How difficult (how many hours) to sync carbs?

by Darren Pralle in 912 / 914 Technical Questions 6 years ago

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Re: How difficult (how many hours) to sync carbs?

by Kevin Stewart » 6 years ago

Kevin Stewart

3 389 1.16k

Likewise, your design has also given me some ideas too ;-) I like the connections without adapting the cable mount.

My servos are driven directly from a pair of double pole switches using 3 x 1.5V AA batteries. Here are all my design documents:

https://drive.google.com/open?id=0B6ytVYfsfAiNY3J3STVTUXZ5OEk

Thank you said by: Garrett Wysocki

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Re: How difficult (how many hours) to sync carbs?

by Alex Morrison » 6 years ago

Alex Morrison

21 46 62

I've got a carbmate which I am not entirely sure if it's working properly at the moment! Roger mentioned that problems can be diagnosed with the gauges. What kind of problems might be diagnosed and why do the gauges enable such diagnoses but the carbmate doesn't?

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Re: How difficult (how many hours) to sync carbs?

by Roger Lee » 6 years ago

Roger Lee

126 5.13k 4.56k

I love this question.
Within 15-20 seconds of a start with gauges you can tell if the bowden cable adjusters have enough adjustment left or if the cable lengths need adjusting. You can tell if an idle jet or main jet is clogged. You can tell which carb you want to adjust and by about how much you may need to adjust it without guessing or playing with the throttle lever to make it show up on the Carbmate. I can watch the needles come together as I make an idle or high rpm change. I know exactly what each carb is doing by looking at it's gauge and if I need to shut the engine off and rework a carb because the needles are so far apart the carb may have an issue of which you can't just adjust it out.

I don't need a power source like an electronic type, I can replace a gauge inexpensively if need be vs a high dollar fix of the electronic one.
Plus a Carbmate cost hundreds of dollars vs $80.

p.s.
I have a Carbmate that was used 3-4 times. Yours cheap. :)

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: How difficult (how many hours) to sync carbs?

by Alex Morrison » 6 years ago

Alex Morrison

21 46 62

Hmmm, thanks Roger. I might look into buying a set of your gauges! I have the carbmate. What might you diagnose if synchronisation can be achieved from idle to around 2500rpm but on applying power the carbs progressively move out of sync? I can visualise the effect of sticking cables and also excess air being drawn in where it should not be affecting the venturi. Also perhaps a perforated diaphragm? The carbs have not been stripped in a long while by looks. What do your gauges do if a jet is blocked?

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Re: How difficult (how many hours) to sync carbs?

by Roger Lee » 6 years ago

Roger Lee

126 5.13k 4.56k

Let's say an idle jet is obstructed. One gauge reads 14" vacuum and the other reads 20 " vacuum at idle. Either you did an out right terrible job on the mechanical sync, but since you know that's okay then the carb with that extreme high vacuum has an idle jet obstruction. Might as well shut the engine off right there because it isn't going to fix itself and clean that carbs idle jet.

I typically see the needles split when going from idle (1650-1750) to 2500 rpm which is still in the idle circuit. This is why I prefer to sync at idle and 3300-3500 rpm. Then I usually see the needles stick together as the rpm is increased even higher. I'm personally (maybe some are) not a fan of using 2500 rpm for my high rpm sync set point. So the split you see from idle to 2500 could be more normal. Try your sync at the higher rpm. I like my rpm to sync let's say at idle rpm since we do sit there a lot and I like my rpm to sync at above 3500 rpm where we tend to run more often. Idle rpm is a range and not an exact number. Depending on your likes, dislikes, aircraft and awareness of proper low engine rpm issues then you may set it for something like 1600-1900. I tend to personally like around 1650-1750 rpm. I know not to sit and idle there, but I use it right at shut down to lower the rpm. Some that like higher rpms for idle may have to ride the brakes a lot during a taxi. This is also plane specific. Some have a lot of drag and a little extra idle rpm is no big deal. Some roll extremely easy so 1900 rpm at idle drags it down a taxiway too fast. All these things have to come into play when you set your system up to suit your needs and maybe just your likes and dislikes.

Some people may disagree here and that's okay because it all accomplishes the same range and operating parameters. Since we spend most of the time well above 2500 and 3500 I would rather those needles stay together at the higher rpms. When we are at the high rpms during cruise the crossover balance tube isn't really doing anything because it's too small. The crossover balance tube helps the idle rpms while in the idle circuit (jets).

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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How difficult (how many hours) to sync carbs?

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