TO-35 possible ignition pronblem

Hey guys. I've owned my 1955 TO-35 for 6 years now. It has always been a good tractor. Every problem I've ever had has been ignition related. Right now I'm trying to narrow down one gremlin that has always affected it.

Heres the deal. Mostly my tractor is used for bush hogging, 1-3 hours at a time. For the first hour or so it runs great. After this, it starts missing and losing power. It does this even with new plugs in it. Disengage the PTO and the problem disappears or at least diminishes to where I don't notice it. The last time I used it, there was a single backfire after I stopped the engine.

The tractor has a Z134 engine with Delco distributor. The plugs are Autolite 388 and I replaced them right before I used it last. The coil, condenser, and points were replaced about 50 hours ago. The cap, rotor, and wires are about 3 years old and free of corrosion or other damage. I set the ignition timing when I replaced the points and condenser. The carburetor mixture screw is set 1-1/8 turns out, which it seems to prefer.

I'm thinking maybe the Autolite 388 plugs are not ideal for this application. According to the Autolite website the 388 is a resistor plug and the hottest they make in this size. One range colder is the 3116, a "power tip" non-resistor plug. Colder still is the 386 resistor plug. I'm thinking that the 388 may be too hot a plug for this application. It runs well for awhile but eventually the hot plug starts misfiring under the load of bush hogging. The hot plug could have caused the backfire when I shut it down last, mabe it "cooked off" the incoming fuel/air to the cylinder.

So, any suggestions here? What plugs do you prefer in your TO-35? Does resistor/non-resistor make any difference in this application? Thanks!

Lance

My 202 (same engine) was doing something similar and it turned out to be a fuel delivery problem. There was rust/paint floating around in the tank and plugging the fuel outlet every so often.
Just for curiosity when it starts doing that, pull out the choke just a little bit and see if that improves things.
If not, I have heard of new coils being bad and doing things like that too.

Take a look at your plugs after it starts "misbehaving". If they look exceptionally clean they may be too hot AND/OR your mixture may be a tad lean for running under a heavy load. These engines seem to prefer the 3116 non resistor plug so the higher heat range 388 maybe marginally too hot. Check the timing with a timing light and make sure the advance is operating at the right point when you are at mowing rpm. Finally check the distributor for bushing/shaft wear. You might be seeing the begining of excessive wear.

Trying making one change at a time and then checking it out under load so you can isolate the problem. I have a feeling it will be a subtle combination of plugs and f/a mixture setting with maybe some timing change but that"s intuitive on my part. Let us know what you find.

Thanks. I am planning to install the Pertronix ignition system sold here at some point. Would the conversion require a different type of plug?

I like the 3116 plugs best in my old TO-35

I installed an inline fuel filter on my tractor, was the best thing i ever did for the old tractor.

normally if its a coil problem it will get hot long before a hour and short out.

I got a heavier duty coil for my 1957 model, however it has 12 volts.

check you gas cap, is it still vented, when tractor starts missing etc: open the gas tank cap and see if you hear a rush of air into tank.

No it would not require a different type of plug
A word of caution on the Pertronix system. i was a propoenent of this electonic ignition system until I had some reliability problems with it. The first unit I bought went 5 years and then the module failed. I bought a new module ($50 + shpg) and the new monule lasted about 3 months before it failed. Peretronix replaced that module under warranty but by that time I put the points back in and never installed the 3rd module. I have had EI on many cars and had trouble free operation on them. The Pertronix unit goes for about $100 +/- and in a tractor should be a lifetimme device. I was very disappointed in the first failure and concluded that it was a one off type failure, but the second failure after three months of use really put me off. I think that Pertronix may have fallen into the "outsource trap" and lost quality control on their product. I"m not willing to use something that I bought for it"s supposed reliability only to find out it"s not reliable.
Other people may have had betterluck with them then i have. I believe Bob in Oz has had them for a long time without trouble. He may have a pre outsource model. All i can say is I"m disappointed in the reliability of the unit.
I just wanted you to know that before you buy one.

Thanks. The gas cap is well vented and as far as I can tell there is no crap in the tank. Apparently Massey Ferguson makes a factory conversion unit, or at least one time they did. Maybe that would be a better way to go?

What coil are you using? Is it a 12v system with a 3.2 ohm primary resistance? Or do you have a 6 v system with 1.6 ohm primary reisitance. You can use the 1.6 ohm coil IF YOU USE A RESISTOR IN SERIES WITH IT to limit the coil current to ~ 4 amps max.

Check that the intake nuts haven't become loose. I too put an inline filter but i took off the bowl under the tank and installed a ball valve.

Jerry, the coil is an actual 12v coil with no resistor required. I got it at
Advance Auto Parts, I don't recall the part number right now. It states "12 VOLTS RESISTOR NOT REQUIRED" or something similar on it. In your opinion, is there any real advantage to the various "hot" coils on the market? I always thought that a hot coil was a moot point on low compression/low RPM engines such as these. Can these coils improve the performance of stock points or aftermarket electronic ignitions?

I see that various companies offer electronic ignition kits with corresponding OEM part numbers, including Tisco among others. These tend to be somewhat more expensive than the Pertronix units. Might these be a better choice or are they likely to be substandard outsourced rubbish also?

2tractors, thanks, I will check the manifold nuts.

the only thing that these "super coils" can do is allow you to open up the spark plug gap or allow you plugs to operate for a longer time period as the gap enlarges. You will not get any more power from your tractor engine over what a well adjusted Kettering ignition system will provide. I agree that for a 2200 rpm low compression ratio engine, I see no advantage to them. As far as other EI systems, I"m not familiar enough with any of them to recommend anything. For me, lomgevity and relianbility of the unit are what"s important.
As I said I am disappointed in Pertronix" reliability even though they are good about supporting their warranty. I may as well replace points every few years if I"m going to have to replace Pertronix modules just as often or sooner!

If I were you I"d check out your distributor and if the shaft and bushing are worn, have the shaft turned and a replacemnet bushing reamed and then have the advance checked and recurved if necessary. That"s a better investment of $100, in my opinion.