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I know this has been mentioned before and I did a search and found some interesting input, but this weekend I did a charity poker run and each time I had to stop I'd have to hit the starter and spin it one time then again the 2nd and it'd fire right up immediately. After it was over I stopped for fuel and as usual I got the typical swoosh. The tank has a vacuum ontop of the gas. So I did a test. Rode back home 40 miles away and opened the cap and let air in before attempting to start. It fired right up. Got home and did the same routine again and it fired right up.

Now I've got 2 stockgas caps so I drilled a vent hole in one. Fired up just like it should the next morning. Again this afternoon. The test continues.

I'm wondering if the vacuum ontop of the gas creates stress on the fuel pump and when the vacuum builds, the short primary spin on the starter just basically primes it then the second time I hitit,it fires right up. The 1st spin the engine is like starved for fuel. I've plans to rebuild a starter this winter and looking for a donor currently. But I'm gonna keep testing it and see where it goes. Maybe a problem and the caps need a tiny 1/16" hole to keep that vacuum out. All the bikes in the past I've had has never had such a vacuum over the gas. JR
 

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if you have a plugged inlet, the bike will be starved for fuel when you run.... I have always gotten that whoose, put I always swore it was air coming out of the tank, not rushing in
 

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The whoose noise is normal. The fuel system is pressurized somewhat by the fuel pump and as gas is taken out of the tank it creates a vaccum. Therefore when you open the cap air rushes in. The first half of the tank flows pretty easy but after that the fuel pump has to work harder.

The carbed wings from this era have extremely long runners and I've always suspected that the bike tends to flood itself a bit when first trying to start. Mine starts really good when cold or hot but in between it sometimes takes a couple of cranks to get it to run.

I find if I run the idle closer to 1050 -1100 rpm as shown on the bikes tack it seems to help starting.
 

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Since venting my spare cap,its fired up 1st time everytime. Only in the low 40's this am though and fired up as usual. Still playing with it. Did 34 miles from work and shut it down and it fired right back up, just pushed the start button and there she goes. I want to do about 50-60 miles down the Trace. If it helped it'll show there much better.
 

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I am very interested to see how this works out myself. I have noticed after about 15-20 miles mine feels a little weaker and idles noticably higher, Also I have to pump the throttle a couple of time to get it to hit. After reading your post and actually thinking about it I realise these are all symptems of a lean condition :gunhead:.

Sence I don't have a spare cap I will have to look and see if there is a way to do a temp vent on mine.
 

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My 2 cents! The gas caps are vented. If you turn it over and examine where the top cover is crimped onto the bottom you'll see three places where the crimp wasn't pushed to the bottom. The piston that sticks out of the bottom of the cap has two holes in it that allow air into the tank. Basic law of nature is that if something leaves a sealed tank then it'll build vacuum unless something else takes its place. I would think oldtoys1961 is seeing the gas in the lines being pulled back into the tank and somehow thats affecting the start. If you pull that cap apart I'll bet you'll find that the condensate that forms in the cap has rusted the passages closed. That's my story and I'm stickin to it!!

:cooldevil:
 

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Good theory.It crossed my mind too. The cap from the factory should be vented. It looks to be a simple layout. It is 2 layers and theyre crimped together. So I drilled a tiny hole through only the first layer right next to the word gas and stopped. Figured if something didnt work right I could always put in screw with some JB weld and keep it with the spare gas tank I have.

Didnt do any good as the vacuum was still there.Puzzling because the 2 holes in the bottom should be allowing a vent.
So I came back and went through the second, that kept the sucking swoosh sound out.

Its a vacuum and not pressure. Gas and pressure dont work well together and I checked many times. So it is a vacuum. There is a fuel pump but it basically suck in the fuel on the input line and pumps it on through output line to the carbs. I'm currently showing right at reserve on the red line on the tank presently, with a notch under the half tank reading last night when I went to work.
Fixing to fill up and go for a short 50-60 mile ride. I'll find out then if it helps. Could be these caps rust up inside even though clean outside and blocks any venting causing just that, a lean condition or starve. THe testing continues.JR
 

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JL Let us know what you find , have a similar observation myself. my idle even changed when I opened the tank while it was running after a short ride.
 

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JL Let us know what you find , have a similar observation myself. my idle even changed when I opened the tank while it was running after a short ride.
 

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I've suspected since I got my 1100 a coupla' years ago that the cap was not venting properly and felt that rust in it might be an issue. Thinking about the posts I've seen I remember that Polyphosphoric Acid can be used to dissolve it. Problem was I couldn't find any. Well a week ago I found some stuff I bought at Ace Hardware years ago that was labeled as "Snow Cap,Well Water Rust Remover". Its label said it could be used on metals. It is a white powder or fine granular substance. Per Wikipedia this type of acid is a white powder. The instructions said use a cup per gallon of water so I decided a heaping tablespoon in 2 cups of water would be cloase enough. I got the water almost to boiling, mixed in the powder and put the cap in upside down. After a few minutes bubbles started coming out of the openings and after about two hours they had mostly stopped. I gave it another hour, blew it out with compressed air and shot it with a little WD-40 just to make sure the water was out. The cap was quite clean and the slight amount of surafce rust on the bottom was gone.

Well since then the best I've been able to do was ride her back and forth to work on two days. I took the cap off at the end of each leg and there wasn't any air wooshing in or out. I'd say it was a complete success.



:action::cooldj::jumper:
 

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Well I havent been able to ride this past week. Its been in the upper and lower 20's here. Bout to go into DT's to ride. Did a short jaunt of about 50 miles and it actually fired up better. I want to take a good ride though of about 100miles to make sure. I dont believe it hurt anything and can only help if only a little. Hoping for some pretty weather next week as I have to go to MS. this weekend.
 
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