i have a set of mikuni bs38 cv carbs, been told there 79/80, least that is the motor, does any one know what the 2 screws above the bore where it mates with the mounts? i think it's like an air thing, only leads just inside the bore in front of the butterflies , thoughts? can't find a picture anywhere.
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screw?
- Thread starter jerry67
- Start date
Air mix screws? Give us some pics of the carbs so we can see what model and what screw you're referring to.
Those aren't 38's... they're BS34's. The needle should be set to wherever it works best. Look in Tech. There's a PDF on carbs. It's pretty much the bible on 'em.
Jim did i measure the bore in the wrong place, got 1 1/2 inch works out to 38 mil, but won't argue with you
You don't need to take my word for it. Look at the carb guide I mentioned. It explains the differences.
If you have an adjustable needle then it's the Canadian one or the "world" one. The U.S. didn't get that adjustable needle, ours was "fixed" with only one clip slot. There's not much info on where that adjustable needle came set from the factory but the middle slot would be a good place to start. That was the normal stock setting on many factory carbs.
opps my fault, when i got the ser# run it came back yes a candian model, that's were i found the clip on both, middle.
got to ask someone, since i have to re jet main has stock 132.5 going to 135 or 137, pilot is 42.5 thinking 45, am i in the ball park? thoughts?, do i need a new needle also? should just buy a dyno kit from mikes?
Pull knob choke and float bowls with the drain screws on the side would indicate an '81 set, but all that stuff could have been changed or swapped. Are the floats brass or black plastic? Black plastic would be another '81 indicator.
I would stick with those adjustable needles, they're quite desirable from most accounts. Your jetting changes look good - 2 up on the mains to a 137.5 and one up on the pilots to a 45. You'll also want to check the air jet size. In the States we got a #135 but you may have 130's. The air jet is for the pilot circuit and can be used to fine tune it. It doesn't have as big of an effect as changing the pilot jet.
Yep.
Stock/modded engine, air filters and exhaust info is all needed to determine a starting point for jetting.
floats are brass, seen them reading the jet size.
is the air jet then same thing as the air mixture screw?
No. The air jet feeds air to the air mix screw. It's more complicated than that, but no... two separate components.
The air jet actually feeds the air to the pilot jet. So, by changing it, you can alter the strength of the air/fuel mix in the pilot circuit. It is located in the bell mouth where the air filter mounts .....
As I mentioned, it doesn't have as big an effect as changing a pilot jet. For example, if a 45 pilot was too lean but a 47.5 pilot was too rich, you could achieve a richness level in between those sizes by running the 45 and reducing the air jet a size or two.
So, the air jet is an actual jet you can change. They used a small round main jet, like used in the BS38s, except in this case, it flows air.
As I mentioned, it doesn't have as big an effect as changing a pilot jet. For example, if a 45 pilot was too lean but a 47.5 pilot was too rich, you could achieve a richness level in between those sizes by running the 45 and reducing the air jet a size or two.
So, the air jet is an actual jet you can change. They used a small round main jet, like used in the BS38s, except in this case, it flows air.
The air jet actually feeds the air to the pilot jet. So, by changing it, you can alter the strength of the air/fuel mix in the pilot circuit. It is located in the bell mouth where the air filter mounts .....
As I mentioned, it doesn't have as big an effect as changing a pilot jet. For example, if a 45 pilot was too lean but a 47.5 pilot was too rich, you could achieve a richness level in between those sizes by running the 45 and reducing the air jet a size or two.
So, the air jet is an actual jet you can change. They used a small round main jet, like used in the BS38s, except in this case, it flows air.
