Blaster 701 carb setup

[jri93]

Hi, so i finally got a chance to take my blaster out for the first time. Bought it and it had bad reeds so after getting the motor all fixed and put back together it had a small running issue. Long story short, it has a lean spot at about 1/3 of full revs. If i roll on the throttle slowly it is ok and will rev out, but if i go from say 1/4 throttle and then slam it, it cuts out and hesitates, and i have to back off the throttle and then lay into it slowly till i get past that point. Once it is past that point it screams like a bat out of hell on the top end.

Anyway im hoping some more experienced members can save me some tunning time and help me out with a base starting point so i can see how far off i am.

My setup is as follows,

61x 701

Milled head, 180 compression
Ported cylinders
factory b pipe
Aftermarket flame arrestor

Stock single sbn carb
all i know about the carb is it has a 145 main jet.
I couldn't find a number on the low end jet when i had the carb apart. also it has a silver pop off spring, i didn't realize at the time there is a dull and a shiny silver so i don't know which it is.
im at about 2 turns out on the low end and 2.5 out on the high. I tried messing with the high end but it didint make much difference so i think it is either a jetting or pop off issue.

If anyone can help me out with a suggested base setup, Jet sizes, pop off spring, ect. It would be appreciated. I know this setup is very common so there should be plenty of knowledge out there.

Thanks!

 

[Yamaha785]

Sbn 44 with that setup.
115 gram spring
1.5 needle and seat
145 main is ok
120 pilot you probably have a 115
1.5 turns out on both

 

[Waveblastermaster]

^^ what i was gonna say maybe even about 2 turns out

 

[Heelz23]

I have a similar issue and getting ready to put it in the water for the first time. Protec kit I used to rejet carb said high end turn out 2 and the low out 1.5.

This is what protec sent me for my pipe set up.

135 main jet ​

120 pilot jet ​

2.3 needle valve ​

65 gram spring ​

 

[jri93]

awesome guys thanks for the help! Im going to pull my carb apart today and see where i'm at.

 

[jri93]

ok so i pulled the carb apart. it has 145 main, 120 pilot, 65 gram spring and 1.5 needle. im confused about the first response saying to use a 1.5 needle and 115 gram spring. that puts my pop off pressure at 55psi. From reading the mikuni manual it says that modified engines require a lower pop off pressure and most performance applications require below 30psi. Based on the chart i am currently at 32psi and it has a lean hesitation so wouldn't i need to lower my pop off pressure, not increase it?

 

[Crab]

Don't use the chart, popoff must be tested every time each Carb. 25-30psi should work great

 

[Matt_E]

I cannot think of a single application where you'd use 1.5/115 popoff combo in a single 44 SBN. That's 100% wrong

 

[jri93]

thats kinda what i was thinking.. according to the mikuni manual with my current set up.. 1.5 needle and 65 gram spring i should be around 32 psi. it seems from the research i have been doing most people with modded 701's are running closer to 20psi. so i ordered a 2.0 needle and think i will start with an 80 gram spring.

 

[Matt_E]

Yes, 20-25psi is typical in your situation

 

[Yamaha785]

I was just going off a factory pipes website. That's how mine is setup and it rips. It maybe wrong but it works on mine no hesitation at all

 

[myusername2013]

Will keep this in mind for my tuning

Sent from my EVO using Tapatalk 2

 

[Matt_E]

I was just going off a factory pipes website. That's how mine is setup and it rips. It maybe wrong but it works on mine no hesitation at all

Yes, those are the specs of Factory Pipe's site....for the stock dual 38 setup, definitely NOT for the stock single 44.

 

[RSKI]

Yes, 20-25psi is typical in your situation

Matt_E is like the all knowing grand father that makes sure you're putting thought and effort into solving the problem before he drops his knowledge bomb on your head. yes, I just respectfully compared you to a frail elderly man.

 

[Matt_E]

My wife would laugh hysterically, because she thinks I am like an overly obsessive-compulsive nerd man-child

 

[Big Kahuna]

My wife would laugh hysterically, because she thinks I am like an overly obsessive-compulsive nerd man-child

Arn't you?

 

[Matt_E]

I didn't say she is wrong.