2-cycle rpm question

[Psalm 99]

You guys have been very helpful with a carb question I recently had so I thought I'd get your opinion(s) on how steady the RPMs should be on a Yamaha 150 2-stk: My dashboard tack reads in 100's of RPM which seems steady enough. When hooking up a Tiny-tach to #1 plug wire, I can read RPMs down to 10's. Both Tiny-tach and dashboard numbers agree in 100's. Tiny-tach indicates that the RPM's at idle vary by about 25 (like from 725 - 750). At 2100 RPM the variance is similar but about 40 RPM. I haven't had this engine long enough to comment on its vibration although a short U-Tube video of a similar 2-stk indicated that my engine may be vibrating a little more than normal. Is this pretty standard performance for a Yamaha 2-stk or should start looking for problems. A timing light shows all plugs firing and plugs/fuel pumps are new. Fuel is super clean (with new 10 micron fuel/water filter), electrical ground connections have been cleaned and carbs are newly cleaned. - Al

[robert graham]

All my 2 stroke Yamahas have vibrated some at lower RPM's including idle....but they smooth out nicely as the RPM's rise to a general maximum of about 5500....That said, I usually run/cruise in the 3500 RPM range , which is most efficient for my boat/motor rig....Check:Yamaha Outboard Performance Bulletins for more in depth information on RPM's, efficiencies, etc..

[TownsendsFJR1300]

That VERY slight variance isn't anything to be concerned about.

Yamaha generally gives a +/- 100 RPM variance on the idle setting(yours may be slightly less) so your well within spec's

How'd the old plugs look? Gaps within spec or worn(on the wide side)

If its running slightly rough, some RingFree wouldn't hurt..

Sounds like a pretty solid engine from your post...

[Psalm 99]

Thanks guys, sometimes I worry too much. Been working on the engine for a couple of weeks and this was the last issue. Sure appears to be a great piece of machinery. - Al