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Discussion Starter · #181 ·
Did you try turning it off and then back on again?
My wife works in IT, she jumped at the opportunity to drop this one on me a month ago.

I think you've got a small leak in the fuel line or fuel filter that is causing the air bubble to break the siphon and causing vapor lock. I would replace the fuel line, delete the fuel filter and use the oem style spring fuel tube clamps. If possible, try to route the fuel line under the carb/air filter.
I'll order some good clamps, I looked around and couldn't find anything laying around.
 

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I'm going to take another shot a curing the fuel problem on MY bike. And this is it.

Hoping to use the 90° barb to lower the fuel inlet of the carb a bit more. I'm not positive that this one will fit...but I'm 95% certain that the ones from a early CT70 carb will fit, if this one doesn't.
I'll report back after I try it.
 

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Fuel flow issues are so annoying, I often get a bubble in my hose like you do in the last picture but I've had no problems like that.

If possible I recommend not going the manifold diaphragm pump route as I have done similar before on a go kart project and whilst it did work it would force the float down on the carb and flood it at higher rpm, I remedied this a little with a fuel return overflow pipe back to the tank to relieve the pressure and it can be made to work but it was a pain to get right
 

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Discussion Starter · #187 ·
Extra gear and 2hp bump in the Grom. If they do the same to the Monkey, I would happily grab it instead.

Speed edit - Apparently they are using the new engine in the Monkey too. Now I'm slightly more interested.

The thing is, I have my Baja which does 60mph already. I think if I were to move over my Baja transmission (4 speed) I'd be plenty happy with that and not need anything else for the street.
 

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I'm about to pull the motor, sell the roller, and buy a 2022 Grom.
I like the Grom too.
I recently seen one at the gas station. A kid was gassing it up...he looked to be about 16 years old.
But I was able to look it over, in person, again. It doubled my interest. Very cool bike. Brand new, Honda quality, etc.
But it's a different thing. Far cry from my vintage Z's and CT70's.
Lots of folks mention their "big bikes". A Grom would be my "big bike".
A vintage car guy might have a bunch of 50 year old Camaros, then be tempted to buy a brand new one. But that's no reason to sell off the vintage cars...it's not a replacement for his collection...but a PART of his collection.
I say, go get yourself a Grom. I bet you'll love it. But, keep your C70.
 

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I'm going to take another shot a curing the fuel problem on MY bike. And this is it.

Hoping to use the 90° barb to lower the fuel inlet of the carb a bit more. I'm not positive that this one will fit...but I'm 95% certain that the ones from a early CT70 carb will fit, if this one doesn't.
I'll report back after I try it.
This doesn't fit. The carb side is 8mm, and I need 6mm.
A Google search turned up a genuine Mikuni version...but I think it was about 25 bucks.
I think I'm better off to pick up a cheap CT70 carb bowl and rob the fuel inlets.
 

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Discussion Starter · #191 ·
Thanks for the feedback Kirrbby.

Update -

Got my nice fuel clamps in. One on the tank nipple, one on the carb, deleted the fuel filter. I opened the bowl drain until gas completely flowed nicely, closed it up and let it sit for an hour. Came back and it was looking like this.

I can run a water bottle from the handle bars with no issues, which is great and all but I'm not going to make that permanent. I need to figure out this tank.

275948
 

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This is crazy! What gremlin is living in your tank…or what damned spirit of the C70 is haunting you?


Sent from my iPhone using Tapatalk Pro
 

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How about checking the oil and seeing if it has or smells like gas?

If it smells like gas, drain the oil completely, leave the drain plug out and refill the fuel line by opening the carb float bowl drain. Put a pan under the oil drain and see if there is gas in it an hour or two later.
 

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Already tried running the fuel line under the air filter?
This has been painful to watch. With everyone making suggestions, the one above is the most useful one (I think someone else also mentioned this a while back.). There are only two places the air can be coming from. If it was coming from the tank end, it would be because there is not enouh gas in there, and occasionally the gas sloshes enough that some air gets in the line. Pretty easy to put gas in and test this theory, but I doubt it is the culprit. The other way is through the float valve. The vibration of the engine may be great enough that the valve never totally closes, or that it sucks gas so fast, the the valve is open constantly. If the second possibility is the case, the vent on the carb may not be big enough, or the tank outlet is too small to keep up, and bubbles are drawn into the system. Setting your float higher may solve the problem. Regardless of how it happens, a longer loop of hose that runs lower than the carb bowl will minimize the problem. Loops like this are common to most motorcycles, to minimize vapor lock.
 

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Discussion Starter · #199 ·
How about checking the oil and seeing if it has or smells like gas?

If it smells like gas, drain the oil completely, leave the drain plug out and refill the fuel line by opening the carb float bowl drain. Put a pan under the oil drain and see if there is gas in it an hour or two later.
Also, have you run or ridden the bike since you rerouted the fuel line?
I will check and report back. I have not ridden it, raining since I had the chance to do the new lines.

Already tried running the fuel line under the air filter?
Yes, I have. It actually ran a bit longer before the line dried up.

This has been painful to watch. With everyone making suggestions, the one above is the most useful one (I think someone else also mentioned this a while back.). There are only two places the air can be coming from. If it was coming from the tank end, it would be because there is not enouh gas in there, and occasionally the gas sloshes enough that some air gets in the line. Pretty easy to put gas in and test this theory, but I doubt it is the culprit. The other way is through the float valve. The vibration of the engine may be great enough that the valve never totally closes, or that it sucks gas so fast, the the valve is open constantly. If the second possibility is the case, the vent on the carb may not be big enough, or the tank outlet is too small to keep up, and bubbles are drawn into the system. Setting your float higher may solve the problem. Regardless of how it happens, a longer loop of hose that runs lower than the carb bowl will minimize the problem. Loops like this are common to most motorcycles, to minimize vapor lock.
As painful as it is to watch, try being on my end attempting to figure this out. I have maybe 30-45 minutes a day and if I'm lucky I can find an hour on the weekend to poke around with it.

Tank - I keep the gas tank full, after I mess with the bike for 5-10 minutes, I top it back up.
Vent - I could drill it out a little more? I drilled out the vent holes on the gas cap already.
Float - I'll see if setting it higher helps, should I be looking to move to a larger carb.
Routing - I have run the line under the air filter (as mentioned above). It bought me some more time but it still ended up drying up the line in the end.
 

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I will check and report back. I have not ridden it, raining since I had the chance to do the new lines.



Yes, I have. It actually ran a bit longer before the line dried up.



As painful as it is to watch, try being on my end attempting to figure this out. I have maybe 30-45 minutes a day and if I'm lucky I can find an hour on the weekend to poke around with it.

Tank - I keep the gas tank full, after I mess with the bike for 5-10 minutes, I top it back up.
Vent - I could drill it out a little more? I drilled out the vent holes on the gas cap already.
Float - I'll see if setting it higher helps, should I be looking to move to a larger carb.
Routing - I have run the line under the air filter (as mentioned above). It bought me some more time but it still ended up drying up the line in the end.
I have been there. This kind of thing is the most frustrating, where it seems like simple physics should be easier to figure out. Stick with it, there is a solution somewhere out there. The other place where air can leak in like this is a loose float valve seat, or a missing seal on the valve seat.
 
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