I think I successfully tuned my first carburetor

[Fried Chicken]

Have an Echo PB-251 that's my workhorse leafblower. Got it on a deal; broken: flywheel locking nut comes loose. Loctite red solves that. Fantastic thing, always started reliably first time, quiet, has a cat that I like (no stink is genuinely nice).

Recently just stopped running right. Did the thing: filter (original), spark plug (original), gas (like 1 year old lol), still doesn't start/run right. Ok, go deeper: check spark, is fine. Go deeper: take it apart and check if the flywheel came loose. It didn't.

Head scratching, inspecting, poking, service-manualing... See the spark plug is consistently wet and unit flooded.

Service manual on tuning the carburetor has some insane and stupid procedure:


**** it, time to wing it. Grab my mini flathead: tune the idle jet just slightly rich of peak (where it's 4-stroking). Tune the high jet slightly rich too... did the leaves.... smelled some stink out of the exhaust, and don't want to fry the cat by running it rich, so I bring it slightly learn (still rich of peak).

I think she's tuned!

This would be the first time I succeeded in tuning a carburetor. Starts first pull. Hopefully it doesn't explode down the road.

 

[Vintage Engine Repairs]

Have an Echo PB-251 that's my workhorse leafblower. Got it on a deal; broken: flywheel locking nut comes loose. Loctite red solves that. Fantastic thing, always started reliably first time, quiet, has a cat that I like (no stink is genuinely nice).

Recently just stopped running right. Did the thing: filter (original), spark plug (original), gas (like 1 year old lol), still doesn't start/run right. Ok, go deeper: check spark, is fine. Go deeper: take it apart and check if the flywheel came loose. It didn't.

Head scratching, inspecting, poking, service-manualing... See the spark plug is consistently wet and unit flooded.

Service manual on tuning the carburetor has some insane and stupid procedure:
View attachment 1240935

**** it, time to wing it. Grab my mini flathead: tune the idle jet just slightly rich of peak (where it's 4-stroking). Tune the high jet slightly rich too... did the leaves.... smelled some stink out of the exhaust, and don't want to fry the cat by running it rich, so I bring it slightly learn (still rich of peak).

I think she's tuned!

This would be the first time I succeeded in tuning a carburetor. Starts first pull. Hopefully it doesn't explode down the road.

There is a very good reason carburetors are adjusted the way they are. The aim is to set the correct relation between fuel / drillings and air flow.

If you just wing it, you can end up opening the butterfly too much and compensating with the low speed screw. This will cause you to have to set the H screw leaner and give you poor performance at idle and off idle too. You may have gotten away with it in one instance, but you’ll quickly discover following a simple set process ensures you don’t chase your tail.

Find drop off on L at spec + 500 rpm
Richer L by 500 rpm
Set H to slightly 4 stroke unloaded and clean up under load.

 

[Fried Chicken]

There is a very good reason carburetors are adjusted the way they are. The aim is to set the correct relation between fuel / drillings and air flow.

If you just wing it, you can end up opening the butterfly too much and compensating with the low speed screw. This will cause you to have to set the H screw leaner and give you poor performance at idle and off idle too. You may have gotten away with it in one instance, but you’ll quickly discover following a simple set process ensures you don’t chase your tail.

Find drop off on L at spec + 500 rpm
Richer L by 500 rpm
Set H to slightly 4 stroke unloaded and clean up under load.

I don't quite get it. Plenty of people wing it as a rule. Tune the carburetors by listening. Having set it now, it runs just as it did before, both sound, performance, everything.
I did set the L screw first using the service manual recommended idle screw position. Then I did the H screw. For a leafblower "under load" means just WOT. Should it be 4-stroking in this circumstance or better not? It should still be ROP right?

Is there a tachometer you might recommend?

 

[Vintage Engine Repairs]

I don't quite get it. Plenty of people wing it as a rule. Tune the carburetors by listening. Having set it now, it runs just as it did before, both sound, performance, everything.
I did set the L screw first using the service manual recommended idle screw position. Then I did the H screw. For a leafblower "under load" means just WOT. Should it be 4-stroking in this circumstance or better not? It should still be ROP right?

Is there a tachometer you might recommend?

Save this chart I made. All small engine rotary are dependant, not many butterfly type are.