I LOVE MY MD, I JUST WISH IT WOULD START ON GAS!!

Hello again folks
STILL tinkering with my MD it use to start crappy on gas and run great on diesel, now it won't start on gas AT all, diesel isn't a problem though. here is what i have come up with

I have removed the intake, on the head, there is a big port for the diesel to get air, and a smaller port for the gas, when I turn the engine over, I can feel air suck from the diesel ports but NOTHING from the gas, no suck no blow no nothing, so from what I can gather this is why my plugs are dry?? because there nothing to suck up the fuel from the carb?? The decompression valves are working because the engine is twice as heavy to turn over on the diesel side, the motor would always switch to gas without a hitch once running on diesel, and when running on gas, the tractor runs smooth as a kitten. now it won't run on gas AT all


PLEASE HELP!!

Make sure the butterflies in intake are closing when switched to gas. Do you have spark from mag or distributor? There's a switch in front of manifold, grounds mag when in diesel and cuts power to coil with distributor. If not working or getting switched that could be a problem. If no leaks in manifold or carb mounting, butterflies work correct, fuel flow and carb correct, spark at correct time, starting valves opening correct in gas position and diesel flow shuts off in starting mode they will start.

Yes ALL of that is working I have the manifold OFF of the tractor, and when you turn the engine over there is aboslutely NO suction from the intake ports for the gas side, I think that is my problem, i as assume that there should be suction there, because how else would the gas get from the carb to the intake

Thanks Matt

That sounds like no intake manifold vacuum. Have you held your hand over the throat of the carburetor when cranking. Should have good suction on your hand, in fact you can choke the engine by doing that. No vacuum or poor compression is related to rings & valves unless there's something not switching back when from diesel to gas. Hal

Maybe the starting valves are stuck?

If you have the manifold off try pluging the big intake ports with something and then see if there's suction at small ports in starting mode, Should have then.

Did you have the spark plugs out when you checked intake vacume? You say the intake manifold is OFF the tractor. So you are holding your hand against the head ?
If your MD can be started on deisel without first warming on gas it's in good shape compression wise. Better then my Super WD6 anyway. Buy a repair manual if you don't already have one and look for the simple problems first.Years ago and more times than ounce I would pull my hair out instead of walking away on various machines only to have my dad come up and put more gas in it or something stupid like that and have it run

Hey Matt, I feel your pain, I spent ten months working on my W450D, it sure was worth it though when I beat it and she fired for me. Unfortunately it was short lived as it is now sitting with a spun bearing and has been since last October. I will get it beat again though, just like you will figure yours out. El Toro was a huge help for me as well as some of the other guys on the forum. My issue ended up being my carb it had just finally given up the ghost due to the previous owner letting it freeze up. Just be patient and listen to the experts they will get you through it.

El Toro, I installed the manifold back on the tractor, seems to be plenty of suction, when you close the choke you can here it sucking, took the carb apart, looks clean and in working order. checked the spark, seem nice and blue, but after lots of cranking, i pulled the plugs, and they are still dry as a bone, keep in mind that the tractor did run on gas before with alot of cranking, it was easier to start it on diesel with a bit of either, then switch it back to gas that way to warm up the motor, because it will switch to gas perfect from the diesel mode. but it won't switch to gas from diesel at all anymore. i am getting no smoke at all, when cranking on gas

frustrated yet hopeful

Matt

I just wish I could find one! I love the W450 for some reason. Saw one on propane at the 05 RPU and fell it love with that thing! I use it for my desktop at work, and here at home.

You have a fuel blockage somewhere between the gas tank and carburetor. Disconnect the gas line at the carb & check for a full stream of gas. Use a clean container to catch the gas. If there's a full stream of gas from the gas line remove the tube fitting and check for a clogged screen behind that fitting. Hal

Remove one of the sparkplug's and pour some gas into the plug hole then see if the engine will fire after replacing the plug. Hal

Hi, I resently purchased a SMD. It started hard and with a lot of black smoke, but it took a lot of cranking. I was new to the MD, so I first read and studied the shop manual. I decided to do everything I could first before taking anything apart. I found the Carb bowl had a lot of debree ,I then removed and cleaned Gas line and bowl. Removed screen at carb input, and it was full of debree. reinstalled and put measured amount of gum out in a full gas tank started and run it through till empty, repeated again. engine started better, but not smooth. Installed new points, dist. cap and wires, plugs looked near new. Engine would then start and run smooth after 6 to 8 turns and with little smoke. I pull choke out full for a couple of turns, push in and it starts a few turns later. Note: Always run on gas before shutting down, this cools the eng. and also burns out any remaining diesel. Don"t forget to throw the lever back to diesel after engine stops to cool starting valve seats. Brissco

Maybe you have already done this but start simple. In gas mode open drain on carb. Do you have good gas flow? When carb was off did the round plate on top with screw have a air gap? All pasages and jets clear? With the 2 piece choke shaft sometimes the inside shaft freezes up and it bends choke plate. Small passages for fuel air mixture end in big intake port above intake valve. If butterflies don"t close properly it will hurt the suction through small passages to carb. Only thing starting valves do when open is lower compression and open path for fuel mixture to spark plugs. Mixture goes into cylinder through intake valve.
So if you have a good fuel flow from bottom of carb, good spark at correct time and runs good on diesel and no fuel mixture on plugs the problem is limited to. Air blockage from intake to carb, carb blockage fuel or air, intake passage block or leak to cylinder or starting valves not opening.

The valve to close off the air flow to the diesel inlet ports in the head is in the manifold. If you have the manifold off, you'll get suction in the diesel position because the decompression valves are closed and isolate the gas ports. If you open the decompression valves, both chambers are now connected together and you won't get any vacuum on the gas port unless you cover the diesel port.

Couple more things to check. Make sure the linkage that operates the butterfly valves in the manifold is working properly. If everything thing is switching like it should, then you're down to basically troubleshooting a gas engine.

Start with the basics. Is there spark? There's a contact on the changeover linkage that shorts the magneto on the diesel position.

Assuming you have spark, check for gas in the carburetor. I've had to clean the inlet port on my WD-6 (same engine) carburetor a couple times. One of these day's I'll get sufficiently ambitious to overall it. Also check to make sure that there's gas in the starting tank and the shutoff valve is open (yes, I know its a dumb thing to ask, but its happened before).

With the starting lever in the gas position, gas should drain out the bottom of the carburetor if you open the drain valve. If it doesn't, something is clogged, or there's a linkage problem. There's a mechanism that lifts up the float in the carburetor to shut off gas flow when you're running on diesel, and you won't have any gas in the carburetor if that's not working (or its in the diesel position). Took me a while to figure that out one time, as I didn't seem to be getting gas in the carburetor. Might be another place to check.

Keep us posted.

Keith

Quick check, try to start it on the gas side, but give it a shot of starting fluid. If it fires up you know you got a gas problem. Sounds like something is still clogged up in the carb or the fuel line.

If you have had the carb and manifold off make sure you instlled the linkage to the carb correctly it my be backwards.