Trouble Getting Going

[ducpainter]

Try opening the fuel screw?

[ChrisK]

Try opening the fuel screw?

3, 4 turns?

[ChrisK]

I turned the fuel screws out to 4 turns. That pretty much solved the takeoff from a stop issue. Now it still seems to be stumbling after decel, after I come into a corner off the gas and then try to pick the gas up again.

Still have that chirpy noise going on at cruise.

[ducpainter]

Does it still pop on decel?

[ChrisK]

Yes I still have some popping.

I turned the screws back in to 3.5 turns and it made the diving problem a little worse, so I'm thinking I need to go back to a larger slow jet.

While I'm cruising at a steady speed it's stumbling pretty bad. Any time I'm accelerating it's pretty great.

[Speeddog]

Air screw can be adjusted by taking the airbox top and filter out.

I took a ~6" length of 1/8" weld rod, bent it to an L shape about like an allen wrench.
Then I hammered the end of the long leg flat and filed it to fit in through the hole.
Takes a bit of futzing around to get it right.
Best to remove the airbox and one bellmouth to get the tool right.

You're band-aiding that 1.5 turns air screw by opening the fuel screw to 4.
Get the air screw to 1 turn, and you're likely to end up with the fuel screw near 2 turns.
And likely run better as well...

Here's a diagram to get a feel for what circuit is active where:

[ducpainter]

Chris...in one post you say 1 turn on the air screw, then you say 1.5.

which is it?

[ChrisK]

Chris...in one post you say 1 turn on the air screw, then you say 1.5.

which is it?

1.5 turns. In one post I said I had planned on doing 1, but I didn't know where the screw was so I never changed it.

I'm still having trouble adjusting it, Speeddog I have a very narrow flathead that will slide down the tube but I'm having a problem getting it to seat in the head of the screw.

I should also add that while cruising at the same speed, I believe I can hear a pretty consistent popping. If I pull an acceleration, then let off the gas completely, then try and pick it back up again it stumbles and dives.

I went all the way back to zero turns out on the fuel screws and it made it much worse, just an FYI.

[ducpainter]

I think what Nick is saying is that air screw will eff you at 1.5 turns.

Koko also recommended 1 turn on the air screw IIRC

If you have to take the air box off...so be it.

[ChrisK]

I just made a tool similar to what Nick described, air screw at 1 turn, going to set the fuel screw at 2 and check it out.

[ChrisK]

Wow it's amazing how much small changes can make. 1 turn air and two turns fuel. Bike did much better at not stumbling through corners, and a little better at cruising.

There were still a couple moments where I felt some 'dragging' at cruising speed and a slight stumble through a couple turns.

I should also add, I have the idle set at about 1500-1600 RPM's, according to my tach. I had to sit at a light for quite a while and it sounded a couple times like it was gonna die. I never touched the throttle and it kept running though.

[ChrisK]

I put the fuel screw at 2.5 and it felt a little better.

Sitting at a light this time the bike died at idle.

I should add that it's about 30 degrees F right now, maybe colder.

I think I'm done for the night. I'm curious to see how the bike starts and idles tomorrow after cooling down to my 50 degree garage.

[Speeddog]

The Keihins are quite sensitive to air temperature, and moderately sensitive to altitude.
I don't know if it's that they don't compensate as well as the CV Mikunis, or they're just a sharper instrument.

You'll need to be a bit richer than what I suggested to run properly below 50 degF.

Try going in on the air screws, 1/8 turn to begin with, so you would be at 7/8 turn.
Then play the fuel screw to find a the best setting.

Then try another 1/8, so you're at 3/4 turn out.
Then play the fuel screw to find a the best setting.

Eventually you should be able to get an idle at 1200 or less.

you may find that a richer idle jet may help, 57's.
Then you'll adjust the air screw and fuel screw to get it running best.

I'm not completely convinced that, for example, the best setting of air and fuel screws with 55 idle jets will be better or worse than the best setting of air and fuel screws with 57 idle jets.

It's going to take a bit of tuning.

Keep in mind, you've got an accelerator pump, so if you're opening the throttle, it's getting more fuel.
You can use that to figure out if richer is better or worse.

I disconnected the accelerator pump on my FCR's for a while to see if they were masking a jetting issue, and just to see what it was like.
It was like back in the day with round-slide Mikunis and no accelerator pump.
As long as you opened the throttle with a tiny bit of finesse, it was fine.
If you whacked it open like a clueless newbie, it'd go flat, then pick up.
I would've left it that way, but it made starting at low temps (for SoCal) difficult, as there's no choke/enrichening circuit.

[ChrisK]

Keep in mind, you've got an accelerator pump, so if you're opening the throttle, it's getting more fuel.
You can use that to figure out if richer is better or worse.

That is good to keep in mind. While I was fiddling with the air screws I twisted the throttle, it was very cool to see the accelerator pump working.

[koko64]

Sounds like you need the 58 slow jets. You might  find yourself back with 60s and wondering why you bought the extra jets. They're not wasred though.

In theory, you are close with your slow fuel jet when your IMS is between 1 to 2 turns out for best idle. Also your slow air jet screw is theoretically correct 3/4 to 2 turns out. Thats according to the FCR bible by Patrick Burns (informative and entertaining). That's the theory anyway.

You know you are correct when you dont have to have an extreme setting on one adjustment to overcompensate for an incorrect setting somewhere else. Examples of this are too small an air screw setting  or the IMS turned out too far because of too small a slow fuel jet.

Just a related line of thinking, I tuned a 900 with FCR39s, that went from 62s with V cams to needing 58s with 900 ie cams. It's making me wonder about the W cams. I need to ask Chris Kelley if the 60 slow jet in FCRs is a SUDCO setting or based on what Pongo needed when it had W heads. Maybe he might see the thread and chime in.