2 Stroke Yam 8B of Unknown Year.-

[Sea Rider]

Trying to make such an oldie motor to work again as used to do in the good old days. It's a 2 cylinder point and condenser model with a non through exhaust prop. Need the electrical DVA output voltage parameters of the Exciter Coil and the Ohm data for the Exciter & Ignition Coil if someone has both at hand and willing to share this data.



Seems the Exciter Coil is bad as both spark plugs outputs when measured with a bulb spark tester shows a very poor lighting, the upper IC lights with more intensity than the lower one but poorly compared to other Yam motors.



The motor had severe corrosion as seen at left hand area that was restored with welded alum filling There's the controversy that old Yam blocks suffered from premature corrosion, wondering if it's a true statement or cheap BS talk ?



The motor retains its original gasket set, made a compression test and the upper cylinder achieved just 40 PSI after 5-6 hard rope pulls while the lower one achieved 60 PSI, both readings are out of this world. That motor should produce at least 100 PSI output per cylinder. Hope the piston rings are stuck on their respective grooves and there's no need to enlarge both cylinders to install next size pistons and rings. Will tear the whole powerhead soon to find that out.

Happy Boating​

 

[boscoe99]

Never heard of an exciter coil on a Yamaha. I am guessing that is the charge coil.

Are there no markings on anything to help ID the motor?

 

[QBhoy]

That’s the old faithful Yamaha 8 from around late 70’s to early/mid 80’s. Still loads going strong.

 

[Sea Rider]

Never heard of an exciter coil on a Yamaha. I am guessing that is the charge coil.

Are there no markings on anything to help ID the motor?

Yep the Exciter Coils varies its name according to each manufacturer, charges the CD if having one, nope simple Yam 8B model.

QBhoy, is it possible for you to get the requested tech data for a nice electrical troubleshooting ?

Happy Boating​

 

[QBhoy]

They have a tiny charging circuit on them sometimes.
it would be very unusual for these to lose compression, unless it’s been seriously abused. I would stick some 2 stroke down the bores and leave it over night. Then turn it over a few times. Repeat as ness. Might find the compression comes up fine. Test across the coil too. Sounds simple, but get new plugs too. They may have lost their insulation, if they still old. These old things are among the best ever made. I had one when I was a boy to my teens. Sold it to a guy in my dads yard. It’s still going 25+ years later. That is about 42 years old now.

 

[Sea Rider]

You can see the exciter or charge coil at right hand in third pic. Squirting WD-40 while the motor was siting fully horizontal for a nice night soak didn't increased a bit both mentioned compression values, the rope it's easy going when pulled. This motor has mechanical and electrical flaws. That's why needed the charge coil output which assume it's measured in DVA volts, tester which have at hand. Spark Plugs are brand new NGK B7HS type.

Down here it's impossible to find any other spare part besides spark plugs and starter rope LOL!!. If can't be repaired will surely be used as a propped anchor...

Happy Boating​

 

[QBhoy]

You can see the exciter or charge coil at right hand in third pic. Squirting WD-40 while the motor was siting fully horizontal for a nice night soak didn't increased a bit both mentioned compression values, the rope it's easy going when pulled. This motor has mechanical and electrical flaws. That's why needed the charge coil output which assume it's measured in DVA volts, tester which have at hand. Spark Plugs are brand new NGK B7HS type.

Down here it's impossible to find any other spare part besides spark plugs and starter rope LOL!!. If can't be repaired will surely be used as a propped anchor...

Happy Boating​

Can’t be that bad searider. There are still so many about from the 70’s. Can’t think of another small 2 cylinder 2 stroke of that size, that’s stood there rear of time like these have.

 

[Sea Rider]

Can’t be that bad searider. There are still so many about from the 70’s. Can’t think of another small 2 cylinder 2 stroke of that size, that’s stood there rear of time like these have.

Yep but this is the only obsolete 8B points and condenser model in the whole country. Without knowing DVA and Ohm readings factory stated won't know if such electrical components are good to go, altered or shot which in most cases are NLA or very scarce. Plan to send an email to Yam Japan and inquire if possible to send the requested electrical data.

Happy Boating​

 

[raczekp1]

i have done few of this kind of motors.
this coils is other way around, yours " exciter coil" realy is lighting coil
and "lighting coil" is firnig coil as loading both condensers

 

[raczekp1]

i thing is big mess under cylinder head.
first i wouls drop cylinder head and have a look at aluminium holding cylinder sleevs.
this epoxy **** is big shortcut

 

[raczekp1]

this typ of motor is called yamaha 6 , 8 hp enduro and copied by many China brand.
have a look here:

https://www.youtube.com/c/%D0%A0%D0%B5%D0%BC%D0%BE%D0%BD%D1%82%D0%BB%D0%BE%D0%B4%D0%BE%D1%87%D0%BD%D1%8B%D1%85%D0%BC%D0%BE%D1%82%D0%BE%D1%80%D0%BE%D0%B2/videos

 

[Sea Rider]

Yamaha always states on their cowlings if being an Enduro motor. The difference between an Enduro and Standard ones is : more SS bolts, heavy duty water pump and probably a better crankcase metallurgy at a higher purchase price.

The 2 spare black wires/connectors seen in second pic corresponds to the lightning coil, a matter to follow them up to check at which coil ends being attached to. Useless if it's a removable portable motor powering small applications.

Happy Boating​

 

[boscoe99]

With nothing else to go on maybe use Yamaha US data for the 1984 8 HP model two stroke charge coil.

 

[Sea Rider]

Thanks Boscoe. Is the charge coil output measured in DVA volts when cranking ?

Happy Boating​

 

[boscoe99]

Yes.

 

[raczekp1]

first drop the the cylinder head!!!!
in other case you will put in a lot of efort to maintain this motor , but aluminium holding cylinder sleev can be badly coroded. and water will be geting into cylinders. motor will never run as it should