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Tags
bendix, carb, idle tube, leak, spitting gas

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  #1  
Old 13th July 2019
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Default 75 XLH Bendix Carb Spitting Gas - Video

So with all the help from everyone here at this forum, I am finally near the end of my project. I will post another thread on that but first of all thank you! Second, sorry if this question has been asked a gazillion times before. But I have searched through all the threads I could find and there are no recent discussions or conclusive posts for my exact problem. So here it goes:

My carb is freshly rebuilt, after all the work I done to on this bike I couldn't believe she fired right up first try. Almost seemed like carb didn't even need tuning other than slight tweak to lower the idle speed and adjust my throttle cable.

Thats when I noticed my carb doing exactly the same thing as shown in this video: https://www.youtube.com/watch?v=-DPXruFqVxw

Exactly, 100% like the video, gas spits out of the idle jet towards the air filter. My question is what is the most likely culprit for this. I have a few suspects and want to work them in priority. Wondering if could just be simple tuning .. like running too rich ... possibly just needing to increase idle speed and back off on the idle mixture or something like that? Other threads mention float adjustment but that didn't make sense to me since the gas is spitting out of the idle tube just like you see in the video. I was very careful to measure the float level properly with a drill bit when rebuilt and careful with spring placement. It certainly is possibly that float is not right but as much as I would like it to be that simple it is not my first suspect. I also read that intake leak could cause this and that is definitely possible. The clamps on intake manifold are pretty cheesy. Last suspect is back pressure. I hope that is not the issue because that might be beyond my skill level. Looking for suggestions of what you think is most likely to help me dial this in. I can't stand the thought of gas dripping on hot exhaust pipes!
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  #2  
Old 13th July 2019
USAFpj USAFpj is offline
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Kenny- isn't that tube seated 180 degrees out?
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  #3  
Old 13th July 2019
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I don't think it is 180 degrees out. I am pretty sure the hole goes all the way through the tube so gas can come out both sides. I did wonder if it was 90 degrees out at first but all of them I could find pictures of look to be the same.
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  #4  
Old 13th July 2019
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From the video it sounds like one cylinder is loafing. Check point gap is equal on both lobes.
Check valve adjustment.
If no joy a leak down test is next.

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  #5  
Old 13th July 2019
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Ryder Rick, thank you. I wont mess around with the carb anymore just yet. I guess I am getting ahead of things. Both timing and valve tappets were already on my to do list anyway. Plus while I'm doing the valve tappets I can replace the old push rod o-rings while I'm at it. Just wondering, would intake seals possibly cause this? Reason I ask is mine seemed to be pretty loose. I tightened them as much as I could but I can still wiggle my intake manifold slightly.

Will do the points and valve tappets first and see how it goes. Thanks for help.
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  #6  
Old 14th July 2019
The Doctor71 The Doctor71 is offline
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Default

A few thoughts / questions:
  • it may not matter but..... is your Bendix/Zenith carb running a fixed main jet or an adjustable main jet ?
  • so where is the gas actually spewing from on your carb ?
    • is it coming from the "idle air bleed" ? (see Figure 3-65B in the pic below)
    • idle discharge holes #2, and/or #3, and/or #4 ?
    • or ?
  • maybe someone, more knowledgeable than me on the Bendix/Zenith, can explain why there "appears" to be a visible hole in that idle tube (in the video). Does your carb have that same hole ?

    That hole is not present on my '74 XLH Bendix/Zenith.
If you get a moment, post up some pics of your carb. Your actual pics may reveal something not previously considered.

Figure 3-65B from the '74 FSM:



And the full page:


Last edited by The Doctor71; 14th July 2019 at 21:40.. Reason: updated pics
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  #7  
Old 14th July 2019
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+1 Doctor. I'm assuming the video is another bike.
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Old 14th July 2019
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Quote:
Originally Posted by curiousgeorge View Post
+1 Doctor. I'm assuming the video is another bike.
Yes, he admits to that in the same paragraph as the posted video.
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  #9  
Old 15th July 2019
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Default

Yes, while looking around on the subject I found that video posted by someone else. But mine is doing exactly the same thing. I have the fixed main jet Bendix. It is freshly rebuilt. The gas is coming out of the little hole near the top of the idle tube. In my fixed main Bendix, the idle tube has a hole that goes straight through it near the top. It is not shown in the diagrams posted by Doctor71. I do appreciate those diagrams anyway since they are still helpful in understanding how everything works.

It only spits gas when idle. If I throttle it it is fine. I have played around with the carb adjustment a little bit. Seems like not much to really adjust with this carb. Starts right up pretty good even if things are way out of whack. I can dial it in to where it seems to idle pretty nicely. But when I throttle, it is nice and responsive but when I let off, it sort of rolls down slowly back to idle which doesn't seem right. I thought I would mention that just in case offers any other hints.

I suspect that there is back pressure coming from somewhere. When I posted originally, I was hopeful that could be something really silly like carb adjustment. I think Ryder Rick might have me on the right track with valve adjustment. It makes sense that if valves are out of whack could blow back through intake on compression or exhaust stroke or something like that.

I am going to post some pictures as soon as I can and will also try to get a video. My next task is going to be to adjust all the valve tappets. Then after that I am going to check the point gap and point timing. After reading up on how to do both of those things (thanks to XLForum and some good videos I found) it looks to be pretty easy. Hopefully this will help me dial things in. If not, I might very well be getting into more than I can handle.
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  #10  
Old 15th July 2019
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if you are running drag pipes, that could be a big part of the problem with reversion. so, if you have drag pipes for your exhaust, you might find some useful info in this link...
http://www.nightrider.com/biketech/exhaust.htm
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