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Identifying jet size

  • Thread starter Thread starter cableguy
  • Start date Start date
C

cableguy

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I just got a 86 GS1150, and the PO didn't seem too connected to the history of it, or what was done to it. It does have a V&H 4-1 exhaust installed, but I have no idea if the carbs have been re-jetted to enrich the fuel mixture. It idles well, and once past 2000-2500 rpm and pulls hard without complaint. It does stumble at the point where the throttle needs to opened just a bit more to go up hill, accelerate slightly, etc., then the it smooths out and all is good. Also, it pops quite a bit on decel. No backfiring, just the pop-pop-pop on coasting from having the throttle open.

When I clean the carbs, and take out the existing jets, how can I tell if there has been a jet kit installed? I have learned that there are ID numbers stamped on OEM ones, but are those numbers standard? I'm hoping that the kit is in and the pilot jet is just gummy, but I also want to learn as much as possible in the process.

Thanks in advance for your help and advice!
 
The number should say something like "112.5" or "115" or whatever. That's the jet size.
 
OK, so are those numbers also stamped on kits? If that's the case then I would need to look up the stock size and compare it what the Dynojet size would be. Right?
 
If it has a stage 3 jet kit, the mains will most likely be stamped somewhere in the 130's (may have a "DJ" stamped as well).

please note, suzuki jet sizes are not the same "units" as dyna jet sizes...

The slide vent hole in each carb body will have been drilled bigger.

The jet needles will be slotted at the top with a clip to adjust their position, the the needles themselves will be more aggressively tapered.

The pilots & air jets have have been changed as well... are you running pods?
 
Why do you need a dynojet? The numbers are usually stamped to the 'top' ring on the jets (bottom, when installed). Some are stamped on the side.

What do your plugs look like?

Have you done a plug chop after holding it at the stumbling point?
 
cableguy said:
OK, so are those numbers also stamped on kits? If that's the case then I would need to look up the stock size and compare it what the Dynojet size would be. Right?
Click to expand...

Dynojet uses different numbers, and they are smaller in diameter than Mikunis.
Other brands of jet kits may be different too.
Look at what you have, post the numbers here. Some folks rejet using kits, other just use different size Mikuni jets, you just need to see what is in there. I don't know the spec for the 1150, but someone on here will.
How does it run at wide open throttle and high RPM? That is where the main jets are controlling fuel flow. If it runs properly wide open, the slight stutter where you open the throttle a little is likely caused by the jet needle being slightly too low, look up "shimming the needles" to learn how to fix it.
If it does have a jet kit, there will be several clip grooves to use to adjust needle height, if no jet kit you will have to use shims, as the stock needles have only one slot.
 
I'm taking it to get inspected today or tomorrow, so I'll pay attention to WOT behavior, then later in the week the carbs will be apart and I'll post what I find. Thanks for the advice to get started in a meaningful direction. I think I saw a chart somewhere that had stock jet sizes...or maybe the manual has it, I forget.
 
120 outside.
122.5 inside.
maybe 122.5 outside.
125 inside.
i forget.

if you go to "quality" air filters then you will need a st.3 jet kit period.
DON'T BUY 30 DOLLAR FILTERS!
you have to check the entire RPM range..not just wide open.
if the bike transitions bad between 4k and 6-7k it makes for a ill manured bike that is not enjoyable to ride.
 
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