Hello all:
I've uncovered the hidden mix screw and now need som e help tuning.
To refresh:
Echo SRM-210
Season fresh 91-octane fuel w/ FP60 (Sta-bil in past years)
Echo syn oil at 40:1 (50:1 in past years)
New spark plug, clean air filter
Location: near Toronto (not high altitude)
I had a REALLY hard time getting it to run at all this time. It's been weeks since I had to use the trimmer last and it would seem that there may have been significant fuel evaporation leaving mostly oil behind. Plenty of smoke and barely running. Put in fresh mix and it ran OK.
When partially warmed up I began to play with the mixture screw setting. As a reference, let's say I found it at 12:00.
At 12:00 it tends to sputter and occasionally four stroke when idling - twitching and bucking around. When cold, opening the throttle leads to intake noise and no extra revs. When warm it has pep, power, good throttle response, but still bucks in and out of four stroke when idling and running at part throttle. (ie. rrrrrrrr-bbbbbb-rrrr-bbb-r-b-rrrrr-bbb-rrr)
At 9:00 it four strokes continually at idle, good throttle response and power off of idle. This confirms to me that CCW is richer. I think it even smokes a little here.
At 3:00 it almost stops four stroking at idle but needs the idle screw increased to raise revs. It will maintain idle at lower RPM than at 12:00. Throttle response is poor, sometimes matching the cold behaviour of just making more noise and not revving up. If you get it going power is good. The idle sounds more like "other people and pros" trimmers I hear that just kind of hum evenly at idle. Anything further than 3:00-4:00 and it can stall out. This confirms to me that CW is lean.
At 11:00 the idle speed noticeably raised and I had to loosen the screw to keep the clutch from dragging. Throttle response was good, but it four stroked more. Turn CCW further from 11:00 and the idle lowered again. 11:00 seemed to be result in the fastest idle.
At 2:00 I got a very low and even idle, but it sounded lean. Sometimes throttle response was good, sometimes it was strangled. I didn't like to run too long here because I'm not really watching the temperature. I wasn't running it really hard but I still don't want to cause damage.
When tuning R/C nitromethane engines we had at least idle, low and high needles. Unlike airplanes and chainsaws, throttle response was very important in a land-vehicle hence the addition of the low needle. You would start from factory settings and then do WOT runs checking that the temp was 220F or lower (newer engines can run hotter) and you could still see a smoke trail (newer fuels have more synthetics and less castor oil so this may not be standard procedure now). Usually "best running" was too hot and you had to richen it up to keep the temp under control with no fans and the body covering on. The low needle was then used to adjust throttle response, how badly the carb loaded up while idling and operating temp at part throttle. That's my main two stroke tuning experience
I'm confused by the fact that the only steady idle I get is where it appears to be too lean. Is there a real danger of running too hot on a pro tool like this at 40:1 with some sort of fan pushing air through the fins? What temps should I be shooting for? (I have an IR thermometer now)
What about the raise in idle at 11:00? The four stroking at factory position tells me 'too rich', but the poor throttle response when cold says 'too lean'. How can it be both? Do I peak the idle and leave it at that?
Open to suggestions, and thanks again to those who have provided input.
Craig.