smartwork

My Feedback: (5)

I've got a used (but low-hour) Brison 2.4 that I've just started putting in the air. I've been adjusting the needles to get what I think is just the right settings, but the mid range (transition point) never seems to get really clean.

Is this common?

Idle up to 1/3 runs great, 1/3 to 1/2 has that little "wurble" type sound in it, and then after 1/2 it sounds clean as a whistle - like a clean-running 2-cycle dirt bike enjoying its powerband.

Although I've tested in several places, I've got the low needle just a little richer than max lean - judging from the "acceleration test" when setting the low. High sounds very clean and adjustments on this didn't tremendously affect the transition as Brison says the low controls the transition.

I've been reading the posts in this forum on the pressures in the cowl and such but they don't sound exactly like what I've got... could be, but doesn't sound quite like the same problem. The "sputtering 50" thread has a little of the same characteristics but not quite the same.

So, anyone have a really clean mid-range?

Thanks!

-shaun

Antique

My Feedback: (4)

The carb generally used on the 2.4 engines is a Walbro WT76A, calibrated for the Sachs 3.2 chainsaw..There are 3 small holes in the venturi, uncovered one at a time by the opening of the throttle..The mixture to all 3 holes is controlled by the low speed needle. The three small holes could be the right diameter for a 2.4 engine if the engine manufacturer wanted to spend some money for a custom carb..As it is, they find one that works and use it stock...A prop with more pitch and/or diameter might load the engine at midrange enough to make the mixture leaner and get rid of the burble....Anything will be a compromise....

rctom

What exactly is this "acceleration test". The engine sounds like it is still rich on the low end. IF you can make the low end leaner with no other ill effects, that will probably help clean up the transition.

TF

smartwork

My Feedback: (5)

Thanks for the carb info, rcign. I somewhat get the feeling from your post that the entire rpm band will never have a really clean sound/run - is that right and is that something in particular the 2.4s? Are there aftermarket carbs?


rctom, the acceleration test I was speaking of is the one that's somewhat standard of the engine not being killed when fast acceleration - thus too lean. I've leaned it all the way out to the point where this occurs and I am then required to richen again to prevent the low from being too lean.

I agree that leaning it is the solution, but unfortunately I so far haven't been able to hit that rpm range that I need to lean without killing my low end totally.

There's just that 1/3 to 1/2 throttle range that has that not-so-clean running and it would be great to eliminate it.

Thanks!

-shaun

Geistware

My Feedback: (16)

I have two Brison 2.4's and that problem is the same for both. I think it is normal for that engine.