M18 Vapor locking

DieselDoctor · #1 05-28-2017, 10:33 PM

A little background first. M18 Kohler in my 1882 had always been undependable starting. It would always crank but 50% of the time it wouldn't fire. After doing some circuit tests I found a bad ignition switch ( mag grounded in run position). Replaced that and it seemed to start ok for about a half dozen times so I ran the tractor to mow 2 acres, and after parking in front of the garage to blow the deck off, it would not restart - no spark. Disconnected the plug at the engine (now mag is not grounded) and still no spark. I pulled the engine from the tractor and removed the cowls to find the typical mess of grease, dirt, lawn clippings and mouse nest, most of which was around the coil. I removed all the tin and degreased the engine, taking extra care to clean the cylinder cooling fins thoroughly. Installed new coil, reassembled tractor and it fired and ran perfectly. By now, it is time to mow again. I run at normal mowing rpm for about an hour and need fuel as the light is flickering. Swing over by the shed, shut off pto and idle down. While filling the tank, the engine idle speed drops and it dies. Note here - the tank had fuel, it didn't run out of gas. Crank and it will fire and die repeatedly. I pulled the air cleaner to add a splash of gas in the carb throat to see if it is a fuel issue and IT BOILS THE GAS BIG TIME!!! This thing is hot!! It fired the fuel I've added and dies again. Do this twice with same results. After leaving the hood open for a half hour and letting things cool down, it starts after cranking a few seconds to fill the float bowl. Runs as good as ever. Now the temp here today was 70 degrees and the entire cooling system just got degreased and cleaned, so why is it running so hot and vapor locking? Your thoughts ?

Jeff in Pa · #2 05-28-2017, 10:38 PM

Just a WAG but is it too lean? Can you richen the mixture and see if it improves?

Jeff

DieselDoctor · #3 05-28-2017, 10:48 PM

Good point Jeff. I had set the carb when I did new filters and an oil change about a month ago (spring service). With the engine at max rpm no load, I cranked the high speed mixture screw in until I got lean misfire, then out slowly until things smoothed out, and 1/4 turn further out. Does that sound about right?

J-Mech · #4 05-29-2017, 12:44 AM

No, screw it out until it goes rich, then in until it smooths out, then out about 1/4. You want it heavy on the rich side. It may end up being close, but I like to err on the heavy side.

DieselDoctor · #5 05-29-2017, 02:14 AM

Thanks Jon, I'll give it a try going rich and coming back. Question - has anyone ever tried installing an oil cooler in series with the remote filter on these M18's? I have a small one off a motorcycle that might help liberate some heat.

J-Mech · #6 05-29-2017, 04:28 AM

There are millions of these out running without an oil cooler. You don't "need" it. Would it run cooler? No doubt. Do you need to install one? No. If the cooling system is clean, and it's tuned correctly, it will run the right temp.

Mike McKown · #7 05-29-2017, 07:46 AM

Do you have number 17 in place?

https://polr.partstree.com/v1/iplima...O2k6MTAwMDt9fQ

Have you checked the shut off valve screens in the tank for blockage? Fuel lines? Next time it quits, pull the line off the fuel pump and drop it below the tank and see if gas runs out of the hose freely.

DieselDoctor · #8 05-29-2017, 10:46 AM

Mike - I should have added that the fuel tank has been cleaned recently, and the bungs, shut off valves, fuel lines and pump have all been replaced within the last six months. I don't believe supply to the pump is an issue because when this thing is cool, it runs great. I did pull the line off the filter when it was acting up and had a good stream of fuel. I'm pretty sure that it's vapor locking in the fuel pump. I do have the firewall seal, but it's a little chewed up in spots.

DieselDoctor · #9 05-29-2017, 11:00 AM

I realize I don't "need" an oil cooler, it should run as designed and I have to find what's wrong. I was just wondering if anyone had ever installed one. This engine was hot enough to curl the label on the NAPA oil filter. I'll add that it had plenty of power right up to needing to refuel and ran without any smoking, or odd engine noise. Kind of scary to think one can get this hot and you have no real clue how close you are to a meltdown/catastrophic failure.

Mike McKown · #10 05-29-2017, 01:37 PM

Quote:

Originally Posted by DieselDoctor

I did pull the line off the filter when it was acting up and had a good stream of fuel. I'm pretty sure that it's vapor locking in the fuel pump. I do have the firewall seal, but it's a little chewed up in spots.

I have had this same problem you have but the problem are confined to the ones that I have removed the heat shield between the engine and the dash. I've been told this will make the engine run hotter and I believe it.

On these tractors, I either pull one of the side covers off and leave open or I prop a beer can under the hood to let the hot air out. That allows them to continue to run. So, to answer your question, yes they can vapor lock.

Depending on the blend of gasoline in your area, you may or may not have this issue. Some gasoline vaporizes faster than others, depending on the blend in your area.

Yes, when I get around to it, all the heat shields I've removed in the last couple of years are going back on the tractors.