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 Post subject: VM Carbs on 76 Buffalo?
PostPosted: Wed Jul 04, 2018 7:42 am 
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I think I found some old posts that cover this, I am reading them now. Any install tips would still be appreciated.



Has anyone put VM or flatslides on a newer Buffalo?

After fiddling a bunch with the CV carbs on my 76 Buffalo, I think I would like to use a set of VM Carbs or modern flat slides.

I know the CV's can work fine. I have 34mm flat slides on my old H2 that has fantastic fueling that I have not been able to achieve on the Buffalo with chambers, pods and the CV's.

Besides the carbs, cables and single pull throttle what is required? I am thinking the carb manifolds to the cylinders could be a problem along with hooking the oil pump cable up to the pump.

Thanks and happy 4th!

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PostPosted: Wed Jul 04, 2018 9:07 am 
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72 (J) and 73(K) models had OEM versions of VM32 carbs and used a cable with 4 way splitter to pull all three carbs plus teh oil pump. Early oil pumps (310) had a slightly different arm. Either get an earlier pump or find a way to modify the arm - I swapped the arm from an early pump onto my later (74) pump).

Next issue is that aftermarket VM34 carbs are bigger than those fitted to J/K models and require different rubber manifolds. I don't remember the ones that people use, but there's a thread on here that mentions them.

Lane (rngdng) fitted a set of 34s to Blueboy and evidently they make quite a difference.

My sometime drag race bike is more or less stock and runs fine with stock OEM BS40 carbs. Where in the rev range is yours an issue and what filters are you using?


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PostPosted: Fri Jul 06, 2018 10:48 pm 
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I am using Uni foam filters. Runs awesome from 3.5K to redline. Idle to 3.5K is the issue.

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PostPosted: Sat Jul 07, 2018 7:57 am 
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Hmm. Have you tried larger pilot jets or altering the mixture screws ? If the idle is OK, you may need to raise the needles.


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PostPosted: Sat Jul 07, 2018 8:44 pm 
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Where are the mixture screws located on these CV's and which way would you go with the screws?

47.5 pilots, starts and idles perfect. Main jet is 117.5. I have dropped the needle one notch, it was in the lowest one and it is not as blubberly as it was. Maybe I should go one more to the middle notch?

The stories of part throttle issues with the CV's and pods have me spooked about dropping the needle too far.

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PostPosted: Sun Jul 08, 2018 7:48 am 
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http://pinkpossum.com/GT750/carb/BS40carbs.htm

47.5 pilot jets are probably OK . Mixture screws are at the front of the crabs close to the rubber manifolds. Unlike slide carbs, out=rich

If needles have the clip in 4th notch down, I would leave it there to be safe, but after tweaking the mixture screws, if it's still flat, you could try raising the clip to the middle slot to drop the needles to see what the effect is.

Are you sure that the flat spot is carbs and not just the pipes?

Try to get it set up on a dyno with exhaust gas analysis so you can see the Air:Fuel mixture.

Another thought is that it might need more advance down low, but do add that you need a programmable ignition.


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PostPosted: Sun Jul 08, 2018 10:34 am 
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Thanks for the advice.

I just checked the fuel screws and they were at 1 3/4 turns out from being closed all 3 carbs.

I am sure some most but not all of it is the pipes. I don't mind it being flat down there as long it is running good. With the needle in the 5th notch it was blubbery like choke was still partially on. In the 4th slot it seems to be better. but still a little blubbery.

The bike has a Dyna ignition on it for a Harley that Wayne the previous owner installed. Not sure I would know how to change the timing with it.

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PostPosted: Sun Jul 08, 2018 11:50 am 
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I'm surprised that no-one has mentioned the diaphragms. If your diaphragms are knackered (too soft, stretched, perforated or cracked) you will find it impossible to correctly tune the carbs.
Genuine items are still available but expensive as they come as an assembly https://www.ebay.co.uk/itm/Genuine-Suzuki-GT750-L-M-1974-75-Carburetor-Diaphragm-Assembly-13500-31210-000/263679981091?hash=item3d648d3623:g:RfQAAOSwx4xa9hZu
You can get pattern ones https://www.ebay.co.uk/itm/Suzuki-GT750-Gasschieber-Membrane-Librane-patentiertes-System-3-Stuck/231461995286?hash=item35e435c316:g:MrsAAOSwwAFbAyiu
Using a proper airbox may also help solve your problem.


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PostPosted: Mon Jul 09, 2018 7:43 am 
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Sounds like time to check the ignition timing.

There are three ways to check timing.

Least accurate: use the timing marks on the propeller to see when it sparks. Take the lugs out and lay them on the head (in the HT leads). turn on the ignition and slowly turn the motor over to see where it sparks. The p[roblem with that is that there is a lot of slop in the propeller so it may be off.

By the book: Use a timing gauge in each plug hole to determine the exact point that it fires on each pot. You can also make up a test light and watch when it lights up. That's how DYNA tell you how to do it.

Use a timing light: You could also fit a degree wheel to the alternator and a pointer and determine TDC with a positive stop and then check timing with an automotive timing light.

http://pinkpossum.com/GT750/Dyna%20S.htm


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PostPosted: Mon Jul 09, 2018 11:42 am 
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The carb adjustment book I read for the Buffalo said set the fuel screws a 1/2 turn. Mine are at 1.75 turns. Should I try turning them in some before messing with the timing?

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PostPosted: Mon Jul 09, 2018 11:52 am 
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I wouldn't mess with timing, but it's a good idea to know where it's set and to know it's right.

On those carbs, IN = leaner, so try that and see how it impacts idle and just off idle.


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PostPosted: Mon Jul 09, 2018 12:03 pm 
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Thanks. I'll try that first, 1/2 turn at a time. It may be the weekend before I can tweak the carbs and ride it.

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PostPosted: Fri Jul 13, 2018 10:55 pm 
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I went to adjust the fuel screws tonight. I turned the screw in 1/2 turn on the left and center carb. The right carb didn't have a screw? Looked like it was never drilled to have one.

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PostPosted: Sun Jul 15, 2018 10:48 am 
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That's odd. Can you post or email me a picture of that?


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PostPosted: Sun Jul 15, 2018 12:31 pm 
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simmons1 wrote:
I went to adjust the fuel screws tonight. I turned the screw in 1/2 turn on the left and center carb. The right carb didn't have a screw? Looked like it was never drilled to have one.

look on the other side of the carb?


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