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Home✈️Aircraft🚁HelicopterGasser Model RC HelicoptersOther › How do carbs differ in fuel delivery...
04-22-2013 02:34 PM  7 years ago
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flyinfriend

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North American continent

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How do carbs differ in fuel delivery...
I pulled this question I asked out of another thread about the 990 carb and was wondering if someone would know the answer.

I don't doubt that different carbs provide varying performance, I'm just wondering why they do.

Thanks for any thoughts.
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04-22-2013 03:12 PM  7 years ago
Pistol Pete

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Seffner, FL

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Atomization...mainly.

google " helifreak carburetor " a must read.
~~Enjoying the hobby one flight at a time~~
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04-22-2013 05:00 PM  7 years ago
Toadster25

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Iowa

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I don't know what the difference is between a wt643 and the 990 but my guess is the size and placement of the three low speed mixture feed holes and maybe some other slight difference. I don't really know how it could make an engine run smoother but maybe it gives a perfect fuel mixture at all rpm and throttle positions. I think a rich or lean mixture can cause more vibration.
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04-22-2013 05:25 PM  7 years ago
flyinfriend

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Thanks pistol_pete.

That was a great write-up by Carey. Very informative. So it really comes down to how the different carbs atomize the fuel?

Thanks Toadster, yeah I'm still trying to understand how it can make an engine run smoother.

Again, not doubting that it can but just trying to understand the why.
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04-22-2013 05:35 PM  7 years ago
chris6414

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Holly Ridge, NC USA

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I just changed out my 643 for 257 and noticed the needles seemed finer on the 257 meaning they had more adjustment with less effect overall. The throttle plate also had a slight grind out on the edge of the plate right inline with the jets and it will idle a heck of a lot better than the 643 which has a perfectly round plate. Haven't put the now clean 643 back on since the 257 runs so nice. Nothing wrong with the 643 other than it was dirty I found when I took it apart.Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo
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04-22-2013 05:40 PM  7 years ago
flyinfriend

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Hi chris6414,

Funny you mention that. Billme had mentioned to me a little while back that I should try switching to the 257. He said it tunes easier and would also result in a smoother running engine. Now I have to flip a coin and decide which carb to go with.

Thanks for the info.
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04-22-2013 06:21 PM  7 years ago
rbort

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Franklin, MA - USA

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If you do try the 990
Let me know how it works for you. I also have a 257 but use it on my airplane nowaays. I did try it on the G20 and it didn't make as much power as the 643 did.

The 257 has no primer bulb so you'll have to pull more to get the fuel to get to the carb and start the engine. Also there is no return so you'll just have to plug up your return line if you go 257.

I think the 990 is a better fit but you do what you like best.

-=>Raja.
MA 1005 Hanson 2703D, 4393 flts
Spectra 27 3DMax, 3455 flts
Whiplash V1-2 Hanson 300, 1982 flts
Whiplash V2 Hanson 300, 907 flts
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04-22-2013 06:54 PM  7 years ago
flyinfriend

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Thanks Raja.

I think I'll go with the 990 since you mention no return and no bulb on the 257. I'd rather just do a straight swap with less hassle.
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04-22-2013 07:15 PM  7 years ago
rbort

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Franklin, MA - USA

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Yeah, my 257 found a good home.
My 257 was much better suited for an airplane. I just electric crank it until it starts (several seconds) and there is no primer bulb or return needed in this application.

-=>Raja.
MA 1005 Hanson 2703D, 4393 flts
Spectra 27 3DMax, 3455 flts
Whiplash V1-2 Hanson 300, 1982 flts
Whiplash V2 Hanson 300, 907 flts
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04-22-2013 07:35 PM  7 years ago
Billme

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MS

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Well, at least you both are trying different carbs now to run better There is no hassle with a 257 btw, but the 990 is good, just not as smooth as a 257...
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04-22-2013 08:48 PM  7 years ago
Gearhead

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Vt

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""just not as smooth as a 257""

well you got to have a smooth head
Jim
Buzz Buzz Buzz
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04-23-2013 03:14 AM  7 years ago
turboomni

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East of the Equator

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Just curious,,is the bore the same in all the mentioned carbs?

I ordered and received my 990 and will try it soon I hope.
Setup is everything, All my heli's can fly far better than I can pilot them
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04-23-2013 03:46 AM  7 years ago
rbort

rrProfessor

Franklin, MA - USA

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That's correct
Just curious,,is the bore the same in all the mentioned carbs?
Yes it is, and

Yes my heads are smooth as silk, flown daily hours on end

-=>Raja.
MA 1005 Hanson 2703D, 4393 flts
Spectra 27 3DMax, 3455 flts
Whiplash V1-2 Hanson 300, 1982 flts
Whiplash V2 Hanson 300, 907 flts
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04-23-2013 05:31 PM  7 years ago
chris6414

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Holly Ridge, NC USA

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If and when I put that 643 back on(next year maybe) I am going to keep that throttle plate with the cutout. I really think it allows better airflow at idle and aids in the transition. I can run the LS a tad richer with a smooth spool up. With the 643, I noticed when I had the hover set right it would burble more on the spool up and idle like it was rich.

Chris
Century Hawk Sport, OS .32, Futaba 7C, GY-601 9251
Predator Gasser SE G-23, Fut 3010 servos, JR gyro/servo
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04-23-2013 07:43 PM  7 years ago
Gearhead

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Vt

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Yes my heads are smooth as silk
as I was suggesting, mine are too
I am going to keep that throttle plate with the cutout
I agree it's a good idea, I was telling people 2 years ago (even before I owned a gasser heli) to buy that plate ($$0.94), or cut out their stock plate.. well I told more than a few people, not the whole world LOL
Jim
Buzz Buzz Buzz
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