mc 21 engine problem ????

**Fri Jul 20, 2007 1:49 am » Post: #1 » Download Post**

hi there fellow riders i need help my mc 21 250 r wet clutch version when i start the bike it starts ok but the front cylinder dosent seem to fire well i belive the spark is good but fires intermititly not very well at all ok so now the bike warms up a bit then it just wants to rev to 11000 rpm on one cylinder the back one at the same time the front cylinder will fire once and a while and also will back fire but i think thats from excess gas not burning off i turn off ignition it still runs until i bump the throttle a few times then it will die it wierd please help thanks alot brent

1991 mc21 r

**Fri Jul 20, 2007 3:49 am » Post: #2 » Download Post**

What do the plugs look like? Have you checked compression.
_________________
james
Its not how fast you go...Its how you go fast.
MC21 Rothmans
RS250
RC31
CRF250X
748R
Porsche (many)
http://members.rennlist.com/j911brick/rennlist3_002.htm

**Fri Jul 20, 2007 8:10 am » Post: #3 » Download Post**

Ever heard of punctuation Brent? Shocked

_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

**Fri Jul 20, 2007 8:11 am » Post: #4 » Download Post**

Sounds like the carbs could do with a service. When did you last strip and clean them? Has it been stood at all?
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

**Fri Jul 20, 2007 3:01 pm » Post: #5 » Download Post**

Dave Ett wrote:
Ever heard of punctuation Brent?

In all seriousness though Brent, it does make it a bit hard for our non-English speaking friends to follow! Wink

Everyone... please just take a few moments to read back through your posts, and think about whether it would make sense to you if English wasn't your first language!! Some of the posts lately have been hard enough to read when English IS my first language!! Confused

_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!

**Fri Jul 20, 2007 5:19 pm » Post: #6 » Download Post**

You might check that your coil connections are clean and snug fitting.
_________________
-Jim
'93 MC21

**Fri Jul 20, 2007 7:32 pm » Post: #7 » Download Post**

ok! sorry for the bad grammer. thanks for the input. but can anyone tell me why the engine wants to rev so high when the throttle is closed.and i turn off the ignition it still runs until i bump the throttle. thanks brent

**Fri Jul 20, 2007 7:43 pm » Post: #8 » Download Post**

Air leak! maybe!

Had the same problem on my KR, found the in-let rubber wasnt secured on the bike. not sure why its still running when you switch it off!!! Rolling Eyes

**Fri Jul 20, 2007 8:24 pm » Post: #9 » Download Post**

It must be an electrical fault if it continues to run with the ignition switch in the off position.

I don't really understand what "until I bump the throttle" means.
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!

**Fri Jul 20, 2007 11:27 pm » Post: #10 » Download Post**

Could be running quite lean, and very hot, causing pre ignition - I have heard of this before, but usually a 2 stroke will self destruct when this happens.

As I asked, has it been stood? Have you serviced the carbs recently?
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

**Fri Jul 20, 2007 11:28 pm » Post: #11 » Download Post**

Lucky you guys dont speak straryeun (read : Australian ). Merg every 2 words together, replacing t's with d's whilst removing the first 2 letters of each word, and add the word mate every 7 words.

Is it just me, or is it not possible for a engine to rev to 11000 rpm with a shut throttle ? Where is all the air coming from ? Im sure if the boffins on here (no insult intended) calculate how much CFM is needed for this engine to rev that high, it would show its not possible with the slide shut.
_________________
Winning isn't everything, but loosing isn't anything

**Fri Jul 20, 2007 11:30 pm » Post: #12 » Download Post**

That's why i asked about the carb service - may have a trapped cable somewhere for starters, let alone an improperly fitted carb rubber...
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

**Sat Jul 21, 2007 12:39 am » Post: #13 » Download Post**

Im sure your right. Probally something simple rather than complex.
_________________
Winning isn't everything, but loosing isn't anything

**Sat Jul 21, 2007 2:28 am » Post: #14 » Download Post**

ok yes i did the jets. cleaned bottem end of carbs. floats to cleaned and blew through jets. was alot of crap in there. the airbox is not on there because im missing the peice on the bottom for the hose from the clinoids the 3 way connector to the airbox. but i heard its mostly for midrange.it shouldn't affect the ildle ? right? . i need to test for air leak and compression but i dont think its compression. and the slides are closed when it revs. i think your right its an air leak. i need to check all tonight i will get back to you with results and go from there. thanks all for all your help! any other ideas are surley apprecated!! thanks again brent