Vintage Dirt Bike Q & A

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PostPosted: Wed Jun 30, 2010 5:22 pm 

Joined: Wed Jun 30, 2010 11:30 am
Posts: 2
Hey guys,
So I am chomping at the bit to get this old beast going. I have a shop manual on its way to me as we speak but I just was hoping for some quick info that I cant find online. I guess the first is: what jets should this thing have in it as stock on a 78 Alpina 350? The Bing 84 is stock on these bikes right? I have been through it a few times now and have soaked, poked and blasted it all throughout but I just still cant get it to rev the bike worth a crap.

Since I have your ear, I'll tell you a little bit of whats going on. First off, I have good spark, good compression. I went through and cleaned it all and put new slide and bowl gasket. The float needle is sealing well and i have it set so the bowl is nearly full before it shuts off. When I drop the bowl, the absence of the floats puts the level of gas to about 3/4 full. I have tried raising and dropping the needle and it doesnt seem to affect things much. I try flipping the choke on and off during running and that also doesnt seem to affect it much which is weird to me. I can feel the choke mashing shut well and I replaced the rubber on the tip of the choke piston so I dont think its that. Now that I'm thinking this all through out loud, I am thinking this all points to an air leak maybe. I'll check the intake manifold and rubber mount when I get home. Never had luck with that spraying of carb cleaner/wd40 around the suspect leak area thing. Wont take any time to pull it off and cut a new gasket. I'm also unsure of the seal on the top of the carb body. I never replaced it cuz it looked good but it might be the wrong O ring altogether.. I'll check that too..I'm open to any other ideas on this.

OH.. actually, the first thing I am going to try when I get home is mounting up this 30mm KeiHin that I have. I know the jets are going to be way off but the carb works great and is sealed up well. For kicks I hooked it up last night but just needed a different mounting rubber which I have right here. So it will just take me a second to throw on there. If I can just make it rev past 3k it will prove to me the issue is carburation related...and yes, I wont run it long so I dont hole the piston in case its way too lean.

Alright, thanks for listening and please add your two cents.

Cheers, Beat

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