Tecumseh Main Jet Carb Question

[threeputtpar]

Simple question. Is is possible to replace the non-adjustable main jet on a Tecumseh carb with an adjustable one? I put a new, non-adjustable carb on a HS50 5hp Tecumseh and it ran pretty well for a little while but now it seems to lack some power when it's under load.

I've removed the fixed main jet and cleaned it out good and that helped a little but it's just not up to the power level of when I first installed the carb. I've replaced the fuel line in hopes that maybe it was partially blocked, but no dice.

Now I'm thinking that an adjustable main jet will allow me to richen up the mixture and it would run properly. Can I just replace with an adjustable jet? Thanks.

 

[eljefino]

If the answer is no, you can get a drill bit kit and go up a size at a time until it runs right. Spare jets in case you screw up.

 

[motorcity]

Did you pull the little screw on the side of the carb, also. That needs to be clean also. Their is a little hole on the side. And the tip is a little pocket, that needs to be clean, also. Spray some carb cleaner in the hole when you take the screw out. Short of this, it sounds like you need to do a complete rebuild and good soaking of the carb. I run them in an ultrsonic cleaner myself.

 

[yeehaw1960]

My suggestions, by the way, depend on if you have a Tecumseh engine made in the last 7 - 10 years.
Shut off gas supply via valve or pinched line. Unscrew bowl nut that holds bowl on. Pull off bowl and wipe out well. Look at bowl nut. It has a hole right down through the middle that needs to be checked for blockage. A stripped bread wrapper will poke through and clean it up. (I use a torch tip cleaner). Carb cleaner will blow through and help out too. The two larger holes at the base of the bowl nut shouldn't be a problem, but look through to make sure they're clear. The tiny pinhole on the side, towards the tip of the bowl nut, right above the threads, needs to be cleared also. You can reassemble and run it or do one more thing.

Another quick step to pretty much finish your carb clean is to...Look at the side of the carb. Notice the round spot where an adjustment screw would be on older models. The round thing you're looking at is a little plastic cup that covers a screw. Trash the cover and take out the screw. While the bowl is off, squirt carb cleaner through the screw hole. It should come out of the bottom of the carb. Then, make sure the holes in the screw itself (in the tip too) are "poked" out. The bread wrapper won’t work on the tip. It takes a much finer wire to make sure that hole is clear. I actually have a piece of multi strand wire with about ½ inch stripped. One strand of the wire will go through the hole at the tip of the screw and should be visible in the larger hole on the side of the screw. The screw just goes all the way in...it's not an adjustment. Reassemble and have fun.

AND, you know...since you have the bowl off and the gas will flow freely from the tank and out of the carb, this is an excellent chance to empty the tank of older gas…most of it anyway. If the tip of the side screw is clogged too much to put a fine wire through it, I use a micro drill bit to clear the hole. Not much else will poke through without bending.

 

[threeputtpar]

Yeehaw, thanks for the detailed response.

It's an engine from 1984, but the carb is a new one that I just installed a month ago. Before running the new carb, I replaced the fuel line and cleaned out the gas tank but didn't replace the shut off valve until a few days ago.

I have taken the bowl and nut off twice to clean them out and did have some sediment both times. I didn't think to try to remove the screw above the bowl as I thought that it was more for idle and not loaded operation. I'll give that a try next and see what happens. If that doesn't work, hopefully they will warranty the carb even with the welch plug removed.

 

[yeehaw1960]

Not a welch plug. Just a mystery screw Tecumseh added when they were trying to meet EPA requirements, which, I believe, eventually ran them to ruin. If it's a new carb (installed recently), it's going to act like it is starving to death on your old motor. The new carbs are designed that way...thanks EPA! Can't imagine a new carb would be that dirty (to keep engine from running right). Remove the bowl nut and take it to a mower shop. Have them match it up to a bowl nut with the screw in it (old style). MAKE sure it's the same length. You may have to go out on EBay to find one. Hopefully, that will solve your problem.

 

[bubbatime]

Newer carbs are run very lean. The fix is to enlarge your main jet a little at a time with a drill bit until you get it just right. This is a common fix and you will be surprised how much power you can get by simply enlarging the main jet.