Carb problems

[Montana Guy]

Sputtering and won't pull under a load. Surges some at an idle. Wants to run somewhat better with the choke on. Will sometimes just stall. It is suppose to have a new needle in it. I was told the linkage going into the carb may be sucking air. What else can i do to doctor this one up? One this machine runs smooth, i will have a nice outfit.

[Paul Buhler]

I'd recommend pulling it off, cleaning and rebuilding it. Usually not too difficult or expensive - be careful with the small and fragile looking parts - get a manual so you have some idea of what you're doing. If you send me an email, I can send you a Marvel-Schebler and Zenith parts and repair manual . Paul

[KenP]

deleted

[Montana Guy]

if the throttle shaft as it enters the carb is worn, then what?

[JD440ICD2006]

For worn shaft bushings, they may be availble at some of the carb rebuild places such as Robert's Carb. Not sure if Lavoy has these but go to him first, please.
I have used properly sized O-rings lubed with silicone grease and they seal it very well.
If you have not been through the carb, while you have it off, take it apart.
The above site has an exploded view of all parts that you can view or print out.
There are three jets that can be clogged. The main jet, idle jet, and the smallest one is the economizer jet. If possible, all of these need to be screwed out of the casting and cleaned.

[CELSESSER]

The throttle shaft is one of the parts you should get in just about any carb rebuild kit along with gaskets ,bushings,seals and a new needle valve and seat.
Have Paul send you the carb manual . When you take the carb off use some brake cleaner to clean the outside up so that you can find the tag riveted to the carb to know what carb you have so that you can order the right kit.
Use the diagram to carefully take it apart. Take pictures as you take it apart if you can. Don't force trying to remove the brass jets - and only use a good sharp screwdriver that just fits the slots - if you bugger them you are screwed. Soak it parts in cleaner, blow out with break cleaner and compressed air. Reassemble. Follow the manual to set your initial settings and install on the crawler. Follow the manual to do the fine setting and load setting.

Chuck

[JD440ICD2006]

Throttle shafts do come in most of the kits that I see, but the other problem can be the brass bushings. If they is worn, a new throttle shaft only gets you part of the way to a better seal.
I would recommend passing on the TSC kits. The gaskets are trash IMHO.
You need a good quality soft gasket so that it will seal well.
If you have the time, money, and resources to flat mill all of the mating surfaces, then the TSC gasket would be OK.

[Montana Guy]

All such great useful info guys. I hope that by cleaning things up it will solvea bunch. But i do know that after 40 years of wear, that shaft entering thru the carb HAS to be creating an air leak. I always seem leary of "kits", but if it would solve things, i would be on it. I will get an exact model number and go from there. Tomarrow i will pull it off. Lavoy might need to set me up with the parts. Bolting on a new cheap carb is tempting too ! we'll see how stuff goes......

[Tigerhaze]

Basic question (so don't be offended), but have you gone through all the adjustment steps for the three jet screws?

I have the M-S carb on my gas 8N tractor and had a heck of a time with surging, rough idling, and stalling. Part of the issue was also wear, so got new parts but still had some of the same problems, especially under load.

I found that the idle speed screw adjustment (screw on back side near throttle lever) was not the problem and is easy to set if you have a tach. Finally found that adjustments on the main screw (large top screw) and idle mixture screw (small screw) as well as idle speed screw are all related and that even small changes in adjustment can make a huge difference in performance. Go through the book adjustments (in the order listed) and see if it makes a difference. if after going through them you still have issues with stalling, make small adjustments on the main jet. It is important on the final adjustments to actually be under load (pulling implements, etc) and not simply at full throttle. it really is an iterative process to get it running right.

If you need more information on adjustments, there is a lot of information on the Y-T website under the wheel tractor discussions. If you have a Zenith, I have heard that most people hate them and try to switch to the M-S. This link is for adjustments on Ford tractor (M-S carb), but should be somewhat similar process if you have a M-S. it will give you at least an appreciation of the criticalness of the settings.

http://home.earthlink.net/~8ntractor/carburetor.html

Good luck!

