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Turbocharged, Supercharged, and Hotrod Motorcycles: Re: [turbobike] BMW question

Re: [turbobike] BMW question

Robert Miles (rmzalbar@hotmail.com)
Tue, 16 Jun 1998 09:48:17 PDT

Hi Gregor,

I would guess that what you are having is an ignition misfire rather 
than a fuel delivery problem.  First look at your plugs.  If you are 
running lean, you will see signs of detonation on the plugs (rounded 
electrodes, little black specks on the center ceramic insulator) as you 
go lean under boost.  Ignition misfire seems more likely from your 
symptoms.  It's harder to put a spark through the denser air/fuel 
mixture that you get when you load up the throttle and generate high 
boost, and as your RPMs climb the coils have less time to recharge 
between firings, exacerbating the problem.  (Rob loses a coolness point 
for frivolous use of "exacerbating.")  An weakening ignition system that 
does fine under normal conditions can begin to experience problems when 
put under such loads as a boosted air/fuel charge.  You may have a weak 
coil or a leak to ground through a bad plug wire.  If your bike has a 
breaker point system, check out the points, dwell, etc. as well.  Bad 
points can cause a weak spark too.  Another cause might be a short in 
the electrical system that grounds out intermittently when the bike is 
thrust forward by acceleration, but I think weak ignition is your 
answer.  Hope this helps some.  Good luck!

-Rob Miles

'73 CB750K
'85 Dodge Omni GLH Turbo

Wish I had a turbo BIKE!

>I have a 1985 BMW K100RS with a kit manufactured by RB Racing and sold
>by Luftmeister (both of California). It's a fairly well sorted system.
>The bike has an intercooler and nonvariable boost set at about 8lbs
>for (I'm told) about 150hp at the rear wheel. Luftmeister has gone on
>to bigger and british things and isn't very interested in helping
>someone with a 10year old kit on their bike. RB Racing is nice but
>they just aren't helpful - I'm always getting the "Let me get your
>number" routine. I bought the bike used and it has about 40,000 miles
>- at least half of it with the turbo I'm guessing as I don't know any
>history for the first 20k.
>The bike runs strong but as I become less fearful of the boost I'm
>finding that the engine won't run clean in first or second gear. In
>first it's a bit slow to get going (no poppet valve) and when boost
>hits at 5000 it rockets really hard but then starts to miss and cut
>out at 7000-8500 (redline). Once you shift your back in the low boost
>and it's great until 7500-8000 or so and the same thing happens again.
>In third it's great and 4th and 5th are fine as well. I believe (but
>have no way of knowing) that these bikes had different chips put in
>for the mapping of the injection (they'd have to wouldn't they?) but I
>don't know. I also don't think that this was a problem when I got the
>bike but I can't be sure as I generally didn't wind it up in first or
>second as the thought of wheelie-ing a big sport tourer over was (is)
>a bit scary. I'm starting to enjoy the power wheelies and would love
>to solve this.
>Could it be old injectors? Could new (different) ones help? Not enough
>fuel pressure? Clogged fuel filter? It seems to do with the _rate_ of
>acceleration rather than with rpms alone.
>My mechanic rode it, got it up to 160mph, out ran a cop and loved the
>bike but had no real thoughts on the matter.
>Ideas anyone?
>Gregor Halenda
>Team Incomplet - NYC
>"Everyone that goes faster than you is an idiot
>and everyone that goes slower than you is a jerk"
>Get your free @yahoo.com address at http://mail.yahoo.com

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