Author Topic: slow return to idle  (Read 1396 times)

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Offline batboy

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slow return to idle
« on: June 10, 2019, 02:03:48 pm »
Ok, I thought this was a throttle cable problem at first, but now I'm almost certain the carburetors need cleaned, probably gummed up pilot jets and/or needle valves. I have done at least 3 hours of searching through forum posts. But, before I pull the carbs, I wanted to make sure, because so far my track record for "correctly" diagnosing ZG1000 problems has not been good.

In the process of repairing a starting issue, I had the starter button apart several times. So, when I  got it back together, the throttle cable was binding up and sticking. I have triple check the throttle cable and return cable and lubed them as best as I could. I'm sure it's all back together correctly now. With the engine off, the throttle feels smooth and if I crack it open and then let go, the throttle snaps back with an audible click. I have the cable adjusted a little on the loose side, because I had heard too tight will cause binding. But, when it's running and fully warm up to operating temp, when you let up on the throttle, sometimes (not every time) it hangs momentarily at 3k or 4k rpm and then slowly returns to idle. The time it takes to return to normal idle rpm is variable. Manually returning the throttle does nothing to speed up the slow return to idle.

From hours of searching the forum, it appears I will need to pull the carbs off and rebuild them (probably has clogged pilot jets from sitting for 6 months). I'm trying to find the tool (3mm ball end allen hex key with a T-handle) in order to drain the carb bowls and see what happens and observe how much trash is in the bowls. I doubt draining the carbs will  magically fix the problem, but this does sometimes gets sticking needle valves to work again (although I don't think that's the main problem). I have resigned myself to the fact that I need to pull the carbs off. I have been reading how to do this and have watched SISF's videos. If you folks concur it's the carbs, I'm prepared to try doing this myself. I know there will be a half dozen guys telling me to have SISF overhaul them. If I get over my head, I can always send them to Steve. The bike was pampered prior to me buying it last summer and it ran fine last fall before I parked it. So, I think it's just gummed up a little from stale gas.

What does the forum think? I guess sooner or later you have to do carb work, it's basically a rite of passage for a  Concours owner, so I might as well start learning how to deal with it. I know for long term I need to have Steve do the overflow tubes to prevent hydrolocking. Eventually, I want to buy another set of carbs and have them done right. That will minimize down time. The petcock  was replaced not too long ago, so I'm hoping that it will hold up for a while longer. Bottom of the gas tank looks clean and rust-free. The previous owner was proud of that fact, because before I bought it, he opened the gas cap and shined a flashlight in there to show me it that it looked brand new. So, I don't think there's rust in the carbs, just gummed up from old gasoline.
1988 Kawasaki Concours ZG1000 - Ninja Edition
Bike has the usual accessories and modifications

Offline DC Concours

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Re: slow return to idle
« Reply #1 on: June 10, 2019, 02:18:57 pm »
If the cable closes the carbs which you can see, feel and hear then I say tackle the carbs. If you want to do it yourself great. Just make sure you don't damage anything and lose any parts. Get an egg carton so you can store the small parts.

If you do the carbs you might want to re-do the rails and change out the fuel tubing. Use OEM tubing. If you do the carbs well you won't need to buy another set. That is a waste of money. These carbs w/o any hard maintenance can easily go 50k+.


While doing the carbs I would recommend sending out the bowls to steve to get them overflowed.


Offline batboy

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Re: slow return to idle
« Reply #2 on: June 10, 2019, 02:42:29 pm »
I forgot to mention mileage... 27k.

Yes, the cables are mechanically working fine. I can see the linkage on the outer carbs moving and returning all the way to the stops. If I crack open the throttle and suddenly let go, the cables snap back instantly and readily.

I'm trying to get the bike roadworthy for a long road trip coming up in a couple of weeks, so I need to get this fixed ASAP.

There's another reason why I might get another set of carbs, but I hesitate to mention it since it's bound to spark an off-topic discussion regarding 32mm vs. 36mm carbs.
1988 Kawasaki Concours ZG1000 - Ninja Edition
Bike has the usual accessories and modifications

Offline DC Concours

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Re: slow return to idle
« Reply #3 on: June 10, 2019, 02:52:47 pm »
OH. That is a very low milage bike! 1988 with only 27K. Great find. Love low milage bikes.

I had to clean my carbs and my bike at the time of purchase a few years ago only had 7k on it. The previous owners let it sit more than ride it.

Regarding the 32/34mm, you are better off putting money in other things than changing your carbs.

