Feeling insane please help. Wildly Asymmetric mix screws.

[nodwick]

Hello all! I posted several weeks ago and got my bike running great. Got some good miles in. But now I'm having more issues.

I went on vacation and didn't ride it for 3.5 weeks and suddenly the carbs acted clogged. Okay this is expected. Even with the e5 fuel that "contains no ethanol" according to fuel companies I would expect this.

I'm having idle issues and I'm totally stumped. I can get the bike to idle fine and we'll but idle hangs a bit on decel and so then when I played with mix screws to get optimal settings they were showing me a clear indicator of -something- wrong I suspected a clog but a bit lost.

LH carburetor needs the mix screw settings at .5-1 turns out from all the way In

RH carburetor needs to be set at 4.5-5 turns out, the mix screw about ready to jump out of the bike!

I rode it around one day to see if that would clear up the issue and it did temporarily suddenly bike acted normal and started shooting on the right side indicating too rich (happy days) and the it started pissing gas out the LH carb intake for the last minute or two of my ride ()

I took them off twice yesterday and throughly cleaned them using a generous application of STP.

Even after cleaning the results are exactly the same.

-Compression reads 130 both cylinders
-Fuel flows well from taps
-With these same jets the bike was running amazing until it very suddenly started acting like this
Checked the float valve and seat everything looked great and swapped out the pointy bit even.(Attaches to float)
-fuel fresh
-voltage from battery is strong
-tried different spark plugs and everything was the same (even when swapping plugs left and right)
-Fuel floats are set the same and have no cracks or anything and it has not been cold enough to freeze here.
-diaphrams have 0 holes and are very rubbery still. Although a couple crease marks but nothing to affect their operation.


but why would one carb be overly lean and one be overly rich

Today I'm gonna swap the diaphragms left and right and reclean the carbs again

Just trying stuff at this point.
I'm so lost. Anyone have any ideas and what would cause this?

 

[Its been a long time]

Hazarding a guess that on the side with the mixture screw so far out. Suggests one or more of the pilot mixture holes in the carb bore is blocked or partly blocked? Over compensating by screwing the pilot screw right out. Gently probe the holes with a piece of small diameter wire. I usually pull a strand off a wire brush for this.

 

[gggGary]

Have you synchronized the carbs?
Done the hot water float leak test?
Dip float in a cup of HOT water for a few seconds, stream of bubbles = fail.
Fuel lines replaced, new?
Drain float bowls into a good container, any rust or debris?

 

[nodwick]

Have you synchronized the carbs?
Done the hot water float leak test?
Dip float in a cup of HOT water for a few seconds, stream of bubbles = fail.
Fuel lines replaced, new?
Drain float bowls into a good container, any rust or debris?
View attachment 336458

They were synced before all this. While they were synced and the problem developed it the idle would hang and that's when I noticed one side ran better and when I was troubleshooting while riding and I pulled half choke the good side would actually overly rich and the bad side would run great. Haven't been able to get them running well enough to sync now

Yes new fuel lines. Installed them recently after the old ones started crumbling into the fuel.

Draining float bowls shows clean. No debris or rust.

Will check floats. Starting to feel like it's the only thing is could be at this point. I even swapped the diaphragms and no change. And everything is clean as a whistle as.ive now throughly probed sprayed and flushed out the carbs 3x now this weekend.

I'll report back on the floats. Thank you for your input.

 

[nodwick]

Have you synchronized the carbs?
Done the hot water float leak test?
Dip float in a cup of HOT water for a few seconds, stream of bubbles = fail.
Fuel lines replaced, new?
Drain float bowls into a good container, any rust or debris?
View attachment 336458

Did the float test, no because bubbles to speak of. and verified float heights at 22.25 before removal. Bs34 carb with the plastic floats. (1981 xs-sh)(4n9 vin code)

I think I must be cursed. At risk of sounding dumb. Ive always been able to adjust the bike while it's on its kick stand. I'm assuming the bike being on its kick stand isn't an issue? (Last owner removed center stand)

 

[5twins]

Well, it might be. I find carb adjustments seem to be easier and work better when the bike is sitting level on the centerstand.

