Yamaha carb

[Dingie]

Does anyone know what company makes Yamaha's carbs and if they have a spec sheet that gives information about flow,bore sizes and applications.

[Markus]

They are made by Nikki, except for the very first V4 and V6 engines up to 86 or 87.

I have never been able to find any data sheets anywhere, though.

[GPI Racing]

Joe,

I have a set of 32's that I was messing with way back when. Choke butterflies removed and nozzles shortened. They worked better than any carb I had when we raced the V-4. Also have a set of 34's that you could run side by side. Just need your address. I do have a spec sheet from every Yamaha carb that they ever made. Nozzle sizes, orifices, passage ways, etc. I'll dig that out for you. I still haven't forgot about "the project".

Randy

[Dingie]

GPI racing, I have sent you a e mail with my address. I have checked everyplace for a spec sheet on the Nikki outboard carbs. without any luck. Randy you are going above and beyond giving me these to try .Thank you so much .I will let you know what changes with the carbs and the exhaust plate. Thanks again

[DonChicho]

Yammy Carbs: Nozzles Shortened ???!!!.
Does This Trick Will Improve The Performance On The Yammys ??
How To Do That ?

Thanks,
Don

[Ray Neudecker]

I found that removing the nozzels, indexing and cutting a notch in the rear gave a slight acceleration gain in a specific application. An old trick from a circle racer. Never tried just shortening, but can see how it would work. It did show a slight gain on the dyno.

[Dingie]

Looks like another cat may be out of the bag.Thinner choke plates cutting screws on the plate clearing anything that is blocking air flow thru the carb may help some.A gutted 32mm carb without choke plates may have as much flow as a 34mm carb with a choke plate installed.

[Ray Neudecker]

We take the chokes out and use a primer. Any real thinning and you will have extra pieces inside the motor.

[GPI Racing]

Joe,

You should have the carbs in a few days, mid week I would think.

Don, The nozzles are from a V6 carb. They were not changed to lessen air flow but to change the signal at the nozzle tip. This is mainly midrange or partially closed butterfly conditions that the short nozzle responds to. At WOT the nozzle really doesn't care where it is in the venturi. Remember guys that airflow thru these carbs (and engines) is not supersonic. It is quite slow actually. Two stoke motors respond to intake tract length tuning (sonic or sound waves that "pull" the charge in) much more than airflow reducers like removing the plates etc. The engine can be tuned on the front end sonicly just as the exhaust tuner shape/length effects it from the back end. (super long{6+ inches} velocity stacks are one such item) I removed the chokes and ran an OMC primer shooting in the oil nozzles to make the motor start better. As far as the nozzle I used, this was 1990 and , to be honest, I can't remember short of taking them out and measuring them. I do think they were from the 225 excel but I could be wrong.

If you guys want some interesting reading, try to locate a copy of "Two Stroke Tuners Handbook" by Gordon Jennings. This book, while writen over 40 years ago, is full of equations and real world facts that are as true today as they were in the '60s. It will amaze you how most of the questions and theories discussed here are featured in this book. All about volumes, flows, sonic tuning, intake shapes, head shapes and designs, and more info than most will ever fathom. I think you'll agree after a quick read that most of this is rather simple and "old" technology.

Randy

[Dingie]

That sounds fantastic Randy.I have bought and read two-stroke performance Tuning by A.Graham Bell a few times. I keep going back over the exhaust section.I wish that someone made a outboard performance book.The 2 stroke basics are the same idea but outboards exhaust seems a lot harder to fine tune to me compaired to the go cart and motor cycles. I cant wait to try and study the carbs. I have to try and find a copy of Gordon Jennings book I have heard it goes deeper into theory than A. Graham Bells second edition that I have. I read about cutting nozles and changing angles I keep trying to compair these two strokes with the four strokes we cut off air horns/choke plates on Hollys and wanted clean cool air off the windshield .The more air the higher we could twist them small block chevys.Thta why the Nascar restictor plate work the motors cant turn those ultra high RPM with out air 15 parts air to one part fuel the more air the more fuel on those small blocks .I have to stop trying old car tricks and go to basic 2 stroke ideas,its a hard change over. Thanks again Randy

[Ray Neudecker]

I thought Jennings book was the two stroke Bible. He certainly covers all the basics.

[Markus]

We have been running 36 mm carbs with an electric primer pump instead of choke butterflies. It works great - the engine starts extremely smoothly. I once posted a picture of the installation of the pump on this forum, so anyone interested should try the search function.

The length of the nozzle influences how early or late the main circuit kicks in. We have had various nozzle lengths, but never tested them against each other in a scientific way.

GPI racing, I would love a copy of that sheet as well. Please send it to me as well when you find it.