Frankenbike with non-stock carbs, need help deciphering

jjdalynh

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Hello! Total newb with XS650s, bought a bobber project for my wife and am in the process of tuning and identifying exactly what we have.

This is an '77 frame, totally irrelevant probably.

The motor is from an '81 XS-H Special II.

The carbs however appear to be early BS38s (nonadjustable pilot air bleed, obvious BS38 float chamber with brass floats and needle/seat assembly as described in carbguide.pdf)

The problem i'm having it trying to determine just what the jets should be on this bike with these carbs (supposedly 1 rebuild, i'm guessing .5 mm overbore).

The pilot jets i took out are BS30 type, 42.5 and main jet of 145. The pilot appears to be of the wrong type, the float bowl is the BS38 type with the non-drilled air passageway. Further disassembly shows that the needle jet is a Z-2 type. obvious plier marks indicates it's at least been removed before. I need to get some longer c-clip pliers to get the needle out to see what type it is though.

Based on this info, does anyone have any further suggestions for determining the exact carb year and what would be a good starting point for jetting this 81 motor (open foam air cleaners and drag pipes). The plugs are kinda oily looking, so i'm thinking it's pretty rich, but i do get deceleration popping..... Also, the thing kicks over on the first try with barely any need for the choke. (which i haven't disassembled yet, perhaps a leaky enrichment circuit is the cause of the richness....). Anyways, any pointers on what else to investigate (i will be figuring out the needle situation today)?
 
Those sizes would be around 2-3 steps up on 78-79 spec carbs. That's all the help I can provide except a pilot that rich is going to over step the screw and damn near eliminate the need for an enrichener to start, but it'll get blubbery when it's hot like that, I'm bettingi have K&N filters in the stock air box and I'm up one step over stock on the main and pilot. It works well. They tend to run like mess with the 76-77 jets in the 78-79 bodies. Several instances of this reported here.
 
ok, these are definitely later BS38. single throttle control. stepped,o-ringed mixture screws (2.75 turns out!) needle secured with snap ring. also, there is no vent in the fuel bowl, there is a brass pipe on the edge of the carb body which looks like the vent to me. a question: i presume that fuel bowl gaskets are now universal, the ones i have installed have an extra hole near the air inlet to the pilot that would match up with the early-style vent tube. i'm guessing this is of no consequence.

i believe though that i should switch to the VM22 style pilots.... the o-rings in the needle jet and the mixture screws need replacing they are pretty ratty too. anyone have any clue what size o-rings they are? (i have a digital caliper, i may just have to measure them i guess.)
 
The o-ring info is in this forum, somewhere. Here's a chart:
XS650-Carb-Orings.jpg
 
If you need long reach E-clip pliers to remove the stuff from the slide, you have the 78-79 carb set. Those were the only years to use that set up.
A few other clues are the 502 needles and the Z-2 needle jet. Stock uses a 135 main, 27.5 pilot. 2 1/4 turns out with 24 mm float height.
The brass tube in the float that comes down from the carb body into the float bowl is the pick up for the enrichener. At the bottom of the hole that tube goes down into is the starter jet, a non replaceable jet. Be sure that hole and jet are clean.
An over flow tube comes up out of the bottom of the float bowl.
Leo
 
So based on a this I have 78-79 carbs that have (the wrong) BS30 pilot jets and probably too-rich mains. I'm pretty sure that this sucker will be completely torn down this winter to see exactly what's what, I just want it to run good enough to have the wife comfy enough to practice riding.
 
But for a newby to practice, spot on carbs are a must.........
The old KZ305s are perfect starter bikes, very low first you could let the clutch out without throttle and it would go.
 
If you want the wife to be comfy fix the carbs as gggGary suggested. Not safe to ride a bike not running properly especially a new rider.
 
Agreed, which is why in going through all this and not just throwing her on it. Plus, as an engineer I'm *compelled* to ensure that everything is as right as possible.
 
A couple of pics tossed up here might be a good idea. There is a possibility of float bowl mismatches creating issues. Check out throttle shaft slop/seals that can make accurate carburetion very difficult.
 
got the needles out, 502 needles, 5th (bottom) clip with a washer on top. go back to clip 3 with no needle to start? couldn't hurt i suppose.
 
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