Anyone seen this happen before???

Just got home from working on an older Ford tractor for a customer. From what I can tell from the serial number, and grill crest it's a 900 series from '55, but the 801 logo on the sides of the hood, the model of the Marvel carb, etc match up with the years given for the 801's built in '58. Either way the engine is a 172 CUIN so that shouldn't be an issue. The problem is this, when you shut the key switch off the engine starts to diesel and continues to run at a rough lope. It doesn't take much to stall it out and make it stop, but that's not the point.

The customer couldn't keep it running without alot of choke use. Since it seemed to be starving for gas I pulled the carb and checked it out. Sure enough there was trash built up in the bottom of the bowl as well as in the hole leading from the bottom of the bowl to the main needle. beyond that I found nothing wrong with the carb but a strange color inside the bowl. By steange color I mean it was Green. Has anyone else out there seen the inside of a carb turn green??? When I pulled the bowl the inside of the carb was a bright blueish green to a full green. It looked to me like the new crap in the gas might have been reacting with the brass parts in the carb and causing the color but I'm not sure. Like I said, I've never seen this in any of the countless carbs I've pulled over the years. Anybody got any ideas on the cause of the color?????

That said I made a new bowl gasket using the old one as a guide, rebuilt the carb, and got the thing running. From there I set the idle speed around 450 per the book, and the set the timing at 4 degrees, also per the manual. With these things done the old girl would run 'like a scaulded ape' and the customer was happy with the way it ran. The problem didn't occur until we went to shut it down after a few minutes of test riding. Again key switch off, definately no spark ( I checked), but the engine still wanted to run.

I know alot of the newer carbs, of all brands, used an anti diesel valve in the carb to provide a positive stop for the fuel flow through the main jet when the key was turned off but this one does not have that. So, basically it's key on, engine runs great, key off, and the engine continues to run and therefore suck fuel through the carb, for no apprarant reason, until you choke it down.

Anybody seen one diesel like this when shut down and any ideas wat could be causing it??? Any suggestions or experiences with similar problems will be greatly appreciated. Wayne

Yup, seen it, just in the past fw months.....problem is that the still turning engine is still sucking gas/air mix and the combustion chamber is hot enough to make it fire. I'd start checking the cooling system. On the one I worked on, IH M, there was enough crud built up inside the engine that although it wasn't over heating the head was still a little on the hot side. A good flush fixed it.

Rick

Over rich carb running, and not working the tractor has got it carbonded up. Carbon has built up on the pistons and valves, the timeing may be a little slow too. So when you run it hard the carbon gets red hot, and it diesels when you kill the spark. Had an 1850 oliver doing the same thing 2 weeks ago when he put the big round baler on it. Got it to normal temp. filled a quart spray bottle with water, set it at half throttle, and sprayed the quart of water into the carb opening. Let it run for a few minutes after that, and when the spark died, it did too.

i've seen carbon coat edges of valves and act like glow plugs...since engine has been run alot lately with choke this could be the problem...i've used a spray bottle of water thru carb throat to decarbonize combustion chamber...idle it up to about 2000 rpm and spray a fine mist in for 45 seconds to a minute.

Too hot of a plug will cause that.

I recall this happening on cars and light trucks in the early "70"s when the idle timing was retarded and the carbs leaned out for emmission control. The fix was an idle speed solenoid that shut the throttle plate completely when the ignition was switched off.

I would check the timing to make sure it is not retarted at idle and that the idle and main jets are the correct size and then look for air leaks that allow air to bypass the carb metering section.

Yep , i have seen the GREEN in the last two i have rebuilt . Now let me tell you that it is tough to get out of there . Chem dip will not touch it caustic soda i think makes it grow more but good old fashioned clorox did the trick I fought with the first one for over a week tryen to get it cleaned out. as for the dieseling yep see that to on gassers . Ya set them to factory spec.'s and the still diesel. (10 make sure that the spark plug is the correct one for that tractor and not some HOT oil burning plug. (2) you are going to think i am nuts here but stop using 87 octane gas and more up in octane try a tank of 89 in that one . The gas of today burns alot hotter then the old gas did and back then the octane rating was higher . The old gas burner big truck back then ran high test . My old 56 Ford rag top would not run on regular with the 292 thunder bird special engine . (3) check the engine running temp also.