The mix screws on the BS34s usually like about 3 to 3.5 turns out on a stock bike, maybe a bit less (around 2.5) if the pilots have been increased. That means both of yours are off from the norm, lol.

 

[nodwick]

Well, it might be. I find carb adjustments seem to be easier and work better when the bike is sitting level on the centerstand.

The mix screws on the BS34s usually like about 3 to 3.5 turns out on a stock bike, maybe a bit less (around 2.5) if the pilots have been increased. That means both of yours are off from the norm, lol.

Yes, I bought the bike non-running as previous owner had put on short pipes and pods didn't rejet and gave up.

I sized up the jets and she ran great all season (except for the hiccup with crumbling fuel lines I posted several weeks ago). And nominal mix screw setting was 2.5 turns for both sides.

 

[nodwick]

I'm really stumped how one carb seems to be delivering more fuel and the other much less in such a dramatic way. And I double checked I hadn't magically swapped one of the pilots on accident. They are the same both sides.

Running lean it must have something in some passage for the idle circuit that my can of carb cleaner isn't getting

And rich with fuel dumping out must be float or float valve issues. But everything checks out and I even swapped the needle and seat. (And it stopped puking fuel......for now)


But everything is so squeaky clean and measures up fine. Feeling defeated.

 

[5twins]

Have you ever removed the mix screws and checked/replaced the little o-rings on them? If not then you probably should. The o-ring goes bad and hardens up, then the screw doesn't seal properly in the hole and doesn't adjust right. But before taking them out, screw them in all the way and check how much of the tip of the screw is sticking out into the main bore. If the screws are assembled correctly and have the o-ring in place, you should see a little bit of the tip of the screw sticking through, maybe a MM or so .....

If the o-ring is missing or has perished, you may see more of the screw tip sticking through. If the o-ring was replaced but the old one wasn't removed, the screw tip may not stick out at all. Many times when you remove the mix screw, the o-ring stays stuck down in the hole and you need to fish it out. These are the parts and their assembly sequence for the mix screw. The little washer must be between the spring and the o-ring or the spring can dig into the o-ring and destroy it .....

And here's an old o-ring (on top) compared to a new one. As you can see, the old one gets all flattened out and deformed. A generic 1mm x 3mm sized o-ring fits and works well as a replacement .....

 

[nodwick]

Have you ever removed the mix screws and checked/replaced the little o-rings on them? If not then you probably should. The o-ring goes bad and hardens up, then the screw doesn't seal properly in the hole and doesn't adjust right. But before taking them out, screw them in all the way and check how much of the tip of the screw is sticking out into the main bore. If the screws are assembled correctly and have the o-ring in place, you should see a little bit of the tip of the screw sticking through, maybe a MM or so .....


View attachment 336478

If the o-ring is missing or has perished, you may see more of the screw tip sticking through. If the o-ring was replaced but the old one wasn't removed, the screw tip may not stick out at all. Many times when you remove the mix screw, the o-ring stays stuck down in the hole and you need to fish it out. These are the parts and their assembly sequence for the mix screw. The little washer must be between the spring and the o-ring or the spring can dig into the o-ring and destroy it .....

View attachment 336479

And here's an old o-ring (on top) compared to a new one. As you can see, the old one gets all flattened out and deformed. A generic 1mm x 3mm sized o-ring fits and works well as a replacement .....

View attachment 336480

I had checked them and one of the screws was in rough shape but I swapped both of them out for brand new ones including o-rings springs and washers.

About to take the carbs out again and soak them in the UK equivalent of pinesol (which is dettol I guess) and see how it goes.

I'm desperate at this point any more things for me to check? I really appreciate the suggestions

 

[gggGary]

Have you checked your vacuum petcock line? A ruptured vacuum diphragm on the petcock can flood the LH cylinder.

 

[nodwick]

Have you checked your vacuum petcock line? A ruptured vacuum diphragm on the petcock can flood the LH cylinder.

