Return to idle RPM troubleshooting

[Momaru]

Ok, I know this sounds like a carb problem at first blush, but I'm trying to figure out of there's anything else I should be checking, so bear with me please.

Bike's been running fine all summer. Did valve check last week, replaced the plugs and put everything back together & resynched carbs. Bike still seemed reasonably happy, but acting a little odd:

When I close the throttle, 1 of 2 things happen:
1) it takes a while for the RPM to drop back to idle. Like 4-5 seconds to drop from 3k to 1.5k with the clutch lever pulled in.
2) It hangs at some random RPM between 500 and 3000 and stays there until I fiddle with the idle mix, at which point it idles correctly, even if I blip the throttle. Next time I get moving and come to a stop, the RPM stops at some other random point. The engine speed/noise agrees with the tachometer, so it's not the meter itself hanging up.

To remedy condition '1' I've tried correcting with mix screws as well as idle speed, using mixture settings from 1 1/2 turns out to 3 1/2 turns out and no significant change. I can't see any gaps in the intakes or any disconnected lines, etc.

Sometimes when I give it choke to start up, it doesn't help in the least, with RPMs just sitting at ~750- 1k whether the choke's full on, off or anywhere inbetween (I checked to see the cable's still attached & everything moves as it should). Giving it throttle seems to help while cranking up as often as choke.

It seems fine over 4-5k RPM.

Here's what I've got for possible causes, feedback on them or additional ideas would be awesome:

-Could FUBAR'd valve clearances cause this? I've done valves before, took my time & went by the book, but can't remember ever having this issue before.

-Cold weather changing oxygen content and thus combustion mix ratios?

-Carbs all gummed up? I usually run a dose of seafoam through at least once a month, but the bike did sit for about a week with stabilizer-less gas while I did the valve service.


For reference: I've got a K&N R-0990 air filter, (thus airbox delete), kleen air delete, running carbs with #40 pilot jet, needle clips on the 4th slot from the point, DJ 108 mains mix screws currently reset to 1 2/3 turns out. None of that has been changed/altered recently save the mixture screws, which have been reset to where I had ;em before this issue cropped up.

[kkim]

have you double checked for loose/damaged/misconnected vacuum hoses?

let's assume you did the valves correct... I'd first back off the mixture screws 1/2 turn (richer) and see if that makes any difference. if not, I'd recheck the valve clearance or pull the carbs and check for blocked pilot jet(s). (perhaps just drain the float bowls and see if crud comes out?)

choke action has me stumped, though... have the temps there plunge drastically recently before the time you did the valves and now? is this the first winter w/ the #40 pilots?

[Momaru]

Thanks Kelly

Daily temps (high and low) have dropped about 10-15F since I did the valves last week.

I did a visual inspect for loose/damaged hoses with nothing out of the ordinary but I'll check again. I wouldn't have any misconnected because the only one I messed with in the last several months is the fuel tank feed, which I'm sure I got right. I'll run in a heavy dose of seafoam when I fill up tomorrow and see what happens.

I've tried mixture settings from 1.5 turns all they way thru 3.5 turns to no avail, but I'll push the range even further in both directions, see what that does. This is the first winter with the #40s but when I installed them I went from ~2 2/3 turns (with the stock #38s) to 1 2/3 turns. I've still got my #38s, so I'll consider tossing them in, but if I have to lean it out that much for the winter-time I'll be very very confused (I'd expect needing to richen for the winter).

I'll pull the bowls, then the carbs if I don't find anything in the bowls, then recheck the valves if all else fails.

I agree the choke behavior is really strange. I just don't know what to make of it. Initially I thought the mix was way too rich after doing the valves as the choke supposedly richens the mix and it wasn't helping. As the behavior didn't change I assume I was wrong.

Anyhow, crossin fingers and toes over here, but have to wait for tomorrow afternoon (if not the weekend) to check any of this as I lack a personal garage at the moment (and I'm leery about riding the bike far with this going on, if it is the valves).

[Momaru]

Something else just occurred to me. When I was doing the valve service, I also went thru and checked/lubed all the cables. I made sure they were all moving right and had proper clearances.

However I remember one of the throttle cables has a slight kink in it just before it meets the carb (due to me being a noob the first time I lubed the cables), which makes the 'barrel' at the end sometimes not sit quite right in the keeper, effectively shortening the cable a hair at random intervals. It hasn't messed up in months, but since I squashed some grease in there, I may've pushed it out of the perfect alignment. I'm almost certain it's the "push" cable so it shouldn't matter, but if I'm wrong, that could be why it's getting 'stuck' at various small throttle openings.

I really have to stop doing a bunch of maintenance to-dos all in the same session. It'd make troubleshooting a ton easier...

