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

Leaky carbs - fuel in the cylinders! - Update


Reply to topic   printer-friendly view
Page 1 of 2  Goto page 1, 2  Next Download Topic





andreb

 
Posts: 131
Joined: 13 Jun 2008

Location: USA
    Send private message View user's profile
    Reply with quote  

Leaky carbs - fuel in the cylinders! - Update

Tue Sep 16, 2008 8:18 pm » Post: #1 » Download Post

Hey guys,

So a few times now on my NSR I have gone to start it and have had to kick and kick and kick, then once it fires fuel shoots out the stingers and of course all over the bike!

I have forgotten to turn the fuel off a few times and had this happen but now its starting to do it even with the fuel off. I have tested the petcock and it works fine.

I suspect the needle and seats in the carbs. When I first got the bike I inspected them and set the float levels, they seemed to be ok. Three or four times now I have gone to my bike only to find a puddle of fuel underneath it. The lower cyl must have had the piston up and the fuel leaks out the exhaust flange and down the pipe.

Any ideas on this one?
_________________
Andre E. Benguerel
1996 Honda NSR250R
Daijiro Kato/Fortuna Replica #74

2000 Honda RS250R (NX5)
2008 Honda RS250R (NXA)
AFM Expert #430


Last edited by andreb on Mon Nov 24, 2008 10:39 pm; edited 1 time in total
Back to top


FruitLooPs

 
Posts: 43
Joined: 23 Aug 2008

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

Wed Sep 17, 2008 12:10 am » Post: #2 » Download Post

Only advice is be careful, I managed to hyrolock my gsxr750 and bend a conrod due to a bad carb.

Sad I'd get it sorted asap
Back to top


apexxn

 
Posts: 397
Joined: 01 Nov 2006

Location: Cali
    Send private message View user's profile
    Reply with quote  

Wed Sep 17, 2008 4:54 pm » Post: #3 » Download Post

I would take a close look at the needle and seats. I've had this kind of problem on other bikes and after chasing my tail it was just worn seats. NSR's are getting up there in years and these types of mechanicals are going to become more common.
Back to top


andreb

 
Posts: 131
Joined: 13 Jun 2008

Location: USA
    Send private message View user's profile
    Reply with quote  

Wed Sep 17, 2008 5:20 pm » Post: #4 » Download Post

I was also thinking a leaky float but in all my years of working on carbs I have never found one that leaked.

I think I'll order new needle and seats anyways and just replace them when I inspect and clean the carbs. I don't want to have them apart and then figure out I need them.
_________________
Andre E. Benguerel
1996 Honda NSR250R
Daijiro Kato/Fortuna Replica #74

2000 Honda RS250R (NX5)
2008 Honda RS250R (NXA)
AFM Expert #430
Back to top


apexxn

 
Posts: 397
Joined: 01 Nov 2006

Location: Cali
    Send private message View user's profile
    Reply with quote  

Wed Sep 17, 2008 5:29 pm » Post: #5 » Download Post

I agree on the float. It's always a solution that get's mentioned, but like you I've never seen one full of fuel on any bike no matter how old.
Back to top


Dave Ett
Site Moderator
Site Moderator
 
Posts: 3648
Joined: 20 Feb 2004

Location: Gloucestershire, England
    Send private message View user's profile
    Reply with quote  

Wed Sep 17, 2008 7:13 pm » Post: #6 » Download Post

If it was the float seal, it wouldn't really explin the fuel in the engine when the tnk is turned off.

How is it getting from the carb into the cylinder when the only fuel available is from the flot bowl?

Have you checked that the tank tap ctually turns the fuel off - and that you're not rotting it to reserve?
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Back to top


andreb

 
Posts: 131
Joined: 13 Jun 2008

Location: USA
    Send private message View user's profile
    Reply with quote  

Wed Sep 17, 2008 7:33 pm » Post: #7 » Download Post

Yeah, not sure really! I was thinking maybe pressure in the tank or fuel line forced it past the seats or petcock? My tank vents to a catch bottle. Maybe the line is pinched? I do run a fuel filter and between that and the line to the tank there would still be gravity pressure on any fuel in the line.

I would say the amount of fuel that shoots out the pipes is about the amount in the fuel line and carb bowls.

I have had the tank off a thousand times and I know the petcock works. Each position has a nice snap to it when you hit the detent. I know I had it in the off position and its done this twice now. I am certainly going to test it again. It's been a few months since I had the tank off. Maybe the seal in the petcock has failed.

