Carb setup suggestions for GS1000G

[JTGS850GL]

Getting my, new to me, 1980 GS1000G ready to fire up. Carbs are off and in the process of a rebuild. I'm waiting on the O-ring set from Cycleorings.com. I did pick up a couple of rebuild kits just for the MISC parts that I anticipated needing and a couple extra new float bowl gaskets. Sure enough I found a couple carbs that were missing the rubber plugs over the pilot jets, one of the pilot jets was pretty screwed up, one was completely missing the float valve and one didn't have the o-ring that covers the metal plug. All needed new float gaskets. Ordered a new valve cover gasket so I can start on the valve adjustment while waiting on parts.

While I'm into the carbs I figured a little tweaking wouldn't hurt.

The mains were 140 OEM Mikuni

The pilots were 40 OEM mikuni but one a little buggered up at the screw slot. Jet portion is not damaged.

The pilot air jets were 160 OEM mikuni

So, it looks like the carbs came from a stock 1981 GS1000.

I'm planning on keeping all the stock jets but I was going to shim the needle jet a little. The stock height of the washer measured in at 2.44mm. I was planning on sanding them down to about 2.00mm. Should I go thinner or leave them alone

The bike currently has the stock exhaust and I will be installing a K&N stock type filter in the OEM air box.

Does this sound about right? I do have 120 mains sitting around. Should I install them or keep the 115's?

I also found one of the intake boot screws missing, or at least that's what it looked like until I removed the boots. Turns out that some PO had broken the bolt head off and just left it that way. I'll have to drill and tap that one out before I install new boots.

Always amazes me at what you find when I get into an older vehicle with no known history.

[Steve]

First of all, I have to ask: any mods to the intake or exhaust?

If the bike is all STOCK, you should have 115 mains in there.

The 40 pilot fuel and 160 pilot air are stock, so no worries there.

Hate to say it, but you probably wasted your money on the carb kits, just to get the few parts that you might need. Bowl gaskets are readily available, as are the rubber plugs over the pilot jets.

Did you also get the intake boot o-rings and stainless screws from cycleorings? If not, get them.

When you get the carbs back together, set the mixture screws three full turns out, to start, then when the bike warms up, do your carb sync and tweak the mixture screws for best idle. If you didn't already know it, leave your vacuum gauges connected while setting the mixture screws. When the engine is running its best, the vacuum level will be just a bit higher on all the cylinders. Watch for that while turning the screws SLOWLY.

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[JTGS850GL]

Thanks for your input Steve. The kits were only $4 extra each then the float sets with the float bowl gaskets. I really wanted new float valves since the ones in there were all leaking badly and one was even missing. The reason I picked up the kits was because the extra little pieces I needed couldn't be purchased alone from the same vender and the shipping from another vender would have cost more then the extra cost of the two kits. Even if I wasted some money I gained piece of mind since I knew that any of the stray parts I needed were going to be there when I needed them. Hell... I can always use the parts on my next GS.

As for mods, the only mods to the bike would be the K&N air filter. I've also verified that the exhaust is completely stock for a 1000G based on the engraving on the mufflers that say GS1000G. The exhaust looks to be in pretty good shape except for a small amount of road rash on the underside of one side. The rest of the bike doesn't seem to show any signs of being dropped. I sanded down the needle jet washers a little just to improve cruise drivability. I still have 4 washers that are stock thickness. Easy to change out without removing the carbs.

The big issue so far is going to be getting that broken screw out of the intake. Probably going to have to grind the remaining part of the screw flat, drill and then tap a new hole. Any other suggestions? The screw is broken off almost flush with the surface of the head.

[Steve]

Sounds like you will be looking for some main jets soon.

The general 'rule of thumb' is to add about 4-6 sizes for pods (congrats on choosing good ones ), so you will be looking for 125-130s when you get them. Z1 has a good price on jets, but I don't think they are Mikuni.

To raise the needle, you do realize that you reduce the thickness of the shim above the clip, right? Most of us will use a short stack of metal washers, rather than sand down the stock spacers, but that's OK. Your sanded washers might have a better chance of being the same thickness than stacks of random washers.

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[JTGS850GL]

The filter I'm talking about is the K&N filter that fits into the stock airbox. No pods right now. That's why I'm going to either stay with the stock 115 mains or just jump to the 120's. I was just thinking that the 1980 ran just a tad lean from the factory so fattening up the needle range and upping the mains one step might be a little smoother then pure stock.

[duaneage]

I would get it running right with stock air box before any mods, that's just my opinion.
I have 42.5 pilots in mine, I've seen three sets of 1000G carbs and all had 42.5 so maybe that means something.

I have a V and H street pipe and it runs pretty good with 115 mains, and 42.5 pilots with an otherwise stock arrangement. I discovered the floats were set way too high, the PO was trying to rich it up for a 4-1 he had. I would take everything to stock and tune from there.
I might try 116.4 ( DJ 124) jets or 117.5 and see how the top speed plug reads look. If that is not brown I'll shim the needs and do a few 30 - 60 timed tests and see if it makes a difference.