[JD440ICD2006]

The basic operation of a carb should be reviewed and understood. They all work basically the same, even though they are shaped different and designed for various applications. Once you know how they work from idle, load, and fast speed, then you know where to look for the issues that you are having.
Typically, there are various circuits or channels that handle the various butter fly settings ("butter fly" is the brass disk that opens and closes for speed control.)
First, make sure that the carb you have is correct for the tractor. I have seen cases where they were not. That brass tag mentioned above is your key on a Marvel. Many of them look the same, but are not designed for the tractor that they are bolted on.
Have a super clean tank, gas line, gas bowl, etc. There can be trash in the tnak that restrics the gas flow. There is a screen in the top of the gas bowl/cut off that can cause many issues that seem to be "adjustment" issues. There also should be a screen built in to the elbow connection where the gas line enters the carb. Sometimes there are restrictions here.
When you need choke to run a properly set warmed up engine, it is lean. That can be air leaks and/or fuel restrictions.
The float must not leak and must be set at the proper level. If it is set too low, it will produce a fuel starvation/lean situation. On the other hand, if it is set too high, it will allow fuel to overflow in to the crankcase. Some engines have been ruined with gasoline diluted oil.
Unrelated to the carb, but will cause similar issues, make certain the points, plugs and everything are set properly and functioning correctly.

[Gil]

If you are concerned that the carburetor is sucking air in around a shaft or fitting, you can spray a little carburetor cleaner or starting fluid around the suspected part. If there is a leak it will suck the fluid into the combustion chamber and the engine will speed up. Don't overdo it and also be sure your air cleaner hose is tight so the fluid doesn't sneak in there.

Before rebuilding the carburetor, or at least while you are waiting for the rebuild kit, do some of the things JD440ICD2006 mentioned. In this order, I would: 1) clean the screens and bowl of the gas separator/filter; 2) clean the screen, if there is one, where the gas line enters the carburetor body, 3) make sure that the air filter is unobstructed, 4) start the crawler and try adjusting the needles and see which ones have an impact (start with one full turn out on each if you don't have the proper specs - and vary in and out from there). If that was not enough, 5) replace both your plugs and points, and set them properly (later after things are running well, you can put the old ones back in if they were not the problem - you need a spare set around anyway). If that wasn't enough, 6) check the timing. By then your carburetor kit should have arrived and you can try that route.

If none of that works you can come back and ask about trouble shooting the coil, the centrifugal advance, and ignition wiring. Good luck.

[Montana Guy]

You guys are super ! I will follow the exact order of adjustment after i pull it off and clean it up a bit(and check screens and lines ect.) I bet it will snap right out of it with some attention. Why the mixed opinion on the carb "kits"? If that throttle linkage is included and a seal for it included(but not the brass orfice) won't that help, or is it beyond that if it is truely worn? No worries, tomarrow we dive in.........

[JD440ICD2006]

It truly depends on how worn the brass bushings are. Typically they get worn concentric due to pressing against one side all the time.
A new shaft that is included in many kit will close the gap compared to a worn shaft, but will not always seal it totally.
There is a difference in the quality of the gasket material in various kits.

[CELSESSER]

Also on the Marvel-Schebler TSX series there is a packing ring that helps seal the throttle shaft. In the kit I got from Lavoy it was a white loose fiber washer about 1/8th inch thick and a retainer. This is what seals up any clearance left between the new shaft and the old hole (at least for a while) When I took my carb apart there was no packing material at all-deteriorated and sucked in?? left out by the last wrench???

Chuck

[Lavoy]

The TSX carbs so not have bushings, they must have figured they were too small to have them as the DLTX carbs do have them. Most kits will come with a small felt washer to use as a seal. There was a cup type seal in them from the factory, they are still available, but not real cheap for what you get.
I personally have never had any carb regardless of wear draw enough air to affect running. Even if it did, you could correct it with the mixture setting.
The primary part of putting in a kit is in a THOROUGH cleaning of the carb and all the passages, air and fuel. While it may do it on occasion, if the carb is really plugged, simply spraying carb cleaner through it will likley not change anything.
A customer sent me a 440 carb once that had been kitted by someone else, and it still would not run. I took it apart, and whoever did it had never even removed the jets. I discovered this because I had to drill both of them out, and pick out the remaining pieces with a dental pick. After new jets and a thorough cleaning, it ran fine.
Lavoy