i've searched the forums and haven't been able to find a diy, setup, walk-through of some sort, for cleaning the carburetors on the mc28/pgm4.

I've done this before on a late fzr250, but was looking for some pictures and text.

thanks.

ps - i fear the worse, i just picked up a sp with 9000kms that's been sitting for years.

Welcome to the Forum "dld".

You can see that section of the English Workshop Manual online as a Supporting Member.

You want page 91.
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NSR-WORLD Forum Index > NSR Forums > Discussion

Carburetor basic clean and set for newbie




Author Thread

Max szeged



Joined: 06 Mar 2006


Posts: 215
Location: Lublin Poland




Carburetor basic clean and set for newbie
Ok I am going to share my experience of cleaning the carburetor for people who had not tried it before.
Things you will need
1st thing is get a back supporter if you have a bad back; you will be spending a great deal of time bending forwards if this is your first time.
2nd Get a good torch light, bright with led but small enough to get around in the body. Have a digital camera around to take some pictures to help you put it together again. And last get good tools for the job and some good cleaners.

Begin by taking off the gas tank, air box… then take a picture of how the carburetor is rigged up to the bike. Take some attention to the cables and give it a clean around the places where the engine will be exposed to dirt.
Take out the carburetor by disconnecting the choke, oil pump pipes and the throttle cables after that remember to block all the openings.
With the carburetor out on the work bench give it a good clean on the exterior and drain the float bows. Make notes of the balancer bolt between the two parts of the carburetor, and check the air screw for how many turns, please write it down!
With the exterior clean start to separate the two parts, keep in mind that the balancer spring and choke recoil spring might fly out while pulling them apart. Take you time on this part so not to break something. Remember to inspect that you have loosen all the bolts required for separation using blunt force on it will not help if you forgot to loosen one of them. Just after separation screw on lightly the bolts to there original place so that you don’t forget or loose them.
With the carburetor separated into 2 parts take some time to clean the medial surface which was difficult to get to while they were together. Now that the exterior is clean on each surface you may loosen the float bow for inspection of the float height and jets! Be very gentle on this part! They brake easily.
I had a problem removing the slow jets because they were on too tight, I further learned that heating the carburetor with a hair dryer will help to expand the casing and make it easier to unscrew the jets. And remember not to use force on them because they round off easily and get a good screw driver for the job!
Clean the jets and make sure they are not blocked! Specially the slow jets! Make notes of the sizes of the jets and compare them to the work shop specs!
Now if you want to remove the needle covers beware that you might need a new set of gaskets, but if you are lucky and careful you might not! Make notes of the positions of the clips for holding the breather pips in position. When you have the needle cover open use the torch light to get a good view of how to take the needle out, be very gentle on this. Make notes of needle type and compare it.
Now that both the internal and external parts are cleaned and settled to the right position with the jets all checked out you may start to put the whole thing back together.
If you were running rough before it may be that the airscrew, balancer, float height is out of position or the slow jets are blocked. With this clean up and reset to the carburetors you should be ok unless your RC valve is not in the right position or there might be an electrical problem.
I hope this will help newbie’s with no mechanical experience to over come some fear and obstacles. If I had said or miss said something please forgive me because I was a newbie as well before I over came this obstacle with the help of this web site!
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Sun Jan 25, 2009 7:27 pm


Max szeged



Joined: 06 Mar 2006


Posts: 215
Location: Lublin Poland




looks like with the new #38 slow jets i am having the symptom of 1/4 throttle rich, killed one sparky today the second one is about to die soon, i should go for the Air screw right?
when i cleaned and set the carbs this time i had fitted a in line fuel filter, would air pockets produced in the filter mess up my cold start mixture or some other thing perhaps?
Started the bike with a few kicks with choke on and ignition off then turned the key, and kicked to start. It reved all the way to 6000rpm with the throttle fully closed, i know for a fact this is bad for cold start and i can feel the engine sounds a bit different after that episolde, what would make it do this exactly? dont think it can stand another one.
any help will be thanked greatly.
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Mon Jan 26, 2009 7:05 pm