It's always when its on the side stand too, never when it's on the rear stand. I am going to pull the carbs and check them out regardless, petcock too. Funny thing is it never pushes fuel out the bowl vents which I think would happen first before it pushes its way past the seats.
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  

Wed Sep 17, 2008 9:32 pm » Post: #8 » Download Post

My thinking is it`s probably just the float level is set too high.
If this is the case, even with the petrol tap turned off. The level of fuel in the carburetor will still be too high.
With the bike on the side stand the excess fuel can leak out of the pilot & needle jet orifices into the engine. Also, as the float level setting is out, it won`t allow the floats to actually close the float valve.
This means the fuel left in the fuel line and filter can drain down, refilling the bowl, in turn leaking more fuel into the engine.
You may want to check that the overflow tube isn`t blocked anywhere also. Not just the plastic pipe but the brass tube sticking up inside the float bowl too.
The float bowl vents are a bit higher than the jet drillings into the venturi throat, so any fuel will reach there first.
The workshop section on this site should explain how to check and set the float levels.
Hope you find the problem.
Cheers, Roy.
Back to top


Dave Ett
Site Moderator
Site Moderator
 
Posts: 3648
Joined: 20 Feb 2004

Location: Gloucestershire, England
    Send private message View user's profile
    Reply with quote  

Wed Sep 17, 2008 10:11 pm » Post: #9 » Download Post

Might be worth cracking the drain screw on the dodgy bowl to let a little out and see if tht helps?
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

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  

Wed Sep 17, 2008 10:16 pm » Post: #10 » Download Post

Sorry, just realised that you said you`ve checked the float levels.
As long as you are sure they are right then you`ll have to check the valves actually close. You can do this by blowing down the fuel feed pipe and holding the float valves closed by hand.
Sorry if I`m stating the obvious but, you do know when checking the float heights you start by holding the carbs upright, then slowly rotate them until the valve closes and the float tab just lightly sits against the sping loaded plunger on the valve needle? Then measure from the gasket face to the bottom of the float.

Another thing you can try before pulling the thing apart is take the bike for a good run to clear out any crap in the cases and exhaust. Before puting the bike in the garage, turn off the fuel tap and run the engine until it dies from emptying the float bowls. If it still floods after this it`s a good indicator of the fuel tap leaking.
Back to top


dunkenb

 
Posts: 706
Joined: 20 Dec 2007

Location: hereford .uk
1989 Honda NSR250 MC18
    Send private message View user's profile Visit poster's website MSN Messenger
    Reply with quote  

Thu Sep 18, 2008 8:46 pm » Post: #11 » Download Post

i had that problem on mine, cleaned the float valve seat with brasso on a cotton bud attached to my cordles drill. just smooths out any imperfections.
also drilled out the rivetts in the fuel tap/petcock ad put new o rings in the tap as it leaked, (not really enough to notice but over the course of a night parked up the amount still build up)
Back to top


Kieran

 
Posts: 323
Joined: 02 Jan 2005

Location: Dunedin, New Zealand
    Send private message View user's profile Send e-mail
    Reply with quote  

Fri Sep 19, 2008 5:52 am » Post: #12 » Download Post

Pull the fuel tap apart, check the seals. Then check the float level, then the seats and needle.
_________________
The Chopster
Back to top


andreb

 
Posts: 131
Joined: 13 Jun 2008

Location: USA
    Send private message View user's profile
    Reply with quote  

Fri Sep 19, 2008 8:04 pm » Post: #13 » Download Post

Thanks guys. I set the float levels properly when I first cleaned the carbs out. I can't imagine they would change that much but I will check to make sure. I thought I had pulled the petcock apart once but that may have been another bike, I have too many to keep them all straight.

I am going to try and tinker a bit with it this weekend. I also thought about your suggestion Chester. If I drain the carbs and park it over night, I can see if its leaking by just looking at the fuel filter. But even if it is leaking, the needle and seats should prevent fuel from flowing into the engine.
Back to top


apexxn

 
Posts: 397
Joined: 01 Nov 2006

Location: Cali
    Send private message View user's profile
    Reply with quote  

Fri Sep 19, 2008 9:14 pm » Post: #14 » Download Post

Hey Andre I wouldn't worry to much about the petcock. You said you removed the tank with it in the off position and no fuel flowed out. But like you say even if you leave it on the needles shouldn't allow any fuel to drain in to the engine. Just for reference my petcock is in the on position right now just like it always is and I've never had a problem.

A stuck needle will usually overflow out the carbs overflow tubes. A worn seat or needle will do what your describing. Replace the seat and needle just to eliminate that issue. They aren't that expensive and fresh carb parts are always a good thing.
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  

Fri Sep 19, 2008 11:09 pm » Post: #15 » Download Post

andreb wrote:Thanks guys. I set the float levels properly when I first cleaned the carbs out. I can't imagine they would change that much but I will check to make sure. I thought I had pulled the petcock apart once but that may have been another bike, I have too many to keep them all straight.

I am going to try and tinker a bit with it this weekend. I also thought about your suggestion Chester. If I drain the carbs and park it over night, I can see if its leaking by just looking at the fuel filter. But even if it is leaking, the needle and seats should prevent fuel from flowing into the engine.


As apexxn says above &, as I said before in my first post, I do think the float valves must be letting fuel past somehow. Whether it`s worn valves or them being out of adjustment.
If you suspect them of sticking, (meaning they are worn usually, can also be dirt/debris, although you have a filter), tapping the float bowl area sharply can shock the valve closed. As has been mentioned, you would normally see fuel leaking from the overflow. That`s why I wondered if the overflow may be blocked?
Also, I`m pretty sure the overflow tube in the bowl sits to the right hand side. Meaning it will be raised slightly in relation to the fuel level when on the side stand.
Good luck. I`m sure you will find it in the end.
Back to top


Reply to topic   printer-friendly view
Page 1 of 2  Goto page 1, 2  Next 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