Re: Rough running crm250 mk3

PurpleCRM · Post by **PurpleCRM** » 16 Jan 2014, 15:18

Hi all, hope you can me with a problem. My 1995 mk3 will rev through first second and third but bogs down in 4th onwards. If you really screw it in third you can get it to rev put in fourth but higher than 4th it really stutters and bogs down. It starts perfectly and pulls from low revs to mid revs in all gears though. I have now found out that it has a mk2 carb fitted that has become porous. In my search for a replacement carb a performance specialist recommend I test the stator first as that would cause the problems I have encountered. Could I have your thoughts please and how would I go about testing the stator? Many thanks in advance.

Post by **knackeredMk1** » 16 Jan 2014, 17:42

First check if the power valve is turning. Take the cover off and watch as the engine revs.

PurpleCRM · Post by **PurpleCRM** » 16 Jan 2014, 18:43

Yep power valve is turning, popped the exhaust off and watched it.

Post by **knackeredMk1** » 16 Jan 2014, 18:52

I hope you had your ear defenders on!

PurpleCRM · Post by **PurpleCRM** » 17 Jan 2014, 09:50

I took the bike to have some new fork seals fitted and whilst it was there I asked if he could adjust the carb floats as it was overfilling. He stated that he had checked the power valve and it operates as it should, the pulley,cables and the connecting splines etc all check out, the exhaust was off to ensure the closed position was set up correctly. I have managed to source a MK3 carb that is jetted correctly 45 and 150 iirc. Lets hope this solves my problem. Thanks for any help so far.

Post by **longmoreuk** » 17 Jan 2014, 09:53

I assume you meant the power valve cover?
You need to check the power valve lines up properly I think.

PurpleCRM · Post by **PurpleCRM** » 17 Jan 2014, 10:03

No, he pulled the powervalve cover to ensure the cables/pulley were operating but he has seen cases where the cable/pulley turns but the valve remains static (sheared or knackered splines due to seized valve). He knows his stuff and I trust his diagnosis. The carb thats fitted at the moment is the wrong model (PE31C) and also has the wrong jets fitted.

PurpleCRM · Post by **PurpleCRM** » 17 Jan 2014, 10:05

In my own mind I cant see it been the stator, surely that type of fault would manifest itself whilst running through all the gears, not just in the higher gears. Time will tell and I hope the carb from LT will solve my problems as I havent got any more cash that I can throw at it this month!

Post by **knackeredMk1** » 17 Jan 2014, 10:58

Type of carb (as long as it is for a CRM) won't make much difference. Jetting will though. If you have aftermarket exhaust/silencer on you may have to change the jetting from the original.

Have you seen the power valve in action?. All you need to do is to take off the cover on the cylinder and watch the PV rotate clockwise as the revs rise a section of the range and then fall back as the revs reduce.

http://www.youtube.com/watch?v=hAjs4oiomAU

PurpleCRM · Post by **PurpleCRM** » 17 Jan 2014, 19:20

Powervalve is good, I fitted the new MK3 carb today on std settings and it wouldnt start without half throttle and ran terribly.......I agree after messing about with the new carb on std jets it looks like the DEP sport exhaust has totally changed the jet requirements, I ran out of time today (dad commitments) but tomorrow I will swap out the pilot jet from the old carb (which would start and idled correctly in the MK2 carb) then go from there. It could be that the channels in the carb are blocked so although the MK3 carb has new jets fitted it still needs a sonic bath clean

Thanks for your input so far.

PurpleCRM · Post by **PurpleCRM** » 19 Jan 2014, 12:50

Problem sorted, I fitted the std exhaust but it would not run with the mk3 carb on std jetting, switched back to the old carb with a smaller pilot jet but 150 main jet and all is good. I replaced the float valve to cure the overflow issue, replaced the fork seals and put a fresh pair of front pads in and she is ready to roll. Thanks to all for their contributions and advice.