misfire under load

Sun Jun 02, 2013 8:00 pm

My 1960 Loboy starts easy and runs good most of the time. I have a new problem this season in that when the tractor gets hot it will sometimes misfire when I am cutting going up a slight grade under a load. If I turn and go back down the grade it cuts fine with plenty of power. Plugs (D-21), points, condenser, cap and rotor were installed new last season. I have had various problems over the years but this is the first time I have encountered this issue and it is weird in that it will not do it every time that I go up a grade. Thanks for any and all help. :)

Re: misfire under load

Sun Jun 02, 2013 8:57 pm

Ignition fault. Plugs or faulty coil.

Re: misfire under load

Sun Jun 02, 2013 8:59 pm

the first and most logical things are water in the fuel system either in sediment bowl or in carb that is getting sucked in when the nose is high. Second thing would be float level wrong. Least likely that drove me nuts last year on my loader was a bad condenser. just because it is new do not assume it is good. A coil starting to fail can also give the same symptoms. Learned that one the hard way too.

Re: misfire under load

Mon Jun 03, 2013 10:34 am

My first suspicion would be the plugs. I've used Champion plugs with limited success, my experience is they seem to go bad before their time. That said, any brand of spark plug will go bad over time and not fire well under load/compression and will run ok with little or no load. For 10 bucks or so it a good place to start.

Re: misfire under load

Mon Jun 03, 2013 11:05 am

the fact that it changes with angle of the tractor would point me toards the fuel system. before i spent any money I would clean the sedement filter make sure i had good flow out of the line where it goes into the carb. then clean the carb and make sure youre float is not binding and has no holes in it.

Re: misfire under load

Mon Jun 03, 2013 12:07 pm

If your losing one cylinder under load like that, it's likely to be ignition. I would first check the ignition wires for continuity. They should be a solid core, if they have been changed to carbon wires. They should measure 0 ohms. Change the spark plugs, and look for tiny cracks on the inside of the cap leading to ground.

Re: misfire under load

Wed Jun 05, 2013 8:42 pm

Thanks for all of your replies. I did clean sediment bowl and I had carb apart at start of season to clean and change bowl gasket. Of all of the plugs that I have tried, my loboy seems to like the D-21's the best, that being said, any suggestions of a better plug that I can try? Easy enough to check the wires and do points & condenser also. I too thought that the problem of the angle making the misfire happen could have been fuel delivery but ut does not really surge so much as it just loses power until the rpm drops so low that it bogs down and wants to stall.

Re: misfire under load

Thu Jun 06, 2013 7:39 am

I won't say they're better plugs but I've had real good luck with Autolite 3116 plugs. For me, they've run great for years without issue. However lots of things going bad and/or wearing out and other issues can affect how well a plug performs like oil consumption, plug wires, coil, points ...

Re: misfire under load

Thu Jun 06, 2013 6:49 pm

Thankfully, oil consumption is not an issue here, pulled engine apart winter before last and oil control rings seized on 2 cylinders. I did a hone job and put in new rings and cleaned everything that I could get to with the block still in the tractor. Went all last summer without having to add any oil at all. The wires I know are 3 or 4 years old, points & condenser were early last year but for all I know the coil could be original.

Re: misfire under load

Thu Jun 06, 2013 9:59 pm

bolt54 wrote:........ I have a new problem this season in that when the tractor gets hot it will sometimes misfire when I am cutting going up a slight grade under a load. If I turn and go back down the grade it cuts fine with plenty of power..............
Had a similar problem with one of my brother's Farmall H tractors. The only difference was that it did it every time and didn't have to be hot. Turned out to be the rub block riveted to the points. It is shaped like an L with the long side rivited to the points arm and the short leg rides on the square distributor shaft. The short leg was broken off and it was riding on the inside of the long side. How that thing ran at all I'll never understand. I know it's not exactly the same but it's also not hard to pop the distributor cover, rotor, and dust cap to have a look. I wish I had before I rebuilt the carb that didn't need it. :x

Re: misfire under load

Fri Jun 07, 2013 8:45 am

bolt54 wrote:Of all of the plugs that I have tried, my loboy seems to like the D-21's the best, that being said, any suggestions of a better plug that I can try?


Plugs, like oil or tranny fluid is a real personal subject. Everybody has their favourite brand. I have used Champion D-15, D-16 and D-21. I have used instead of the D-16's, Autolite 386s (3116) and NGK A-6's, all are good plugs, however I find the D-16 range and it's equals in other brands to be far too cold for my liking. I use the D-21's all year round. Ellie gets a fair amount of use but not the amount that would require a colder plug. I have also used the D-21 equivalents - Autolite 376 and NGK AB-2. I much prefer the Champions.

With that said, any good quality plug should perform well. The rest is personal preference.

Re: misfire under load

Sat Jun 08, 2013 8:38 am

I strongly suspect the plug wires since you have done everything else and it misfires under load. For you information I worked at a auto parts store once and needed plug wires for my cub. Having access to hundreds of wire sets, I took the cub wires with me and spent almost a week trying to match a automotive set for the cub. I found Geo Tracker 4 cylinder wires were the closest match. Not to long and close to the original size. Also since they are made for electronic ignition systems they have more than enough voltage that a cub needs and are moisture proof. I had them on for over four years without any problems.

update 6/15/13

Mon Jun 17, 2013 6:45 pm

Finally got to go see what is ailing my Loboy, went to start it Saturday morning to cut some grass and it cranked but would not start. Had plenty of fuel, no spark. Pulled the cap, full of moisture (rained a lot in Catskills the previous 2 weeks I guess) so I thought this would be easy...dry out the cap, clean up the contacts and away we go. Not so good there, still no spark. Made sure I had power going into coil, then just cause I had one, took the coil from my CJ2A and tried that. Still no spark so now I pulled the distributor to put in the new points and condenser that I knew that I had in the shed (because when you are a 90 minute round trip from the nearest store you always keep spare parts around). Spent far too much time looking for something that I could not find. Tried a used condenser and filed the points and put it back together. Had spark and it would run on starting fluid a bit. Noticed a tiny lock washer on top of the starter that I surmised must have come off when I had the wire off of the distributor so I decided to put that back before I started the tractor. Put the lock washer back in place and now no spark again. Pulled distributor and brought it home...condenser wire had come loose (probably when I was 'fixing' the lock washer issue) and may have been grounding on the base plate of the distributor. New parts on order, changing cap, rotor, points, condenser and plugs and starting from scratch next weekend, will bring meter and test wires also.

Re: misfire under load

Mon Jun 17, 2013 7:08 pm

Oldthings, I would suspect that the Geo plug wires are carbon core. The Cubs run better on solid copper.

Bob

Re: misfire under load

Tue Jun 18, 2013 9:02 am

I suspect that the fuel mixture is slightly lean. Could be a partially (slightly) blocked high speed jet. either a flake of rust or some gum. Try the Seafoam or Mechanic In A Bottle. They will help with the gum, but not rust flakes.