Motor starts then dies.

[davespurlin]

Continuing this thread here so pictures can be posted. The original post was…

"Let me begin by saying that the ignition system of my 1956 Johnson QD-17 10 horse is brand new OEM from stem to stern and has been checked and rechecked numerous times against the OEM manual so I feel pretty confident this isn’t an ignition issue. Compression is good and the motor usually starts, on the initial try, on the 2nd or 3rd pull. Problem is that it won’t stay running. Back in my hotrod days, we would sometimes test an engine on a motor stand by pouring a couple teaspoons of gas down the carb. The engine would fire off but run only as long as the prime lasted. Usually a few seconds. Very much like what I am experiencing with this motor. However, every time I pull the starter cord, gas pours out of the intake opening of the carb (about a half teaspoon per pull) so I doubt it’s fuel starved. The carb has been rebuilt using a OEM kit. I have also disassembled and reassembled the carb 3-4 time per the OEM manual instructions and can not find anything wrong. Should add that the powerhead has been modified to use a fuel pump, but it seems to be working fine and I still had the same problem when I set up a temporary test gravity feed bypassing the fuel pump, to the carb."

General layout of the fuel system.

What happens when the motor is primed or the starter cord is pulled.

View of the new float and body half gasket from the top.

View of the new float and body half gasket from the side.

This has got to be a problem with the float/valve, but earned if I can see it. Since it is the same thing that was happening before the carb was rebuilt, so I hesitate to assume it was a detective kit and order another.

[jcrigan]

Looking at the picture number three, it looks like there is debris in the nozzle 0303618. It may my eyesight though.

[garry-in-michigan]

The area I have outlined in red is the float bowl vent. If it gets blocked, the air bubble in the bowl will not allow the float to rise and gas will run out by way of the high speed jet. Squirting gas when you crank the motor indicates the fuel pump is working. . . 😆

[david-bartlett]

Also, in your picture, the gasoline does not seem to have much color to it. What are you using for oil?

[frankr]

Garry beat me to it and said what I would have said,only he said it better. The symptoms almost shout out "plugged vent".

And yes, what is that chunk of crud doing in the main nozzle?

[davespurlin]

Thanks for the input, guys. What you suggested makes perfect sense. When I first disassembled the carb, it was considerably scaled up on the inside with white or yellow crystaline deposits that were quite stubborn to remove. Obviously, I did not get the passages as clean as I thought i had. i will pull the carb again and start over with cleaning and inspection today.

David, the current load of unleaded gas is about a week old, mixed 24:1 with Poulan Pro 2 cycle oil and the recommended amount of fuel additive. In the tank, the gas is dark blue. Hard to see in the photo, but the gas in the bowl is a very, very pale blue.

[Tom]

Oil for air cooled two strokes is not the same as oil for engines that run at lower temperatures (water cooled). If you get the motor running, you might want to switch to TCW type oil.

T

[Mumbles]

Once you get your carb issue figured out, it’s highly recommended to save your Poulan oil for your hotter running, air cooled weed eater and chainsaw, which it was designed for. Non thermostat and thermostat temperature controlled outboard motors run at much lower temperatures and require an outboard rated oil in the fuel mix to avoid carbon and sludge buildup in the motor. A quality oil with a TCW-III (Two Cycle,Water Cooled) rating will keep your motor happy. I don’t think you can even get TCW-II oil any more.

Without starting an endless debate here, I know air cooled oil will work and I will admit I have used it myself occasionally but it just isn’t right. At least it isn’t as bad as using TCW oil in a chainsaw.

[davespurlin]

Ok guys. You hit it right on the nails head. The exterior opening next to the bowl vent was so packed with crud, I thought it was a factory plug. I cleaned out the passage back to the point where it turns downward to go into the bowl and tried flushing it out with carb cleaner and compressed air. However, it still appears to be plugged up. I want to try a back flush through the passage, but i can not find the opening to the passage from inside fuel bowl. Any idea where that opening is?

[davespurlin]

That got it, Gentlemen. The motor starts on 1st or 2nd pull and continues to run now. Idles and accelerates but rough with an occasional stumble, but the high and low speed needle valves have not been adjusted yet. Mostly tuning issues now, I think,, but I guess I should get fresh gas and the right oil first. I seriously appreciate your help and advice.

[Author]

Posts