Echo SRM-225 maximum RPM?

[FergusonTO35]

I have an Echo SRM-225 weedeater about 6 years old that I like very much. I've removed the plug over the mixture screw and always kept it tuned to where the four stroking just cleans up at WOT and produces that smooth as glass whine characteristic of Japanese two strokes.

Anyhow, I put the tach on it for the first time and found that I am actually exceeding the factory RPM by quite a bit. The maximum rpm given in the manual is 7600-8700. I'm doing around 9400. I tried richening it and did get the rpm down, however with noticeable four stroking and it doesn't cut as well. Anyway, if you hold it at WOT the rpms will continue to build until it starts to bounce off the rev limiter.

So, what should I do? Should I try to keep it within the recommended RPM range? Or, leave it at the higher setting since this has always worked well? I'm using 93 octane gas with fuel stabilizer and VP synthetic oil at 36:1.

 

[CR888]

Factory recommended RPM figures are just that, they are recommendations. Every engine is going to be slightly different and what you need to focus on is 'correct tune'. Your unit can be safely tuned @9400rpm while another unit could be 8500rpm. I'd go back to where you were. Spark advance, muffler, ring seal from break in, filters, cylinder casting, gearbox condition, oil ratio, fuel and tune can ALL affect final max rpm. I tune them for max power not a conservative safe figure concocted for the user manual or spec sheet. Many sacrifice performance as they follow the rules on a piece of paper rather than focussing on the unit in front of them & what its telling you.

 

[FergusonTO35]

Thanks, that is what I'll do. Doesn't make much sense for a modern Echo to sound like a 40 year old Johnson outboard, nothing wrong with the latter of course!

 

[AVB]

See if this makes sense.

SERVICE BULLETIN #08-14 R3
©2014 ECHO, Incorporated All Rights Reserved

SUBJECT: PAS-225, SRM-225 Emission Carburetor Adjustment Zama RB-K93.

CARBURETOR ADJUSTMENT ENGINE LOAD: CUT LINES TO 5.5 INCHES
Engine load is the nylon head with two .095 lines cut to 5.5 inches ( 140mm ).

Initial Carburetor Needle Settings
Lightly seat needles & turn CCW Turn CW from 1st contact with idle plate
Low Mix 2 5/8 turns Hi Mix 3/4 turns Idle Speed 2 3/8 turns

FINAL CARBURETOR ADJUSTMENTS

LOW MIXTURE ADJUSTMENT: Allow engine to stabilize 20 seconds between low mix adjustments.
1. ADJ. LOW MIX TO MAX IDLE SPEED: Adjust the Low mix screw clockwise or counter clockwise until the
engine idles as fast as possible.
2. SET IDLE @ 3,800 RPM: Adjust the idle speed screw until the engine idles at 3,800 RPM.
3. DROP IDLE TO 2,900 RPM WITH LOW MIX NEEDLE: Turn the Low mix needle counter clockwise until the
engine idle speed drops to 2,900 RPM.

HIGH MIXTURE ADJUSTMENT:
1. ADJ. HI MIX TO MAX WOT SPEED: Adjust the Hi mix screw clockwise or counter clockwise until the engine
runs as fast as possible at WOT.
2. DROP WOT SPEED 10-20 RPM WITH HI MIX SCREW: Once engine reaches max WOT RPM turn the Hi mix
screw counter clockwise until the engine drops 10 to 20 RPM. Shut the engine off when final adjustment is
complete.

VERIFY CARBURETOR ADJUSTMENTS: IDLE: 2,500-3000 RPM, WOT: 7,600-8,700 RPM
Extend nylon trimmer line to proper length 155mm (6 in). Restart the engine and verify the engine idles between
2,500 and 3,000 RPM. Check to make sure the engine quickly and smoothly revs to 7,600 to 8,700 WOT RPM.
IMPORTANT! THE HEAD MUST NOT TURN AT IDLE.

Note : Aftermarket heads will change the loading due weight differences.

 

[FergusonTO35]

Thanks very much. My machine uses the later rotary style carb with one mixture adjustment. Mebbe the 8700 max rpm is correct for the older machines with standard hi/lo carbs but not mine. I'll get on the Echo website and compare it to the manual for the latest and greatest SRM-225.

 

[AVB]

Older models actually ran nearly 1000 rpm slower at WOT.

In the center of the rotary barrel should be the idle mixture screw. It will have EPA compliant plug over it.

 

[FergusonTO35]

Looked up the latest owner's manual for the SRM-225 and it still shows the max rpm as 8700. I'll just tune it to where it runs the best as I did before. By idle mixture, are you referring to the screw on the back of the carb under the primer bulb? I though that was the only one this carb had.

 

[FergusonTO35]

Did some cutting with the SRM-225 today. Made sure it was filled with fresh fuel mix and had a head full of line. Using my tach I adjusted the mixture screw up and down until it seemed to find a sweet spot. The machine seems to prefer around 8700 at WOT. This produces a teeny tiny bit of outboard four stroke sound with no load. When cutting, it sounds smooth as glass with the occasional interruption of the rev limiter. The cut is really sweet too, even with .095 line you can trim like a scalpel. Think I'll leave it here!

 

[AVB]

Looked up the latest owner's manual for the SRM-225 and it still shows the max rpm as 8700. I'll just tune it to where it runs the best as I did before. By idle mixture, are you referring to the screw on the back of the carb under the primer bulb? I though that was the only one this carb had.

Sorry taking so long to respond but been fairly busy this week. I should be able get you a couple pics or more tomorrow as I just got in a 225 trimmer that needs carburetor work. But for it not the one by primer but the in the rotary barrel that is the idle mixture. The one by the primer is the main mixture.

But it does sounds like you're already got it tuned out according to post #8. Still post the pics as someone else might need them.

 

[FergusonTO35]

Thanks, you bet. Gonna apply the same treatment to the little GT-210 also.

 

[backhoelover]

here is the service data. same as above just from echo

 

[AVB]

Going just show pictures from the service bulletin instead since someone had put on an older K70 with the brass plug on the SRM 210 I am working on. BTW the adustment will require a small single D adjustment tool or small flat blade screwdriver depending on the design.

 

[FergusonTO35]

Thanks a lot guys!!

 

[FergusonTO35]

Put the tach on the little GT-200R last night. 7500 rpm WOT with a head full of line seems to be the sweet spot. No four stroking that I could tell although the exhaust note is more choppy than the 225. Most importantly it has plenty of power when you put it in the weeds, doesn't seem to slow down very much. Unlike the 225, leaning this one actually makes the rpms drop once you get past the sweet spot. I would assume the bent drive cable and rather large speed loader head take a fair amount of power to keep turning.

Anyhow, these Echoes are just as sweet as can be when they are dialed in right. Hopefully I can give the CS-400 some exercise tonight.