Not sure if it's factory, but I have the manual petcocks.

my vacuum barbs are sealed well. And the boots don't seem to be leaking. I sprayed carb cleaner on them while it was running (out of frustration ) and there was no change in idle.

Might buy new float needles/seats just for the sake of it at this point.

 

[gggGary]

Have you replaced the float needle seat o-rings?

 

[nodwick]

Have you replaced the float needle seat o-rings?

Indeed, the o-rings were a bit over sized even. So they installed -very- firmly.

 

[nodwick]

Have you replaced the float needle seat o-rings?

I've found something! I noticed on the most recent test there was some white smoke. And have up and went to bed.


This morning on a hunch before riding into work (on the daily bike) I found th oil level was incredibly high and very thin.

Compression is good but it seems the oil has a BUNCH of fuel in it and is super thin.

I have the oil on hand. So I'm gonna change the oil and we'll see how it goes. Feeling less insane now.

Seems like the float got stuck and fuel drained into the cylinder and the predictable happened

Will update once I have more conclusions

 

[gggGary]

While rare "sunk, filled with fuel" foam floats can happen.
Aftermarket rubber float needle tips can swell also.

 

[nodwick]

While rare "sunk, filled with fuel" foam floats can happen.
Aftermarket rubber float needle tips can swell also.

Changed the oil. And at its normal settings it started super easy, much easier than before and audibly runs much smoother and is no longer blowing white smoke. And acted in a much more familiar way. So I think I got it closer.


Carbs still want to be set wildly different but now I'm starting to think it's just because I haven't changed the sync from when they were being crazy. And I forgot to bench sync.

Tomorrow I will set the sync. My clear hose just showed up today.

What's the best way to set mixture? Dead jugging or otherwise?

Thank you for your time!!

 

[badlegbill]

I have age and experience on this point - so, I have found it wise to drain the float bowls of CV carbs if I am not intending to use the bike for a few days and it is on a kickstand, I do slide carbs as well if I know it will be a few days, always if it is a classic Brit..
It saves any varnish as the fuel evaporates off while the bike is hot, or the sun is out, it will also save fuel from time to time if the petcock leaks through because needle valves are designed to regulate fuel not stop it.
Keeping a container handy means you always have a little fuel to clean with or throw back in the tank, it is just a good habit and is usually done by the time you have got your gear off and security on.
I suppose that some of that applies on a centre stand but you don't have a downhill carb then.
It doesn't stop me having carb problems, see previous posts, but I do what I've learned helps when I remember.

 

[Its been a long time]

I have age and experience on this point - so, I have found it wise to drain the float bowls of CV carbs if I am not intending to use the bike for a few days and it is on a kickstand, I do slide carbs as well if I know it will be a few days, always if it is a classic Brit..
It saves any varnish as the fuel evaporates off while the bike is hot, or the sun is out, it will also save fuel from time to time if the petcock leaks through because needle valves are designed to regulate fuel not stop it.
Keeping a container handy means you always have a little fuel to clean with or throw back in the tank, it is just a good habit and is usually done by the time you have got your gear off and security on.
I suppose that some of that applies on a centre stand but you don't have a downhill carb then.
It doesn't stop me having carb problems, see previous posts, but I do what I've learned helps when I remember.

Wise words. I do it a bit differently. I dose the fuel tank with fuel stabiliser then I run the bike for a while to get the dosed fuel into the float bowls. Then I turn the fuel taps off and run the carbs dry. Finishing off with a couple of cranks on the starter to draw air through the carbs. For a good while doing this has served me well and seems to have prevented issues from fuel evaporating off in the carburettors and leaving gunk in there.

 

[gggGary]

On BS34's the idle mix screw only controls one port out of 4, the other three, right at the butterfly, are the main factor at idle. So mix screw changes are not super noticeable. In general "one turn beyond the factory setting" is where they usually end up.

You are chasing a LH carb that is not stopping fuel flow. By design when the diaphragm piston is down fuel eventually rises high enough to pour out of the float bowl vents in the intake bell.

You would probably be well served observing float bowl level with the "clear tube in the drain port" method. Get that fuel level functioning/correct, return other "compensating settings" back to balanced and the problem will be solved.