Trying to locate the main jet size on a Mikuni round slide Carb

[kat266]

I have an Attex Chief with a 440 JLO and a Mikuni Round Slide Carb. I cannot find any numbers on the main jet. The needle is 5DP7 and the Idle Jet is a 40. I live in Alabama and now it is close to summer with these above average temperatures the engine is bogging on the main jet. I had to put the clip in the first place on the needle for it to rev up in mid range. It ran fine in colder weather. The 440 was already in the Attex and I have the 400 JLO that came in it, but I am not sure if it runs. It also had the same Carb with the same needle and idle jet size in it and there are no numbers on the main jet either. I was wondering how old the carb is and also where is the best place to find parts. What is the best way to seal up the exhaust, it blows out some oil from around the manifold and where it connects to the flex pipe and muffler? Sorry I am having trouble getting the pics to upload

Thanks,
Keith

[Bazooo guy]

If its blowing oil out the exhaust pull the plugs and make sure they both have spark and are not fouled.
Might not be a carb problem.

[kat266]

Oh the sparks plugs r fine. The oil leak is a different issue. I used permatex and it helped a lot. I will just have to do it again and get a better seal. I believe the main jet is too large for summer time. It ran great in the winter time. I have not had the Attex long and the guy I bought it from never drove it. He lost interest and it needed alot of work. I can't find any numbers on the main jet to see about ordering a smaller jet.

[kat266]

I guess a better question would be. Does anyone know what the stock main jet is for a Mikuni round slide Carb used on stock JLO 440? Do u have to jet these engines for summer and winter or no need too because they should run in any temps? Someone may have put a larger main jet in the Carb. I called Richards Relics and they had no knowledge about these carbs.

THANKS FOR ANY HELP.

[Don]

Hey, Kat;

Two-strokes can be a little finicky. You may have to rejet for higher temperature or altitude. Some complain that you have to rejet if the wind changes direction, but it's not quite that bad. I'd start with a 175 or 180 main jet and see what it's like from there. The size should be stamped on the side or bottom of the jet itself, but I've run across some that aren't marked anywhere.

Good Luck!

[kat266]

Hey thanks Don, Yes just my luck the main jets in these 2 carbs have no markings what so ever on them. The only parts with numbers are the Needle and the Pilot Jet and they have the same numbers. I guess this means that the JLO 400 and 440 have the same carb set up because they came off these engines. The the main jet is very close and worked great this past Winter. Yes thanks this is exactly what I needed. I had no idea where to even start with the Jet size. I have learned so much once again from everyones help !!

Thanks so much Don

Keith

[lewis]

For jetting parts you may check these sites:
http://www.mtsac.edu/~cliff/storage/...d_Tutorial.pdf
Mikuni BS Type 2 Carburetor
http://www.mikunipower.com/Catalog/M...atalog2012.pdf
Carburetor Choke Kits, Levers & Cables | Snowmobile Parts | MFG Supply

I am running the twin cv mikunis on my 20 horse vanguard. So far they are dong great.

These locations may or may not help you find what you need but it is somewhere to start. Good Luck

[kat266]

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