FCR Tuning help needed

[Howley]

It wouldn't idle initially but now idles fine after I move the idle speed knob. Should I have done that with the ims?

[koko64]

Thats fine, you got it running, so now do IMS adjustment and see if the idle rpm increases. As fast and strong as it will go then reset the idle speed knob to 1200-1300 rpm if it gets too high. Too rich or lean an idle mixture can easily cause the stumble.

I'm trying to get you to do the basic tuning before even having to consider friggin' around with accelerator pumps! APs are best left alone if you can get away with it. There's a world of pain in tuning those things. Fortunately, adjustable APs can be sourced from the MX scene. Don't worry about that.

[Howley]

Right, that makes perfect sense now. Thanks both you guys, I'll let you know how I go!

[greenmonster]

Throttle sync is cruisal, 1mm off is quite noticeable in response, FHE.

Second hand carbs could be dirty/worn, i e inadequate working.

Good luck, keep us updated!

[Howley]

Carbs are from jv, and they are CLEAN. I'd say they were new if I didn't know better. Do I check the sync at the carb throat? Between the slide and the throat?
I took it for a ride and HOOOOOLY CRAP! The difference is insane. They ride real nice.

[koko64]

Do you have a manometer? If you don't you can use the drill bit method. Light drag between the slide and carb mouth. Is that stumble still there?

[Howley]

I do but I think I don't have the right fittings to fit the manifolds. It it just me or are they different thread sizes on each manifold. There is still a stumble, but only if I crank the throttle really fast. Is that normal?

[koko64]

Should be the same. They are little flat head screws on the outside of each manifold.

With very fine tuning you can eliminate any stumble, but it is necessary to experiment with small changes to the slow air jet and IMS. Focus on any stumble under load when riding and asking for power which is more important than blipping while the bike's sitting in neutral.

Well synched carbs certainly help with crisp throttle response.

[greenmonster]

Drill bit sync works good enough.

Now, w 1.5 turns on air screw, how many turns on idle mix screws?

[Howley]

Can I drill bit synch from the outside? I don't really get what I'm trying to achieve. Is it just testing that the edge of the slide to the inside of the barrel is the same on each.
I think I ended up at 2 turns out on the fuel screws.

[koko64]

Yeah, you want the same gap or clearance so the slides open simultaneously from the
same start point.
In regards to the idle mixture, it idled fastest at 2 turns out?

[Howley]

The idle speed wasn't changing much, but that's where I felt I was getting the best response, and where the revs were dropping back to idle speed the fastest. This stumble is really only if I suddenly jam the throttle more than half open. I guess it's just getting way too much air. I still don't think it's 100% right.

[koko64]

Sounds like you've got it close. Might just be the synch in it.

[Howley]

Yeah I'm certainly happy with it for now. I might ride it for a bit and make some notes, then sort the sync next time I have time to pull it apart. Thanks for your help, I had a dumb grin on my face for the whole ride.