I have seen that green in a few.

I have had several of mine diesel when shut off.
I "fixed" them by setting the idle really low so as to cut off the throttle plate. I just adjust the throttle lever to where I want it when I idle them.

The green stuff (verdigris) comes from water left in the carb. Water could be from condensation, or from ethanol in the gas. (The ethanol in regular gas and E85 will always have a bit of water, and depending on how the fuel is stored it could pick up a lot of water.)

There are a lot of things that can cause dieseling. Make sure the idle mixture screw is working (which means the idle circuit is OK). It may be that the idle stop has to be screwed way in to make up for a plugged idle circuit.

Make sure all four cylinders are hitting by pulling the plug wires one at a time. These engines run very smooth, and you can have one or even two missing cylinders and it will sound like it's running fine.

If everything seems to check out, it may have carbon deposits in the combusion chambers. I've had some success with using snake oil gas treatments that supposedly remove carbon deposits. I'm not sure if they really work or if it's in my head, though.

Run on after turning off the ignition is very common if the idle is set too high, the engine is shut off without returning the throttle to idle OR if the throttle shaft bore is worn enough to allow the engine to draw air around the throttle plate (very common).

I have never seen an engine idling at 450 RPM run on upon shutdown.

Dean

Reading this I was going to suggest Carbon deposits like Mark below. Try Seafoam. Dean knows these engines really well so I would follow-up his suggestion for worn throttle as well since it sounds reasonable.

Good Luck,

Kirk

Mark where did you get the infromation about ethanol containing water. That is a myth started by someone that knows no better.

If you have water in your tank the ethanol will absorb the water and take it out of the tank as it burns but it did not come in the ethanol unless your supplier has a tank problem.

I have said this many times on here I know but we have been burning ethanol here in Iowa for 38 years with no problems once the ethanol cleaned all the old gunk out of the tanks that was there before ethanol.

Gary

why not just put a new oxygen sensor in it <eye roll>

Just wanted to say thanks for the replies. After posting the question I got to thinking about the whole situation, and talked to dad about what happened too. Given what I saw with the idle and timing both being so far off,etc, etc, and the way it was running immediately after I put the carb back on, but before I set the timing and idle speed, I've pretty much come to the conclusion that it as to be carbon deposits heating up and keeping it running. That's really the only thing that makes sense as regardless of wether the throttle shaft was stuck, it had an air leak, etc, etc, it should still shut down when the key is turned off. Not because the fuel or air flows stop, because they actually don't until the engine completely stops turning. Think about it this way. You can put the engine at wide open throttle and hit the key and it will die because there is no spark/heat to ignite the mixture. With a glowing ember of carbon in one, two, or in this case what appears to be three cylinders, the mix doesn't need a spark to make enough heat to ignite it. Give that it will self perpetuate the problem because each explosion will keep the ember hot which causes the next explosion...and on and on.... In that case it's like a runnaway Detroit and the only way to shut it down is to remove all the fuel or completely block off the intake air.

I've already suggested the use of some Seafoam to the guy but I'll give him a call tomorrow and suggest the water mist idea. I've heard it works so why not. Anything is better than having to choke it down every time you want to shut it off.

Again thanks for the replies. Wayne

Gary,

As you point out, alcohol has an affinity for water. In fact it's not possible to have 100 percent alcohol in normal conditions, because it will absorb water from the atmosphere to bring it down to about 98 percent. (Which is why "pure" grain alcohol is "196 proof".)

If you have a good fuel supplier, water in fuel should not be an issue. But suppliers can and will add water to fuel. It is not that uncommon for someone to gas up their car at a discount filling station and have it quit down the road with a tank full of water. The difference with E10 or E85 fuels is you can have a lot more water in the fuel before it separates out.

WE have been spoiled with the reliability and drivability of fuel injected, electronic ignition gassers since the mid 1980's. We have forgotten how bad the good old days were.

Our 861 did it from day one, brand new. I've driven and worked on numerous others of these that had the same problem. The thing that has worked for me has been: richening the IDLE mixture (more fuel on whatever's glowing, cools/reduces the glow, by evaporation) and, if necessary, letting the engine cool down for a bit before shut down.