UK and Australia versus USA specs GS850 carbs

[uteman]

I am doing a complete rebuild (back to frame) of a 1980/82 GS850G that is an Australian delivered bike.
I purchased a carb service kit early on on the project and am only now getting to the carbs.
What I now realise is that the after market kit being from USA suits the Mikuni BS32SS ID No.: 45110 carbs whereas mine are BS32SS ID No.: 45120 which is the same as those used in UK..
You will see from the attachment that whilst the main jets are the same others differ.
What gets me wondering is "why"?
There are many parts of USA that would similar climatic conditions to Australia so it is not for that reason.
I am not an officianado on carbs but as these carbs are 36 years old and I do not know there history I will like to install a full service kit with new jets.
Buying every jet as an individual part from the dealer is going to be quite an exercise.
Does anyone have experience with these carbs to the extent that they could tell me what the effect would be if I fit the kit designed for 45110 carbs to 45120?
I have attached an extract from a manual that shows both carbs.

[steveb922]

I'm not certain, but I believe that at the time of manufacture, US emission laws were stricter than ours (as in both UK and Oz), and so carbs destined for the US market were jetted a little leaner than the ones that came to us.

Bear in mind that jets don't normally wear. If they haven't been mangled by a PO, you should be able to clean and re-use them.

[uteman]

I'm not certain, but I believe that at the time of manufacture, US emission laws were stricter than ours (as in both UK and Oz), and so carbs destined for the US market were jetted a little leaner than the ones that came to us.

Bear in mind that jets don't normally wear. If they haven't been mangled by a PO, you should be able to clean and re-use them.

steveb922; Thanks for responding. Yes, I had thought that it may have been about USA emission laws.
I am considering just putting old jets back but as I have no history on this bike that was not running when purchased before I stripped it I guess I just have to hope that nobody has stuffed around with jets.
As a young man I was a heavy diesel machanic ( a long time back) but have little experience on multi-carb small engines.

[Steve]

The only difference on that chart is the pilot jet, pilot air jet, needle jet and needle.
All of your specs are one size richer, for better running.

Better to clean everything and put it back in, but do get a new oring kit from cycleorings.com and some new bowl gaskets.

[geol]

The assumption that US market carburetors were a little leaner through most of the operating range is correct. Note the needle jet was one size smaller. The difference is VERY small as there is not much between one size and the next. The other thing to note is the different jet needle. The US jet needles generally had no slots (such as five slots), only the one slot that made it a fixed position. The main difference is that US pilot mixture screws were set (not sure if at the factory or Mikuni manufacturing plant) and a cap was placed over the screw. The aluminum cap is largely removed from most bikes to remove or adjust the screws. I doubt the overseas models had these caps. If they do, keep in mind that the person applying the glue to hold them in place was often sloppy on Suzuki models and dripped a bit of glue into the pilot well. This effectively glues the screws and the slot on the screw head is very shallow. Even using the correct sized screwdriver, the screwhead slot can easily strip so take care removing them. Heat is often needed to move them all the way out. Under the spring that provides mechanical hold for the screw (so they don't rattle out), there is a small washer and a small oring to provide seal.

I like to change out the pilot jets for sure. They shouldn't be cleaned with an abrasive wire since this changes the size and can ruin the chamfer on the end that supplies gas and flow will splatter rather than flow smoothly. You will also get the orings and the small washer in most kits for the mixture screw. You might want to buy the correct sized pilot jets as it will allow your bike to start more easily. These are Mikuni type BS30/96 sized #42.5 as noted in the spec. I suspect the bike will work OK using the ones in the kit anyway.

[OldVet66]

Use the original parts. The aftermarket kits have a reputation for being bad news.

[uteman]

Thanks to OldVet66 for responding.
I guess I will make use of O rings and gaskets in the kit and refit most of the original parts.

[uteman]

The assumption that US market carburetors were a little leaner through most of the operating range is correct. Note the needle jet was one size smaller. The difference is VERY small as there is not much between one size and the next. The other thing to note is the different jet needle. The US jet needles generally had no slots (such as five slots), only the one slot that made it a fixed position. The main difference is that US pilot mixture screws were set (not sure if at the factory or Mikuni manufacturing plant) and a cap was placed over the screw. The aluminum cap is largely removed from most bikes to remove or adjust the screws. I doubt the overseas models had these caps. If they do, keep in mind that the person applying the glue to hold them in place was often sloppy on Suzuki models and dripped a bit of glue into the pilot well. This effectively glues the screws and the slot on the screw head is very shallow. Even using the correct sized screwdriver, the screwhead slot can easily strip so take care removing them. Heat is often needed to move them all the way out. Under the spring that provides mechanical hold for the screw (so they don't rattle out), there is a small washer and a small oring to provide seal.

I like to change out the pilot jets for sure. They shouldn't be cleaned with an abrasive wire since this changes the size and can ruin the chamfer on the end that supplies gas and flow will splatter rather than flow smoothly. You will also get the orings and the small washer in most kits for the mixture screw. You might want to buy the correct sized pilot jets as it will allow your bike to start more easily. These are Mikuni type BS30/96 sized #42.5 as noted in the spec. I suspect the bike will work OK using the ones in the kit anyway.

geol: There were no caps on pilot jet screws on either of two sets of carbs that I have.
All jets were removed without any trouble.
I will take you advice on board and thank you for your detailed response.

[pete]

Yep, different jets is all it will be to lean it out. I had the exact same situation on my 450 carbs.

The Aussie delivered bikes also have adjustable needles where the US will have only one slot in them also.

None of the mixture screws or jets will have plugs over them.

If you want to be sure about putting new jets in, mikunioz.com is the best place to go, but you will likely need to check some measurements to make sure you get the right jets, and he probably won't have needles to suit as Suzuki still seemed to put some weird sized needle in.

At least that's how I found things on the 450...

[uteman]

Yep, different jets is all it will be to lean it out. I had the exact same situation on my 450 carbs.

The Aussie delivered bikes also have adjustable needles where the US will have only one slot in them also.

None of the mixture screws or jets will have plugs over them.

If you want to be sure about putting new jets in, mikunioz.com is the best place to go, but you will likely need to check some measurements to make sure you get the right jets, and he probably won't have needles to suit as Suzuki still seemed to put some weird sized needle in.

At least that's how I found things on the 450...

pete: Thanks for the information.

[pete]

No probs, hope it helps!