Offline Stasch

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Re: slow return to idle
« Reply #4 on: June 10, 2019, 03:42:16 pm »
If pilot jets are restricted, it can cause hanging rpms on return to idle.

This is often accompanied by a turned up idle thumb screw by owners to compensate for a lag, while hanging rpms persist.

If you left untreated ethanol laced gas in there for 6 months it could have clogged some things.

Quote
I guess sooner or later you have to do carb work, it's basically a rite of passage for a  Concours owner,

Once you get them right, and proper pre-storage maintenance practices are observed, it shouldn't be an every couple of years thing.

I met one owner with 278,000 miles on his '86 C10 and the carbs had never been touched.

Mine haven't been touched for almost 15 years and 83,000 miles, and the bike starts and runs like new.  Only reason I had them off at only 16,000 miles was to put an SISF jet kit (pre 2 minute mod) in.

I have helped R&R'd several C10 carb sets from other bike's to deal with the aftermath of improper storage / maintenance.

Those memories motivate me to do proper end of season maintenance to avoid it!


Stan Visser - COG#: 6830  - - - - - - - - - - - - - - - - - - - > C10 STUFF FOR SALE - Parts List

He IS a racer, hence the forward lean!!  by: Mettler1

Offline DC Concours

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Re: slow return to idle
« Reply #5 on: June 10, 2019, 04:59:40 pm »
This will put Sisf out of business. Don't tell us your secret.


I met one owner with 278,000 miles on his '86 C10 and the carbs had never been touched.

Mine haven't been touched for almost 15 years and 83,000 miles, and the bike starts and runs like new.


Offline batboy

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Re: slow return to idle
« Reply #6 on: June 10, 2019, 05:26:01 pm »
Yes, I confess, I did not properly prep the bike for storage. I had not intended to leave it sitting that long, but we had a real winter this last year and I was also unexpectedly away from home for a long time early this spring. So, things did not go as planned. The gas left in the tank was probably 10% ethanol, since that's about all you can get in the middle of nowhere Kansas. But, this spring I've been using 91 octane gas with no alcohol. I usually put Sta-Bil in my GTO that sits all winter. Not sure why I didn't put it into the bike, other than I had planned to work on it some over winter (but, never did).

I have some time to work on it right now, think I'll start yanking fairing pieces off and then drain the carbs to see what junk comes out. I went into town and found a 3mm ball end hex key T-handle tool (to drain the bowls). I also stocked up on Gumout Carb Cleaner. I still need to find a heat gun before I actually pull the carbs off. I'll report back in a while.
« Last Edit: June 10, 2019, 05:36:47 pm by batboy »
1988 Kawasaki Concours ZG1000 - Ninja Edition
Bike has the usual accessories and modifications

Offline bajasam

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Re: slow return to idle
« Reply #7 on: June 10, 2019, 05:31:55 pm »
This will put Sisf out of business. Don't tell us your secret.


if you keep up with his posts he's finished building his new ranchito and already paid it off, he most likely doesn't care if he ever see's another set of C-10 carbs ever again..

Offline m in sc

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Re: slow return to idle
« Reply #8 on: June 10, 2019, 05:46:31 pm »
yeah, hanging idle is almost always a lean condition. time to strip and clean. (the carbs that is). check all vacuum connections, etc first.

Offline DC Concours

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Re: slow return to idle
« Reply #9 on: June 10, 2019, 05:51:50 pm »
hahahaha that is true. Kawasaki has been good to him. Never say foreign vehicles don't help the American economy. It buys a ranchito in cash plus pays off your other debts. I am in the wrong business.


if you keep up with his posts he's finished building his new ranchito and already paid it off, he most likely doesn't care if he ever see's another set of C-10 carbs ever again..

Offline crag antler

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Re: slow return to idle
« Reply #10 on: June 10, 2019, 07:17:17 pm »
This will put Sisf out of business. Don't tell us your secret.


if you keep up with his posts he's finished building his new ranchito and already paid it off, he most likely doesn't care if he ever see's another set of C-10 carbs ever again..
Lets hope not. I’m sending mine down to him  :)
Doug aka crag antler
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Offline batboy

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Re: slow return to idle
« Reply #11 on: June 10, 2019, 07:41:27 pm »
The #2 carb was really hard to get a drain hose attached. Finally got it with a pair of long needle-nosed pliers. Okay, I have all four carbs drained now. Those bowls hold more than I thought. Not sure what I expected, but the gas looks perfectly fine. No crud, no gunk, no rust (no water either). Looked and smelled like normal gasoline.

