Sneeze, Cough, Whatever...

[Jason2tpa]

I posted about this same topic last month, including a youtube link so the audience can hear what I'm hearing. I received a few replies, all stating the engine sounded ok. But it ain't ok.

I wish I could tell you it's coughing or sneezing, or whatever, but there seems to be a number of different definitions for each...probably because these words are slang.

So if you please, take a look and listen to this 30 sec youtube video. You will hear the rpm reduction at the 10s, 16s, 24s, and 26s marks. And if you watch the prop hub exhaust you will see the exhaust spit water out a moment before rpm reduction.

https://www.youtube.com/watch?v=qMVVb1jNkHE

Pilot screws per spec is 5/8 +/- 1/4. After rebuilding carbs over a month ago, and during the timing/sync process, the engine sounded worse than what you hear in the video with spec mix settings. So I kept turning out screws 1/4 turns until the idle normalized, along with adjusting idle speed screw. They are set at 1.25 turns out.

Your thoughts? And I'd love a definitive diagnosis as to what you call this sound you hear. Then I can at least start working from there.

[pstephens46]

Sounds like a 2 stroke to me. Maybe Rodbolt will comment?

[Jason2tpa]

Sounds like a 2 stroke to me. Maybe Rodbolt will comment?

Appreciate you taking a listen. Even a 2 stroke of this age, I find it hard to believe that this sputter, cough, sneeze, whatever, is normal. I don't know. Yeah, I'm hoping someone with a lot of experience with 2 stroke timing/syncing gives their 2 cents.

[pstephens46]

[QUOTE=Jason2tpa;130763]Appreciate you taking a listen. Even a 2 stroke of this age, I find it hard to believe that this sputter, cough, sneeze, whatever, is normal. I don't know. Yeah, I'm hoping someone with a lot of experience with 2 stroke timing/syncing gives their 2 cents.[/QUOTE
.

Hope that my post didn't come across as a smart-a__! I do hope Rod can listen, sometimes he has trouble opening attachments.

[robert graham]

Sounds pretty normal to me...it ain't a 4 stroke after all!

[Jason2tpa]

[QUOTE=pstephens46;130769]

Appreciate you taking a listen. Even a 2 stroke of this age, I find it hard to believe that this sputter, cough, sneeze, whatever, is normal. I don't know. Yeah, I'm hoping someone with a lot of experience with 2 stroke timing/syncing gives their 2 cents.[/QUOTE
.

Hope that my post didn't come across as a smart-a__! I do hope Rod can listen, sometimes he has trouble opening attachments.

Not at all my man.

[Jason2tpa]

Sounds pretty normal to me...it ain't a 4 stroke after all!

Man, if this is a normal sound then I guess I'll need to recalibrate what I believe normal sounds like.

So neither of you guys think this is a sneeze or cough?...Even though you can see exhaust/water spit out the hub the moment prior to misfire.

[boscoe99]

Sounds like a normal two stroke idling out of the water to me.

[TownsendsFJR1300]

Its NOT a lean sneeze nor a cough..

I hear it slow down, (drops maybe 100-150-RPM's) almost like a carb idle jet not flowing momentarily, then recovering.

And I agree, it shouldn't drop that RPM's as smooth (extremely smooth actually) as it runs otherwise.

I gather it does it in the water too (with water back pressure)?

I would start by simply draining (primer bulb too) the carbs looking
for one small piece of crap. Catch what comes out.

As slight as that RPM reduction is, it doesn't sound like ignition but a momentary fuel delivery issue..

Do you use RingFree? If not, that would be the first thing I would try, (shock dose).

(if the spark plugs are oldish, change em and gap to the tighter end of spec's)

[rodbolt17]

does not sound bad.
myself I would like to know what is the idle speed, what is the idle speed in gear *****ing?

backpressure will affect two stroke engine running.
most Yamaha run about the same on a flusher as in the water but not all.

test run it in the water and see if it smooths out.

[walleye1]

The tune up specs guide calls for 5/8 of a turn out,
I would try to stay around that. Make sure you are
running a resister plug, BR8HS-10. Idle in neutral
is 750, in gear 650 rpm with prop in the water.
Have to have back pressure against the exhaust.
Idle timing at 5 ATDC. Those carbs need to be
flow tested before assembled.

You need to dump it in the water and run it at
wot at full trim to see if you have any surging,
If you do the carbs are still dirty. They can be a
pain.

[99yam40]

The tune up specs guide calls for 5/8 of a turn out,
I would try to stay around that. Make sure you are
running a resister plug, BR8HS-10. Idle in neutral
is 750, in gear 650 rpm with prop in the water.
Have to have back pressure against the exhaust.
Idle timing at 5 ATDC. Those carbs need to be
flow tested before assembled.

You need to dump it in the water and run it at
wot at full trim to see if you have any surging,
If you do the carbs are still dirty. They can be a
pain.

What is this flow testing of carbs before being assembled?

I do agree if the motor will not run properly with carbs set to factory spec then something is wrong.
even the air jets/passages being plugged can cause strange things

[rodbolt17]

that flow test is something that is rather useless.
Yamaha even offered a kit to add a clean out port to the side of the carb where the fuel flows from the inlet to the needles.
personally I have never seen one blocked with casting flash.

if the idle speed is to fast or the shutters not syncd correctly that is exactly what it would sound like.

[99yam40]

OK , so it sounds like you test to make sure the fuel flow thru the inlet & needle and seat is checked for proper flow into the carb to make sure there is no restriction there.

I would think that would be more for high RPM problems than idle.

Rodbolt, from what you are saying it sounds like the problem could be some cylinder(s) fighting others to run at steady RPM if not synced properly

[walleye1]

I have had that style of carb I couldn't get
clean setting in carb cleaner over nite.
The problem is with out flow testing you
don't no. I've had to drill out the lead
bb's to clean the passage.