carb brainstorming...

deacon

minor bike philosopher
Jan 15, 2008
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north carolina
I have been having carb troubles. I am beginning to look at outside influences. For instance I can't get the carb on the homelite to pull gas from the tank. It seems I have had more than one act that way. I also had it happen on the 33 bike. I am beginning to wonder if it isn't something more than a weak carb.

For one thing my gas lines from the walbro carb to the gas tank are bout three feet long. Then I think on this current on at least the gas tank is lower than the engine forcing it to pull up hill. I wonder if those two thing influence the carbs ability to suck gas. I'm going to make some test tomorrow. using shorter runs and tanks that are higher than the carb. I know that chainsaws suck gas from tanks that are below the carb but they are also within a few inches of the carb. I don't know but it would seem to make a difference.

I'll let you know what if anything I find out... and if you know please let me know so I can save the experiment..
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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up north now
That is kind of long...you can put a one way valve or check ball valve in line like the Bike Bug has.

Make one of your own with a model airplane fuel filter and a ball bearing or BB of the right size. When you unscrew the two halves of the filter, there is a screen in there. Put the ball bearing on the screen and screw it back together. When you try to run fluid through one way, the screen holds the ball away from the opening, the other the bearing seals the opening. Check ball valve- under 5 dollars at your local hobby shop.
 

deacon

minor bike philosopher
Jan 15, 2008
8,117
3
0
north carolina
Im going to check it out but you might well have hit on it. Today I noticed that the engine would run when I pumped gas to it with the bulb direct to the tank then stuck the line on but a few seconds later the engine stopped and the line was empty. it could be running back into the tank. It is running back into the tank come to think of it,

I'll know more tomorrow.
 
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deacon

minor bike philosopher
Jan 15, 2008
8,117
3
0
north carolina
Results of the carb experiments.

I moved the carb closer no change.....

I raised the fuel tank above the carb, and as i expected the fuel line stayed full of fuel, but the carb still wasn't pulling it in.

Changed carbs and the fuel flow is now correct, now sure how the bike will run yet but it is getting fuel correctly. It was the carb for some reason it worked on the 42 bike till i pulled the engine, then it didn't work on the homelite 26cc. Oh well.
 

deacon

minor bike philosopher
Jan 15, 2008
8,117
3
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north carolina
conclusions...

The carb should pull gas from a tank a couple of feet away and should not allow it to drain back. A carb with a weak but almost working diaphragm will allow it to be pulled into the carb and start, but then it will run out since it isnt creating enough vacuum on it's own to pull the gas from the tank.

So when you read in an advertisement that the engine will start but only run a few seconds, it has a weak diaphragm most likely. If it will only start by pouring gas in the engine through the plug the diaphragm is gone. either way expect carb problems on these small engines to be your trouble. Sometimes cleaning them will help, sometimes it wont I think.

I wonder what effect carb cleaner has on the rubber of the diaphram does anyone know? Will it soften it up? If not is there anything that will. It would be nice to open the bottom of the carb and spray something in to rehabilitate the diaphragm.
 

deacon

minor bike philosopher
Jan 15, 2008
8,117
3
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north carolina
I just did what I usually do for a carb that isn't working at all. I shot a half dozen sprays of carb cleaner into the tank then added a couple of ounces of premix. I pumped it through with the bulb and I pulled it through with the plug wire off. I'm going to do that once or twice a day till I get it mounted and see if it cleared up the problem. Cleaning the inside of the carb might help. It sure can't hurt any.
 

deacon

minor bike philosopher
Jan 15, 2008
8,117
3
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north carolina
Here is your change to show how much smarter than me you are. I have no problem admitting it lol.

I walked by the homelite carb which I had removed. I managed to pull off the adjustment block so I in theory could reuse it now. There was only one problem there is an extra fitting on it. I have no idea what it does,

There is one small fitting which is usually the gasoline input connector. But then there are two large fittings. Both are brass tubes larger than the one I think is the gasoline input tube. So what the devil is the second large brass tube for. I don't remember taking anything off it which may be the problem with it to begin with.

So all you guys who know a lot more than me one of you should know the answer to this one. You know the homelite had the squeeze bulb on the tank lid. I wonder if the line was a second return tube for some reason.