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Discussion Starter · #1 · (Edited)
So this ‘93 Fourtrax I picked up. I’ve been working on it component by component.

The first priorities were to get rid of old gasoline and clean up the carburetor, and fix the idle. So it was all fuel line and air intake.

I already posted the petcock cleaning in the greeting thread, and the air cleaner intake in another thread.

I ordered an $11 tusk carb rebuild kit from Rocky Mountain ATV parts. Not OEM but gave it a try and it had gaskets and a new needle, three jets and springs and a pilot screw. Most importantly, this four trax used to live at 6000 ft above sea level and had a #120 main jet. I am now at less than 500 ft above sea level and need a #125 main jet.

Also, i learned it was illegal in California
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New #125 jet to replace the #120. I didn’t end up using the jet tube that sits underneath the jet holder. The carb body has really precise machine tolerance margins, and it almost needs to be pounded in place and I don’t want to damage or score any soft metal. The old one cleaned up just fine and fits well. So I reused it.
You can kind of read the engravings of the #120 OEM jet on the left, and the #125 aftermarket jet on the right.
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I was a little intimidated at rebuilding and cleaning a carb, I’ve never worked with engines or carbs, but figuring this stuff out has been outright a JOY. Marvelous pieces of engineering.

So I took apart the whole carb, cleaned it, and cherry picked the parts to replace out of the kit. The only rough part was an old stripped screw on the vacuum cylinder case. I had to drill through it because I didn’t have an easy-out handy. I did it by hand. It worked, it was risky, and I don’t recommend it!
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Phew! I didn’t drill into the carb threads!

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The pilot screw with a new gasket set felt very different compared to the old set. The place where it set lightly changed. I could see the difference in the length of the needle tip poking in the carb body.


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Nevertheless, after putting new o-rings and washers on, I just went with the factory setting of 2 and 1/4 turns out from light setting, and so far my idle is running great.

Most of all, I’m just so impressed at how cool this carb is. I spent a lot of time with my air compressor spraying air in the various holes and figuring out where the air came out. I was trying to understand the fuel and air flow. It’s all very neat engineering and i love that it works and continues to work when the machine is bouncing down a bumpy road.

Otherwise, besides the carb rebuild and clean, i replaced the battery and cleaned all the electrical contacts, It started up and i let it warm up and then changed the oil and the oil filter.

I had to make some adjustments to the idle. I don’t own a tachometer so I just used this cheap craftsman multimeter I bought at sears 20 years ago. I put it on the frequency setting, wrapped a 12 AWG wire around the spark plug wire, and jammed bare copper into my multimeter. This worked, and I multiplied the hertz reading by 60 to convert it from hertz to RPMs, but also again multiplied by 2 because of the wasted spark on the engine.

For example 9 kHz * 60 * 2 = 1080 RPMs. The manual says idle should be at 1400 +- 100 RPMs. So I had to tighten the screw a half turn or so.

Anyway, it’s a hack with a crappy piece of equipment, but all I needed was some sort of ballpark reading to be sure I wasn’t way off, and to understand how much my adjustments to the throttle screw were impacting the idle RPMs.

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So now I’m at a point where i have clean air intake, clean fuel line and carb, and clean electrical.

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I even put on a battery tender.

Next steps are to take off the crankcase cover and clean the oil screen, and then keep working my way down the maintenance items, which are going to come down to lubricating the chassis, wheel bearings, brakes, and suspension.

I’ve never worked on a machine before. Im really liking it.
Edited: fixed some language
 

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Nice to see that people are still getting into the "hobby" of engines and everything related to them. Buying and riding some brand new atv or utv is one thing, but fixing them is totally different. Most people just go out and spend $200 just to something as simple as changing the oil. Sorry about my ranting. Good luck with all you future projects!
 

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I had to use sad emoji to get your attention
You assembled the pilot screw incorrectly that fat oring goes on the base of the screw like your old one. That’s why it doesn’t fit like the old one
 

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The needle jet you didn’t replace—you have to gently push down on it from the top of the carb. I use a screwdriver handle. And then it’s usually not snug at all going in, shouldn’t have to tap it in. Jet holder keeps it in place

i use Shindy or K&L carb kits. Did you get a starter jet passage plug with your kit? K&L comes with new screws

also you can sometimes use a dremel cutting wheel to cut a slot in a stuck screw. But you did a great job drilling it out.

 

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It’s pretty common mistake because the manual has tiny pictures lol. Otherwise @DonKarnage i like what you’re doing and also really enjoy working on these machines.

Consider buying only OEM parts. Use the oem parts finder at Rocky Mountain atv and or Partzilla.
Unfortunately Honda doesn’t sell a rebuild kit with rubbers, jets and screws. The oem gasket kit for this carb only contains the rubber bits but includes a new starter jet passage plug! K&L makes a couple great kits for these one with bare essentials and the other with everything but the passage plug. Shindy is a great kit too but again omits the passage plug.

When I rebuild a carb, I replace the primer pump and the enrichment plunger (AKA choke valve). The primer pump diaphragm deteriorates and you can pump debris into the bowl of your freshly cleaned carburetor.

The choke valve uses a special conically shaped seal that gets brittle and sticks in the bore when it gets old.
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Discussion Starter · #8 ·
I had to use sad emoji to get your attention
You assembled the pilot screw incorrectly that fat oring goes on the base of the screw like your old one. That’s why it doesn’t fit like the old one
In the photo I was just arranging parts. I hadn't put the o-ring at the base yet. I did so by the time I put the pilot screw in. But I agree with you the manual has tiny low quality photos!
 

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Discussion Starter · #9 ·
i use Shindy or K&L carb kits. Did you get a starter jet passage plug with your kit? K&L comes with new screws
No, unfortunately the tusk kit didn't come with a jet passage plug. And now that i'm feeling WAY more comfortable about what the carb does and each of the parts, replacing the primer and jet plug will be something i look forward to doing. As for rocky mountain ATV, I really like those people so far. they have been helpful and reasonable.
 
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