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Discussion Starter · #1 ·
Hey all,

I have a 1976 CB200, and I have actually posted a thread about it already, but that was a different issue. I am working on figuring out why it doesn't always run on both cylinders. I started with spark, and it is good. Then fuel. That's where I have a problem. To make sure I was getting fuel to both carbs, I put a short piece of hose on both outputs on the petcock. Then I got 2 quart bottles and put them under those hoses. I turned on the fuel, and one of the outputs started running fuel, but it was full of bubbles. The other line was doing nothing, almost sounded like it was under a vacuum. I pinched off that line, then the first one started running the fuel as it was earlier, but without bubbles. Then I pinched off the first line, and now the second one runs fuel without bubbles. Is there something in the petcock that could be going south? I have taken apart the petcock, and it is super simple. I don't know what could be causing this. Any ideas, feel free to chime in!! Thanks!! :D
 

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Did you tried without gas cap on? I had problems with the rechromed gas cap on my CD175. The air hole was blocked and gas wasn't flowing properly. Try without the gas cap on and if it work, that mean you have problems with the cap.
 

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There is a possibility the vent in your CAP may be clogged but more likely just nothing wrong at all.

The fuel will flow to the path of least resistance.

The Dual Lines would have to be identical in length... and all other characteristics for them to flow evenly.

The Floats in the Carbs open and close randomly as the fuel is used from the bowls.
No different then pinching off one line and the other flows.
 

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Discussion Starter · #5 ·
Ok, thanks for the replies guys!! Well I have had trouble with the bike running on both cylinders all the time, so I thought if there wasn't a steady flow of fuel to each carb, then unless one bowl is full the other won't get any gas. I had the gas cap open when i was doing this, so no possibility of a plugged vent, but I will make sure it is clear. It just doesn't make sense that one carb bowl would have to be full for the other to re-fill. But if that's how it's supposed to be then I will leave it alone.
 

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The fuel tap is working normally.

The fault, if it is fuel system related, will be with the float valves in the carbs. When worn, or replaced with aftermarket parts, these can randomly stick open or closed, causing flooding or fuel starvation.

Been there, seen and done both the fuel tap and float valve issues.
 

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Discussion Starter · #8 ·
Funny question- I have a buddy who owns a 1981 Honda XL500. No, it's not a twin, but I thought I could get a little advice. Twice now it has jumped a tooth on the timing chain. It has a tensioner, and it appears to be spring loaded like normal, is it possible that the chain is worn so bad it needs a new chain? Or possibly a link removed??
 

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From my experience, both tubes should flow freely, whether you're on Open or Reserve, or your petcock is clogged up inside the tank. That was my problem. Luckily, it's an easy fix. A few minutes with the tank off, some compressed air, and I was good to go. I did a video on it...


good luck!
 

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Interesting to see your topic. I've noticed something very similar. Maybe the exact same thing actually.

If I put two fuel lines on the petcock and open the valve fuel only seems to flow out of one hose at a time. It will flow fine through either of them but only ever seems to really flow through one at a time. If you pinch off one hose fuel will flow out the other. You can go back and forth and it's a nice steady stream through both. Is this normal?
 

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Entirely normal in my view. Fluid flow will always take the path of least resistance.

My garden fish pond has a submerged pump, which pumps water to a filtration box. Water returns to the pond from this box via twin pipes, identical in run and dimension. One pipe always runs slightly more water than the other, but if you block it off the other pipe runs more strongly.

At the end of the day, the flow from the petrol tap only needs to keep up with the flow through (the much smaller) main jets.
 

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Discussion Starter · #13 ·
I agree, but if both bowls are empty, one would have to fill before the other would fill. So in my case, it will run for awhile, but as soon as one bowl is a little less full than the other, the fuel flow runs to that bowl, then the other cylinder dies. Coincidentally, it is the one with a longer fuel hose. (the right side)
 

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The motor will run or quite some time before the float bowl has emptied to a point of total fuel starvation.

I typically turn OFF my fuel petcock about 3 blocks from home and have no trouble making tit the rest of the way and still have time to allow the motor to run for 30 seconds or more before shutting it down.

So your theory of fuel starvation on one side is bunk.
You would have to run on one cylinder for more than a full minute with zero flow to the other side for it to be an issue.
 
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