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BS38cv & unipods
- Thread starter 2BallCane
- Start date
Id put a few miles on it and read the plugs before I made any jetting decisions.
Well it's a project in process, so I won't find out until spring. But I imagine I can wait.
With BS34's and foam pods I did not need a re-jet, just turned the low speed mix screws out roughly 1/4 turn.
It’s all about air fuel ratio. I think it’s 14:1
Pod filters let more air in, so you’ll need more fuel.
I had made a slip on pipe with a welded bung. Have a gauge set up. Never did finish it. Haha These carbs work in a series. Idle first. There’s a chart on here if you search. If you’re idle is fine, doesn’t mean the mains are ok. Sorry if I insulted your intelligence. Also these carbs are decades old. Don’t assume they have the right parts inside. I just found missing orings in a set. Took a good long while to figure this out.
Pod filters let more air in, so you’ll need more fuel.
I had made a slip on pipe with a welded bung. Have a gauge set up. Never did finish it. Haha These carbs work in a series. Idle first. There’s a chart on here if you search. If you’re idle is fine, doesn’t mean the mains are ok. Sorry if I insulted your intelligence. Also these carbs are decades old. Don’t assume they have the right parts inside. I just found missing orings in a set. Took a good long while to figure this out.
I'm aware of the need for more fuel in regards to the higher air flow associated with the unifilter, but I was looking to see if anyone had already done the work and determined the best sizes to use.
There's no straightforward answer to this.
I just rebuilt my Bs34's with standard new jets etc... All seems good so far on a few short test runs. It just trial and error to get this right in your climate and altitude etc.....
I've not put many miles on my bike and winter has arrived. So now it's a rewire and back to carbs in the spring.
Have to take into consideration other aspects of you bike as well and not just the change to uni-filters. Muffler and or header pipe change. What set of carbs are you using. BS38's changed every 2 years between 70-79. Needles and needle jets varied a lot between sets and this altered the jetting so some carb sets require a bigger change in jet sizes with the same alteration to the bike. Not uncommon the find the carbs from different years put onto other years/model. Say a 76/77 set on a 78/79 model or the other way round..........pays to identify the carbs and not assume they are the right ones for that model
Yes, you'll need to positively I.D. the year of your carb set and then base the re-jetting on what came stock in that particular set. You base your jetting and/or re-jetting on the year of the carb set, not the year of the bike.
TFR Aussie
XS650 Enthusiast
How can you tell what carb is what year?
Mike's XS has a carb ID chart. My 81 Special has 76/77 38's on it.
Do not be dismayed with the information that has come at you here. 1. ride then read your plugs. New plugs are cheap, put a set in and put 30 or 100 miles on them. 2. If you have no color or almost no color you are running a touch lean. If you have a light to darker tan, worry about something else. If you have black you are running to rich. Then go to the guys on this forum who know about this stuff, I am still learning.
TFR Aussie
XS650 Enthusiast
TFR Aussie
XS650 Enthusiast
These have of course been cleaned and rebuilt since then.
Edit............74/75/Carbs
(look to be 72/73 carbs)
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No, that's a '74-'75 set. The "tells" are the #120 butterfly plates and the lowered floors in the main bores. '73 and older carbs use #125 butterfly plates and have a raised floor in the main bore .....
And because of that raised floor, '73 and older carbs use a longer needle jet .....
'74 and later carbs use a shorter needle jet .....
And because of that raised floor, '73 and older carbs use a longer needle jet .....
'74 and later carbs use a shorter needle jet .....
Your right. My bad. I was looking at the bottoms, (bowls) and not the inlet. Corrected earlier post
74/75 carbs i got from a 74TXA. I was basing my post on these and i think the bowls are from a set of 76/77.
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Bowls are '78-'79 because they have no hose nipples for the overflow pipe. In fact, if you look inside, you'll see that's because they don't have an overflow pipe, lol. It seems that in '78 when Yamaha came out with the vacuum petcocks, they figured we didn't need an overflow tube in the float bowls anymore because those fancy new petcocks would never over-fill the bowls. Well, that may have been fine 40 years ago when they were new and functioning properly. Today, not so much, lol.
