1980 gas flowing out of carb mouth

[padgett]

Hey guys,

I think I know the problem, but I want to get a confirmation if I can.

Rebuilt my chopper yet again and put a TC bros kickstand on there. While on the kickstand the bike sits far over to the left, further than before. If left sitting, it will start to dump gas out of the mouth of the left carb. Right carb does not have this issue. Fuel shut off too, I should note

So the obvious place to start looking is the float on that carb, but i checked height and its bang on 21/22mm. Plastic floats btw.
The float needle's stopper/plunger isn't stuck, I can move it with my finger nail and it springs back to position. Carbs upside down with the bowls off, i can tap the floats themselves and see the spring action, same as the right.

Everything seems in order, but I don't want to start fixing stuff with my wallet. Should I be adjusting my kickstand, or buying a new float needle even though it seems fine? Anything I might have missed?

Gonna put the carbs in the ultrasonic tonight just for sanity's sake.

Thanks as always, gents

 

[TwoManyXS1Bs]

Could check to see if the float(s) have enough pivot pin slop or improper bend to allow their edges to rub/catch on the side of the floatbowl, or the middle section. The bike leans to the left, so the float(s) will float/move to the right.

 

[padgett]

Thanks. Great answer, didn't think about that.

I did notice that the left side carb in question's float pin was very hard to get out. Might see if i can get that moving better.

BTW, whats the accepted slop?

 

[TwoManyXS1Bs]

...BTW, whats the accepted slop?

No real spec, just enuff to let them move freely, but not so much that they'll flopsy/mopsy and drag on things...

 

[5twins]

It's pretty normal for the BS34 float pins to be hard to get out. They're splined on one end and stick in the posts pretty good. I'm thinking your problem may be related to the extra lean of that new side stand. Gas from the right carb may be transferring over to the left one and over-filling it. I bet if you re-work the side stand so the bike doesn't lean so much, the problem will go away.

 

[jussumguy]

Do the float needle seats on your carbs press in and seal with o-rings?
Perhaps dried o-rings are part of the issue

 

[fredintoon]

Hi Padgett,
dunno about the gas leak but here's a good way to remove the float pivot pins without the risk of busting off a support post.
Hit the pivot pin end with a spring-loaded centerpunch. Pops them out every time.

 

[padgett]

Do the float needle seats on your carbs press in and seal with o-rings?
Perhaps dried o-rings are part of the issue

Yep, they do. And i checked them and they were pretty hard, so i'm going to hope the hardware store has some replacements. Ideally that whole assembly that takes the oring shouldn't have any play if its all correct?

 

[TwoManyXS1Bs]

The guys cooked this up awhile back, might be useful.

 

[peanut]

Hey guys,
. While on the kickstand the bike sits far over to the left, further than before. If left sitting, it will start to dump gas out of the mouth of the left carb. Right carb does not have this issue. Fuel shut off too, I should note

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with your bike tilted over further suddenly causing a leaky fuel bowl the first thing I though was that your fuel needle jet is dragging on the jet tube wall and preventing the needle seating properly.

I would check the float needles and the float pivots carefully for any rubbing or friction whilst holding the carbs at an angle similar to the bike lean. Maybe gently rub the float needle bodies on some fine wet and dry

I should think it unlikely to be your needle valve tip or jet set because you would expect it to give occasional flooding issues during normal running

 

[madjap]

Know what it was on mine? (same conditions) Dang float was a tiny bit 'bent' over and would drag just a tiny bit from time to time on the carb body when tilted. Not EVERY time mind you, just when I thought I had it 'fixed'... Shaved a little off the float side (plastic) and fixed it!

 

[peanut]

Know what it was on mine? (same conditions) Dang float was a tiny bit 'bent' over and would drag just a tiny bit from time to time on the carb body when tilted. Not EVERY time mind you, just when I thought I had it 'fixed'... Shaved a little off the float side (plastic) and fixed it!

tuning Mikunis is like brain surgery

you have to be so incredibly meticulous about everything for them to work well.

 

[vincejames]

I understand that there is a twist in this post with a kickstand that makes the bike lean way to much, but here is how I have had success. I always replace the float needles with the ones from boats.net. I've come across 4 bikes that have the crappy/worn out OEM floats or were bought from MIKES that just don't work. Once you get those, ensure your float height is correct. I prefer not to measure and do a float test using clear tubing. I think this is the best way to truly see how much fuel is in my floats.

I also do something that I have not seen anyone on here do. Instead of pouring the gas out of the carbs when I'm doing my adjustment, I pour all of the gas into a large container and measure how much gas came out of the carb. It's meticulous in making sure you get all the gas out, but it has worked for me. I adjust my float height from there.

Ensure your petcocks is working correctly, ensure float seat, needle, assembly is working correctly, and problem should be solved.

Vince

 

[padgett]

I love how this silly question is garnering so much spitballing from the pros.

Ya'll must be bored!

Anyways, I found some oring replacements for the float assembly, pressed them in, and they're flush. Worth noting that the assemblies would fall out if the bowls/floats weren't on there and it was right side up. So as that might not have been the issue, looks like it needed to be done

I'm gonna check on that float issue you talked about, Jap.

And i'm not against replacing the float needles again, but just wondering if anyone can confirm what vincejames said about boats.net needles vs anyone else. Again, mine seem fine as the plunger on them is moving well.

 

[5twins]

You have the Viton rubber tipped float needles. They usually work pretty good, even the aftermarket ones. But, there have been reports of bad aftermarket ones. On some, the rubber tip swells up and deforms after a short time in use. As long as yours aren't doing that, I'd say they're still OK.

The float needles that Vince was specifically referring to are the all metal ones used in the '79 and older carbs (BS38s). However, I have no doubt that original Yamaha rubber tipped replacements for your model would be better than the aftermarket ones.