Fouled Plugs

[Bob Grieb]

I just returned from the Tulare, California tractor show. I took my Cub and it started and ran well until the last day. On the last day it would not start even when towed. When I got home I charged the battery and still it would not start. I then remeved and cleaned the plugs. They had a thin black deposit on them but I didn't consider them that bad. When I replaced the cleaned plugs the engine started and continues to start.

My question is -- Is the Cub engine that sensitive to starting with slightly coated plugs or is there another issue I need to take a look at ??

Thanks

Bob

[Gary Dotson]

That depends, Bob. If the black deposit is dry & sooty looking, it shouldn't be too sensitive to it, but if it's wet & black it will short a plug very quickly. Either way, it's indicating rich fuel mixture, or plugs that are too cold. You might want to check, to be sure your spark, to the plugs, is good & strong. Which plugs are you using? Unless you're working the tractor hard, you should be using the hotter plugs.

[Bob Grieb]

Thanks Gary -

The deposit was very black but not wet. I will check the heat range of the plugs today. Is there an adjustment to lean the carburator? It seems to me that it is pretty much a non adjustable setting. I am not an expert on the carb but I did rebuild it with an IH Kit.

I would appreciate input for adjusting the carb

Thanks

Bob

[Bigdog]

Bob - you can check the bore of the main jet. there are different sizes. (CRS prohibits me from remembering how many but I think about 4 different ones)

[Bob Grieb]

Thanks Big Dog

Where do I purchase different size jets? BTW at times the engine does emit a dark exhaust. It sounds like a rich mixture may be the culprit. I did not know the jets were replaceable.

Thanks

Bob

[Ron Luebke]

tm has 2 jets i believe. i changed my 53 from .034 to a .032 and it helped alot, not burning rich any longer

[Bob Grieb]

I feel a little embarrassed that I did not know that the main metering jet came in different sizes. In any event I have an .034 Jet and I just placed an order with TM for an .032. I will let you know how if effects the fouling problem.

Thanks to all who helped me with my problem

Bob





]

[schmibm]

Seems like there is three sizes available. You can turn the carb adjust screw out a bit to see if that helps. It is the air bleed circuit not fuel, so yes back it out to lean it out. This mainly just effects the idle side, but may help on the off idle a bit. You might want to put a new coil on it. It may be getting weak and not allowing enough fire to go to the plugs. You may also want to replace your condenser.

[Bob Grieb]

Thanks schmibm

I will try the idle adjust scew and see if it helps. A large part of the time when the engine was running at the show it was in idle. There was a parade on Sunday and I must have idled for an hour. I have a 47 Cub with a mag and I replaced the condensor a little while back. When the plugs are cleaned I appear to have a great spark that will jump a gap of 1/4 inch or more.

Thanks for the input

Bob

[Don McCombs]

Bob,

This always generates a lot of debate, but... use a Champion D-21 or equivalent heat range plug.

[Bob Grieb]

Hi Don

Thaknks for the response. I have NGK AB6 installed. I am not sure if that is evuivalent or not. Do you have a cross reference?

Thanks
Bob

[Hengy]

I have used the NGK AB6 as well as the Champion D21... D21 just happens to be what I am running now. The AB-6's are a great plug and are the correct one from this manufacturer to go in the Cub... Just don't use the Autolite plugs that they would recommend to you at the auto parts store... they do NOT work well...

Mike in La Crosse, WI

[Don McCombs]

According to the NGK cross-reference chart, the D21 crosses to an AB2.

http://home.att.net/~ngkaz/wsb/html/view.cgi-home.html-.html

[Bob Grieb]

Thanks for the input Mike

Bob

[Hengy]

According to the NGK cross-reference chart, the D21 crosses to an AB2.

http://home.att.net/~ngkaz/wsb/html/view.cgi-home.html-.html

Very interesting, Don,

Though I didn't open up the spreadsheet because it was in Excel and I don't have that on this "puter", does it say what AB-6 cross references with? Both Donny and BigDog highly recommended AB-6s in my tractor, and I have had minimal problems with fouling since I got the timing corrected on Merlin(cub)...

Thanks!

Mike in La Crosse, WI