In a last desperate attempt, I'll spray the outside carb linkage real good with Gumout and spritz it with WD-40 like MOB says to do. Then try running it one last time before I knuckle down and pull the carbs off.

Seems like a lot of the young crowd will insist on trying Seafoam at this point. That stuff is way overrated, in my opinion. Besides, if jets are already clogged, how is a fuel additive going to work? I'm going to pass on Seafoam.

Carbs are now empty and drain plugs tightened (not too tight, I don't want to crack the bowl seat). Do I need to set the petcock to PRI (prime) for a minute or two to refill the bowls prior to starting?
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Bike has the usual accessories and modifications

Offline DC Concours

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Re: slow return to idle
« Reply #12 on: June 10, 2019, 08:02:54 pm »
Yes prime for 45 secs

Offline MAN OF BLUES

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Re: slow return to idle
« Reply #13 on: June 10, 2019, 08:52:55 pm »
This will put Sisf out of business. Don't tell us your secret.


if you keep up with his posts he's finished building his new ranchito and already paid it off, he most likely doesn't care if he ever see's another set of C-10 carbs ever again..

I'm pretty sure that comment would not make Steve a happy camper.. I know he has many irons in the fire, but I don't think he will ever say he's not willing to service C10 carbs.. It was his bread and butter, and he can turn them around and do it blindfolded...


as for this "failure to drop rpm" thing, check every hose, and rubber plug, along with the boots.... vacuum leaks are the prevalent cause for failure to drop to idle.

30 YEARS OF KAW.....Rich R. (the other one..)  COG 5977  JUSTAMEMBAHNOW
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Offline batboy

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Re: slow return to idle
« Reply #14 on: June 10, 2019, 09:05:54 pm »
M in SC mentioned vacuum lines too. Okay, that's the next thing to do. For the boots and vacuum lines, am I mainly doing a visual inspection (looking for cracks/obvious damage) or is there a way to test them?
« Last Edit: June 11, 2019, 11:33:29 am by batboy »
1988 Kawasaki Concours ZG1000 - Ninja Edition
Bike has the usual accessories and modifications

Offline DC Concours

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Re: slow return to idle
« Reply #15 on: June 10, 2019, 09:16:53 pm »
MOB, I'm sure he didn't mean it like that. Just that maybe Steve wants to retire, relax, smoke some pot and enjoy his free time and not mess with carbs.

Offline MAN OF BLUES

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Re: slow return to idle
« Reply #16 on: June 10, 2019, 09:23:29 pm »
M in SC mentioned vacuum lines too. Okay, I that's the next thing to do. For the boots and vacuum lines, am I mainly doing a visual inspection (looking for cracks/obvious damage) or is there a way to test them?

start with the visual/flex the lines/look close thing...
Old school trick I've used also, is get your bernzamatic propane torch... (do NOT LIGHT IT), and with the bike running turn the propane on and probe the end around the hoses, boots, plugs, anyplace that "could suck in air", and if it sucks propane in, you will hear a defined change in the engine rpm...   oh, do this outside.. ok?
 :great: :rotflmao:

30 YEARS OF KAW.....Rich R. (the other one..)  COG 5977  JUSTAMEMBAHNOW
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Offline batboy

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Re: slow return to idle
« Reply #17 on: June 10, 2019, 09:31:32 pm »
UPDATE: The intake boots look good and clamps are tight. The air box boots look fine too. Vacuum hoses looked okay and retain some flexibility.`

QUESTION: Is #3 carb vacuum fitting supposed to be blocked off? It has a rubber cap over the barb fitting. Seems odd seeing it blocked off. Never mind, I looked it up in the service manual and the diagram on page 2-2 does show that carb being capped (except the California version and mine is not from Californification).
1988 Kawasaki Concours ZG1000 - Ninja Edition
Bike has the usual accessories and modifications

Offline MAN OF BLUES

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Re: slow return to idle
« Reply #18 on: June 10, 2019, 11:36:54 pm »
UPDATE: The intake boots look good and clamps are tight. The air box boots look fine too. Vacuum hoses looked okay and retain some flexibility.`

QUESTION: Is #3 carb vacuum fitting supposed to be blocked off? It has a rubber cap over the barb fitting. Seems odd seeing it blocked off. Never mind, I looked it up in the service manual and the diagram on page 2-2 does show that carb being capped (except the California version and mine is not from Californification).

depending on model, either 1 or 2 will be capped... (not necessarily carb #1, or carb #2), just either cali models will have one capped (usually #3), and vac lines run to petcock, air pump/reed pump valve, and cali evap can...  other models only have runs from petcock, and air valve/reed pump .... thus 2 plugs.   also, don't "Tee" any together, just makes for pulse problems.

