BS34 Diaphragm Drop Rate

[Hyde]

Heya folks. I’m curious is there’s any recomended/baseline for plunger drops while looking at diaphragms. Paul linked a video for Chito’s post earlier showing the slide drop rate in order to determine if new diaphragms are needed. Is there a good “range” to be in for the drop? What’s a really well sealed set of carbs look like vs. a well worked runner that’s going strong?

Fooling with a 2nd set of all original 34’s from fleabay, internals (for the most part) in excellent condition. No cracks/tears in the diaphragms. Original enrichner plungers - rubber is pliable in tips, replaced the enrichner seals. Drop count = 13 seconds.

The originals have new JBM diaphragms, new plungers (I admit these are Mike’s) which were a really tight fit & new seals. Drop count = 24 seconds.

I’ve seen varying reports when scraping out BS34 articles here mention 10-15secs as a target while a few posts mentioning the 20s. What impact does this have on properly timed/valve adjusted engine under load overall?

Heh sorry for the long post, just trying to get a better understanding.

 

[xjwmx]

What impact does this have on properly timed/valve adjusted engine under load overall?

One of mine had several pinholes and dropped in about 2 sec., but I couldn't feel much if any effect on the ride. Maybe I would have if I'd been racing it. If you have two with good diaphragms but one falls a lot faster the difference might be the rubber seals on the chokes.

 

[Hyde]

Ty for the reply XJ, the faster fall of the 2 are the carbs with original diaphragms. Though I can’t spot holes, they have a few cracks in the thick lip running arround the top which could account for the drop time. Both units are running new enrichner seals so it must be the diaphragms themselves.
Interesting you say a 2 second drop time didn’t affect the ride at all. Had a borrowed set of 38’s over the summer for troubleshooting that were about the same, bike ran fine - mind you i was just seeing if it would run and didn’t try tuning it heh.

 

[xjwmx]

I got a pair of diaphragms with pistons on ebay from Cruzinimage that are surprisingly low in cost. I did a mini-review of them here somewhere. My originals had gotten thin and brittle feeling with lots of cloth showing through.

 

[gggGary]

Top secret heads up, a damaged rubber seal on the choke plunger will affect slide drop rate. IMHO pretty much as long as it don't drop like a rock you're good.

 

[xjwmx]

2M had good results with that spray on tool handle coating fix for diaphragms. The problem if it was a problem was they weren't resistant to carb cleaner anymore. But there are brands of that stuff that are more resistant I'm sure. But new ones are a good deal too...

Interesting we have three votes saying it doesn't matter if they have holes. Little holes anyway.