Jetting a gsx1100SZ with mikuni BST36SS carbs

[MSteenJ]

Hello,

I want to know if anyone has experience with the base jetting, when swapping out the carbs on a gsx1100 with a pair of bst36ss from a gsxr750.

my gsx1100sz has no modification other than a free flowing racing exhaust.

regards

Morten 

[minx]

Hey Morten. Welcome on in. 

We love photos 

Have you already done the swap and experiencing issues or just preparing? What exhaust is on it? 

[MSteenJ]

I will be home tomorrow, where i'll take some pictures.
I am just preparing for the jetting, before i get the BST36ss, which seems to be really hard to come by.
I think the exhaust is a Barracuda MGP 4-1 exhaust, with no db killer (it really screams) :-)

 

[MSteenJ]

Here the bike is but without the exhaust, (cannot get it out of the shed with it on).

 

[minx]

Looks tidy. 

BT36s are pretty agreeable across the range and were only used on a couple of years hence in short supply. If the carbs are off a standard bike that ran ok, rule of thumb for air filters & better breathing exhaust system would be to up the main jet by 11% in size. Check the carbs are original sizes too as many had the dynojet upgrades. Ideally you'd be able to get it on a dyno for a proper check but if it was me,  I'd try it out as is. With new plugs in, take it for a run and do another plug check to indicate what's going on with the mixture.

But remember, they're an old set of carbs now so you have to allow for wear and tear, they're all a little different. Depends how accurate you want to be be. 

Standard ignition? Or been swapped out? 

[Toecutter]

Agree with what minx said. Before you start messing about with carb settings, ensure your eleccy system is delivering the goods  though. Nice fat blue sparks on all cylinders, adjust one thing at a time with the carbs and go from there. Make a note of the changes you are making between runs and what the plugs look like after each run etc. The BST36 carbs are quite easy to set up to get you in the ball park before final tuning via dyno run. Ensure carbs/filters are sealed correctly before anything else as air leaks will play havoc with any adjustments. I have them on my 1100et and they transform the throttle response immensely over standard carbs. The K&n dual pods seem to work best with these carbs on the GSX range. Can't remember jet sizing off the top of my head as completed swap few years ago. I didn't need to change pilot jet size, just had to increase main jets and mess around with needle height a little. I may have the settings written down somewhere still. Will have a rummage. You can use standard throttle cable also. Just need to click it on the second position on the throttle twist grip.  

[MSteenJ]

Hey guys, been on holiday, so haven't been checking in here.

The setup with original carbs, and the free flowing exhaust works alright, at least the spark plugs tells me so. The ignition is standard, and delivers a good spark over all four plugs. 

By pure luck i would say, i got a hold of a set of BST36SS in very good condition for only 80$, i plan to attach the K&N dual flange filters as you mention. Now the question comes to what jetting i need to use. If you could find the jet sizing, that would be a huge help, but if not, i'm going to be a pro with uninstalling and installing the carbs i guess .