Replacement Adjustable Main Jet for Craftsman/Briggs 7 horse??

[Vettepilot]

Working on a Craftsman 7 horse engine on a pressure sprayer. It sits, I forget to drain fuel, fuel goes bad, I rebuild carb. Rinse and repeat. God how I hate todays gas!!!

Anyway, like many modern engines, this thing has always run lean. Hard starting when cold, and it will happily run on some choke even when warm. Classic "smog tune". I really want an adjustable main jet for this. I would drill out the main jet a bit, but it is smaller than my smallest bit, (a #60.)

The carb is a Stens Carburetor 520-964. Is there a replacement adjustable main jet made for it?

It has the main jet that also is the bolt that holds the fuel bowl on.

Carb is like the pic.

Thanks,
Vettepilot

 

[FZ1]

Working on a Craftsman 7 horse engine on a pressure sprayer. It sits, I forget to drain fuel, fuel goes bad, I rebuild carb. Rinse and repeat. God how I hate todays gas!!!

Anyway, like many modern engines, this thing has always run lean. Hard starting when cold, and it will happily run on some choke even when warm. Classic "smog tune". I really want an adjustable main jet for this. I would drill out the main jet a bit, but it is smaller than my smallest bit, (a #60.)

The carb is a Stens Carburetor 520-964. Is there a replacement adjustable main jet made for it?

It has the main jet that also is the bolt that holds the fuel bowl on.

Carb is like the pic.

Thanks,
Vettepilot

View attachment 309699

View attachment 309700

Stabil in the gas and/or run it dry.

 

[ripcord]

Here you go...

https://www.amazon.com/Carburetor-Numbered-Jewelers-Miniature-Drilling/dp/B0DFHQL3G8

 

[Vettepilot]

Yeah, I even have a set around here somewheres... can't find them. I was hoping for the adjustable main jet option actually. It's better for getting dialed in quickly/easily.

Anyone? I'm sure it's a very commonly encountered problem. Hopefully someone hates the EPA as much as me (as well as out of tune engines), and manufacturerd a fix??

Vettepilot

 

[ripcord]

Maybe you could adapt one of these Honda gocart racing jets. I'd be interested to know how it goes.

https://www.nrracing.com/GX200-Gas-Adjust-Jet-p/adj-jet-200-g.htm

 

[The_Jeff]

I'm not confident the bottom nut, which passes fuel, is the calibrated restriction. Have you looked up inside the carb for an emulsion tube and another jet?

The tiny drill bit set is a game changer, go for it and never look back. I find about 2 1/2 numbered bit sizes bigger is right for me and the E10 gas I get. The carb makers know what they're doing and they go precisely lean repeatedly, LOL.

 

[The_Eric]

I'm not confident the bottom nut, which passes fuel, is the calibrated restriction. Have you looked up inside the carb for an emulsion tube and another jet?

The tiny drill bit set is a game changer, go for it and never look back. I find about 2 1/2 numbered bit sizes bigger is right for me and the E10 gas I get. The carb makers know what they're doing and they go precisely lean repeatedly, LOL.

I've always figured the area of the jet (area of a circle) and added 10-15%

 

[The_Jeff]

I've always figured the area of the jet (area of a circle) and added 10-15%

Yeah remember your pi-R^2, the diameter just has to increase a few percent to get that much fuel.

 

[The_Eric]

Yeah remember your pi-R^2, the diameter just has to increase a few percent to get that much fuel.

Do you mean just a few thou to get 10%?

 

[spasm3]

Do you mean just a few thou to get 10%?

Depends on the size of the hole you are starting with.

 

[The_Eric]

Depends on the size of the hole you are starting with.

Agreed. I was just seeking clarification from him.

Personally I've found that as little as .002" increase in diameter will do the trick.

 

[repairman54]

I stabilize my gas cans when ever they get refilled. No more fuel related issues as all my equipment is automatically storage ready.
Most adjustable jets only clear out the junk when turned in anyway, so prevention is best.

 

[Vettepilot]

Yeah remember your pi-R^2, the diameter just has to increase a few percent to get that much fuel.

Yeah, this is what I generally do; calculate the orifice size, then calculate a percentage larger to get a new orifice size desired. 10% is a good bit more fuel. You can always go larger. Going smaller requires soldering. Been there too.

Stabilizers! Project Farm on YT did a study on that, and basically proved what I already knew. NONE OF THEM REALLY WORK. I am still working on cleaning up a totally wrecked fuel system on my Vette, CAUSED by a name brand fuel stabilizer that not only did not work, it made things far, far worse.

Bottom line is: If it is an ICE that you care about, and it's going to sit unused for more than 3 days, use Avgas!!

Looks like no adjustable main jets for my sprayer engine?

Thanks for the responses!

Vettepilot

 

[wag123]

use Avgas!!

Yep!!! THIS will solve your problem. AVGAS will last at least 5 years without any treatment, both in the can and in the machine. The only problem with AVGAS is that you can't dump it into your catalyst equipped vehicle to dispose of it. They are producing unleaded AVGAS now, but it is not readily available.
IMO drilling out the main jet would not be a satisfactory solution to your problem.

 

[Vettepilot]

That Honda adjustable jet does not have a seat. Also, with no adjustable packing on the shaft, I would worry about leaks.

Hmmm... I wonder if that's why nobody makes them; liability!! It would not do much good to successfully outrun the EPA, only to be hit with a law suit for a fire!!

:~(

Vettepilot

 

[Vettepilot]

Yep!!! THIS will solve your problem. AVGAS will last at least 5 years without any treatment, both in the can and in the machine. The only problem with AVGAS is that you can't dump it into your catalyst equipped vehicle to dispose of it. They are producing unleaded AVGAS now, but it is not readily available.
IMO drilling out the main jet would not be a satisfactory solution to your problem.

Drilling out the main jet will definitely solve the lean running problem it has had since new. I have done this fix on too lean smog motors before, and the improvement is amazing.

Solving the fuel problem means either running Avgas, or just remembering to drain the dam thing and run it dry after every use.

It gets to 130 degrees very often here, and being right on the border, our fuel comes from Commufornia so it's the very worst. Fuel truly goes bad in two weeks, and starts wrecking things shortly thereafter. It's a nightmare. Even fuel injection clogs!!

I have rebuilt so many carbs here that I should have interest in carb cleaner companies!!

Vettepilot

 

[ripcord]

Here is a site listing places to buy ethanol free fuel. Maybe you'll get lucky and find one near you.

https://www.pure-gas.org/

 

[wag123]

Drilling out the main jet will definitely solve the lean running problem it has had since new. I have done this fix on too lean smog motors before, and the improvement is amazing.

The problem with doing this is that if the jet becomes clean during use the engine will run rich.

 

[ripcord]

One of the best things for small gas engine repair that I ever bought was an ultra sonic cleaner. I fill mine with plain hot water, then I put my OPE carb parts in a glass jar filled with gasoline and set it in the cleaner. It really gets those passages clean.

 

[Vettepilot]

The problem with doing this is that if the jet becomes clean during use the engine will run rich.

You have totally lost me there...

3 separate problems.

1. Crappy fuel = Drain after use or use Avgas

2. Dirty carb = Clean the carb. (Yes, Ultrasonic is great--> Love mine!)

3. Engine runs lean with CLEAN carb. (Set too lean at factory) = Install adjustable main jet, OR drill out jet.

Vettepilot