18 Mag Starting Issues
 

Hello all! I have a 784 with an 18 Mag & Walbro Carb. Having problems with the engine starting consistently. If I get it to run once, it will start every time. Once it sits for a day, it will try to fire and sputter on the first crank and will never take after that. Went through and cleaned the carb. When my buddy and I took the carb apart, we found a lot of dirt, so we installed an Advance Auto fuel filter in the line. Haven't had the carb back apart to see how well it worked, but I'm thinking there's still dirt in the carb somewhere.

Anybody have any suggestions?

Where is the Fuel Filter installed...??? And what type of Fuel Filter did you install...???

Fuel filter is intstalled on the engine side of the firewall. It is a $3 part from advance that is a small fuel filter for small engines. However, it is important to know that the starting issues were not affected by the installation of the filter; it was doing the same thing before.

My 1812 did about the same thing. (same tractor as your 784). I would start than would not start again. I had to pull the motor and put a new coil on in it. it is on the back side of the motor. The coils are around 120$ but it worth it! Pulling motor is not hard six bolts and wires and the gille and then it is out. Put new motor mounts it and aircraft bolts and blue locktite. Than clean the motor super clean. Gap the coil at 10 thoundths. Put the motor back in and it will fire right up! My 1812 runns 10 times better now and you bump the key it starts right up.

Does it fire if you give it a shot of gas down the carb? You could have a fuel pump problem also. If it fires by putting gas down it then bypass the fuel pump and have at least a 1/2 tank of gas an try to start it. I would try this first and then move on to the other possible problems. Good luck and keep us posted.

My 1872 is the same way today, but , I know what the problem is because I created the problem.

The 90 degree snorkel kept vibrating loose, so I used Locktite on the screws.

Some Locktite got on the choke shaft somehow, now it is difficult to pull the choke all the way out.

Partial choking causes the exact symptoms you described.

I keep waiting for the Locktite to wear away, but, 6 years and the choke on the SuperCub still requires a SuperYank!!

As for the coil, it's not an ignition problem, it's a fueling problem as far as I can tell. A shot of gas in the carb will start it right up. Also, I will add that when we put the fuel filter on, we cranked the engine to run fuel through the lines. The fuel pump was putting out a lot of fuel.

How old are the fuel lines? Are they original?

They seem to be in pretty decent shape. I'm thinking tomorrow will yield another look at the carb and see if there's still sediment in the bottom of the bowl - this would prove whether or not the grit is coming from the lines or from the tank.

Dog

If you have dirt back in the carb, then take the time and wash out the tank, and replace the fuel lines from the tank to the carb. Youll thank your self in the long run. also like Lew said the fuel lines can look good on the out side but rotting on the inside.

On another note, its about time for you all in Western pa to hit the woods. Wish I was making it up there to hunt this year.

Nate, I'm sure I replaced the fuel lines on it when I put the 18 mag in it. I don't think I washed the tank out but I did look in it and don't remember anything in it. Doesn't mean there's not though. It seem's like it's not holding fuel pressure. So it needs primed if it sit's for a long time. Like an old car if you run it out of gas, most time's you have to prime it to get it running. I think if you find something in the tank you should just replace the lines again while your at it. Good luck!!

It's starting to sound like you need to put a fuel pressure gauge on the output of the pump and crank the tractor to tell you if it is or isn't the fuel pump that is bad. If the pump is good, the gauge will jump to about ~2.5psi and stay there; if it is bad, the needle on the gauge will just flop around as you crank the engine.

Matt,

I cleaned the carb again this afternoon and after reassembling it, it didn't seem like it was getting any fuel. A buddy of mine is picking me up a pressure/vacuum gauge at Harbor Freight(cheap tools, but they work) and we're going to look at that tonight - just got off the phone with him. If we do find a fuel pump problem, what do they go for? Is it possible (or even worth it) to rebuild one?

Thanks for all the advice everyone - just trying to get it to start the first time, every time.

I have one I'll send you if you need one. Let me know.

Bypass it for now. It's not needed.

Status Update
 

For now, the mower is doing the exact same thing. Here's what I did to try to remedy the problem:

1. Soak the carb overnight. Cleaned out and reassembled.

2. Replace all the fuel lines. I'm sure Eric replaced them when he did up the engine, I just wanted to rule out any possibilities. Cost me all of $4 and I moved the new fuel filter. Put the fuel filter after the fuel pump; I was thinking that dirt may be working itself out of the pump and clogging up needles/jets.

After this, it started just fine. Time always tells the story though, as the next morning it was back to the same old thing. Really getting fed up with it. I have an older Carter 26, but the choke and throttle adjustments aren't lined up the same way.

Any words of advice?

Hey Maddog, It sounds like you might have a slight vacuum leak. The carb has a float bowl yes? Is there a solenoid on the carb? Providing the needle/seat is good it should be full of fuel after shutting down (you do bring the engine to idle speed for a few seconds before shutdown Right) and have a ready supply of fuel for restart. I didn’t read if there was more dirt the second time you removed the bowl, there could also be some water in the fuel this would be at the bottom of the bowl and want to be sucked up first on starting and would cause the same symptoms. The filter should be a paper element one not the brass type the latter will let some water to pass through. There are several ways to check for vacuum leaks, carb cleaner, propane, water … all have some drawbacks use all with CAUTION!!!!!!!! CHWNY

Did you check the fuel pump like I've suggested? You've pretty much eliminated everything else.

When you get it running, I would put the filter before the pump so any crap that gets sucked in doesn't tear up the fuel pump.

There was a little dirt in the bowl, but nothing that seemed to be a problem. After soaking, there was a lot of dirt in the bottom of the bucket, but I think that was from the outside. Fuel pump works fine. Water in the fuel makes the most sense in that once it starts running, it will cycle between running and stopped with no problem; however, once it sits overnight, the water settles to the bottom and becomes the 'fuel,' thus causing it to not fire. Also explains how a little bit of gas in the carb will start it right up. Also explains why it sputters a little bit at the beginning, but after that, won't fire.

I forgot, solenoid on the carb? Like a primer pump? No - there is no such thing on this model.

The solenoid would be an electric shutoff valve requiring a full 12v any corrosion on the supply wire could cause erratic operation. I have had an abundance of water/fuel issues this year, too much rain here in the north east. Whatever additive the EPA requires in our fuel seems to be hydrophilic . You could collect some fuel in a clear container and see any water at the bottom.