Use 15-40 W oil that is JASO MA or MA2 approved, equally an oil of the same weight that is SAE SF or SG approved. Don't use regular car engine oil as it may damage the wet clutch of the bike. Check the oil frequently and add more if the engine burns some oil. Oil and filter change every 2-3 thousand miles.
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In the back of any repair manual.
4
Clymer 1982 - 1988 Honda V45 & V65 Magna/Sabre repair manual has 0.031 - 0.035 in.
See related link from Cycle Magazine. 105hp
1984 v65 sabre plug gap and NGK Spark PLug and heat range
105 horsepower at the rear wheel, as measured by Cycle magazine in 1983.
There is no gas gauge on the 1983 Honda v65 magna. However this bike will get around 165 miles on a full tank. The best way to know how much fuel you have is to reset the tripometer on the speedometer each time you fill up, and refill at around 160-165 miles.
The 1983 v65 magna "Winker cancel unit" or "Cancel unit" or "Turn signal Cancel unit" Honda part number 35220-MB4-005 is located inside the fuse box below the headlight, looks like a small black box about half the size of a deck of playing cards.
.35
If it is the same as a V65 Sabre, with the dipstick. I just don't know what marks mean what level...
On the front of the bike next to the horn under the headlight.