Wednesday, June 10, 2009

straight to video

OK! Well I yanked off 1/2 the discs from the supertrapp. Also backed the fuel-air mixture screw out 2,1/2 turns (from 2). Here you see two vids below, the cold start just to prove it starts after a day of rest, and then a few minutes later after it's had some time to warm up, maybe 2 minutes, I switch off the choke and directly after a backfire (cough) with a puff of smoke. Curiously it won't restart, even with the choke i startled it or something...motorcycle foreplay is a dark art when dealing with large bore thumpers: such sensitive beasts.

Now, IF there was an air leak, I would imagine that the idle would be surging much more than it is, even with the starter enrichener engaged, right?

Maybe something else is awry here.

Here you see it die and me go at it with the kickstart. Yes, I strap those lineman's boots on every time. Doing it with flip-flops would ravage even the heartiest Barbarian size 13.


  1. So it only starts with the choke/enrich circuit engaged? It revs happily enough it seems whilst the choke is on? Can you firstly bring the idle speed up with the adjuster (probably acting against your throttle stop on the carb) to see if you can pick the revs up whilst it's running on choke then back the choke off and see if it continues running at reasonable revs? You won't need much adjustment, you want to get it to sit at 2k rpm and if it stays running after the choke's off then your problem is in the idle adjuster and it's sorted (hopefully).
    Secondly if you're happy with where your idle adjuster is then try and get at the mixture screw whilst the engine is running and wind it out 1/4 - 1/2 turn at a time and see if the revs pick up. If they do then you may need to go larger on your pilot jet.
    Finally as it's running ok on choke but not other wise, your pilot jet may be blocked. Two choices; remove and clean with fine copper wire so as not to damage the brass jet, or buy new pilot jet.
    Good luck.

  2. Thanks for the review User.One - All seems reasonable. I'll recheck the idle screw from the weekend; I had turned it "up" a bit at that point, but maybe it needs more.

    I yanked the pilot jet this morning just to check it out. It looked clean. XR's Only sent me a different pilot jet than the stocker after rebuilding my engine. At some point I'll try the new one, tho it looks very similar, they've got very different size designations. Stock is: 65, XR's Only: 48. The XR's Only one has larger aeration holes drilled in the side of the barrel, but the ID of the two is hard to tell apart (Not that I'd expect to with pilot jets).

    Then there's the air/fuel mixture screw. I'll try fiddling with that today when I get home. Just to see if it does anything.

    When the bike refuses to restart like this, my intuition says it's flooded. Too much fuel; perhaps I'm running it with the enrichener too long. I don't recall other RFVC engines from my past needing choke for more than maybe 30 seconds.

  3. To be honest I was surprised that you ran it for 2min on choke, but anyway. If it was running very rich it would be putting out black smoke quite a bit. The XR's only pilot is a bit smaller then, I wonder if that lean-ness is your problem? I read that you rebuilt the carbs, so the dirt would have to have come from your tank, but you run a filter as I've seen. The mixture screw will help a little with the lean-ness of the pilot, but only a little.
    My intuition would say that if it was flooded, kicking it over 2-3 times with the decomp lever held on and throttle shut will clear any fuel out and on the next kick it should do the biggest firey fart you've seen and then start on the next kick. I don't think that's the case. Like I said, good luck as I know it's a bugger to sort, but worth it.