I think she's a little rich

[gunwhatgun]

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All I have ever been taught about spark plugs is telling me that I have a rich condition. This is a dry black soot that wipes off. My issue is I can't seem to find a mixture screw on this carb. It is a Duromax 18 hp 440. If anyone has experience with tuning these carbs and can either tell me that I'm right and there is no screw, or tell me I'm blind and where it is, I would be forever in your debt. Thanks

[slonomo]

I've never had a Duromax, but most GX390 clones have a screw hidden underneath a plug. The EPA does that so the factory sets the idle speed/mix. If there is a screw it will only adjust the pilot air/fuel mixture which controls the idle circuit. For mid/high rpm tuning you need to change the main jet, which is in the bowl of the carb.

If you clean that plug and reinstall it, how long before it fouls out like that?

[gunwhatgun]

Full disclosure, I think the reason it is running rich is that I changed the main jet. I ordered a performance kit that consisted of a K&N style air filter and breather filter, heavier valve springs, and a header. I got the kit because I deleted the governor and was under the impression that these things needed to be done. Hence me searching for the screw to back it down, because it is very clearly over jetted. I also have no clue where the original jet is. I can clean the pug and put it back and I get about 10 minutes before she acts up again. I ordered a factory size jet and 2 sizes up for some tuning room. I'll see if that helps.

[slonomo]

Originally Posted by gunwhatgun

Full disclosure, I think the reason it is running rich is that I changed the main jet. I ordered a performance kit that consisted of a K&N style air filter and breather filter, heavier valve springs, and a header. I got the kit because I deleted the governor and was under the impression that these things needed to be done. Hence me searching for the screw to back it down, because it is very clearly over jetted. I also have no clue where the original jet is. I can clean the pug and put it back and I get about 10 minutes before she acts up again. I ordered a factory size jet and 2 sizes up for some tuning room. I'll see if that helps.

Sounds like you need to go back down one or two sizes on the main. If it idles good and smooth you don't need to touch the pilot air screw. There is no adjustment for the main.

[gunwhatgun]

Originally Posted by slonomo

Sounds like you need to go back down one or two sizes on the main. If it idles good and smooth you don't need to touch the pilot air screw. There is no adjustment for the main.

I figured that was the case. I was just hoping it wouldn't involve ordering more stuff. Overall I'm pretty happy with the Duromax and how it runs. I'm really impressed with my son and myself for getting it in the cart and working in the first place I like how it has made the cart a little more ATV like.

[raydhd]

You can buy an adjustable main jet for that type of carb from someone like NRracing or ECcarbs . It is not cheap but you can dial your mixture as needed. The EC unit is part #169F-43G390. It list for $21.99. The NR version is $44 or so. I have the EC version in my 22mm carb.

[gunwhatgun]

Originally Posted by raydhd

You can buy an adjustable main jet for that type of carb from someone like NRracing or ECcarbs . It is not cheap but you can dial your mixture as needed. The EC unit is part #169F-43G390. It list for $21.99. The NR version is $44 or so. I have the EC version in my 22mm carb.

That is a good piece of info to have, thank you for it.

[gunwhatgun]

She is fixed!! I re-jetted (is that a word?) the carb. To the best of my abilities I sized the jet that marked as "mandatory" by Go Power Sports, if you used the stage 1 kit on a Honda 420 clone. the jet they dent seems to be a .041 and, as you can tell from the pic above, she was way to rich. I dropped down to a .039 and what a world of difference. No more popping and backfiring, full throttle is as smooth as half throttle but terrifying LOL. I know a lot of you have carts that a lot faster that a stock 440 clone, but 30ish mph across an old cow pasture is more than I can handle.

[BIKERMIKEYBLACK]

I have an older duromax 420 and like everything else the low speed adjuster is soldered in and high speed jet was way lean

[BIKERMIKEYBLACK]

U say 30mph wow be happy mine has never gotten over 21 mph at 5600 rpm unless going downhill lol