VM29's on '77 GS750 with wiseco 850bb kit

[GS750]

Gday all, I have recently had the pleasure of receiving my "newest" GS750 workshop manual (haynes first edition)

Reading through there and noticed a page in the back section on performance enhancements which says to stick the VM29's on and it will really run nicer, especially with the 850+ bb kits.


Ok, my next question as the manual didnt really say too much more, is,
Are they $till available, and if $o how much?? Also do I need to change the inlet boots or anything else>??

[sharpy]

i Oz you be paying 700+ for 29s and 400+ for 33 smoothbores unless ure real lucky.

[GS750]

Thanks Sharpy,

Does anyone have any ideas on donor model bikes? I heard from my Uncle that Kwakka's had them but he cant remember the particular models :'(

[Nessism]

VM26's were used on the GS1000. I suspect they are just fine for your 850 build considering the K&N's you installed.

[GS750]

Ummmm. I decided I will change it back to the airbox (with a K&N) in the next few weeks.


I do loads of highway riding and often in the rain and I have noticed that the 1&4 filters are often either dry or saturated with water from teh rain.

I have noticed that when this happens the bike leans off on them 2 cyls.


Yes I do regular maintenance on the filters, usually at 500-600km, and on a long trip I pull up and give them a quick check and spray if needed.

[Coady]

Ummmm. I decided I will change it back to the airbox (with a K&N) in the next few weeks.


I do loads of highway riding and often in the rain and I have noticed that the 1&4 filters are often either dry or saturated with water from teh rain.

I have noticed that when this happens the bike leans off on them 2 cyls.


Yes I do regular maintenance on the filters, usually at 500-600km, and on a long trip I pull up and give them a quick check and spray if needed.

That does sound like a hassle. I recently upgraded to 850 pistons in my GS750 (standard pistons, not wiseco) with VM26's and jetting's pretty much the same as before - just a minor tweak to the pilot screws, but that may be cause I don't foul plugs like I used to.

I'm running a foam unifilter and 4 in 1 formula 1 pipe and performance is pretty good.

[GS750]

That does sound like a hassle. I recently upgraded to 850 pistons in my GS750 (standard pistons, not wiseco) with VM26's and jetting's pretty much the same as before - just a minor tweak to the pilot screws, but that may be cause I don't foul plugs like I used to.

I'm running a foam unifilter and 4 in 1 formula 1 pipe and performance is pretty good.

Hey Coady, when I stripped my 750B I discovered that it had already been 850'd using Suzuki 850 pistons. It was a real half arsed job though, they didnt use the 850 gasket, several rings were upside down, and the Orings on the bottom of the barrels were non existant, it also had a "kit" stuck in teh carbs with 120 mains.... It went really good but the bores were being washed down with the excess fuel.

My bro followed me on a 300km ride one day and after 60km behind me he flashed me to stop, and told me my bike was fueling in the exhaust. His face was RED like it was sun burnt.

I knew that the bike had fuel issues because when I got it a few weeks earlier I was only getting 180km from 16 litres.


Since then I did the wiseco 850 kit into my bike and it is running very well, tuned nicely, but there are still small issues with performance which I would like to address.

In the past few days I have thought more and more about this avenue, hence this thread on upsizing the carbs because I figure that if the GS850's had the 32mm carbs then surely it could only be of benefit to change mine since it is also 850cc.

[Coady]

In the past few days I have thought more and more about this avenue, hence this thread on upsizing the carbs because I figure that if the GS850's had the 32mm carbs then surely it could only be of benefit to change mine since it is also 850cc.

To be honest, sounds like a big hassle and expense to get a 1980 or later 850 head and CV carbs. Your still gonna have to tune them to match your setup and I don't believe there'd be a performance boost over properly jetted VM26's unless they do allow more mixture throught at WOT? Maybe an improvement in mileage however?

I haven't ridden an 850 with CV carbs however so I'm speculating.

[7981GS]

Just jet the 26's accordingly and you will be quite happy with it.
When I built my 750/850, I bought an '81 850 head so that I could use the 34CV's off of a 1000.
Yes, it ran great!
Would it have ran equally as good with the 26's? Don't know for sure but, if they were good enough for the 1000's, why not?

Daniel