Black Jack problems

Mike1nw · Post by **Mike1nw** » Thu Apr 19, 2018 10:33 pm

My wife's boss has a Black Jack.

I replaced the Keihin Carb with the stock one a week ago.

It ran great! For about a day.

Now it won't idle- Feels like it's trying to shake apart. Like it's missing, until you get it above 25 or 30 mph.

So I'll check:

vacuum leak
is it getting gas?
Spark plug (easy to put a new one in)

What electrical fault would cause this?

It's so noisy, I wonder if variator has a bad roller(s) or is stuck somehow.

Stanza · Post by **Stanza** » Fri Apr 20, 2018 1:30 pm

Wasn't Keihin the original carb that was used on these? Where did you source the replacement carb? Was it jetted correctly, or did they just send you a 125 carb and call it done? Stock jetting on a blackjack should be 92 and 38, possibly 94 depending on elevation.

k1dude · Post by **k1dude** » Fri Apr 20, 2018 4:43 pm

Why did you replace the carb in the first place?

Mike1nw · Post by **Mike1nw** » Fri Apr 20, 2018 7:12 pm

Replaced carb about a week ago because he wanted the other one installed.

Like I said, It ran good for about a day or two. Now it "misses" at low speeds.

He already had the replacement carb. So I dunno where he got it.

So I don't know the history of the carb nor the needle sizes.

It ran good. Suddenly it doesn't.

That's the weird part. Like it's a failure of some component.

k1dude · Post by **k1dude** » Fri Apr 20, 2018 8:49 pm

Did it run fine with the old carb?

sc00ter · Post by **sc00ter** » Sat Apr 21, 2018 4:13 am

I had the exact same problem with my old Buddy 125. I had a shop fix it (thread is on this site), they messed up the stock carb (broke accelerator pump tang), didnt bring it back to get it done right, ended up buying a new carb, problem came back, sold scooter "as is". The guy who bought it replaced a vacuum hose and the low speed stuttering and such went away! Still not sure exactly what he changed out but if I stop by his place this weekend I will ask. I also need to take rear rack repair pics for another member here. Im lazy and the guy with my old Buddy(s) works strange hours.

Mike1nw · Post by **Mike1nw** » Sat Apr 21, 2018 4:04 pm

yeah I will replace vac hoses, there aren't that many of them anyway, thanks

Mike1nw · Post by **Mike1nw** » Sat Apr 21, 2018 11:32 pm

FOUND IT!

After replacing vac hoses, new spark plug, recheck carburetor, adjust valves....

Took belt case apart- one roller was half gone and jammed in the variator, another was flat spotted.....

Runs like a turbine now! Needs rollers and a ramp plate.

What an adventure

Mike1nw · Post by **Mike1nw** » Sun Apr 22, 2018 2:14 pm

"Wasn't Keihin the original carb that was used on these?"

Might have been. The one I put on, has "Keihin" on it. I didn't notice that before. It looks much different than the Keihin I took off. Again, I don't know how it ran before.

Because he has a loud exhaust pipe on the bike, I think I will add a shim to the main needle. Once I get the variator re-installed