WD continues to diesel after shut down

Anonymous-0

Well-known Member
Good evening. I just got done overhauling my WD with a 45 crank and 175 pistons, stock cam and zeinth carb, and converted to distributor igntion. It starts and runs beautifully and smooth as you could ever ask for. The only thing is, when I shut it off with the kill switch, it slows the rpms but continues to diesel for some time. I can even pull the coil wire off and it will continue to do this. Choking it will kill it immediately. Any ideas? Haven't ran into this before. Thanks in advance.
 
Dieseling is not an electrical issue. It is caused by hot spots in the combustion chamber that ignite the fuel/air mix without the benefit of a spark. Or perhaps a hot spark plug. Maybe try changing to a colder plug?
Choking shuts off the air. Or enriches the mix to the point that it can"t sustain operation.
 
What the others said is right on. One more point is that running on like that is telling you something that you should be paying attention to and that is you are running at, or darned close to detonation levels due to compression ratio and fuel quality.
If it diesels or runs on only after a hard load and coolant is hot then you could be OK but should be listening very carefully for detonation under load. BUT!! If it is doing it when not hot or no loads have been applied then you are being duly warned by the engine that you need to do something now, prior to ruining it due to detonation. Cooler plugs? Maybe. Hot spot in chamber that can be fixed? unlikely. Better fuel needed? Most likely the problem. The cost of upgrading compression ratios in old tractors running todays junk fuel is you need to run mid grade or high test gasoline.
 
Thank you for the responses. I have went to 91 octane fuel and that did seem to help but still dieseled some. The pistons are only supposed to be about 8.5:1 ratio, not extremely high. Right now I am running AutoLite 295 plugs, any recommendations for cooler ones? 303's possibly?
 
(quoted from post at 20:26:47 05/27/14) Good evening. I just got done overhauling my WD with a 45 crank and 175 pistons, stock cam and zeinth carb, and converted to distributor igntion. It starts and runs beautifully and smooth as you could ever ask for. The only thing is, when I shut it off with the kill switch, it slows the rpms but continues to diesel for some time. I can even pull the coil wire off and it will continue to do this. Choking it will kill it immediately. Any ideas? Haven't ran into this before. Thanks in advance.

From your post it sounds like this is the first time the engine was started after overhaul. Therefore, the problem occurred at the first shut down after a short running check out. Some cooling systems, especially if the thermostat seals tight can trap air until the thermostat opens and water actually flows. As a result the cylinder head is not filled with water and can have hot spots. In this case the problem should go away once the system is actually filled. To this end, I like to drill a small vent hole in the thermostat flange (some have them) to bypass water preventing this problem.

I am not an AC expert and do not know what compression results with a 45 crank and 175 pistons. You will need to use gasoline with an octane rating to account for any significant increase in compression. Also, if the bore was increased you should run a head gasket which accounts for that. If the gasket extends into the cylinder it can run hot resulting in problems.

Good luck
 
Hot spot from carbon build up was uncles problem- but since you put in new cran and pistons the head should have been cleaned. Try to use fuel shutoff drill instead of ignition off and see if that helps. WD45 crank was stroked compared to wd- 4.5 instead of 4 inch. What rods are you using? the old WD rods? WD45? Need to double check but rod length was a tad shorter on the later WD45? means the older rod and newer piston rated for 8.5 to one is actually pushed up higher in cylinder and compression is 9.5/10:1 or so and dieseling occurs. IHC with Firecrater or high altitude pistons got same problem sometimes- H and 300 rods had about thickness of bearing shell difference- AC WD/WD45/175 may have same situation. Valve edge may be "sharp", that can develope hot spot also. RN
 
Thank you again for the the info. To help clarify a few items... I reused the original WD rods, and the they are 175 dished/cupped alum. pistons. Bore is standard 4". I updated to the 4" head and the valves were ground and seated at the machine shop. RN you mentioned a fuel shutoff drill?? I assume you mean shutting the fuel off/running out of fuel? IF the compression is higher like 9.5 or 10:1 what octane rating would you recommend? Also I drilled a 1/8" hole in the thermostat flange to allow water to pass through during warm up. Thanks again.
 
(quoted from post at 06:08:53 05/28/14) Thank you for the responses. I have went to 91 octane fuel and that did seem to help but still dieseled some. The pistons are only supposed to be about 8.5:1 ratio, not extremely high. Right now I am running AutoLite 295 plugs, any recommendations for cooler ones? 303's possibly?

My 1994 Autolite catalog shows a 295 as a 18mm, 3/8" reach, standard tip and non-resistor. The 303 is three heat ranges cooler (resistor type) however there is a 292 (non-resistor)which is the coldest plug in the heat range. I would suggest going with the 292 just to remove the spark plug as a possible problem cause. Since you have raised the compression ratio you will likely want to run a colder plug as standard practice and the 303 may be the right plug after you get the problem sorted out.

As others have posted high idle speed can/will promote the run on problem. If you remember many cars in the 70's used a solenoid to set the idle speed. When the ignition was shut off the solenoid allowed the throttle butterfly valve to close off. I am not suggesting you need a throttle solenoid; only to say the idle setting is important.

91 octane fuel should be plenty good for 8.5:1 compression however two octane numbers can make a big difference. If 93 octane is available I would suggest trying it. If 93 octane no ethanol is available then adding 10% -15% of E-85 would kick it another 1 to 2 octane numbers. After that you will need to go with race gas or airplane fuel. Once you find a fuel that actually allows it to shut down without run on you will have an idea of how big or if you have a problem.

The real issue (to me) is what is the compression ratio. Yes the pistons may be 8.5:1 but with what deck height, head gasket thickness, chamber volume.....? Shutting off at idle is one thing but to develop full cylinder pressure at power and not detonate is the bigger concern. Detonation at full power will fail parts - run on at idle sounds nasty but does little damage.
 
Thank you again for the info. This gives me several things to try and will update with results. Just as an FYI, I have not put a tach on it yet for the exact idle speed, but my ears tell me 400-500 rpm.
 
10:1 compression engines used by pullers get premium with some aircraft fuel used a lot- 100 octane low lead from the airports or racing fuel from track suppliers. "Drill" = procedure meaning in this case put engine to idle, shut off fuel valve at fuel tank and let engine run out of gas- this used to be more common with old JDs and F20s.
 
You basically have a 175 engine in a WD. What plug does the 175 use? I'd try that for starters. No need for the high test gas, didn't even exist when the 175 came out new. Might want to play with the carb a bit to make sure she's set right for the displacement and compression you have.
AaronSEIA
 
Good evening. Thank you to all that contributed. I changed to 303 plugs and that did help considerably. Then adjusting the ignition timing took care of it completely. It shuts down just like it should when the switch is pushed. Thanks again.
 

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