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 Post subject: sticking slides
PostPosted: Sat Jun 24, 2017 9:10 pm 

Joined: Mon Aug 01, 2011 8:24 am
Posts: 184
Location: Waterloo, IA
I was reassembling my carburetors today, diligently checking that the slides moved freely once installed by reaching a finger into the opening of the carbs and manually moving the slide up and letting it snap closed. I noticed that 2 of my slides were sticking open a little bit.

This got me thinking about the last time I was running the engine: I had a hanging idle around 2000 rpm. Could not get it to go away by adjusting idle setting screws; checked for air leaks and found none.

Fast forward back to today. After reassembling the carbs and hooking everything up I still had the hanging rpm problem. I think it is related to the sticky slides. Does anyone have any experience with this problem? I pulled the slides back out and made sure they were clean. I even checked the bottom edge of the slides to make sure there weren't any burrs on them.

I am currently running my home-made throttle cable that eliminates the need to adjust the traditional idle setting screws on the sides of the carbs, if that makes any difference

Thanks in advance!

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ride hard, ride long, ride safe!
Jason
72 h2 in a 93 Katana
03 cbr600rr
80 kz750 ltd
94 pw50


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 Post subject: Re: sticking slides
PostPosted: Sat Jun 24, 2017 9:20 pm 

Joined: Tue Jul 24, 2012 6:06 pm
Posts: 1135
Location: Honolulu
I would remove each carb and check one at a time to see the slide sticks when it's assembled. If none of the slides stick then it might be related to your custom cable or how the cable is routed.


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 Post subject: Re: sticking slides
PostPosted: Sat Jun 24, 2017 9:31 pm 

Joined: Mon Aug 01, 2011 8:24 am
Posts: 184
Location: Waterloo, IA
I've verified that the slides are sticking in two of the carbs. once I lift them up and let them snap down they return to the proper position. however, twisting the throttle wide open and then letting it snap shut allows the slides to stick for some reason.

First thing that comes to mind is possibly a worn slide bore in the carbs? I don't feel any ridges or grooves but who knows?

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ride hard, ride long, ride safe!
Jason
72 h2 in a 93 Katana
03 cbr600rr
80 kz750 ltd
94 pw50


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 Post subject: Re: sticking slides
PostPosted: Sun Jun 25, 2017 4:08 am 

Joined: Thu Jun 09, 2011 11:25 am
Posts: 3137
A question, are the carbs stock sized 30 mm's? The first series of H2 carbs had chrome plated brass slides in them that used to wear the bodies, guide tabs and slides out. Sticking throttle was one issue.

The combo of slide weight and intake pulses caused the slides to dent/distort the carb bodies, and forms​ curved cuts in the port side of the slide.

If you would look for the service bulletin for the FDM on it, you will find the change went to an anodized aluminum slide.

Of course, if you already have the aluminum slides, probably won't have those slide problems.

I'd also go back to the stock idle stop screws as well. If the throttle cable junction moves around enough, and that controls the idle, that could be an issue as well.


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 Post subject: Re: sticking slides
PostPosted: Sun Jun 25, 2017 9:18 am 

Joined: Mon Aug 01, 2011 8:24 am
Posts: 184
Location: Waterloo, IA
I found the service bulletin you are referring to, #73-h19. I definitely have the chrome plated brass slides. It looks like the aluminum ones are green, mine are silver.

The bulletin doesn't mention anything about what the wear looks like and I'm not sure what you mean by "... curved cuts in the port side of the slide"?

I'm assuming that if this is my problem there is likely no remedy except new carbs?

I'll also try going back to using idle stop screws to see if that helps at all. If memory serves I had this problem before I made my cable so I have little hope :(

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ride hard, ride long, ride safe!
Jason
72 h2 in a 93 Katana
03 cbr600rr
80 kz750 ltd
94 pw50


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 Post subject: Re: sticking slides
PostPosted: Sun Jun 25, 2017 9:29 am 
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Joined: Tue Jun 07, 2011 6:37 am
Posts: 10460
Location: Rio Rancho, New Mexico
Things would have to be unbelievably worn to cause slides to stick. If anything they would be loose. If they don't stick when the throttle cables are not installed, then it's something in the cable or routing. Look there.

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Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........


