Trubs? Engine dies - but only twice.

[Butch (cb)]

Nipped out to the SoF (Sunbeam Club) rally in Derbyshire this weekend. A round trip of around 320 miles for me.

My recently bought S7D being of a somewhat sickly disposition I ventured forth on the A10 (nominally '58 iron head bitza). Now I must confess I've really not used the bike a whole lot in the last couple of years, but she's always been real peachy.

First up, took an awful long time to get the carb to flood on the tickler when heading off. This with both taps on. I mention this only as an aside. Fired up in a kick or two as usual. No choke required. Rolling down the bypass not more than half a mile from my house the engine dies - both cylinders gone. I check for the taps though I know they are on, and do the usual desperate throttle wiggling as road speed falls away. Within just a second or two the engine lights up and all is well.

Later in the trip - outbound still, I get a similar thing. This after the bike has been parked up and with the fuel taps switched off. Engine stumbled (more noticeably then the previous time). Then died for a moment. Then all chimed in again.

I had no such problems today on the return, though the only time I switched the fuel off was for the refill when I add Castrol Valvoline to the mix. Tickled fine from cold this morning. Run with both taps on throughout.

Bike has done 3k miles since it was put together, and that included a magneto refurb. I'm inclined to think fuel but can't see how or why. I'll probably drop the taps and the float bowl when I'm nearer the bottom of this tankfull.

Thoughts? Thanks.

[bsa-bill]

 suggestive of classic tank cap blockage symptoms (intermittent maybe), when a fault happens like that it's always at the back of your mind that it's still there like some evil gremlin

[Greybeard]

I think I wrote up my similar experience: I had a plastic sleeve containing my route notes bungied over the fuel tank and the plastic was getting flattened over the filler cap vent hole which caused complete engine cut out every five miles or so! 

[Butch (cb)]

Indeed. I was running with just the base of a magnetic tank bag fitted to hold a map. I must admit, I moved that back a little from the filler on the first occasion, maybe it sat back over after a later fill up. Thanks.

[KiwiGF]

Based mainly on the fact that tickling took a long time maybe check the float chamber vent is not blocked ?(the vent is a small hole in the tickler).

It takes only two mins to check, by removing the tickler, it was blocked on my bike by a bug.......symptom was the bike starting ok but stalling after a short while, as the petrol could not get to the right level in the float.

[Butch (cb)]

OK - thanks folks; looks like fuel supply is favourite. And as usual I was lazy enough to post here before even taking a look. As noted, she ran fine all day yesterday over around 170 mile or so. I'll give the supply side a clean through from top to toe including that tickler vent Might experiment with some tape over the cap vent to see if that will trigger a similar problem.

Cheers.