The point of all this is to start with a known baseline before you venture off into tuning based on someone's advice or guesses. A lot of things can throw off a tune so start with known parameters.

Pods are going to change the bike a lot, I would reconsider since the 1000G is real easy to remove an airbox from and the performance gains are minimal at best. You should see 40+ MPG from it in stock form, but with pods, a DJ 3 kit, et al I would think mid 30s would be about right.

Good luck with it and let us know how you make out.

[duaneage]

"The big issue so far is going to be getting that broken screw out of the intake. Probably going to have to grind the remaining part of the screw flat, drill and then tap a new hole. Any other suggestions? The screw is broken off almost flush with the surface of the head."

I had the same problem. Fortunately the head was off for a rebuild. I started with 1/8 n bit about 1/8" deep to get it going and went through the drill index until I got to 19/64"
I picked out the first three threads with a dental tool and used a tap to take out the rest. About 4 hours of work. But I ended up with a completely clean hole when i was done.
I would consider removing the head for it, there just isn't any room to work in there as it is.

[JTGS850GL]

I'm not going with pods. The filter is a stock type K&N so jetting will remain stock except for a slight movement of the needle upwards by about .45mm by shaving the plastic spacers.

I checked and I have enough room for the drill and bit if I chuck the bit deep. I'll work slow with a left hand drill bit and see if I can get her to spin out. If not, I'll have to tap a new hole. Already have the 6mm x 1 tap so now I'm just waiting for a little warmer day to work in the unheated garage. Don't want to be cold and shaky when trying to drill a straight line.

[Guest]

I'm not going with pods. The filter is a stock type K&N so jetting will remain stock except for a slight movement of the needle upwards by about .45mm by shaving the plastic spacers.

I checked and I have enough room for the drill and bit if I chuck the bit deep. I'll work slow with a left hand drill bit and see if I can get her to spin out. If not, I'll have to tap a new hole. Already have the 6mm x 1 tap so now I'm just waiting for a little warmer day to work in the unheated garage. Don't want to be cold and shaky when trying to drill a straight line.

Don't shave the spacers
Get some washers from Radio Shack and replace the spacer with less height of washers.

[koolaid_kid]

Don't shave the spacers
Get some washers from Radio Shack and replace the spacer with less height of washers.

Radio shack sells a variety pack of SAE washers; the small ones are "close enough". If you want to do it right, go to Ace Hardware and buy stainless steel washers (3mm IIRC). 5 per carb is stock. Many reduce the count to 4, which is the equivalent of shaving the spacer.

[twr1776]

02-09-2014 07:32 PM JTGS850GL The filter I'm talking about is the K&N filter that fits into the stock airbox. No pods right now. That's why I'm going to either stay with the stock 115 mains or just jump to the 120's. I was just thinking that the 1980 ran just a tad lean from the factory so fattening up the needle range and upping the mains one step might be a little smoother then pure stock.

I have a similar set up with the K & N filter, stock box, and V & H pipe and bumped the pilot to 42.5 and the main to 120 and shimmed the needle with I think with two of the Radio Shack shims instead of the stock spacer. Plugs read black but no fouling so I have left it alone.

MPG depends on the right hand but is usually around 36/37 but can be in the low 30's.

[JTGS850GL]

"The big issue so far is going to be getting that broken screw out of the intake. Probably going to have to grind the remaining part of the screw flat, drill and then tap a new hole. Any other suggestions? The screw is broken off almost flush with the surface of the head."

I had the same problem. Fortunately the head was off for a rebuild. I started with 1/8 n bit about 1/8" deep to get it going and went through the drill index until I got to 19/64"
I picked out the first three threads with a dental tool and used a tap to take out the rest. About 4 hours of work. But I ended up with a completely clean hole when i was done.
I would consider removing the head for it, there just isn't any room to work in there as it is.

Got the screw out. Had to drill and tap it but all is OK now. I tried to use the left hand drill bits but it wouldn't budge. I was able to get the drill into that tight space but only after I ground down the shank of the drill bit to gain room. The butt end of the drill was almost against the battery housing but I was able to drill straight through the original bolt with little variance in angle. Got lucky I guess.

Carb boots are installed and almost ready to install the freshly rebuilt carbs. A GSR member is sending me a replacement stock oil pressure switch housing to replace the the oil cooler adaptor. Once that arrives I'll be installing the carbs. Z1 is shipping out the air cleaner box intakes so once they arrive I'll be ready to fire up the beast. I still have to do the valve adjustment before that though.

I love bringing older machines back to life. They seem to appreciate it more.

[Guest]

I am running the same set-up you are stock 1000, stock exhaust , stock air box with K&N filter I am running a 122.5 main and stock pilot and air jets . The bike runs great.