I put a Zenith carburetor on the 154 LoBoy this Spring in place of the IH original carburetor. The tractor runs fine when it is cold, but after it warms up it will start to miss. I can mow for probably an hour before the miss starts. If I pull the choke out about halfway the miss will go away and the tractor will run fine with the choke out. Because pulling the choke out fixes the miss I'm thinking it is fuel related instead of a spark issue. I'm wondering if I'm getting a partial vapor lock that is causing this issue. With the Zenith carb the fuel line does run a little closer to the engine compared to the IH carb. This did not happen prior to putting the Zenith carb on the tractor. Any ideas on the cause and how to fix it?
- Thread starter DRussell
- Start date
I would start by checking for a leak. When the tractor is missing take something like an unlit propane torch and go around the carb area making sure to go around the gasket and also around the manifold gasket. If there is a leak the tractor will suck in the propane and run better. Its also possible to have hole or crack in the manifold its self so look for that also. I had a similar skip in my 184 (just a newer version of what you have) but choke didn't make a difference. Mine needed the valve clearances adjusted. There also an adjustment from the carb to the governor and maybe the Zenith carb changed that adjustment. Have you got a manual - that will describe the adjustment.
I can try that to see if there is a leak around the gasket, but if there was a leak I would think it would miss when cold as well as warm. It does not miss when cold. By warm, I mean the engine is fully warmed up. The miss doesn't start until after mowing with it for an hour or so.
gene bender
Well-known Member
coil,condenser,plugs do a compression check fuel is not the problem because it runs fine for an hour so the problem is electrical
gene bender
Well-known Member
So what is going to make the fuel stop after it has ran just fine for an hour is there a magic sw someplace that slows down fuel after engine has ran for a long period
47fivewindow
Well-known Member
- Location
- Davidsonville Md.
My Cub did that, I turned out the wire from the switch to the coil was broken except for a few strands that would heat up and lower the voltage to the coil. Check + voltage when cold and hot. Points too tight can act like that too. Touch the coil when missing, you should be able to put your hand on it without burning your hand. HTH
Go out and run it till it starts to miss then trouble shoot simple as that.
#1 check that you have a good blue/white spark at the center wire of the cap and at all the plug wires that jump a 1/4 inch gap.
#2 pull the carb drain plug and make sure you have a steady flow of gas that will fill a pint jar in less then 3 minutes.
As for running better with choke that can be spark since a weal spark needs more fuel to be able to run.
#1 check that you have a good blue/white spark at the center wire of the cap and at all the plug wires that jump a 1/4 inch gap.
#2 pull the carb drain plug and make sure you have a steady flow of gas that will fill a pint jar in less then 3 minutes.
As for running better with choke that can be spark since a weal spark needs more fuel to be able to run.
47fivewindow
Well-known Member
- Location
- Davidsonville Md.
Yes, maybe the richer mixture is easier to ignite, but sometime it is the case.
Janicholson
Well-known Member
The manifold can warp as it heats and cause a leak after time. Charlie's idea is a good one. If no joy, and the misfire is one cylinder, Identify it by pulling wires one at a time. change the spark plugs from cylinder to cylinder. to see if it follows the plug. Jim
I ran the tractor last night for a couple of hours and it never started to miss. I was not mowing, it was just sitting and running. While it was running I felt the coil a couple of times. It was too warm to lay your hand on for more than a few seconds, but not hot enough to immediately burn my hand. Is this an indication of a problem with the coil? I'll try the other things you have suggested and report back.
47fivewindow
Well-known Member
- Location
- Davidsonville Md.
I think I would try a new coil.
A coil will get pretty warm and warm enough that one does not want to hold it for long. But it should not get so hot that if you spit on it that the spit steams away fast. Also when coil goes bad it will work for about and hour then start having a poor spark and in most cases soon after stop working till cool again. That is when you need to check for a good blue/white spark that jumps a 1/4 inch gap
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