1995 Yamaha 70 BETO Carbs

[sasko1980]

Hi all.

Has anyone tried to swap the middle carb with a upper or lower ?
Let me explain.
Yamaha 70 : 3 carbs :
Cyl 1 upper carb
Cyl 2 middle carb with enrichment
Cyl 3 lower carb

Has anyone tried to remove the middle carb with enrichment and to install a
(lets say) a spare carb from cyl 1.
So it will be 1-1-3.(upper-upper-lower) In this set up the prime start will be disabled as the middle carb is removed.

Will it work ???

Stupid as may sound, has anyone tried this setup??

What about No.15(90445-07M02-00 diagram) hose that goes from middle carb to body and another hose No.17 (6H3-14349-00-00 pipe)

[99yam40]

It will be very hard to start and warm up without the prime start enrichment would be my guess.

Not sure about your 70 but my C40 has a different main jet in the middle carb

[sasko1980]

The middle carb has a different main jet, it smaller compare to other two.

What do you think about those two pipes that goes to the motor from the middle carb. Are they providing suction or vacum for the enrichment??

[99yam40]

I believe my C40 has a bigger jet in the middle carb.
been awhile since I bought new main jets for the motor, so I could be wrong

How do you plan on starting this motor of yours with no choke or enrichment system?

one is a pulse port the other sends extra fuel to all cylinders during start up and warm up

[sasko1980]

How do you plan on starting this motor of yours with no choke or enrichment system?

I can fire it up with no choke, no prime start, so my idea was what you dont use,you dont neee it.

What do you think??

Another question , this may require a new thread!!

How does the A/F screw acts to the carburator. How can you tell that is ok,or not ok setup?
Manual recomends for 70 yam 1—1/4 +-1/4. If you open up one of the carbs screw what about other two, how the motor acts?? Never tried to mess up with these screws. How can you adjust the middle carb, when the middle spark is starting from 1500 rpm up??

Why pulser, why had to be a pulser for middle one??

What CDI are compatible, like ,will the CDI from a 90hp work on 70hp and back 70 to 90??

[99yam40]

all I can recommend is to run it like the engineers designed it

Or play with all sorts of parts if you have the money and time

[sasko1980]

The middle carb has a different main jet, it smaller compare to other two.
?

My mistake, all three main jets from the carbs are the same in size !!!

[sasko1980]

all I can recommend is to run it like the engineers designed it

Or play with all sorts of parts if you have the money and time

I have three spare carbs from that 70 yam.
so i wanted to swap the middle one with a different, tought that someone tried that before me.

Thx for your help.

[rodbolt17]

not gonna happen.
without some type of enrichment for cold start that motor will NEVER start cold.

why not simply fix it???

BTW your motor is prime start.

you can push the choke switch all you wish but that witch does NOTHING on the motor.

when the prime start system works, it works well.
when it does not work it is simple to fix.

[sasko1980]

you can push the choke switch all you wish but that witch does NOTHING on the motor

Did you mean a red switch on middle carb???

[rodbolt17]

do you have a clue on how that prime start system works?

do you under stand why ALL articulated rod internal combustion engines REQUIRE a richer air to fuel ration when cold ?

why re-engineer a system that is very simple, works very well and is easy to repair on the rare failures?????

[99yam40]

the red lever in not a choke switch.

the key switch on con*****er when pushed energizes the choke on some motors that have chokes, which your motor does not have.

Why in the world would you want to start messing with the systems the engineers created and work so well on your motor?

[sasko1980]

Not messing up, just wanted to try to solve my problem with motor.


As im waiting for dva to arrive to check the cdi outputs lets recap.
I once again checked the fuel system, clean already clean carbs, tested the pump, clean the filter.
So Im shure that the fuel lines are ok, and all clean. It does the same thing with remote tank.
Mounted the carbs and did a link adj.

Today i took it for a ride with a remote tank, and to 1700 rpm there is no problem, beyond 1700 to about 2800 wont take the throtle beyond 2800rpm.
Try to swap the sparks from cyl 2 to 3 and it came to 3500 with a poping electric miss.
Stoped then tried again but as same as i started wont go over 2800.
All electonic parts were checked with ohmmeter and results were like in the manual.

Are there any straight tests (advices) that i could test until dva arrives like :
I know that the reving motor on carbs are not advised, but does motor has to respond of that rev good or ???

Unpluging no 1cyl spark , the motor should run or not???
The cyl 2 is not working till 1500 rpm right???
No3 unpluging should work or not.



Thx

[sasko1980]

Not messing up, just wanted to try to solve my problem with motor.


As im waiting for dva to arrive to check the cdi outputs lets recap.
I once again checked the fuel system, clean already clean carbs, tested the pump, clean the filter.
So Im shure that the fuel lines are ok, and all clean. It does the same thing with remote tank.
Mounted the carbs and did a link adj.

Today i took it for a ride with a remote tank, and to 1700 rpm there is no problem, beyond 1700 to about 2800 with the wont take the throtle.
Try to swap the sparks from cyl 2 to 3 and it came to 3500 with a poping electric miss.
Stoped then tried again but as same as i started wont go over 2800.
All electonic parts were checked with ohmmeter and results were like in the manual.

Are there any straight tests (advices) that i could test until dva arrives like :
I know that the reving motor on carbs are not advised, but does motor has to respond of that rev good or ???

Unpluging no 1cyl spark , the motor should run or not???
The cyl 2 is not working till 1500 rpm right???
No3 unpluging should work or not.

Can you point to a good explanation for setup the timing and how to perform it.

Thx

[99yam40]

Never saw a 3 cylinder motor that did not run on all cylinders all of the time.

have you checked or replaced the fuel pump?
have you used a timing light on the motor to see what the timing is doing and if it meets spec?

timing light or spark tester will show if all spark plugs are getting spark.

good compression, spark, and spark at the correct time is needed along with proper fuel to air mix for the cylinders to burn the fuel properly and may power.
get a service manual for your motor if you want to work on it, it will have lots of info and specs