First of all - I love the sound of it now. I think it's going to be a great bike, as soon as it's running on all four. Let's recap a bit... I remember all Your cylinders had 140 to 145 PSI compression. A little low, but... Three cylinders are running just fine, and one isn't. And - You have a good spark on cylinder one. So - it is either air, or fuel that is the problem. If the vacuum membrane on the top doesn't lift the needle, that cylinder will be starving for fuel. Try a bigger main jet on that cylinder, and see if that fires it.If it does - and it really should because three cylinders are firing, so You know there is fuel getting through the system, but the normal jet can't deliver it because of bad vacuum. That leads me to think You have a vacuum leak somewhere? Or a vacuum tube is connected wrong? What to do? Check for air leaks or vacuum leaks, especially on number one. Also recheck the actual fuel level on all four float bowls. And I mean the fuel level, not the float height. To do that, You need a clear vinyl or plastic tube connected to the bottom of the bowls, and by that see how high the level is. I can't remember seeing that You have done this, so I'm mentioning it now. Maybe I've just forgot seeing it in Your video, so forgive me for being old and senile! 🤒 Also another thing... Many carburetors have their pilot circuits fed by the main jet. The main jet picks up fuel from the bowl, and some of that fuel goes to the side - through a small channel, and into the pilot circuit. If the membrane at the top doesn't lift the needle, the pilot circuit may also be starved for fuel. The MotoResto Florida guy here on TH-cam has some very nice videos on these kinds of carburetors. Check out this one, where he explains very good, how they are built. Search for this title on TH-cam; "Taking a look at the Mikuni BS34's from the XS1100 project." And subscribe to him, and leave him a comment! Great guy, that has thaught me a lot!
First, thank you so much for your comment! All things that you mentioned are valid. The Vacum leak was my thought also, but the test with starting fluid didn't detect anything. After making this video, I stripped down carbs (5th time 😅) and checked membrane on the first one (I put it on bright led light), but I see no pinholes on it. I dipped floats in water to see if they were leaking. It passed the test. Now, I will focus on just the first carb, as I think too that problem is in fuel mixture delivery. To start, I never take off carbs from rails as the screws on it are stuck (maybe someone put lockthight on them) so I can clean everything, including chocke mechanism. We will get to the bottom of it.... I subscribe to the channel that you mentioned, end I will find the video. Thank you so much for all your help!
First of all - I love the sound of it now. I think it's going to be a great bike, as soon as it's running on all four.
Let's recap a bit...
I remember all Your cylinders had 140 to 145 PSI compression. A little low, but... Three cylinders are running just fine, and one isn't. And - You have a good spark on cylinder one.
So - it is either air, or fuel that is the problem.
If the vacuum membrane on the top doesn't lift the needle, that cylinder will be starving for fuel. Try a bigger main jet on that cylinder, and see if that fires it.If it does - and it really should because three cylinders are firing, so You know there is fuel getting through the system, but the normal jet can't deliver it because of bad vacuum. That leads me to think You have a vacuum leak somewhere? Or a vacuum tube is connected wrong?
What to do? Check for air leaks or vacuum leaks, especially on number one.
Also recheck the actual fuel level on all four float bowls. And I mean the fuel level, not the float height. To do that, You need a clear vinyl or plastic tube connected to the bottom of the bowls, and by that see how high the level is. I can't remember seeing that You have done this, so I'm mentioning it now. Maybe I've just forgot seeing it in Your video, so forgive me for being old and senile! 🤒
Also another thing... Many carburetors have their pilot circuits fed by the main jet. The main jet picks up fuel from the bowl, and some of that fuel goes to the side - through a small channel, and into the pilot circuit. If the membrane at the top doesn't lift the needle, the pilot circuit may also be starved for fuel.
The MotoResto Florida guy here on TH-cam has some very nice videos on these kinds of carburetors. Check out this one, where he explains very good, how they are built.
Search for this title on TH-cam; "Taking a look at the Mikuni BS34's from the XS1100 project."
And subscribe to him, and leave him a comment! Great guy, that has thaught me a lot!
First, thank you so much for your comment!
All things that you mentioned are valid. The Vacum leak was my thought also, but the test with starting fluid didn't detect anything.
After making this video, I stripped down carbs (5th time 😅) and checked membrane on the first one (I put it on bright led light), but I see no pinholes on it.
I dipped floats in water to see if they were leaking. It passed the test.
Now, I will focus on just the first carb, as I think too that problem is in fuel mixture delivery.
To start, I never take off carbs from rails as the screws on it are stuck (maybe someone put lockthight on them) so I can clean everything, including chocke mechanism.
We will get to the bottom of it....
I subscribe to the channel that you mentioned, end I will find the video.
Thank you so much for all your help!
.... I did check for fuel height on one video, but I will check and recheck everything once more....