Need Help with Carburetor Air Jet

[Guest]

I've installed the 1150 carbs (fully rebuilt) on my 1100 (air pods and MotogpWerkes exhaust). It runs like crap. Its got a slow reponse when blipped and a hanging rpm before dropping to idle. I tried turning out the fuel mixture screw 4 turns with no improvements.

Here is the setting I've got on the carbs right now:
-Air Bleed Jet: 170
-Pilot Jet: 45
-Main Jet: 138

So, I went and checked the Haynes manual and was shocked to find out that the 1150 came stock with 125 Air Jet, 47.5 Pilot Jet, 120 and 122.5 Main Jets.

My questions:
-Why did the 1150 come with a 125 Air Jet when the 1100 came with 170 Air Jet?
-What should I do to fix this?
-Should I get a smaller Air Jet?
-Should I get a bigger Pilot Jet and Main Jet?

Here is the setting that I'm considering. What do you guys think?
-Air Jet: 125
-Pilot Jet: 50
-Main Jet: 165

[kdo58]

what do the plugs look like?
hanging idle is usually an air leak, maybe to lean,

[chef1366]

Dynojet stage three kit #3133
Get a 125 pilot air jet

[Steve]

Why was the jetting so different?

Because they had different carbs.

According to the chart that I use, the Canadian model (sorry, that's all I have ) 1100E had 112.5 mains, 47.5 pilot fuel and 160 pilot air jets in BS34SS carbs.

The 1150 used BS36SS carbs and had 120 mains in the outer carbs, 122.5 mains in the inner carbs, 45 pilot fuel and 125 pilot air jets.

Assuming the general rule of thumb for increasing jet sizes, you would add 2-4 sizes for a pipe and 4-6 sizes for pods, depending on the flow capabilities of each. Let's go middle of the road at 3 and 5 sizes, for a total of 8. That means that you would go with 140 in the outer carbs, 142.5 in the inner carbs.

Now, let's toss in the fact that you are installing these carbs on a smaller engine than what those jetting specs are designed for. Following the example of the smaller bikes (the 550, 650, 750 and 850 all used the same size carb), I would knock those sizes down by 1 or 2 and start there. Your idea of starting with a 165 is going to have you WAY rich. Your pilot fuel jet will not need to be as large, either, I would go with the 45s, but have the 47.5s on-hand. For the pilot air jet, it would depend on which pilot fuel jet you go with. If you go with the 45, go with a smaller air jet, probably the stock 125. If you go with the larger 47.5, get a larger air jet, probably close to the stock 160.

By the way, if your main jets are 138s, they are likely DynoJet jets. They are the same size as a 130 Mikuni.

.

[dagreatgatsby]

Dynojet stage three kit #3133
Get a 125 pilot air jet

I've already got that kit. The kit doesn't come with a 125 air jet. However, I am using the 138 main jet and needle (e-clip on 3rd groove from the top) from the kit.

what do the plugs look like?
hanging idle is usually an air leak, maybe to lean,

I'm not sure what plug you're talking about. If you're talking about the rubber plug that covers the pilot jet, I replaced them with new ones when I rebuilt the carburetors. I checked for an air leak around the carburetor tubes and couldn't find any. I agree that the carbs are running too lean; probably because the 170 air jets are too big.

Your idea of starting with a 165 is going to have you WAY rich. Your pilot fuel jet will not need to be as large, either, I would go with the 45s, but have the 47.5s on-hand. For the pilot air jet, it would depend on which pilot fuel jet you go with. If you go with the 45, go with a smaller air jet, probably the stock 125. If you go with the larger 47.5, get a larger air jet, probably close to the stock 160.

I've decided that I'm going to set the carburetor back to stock specs except the main jets. My Haynes Manual says:

Air Jet: 125
Pilot Jet: 47.5

I'm going to keep the Dyno Jet 138 main jets in there until I've ridden the bike around and see how it feels.

[chef1366]

"What does the plugs look like" is referring to the spark plugs. You can read them to determine if you are running rich or lean.

[chef1366]

http://www.motorcyclecarbs.com/_B42_55_125_MIKUNI_AIR_JET_P2162C13.cfm

[Steve]

I've decided that I'm going to set the carburetor back to stock specs except the main jets.

"Stock" for which bike?

It would be better to jet "stock" for the 1150, knowing that it will be a little bit rich, then go from there.

Whichever way you go, make systematic changes, and only change ONE thing at a time, or you won't know which one of your several changes is actually working.

.