Idle jet mystery...

[Dave H (MI)]

...to me anyway. WHEN I get this tractor back up to speed I will confess how long I have been working on it. For example, I have had the carb soaking in good clean carb cleaner three times and have meticulously blown out the tiny passages with compressed air. Yet the same issue continues to arise.

No matter how far in or out you turn the idle jet (the one that sticks out sideways) on my MS carb it has absolutely no effect on the idle. Might as well not even be there. The adjustment on the back of the carb does work. Given that I have cleaned that carb so carefully, so many times, what other possible causes might there be for such a phenom? Is there some packing or seal on this adjusting screw/needle that maybe I lost in the beginning and never knew it? Or is there some other possible reason for this? I have looked at pics and read text over and over. Can't seem to answer this one.

 

[JMOR]

If idle speed is not low enough, then it does not come into play. Look at these photos & drawings and you can see that unless the throttle plate is nearly closed, the idle port will not be the only place the engine can suck fuel from.
You may have air leaks from places like around throttle shaft, bowl to throttle body gasket, carb to manifold gasket or engine to manifold gasket or internal to the manifold casting leaks. There are many possibilities.
http://ytforums.ytmag.com/viewtopic.php?t=530090

 

[NOXJohn]

Most guys will tell you that rebuilding a carburetor for an N tractor is very easy. It is not for me. I think it depends what is wrong with it to start with. I soaked one several times and replaced all the guts only to have it run terrible. After I got tried of messing with it I sent it to GB in MT., a poster on this board. I am not sure what all Gary did but when I got it back and put it on my tractor ran great. I think you need to run a fine wire through every opening in addition to soaking and blowing out with air. You need extreme patients if it is messed up. If you are sure it is your carburetor get a new one or talk to Gary.

 

[ZANE]

CARBURETOR WON’T IDLE

First do a thorough cleaning of the carburetor and replace the gasket between the two halves. Be sure that the float does not have any gas in it to cause it not to float properly.

The reason the carburetor may not want to idle is that the gasket that goes between the two halves of the carburetor is not sealing good. The castings are not finished too good to begin and lots of people damage the mating surfaces at the outer edge of the carburetor by banging on the side of the carburetor to stop it from flooding when the float sticks or there is foreign material between the needle and seat. (this treatment does work) :O) This gasket must be tight at the middle where the idle orifice gets it’s gasoline.
Remove the float attaching hinge by carefully prying it up until you can get a small screwdriver under it. Don’t bend the two small blind rivets. They will have to be re used to re assemble the float hinge.

Use a new sheet of 80 grit wet or dry sandpaper that is laid on a hard flat surface and lap both the mating surfaces until it is perfectly flat on both mating surfaces.

Re assemble the carburetor and you should be able to adjust the idle.

Adjust the idle by lowering the RPM and then turning the idle mixture screw in or out until the engine runs at the highest RPM. The RPM is what you will be listening for and not the way the engine runs. MAXIMUM RPM!!! At idle.

First let the engine warm up a bit.
With the engine at full throtle,turn the main needle in clockwise untill the engine stumbles (not out) Then turn the main needle out until the engine runs smoothly. Reduce the throttle to idle and then quickly advance the throttle and see if the engine falters. If it does then open the high speed needle a fraction more and repeat until the engine will accelerate without stumbling.
Reduce the throttle to a low idle speed. Turn the idle needle in and out until the highest engine speed is found. This is where to leave it, regardless of how many turns in or out. HIGHEST SPEED! Not sound of engine. The highest speed will be the best idle. Reduce the RPMs to where you want them after the highest engine speed at idle is reached when adjusting the idle needle.
To adjust the high speed mixture you should start the tractor with the high speed needle open about two full turns and allow the engine to warm up before attempting adustment of the high speed mixture.
With the engine at high RPM begin to turn the high speed mixture needle in clockwise until the engine begins to falter. Be ready to use the choke to keep the engine running. Open the needle counter clock wise until the engine does not falter and then idle it down and suddenly accelerate by opening the throttle to full throttle. If the engine falter or hesitates you should open the high speed needle another 1/8 turn and try the sudden acceleration unit the engine does not falter on acceleration.

Zane

 

[GB in MT.]