Pull the rubber caps off, and "flex them", look for cracks, same with hoses.. they crack also.

30 YEARS OF KAW.....Rich R. (the other one..)  COG 5977  JUSTAMEMBAHNOW
and if you are gonna call me names... it's MR. Analdweeb if you please...

Offline Stasch

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Re: slow return to idle
« Reply #19 on: June 11, 2019, 12:38:20 am »
OK, time to clear up something up - I am not wanting to see SISF not have to do carb work and I am pretty sure he'll continue to see them come in. 

I had mine out 83,000 miles ago to install his products, and have sent 3 other sets to him while resurrecting other's C10's that had sat a while.

Just saying once you get it done (overflow tubes, etc) you can go a long time without having to mess with them given the proper care.

The 278,000 example I saw was 4 or 5 years ago (or more ?) at Tomah, (with 258,000 mi.) WI and Mt. Snow, VT (with 278,000 mi.)

Stan Visser - COG#: 6830  - - - - - - - - - - - - - - - - - - - > C10 STUFF FOR SALE - Parts List

He IS a racer, hence the forward lean!!  by: Mettler1

Offline batboy

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Re: slow return to idle
« Reply #20 on: June 11, 2019, 12:57:29 am »
I'll be working on the bike again tomorrow morning. One vacuum line(s) has a 3 way T fitting (#4 carb goes in it) while one is capped off. I need to look at the petcock vacuum hose yet. Do you think it's a vacuum hose or is this just to narrow things down and make sure the carbs really need to come off?

Not sure how serious you were about the propane torch thing, although I'm sure it's been done under many a backyard shade tree. Many moons ago, I used starting fluid to check for engine vacuum leaks. Engine rpm changes and the sound is different too. Same basic principal I guess.

No worries, Stasch, there are enough of us dingbats around to compensate for you diligent folks. We'll keep Steve busy for a while longer. Having Steve eventually do the overflow tubes is a must and many bikes haven't gotten those done yet..
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Offline Bud

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Re: slow return to idle
« Reply #21 on: June 11, 2019, 10:04:06 am »
I'll be working on the bike again tomorrow morning. One vacuum line(s) has a 3 way T fitting (#4 carb goes in it) while one is capped off. I need to look at the petcock vacuum hose yet. Do you think it's a vacuum hose or is this just to narrow things down and make sure the carbs really need to come off?

Not sure how serious you were about the propane torch thing, although I'm sure it's been done under many a backyard shade tree. Many moons ago, I used starting fluid to check for engine vacuum leaks. Engine rpm changes and the sound is different too. Same basic principal I guess.

No worries, Stasch, there are enough of us dingbats around to compensate for you diligent folks. We'll keep Steve busy for a while longer. Having Steve eventually do the overflow tubes is a must and many bikes haven't gotten those done yet..
I believe Rich was serious about using the unlit propane torch.  No mess and it should sucked in pretty easily.
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Offline batboy

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Re: slow return to idle
« Reply #22 on: June 11, 2019, 02:57:06 pm »
Apparently, the previous owner installed a fuel filter, probably at the same time the petcock was replace a few years ago. All the fuel hoses and vacuum lines that attach to the petcock look newer than the rest. I don't see anything amiss. The rubber parts all seem to be in good condition.

UPDATE: I took the fuel filter off and while it don't look bad, I tried to blow through it and it seems partially clogged (or at least I can't seem to blow much air through it). Trying to decide whether to replace it or eliminate it. I like the idea of an inline filter. Guess I'll try replacing it (if I can find one this size).
« Last Edit: June 11, 2019, 03:51:37 pm by batboy »
1988 Kawasaki Concours ZG1000 - Ninja Edition
Bike has the usual accessories and modifications

Offline DC Concours

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Re: slow return to idle
« Reply #23 on: June 11, 2019, 04:25:11 pm »
These little inline filters are crap. Use the big napa ones.

Offline m in sc

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Re: slow return to idle
« Reply #24 on: June 11, 2019, 06:22:51 pm »
These little inline filters are crap. Use the big napa ones.

+1 big time.