Ultra rich idle circuit

[Pat D]

So here are the particulars- '74 TX w/stock carbs(or at least 74-75 style). Left side is a dream, idles steady, quick response(I can open the throttle plate on each carb individually, they are not tied together). Right side does not fire at all at 1200 rpm. If I open the throttle on the right side, it will fire intermittently and puff black smoke until the main circuit starts kicking in, then revs right on up. On the road the bike runs fine above 3500 rpm or so, rock solid. Mix screw position has no influence. I have good, hot spark to both plugs, timed correctly, and the battery is new. Right side exhaust smells super rich as well.

The backstory- Right side carb has been giving me issues since I started riding the bike. Cleaning and inspection revealed that the pilot jet was all buggered up where someone tried to remove it. Carb also had the wrong needle in it, but that does not concern the idle issue. I tried every method I could find to get the old pilot jet out, but no joy. I finally chocked it in the drill press, and drilled out the old jet and re-tapped/chased the hole. The new jet threaded right in. It is the correct BS30/96 jet, size 45. Also replaced the floats in both carbs as they both had a wee bit of fuel in 'em. Set the new floats at the 24mm spec. Replaced the O-rings on the needle jets.

So- I'm guessing that I got out of shape with the drilling/tapping of the pilot jet, and excess fuel is somehow getting past the jet w/o being metered through it. Or- is it possible my new O-rings around the needle jets are problematic? Not sealing properly?

Finally, because I haven't pulled the carbs back off yet to check, will the bowls interchange side to side, or are they mirror image? Be nice to swap the bowls and see if the issue follows them. I have no reason to believe my issues are within the main carb body, but maybe I'm missing something. Thanks for any insights.

 

[TwoManyXS1Bs]

Hey, Pat. Coupla thoughts:

The bottom taper of that new jet needs to fully seal against the matching seat in the bowl.

Ensure that the air bleeds aren't blocked.

Check that the bowls fit fully flat to the carb body, especially in the center region. Gaps here cause fuel metering problems. When the needle jets aren't fully seated, previous owners tend to warp the bowls and/or the carb body (at the corners) trying to tighten the screws.

The bowls should interchange, just be sure you don't have frankencarbs with different bowls.

The carb bodies are different, one has the enrichner draw tube, the other is blocked-off. Ensure that the enrichner wells in the bowls are identical and clean before swapping bowls.

 

[Pat D]

Excellent, I'm betting that I did not tap the jet well deep enough and it is not, in fact, seating against the bottom. It's a couple threads higher than the good bowl/jet when it tightens up. I was kinda hoping it wouldn't matter(d'oh!). I've got nothing to lose by chasing the threads a bit further, maybe I should cut the tip of my cheap tap off and make a bottom tap- I don't want to bugger the seat. Hopefully the gasket surfaces are flat, there is no seepage.

Stay tuned, and thanks!

 

[Pat D]

So I swapped the bowls today, and the problem followed. I chased the threads some more and the jet bottomed in the hole is it should. I expect I went a little deep when I drilled out the old jet, and buggered the seat. Oh well, lesson learned. Nice to get the issue isolated, though. Thanks for the insights.

 

[TwoManyXS1Bs]

If the seat isn't boogered-up too badly, it could be saved, but would require a custom machined long-stem countersink tool to gently reface the seat.

Otherwise, I believe DogBunny may have some bowls that'll work...

 

[Pat D]

Aye, he's definitely done right by me re:carb parts.