[huckster]

Hello all

My JD 420 is not running well. It idles very well but at high idle and under load it spits and sputters with some backfiring. With the air cleaner off I can see the gas dribbling out of the brass tube that sticks out into the throat of the venturi. What is this tube and what is wrong? The top of the carb looks very clean as well as the jet that can be removed from the top. I have not taken the main jet out because it's hard to get at. It doesn't seem like its clogged but I thought the gas should be spraying into the venturi rather than dribbling. Any thoughts?

 

[knottyrope]

what is your float level set to?

you could also have a worn float seat letting fuel in as well

 

[huckster]

If I pull the top of the carb off after it has been running, the bowl is probably 3/4 full of gas. The top of the floats are about even with gasket surface, maybe a bit under. It runs ok at first but more and more gas can be seen pouring down the venturi as it runs for a bit.

The float tip does look a bit worn, I think I'll try a carb kit.

Where should the float be set?

 

[knottyrope]

has a instructions on how to set it

http://www.wfmachines.com/discus/messages/335/277289.html

 

[huckster]

I broke down and bought a new carburetor hoping that it would solve this engine hunting issue, but it did not. So I guess I can rule out a fuel issue. My next guess is the ignition. I noticed my breaker points have no gasket underneath against the engine block. Is this a problem? Also, when I set the breaker point gap to the .016, the adjustment is maxed out and .016 is barely attainable. The points do not line up completely square either. I have disconnected the governor and held the throttle open but the engine still hunts around. Engine idles great, but as soon as I throttle up, it starts missing or hunting around. Any suggestion? I need the tractor for snow removal soon. Oh, I rebuild the engine a few months ago and this problem started soon thereafter. Spark plugs are new and set properly. Plenty of fuel delivery too. What am I missing?

 

[chuckv]

Michael,

Low speed hunting/surging is often a fuel issue or an air leak in the manifold (and far more rarely the throttle shaft bushings...)

High speed hunting is more likely a mechanical linkage issue with the governor setting -- but if you held the throttle position constant and still had the hunting then it almost has to be a fuel mixture issue in some way. Are you sure you are getting enough fuel delivered via the fuel pump? Was that pump replaced when you rebuilt the engine? Did you replace the impulse hose on the back side of the pump that connects to the crankcase and provides the pressure pulses that drive the fuel pump diaphragm? Those hoses can leak after decades of aging and cause poor fuel delivery at higher usage rates under load.

The ignition cannot cause the types of hunting issues you describe...

Chuck

 

[chuckv]

Michael,

One more thing to try which may help determine if the surging is related to too rich or too lean a mix varying with time... Does pulling on some choke when the symptom is occurring help smooth things out or make it worse? If it helps, that also points to insufficient fuel delivery at higher usage rates of under load or higher engine speeds... If it makes it worse, then maybe the float valve is not sealing fully under engine vibration, or the fuel pressure is too high -- do you still have the mechanical pump that was originally on the engine or are you using an electric pump now?

Chuck

 

[huckster]

Chuck,

I just deleted my response. Again, the carb is brand new so I don't think its a fuel issue. The mechanical pump pushes a lot of fuel. The impulse hose was in good shape so I kept it. Choking makes the condition worse. Engine idles great but hunts at high speed.

I looked at the points today and sanded them down a bit...low and behold the engine actually ran pretty good..I was able to mow the lawn! Looks like the points were the issue. How does this make sense? Where is the best place to get new points and condenser? What cause oil to build up in the air cleaner?

 

[chuckv]

Michael,

Excessive oil in the air cleaner is a sign of a poorly working breather reed valve or a bad seal on the o-ring on the dipstick.

Your choke test indicated that the mix is a bit rich, and a weak spark may contribute to missing at higher speeds under such a rich mix -- particularly if the condenser is starting to fail. When you rebuilt the engine did you renew BOTH the points and the condenser?

A loose fitting O-ring on the dipstick can also make the fuel pump work poorly at speed but nearly normally at low idle, since that pump is powered by crankcase pressure pulses.

OnanParts.com has quality ignition parts. Do not try to get by with imported "equivalents"...

Chuck

 

[huckster]

I did not renew the condenser and points during the rebuild. I thought the PO had recently changed them, but then again, he had the points set incorrectly and was unaware a head gasket was blown. The carb on this model has no high speed mixture adjustment, so the mixture should be correct in theory. I think you're right about the "weak spark"

I checked and cleaned the reed valve during assembly and if I recall it's only a thin piece of metal and a spring. What would cause it to not work properly? Thanks for the tip on the o-ring on the oil dipstick...I don't think I used that part of the gasket kit. I will order a tune up kit from Onanparts.com

I guess am going to have a perfectly good carburetor for sale since that was not the issue.

 

[huckster]

Can a B48G be upgraded to electronic ignition? And if so, is it worth it?

 

[gzec]

Have the fuel lines been cleaned or replace back to the tank. Has the fuel pump and filter been changed. It usually takes a couple of tries to get the points set right. If you can't adjust the points get new ones along with a condenser.

 

[huckster]

Glenn,

I did not replace or clean the fuel lines back to the tank. I never thought of doing so. Going to get new points but I don't think that is all that's going on. The other day while mowing the tractor just died and when I popped the hood the fuel filter was empty. I'm suspecting there may be a fuel delivery problem somewhere.

 

[gzec]

If the fuel lines are 30 yrs old,the pick ups and fuel pumps need some attention. Replace the lines and pickups and clean out the pump.

 

[Hammerdown-7]

Hello Michael
Electronic Ignition is Nice but it has issues as well when it Get's Old. It id far easier to Place one of David Kirk's Modules on your Tractor. I would suggested that you Buy a new set of Point's before Installing the Point's saver Modual. Set them at 0.019" and Place the David Kirk Modual on your firewall like I did. It is simple to wire in and Kirk says that you will get Thousands of Hour's out of the Point's. To me, it is a Lot easier to Place the "Point's saver Modual" than it is to work on or replace the Onan electronic Ignition. The Point's saver modual is Cheap being $32.00 shipped to your door and they have a Warranty on them. Here is a Link to Kirk's web page where they have this Moduel, I have had Mine since 2012 and it has not missed a Beat so Far. I hope that this help's. Regards, Kurt

http://www.kirkengines.com/index.php#PositiveGroundPointSaver

 

[boomers_influence]

kurt
why are you saying .019 for the point gap?
i believe it to be .016.
thank you boomer

 

[huckster]

Here's an update to my ill running 420. After chasing a fuel issue around in circles, I bought a new set of points and condenser and the tractor runs great now! I cleared 12" of wet snow the other day with no issues at all. The fuel lines in the back look ok so I left them alone. The tractor idled fine before but balked when under load. All she needed was some more spark. Thanks for all your help!

 

[chuckv]

Michael,

Glad to hear that you got it running as it should.

Thanks for getting back to this thread with the solution that worked for you, as it may help other members with similar symptoms reading this when it is an archived thread.

Chuck