1978 GS1000 carb troubleshoot

[2-Bit]

I just found this website recently and am amazed by all the info and help you GS fanatics give each other. Hope I can contribute, but first I have a problem that I need help with. I am fairly mechanically inclined but do not have all the fancy shop equipment. Here we go, my 1978 GS1000 hasn't been running as well the past year or so. I decided to start with the carb and installed a DynoJet Stage 3 kit. Reinstalled the carbs, started the bike and it idled and responded like a champ. Got it on the road and it had a nice sharp acceleration at first then it became very jerky and erratic followed by every 1/2 mile my engine started to cut out and then I have problems getting it started again. Took out the plugs and they were wet with gas/oil, and black so I suspect I am not getting a spark and that causes my engine to stall. My bike has almost all of the stock parts, E-clip is in the jet needle at slot #2, air screw is out 1 1/2, and other than that the carb should be factory set unless the previous owner tinkered with it. Any ideas where to start?

Lost and confused at the start of the riding season in the Colorado Rockies. Thanks for all the help...

[hampshirehog]

Is your bike fitted with the standard air filter and exhaust? If so you need to revert to the standard jets and needles etc. Could also be your choke mechanism is sticking open (rich mixture) or your fuel tap isn't working properly (would account for the 1/2 mile breakdown though not your black plugs).

[BassCliff]

Greetings and Salutations!!

Hi Mr. 2-Bit,

The Stage 3 kit is usually used when pod filters and a 4-n-1 exhaust have been added to the bike. The kit has larger jets to compensate for the increased air flow through the motor. If you have stock airbox and exhaust, perhaps the Stage 1 kit would suffice. But usually it's best to get the stock setup working well before you start modifying.

Now let me roll out the welcome mat for you...

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[Big T]

Okay, why did you install a Dynojet? Do you have a 4-1 header, pods?

Did you ever clean the carbs per the carb clean up page?

What does your spark look like? Do you have poinst?

[2-Bit]

Thanks for the quick response. I went with the DynoJet upgrade based on the recommendation of the Suzuki service guy I spoke with. Maybe a mistake. No pods, not too against using them. No 4-n-1 exhaust, 2 newer stock 2-1 exhaust. Previous carb seemed to be working fairly well, just could barely get over some mountain passes though due to lack of power. Cleaned the carbs when I rejetted them, though seemed fairly clean to begin with. Revert to original jets? Upgrade exhaust/pods? Not necessarily a speed demon, just want a well running bike that can hang, especially here in the high elevation(10,000 ft.). Ideas???

[hampshirehog]

10000 ft - that explains it. You've gone the wrong way with the Dynojet kit. You're running around a bit under 80% of the air at that altitude so you should decrease the size of your jets. (My chart only goes up to 2000m altitude - someone else might have a better handle on this)
Your standard set up would be (for running at 'normal altitude where us mortals live..)

Bore Size 26
Float Height 23 ~ 25
Fuel Level 3 ~ 5
Air Screw 1.0
Pilot Air Jet #15
Cut-Away 1.5
Jet Needle 5DL36-3
Needle Jet O-4
Main Air Jet 1.5
Main Jet #95

I would start by running around 90% of these figures so try an 85 or 87.5 main jet and drop your needles by a notch (ie raise the clip 1 position). You might need to change your cut-away as well but that gets expensive to do using the trial and error method.

For your slow run I'd try setting the fuel screws 3/4 of a turn back from lightly seated and play with your air screws to around 3 turns out - any more and the spring might not hold the things in place. If you can't get a decent slow run you'll have to try dropping down a size.

You're going to need to do plug chops on all this - better to run rich than weak and booger your motor.

If you drop down to lower altitudes you will also start to run weaker so you'd be best to set up a 'best compromise'.

Where are you by the way - the Himalayas?

[Big T]

That Suzuki tech is an idiot.

Ignore anything he tells you.

Your carbs are rich because you jet down, not up, for 10,000 feet.

so, Step #1 - adjust your valves if they have not been adjusted in the last 4,000 miles
Step #2 - compression test and post up the numbers
Step 3 - pull your carbs, strip them per the VM carb cleaning page and take out that Dynojet kit and put the stock parts back in with new O rings

https://www.cycleorings.com

Step 4 - If you haven't replaced the O rings between the intake boot and the head, order those also

Step 5 - check the intake boots for pliabiltity. If they have cracks or are hard, order some new ones from Flatout or bikebandit or etc

Your poor running problems are most likely from air leaks due to old age. The tech probably thought you were lean and proposed the Dynajet kit.

The bike came pretty lean from the factory, it should run good for you up there.

