Drilled hole in my gas cap (removes tank vacuum)

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Local time
2:05 AM
May 9, 2008
Mesa, AZ
I'd been having problems with my fuel cap sealing up with a full tank and getting unreliable fuel delivery to the carb.

I took the tinyest drill bit I could find in my garage and drilled a hole in the top center of the gas cap. That completely solved the problem, and due to the way the gas cap is built, fuel does not splash out the tiny hole.

Took it out for a 10 mile ride yesterday and its running better than ever.
I did this too and now I never get air locks at all. When I'm leaving the bike in the garage for over a week or so I always put a bit of blu tac (i think its white tac in US) over the whole to stop the petrol evaporating and leaving nothing but oil in the tank. I have noticed that around the hole you get a bit condensation from the petrol vapours so it must come out a bit.
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Tank vacuum relief

I thought about drilling a hole in my Whizzer cap, but was wondering... is there a vented cap that fits the Whizzer tank?
Tank cap breather

The best way around this I have found is to buy a tank cap breather for a dirt bike, drill a hole just big enough to push the breather in and you're away! I do this on all my bikes and it works great. This is a good preventative measure that is usually not considered until your bike starts playing up miles away from home lol.
:unsure:Since you guys drilled the cap, why don't you make a crude fuel gauge using a stiff long wire and a "Jack-In-The Box" ball?
Hey mate, Just noticing this, i've got a mate who has a 70cc motor, when he takes the throttle up, it cuts down. such as to say when he puts it to max throttle it just dies.
have you had the same problem caused by the Vacuum seal in the petrol tank?
The 70 may need bigger carby or jetting.

From my experience the bike usually rides with no problems, then experiences the same as running out of fuel all together, with a cough and splatter, then nothing at all. The 70 sounds like it is possibly starved of fuel/air. Depending on where the engine was purchased it may be running the same carby as the 50's which means the engine cannot run to it's full capacity being starved of fuel and possibly air particularly at top end. You could try bigger jetting or better still a bigger carby. As a suggestion Skyhawk distributors have a carby designed with bigger jetting and air flow that seem to work quite well.
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