Main jet thread too large.

[Vamisk]

On the suggestion of the forum I've finally started to go and rejet the carbs from my GS1100.

I've not messed with motorcycle carbs ever really so I apologize in advance but I ordered some main jets from BikeBandit.

These came in a bag marked Genuine Mikuni parts however the thread pitch of the main jets is larger then the orifice of the emulsion tube (?) Where they screw into.

Additionally I found that carbs 1 and 4 had mismatched jets (107, and 115 respectively) so I can't be sure even the correct tube is in there.

My question is do larger mains always warrant a slide, slide jet and pilot jet change and also if there are different sizes of emulsion tubes that I'm unaware of?

 

[Steve]

Sorry, we are going to need a little more information. :-k

It's nice that you have a GS1100, but what year and what model?

There were subtle jetting changes over the years, and the 16-valve engines in the chain-driven bikes had different jetting than the 8-valve shafties.

We will also need to know if you still have the stock airbox and exhaust, or if you have changed to aftermarket stuff.

.

 

[Big T]

No, changing main jets sizes does not require changing any other hardware

 

[Vamisk]

Sorry, I have a 1982 gs1100 L with a driveshaft I think based on the badges.
Maybe I bought the wrong jets? BikeBandit listed it for the Bs34 however. The bike currently doesn't even start currently even when I hose out a carb with starter fluid. I doubt the pilot jets have ever been cleaned.

 

[tom203]

Do you mean the thread pitch is wrong...or the diameter? Ditch the starter fluid ASAP....and these critters don't need the correct main jet to start....they need properly cleaned low speed and "choke" circuits.

 

[Vamisk]

The entire diameter of the jet thread is larger however the screw face is the same diameter. I haven't gone to the pilot jets yet because I figured they might need changed as well.

 

[Big T]

You are working under the assumption that replacing the jets will make your carbs work.
This is incorrect.
You need to completely clean the carbs and replace the O rings

You need to go to this page and read all of the links

https://www.thegsresources.com/_forum/showthread.php?196338-New-Members-CLICK-HERE!!

Especially the link to BassCliffs site and the CV carb cleaning tutorial

 

[Vamisk]

I neglected to mention that the engine will fire while cranking at WOT however will not continue to run. The main jets are just one part of going through these carbs but I want to understand what the situation is with these jets before I put everything back together and forget something. Please be patient with me, my carb experience is basically only cleaning out a Holley 4160 once in a while.

 

[Steve]

Click HERE for the carb rebuilding guide.

Can you post a picture of the jets you have? And we still don't know about the airbox and exhaust situation to know whether you still need stock jets or larger ones.

.

 

[Vamisk]

My apologies, I thought I had mentioned that someone put pod filters and a 4-1 header on it with no muffler.

It's hard to tell but the darker one (one out of the carb) is physically smaller.

 

[Big T]

You bought the wrong main jets

Clean your carbs, do the maintenance and see how it runs

 

[Vamisk]

Rest assured they will be cleaned before being put back on the bike but the fact that i have 3 different main jet sizes across 4 carbs is no bueno. While I have these apart I would at least like to get 4 main jets of the same size and since I apparently bought the wrong jets then I have the wrong model of carbs in my head.

Does Mikuni stamp a model number on the carbs In any location? I've checked several spots and found nothing

 

[Big T]

Post up some pictures of your carbs and they will be identified by the group.

Stock will be Mikuni BS carbs

 

[Vamisk]

Heres a pic of the carbs from the airbox side, I can get another one from the throttle side if needed.

 

[Steve]

Those are definitely Mikuni BS-series carbs, found on the '80-and-later bikes.

There is a model number. It is printed on the side, just below the cap. Not sure exactly which side, but it's there.
It's likely a 5-digit number on one line and some other information on a second line.
In your case, the 5-digit number should be 47160 or 47170.

.

 

[Vamisk]

Strange. My number is 49400. The plot thickens.

 

[steve murdoch]

A search turned up that 49400 belongs to an '82/'83 8 valve GS1100 G/GL/GK.
https://www.pirate4x4.com/forum/motorcycles-atvs/2162498-suzuki-standard-factory-jet-sizes.html
Third or fourth post in this thread lists the jet sizing.

 

[Vamisk]

Wow thanks, that's incredibly useful. Is there any ballpark jet size that's understood to work well for pod filters and aftermarket exhaust or is rejetting just a bunch of trial and error?

 

[Steve]

If your carbs are, indeed, 49400s, they are 34mm carbs, which are too big for the bike. :-k

It's interesting enough that the same 32mm carbs are used on engines from 550 to 850 (with jetting changes, of course), but it will be hard to get the 34s set up for your small engine.

I am also curious how somebody found boots that adapt the carbs to the head.

.

 

[Vamisk]

Well I specifically ordered new bs34 boots (previous owner thought high temp rtv was an acceptable sealer for cracked boots) and they fit right on the head. The question now is if the carbs will fit the boots. I'll go test fit that before anything else.