Yamaha 701 tuning...

[Bad-Duck]

Hi everyone

Hi just finished to assemble all my performance parts on my 701 yamaha motor

I have a :
match case with cylinders
cylinders porting ( top shaved )
original head ( 190 Psi )
match the exaust manifold with cylinder
double 44mm carbs
Factory Type B pipe

I did the "jetting" today ...
110 low
140 hi
1.5 N&S
Spring ??? ( I don't know the force of the spring)

I put the SJ in the water on the trailer , and try to tune the carb ... something was wrong ...

My card was fresh rebuild , but I dind'nt change the needle ,the seat ( it was okay)

My question is : what could the spring change in my carb , and how do I find out if they are the right ones?

can anyone help me please ???
thanx in advance

Donald the Bad Duck

Québec
Canada

[skraggy]

Re: Yamaha 701 tuning...

http://server1.sbtontheweb.com/forum...ad.php?t=13965

[Bad-Duck]

Re: Yamaha 701 tuning...

Thank you Skraggy,
But the link that you gave me does not help me to find the kind of spring that goes in my carb ...

I have a :
match case with cylinders
cylinders porting ( top shaved )
original head ( 190 Psi )
match the exaust manifold with cylinder
double 44mm carbs
Factory Type B pipe

carb jetting:
110 low
140 hi
1.5 N&S
Spring ??? ( I don't know the force of the spring)

[skraggy]

Re: Yamaha 701 tuning...

If you are talking about the pop-off spring...it does...

It is adjusted by changing the size of the N&S, and the spring tension. There are 4 general strengths of springs - the less the spring is rated the lower the pop-off pressure will need to be to unseat the needle. For example, a 65 gram spring may give you a pressure of 15 psi, where a 115 gram spring may give you 50 (not actual numbers).

You test the pressure with a pop-off pressure gauge. With the regulator chamber open, wet the N&S with WD-40 or gas. With the pump body removed, attatch the gauge to the fuel inlet fitting on the body. Pump the gauge until it 'pops' noting the pressure gauge. Repeat this 3 times to get a nominal reading. Installing a heavier spring will raise the pressure. To adjust in small increments lower, cut coils 1/2 coil at a time and re-test.

If you are speaking of a different spring...let us know which one.

Hope that helps.

[Bad-Duck]

Re: Yamaha 701 tuning...

Yes , im talking about pop-off pressure spring ... how do I find out if they are the right ones ??? ... can I run with the original spring ? if my motor was modified ??? how many psi is the best for my motor ???

can anyone Help me !!!

Sorry for my very bad english ! lol

[skraggy]

Re: Yamaha 701 tuning...

When I rebuilt my carb,I put the normal spring in...and all worked fine.

If you put too light of a spring in,you will end up dumping too much fuel into the system.Too heavy and you will be starving for fuel.The best way to check it is to buy or borrow a guage and do it the way it is explained in the tech article.

I am not up on the mods too much,so this is the best I can help you.

And btw,,,your english is fine :)