Tillotson HL-186A - What's up with that fixed High Speed Jet

[Go Go Diablo]

Hi Hus Ski Guys,

Tom from Ontanagen, Michigan is struggling getting his 444 to run right. He has a fixed High Speed jet and he is not the first one to ask me about why that is. I don't know what to tell him. Can anyone explain why this carb has a fixed jet and how you might adjust around that?

Also, I looked for some posts explaining in detail that HL-186A carb but could not find any. I remember Peter from Calgary having some posts, but I must be missing them somewhere. If somebody has some good detail to share, please do.

Thanks,

Bruce

[myoldhus-ski]

back when my Hus-ski was still fairly new, someone who also had one suggested that he would drill the jet out a little bigger. Once he did that it didn't two cycle right. Inorder to get it right he found that by turning the shut off valve on the bottom of the gas tank in to almost shut he could adjust the mixture and get it purring. We were constantly adjusting the valve a little.The jet in the carb that I used for the restoration has not been modified. When you first start up and until it has warmed up a bit it doesn't two cycle either, but by the time I've gone maybe 100 yards it starts running right and stays there.
If the person is having trouble getting it to quit over fueling try shutting the valve on the bottom of the tank. Jim

[snocatpete]

On the fixed jet there is no external adjustment. The only way to adjust the main jet is to remove and replace it for a different size of jet. As to why it has a fixed jet, the only anwer I can offer is the design of the carburetor. I am thinking too for simplicity – once the jet has been installed, there is no further maintenance to be done.
The fixed jet has a very exact size orifice to allow a certain amount of fuel through it and if any part of the main (hi) circuit becomes blocked (plugged) or partially blocked this condition will give little or no response when trying to rev (speed) up the engine. For a Hus-ski it should be .035 jet.
The 186A is also a balanced carburetor so the brass balance tube must not be blocked or damaged as this will affect its performance.
Some things to check on the main circuit:
inlet passage from metering chamber to main circuit is not blocked or damaged
the hex plug screw (cap) has a good gasket and is tight
The main jet is not blocked or damaged and has a good gasket and is tight.
Make sure the inlet orifices are not blocked or damaged on the main discharge port (aka nozzle check valve) and the check ball is not stuck and is free to move
Other problems?
Is it getting enough fuel?
Is the gas cap vent ok?
Fuel line blocked or kinked or loose on connections?
Fuel filter blocked?
Inlet screen filter in carb blocked?
Fuel pump working properly?
Inlet needle valve working properly?
Pulse passage blocked or partially blocked?
If all the above checks out, you need to look deeper into possible engine problems. I am also including some photos to help explain the above a little more clearly. Please feel free to comment or ask questions. I hope this helps.

[snocatpete]

Balance tube going to the metering chamber

[snocatpete]

These two pictures are different views of the fixed main jet and gasket and the hex cap screw and gasket

[snocatpete]

This picture is showing the fuel inlet from the metering chamber into the main circuit

[snocatpete]

This first picture is showing where the main fuel discharge port (aka the nozzle check valve) is located.

[snocatpete]

These two pictures are showing Hus-ski's description and breakdown of the carburetor and parts

[snocatpete]

Tillotson's description of the carburetor and parts

[tomsservicecenter]

Thanks for the info. I did get it running well by adjusting the pop off pressure to 15-16. I'm not sure why it has to be so high on this carb but it works. I did a plug reading after a wide open run and all looks OK. Thank you again