GK hesitates at 3000 rpm

[Redman]

On this GK I got in November, I have cleaned out carbs and it runs a lot better now. BUt still have one situation, especially in first few minutes, it idles well, can turn choke down and then off in less than a minute or so. Seems to rev up okay, but when I pull out into the road and accelerate, then it will hesitate and boog at about 2500 or 3000, doesnt accelrate thru there for a while, then takes off. Then after it is warm-warm after 5 minutes or so then it doesnt do that as much, after 10 minutres its not hardley noticable at all.

I know that sounds like a carb problem. I previously had carbs all apart, all jets taken out and cleaned with carb cleaner and probing the little orifices with a stiff wire. Well, I didnt take out the pilot screw air jet that is under the metal plug, but did spray carb cleaner in there from both directions.

What else can it be that goes away as it gets warmer and perrty much goes away when its hot?

How about those rubber plugs inside the float bowl over the low speed jet. Three of my four seemed a bit hard and fit in not so snug, not like they are going to fall out, can wiggle just a little bit. Whats the chance thats my problem?

And just for some quantifiable preformance spec I have this: In top gear, max speed/rpm tops out at 7000rpm, judging by 55 mph at 3500, that would be 110mph. That what I should expect for a GS1100GK?

 

[tfb]

I had a problem similar (in a way) to this with my GSX1100 Katana. It turned out that the fuel mixture was hopelessly rich at about the rpm you describe. Reason? Previous owner (or maybe even the one before that) had raised the diaphragm needles by one notch. I returned the needle circlips to the standard (center) notch and the 'flat-spot' and hesitation completely disappeared.

Now the thing is, the problem was the other way around to yours: it was hardly noticeable when cold, but the warmer the engine got, the worse it was. So if my problem was a mixture that was too rich at that spot in the rev-range... yours might be that it is too lean.

Leanness has other causes, too... eg. leaking inlet manifolds. Might want to ensure one or more of those, aren't sucking in extra air.

BUT the fact that the problem almost disappears when warmed up, suggests that it is not that far out.

Besides the needle clip settings, another possibility is the pilot jets. Try fitting a richer set, if all else fails.

Sometimes it's just quicker and less heartache with these fuel metering problems, if you get the bike put on a dyno; takes all the guess work out of it, and a skilled operator can give you some suggestions about how to rectify what is revealed on the readouts.

Question: is your engine in bog-standard form, or has it been bored out, K&N filters, etc. all the usual mods?

I don't really know what you can expect from the GK in terms of top speed, but 110mph with that huge fairing seems a pretty impressive clip to me!

Keep sleuthing,
Mike.

 

[Redman]

Stock - Stock Stock. Only 28 thous miles.

WHen I had carbs apart I didnt notice anything about clips on the diaphram needles, quess I didnt know to look. Duh.

Adamgagne posted about similar symptoms, siad he had one of the four rubber plugs missing. My four plugs are hard and not dont fit real tight.

View attachment 323

 

[83'GK]

Thats becasue there won't be, the GK's carbs are non-adjustable in regards to needle height, at least the USA ones arent. When you had those carbs off, ddi you by chance replace the intake 'O-Rings' located on the removable manifolds? If they are stiff and hard, they will leak, and it will run lean, and match the problem you are having.

 

[Redman]

83GK,

No didnt replace manifold o-rings. You are refering to the ones in intake boot up against the head, right? Didnt have any reason to think they were bad. My understanding is that if those are bad then it will idle way high when warm, but maybe thats if they are real bad. Maybe I can check them, have heard of the test of spraying WD40 where the boots meet the head while bike idling, and see if it effects the idle speed. Sound like a good idea? Both these ideas are what I have seen mentioned here on GSR, dont have the practical ecperience myself.

 

[tfb]

OK, well if your engine is stock, and the carb. settings are stock, we should be looking for air leaks somewhere. Try the WD40 thing; if you notice any change in rpm then you'll have an air-leak.

