mint 400 jetting spec

[troy327]

I need the jetting numbers for the bing carb #54-38-101 for the mint 400. I have raced it with a 185 main, a 35 pilot, 285 needle but it seems to run lean on the bottom. I went to a 50 pilot, a 195 main, a 324 needle thats what the manual says to use but it runs very rich. If any one is racing a 400 with a 38 bing let me know what you are using. Thanks Greg

[Rocket]

I don't know if you made all of the changes to your jetting at once or if you did them in steps.  The best way is do one thing at a time and take notes of the effect the change has made.  If it just runs lean on the bottom, a richer pilot jet and maybe lowering the clip on the needle might be enough.
Rocket

[farmer58za]

Hi Troy
If the 400 carb is original, the carb slide will amost certainly be worn and loose in the carb body. Additional air will flow around the sides of the carb slide and cause a lean situation around idle. To check this take the slide out and you may see, on the front or rear of the slide a crescent shaped wear pattern ("smiley face") If you push the slide , when closed, forwards and backwards and get a few mm of movement then it's worn. also check the pilot jet and passages to make sure they are not partially blocked.

At the same time, if the slide is worn, the needle jet may have also been worn by the needle rattling around in it causing richness in midrange. The needle jet on my 400 had worn out from a 283 to almost a 300.

185 main/35 pilot/285 needle is stock. Try (borrow) another slide and see if the condition clears up.

Regards

David ('75 KTM GS400)

[tomale]

David,
Nice to hear from you again, Thankyou for the information. I am not in need but that was really good. That makes so much sense. I had not thought that the needle jet could be worn like that but it does make sense. Any ideas on how to make sure that the pilot jet circuits and not partially blocked? I have had a carb apart a time or two where I wondered if something like that could have happened and I usually end up replacing the Pilot jet, but that maybe only part of the solution. I can see if a carb has been left with gas in it for along time how all those little circuits could get plugged with varnish and you would not know for sure.
What I have done and has work so far is to take the pilot jet out, pull the air mixture screw and begin to flush it out with a good carb cleaner. check to see if I got the pilot jet clean and if the air mixture screw is clean. if there is varnish on there then I would think that that would be some indication of varnish in the hidden places, am I on track?

Thom Green,I own and ride a 76 250 MC5 MX which I bought new.

[farmer58za]

Hi Thom
I keep a few bits of guitar wire (donated by my guitarist nephew) in my toolbox. I poke them through the idling jet and the small idle bleed hole in front of the slide. Carb cleaner works too if a carb is really gummed up. Once there is fresh petrol in the carb and the bike sees regular use, small varnish deposits will eventually dissolve.

Regards
David


Regards

David ('75 KTM GS400)

[farmer58za]

Hi Thom
I keep a few bits of guitar wire (donated by my guitarist nephew) in my toolbox. I poke them through the idling jet and the small idle bleed hole in front of the slide. Carb cleaner works too if a carb is really gummed up. Once there is fresh petrol in the carb and the bike sees regular use, small varnish deposits will eventually dissolve.

Regards
David


Regards

David ('75 KTM GS400)

[troy327]

Hey Guys I messed with the bike for a few hours, and I think I have it figured out. I went with a 195 main 50 pilot and a 2.85 needle the needle seem to be the problem. The manual that I have, said to use a 3.24 needle but that was to big. Bob, I will see you on Sat. at mid ohio and thanks for the info.