96 m900 fcr41 carb leaking issue

[ducpainter]

I don't think the 'hesitation', as you describe it, is related to the idle speed setting.

I think you said you synched the carbs. Did you use carb sticks to do it?

[ducriderinct]

Ok. No, I have not synced them. They have less than 2k miles on them since new.

Is the idle hang normal for these carbs? I'm starting to think I have some sort of clogged jet somewhere or something...

[Howie]

When the bike gets warm and idle speed is too high you hit the part of the ignition curve where ignition advance gets pretty steep which is probably the cause of the high idle.  Idle speed should be set with a real tach.  But, since you have FCRs with the idle speed knob, what ducpainter said is a great alternative.   Also, as ducpainter said, poor synch can cause that problem.

The idea of going a little rich on the idle screws during the cold weather season is for easier starting and better operation during warm up.  Can you describe your present hesitation symptom to us?

[ducriderinct]

Ok, I'll have to look up how to sync the carbs.

As for the hesitation, it's only at a specific part throttle  portion close to the idle. As far as exactly where, I can say that it's right before where the FCR's start to make that wonderful sound they make under acceleration.  That point where you're off coasting and just giving it enough gas to maintain speed.

The best word I could use to describe it would be sputtering. It never quite falls on its face, but it feels like it's constantly about to. The longer I ride it with the throttle in this position the more obvious the hesitation becomes. As soon as you twist it a little more and get into acceleration, it's goes away.

I have noticed, during my test rides, that the bike feels like it has more power at 3/4 throttle than it does at full throttle. When I'm at full throttle and I back off a little the bike feels like it pulls more.


I most notice it at about 65 miles an hour in sixth gear in about 4500 RPM which is where I tend to cruise on the highway. It's very hard to duplicate at surface street speeds or around town. Other than the inconsistant hanging rpm before returning to idle, it's behaves perfectly around town.

The more i turn out the fuel screws, the longer the rpms seem to hang. Sometimes they don't drop for almost a minute.

[koko64]

Sorry to ask again, but I couldn't find it looking back through the thread; are you running pods, drilled airbox lid, fully open lid, stock airbox lid sans snorkles or stock oem airbox? I'm sure I've missed it somewhere. The intake set up has significant implications for your jetting requirements.

[ducriderinct]

No worries. It's a stock airbox, open lid ( top completely cut off) running a k&n filter. This is the exact setup from the other bike transferred to the new bike along with the carbs and fuel pump.

[ducriderinct]

After doing some more reading, it appears that some people have experienced something along these lines that was remedied by moving the clip on the needle, raising the needle up to richen the mixture. Any thoughts on this? 

This entire scenario is so confusing to me because all of these components worked perfectly together on a different engine. Is there that much difference between engines? Same model and year?

[Speeddog]

There are differences due to parts tolerance stackup, especially relating to cam timing.

I'd close the air screws 1/8 turn and see if that cures it.

I swapped in a set of 'EMS' needles on a customer's hotted-up FCR-equipped 900SS, and it worked well.

[koko64]

Ok thanks. Try main jets in the 160-165 range as there are probably 155s in there as delivered. 155s with a fully open airboxp cam cause you to run out of gas at 3/4+ throttle.

Try 55 or 58 slow fuel jets to stop the low end stumble or open the slow air jet screws a1/4 or 1/8 turn instead. Even 1/16 a turn does something. Speeddog referred to them and they are indeed a strong adjustment.

Your fuel is probably a bit different so locals can advise you you with the fine points but that should give a base for an open airbox. Unfortunately too rich and too lean can give a similar feeling symptom to people when they are starting out tuning.

Sometimes its better to give the job to a good tuner and pick up some overtime instead to pay them. If you have to do it yourself then you need to be able to recognize when you go a step in the wrong direction and what that means. An extra shift is often much less time than doing it yourself.

Speeddog can take it from here

[koko64]

  Speedog wants to close the air screw and I want to open it. What matters is understandibg the motor's response when you do and reacting appropriately. You see it could be a rich or lean issue down low and we want to test how the bike reacts.

[ducriderinct]

Yeah there's quite a bit of a learning curve here...ill get it eventually : )

Truth be told, As frustrating as it can be, I really am enjoying the learning process and collecting the knowledge of how to dial in carburators. I just wish I had more time to devote to it...

I'll give the airs screws a try the next time I have some free time. I'm running out of usable temperature days unfortunately.

I'm assuming I need to pull the airbox to adjust the air screws as they look to be on top of the carbs if I'm reading the diagrams correctly?

[Speeddog]

You can just pull off the airbox lid and filter, then access the jet through the hole in the air horn.

You may need to drill the hole in the air horn a bit larger to be able to get a screwdriver in that's big enough to turn the jet.

I didn't have a screwdriver that was appropriate, so I grabbed a short piece of 1/8" welding rod, hammered the end flat, filed it down a bit, and bent about 2" of the other end 90 degrees.
It wasn't optimum, but it's good enough.

[clubhousemotorsports]

If you have a stock airbox lid try the closed lid first. It will richen it up enough for you to get a clue which way to jet/adjust. Ducpainter is correct on the idle hang up, when warm keep lowering the idle until it simply does not hang. If it will not idle at that idle it is telling you something else is wrong, a warmed up motor should idle around 1000 rpms with FCR's, Mikuni's CV carbs wabnt to be about 100 rpm higher.

I would get the bike up to normal temperature and then do a more air/ less air test using your air filter/ airbox lid. Watch for improvements in the area you have the problem now, you are just looking for direction which way to go.

[ducriderinct]

I didn't have a stock airbox that works with the m900 so I decided to take some time today to ride and try to work it out.

Armed with several different screwdrivers and after a bit more fiddling, and more riding, and some more fiddling with the various adjustment screws, I've found a combination seems to work fairly well.

The fuel screws on the bottom are about 1/16 of a turn out from the baseline setting ( I believe it was 3/4 of a turn out), the slow air screws are about an 1/8th of a turn in from wherever they were which I'm assuming was probably stock settings as well.

In 45 degree temps, the problem seems to be solved for the moment. I did have to significantly increase the idle screw setting to get it to stay running however, not sure if that means anything or now.

There is a bit more rpm hang than I'd like and it sometimes hunts a little at idle ( it will dip down a little then come back up here and there, enough that I didn't want to bring the idle down anymore as I thought it might stall) and there's definitely a smell of fuel coming out of the exhaust now when I'm stopped at a light, but at least it's rideable, so I guess I'll have to deal with it for now. Good enough I suppose.

Now that I think about it, I seem to remember my girlfriend complaining that my bike smelled like fuel when she would ride hers behind me last fall, so I guess I'm on the right track... Hopefully the next time I take a ride, she will still be running as well as right now, or I'll be posting back in this thread again looking for more help.

We'll see what happens when the weather warms up. I imagine I'll have to do more tinkering again but at least this time I'll have some idea of what I'm doing thanks to everyone on here who contributed to this thread.

You guys are awesome!

[ducpainter]

Seems like you richened it up a bit.

Check your plugs after a couple of rides to make sure you aren't going to have a fouling problem.