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 Post subject: Re: sticking slides
PostPosted: Sun Jun 25, 2017 3:17 pm 

Joined: Mon Aug 01, 2011 8:24 am
Posts: 184
Location: Waterloo, IA
I took apart my handgrip/switch housing and cleaned everything that could be cleaned
lubed the cables
lubed the right handlebar where the grip contacts it using cable lube
made sure the choke cables had plenty of slack, even turning them in a couple turns, just to make sure
took the slides apart and made sure everything is clean
checked all slides to make sure they have free range of motion with the cables installed
checked all slides to make sure they have free range of motion with the cables uninstalled
snapped the throttle closed multiple times, feeling each carb by hand to make sure the stops 'slam' into the bottom of the carb
adjusted the throttle stop screws so they were driving the idle, not my cable arrangement
verified that there is slack in the cable at the grip as well

Started the bike, idles like a champ at 1000 rpm
Rev it past 2500 rpm and it won't come down
hit the choke for a second, idle drops and it comes back to 1000 rpm

Observations:
I don't need to choke the bike for long to get it running on it's own, even from a dead-cold start. Maybe 2-5 seconds and it will hold idle. My 4-stroke experience says the bottom end is too rich if it will do that?

My air mix screws are turned out about 1.5 turns for best idle. turning them in will cause the idle to drop a bit

My slide needles are at the second-to-top groove - could I be creating a lean condition as the slide closes that causes rpm to hang?

plugs look plenty dark and very wet

I sprayed carb cleaner on everything I could looking for an air leak - base gaskets, head gaskets, spark plugs, carb boots, throttle slide caps, etc. Couldn't find anything

Crank has less than 500 miles on it since it was rebuilt so I doubt the seals are bad, plus the plugs are dark and wet

slides have been modified by cutting off the bottom of them to get to 1.5 cutaways

Could I be running rich? could that cause the engine to hang at an rpm? I have always found the opposite but nothing else seems to make sense....

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ride hard, ride long, ride safe!
Jason
72 h2 in a 93 Katana
03 cbr600rr
80 kz750 ltd
94 pw50


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 Post subject: Re: sticking slides
PostPosted: Sun Jun 25, 2017 3:46 pm 
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Joined: Wed Jun 08, 2011 11:34 pm
Posts: 9826
Location: North Central NC
Idle speed not coming down is most likely do to lean running and/or an air leak. Since it's a closed throttle problem, the needle position is not related. Air leaks can be in quite a few places, like carb boots, cylinder bases, and crank seals. Was the crankshaft rebuilt recently? If not, have you done a pressure/vacuum test to find out the condition of the seals?

2 to 5 seconds of needing the enrichers to be able to idle is not unusual. In cold weather you may need to stab the enricher lever a couple more times.

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 Post subject: Re: sticking slides
PostPosted: Sun Jun 25, 2017 5:05 pm 
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Joined: Tue Jun 07, 2011 6:37 am
Posts: 10460
Location: Rio Rancho, New Mexico
Why in the world would you go to 1.5 on the slides? :shock:

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Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........


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 Post subject: Re: sticking slides
PostPosted: Sun Jun 25, 2017 7:09 pm 

Joined: Mon Aug 01, 2011 8:24 am
Posts: 184
Location: Waterloo, IA
Ja-Moo wrote:
Why in the world would you go to 1.5 on the slides? :shock:

If memory serves I was trying to get to 2. Probably got a little happy with the grinder. Any thoughts on how to fix it other than adjusting the cutaway bevel with a grinder?

Jim wrote:
Idle speed not coming down is most likely do to lean running and/or an air leak. Since it's a closed throttle problem, the needle position is not related. Air leaks can be in quite a few places, like carb boots, cylinder bases, and crank seals. Was the crankshaft rebuilt recently? If not, have you done a pressure/vacuum test to find out the condition of the seals?


I haven't done a vacuum test. I checked all of the other usual air leak points and didn't find anything. I'm not inclined to believe it is a crank seal since I can get it to idle well and the crank has less than 500 miles on a rebuild.

The only other thing that I can think of that could be contributing is my float heights. I know my KZ is very touchy when it comes to float heights, are H2's?

With all of that said:
raising the needles 1 groove has taken care of the problem. It doesn't make any sense to me but the bike runs well and pulls well in the mid range. So, I'm guessing I had a 'perfect storm' of symptoms:
My twist grip was sticking to the right handle bar, causing the slides to hang. Cleaning and lubing took care of that problem, allowing the slides to snap closed (they were not before the cleaning).
My needles were too lean (lowered too much). Normally not a reason that would cause this but....
My slides have too little cutaway, causing an overly rich condition down low. Not sure how that in combination with the needles causes the issue but ok.

None of that seems like it makes a lot of sense and I hope I am not just covering up a problem with the needle adjustment.

_________________
ride hard, ride long, ride safe!
Jason
72 h2 in a 93 Katana
03 cbr600rr
80 kz750 ltd
94 pw50


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