Help troubleshooting my idle

[Speedwagon]

94 YZF750R. Quad carb, slip on exhaust, K&N drop in filter, dynojet jet kit for altitude.

Here is a video of it once it has warmed up:



The bike stalls at the end, when I blip the throttle too quickly. If I slowly roll on the throttle, it will rev up like shown just before it stalls. Also, there is black smoke(rich condition) coming out the exhaust, when I blip the throttle. I don't see it any other times(though I'm not looking directly behind me when I ride).

[rybo]

This is definitely a carburetor issue.

Did it run really well before and this is a change, or did it never run well?

I would start with a basic disassembly and cleaning. Things that could easily cause this:

stuck needle, stuck floats, worn out float seal, improperly adjusted air screw, poor pilot jet size choice, worn needle, poor needle setting

at at these loads / engine speeds you aren't anywhere near using the main jet, so pay close attention to the pilot, needle and air screw. Just because the jet kit says it's for altitude, doesn't mean that it's right, it's just closer (maybe) than the stock parts. Unless someone worked up your motorcycle on a dyno or spent some real time tuning the jetting, it's really just a guess.

Its a a great bike! Good luck.

[Speedwagon]

Since I bought it in 2009, it has never run "right" like it should. I've come close at times, but never fully there.

I did recently take the carbs off, and cleaned the pilot jets. I know the needles are not stuck, nor are the floats. Float height is within the range Factory Pro recommends for this bike. I don't know about the float seals, and I've been futsing with the mixture screws.

edit: the past few days, something I did made the bike not start cold now. Got to thinking about that today, and made an adjustment just now. I turned the mixture screws out 1 turn(now set at 3.5 out), and moved the idle set screw out .75 turns. It was popping just after I started cranking, but it wouldn't actually fire up. This adjustment seems to have made it able to start on its own. We shall see how it goes, after I take it for a ride. Initial observation is that while it is still idling low, it doesn't seem to be hanging up around 3-4k anymore when I blip the throttle.

[Speedwagon]

Well, it's better:

[FZRguy]

Have you checked for a vacuum leak? Are the manifolds in good condition? Does the problem get better or worse as the motor warms up?

[Speedwagon]

I had suspected a vacuum leak, so I took the manifolds off and resealed them.

From the last video there, it started hanging after I rode it, but not before.

Tried to start the bike this morning, and it wouldn't turn over. Popped a few times, but that was it. I think it was low 50s when I tried(about 0645 this morning).

edit: Just got home from class, and turned the idle set screw out another 1/4 turn, then tried to fire it up. Got a few pops, then it turned over and ran after about 8 seconds or so.

[FZRguy]

I've had similar issues with my FZR. Have you done a valve clearance check? Compression test while you're at it.

[Speedwagon]

I've had similar issues with my FZR. Have you done a valve clearance check? Compression test while you're at it.

I haven't done one this year, no. I did just order the proper adapters for my compression tester, so I can actually do a compression check now on the bike.