XS360 carbs on Xs400 jetting

[Supercoyote]

I know there's a few of you out there that have done this. I swapped my 360 engine for a 400, and have the mk1 BS34's with the 17.5 pilots that are apparently a pain to get. Just wondering if anyone could share their jetting and to what surface they're doing their float adjustment from? My carbs also have screws plugs instead of drains so the "3mm below body" method won't work for me. It seems I'm running too rich/not rich enough depending how to bike warms up, and want to be sure I'm in the ballpark of jetting. Choke kills the engine unless the pilots are 1/4 turn out, which seems odd to me, but then as it warms up the idles hang like it's too lean.

 

[xschris]

Make sure the carbs are synced with a manometer. What exhaust and intake are you using. I have a 81 xs400 with xs360 carbs that uses 17.5 pilot jets third clip on the needle and 135 mains. 26mm float height from the carb body ( no gasket to do this). The mix screws are set at 1 turn to 1 1/4 turns out. The bike has stock air filters and stock 81 xs400 exhaust. My 80 sg xs400 has xs360 carbs also but has mac mufflers with stock 78 xs400 head pipes and uni 6" air filters (with NO oil on them) on the stock H-pipe. The only difference is that I run 132.5 mains. I also run xs360 carbs on my 82 sohc xs400. Same setup for the carbs as my 80 sg but with stock 82 xs400 exhaust and 4" dry uni filters on the stock H-pipe.

 

[Supercoyote]

Everything is stock. Air leaks have been searched for and not found. One exhaust leaks a mild amount from the collar. Since I recleaned thoroughly I'll have to resync them. I had set mine at 26mm from the upper lip (not the gasket surface, but the portion of the body that shrouds the joining surfaces) as per the manual. I feel as if I went any lower, I'd be running even richer. I'm a t a higher altitude (edmonton, AB) but could that really makes a difference so much I'd have to switch to a smaller pilot jet?

 

[xschris]

Set the float from the surface where the gasket goes not the lip.

 

[xschris]

It looks like you mufflers are not stock which may affect tuning. Also what plugs are you running and what is the compression on the motor?

 

[Supercoyote]

Mufflers are stock as far as I know. This bike sat outside my aunt's place for 25 years untouched so if it isn't then they're vintage aftermarket mufflers.

Compression is good, freshly rebuilt. I'll have.to double check but the plugs are stock manual recommendation.

Also that isn't my float bowl. Is that the fuel line nipple off the right?

 

[xschris]

The pic I posted is a xs360 carb body. The nipple is for the cross over pipe. What are the compression numbers? Should be around 150+ if the motor was rebuilt. Make sure to use the xs400 plugs as the xs360 used different numbers.

 

[Supercoyote]

Ah ok, that makes sense. Compression numbers were 110 before, but I'm at a higher altitude. If these seem low I'll retake to be sure I didn't have any leaking in my tester o rings.

I'll also double check my plugs. I have a near 1 volt drop from key off to key on not running. Is this normal for yours?

Here's some XS shots to keep interest in helping a fellow 360'er

 

[xschris]

My bikes that run xs360 carbs all have TCI ignitions in them.