Dave Ett
Supporter - Carbon



Joined: 20 Feb 2004


Posts: 2676
Location: Witney, Oxfordshire, England




Hmm, so you have oily plugs but it revved its nuts off on starting? High revving is usually a sign of a weak mixture - I'm thinking air leak, but fouled plugs would contradict that...
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Tue Jan 27, 2009 10:59 am


Max szeged



Joined: 06 Mar 2006


Posts: 215
Location: Lublin Poland




yep was a kind of an air leak, was being busy for the past few days and the weather was bad, so the carbs were dry didn’t wait long enough for the gas to go down and push the air out so there was a air pocket. Now it’s fine during starting! Went out today after adjusting the air screw it is now 2 turns out.
During warm up the revs drop by 1000 rpm when trying to idle at 4000 rpm but after it had warmed up it will rev over 4000 rpm while trying to idle at 4000 rpm. What does this mean? Oh and big hesitation for higher rpm MJ is 115 going to post for some 110 on the net.
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Tue Jan 27, 2009 3:30 pm


DifferentStrokes
Supporter - Titanium



Joined: 13 Feb 2008


Posts: 475
Location: OC CA




Forgive Me,

quote:
--------------------------------------------------------------------------------
Originally posted by Max szeged:
Oh and big hesitation for higher rpm MJ is 115 going to post for some 110 on the net.
--------------------------------------------------------------------------------



110 seems very, very lean. Don't know what the 16 runs stock but for a bone stock 250 seems very lean. --- Forgive me, I am speaking without knowing... Never had a 16 , never will.

I must ass/u/me that stock 16 jetting runs these low #'s or someone with much more experience would have posted a warning.

However, if your bike is stock... & is in good shape... My suggestion would be jet it back to stock to start. (Honda's specs) and jet from there... Easy to fix one issue at a time. Much harder (more expensive) to solve all issues at once.

Be Well

Wed Jan 28, 2009 12:13 am


Max szeged



Joined: 06 Mar 2006


Posts: 215
Location: Lublin Poland




its #110 or 115 on the manual i have 115 right now and its giving me a bad time, so just want to try out 110's before i do anything else.
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Wed Jan 28, 2009 9:36 am


DifferentStrokes
Supporter - Titanium



Joined: 13 Feb 2008


Posts: 475
Location: OC CA




Re: Forgive Me,

quote:
--------------------------------------------------------------------------------
Originally posted by DifferentStrokes:
(I) Don't know what the 16 runs stock
--------------------------------------------------------------------------------



Thank you for the information Max, I did not know that.

Wed Jan 28, 2009 5:23 pm


Andy
Site Admin


Joined: 19 Jan 2004


Posts: 6709
Location: Devon, UK

1991 Honda NSR250 MC21


http://tech.nsr-world.com/nsr/nsr-all/carb-settings/
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Wed Jan 28, 2009 6:56 pm


Dave Ett
Supporter - Carbon



Joined: 20 Feb 2004


Posts: 2676
Location: Witney, Oxfordshire, England





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Thu Jan 29, 2009 8:49 am

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So I got around to pulling the carbs off the bike, really not so bad, a bunch of dried up rust that cleaned out easily. The gaskets were crusty dried chips, so I got my local shop to order me some new ones for a hefty cost.

At the base of the float bowl, the air mixture screw was seized and had rust filled in the hole. So i assume I should now set the screw to the default location,which is 13.7mm, found here
http://tech.nsr-world.com/nsr/nsr-all/carb-settings/

How do i measure this?

reading the figures on my jets, im seeing 145 on the MJ, and 38 n the SJ. Not stock?



Looking at what came in the bag, can someone help label what the medium sized circular rings are for.



Should I be worried about the slightly misaligned needle below.




Last edited by dld on Sat Jul 04, 2009 1:12 pm; edited 1 time in total

dld wrote:
At the base of the float bowl, the air mixture screw was seized and had rust filled in the hole. So i assume I should now set the screw to the default location,which is 13.7mm, found here
http://tech.nsr-world.com/nsr/nsr-all/carb-settings/

How do i measure this?

Er... that's the float bowl drain screw in the photo, and the float level measurement, not the air screw and its' setting!!

I think you should invest in a manual and some time in searching the forum!
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Please keep all responses to Forum posts on the Forum so that others may benefit.

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