Do you have:

1. Racing idle?
2. Pinging at full throttle?

Inquiring minds would like to know.

[Sandy]

Like everyone suggests, go back to stock jets. Where do you live? If you consistently run at those high elevations you might consider running slightly smaller than stock jets but then it will run lean at lower elevations which could cause engine damage. I've got a box stock '79 GS1000 which is mechanically identical to yours and it's jetted totally stock. On my Yosemite trip last summer I spent at lot of time at over 8,000' and as high as 10,000' over Tioga Pass. For the most part it ran fine, 8,500 to 10,000 it was a little off but not too bad, definitely rideable. The only thing I have not stock that might help a bit is a stock replacement K&N air filter. If it hasn't been done yet a full compliment of o-rings is in order as mentioned.

[2-Bit]

Thanks for all the info. Today I will take out the carbs then return them to the stock specs. Once I get to that point, I guess I will just start tinkering with them slowly to get them adjusted to this altitude. Thanks for getting me headed down the right path. Any other ideas to boost performance in this altitude? I understand what some of the stock settings mean but will have to peruse the sight to find out what a few of them mean. I just a rookie, forgive me. Thanks again from Vail, Colorado...

[KEITH KRAUSE]

Too bad the Suzuki mechanic gave you bad info.
Sandy has it right. Stock jetting should be fine. In theory, the jetting may need to be leaned a tad but I would give the stock jetting every chance first.
95 mains. Use genuine Mikuni ONLY. Be sure they are the correct design.
Stock jet needles with the e-clips in the 3rd (middle) position. Be sure the thicker plastic spacer goes directly on top the e-clip and the thinner goes under the clip.
15 pilot jets.
The fuel screws underneath and the side air screws may need some tinkering to get right. Start with the fuel screws underneath at 3/4 turn out from LIGHTLY seated. The side air screws set initially at 1 3/4 turn out, then warm up fully and adjust for highest rpm using 1,000 rpm's as a base idle. Before first start up, you must bench synch the carbs, followed by a vacuum tool synch. This is more involved than you may be used to but the synch is very important. Much info around here to show you how and how to learn to synch if you want/need to learn.
Before any jetting/carb adjustments, be sure the ignition advance timing is correct. If points, be sure of dwell setting and good clean/not pitted point surfaces.
Also, if you think you DO have oil on the plugs, then that will need to be fixed to have the plugs fire correctly/good combustion.

[tkent02]

A stock GS 1000 with VM carbs will barely make it over the higher passes in CO, that's just how it is. Mine is jetted down as lean as I can go living at 5,500 ft, it screams from about 6,000 to 8,000, and is still a half dead dog at 11,000 and above. Get CV carbs or Fuel Injection if you want horsepower up high. Better yet turbo or supercharging. VM carbs are great at one altitude range, they just don't work well up here.
I can help you get your jetting as close as possible.

[KEITH KRAUSE]

Interesting how there are different opinions on actual performance in higher conditions running stock jetting. Some say it's adequate while others say barely rideable. I guess if the bike is ridden strictly in that high of elevation then it should be re-jetted IF the rider has tested and doesn't like the stock jetting.
If you run leaner jetting then you do correct the air/fuel mixture but you still lose overall performance. Less air to begin with and then less fuel introduced...
If the bike is ridden in lower elevations then it will run lean which is never good.
What amount of compensation are we talking about? 95 mains are stock. 92.5's or 90's? What jet needle position (which would be the most important)? A 1/2 position change? Use the stock pilot jet and lean the pilot fuel screws further?
Maybe simple advance timing changes would be better? Even tinker with the gearing (1 tooth down on the front sprocket) to gain some lost power could be easier to achieve good results and easier to change back if desired?

[2-Bit]

Alright, finally got around to removing the carbs and replaced the jets to the original (#95) size. Moved the e-clip to from the #2 slot back to the middle (#3) slot, adjusted everything to factory settings and remounted the carbs back on the bike. Back to square one. My bike always ran good, but not great. Only problem is I still have the same issue of my bike cutting out after about a half mile. After waiting about 10 minutes and using a little starter spray n the front air box it starts right up and idles like a champ. I get going again and the same thing happens. Arghhhh!!! Could this maybe be a petcock/fuel issue or is something else wrong besides the rich/lean issue? Any ideas are appreciated...

Thanks,
Steve

[tkent02]

unhook your fuel line, aim it at a bucket. Suck on the vacuum line to turn on the flow. How fast does the fuel flow?
Should be a good solid stream of gas.

[hampshirehog]

As TKent02 suggests - classic fuel tap problem. I've had this on loads of bikes and it's an easy cure.