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Post by katt on Jul 19, 2018 20:10:14 GMT -5
When gas runs low and i am going uphill i often notice misfires i run lean and then at a stop my engine dies. I got to turn starter with throttle open for 10-15 seconds and then start regular and if it catches spark need to instantly rev up to start engine, then it runs normal again until next hill or until i top up on gas.
Guess this is due to catching air trough gas tank instead of gas and then that air bubble got to travel trough fuel line into carb and exit trough the combustion chamber?
I am very tired of this and feel like i might burn my starter doing, will removing petcock and running fuel line directly from gas tank to crab make this problem go away? petcock
Another observation when my gas level is low it runs lean again probably catching some air from gas tank making mixture more lean, enough to work but lean. I can notice instant performance improvement when i fill up the tank.
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PirateLabs
Scoot Enthusiast
Posts: 296
Location: Bowling Green, KY
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Post by PirateLabs on Jul 19, 2018 20:32:31 GMT -5
Maybe a partially clogged fuel filter and having a full tank creates enough pressure to overcome it? I have run out of gas on my scoot and it ran just fine...until it quit and the tank and fuel line were dry. Also could be a partially clogged vent hole in your gas cap. Air has to get into the tank for the fuel to flow out of it.
Other than that...I have no idea.
Bill
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Post by katt on Jul 19, 2018 20:50:55 GMT -5
I have changed gas cap not so long ago.
Fuel filter maybe its kinda always only 30% full every time i look at it and when this thing happens its like 5% full.
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PirateLabs
Scoot Enthusiast
Posts: 296
Location: Bowling Green, KY
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Post by PirateLabs on Jul 19, 2018 21:18:03 GMT -5
I have changed gas cap not so long ago. Fuel filter maybe its kinda always only 30% full every time i look at it and when this thing happens its like 5% full. Yes, mine is only about maybe 1/2 full no matter what I do to try to get it filled so, I guess that is the way they are on these things.
Bill |
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Post by GrumpyUnk on Jul 20, 2018 9:21:44 GMT -5
Maybe check the outlet from the tank. Most have a length of plastic tubing with screened holes built in that slightly filters the fuel before it flows out the bottom. If plugged, that 'last bit' of fuel in the tank may not flow as well as it has to get past the accumulated crud that will be gathered at the outlet.
You can remove the fuel outlet from the tank and check. The outlet is at the lowest point in the tank, so going uphill should not have much effect, IF the outlet is clear. The lowered vacuum in the intake may allow the vacuum operated petcock valves to slowly close, limiting flow from the tank through the petcock. A manual petcock would not have that characteristic.
tom
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Post by pinkscoot on Jul 20, 2018 20:14:11 GMT -5
If you go the manual route be sure to put a cut-off valve and fuel filter in line.
Edit: And block off your vacuum line. |
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Post by katt on Jul 22, 2018 16:26:54 GMT -5
After day struggle with engine taking apart for inspection due to false impression that i have broken chain or piston and in reality it was fuel supply issue i got a new filter, and run it trough petcock with a nice clear fuel line (yes its fuel line hose) so i can see the gas flow.
Filter from AutoZone. Small one was $6 something this 3-4 times bigger and was just $4 i decided to put it to have better flow.
Yeah its like having grenade with gasoline under the seat, oh well, i don't think its dangerous.
 
Used remaining fuel line as vacuum line.
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Post by 90GTVert on Jul 22, 2018 17:21:36 GMT -5
If you start having problems now, make sure the fuel hose isn't collapsing when used as vacuum hose.
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Moat
Scoot Member
Posts: 88
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Post by Moat on Jul 24, 2018 4:10:31 GMT -5
See that upward loop in the fuel line where it's red zip-tied to the frame? If that's above the lowest point of the fuel tank, your problem could be there. Fuel lines should be routed to flow downhill all of the way from tank to carburetor, if at all possible.
Bob
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Post by jdl357 on Jul 24, 2018 6:06:17 GMT -5
I think I just figured out my problem by reading this post. I just started using very soft fuel line as my vacuum line too and damn if it's acting as if fuel starved and running lean! I didn't even think about it being compressed by the force of the vacuum!! I'm having the same symptoms as you, I think putting the original vacuum line back and routing the fuel line 100% downhill from the tank will likely solve both our problems!
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Post by katt on Jul 24, 2018 13:07:13 GMT -5
See that upward loop in the fuel line where it's red zip-tied to the frame? If that's above the lowest point of the fuel tank, your problem could be there. Fuel lines should be routed to flow downhill all of the way from tank to carburetor, if at all possible. Bob You right its not perfect however i did not want to let it loose because it goes around the shock and might eventually rub on it, i left it like this for test run.
That clear line setup is what i did after adding filter, perhaps i did not need that long of a line going to petcock, but if petcock fails i can simply plug line directly into carb.
I think I just figured out my problem by reading this post. I just started using very soft fuel line as my vacuum line too and damn if it's acting as if fuel starved and running lean! I didn't even think about it being compressed by the force of the vacuum!! I'm having the same symptoms as you, I think putting the original vacuum line back and routing the fuel line 100% downhill from the tank will likely solve both our problems! Perhaps i should do the same my old line was very small OD and it cracked this why i had to replace it, new tube that was bigger diameter, and this fuel line even bigger diameter, however it is soft.
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Post by jdl357 on Jul 24, 2018 15:22:31 GMT -5
If you can, go to an auto parts store and get some designed vacuum line or at least use fuel line that's not too soft that it gets compressed. I'm not sure how strong the vacuum is coming off the intake, kind of curious about that.
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Post by katt on Jul 24, 2018 15:29:15 GMT -5
If you can, go to an auto parts store and get some designed vacuum line or at least use fuel line that's not too soft that it gets compressed. I'm not sure how strong the vacuum is coming off the intake, kind of curious about that. Pretty sure its stronger with more RPM, but not as strong to fold the hose, i am running fine now, any thick rubber hose will do though does not have to be for vaccum line hose, i prefer home depot for better price will check next time i am there. |
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PirateLabs
Scoot Enthusiast
Posts: 296
Location: Bowling Green, KY
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Post by PirateLabs on Jul 24, 2018 20:23:03 GMT -5
Vacuum is highest when the throttle plate is closed and drops as the throttle is opened.
Bill
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