Taz_Hobbies

My Feedback: (15)

Interesting... Now that my DLA-32cc gasser sounds and feels fully broken in, it has a reversion issue where fuel is sent "out" the carb venturi in the opposite direction that the air is flowing while running.
I have seen reversion on automotive engines using very high lift, long duration, high overlap camshafts, but never on a reed valved two stroke.

And it didn't do this before todays warm up and test run.

It runs perfectly fine, transition is crisp and overall it sounds better than it ever has so the tune is very, very close. Not overly rich for sure.

Any ideas from you guys who know gassers more than I do?

Truckracer

My Feedback: (19)

Sounds like a leaky reed valve. Probably not seating fully and at low speeds you get some blow back before the reeds close. Reseat / repair the reeds and the problem should go away. And yes, depending on how bad the problem is, an engine can run just fine with this condition.

Taz_Hobbies

My Feedback: (15)

Thanks. I pulled the carb & reed block, they are perfect. Nothing obvious. Reeds are tight and fit perfectly even.
It's just very odd that it didn't do this until fully broken in. Prior to today, this motor had zero reversion.

Truckracer

My Feedback: (19)

Hmmmm, I can't see how there could be airflow out of the carb unless the reeds were leaking. Oh well, at least you checked and eliminated that as a source of the problem.

pe reivers

prop rpm and reed resonant vibrations are not in tune. try a larger prop or check the reed stop angles. They may swing open too wide in search for that teenyweeny bit of extra power. If that is the case, a carb extension will work too.

Taz_Hobbies

My Feedback: (15)

Has an 18x8. Reed block has no stops. Doesn't seems like reed flutter.
It does it at idle and really does it at around 2500 rpm.

Purchased a velocity stack today.

Truckracer

My Feedback: (19)

I'm not sure about the DLA but on the DLE engines they do have a reed stop of sorts. When the reed assembly is inserted into the housing, the housing itself limits reed travel. Quite a nice design actually as it eliminates any area at the base of the reed where fuel could puddle at low speeds.

pe reivers

DLE has many tidbits of knowledge incorporated in their designs.

JRgraham

My Feedback: (1)

Im sure you probably think the reeds are seeting fine, but Id suggest looking at the reed block once more. The problm with them is they are sand casted, and they do not clean the surface at all where the reeds mate to the reed block. It has a rough surface. The surface must be sanded to a smooth finish, otherwise, the course/porous surface never does seat perfectly with the reeds, and will leak.

Taz_Hobbies

My Feedback: (15)

The DLA 32 has a phenolic reed block. The surface the reed seal to are perfectly flat. This is cooberated when using light machine oil on the reeds and you can clearly see the contact patch. It is consistant and complete. All four reeds seat evenly and fully. I am 100% sure of this as this is nothing new from my old motorcross engine days. These reeds are about as perfect as a set can be.