Nissan Carb issue?

[pvanv]

3B7702004M

PRIMER BULB ASSY (2-STROKE/5HP -90HP) Part 345702000 was superceded to 3B7702004M

98AB501000M

FUEL PIPE 5MM (3/16") (1 EA.=1 METER)

If you place a tank above the level of the motor, then gravity should assist filling the fuel system, so that is a good test. If a connector weeps fuel under those conditions, that will also be an air leak under vacuum.

 

[Sea Rider]

Bad music...other simple test you can do is : connect both fuel connectors, wrapp several turns of a good quality say 3M electric tape around male portion and female of both connectors at both ends of fuel hose. If OB doesn't bogs down at speed, o'rings are the culprit. The complete fuel line should cost around 70 bucks, right ?

Happy Boating

 

[mikkydee]

ok an update on my issue. Replaced all fuel lines and clamps. New fuel connectors. new gas tank and fuel lines. Removed carbs and cleaned again. Still having fuel starvation issues at WOT. I got a new fuel pump in today so that is my next and male fuel line connector. (already replaced female connector). I am hoping at this point that it is the new fuel pump that I put on it previously was just faulty and the new OEM pump will be the cure. Fingers crossed...

Speaking to my boat mechanic (who is not certified in Tohatsu/Nissan), said when he adjusts carbs on the old outboards, he screws them in all the way and then backs them out 1.5-2 turns and then tweeks the adjustment to run smooth. Is this a sound procedure on adjusting nissan carbs?

 

[Sea Rider]

Carb adjusting procedure is correct backing turns from fully light seated in, unless mechanic has a well trained musician ear, will be impossible to adjust multi carbs 100% right that way. Better is adjuting each carb with a multi vacuum electronic meter. More precise than by ear...

Happy Boating

 

[mikkydee]

Thank you Sea Rider, I was unaware there was actually a device for this on the old carbureted motors. I have never even heard of a multi vacuum electronic meter. You have peaked my interest now. Is this the device you are referring to? :
https://www.coleparmer.com/i/supco-...nrwSFETFQyWVwzqdz6nYGB7_y_FJ-Edi5JhoC9aLw_wcB

 

[Sea Rider]

Sort of, the one I'm referring to is a 3-4 led tape like with multiple light colors showing different vaccum readings. Paul will surely enlight you about model, brand, where to get it. Wacuum hose must be connected to carb's vaccum port or on manifold ports if having one to read & adjust properly.

It's one hose per carb. Will see all carbs showing individual readings at same time. Check carb's vacuum ports availability before buying.

Happy Boating

 

[pvanv]

Something like this:
http://www.carbtune.com/Images/SSL11411LC.jpg

 

[mikkydee]

thanks Paul. Will this work on the 2 stroke motor?

 

[pvanv]

thanks Paul. Will this work on the 2 stroke motor?

They work on both 2 and 4 stroke motors. Because you can see all carbs at once, these types of manometers are faster/easier than the single carb units.

 

[Sea Rider]

Awesome seeing and adjusting all carbs working at same time. More precise than single carb adjustments or even having a expert fine tuned musician ear LOL!! Now the issue is , does 70 HP carbs or manifolds have ports in which can connect individual manometer's hoses ?

Happy Boating

 

[mikkydee]

I have looked into the Carbtune Pro4. It certainly has rave reviews and can be purchased for under $100 including shipping at the carbtune website in the UK. I would love to be able to fine tune the carbs on my 70 hp nissan and anything other outboards I work on in the future (have a 60 hp Johnson in the garage on a stand and a 80 hp Merc in the back yard). I am a fairly decent shade tree mechanic but working on 2 stroke outboards is a whole new universe for me. Anybody know if the old MS70A2 70 hp Nissan or tohatsu has the ports to hook this thing to? I am not even sure what I would be looking for yet.

 

[Sea Rider]

Adjusting idle adjustments that way is very sophisticated. Check if individual carbs has built in small nipple, screwable small ports protruding, if not useless buying tester. A friend of mine installed 2 vaccum gauges on his old carbed VW dash board , had to drill and screw a plug outlet on each individual Weber manifold. Worked as a charm, good for optimizing fuel consumtions while stepping on accelerator.

Bear in mind that idle carb adjustments are only good for smooth OB operation while at idle at neutral or just geared, once throttle passes idle speed, OB works with non adjustable fixed jets, so are not part of the idle equation.

Happy Boating

 

[pvanv]

I have looked into the Carbtune Pro4. It certainly has rave reviews and can be purchased for under $100 including shipping at the carbtune website in the UK. I would love to be able to fine tune the carbs on my 70 hp nissan and anything other outboards I work on in the future (have a 60 hp Johnson in the garage on a stand and a 80 hp Merc in the back yard). I am a fairly decent shade tree mechanic but working on 2 stroke outboards is a whole new universe for me. Anybody know if the old MS70A2 70 hp Nissan or tohatsu has the ports to hook this thing to? I am not even sure what I would be looking for yet.

There are L-nipples, one for each carb, in the inlet manifold. In normal operation, they are connected by a tube to help balance the carbs if they are a little off. To connect the manometer, pull the balancing tube off, and connect to the nipples.