420 crawler engine surging

hokster · Post by **hokster** » Mon Jan 27, 2014 10:53 am

looking for some advice. Rebuilt my carberator in 420 crawler and now i cant get engine to run smooth . it surges up and down. It is a little better with more throttle and worst at idle any suggestion out there would be helpful

Tigerhaze · Post by **Tigerhaze** » Mon Jan 27, 2014 12:19 pm

This sounds like an adjustment issue on the carb. I am assuming this is a Marvel-Schebler carb which is linked to the governor. I have some familiarity dealing with them on my 1952 Ford 8N tractor. It sounds like your governor (which is linked to the carb) is kicking in and out to compensate for the mal-adjusted carb, causing the surging. You should be able to watch at idle and see if the governor linkage is moving in and out with the carb when it does this.

If so there are usually three external screw settings that can be adjusted and if not done according to spec and in the proper order it will cause issues with surging. It is not an exact science on those adjustments but they need to be reasonably close to what is in the manual or you will have problems.I can't speak to the specific procedure as I am not sure of the exact M-S carb model that is on the JD crawlers, but it should be in your manual.

A mal-adjusted float in the carb could also potentially cause that issue, but I am assuming you adjusted that during reassembly.

hokster · Post by **hokster** » Mon Jan 27, 2014 1:02 pm

OK thanks it will smooth right out if I pull the choke out just slightly also really appreciate you help

1010c · Post by **1010c** » Mon Jan 27, 2014 2:24 pm

Also have you looked to see if their is exesive play on throttle or choke shaft. This can make them surge because there is extra air in the air to fuel ratio. Steiner sells replacment bushings for these.

Paul Buhler · Post by **Paul Buhler** » Mon Jan 27, 2014 2:28 pm

Send me an email, and I can send you a copy of the M/S carb manual as a .pdf.
Short term, try one turn out for the idle screw, and 1 1/2 for the load (if you have one) then tweak as needed. On my old, but rebuilt carb, I actually have the idle screw turned in completely to get a slow idle (air leak somewhere), but I've found that I had to spend some time finding the sweet spot with the load screw - too rich, ran rough (surged), too lean, no power or pickup under load.

Post by **Lavoy** » Mon Jan 27, 2014 5:39 pm

What all did you do when you rebuilt it?
Lavoy

hokster · Post by **hokster** » Mon Jan 27, 2014 8:18 pm

Lavoy I put the basic kit in. Clean and blew all ports out. Going to checkout throttle shaft for wear next. Adjusted float to proper height. Cleaned complete fuel system. If I pull choke very slightly it will smooth out. Any tips for me!

jtrichard · Post by **jtrichard** » Mon Jan 27, 2014 10:17 pm

IT is running lean ....clean main jet and galley again

DukeofDeere · Post by **DukeofDeere** » Mon Jan 27, 2014 10:34 pm

Main jet or nozzle needs to he removed and cleaned .
On the inlet of the carb is usually a screen which is often overlooked and loaded.
Often the sediment bowel is plugged as well as the out feed of the gas tank.
All options for starved for fuel.

Duke

Post by **Lavoy** » Mon Jan 27, 2014 10:41 pm

As has been mentioned, you need to pull all jets and the nozzle. Then soak in a good carb solvent, no just spray carb cleaner through. Once done soaking, rinse with water, blow out with air, then with the little tube doohickey on a can of carb cleaner, blow carefully through every passage on the carb, and observe very carefully if spray comes through. Inevitably, the ends up being one passage with crud in it.
Lavoy

DukeofDeere · Post by **DukeofDeere** » Tue Jan 28, 2014 4:01 am

Main jet or nozzle needs to he removed and cleaned .
On the inlet of the carb is usually a screen which is often overlooked and loaded.
Often the sediment bowel is plugged as well as the out feed of the gas tank.
All options for starved for fuel.

Duke

hokster · Post by **hokster** » Tue Jan 28, 2014 5:34 am

OK guys I will tear down and do a try this again taking much more care and detailed job. Thank you so much for your advice. Rest of tractor is complete and I guess I was hurrying a little to try this thing out.

hokster · Post by **hokster** » Tue Jan 28, 2014 5:51 am

Oh and I also installed a new inline fuel filter in the fuel line ( and correctly) would this be to much restriction?

DukeofDeere · Post by **DukeofDeere** » Tue Jan 28, 2014 7:20 am

In line filter is highly recommended.
These older machines often have junk in the tank which is good to keep out of the carb.
Also the gas now a days is not good for more than 6 weeks.

I have had fuel separation in as short of time as 30 days.

Duke

gregjo1948 · Post by **gregjo1948** » Wed Jan 29, 2014 5:38 am

Seems to me that, the rebuild kits come with 2 idle jet screws and possably the wrong one was installed. gregjo1948

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