Board index Flathead Power-Technical Questions, Answers, and Suggestions Knuckles Old Faithful?

Old Faithful?

Post Tue Mar 28, 2000 1:36 pm

Posts: 732
Location: nekoosa,wisconsin,usa

I have the most perplexing problem. Dago Red, my 47Fl doesn't want to hold his gas. No he's not being polite for the ladies. If I fill the tanks and go for a ride of thirty miles or so[far enough to warm up the motor],the right tank will flood thru the cap when the bike is placed on the side stand.Both caps are vented on these stock tanks.Can anyone shed some light on this potentially dangerous situation? BTW, I'm not overfilling the tanks.

Post Tue Mar 28, 2000 3:14 pm

Posts: 3158
Location: Central Illinois, USA
There can be other reasons, but beware of V-Twin Mfg.'s repop caps: the vents are not as original! The rubber gaskets swell from fumes and block the vents. I lost a flamed paint job to them! (I clipped the rubbers after they expanded, now they work.)

[This message has been edited by Cotten (edited 28 March 2000).]

Post Tue Mar 28, 2000 5:39 pm

Posts: 109
Location: holland
i had the same problem as cotton with those rubber gaskets and use the leather ones now.
also be sure all the ventholes are in the caps,maybe it sounds strange,but i have 2 militairy eaton (H-D?) caps with the topventhole (fumeoutlet) next to the gasketsurface drilled,but without the lower inletventholes in it!! I'll have to drill them myself.
also sometime ago a friend of mine had his caps chromeplated,somehow they closed off after this, and it took a long time to find out why his bike stopped every few miles!!

Post Wed Mar 29, 2000 2:56 am

Posts: 732
Location: nekoosa,wisconsin,usa

I believe that my caps are repros. There are vent holes in each cap. The caps both have rubber gaskets..... which I made an installed myself over twenty years ago when I restored the bike.The right cap rattles when i shake it .Is this normal?[ I have repop tanks on my Knuckle bobber and the style of cap is different but the right cap also rattles[ this suggests an internal check valve to me]. Cotten, You mentioned trimming the rubber gasket. Could you elaborate.I have experienced other troubles with venting over the years and have never really figured out the cause/effect relationship.I would run down the road at highway speed[60-65mph] with a staedy throttle and everything was fine. As soon as I would put a little more load on the motor[ such as a head wind or a steep hill the motor would give little warning and just quit.There would be no throttle response. I would slip in the clutch and coast a couple hundred yards and try the throttle only to have it recover and continue down the road like nothing had happened. I tried everything from new coils to different carbs to a magnito to no avail.I even went so far as to take a pair of repop caps which I drilled and tapped for external vents ala dirt bike. I have never been able to figure it out.

Post Wed Mar 29, 2000 5:07 am

Posts: 3158
Location: Central Illinois, USA
The original caps vented down on the edge of the cap in four places. The repops vent up under the cap above the line of the rubber. I clipped four notches to correspond to them, and had no further problem.

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