Today's Message Index:
----------------------
1. 12:22 PM - Re: Carbs - enrichener - cold start. (Ducati SS)
2. 02:11 PM - Re: Re: Carbs - enrichener - cold start. (Stuart Harner)
3. 02:49 PM - Re: Carbs - enrichener - cold start. (Ducati SS)
4. 03:37 PM - Re: Re: Carbs - enrichener - cold start. (Larry Cottrell)
5. 06:12 PM - Re: Carbs - enrichener - cold start. (Airknocker)
6. 08:20 PM - Re: Carbs - enrichener - cold start. (Richard Pike)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Carbs - enrichener - cold start. |
OK, a bit of background. I am a retired mechanic with eight ASE certs, started
my career as a motorcycle snowmobile mechanic, have a top technician award from
US Suzuki. Here is the basic carb sequence, 0 to 1/8 throttle= pilot air or
pilot fuel, 1/8 to 1/4= pilot jet, 1/4 to 3/4= needle jet and jet needle, 3/4
to full throttle=main jet. If you look at the air intake side of the carb you
will see a small hole which feeds air into the enricher circuit. The entire purpose
of the venturi is to create a pressure drop which allows atmospheric pressure
to push fuel up thru the jets. The main jet has little to no function at
start up or idle. The enricher circuit relies on high vacuum ahead of the slide
to pull fuel up the dedicated enricher circuit. If the throttle is opened the
vacuum drops and the enricher becomes ineffective. This has been going on for
at least forty years and is still grossly misunderstood. If your low speed
screw is behind the slide it is a pilot air screw, if in front of the slide it
is a pilot fuel screw. They adjust the same circuit but must be turned in opposite
directions for the desired outcome. Pilot air.. turn out for lean, pilot
fuel, turn in for lean.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=510021#510021
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Carbs - enrichener - cold start. |
Yes, this all makes sense and follows what others told me when I first
started working on the 447 setup. Even the air screw being in front of
the slide and the confusion it caused when I first adjusted it. Didn't
figure it out until it dawned on me that I was opening up the air
passage, not the fuel.
My confusion about the enricher being able to cool the EGT remains. If
the enricher becomes ineffective due to loss of vacuum, why does it
still work at 4000 RPM?
Please understand I am not trying to argumentative, I am just trying to
understand why what I have experienced does not fit with what has been
said. Unless there is some other factor at play that I don't know about.
I learned to fly in a 1941 Aeronca Chief and the only temp gauge was for
oil. Also no mixture. Then I had a Cherokee 180 with oil temp and
mixture, nothing else. I was always taught that with mixture keep it
rich at high power settings to keep the engine cool. Without EGT the
procedure was to lean until it stumbled then go a bit richer until it
smoothed out. I also know about leaning either side of peak, but without
the gauge running more rich was the safe bet.
Moving on to the 447 with all the warnings about EGT and frying the
exhaust ports, I put in probes on both cylinders. In flight everything
is fine until I unload the prop or power back to the 4000 range for
descent. The EGT goes up, I open the enricher and it cools back down so
I my mind it must be adding fuel.
Is it possible at that RPM range there is still enough pressure drop to
let some fuel flow through the enricher, enough to cool the EGT?
Also, would it be better to raise the needle (lower the clip) one more
notch or to be looking at a different needle/jet set? I am reluctant to
try something different as it performs perfectly as long as the prop
stays loaded and the fuel economy is pretty good at a little over 4
gallons per hour.
Thanks for the info,
Stuart
On 1/24/23 14:22, Ducati SS wrote:
>
> OK, a bit of background. I am a retired mechanic with eight ASE certs, started
my career as a motorcycle snowmobile mechanic, have a top technician award from
US Suzuki. Here is the basic carb sequence, 0 to 1/8 throttle= pilot air or
pilot fuel, 1/8 to 1/4= pilot jet, 1/4 to 3/4= needle jet and jet needle, 3/4
to full throttle=main jet. If you look at the air intake side of the carb you
will see a small hole which feeds air into the enricher circuit. The entire
purpose of the venturi is to create a pressure drop which allows atmospheric pressure
to push fuel up thru the jets. The main jet has little to no function
at start up or idle. The enricher circuit relies on high vacuum ahead of the slide
to pull fuel up the dedicated enricher circuit. If the throttle is opened
the vacuum drops and the enricher becomes ineffective. This has been going on
for at least forty years and is still grossly misunderstood. If your low speed
screw is behind the slide it is a pilot air screw, i!
> f in front of the slide it is a pilot fuel screw. They adjust the same circuit
but must be turned in opposite directions for the desired outcome. Pilot air..
turn out for lean, pilot fuel, turn in for lean.
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=510021#510021
>
>
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Carbs - enrichener - cold start. |
Because at starting RPM there is precious little flow thru the venturi so if you
raise the slide you have next to nothing left in the way of air flow to reduce
pressure. At higher operational speeds there is significant airflow and drop
in venturi pressure.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=510025#510025
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Carbs - enrichener - cold start. |
Stuart, I am not a mechanic , but I have flown several 447's. If you
need to cool your egt's when you chop the throttle, then your needle
jet is set wrong for your altitude.
Larry
Message 5
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Carbs - enrichener - cold start. |
Ok, now I get it. When Boyd originally said that "the enricher does not work unless
the throttle is closed" I took it too literally.
What he was actually saying is "at cranking speeds there is not enough vacuum to
make the enricher work if the throttle is not closed"
That makes total sense. It also makes sense that the enricher has some effectiveness
with the throttle open once the engine is running.
Some days I feel dumb. Thanks for explaining it to me.
Larry, I don't remember the jet and needle numbers off the top of my head but they
are the correct ones for sea level and up to my elevation based on the charts
from Bing. It was my understanding that changing up the chart would make the
engine run more lean because they are for less dense air at altitude.
I'll have to delve into this a little more once I get back to flying.
Thanks everyone!
--------
"I don't care, I'm still free. You can't take the sky from me" - Josh
Wedon
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=510027#510027
Message 6
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Carbs - enrichener - cold start. |
Copied & pasted from the CPS tech articles page:
This is why - when the gasket at the bottom of the plunger that sits on the bypass
was damaged - we could not get the carb on the 277 properly jetted.
Yes, the throttle slide has to be all the way down to generate enough vacuum for
the enrichner to work when starting.
However, once the engine is running, then there is enough vacuum throughout the
carb to constantly suck fuel through the enrichner bypass if the plunger is not
sealing it off for whatever reason.
--------
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=510028#510028
Attachments:
http://forums.matronics.com//files/enrich_943.jpg
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|