BS 38 Carb Guru question

[hard_y_rd]

Quick question for you carb gurus. I have stock BS38's from a 73 TX650. I was putting an order together for some carb gaskets and such. It says on MikesXS (XS650direct) that the 70-73's don't use a carb choke body gasket. Mine had one on there (choke lever side) but not on the other. Should i buy the gasket or put one on both sides or none?
Also the jets that were in the carbs were 120 Main and a 42.5 pilot jet. I thought the main was supposed to be at least 130. If i ever fire the bike up and get it running, i'm probably going to have uni-filters and a custom exhaust like the high pipes from Dan at Pandemonium.

 

[TwoManyXS1Bs]

Hi, hard_y_rod,
My mindset, in situations like this, is:
1 - Previous owners, a wonderfully ingenious group, sometimes do things beyond comprehension.
2 - Post-mortem on a strangely configured part is a fascinating passtime, could start a game show.
(Like Jeopardy - Alex, the question is: "Why is the head mounted backwards")
3 - To maintain sanity, completely disassemble, inspect thoroughly, reassemble per the book.

My 2 cents...

 

[5twins]

The problem with the choke set-ups on the early carb sets is there's not much info available on them. The parts diagrams show the choke assemblies for the '70-'71 and '76 -on BS38s but no info is given for the '72-'75 sets. These particular sets are the ones using one choke assembly on the left carb and sharing it's rich starting mix via a cross-over tube with the right carb. There is no choke on the right carb, just a blanking plate where one would mount. I have a '72 set and it's like yours - gasket on the left carb, on the choke assembly, no gasket on the right carb under the blanking plate. This set has been "worked" so I have no idea if that's correct but I almost think it might be. The right carb doesn't need a gasket there because nothing is happening through that choke area. In fact, I don't even think there is a choke take-off tube in the bowl on that carb which means no fuel would go up into the choke area. The passageway for that tube may even be plugged.

 

[hard_y_rd]

Thanks 5twins, what about the 120 main jet and 42.5 pilot. Would you bump those up fora custom exhaust and uni filters?

 

[5twins]

The 120 main for sure, the pilot maybe, you'll have to see if it needs it. I would at least go back to stock on the mains to start. You will probably need a size or two up from that but it's always best to try stock so you have a baseline from which to work. The pilot may be fine as long as you don't lean the needle settings. If you do, which is a common need when increasing main jet sizes, then you probably will need a larger pilot.

I have no idea why someone would reduce the mains 5 sizes from stock, that's a big jump. Maybe there were other problems with the carbs like bad floats or float needles and seats that were causing rich running and they tried to "fix" that with smaller mains.

 

[hard_y_rd]

So i wish i kept my original carb choke gasket. I ordered the 7 hole for the 74 model. i figured it would work but the holes don't line up. There is not a gasket even listed for a 73. Where do i get one.

 

[seven4eight]

I have run into the same problem, I had a gasket on one side on my 73 TX. I know the carbs have never been serviced, it had to be from the factory. Oh well, putting it back together without one

 

[hard_y_rd]

I think the 8 hole gasket might work from Mikes. Just haven't ordered it yet.

 

[XSLeo]

Make one. Use a cereal box. Put the part on the box, trace around it. Mark the holes. Cut out. Get a set of hole punches. Punch holes.
You now have a gasket.
A thin coat of grease on both sides, install. Be happy.
Leo

 

[hard_y_rd]

It's hard to be happy Leo when you're OCD. Lol

 

[dave650]

Question for all. I have 1975 bs38 carbs bought off ebay, one carb is not giving the
Right side cylinder fuel ........ is it cheaper 2 rebuild both carbs.,? or just buy new 1s ?.. if so where do I get the best carbs for my xs650 cheap but new......any suggestions??????? Thanks

 

[5twins]

New carbs will set you back $400 to $600. A "rebuild" usually consists of a thorough cleaning mostly. Most of the original parts can be re-used so it costs very little. If you're careful not to damage them, you can even re-use the original gaskets and I recommend you do. They were very good.

But ..... this all depends on whether you know a thing or two about what you're doing. Let me relate a little story that just happened recently. I'm helping a numb-nuts, know-nothing newbie across town rebuild his 650. Well, I should say he's (somewhat) helping me, I'm doing the work. He's mostly cleaning parts (and he's not very good at that either, lol). Over the last several years, I've been into his carbs more than a few times, at first just to check them, then a full tear-down and cleaning. I was careful and was able to re-use everything. Now he let the bike sit for a year without draining the carbs. I told him they should be looked into because they may need a cleaning. He took the float bowls off and promptly broke both bowl gaskets in the process. The bowls were green inside, lol. After he cleaned them, they were still half green inside, lol. Like I said - numb-nuts ..... know-nothing ..... newbie. If you're a guy like this, buy the new carbs.

 

[dave650]

Thanks 5 twin.. well I am kinda new, but. I know both rubbers up top have to be replaced. Those cost 150 or more a peace as far as all the needles idk about yet. Do you think I should buy a cheap carb just to practice on first. ? ????

 

[5twins]

There's a place called JBM. They sell just the replacement rubber diaphragm for these at around $50 a pair. Yes, a complete slide/diaphragm assembly is expensive, but you needn't go that route. Working on carbs isn't hard, it just takes a little finesse. Most of the parts are soft brass or aluminum. You need good fitting screwdrivers and mustn't over-tighten things. You can send them out for a complete overhaul but that will cost you about $300. I don't know what to tell you really. They say knowledge is power but in this case, it's just a real money saver. If you do some studying and gain some carb knowledge, and you're careful (remember the "finesse" part), you can probably handle it. It's not rocket science (although it may as well be to some, lol).

 

[XSLeo]

Have you read the carb guide? www.amckayltd.com/carbguide.pdf
Leo