Questions RE: GS750B, extra work after installing wiseco K844 bigbore kit

[GS750]

Hi again to everyone here on the forum,

Well I have finally managed to get myself one of the Wiseco K844 kits for my good ole GS750B (1977), and I'm about to embark on the installation.


I was thinking and sorta confused myself with some questions I just wouldnt answer myself........


My current engine setup is as follows:
Stock cams
4-1 transac eggsauced (at least I think thats the brand):
112.5 main jets:
Boyer Brandsen CDI ignition with stock ignition coils and NGK Iridium plugs



My questions are:

1: will the carbs require re-jetting at all after installation? Idle jets etc?? I was thinking it might be necessary to re-jet, but am not certain...

2: Would (or should) the valve shim sizes vary greatly after installation?

3: Is the compression ratio shown as 10.25:1 going to be suitable for a street bike running 98 octane unleaded fuel or would it require cam duration to be changed (current compression ratio is from memory, only 8.7:1).

Thanks for your assistance.

Andrew
Bundaberg Australia

[trippivot]

you should be concerned with deck height and top ring end gap.

valve adjustment shims will be the same unless you resurfaced the valve or seat faces and valve tips. (now is the time to do it)

10.25/1 is in need of 93 or higher octane ( ron/mon) and duration of camshaft lobe has nothing to do with it. more deck height will lower the comp ratio. = thicker base gasket or thicker head gasket=

you might need to retard the ignition timing a little.

rejetting is going to be around a 10% increase of fuel across the board approx. more testing to be exact after break in period.

[tone]

Wot trippivot said with the added observation that to get the best out of this setup a decent flow & valve job will work wonders :-D

[GS750]

Wot trippivot said with the added observation that to get the best out of this setup a decent flow & valve job will work wonders :-D

Thanks for the reply's.

What is involved with the valve job? New oversize valves etc?

Thanks again,
Andrew

[tone]

Yep oversized valves better springs & a gas flow job by a reputable tuner/engine builder with the right kit, its not cheap but if done properly its the best tuning mod there is even on a engine with stock bores the results are surprising :shock:

you will see an improvement in torque & power with the setup you have but the limiting factor for making power will always be how much the head can flow.

[psyguy]

andrew, mate, it's a fine ginger ale you've got flowing in bundaberg :-D

[SqDancerLynn1]

Cam duration/ valve overlap can effect fuel requirements. It will change Cranking cyl pressure.Ideally you want 130-160 psi Your 98 octane is probably = to our 91 octane just measured different. Still you should be Ok. Jetting will probably be close, maybe go one size up. A little extra fuel will help cool the motor

[needtoride]

Wiseco 844cc conversion

I have a 1978 GS750 that is need of a rebore and wanted to go for the Wiseco K844 kit.

they say it increases the bore from 67 to 69 mm however all the technical spec on the GS750 is that it is 65mm (so is mine having measured it).

The external diameter of the liner as measured at the bottom where it sticks out of the block is only 72.5mm meaning the liner wall thickness would be a little over 1mm thick. Surely this is to thin??

has anyone actually fitted one of these kits to a stock GS750 block. Wiseco tech info says just a rebore is necessary. Tried to email Wiseco several times but no response