Share on other sites

Surging could be air leak, spray around reed block and dry side seal. But I'm guessing it's running a bit fat on the needle, try the clip higher up on the needle. Main somewhere between 128 and 125 in hotter conditions.

Share this post


Link to post
Share on other sites

thanks for the fast response

the bike is all stock and i dont have much knowlege on jetting but the clip is set on the 3rd so will move it up 1 to the 2nd position tomorrow, as for the reeds what do i spray them with ? and is it worth taking them off to inspect them? dont really know much about these bikes sorry

Share this post


Link to post
Share on other sites

"Starting fluid" will give you the best response. Dry side seal is the one on left behind the ignition pull the cover off and spray behind stator plate with motor running. Easier if you have the little red spray tube attached. Try the jetting 1st if it's really hot there leaner on the needle and near a 125 main.

Share this post


Link to post
Share on other sites

thanks JBFL, will get some starter fluid tomorrow and give it a spray and see what happens, i adjusted the air/fuel screw 2 turns out as stated in the pdf manual i have just got hold of and took it out for a few hrs for a blast and the surging seemed to be less but fouled my plug with oil the first 5 mins of warming up(cleaned and ran good again) there was a fir bit of oil coming from the exhaust pipe and powervalve overflow also , could that have anything to do with my fuel ratio (166mil oil per 5litres fuel) i did howerver forget to put the clip on 2nd position so this may help, am i right in thinking that the oil from exhaust and powervale overflow is unburnt 2 stroke or could it be a crank seal?

the weather is kinda hot over here atm

also as stated i have no knowlege of jetting at all so maybe its easier to let a shop repair it just thought id give it a try myself and maybe learn a thing or 2 along the way :-) but dont want to make it to lean/rich and lock my sons bike up lol

dave

Share this post


Link to post
Share on other sites

The silencer packing will need to be re-done now also. You'll be able to smell if it's premix oil or if it's gearcase oil, if it's gearcase, you'll probably need to take it to a shop. Jetting is easy just loosen the 2 clamps on the each end of the carb and rotate so the bowl plug is facing more towards you then take a 17mm to take the bowl plug out. I use a 6mm socket with a small pair of vice grips to get the jet out and back in. I can't remember if you need to take off the chain guard over the front sprocket for easier access but the 2 bolts are easy.

Also I use a ratio rite cup to mix fuel it's a no brainer for me.

Share this post


Link to post
Share on other sites

i will take a trip to my local moto-sports shop this afternoon and get new jets - silencer packing ect and see how i get on, im 80% sure the oil is premix but will check again to be sure. do you still recommend the clip on 2nd?

as stated in my last post the surging is less after turning the air/fuel screw but the oil from exhaust valve and silencer is a little worse so now focusing on correcting that aswell. how do the ratio rite cups work? may invest in 1 myself to stop all the guess work,,,, sorry for my lack of knowledge but motocross bikes are new to me and my son but this forum seems a really good place for advice and to start learning :-)

edit

just looked at the ratio rite cup its basicly a precise measuring jug i believe and now on the order list ;-)

Edited by davva_akz

Share this post


Link to post
Share on other sites

Yes lean the needle (2nd from top) see how it is then. If still a little off lean the main 1 and go from there.

Share this post


Link to post
Share on other sites

ive re-packed the exhaust and put clip on 2nd aswell as running 40:1 again with air screw 1 1/2 turns out does this sound about right ? i will try clip 1 if still a little off before buying new jets, cant get to try it out until sat so will get back to you and let you know how it runs..

thanks again for all the advice :-)

dave

Share this post


Link to post
Share on other sites

hi

took the bike out for a full afternoons riding and the sputter wasnt as bad(still there slightly) with the clip on the 2nd position but there is still a trail of oil running out and under my silencer are these bikes supposed to do this aswell as leak unburnt 2stroke from the powervalve overflow or is my jetting still off slightly? another thing would the carb float level being slightly off make this happen?

thanks

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  

×
×
  • Create New...