[SCREEM]

I have not noticed anything but more torque in the cold (around freezing) takes a bit longer to warm up but runs great, my bike is stock though.

[kkim]

Originally Posted by Momaru

Something else just occurred to me. When I was doing the valve service, I also went thru and checked/lubed all the cables. I made sure they were all moving right and had proper clearances.

However I remember one of the throttle cables has a slight kink in it just before it meets the carb (due to me being a noob the first time I lubed the cables), which makes the 'barrel' at the end sometimes not sit quite right in the keeper, effectively shortening the cable a hair at random intervals. It hasn't messed up in months, but since I squashed some grease in there, I may've pushed it out of the perfect alignment. I'm almost certain it's the "push" cable so it shouldn't matter, but if I'm wrong, that could be why it's getting 'stuck' at various small throttle openings.

I really have to stop doing a bunch of maintenance to-dos all in the same session. It'd make troubleshooting a ton easier...

well... if it's the push cable that's the problem, you do know the bike runs just fine w/o it, don't you??? jus sayin'.

my push cable has been off the bike for years.

[Momaru]

Well, you were right: I had a mostly clogged pilot jet on the right cylinder. Probably reduced it from a #40 to about a #15. No trash, water or obvious varnish in the bowls though. Cleaned/reamed it out with a twist tie wire (as well as its counterpart), but may've overdone it: not sure how soft this brass is. Worst case, I've still got my #38s on hand. Unfortunately I don't trust myself to reattach the carbs correctly at 3am, so I'll put it back and test things out tomorrow. Will also clean/lube everything, esp the choke arm.

Before I pulled the carbs, realized I'd had another brainfart. My 'cruise control' was binding the throttle tube a little bit. Lubed/loosened that, but no real change to the problems mentioned in the OP, including the RPMs 'sticking' at random values between idle & 4k.

It is the 'push' cable that's kinked a tad, but it was behaving itself. Bike probably would go faster, losing 50g of cable weight, but even with it grumping along with the cable it'll beat green bikes anyday

Also discovered the reason the first half of the choke doesn't really do anything, even when it's operating normally. Half of the range of motion at the carb is just pulling back the section of the pin that doesn't change thickness. In essence it doesn't start 'choking' until the pins are about half way withdrawn, at which point the get reduced to about 20% as thick. Should've taken some pictures. Not related to my problems, just the way it's designed, but of interest.

Thanks again for the help. Even if this doesn't solve things, it needed to be done and I didn't think of it.

[kkim]

glad you found the source of the problem. I never use anything metallic to clean jets. They use brass cause it's a soft metal... dunno why, but I think it's because the carbs are aluminum and the want something soft in there so you don't screw up the carb threads before the jets??

I usually use compressed air to dislodge crud from the orifices.

interesting info about the choke circuit. I've never taken the ninja's apart before so it's interesting to know exactly how it's put together. thanks.

[Momaru]

I'm not sure that's all of the problem, but that was definitely a contributor.

That seems a highly likely reason for using brass; softer than aluminum to save the considerably more expensive carb body threads.

Which orifices are we talking about using compressed air on here?
I agree metal wasn't likely the best idea for cleaning those jets, and there's a fair chance I reamed out some brass in the process. I just wasn't having any luck with compressed air and/or chemical carb cleaner. Maybe I just don't have a sufficiently beefy compressor or the right technique. In retrospect, I should've tried a nylon brush bristle...

I'll snap some pics of the choke circuit when I'm fiddling with it tomorrow and post 'em up. Knowledge is power! Be interesting to see if someone wanted to make tapered choke pins

[Momaru]

Long story short, that clogged jet does seem to have been the whole of the problem. The bike's back to it's usual self after setting mixture screws to 3 full turns out (probably cold weather adjustment) with the just-cleaned #40 pilots. For some reason I still wanna pull the top end apart to recheck the valves though I know I did 'em right... maybe next season for an early inspection.

Thanks again Kelly! I owe you a pint of your favorite beverage next time I'm in the islands

[kkim]

Paul,

good to hear the bike is back up and running up to par. sometimes it's the little things that get us... thankfully it wasn't anything major.

anytime, bud.

[Momaru]

Sorry to revive a dead thread, but realized I never followed through on actually posting those promised pics of how the carb choke pins move.

In the three pictures from the top inside of the carb (with cap, spring and diaphragm removed) notice the position of the bracket at the very top of the pic (pointing at it with my finger) vs the opening in the upper carb gallery (just right of about center, above & to the right of the holes for the diaphragm slides). Only the back half or so of the choke movement actually does anything and this is why.

Other two pictures are there to show how the choke slide moves (the cable terminates next to my thumb), and that the pins are actually pulled out of the carb