[b:2f4fac6e0c][i:2f4fac6e0c]
Dave;
First off, it is VERY hard to explain everything to do, when overhauling a carb.
Some will tell you, that it is very easy, or they say it is only a 1 1/2 hr. job or less. For starters, I go VERY slow on an overhaul, and remove everything in the carb, after soaking it for at least 12 hrs., I then inspect every inch of the parts, for dings, wear points, and always replace the worn parts with NEW ones. Every passage gets a good spray of PB Blaster, then I run a wire through every passage to bust up the debrie, and hard deposits. Then an air blow, with a rubber tipped nozzel, through those passages. 80-90 lbs. of air......(don't get wimpy with the air.)!!!
I usually replace the throttle rod and seal, with New, out of the carb. kit, and I NEVER use the gaskets more than once. Used gaskets will not conform correctly after use, and usually suck air into the matings.

You already have great info, from all the other posters/replies, so I won't
re-tell all that they have already said. Justtake the carb. apart and do it all over, in a methodical, slow, pace. Then report back.

What ever ya do about buying a NEW carb........DO NOT BUY one of those black M/S replacements......Most of those are porely cast, and JMHO,...
peices of junk!!!
Help is here, if ya need it....all ya gotta do is ask!!!!!

Gary [/i:2f4fac6e0c][/b:2f4fac6e0c]
BTW: From start to finish, usually takes me about 16 hrs of work, counting testing and settings. :shock:

 

[Dell (WA)]

Dave.......first off, carb drawing LIE!!! You've been given excellent advice, but remember, the side-pointing idlemix is BASSACKWARDS; out fer lean, IN fer ENRICH. Set yer down-pointing mainjet to 2-turns and LEAVITT!!!! My eazy starting 6-volt 52-8N idlemix last time was 1/4-turn and idles at 435rpm on new proofmeter. It can be done ......Dell

 

[GB in MT.]

[b:a499943ca8][i:a499943ca8]

Morning Dell;
Hows yer stump???
NOT yer short one......The long one!!!!!!!!! :lol: :lol: [/i:a499943ca8][/b:a499943ca8]

 

[Dell (WA)]

Gary......notta much pain or much limping either. maybe that rat poison is working? ......Dell

 

[GB in MT.]

(quoted from post at 10:16:24 09/15/09) Gary......notta much pain or much limping either. maybe that rat poison is working? ......Dell

b:8011de08ff][i:8011de08ff]

Mebby so!!!!!!

[/i:8011de08ff][/b:8011de08ff]

 

[Dave H (MI)]

Hey Gary, thanks to you and the rest for the great info! I hope I can get this thing to work without going to a new carb. My gut feeling is that the idle needle is fine and the many cleanings have been done properly (but will do it again). I think the problem is that I have probably accidentally sabotaged the operation of the idle adjustment system by not assembling the carb properly. I have some memory of not fully understanding how the packing for the two shafts was to be installed. From your knowledge, is it likely that a poor seal at one of these shafts would cause me to get no response from the idle needle adjustment? I mean NO response, nada. I AM able to get a nice slow idle, but I do so using ONLY the screw on the throttle shaft. I am going to take the carb apart again later and review it with the info provided by you and the others. Don't know if I can buy just the packing...hate to replace a brand new carb kit for a couple gaskets. Let me know what you think. Thanks!

 

[GB in MT.]

[b:65eadde17e][i:65eadde17e]
Yes Dave;
If there is any air leaking into the carb., anywhere, It will/can mess up the Idle air adjustment.
I really think that yer prob. IS anair leak into the carb. somewhere. IE:
The rubber seal at the throttle rod....The big gasket where the two halves meet.....Possibly the gasket at the carb. to manifold.....somewhere the carb.is sucking air and messing up the Air to fuel mixture.
Like I said.....Hard to explain....Makes me wish I was there to help find it!!!!!!
Just take your time and if ya get frustrated.....Quit for awhile and go back to it later!!!!!!!!!!!!!!
Let us know how it goes....I'll be pullin' fer ya!!!!!!!!!!! :lol: :lol: :lol:

Gary [/i:65eadde17e][/b:65eadde17e]

 

[r geiger(oR)]

Might try a unlit propane torch around the areas that GB mentioned with the engine running and listen for the engine to change RPM or sound.

 

[Swift III]

Not to hijack the post but....I LOVE this board!
I am having the same problem with my carb, soaked her 24 hours blew out with 90psi, cleaned all the little holes took my time then bam idle wont adjust. :?

Before I can even post my problem here is the answer!
Now to check my gaskets for leaks, Thanks ya'll are amazing!

 

[JMOR]

(quoted from post at 23:11:17 09/15/09) Not to hijack the post but....I LOVE this board!
I am having the same problem with my carb, soaked her 24 hours blew out with 90psi, cleaned all the little holes took my time then bam idle wont adjust. :?

Before I can even post my problem here is the answer!
Now to check my gaskets for leaks, Thanks ya'll are amazing!

A leaky gasket will in fact eat your lunch! BTDT....unhappily!