What do the spark-plugs look like? You might be able to tell from them which cylinder(s) are running lean.

Mike.

 

[Redman]

Bingo.

Tried the WD40 spray test. Had engine idling at about 1000, sprayed WD40 where intake boots meet up to the head intake, both sides of each four. Didnt have any effect on the idle speed, but with a good light I thought I saw the WD40 getting sucked into the boot on outside of #4. Did same thing with starting fluid, engine about died. Ah Ha! So apparently I do need boot o-rings. The boots themselves seemed soft and plyable when I was removing/replacing carbs.

Thanks Guys.

Scheesch. This '82 GK I bought with 28K miles has more problems than I have ever had with my '82 850G that now has near 70K. Well, have taken care of other problems - one at a time, will get there.

 

[83'GK]

Alot of times those low-mileage bikes have been sitting and basically rotting away. I had to change mine and it made a big difference. You will be suprised at how bad and hard they get, but remember they are 20+ years old!

 

[tfb]

Yep, low mileage is great, but some things -- esp. rubber -- get hard regardless of usage. I'm glad you've nailed the problem!

Mike.

 

[KEITH KRAUSE]

Yup. If the problem gets better as the bike warms up, it's a lean problem (if carb related).
Always a good idea to change the manifold o-rings.
Apply a coat of high temp bearing grease to help them last and torque to 6 ft/lb.
Not positive your problem is the manifold/manifold o-rings, but let us know.

 

[tfb]

PS. Nice-looking GK too, Dave.

 

[Redman]

I'll get better picture of the GK under better lighting sometime, but, yah, did a lot of rubbing and shineing (although nothing like Keith Krause would do) over the long winter months.

SO those testing did find air leaks between the intake boots and the heads as described above. Have ordered replacement o-rings, at $2 each I should have done that when I had carbs off (have also ordered the rubber plugs under the low speed jet). Back when I had the carbs off, I did inspect the intake boots, they were still soft and plyable, so I didnt look any further.

WHat I did do as a further test was this: Took a dab of axle grease and worked it in between the intake boot and the head in places where I could reach. Went for ride, the hestitation/bog was greatly reduced, and went away much faster, went away when bike was only a little bit warmed up after just a minute or so. So I am fairley convinced the o-rings will take care of the problem. . . . . AND AND AND this should be the last problem.

 

[argonsagas]

II don't really know what you can expect from the GK in terms of top speed, but 110mph with that huge fairing seems a pretty impressive clip to me!

Keep sleuthing,
Mike.

The GK will cruise at 110. I think the longest I did that was about a half hour, before running into a bit of traffic.


Unfortunately, if you do not have lowers on it, above that speed you can also expect some lifting on the forks as the air gets under the fairing. The bike is very stable at that speed, and higher if the wind is calm or behind you. Mine has found its way to 125 while in the company of a couple of others, and that was with the carbs running a bit rich.

It has not caused me any problems, but the lightening is noticeable, so I stay away from those speeds.


I have not hit that speed with lowers mounted on the bike, so I cannot comment on what the difference may be.

There is a second drawback to running the big bike at high speeds, and that is gas consumption. It is perhaps more efficient than an un-faired bike at lower speeds, but at high speed it sucks its fuel quite heartily.

 

[Giblet]

Dave, you are having the same problems I had, most due to sitting up. Good news is the engine should be in really good shape but anything rubber can be a problem. I replaced the carb plugs when I replaced the needle & seat valves, o-rings, etc. The o-rings between the carbs & intakes sound like they need to be replaced too. I had a similar "bog" that I diagnosed the same way. They are only a couple of bucks fom Suzuki (unless my memory is bad). Get OEM ones. The hardware store variety may not stand the heat. Let me know if you have trouble getting them. Watch your #2 cylinder for carbon fouling. The vacuum OEM petcocks are bad about developing a leak through the diaphram and will foul that plug. 85 is no stretch for the GK but,I don't recommend anything over 85mph on a GK. Things start getting squirrely around that speed if the wind hits you just right.