NSR250.net Forums Logo: Honda NSR 250 Forums, Classifieds and Service Manual in English. Covering All Honda NSR 250 MC16, MC18, MC21 and MC28 models
NSR250.net Forums

#
 
#
 
Performance Engineering

  • NSR250 Forums Index ‹ NSR250R Discussion
  • Members Content
  • Members Garage
  • Subscription
  • Transactions
  • FAQ
  • Search
  • Register
  • Log in

Exhaust sucking air.


Reply to topic   printer-friendly view
Page 1 of 1   Download Topic





bandit_7
Supporter - Titanium
Supporter - Titanium
 
Posts: 247
Joined: 29 Jun 2009

Location: Brisbane, Australia
1991 Honda NSR250 MC21
    Send private message View user's profile
    Reply with quote  

Exhaust sucking air.

Sat Jan 08, 2011 12:41 pm » Post: #1 » Download Post

Well I'm stumped. I have just put a used bottom end on my mc21 as the last one had a worn crank, seals and bearings. Now for some strange reason the lower cylinder is sucking air into the exhaust while idling. It has a little putt every now and then with a bit of smoke coming out but that's it. When I give it a little throttle around 2500rpm it gets a bit better but the exhaust gas seems colder than the top cylinder. At around 5000rpm it heats right up and appears to be good.

The top cylinder is running great, no complaints at all.

I have cleaned the carbies, rebuilt the reed cages, swapped the coils over and had a good general look over to eventually find nothing out of the ordinary.

Any advice or idea would be great as I can't think of a single thing to try now. Don't hold back, I'm willing to try anything.

Cheers

Andy
Back to top


Chester362
Supporter - Titanium
Supporter - Titanium
 
Posts: 940
Joined: 19 Jun 2005

Location: Cheshire, U.K.
    Send private message View user's profile
    Reply with quote  

Sat Jan 08, 2011 1:04 pm » Post: #2 » Download Post

First place I would start is making sure there are no air leaks, etc.

Then clean/blow out the carbs.

Then balance the carbs.

Then check spark plugs/ignition coils,pick-ups,etc.
Back to top


bandit_7
Supporter - Titanium
Supporter - Titanium
 
Posts: 247
Joined: 29 Jun 2009

Location: Brisbane, Australia
1991 Honda NSR250 MC21
    Send private message View user's profile
    Reply with quote  

Sun Jan 09, 2011 9:44 am » Post: #3 » Download Post

Carbies have already been cleaned and balanced, ignition checked and ok. I have sprayed aero-start all over the engine whilst running and that had no effect aswell. All air solenoid assembly has been cleaned and checked.

Today I removed the airbox and ran the bike for a few minutes just to see if there was anything out of the ordinary. I did notice a small amount of fuel being expelled out the carby throat on the lower cylinder while giving a little throttle. At idle there was only a sucking effect. At this point the exhaust is still sucking.

It would appear that there is only one place for the air/fuel mixture and air from the exhaust to be going. I guess it's time to break out the old leak down tester.

You would think the cylinders would work as a team but NO, one has to get greedy!!!

Andy
Back to top


Middo
Supporter - Titanium
Supporter - Titanium
 
Posts: 303
Joined: 15 Apr 2008

Location: Melbourne, Australia
    Send private message View user's profile
    Reply with quote  

Sun Jan 09, 2011 9:03 pm » Post: #4 » Download Post

Sounds like the same thing that my bike is doing. Keep us all updated of your progress. Good luck!
Back to top


bandit_7
Supporter - Titanium
Supporter - Titanium
 
Posts: 247
Joined: 29 Jun 2009

Location: Brisbane, Australia
1991 Honda NSR250 MC21
    Send private message View user's profile
    Reply with quote  

Tue Jan 11, 2011 10:08 am » Post: #5 » Download Post

Hooray!!!

I get to pull another motor apart. Who likes riding bikes anyway. Rolling Eyes

The center crank seal almost holds 2 psi for 1.57 seconds.

All 3 crank seals failed miserably but the center one is by far the worst. It is passing air from bottom to top cylinder way faster than top to bottom.

I guess that's what you get when you buy a bottom end from the worlds most popular auction site. Evil or Very Mad Evil or Very Mad Evil or Very Mad

Almost time to give up on the bike and concentrate on the rx4.

Andy
Back to top


bandit_7
Supporter - Titanium
Supporter - Titanium
 
Posts: 247
Joined: 29 Jun 2009

Location: Brisbane, Australia
1991 Honda NSR250 MC21
    Send private message View user's profile
    Reply with quote  

Tue Jan 11, 2011 10:15 am » Post: #6 » Download Post

It was advertised as "mc21 bottom end with good crank seals"!!!

Not very accurate.

Andy
Back to top


{.bLanK}GoD

 
Posts: 174
Joined: 15 Oct 2009

Location: Christchurch, NZ
    Send private message View user's profile
    Reply with quote  

Wed Jan 12, 2011 12:10 am » Post: #7 » Download Post

Keep note the center crank seal will leak air from right to left (bottom to top cyl) within hours after the engine has been shut down. This is normal. With the engine running, the 2t oil will seal it completely.
Back to top


bandit_7
Supporter - Titanium
Supporter - Titanium
 
Posts: 247
Joined: 29 Jun 2009

Location: Brisbane, Australia
1991 Honda NSR250 MC21
    Send private message View user's profile
    Reply with quote  

Wed Jan 12, 2011 5:11 am » Post: #8 » Download Post

All primary chEcks were done with the engine running. Seals are gone ( all 3). Please excuse the short posts as seq where I live are experiencing the worst floods in 35 years. Smile

Sinking Andy
Back to top


Andy
Site Admin
 
Posts: 11950
Joined: 19 Jan 2004

Location: Devon, UK
1991 Honda NSR250 MC21
    Send private message View user's profile
    Reply with quote  

Thu Jan 13, 2011 12:46 am » Post: #9 » Download Post

Post deleted for shorthand TXT.
_________________
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!
Back to top


shmokica

 
Posts: 159
Joined: 27 Feb 2008

Location: Brisbane, Australia
1990 Honda NSR250 MC21
    Send private message View user's profile
    Reply with quote  

Thu Jan 13, 2011 9:36 am » Post: #10 » Download Post

bandit_7 wrote:It was advertised as "mc21 bottom end with good crank seals"!!!

Not very accurate.

Andy


Bugger, glad I didn't win it now, I think I was the second highest bidder.
Back to top


bandit_7
Supporter - Titanium
Supporter - Titanium
 
Posts: 247
Joined: 29 Jun 2009

Location: Brisbane, Australia
1991 Honda NSR250 MC21
    Send private message View user's profile
    Reply with quote  

Thu Jan 13, 2011 8:12 pm » Post: #11 » Download Post

A couple more sets of red traffic lights and I wouldn't have made it home to bid at all!!! By the time I got the computer on there was about 5 minutes left.

Andy
Back to top


Reply to topic   printer-friendly view
Page 1 of 1   Download Topic

NSR250R Discussion

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum

  • NSR250 Forums Index
  • All times are GMT
Powered by phpBB © 2001, 2005 phpBB Group


Hosted by NSR250dotNET © 2008 NSR250dotNET