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Turbocharged, Supercharged, and Hotrod Motorcycles: Re: [turbobike] turbo gsxr

Re: [turbobike] turbo gsxr

Rick (gsxr1100@ptw.com)
Mon, 14 Sep 1998 21:42:24 -0700

HI all
    I have played a little with cam timing and so far it seems that 104 in
and 106 ex seems to work ok on my bike
Turbo Rick
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>> hello everyone,
>> I would like to get some info from other turbo gsxr owners who have a
>> Mr.Turbo draw thru system.
> I am using a modified MR.Turbo draw-through kit with an S&S Super E
>shorty carb on my 92 GSX-R11. I can't comment on the Mikuni HSR as I
>haven't tried one, but I can tell you about my experiences with the S&S.
>Firstly, I'm only running about 14psi of boost at the moment so my
>settings my not be relevant to you if your going to use significantly
>higher boost.
>As you have already said the transitioning on these carbs leaves a lot to
>be desired, and you will probably have to compromise a bit on the jetting.
>When I set the bike up on the dyno I found the best settings were:
>Main jet = .095
>Pilot jet = .038
>Float = level
>Air Screw = best fast idle
>Accelerator pump = not very much
>Ignition = 36deg BTDC off boost and 28deg BTDC on boost
>Plug gaps = .018
>With these settings the idle was a bit erratic but acceptable, varying at
>worst between 1,000-1,300 RPM, you could wack the throttle open under load
>in any gear from low revs and the engine would respond cleanly. These
>settings gave a nice clean power curve that looked great on the dyno and
>would have been fine for racing or hacking round the lanes. However when I
>rode the bike on the road at a steady speed and at low throttle using any
>rev's between 3,000 and 7,000 it would jerk and misfire (almost
>un-rideable!). So back to the dyno. The problem turned out to be that we
>were having to run the pilot circuit rich to get clean transitioning.
>I should point out at this point I have a compression ratio of 8:1. You
>may find that a higher compression engine is less susceptible to this sort
>of problem. Although I doubt you will be using high compression if your
>looking at 28PSI boost!
>For road use I have now found that a pilot jet size of .029, the
>accelerator pump set quite high and the ignition advanced to 40deg off
>boost and 28deg on boost works well, but I have to be gentle with the
>throttle below 3,000 RPM or the engine will die lean. Looking at the spray
>pattern from the accelerator pump nozzle I feel it's a bit weak at small
>throttle openings, so I'm going to try fitting a stronger spring to the
>pump. I hope this will cure the problem. (Fingers crossed).
>One other thing I found was that cylinders 1&2 tended to run richer at
>times than cylinders 3&4. I took a tip from Joe Haile's book and welded a
>divider plate in the plenum chamber, this seems to have cured that
>As for fuel delivery, I haven't had any problems with the S&S. At the
>boost level I'm running at the moment I've not even found it necessary to
>fit a fuel pump. I'm just gravity feeding the carb via a Pingle high flow
>fuel tap without any sign of leaning out.
>While I have got the attention of the [turbobike] mailing list I have a
>question. I'm currently running my bike with stock cams and cam timing. I
>wonder if anyone else has experimented with cam timing on a turbo M or N
>engine, if so what did you find were optimum cam settings?
>Tim Drew
>> hello everyone,
>> I would like to get some info from other turbo gsxr owners who have a
>> Mr.
>> Turbo draw thru system. The kit I just purchased came with a Mikuni HSR
>> 42
>> mm carb. From speaking with other people most prefer the ss super e
>> carb.
>> Now from what Ive been told from Mr.Turbo the mikuni carb offers better
>> transitioning thru the power band but has a smaller float bowl. The ss
>> suffers from poor transitioning but has a bigger float bowl. Both are
>> good
>> carbs for this application but if there is someone out there who has
>> tried
>> them both please let me know. I can return this carb for exchange if
>> needed.
>> This bike will be seeing 20-28lbs of boost  so if either carb has a
>> problem
>> with high boost fuel delivery Id like to find out before its put on the
>> motor. Thanks.    sebastian