Pamco jetting on a stock set up.

[WideAWAKE]

Stock 76 with the exception of a pamco.

Was chasing a wondering idle and an air leak (go those sorted) but I figured what the heck, I’ll just clean the carbs while I have em off.

PO had 130 mains??? I get that an electronic ignition will/may burn slightly hotter but I’ve never had to jump jet sizes on other bikes I’ve owned that have had electronic ignitions installed. Am I missing something here? All my previous XSs were points. I saw some vague references to increasing mains in the archives but couldn’t find any definitive answer.

from first receiving the bike the plugs looked RICH. I put the stock mains back in.

I also have some 127 but even that seems like a big jump.

anyone got a definitive(-ish) answer.

 

[JRay77]

Stock exhaust? Maybe it is your charging system. Has nothing to do with your ignition or carb. I'd check your voltage at idle and higher rpm.

 

[WideAWAKE]

Stock exhaust.

my wandering idle and air leak have been sorted. Needed boots, butterfly seals and a sync.

just wondering why the PO would have stuck 130s in the mains.

 

[JRay77]

Ok sorry, misread. Right on. I have a digital AFR gauge. O2 sensor welded into a slip on exhaust tube. Then I'll go on a small trip, go thru gears and have it up to temp while watching the ratio. Let's me know where I need to adjust.

 

[WideAWAKE]

Anyone know about the jetting?

 

[gggGary]

Need to verify what year the carbs are?
Plenty of kits have the wrong mains.
76-77 had the smallest mains used in BS38's
A PO might have been trying to fix an air leak with jets? stranger things have happened....

 

[WideAWAKE]

Stock 122.5

I’ve given up on trying to understand the POs way of thinking (I double even he understood it)

 

[WideAWAKE]

I think at one point the bike had an open exhaust so he might have bumped it up - then put the stock exhaust back on and let the bigger jets.

was just trying to verify that I wasn’t missing something in terms of swapping points for a pamco and needing to increase the mains. (Everything else in the carbs is stock)

 

[5twins]

No, an ignition change shouldn't affect carb jetting. The '76-'77 carb set is a very good one, considered one of the best of the 38s. Yes, the mains are small but work just fine on an all stock machine. But they are quickly outpaced should you start modding things. Then something around a 130 would be needed. If you look at the needle jet sizes, you'll notice this carb set has the largest ones ever used in any set. That's what allows for such a small main jet size.

 

[Team Junk]

You need to ID your carbs. Just for example my 78 special carbs turned out to be 76-77. P.O. may have bought a generic carb rebuild kit and put in the 130s from that.

 

[WideAWAKE]

Thanks guys!

that’s what I needed to clarify. the vague references to upjetting when swapping over I had read in the archives had me scratching my head a bit.

really appreciate the help.

I stuck the stock mains back in and it seems to be much happier. I’ll keep the plugs monitored.

 

[JRay77]

Glad you got it. Like the guys said, there are variations of slide needles and jets for the BS38 carbs. Gotta know the carb model. There are pics on here of the needles per years and whatnot. I've put the wrong slide needles in before. Not cool. Also diaphrams. Do the thumb drop test. AFR gauges can be expensive but the only way to get carbs dead on.