RMTripper

New to this forum, but I definately could use some good advise. I own several two stroke dirtbikes, and two of them have developed the same problem. I do practice good maintenance procedures and can change most parts myself. Including top end and swing arm/shock/linkage bearings. But, I am not a mechanic by any means. Carburetors are a weak spot for me. The bikes are a 95 CR125 and a 99 RM125. The problem is at low engine speeds there is a BOG, and then when least expecting it, full powerband. If you ride in the band at all times everything is okay. Both have had recent top-end rebuilds,exhaust valve system cleaned, and have good compression. This was not a problem until several hours after rebuild. Hope to hear some response and thanks...

tigmaster

has anything changed like a new pipe or anything? how are the reed valves and was there a climate change or anything like that? not many things that can break to cause 2 stroke bog

__________________

Check Our Latest How-To Here

RMTripper

The CR has new reeds but no other changes. The RM reeds still have good action in them. The only thing I can think of is jetting. I dont know, do jets just wear out and cause this problem?

RMTripper

I just read your post on carb jetting, and I remembered that when I did the top end rebuild on the CR, I polished the cylinder head and exhaust ports. I did not cut away very much, but enough to make it a very smooth surface. And also, this problem could have started immediately after that. I am going to try the plug test as you suggested, I think it is going to be BLACK, as it has been most times that I have changed it in the past.

tigmaster

did u do anything to the intake ports? polishing the exhaust should create a lean condition, same with the head. obvious question, but is the filter good?

__________________

Check Our Latest How-To Here

RMTripper

Did not polish intake ports, only exhaust. Yes, filter is good and always cleaned regularly.

tigmaster

what are yourunning your mixture at, did u change it after the rebuild? i would suggest 40-50 : 1 if u changed your mixture, you kno u need to rejet. less oil = leaner on jetting, more oil = richer on jetting. it can be thought of this way, you get the same amount of fuel and oil mixture going through thejets, but if there is more oil than the gas then you need to give it more gas and vice versa. you probaly already know this, but im just clarifying this for everyone so they can follow also.

__________________

Check Our Latest How-To Here

tigmaster

did u clean the exhaust valve yourself? if so are u sure that you put it together right? because that would explain the slamming you into a powerband because some powervalve assemblies are adjustable and some just have a spring that u can install wrong.

__________________

Check Our Latest How-To Here

RMTripper

Yes, I changed to Amsoil (50:1), was using Yamalube (32:1). So are you suggesting that I should go UP a few steps on the jet?
I did clean the exhaust valve system myself. I have a Clymer repair manual for each bike, it is very descriptive on repairs and maintenance procedures, so I know just about enough to be dangerous... I know I installed all parts correctly, but I may not have the spring adjustment exact.

tigmaster

sorry about my previous post and the wrong jetting information, however jetting is your problem. you need to go leaner on the main and leaner on the pilot. to determine the number of steps, you need to do a plug test. warm the bike up and make several high speed passes. while at full throttle, kill the bike and pull in the clutch and bring the bike to a stop. the whole point of this process is to see what the plug looks like at full throttle so dont let the engine idle. check the plug, u are looking for a light tan color. darker = need to go leaner, lighter = dont run your bike again until you richen up the main. if you said that the plug was black u will need to go down at least 3 steps on the main. just keep making passes and rejetting until your plug is light tan. you may have to buy several jets to get it right if you have never done this before, sorry jets arent that expensive though. next is the pilot. tuning this is a little harder on a 2 stroke, but still relatively easy. its basically trial and feeling. buy at least 2 steps down and 3 steps down for the pilot. start with the 2 steps down and start the bike up and warm it up after making a few passes, let it idle for a sec, twist the throttle sharply and listen for bog. if you dont hear any bog, then let the bike idle for about 45 seconds and try again. if no bog still then you are good to go, if not put in the 3 steps down jet and recheck. this whole process shouldnt take more than an our and after the first bike the second will be a breeze. also if you were wondering, a step is measured in incriments of 5. say you had a 175 main jet and needed to go down 1 step. it would then be a 170. this process will fix all of your bogging blues. any questions, let me know.

__________________

Check Our Latest How-To Here