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HelicopterMain Discussion › Zenoha carb tuning
09-03-2017 08:53 AM  80 days agoPost 1
myjane

rrApprentice

new zealand

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What's the favoured carb tuning to the zenoha mine is bogging at around mid stick I notice today , off the ground it seamed a bit sluggish

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09-03-2017 01:53 PM  80 days agoPost 2
fastflyer20

rrKey Veteran

N. Tonawanda, NY

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The Walbro 990 has proven to be the best carb for helis on any size Zenoah. Make sure to install new gaskets to prevent air leaks.

http://www.davesmotors.com/walbro-w...r-fg-07855.html

I re-read your post, if your trying to adjust yours, it sounds like it may be lean, open the low (screw closest to engine) 1/16 of a turn and see if it improves. If it does, open another 1/16 of a turn and see how it runs. If it takes 1/8 of a turn to run better the carb low speed passage is partially plugged or you have an air leak. To check for an air leak, use an aerosol can of computer duster with the extension and spray around the carb adapter gaskets. Its normal for it to leak around the throttle shaft so block it when spraying. If engine RPM's decrease then you have an air leak.

Tom
CAUTION - my posts are based on my experiences, yours may be different.

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09-08-2017 10:12 PM  74 days agoPost 3
3dorbust

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Hudson Florida usa

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Zenoha carb tuning

Yes I agree to check for air leaks but it can be hard to know exactly where it is unless you do it at idle and stay away from the intake and the throttle shaft as said before. If you use carb cleaner with the red straw it comes with and spray vary lightly around the intake gasket. But there is an easy way to see if your engine is running rich or lean before you turn the mixture screws. Bring the engine rpm's up to the point where it has the problems you mentioned and then slowly bock off the air intake of the carb with your finger or a piece of cardboard whatever you feel is best. By slightly choking the engine so if it starts running better then it's lean if it starts running worse it's rich this can be done at idle, midrange or wide open which are the 3 separate circuits of you're carb and any one of the 3 can become rich or lean so this works if you choke of at the time it's not running right so if its lean at the midrange both mixture screws are in play turn both counter clockwise 1/8 of a turn and do the opposite if rich

I know how Icarus felt

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09-09-2017 02:38 PM  74 days agoPost 4
Pistol Pete

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Seffner, FL

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You can also swipe a dry finger between carb and engine, if it gets wet with fuel, you have an air leak.

~~Enjoying the hobby one flight at a time~~

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09-13-2017 11:52 PM  69 days agoPost 5
jharkin

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Holliston, MA - USA

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Walbro carb's only have two fuel circuits... not 3 like nitros.

The idle circuit supplies fuel at all times and adjustments to that screw effect the entire range. The HS circuit only kicks in at high speed.

I would agree with To,pm, keep adjustments to 1/16 turn at a time. 1/8 is a large change on a walbro.

-Jeremy
Whiplash-G
Helix 700G
T-Rex 450 fbl conversion
alot of planks

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09-14-2017 12:29 AM  69 days agoPost 6
3dorbust

rrNovice

Hudson Florida usa

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Zenoha carb tuning

Yes that's right. After repair or rebuilding more than 30,000 walbro and zama carbs over 25 years I found that the rubber diaphragms fail for many reasons and must be replaced periodically. If it bogs at half throttle and a small adjustment don't help have it rebuilt by a qualified repair shop and insist on a OEM rebuild kit. The amount of problems you can have is so vast I cannot in good faith tell you exactly what to do here. But if you remove it and have a bench rebuild at a good small engine shop you should be happy. By the way most carbs are set at 1and1 half turns out from all the way in as a starting point for both high and low speed mixture screw's.

I know how Icarus felt

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09-16-2017 01:09 PM  67 days agoPost 7
jharkin

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Holliston, MA - USA

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Not disputing your experience 3D... but some thoughts.

#1, Replacing the diaphragm kits is VERY easy and any gasser pilot should learn how to do it. I would not bother paying a small engine shop - the bill would probably be more than purchasing a brand new carb (can be had for ~$40 for a new 990)

#2 - Everybody who flies these should grab and read the walbro service manual
http://www.wind-drifter.com/technic...rviceManual.pdf

#3
Yes, I agree the generic "safe" starting points for Walbros on most engines are around 1.5 turns. But its still worth reading hte manual for specifics....The tuners Hanson and TRM both document heli specific start settings in their manuals. Hanson calls for 1 3/8 Hi, 1 1/8 Lo on a 990 and at least in my climate this gets you to within 1/8 turn of the optimal setting. (On the other end of the range some airplane engine manuals want you to start closer to 2 turns)

-Jeremy
Whiplash-G
Helix 700G
T-Rex 450 fbl conversion
alot of planks

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09-16-2017 01:13 PM  67 days agoPost 8
jharkin

rrApprentice

Holliston, MA - USA

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One other point-

Tom mentioned above the WT990 being the preferred carb on Heli Zeonah's. I've been told that one of the reasons is that the WT603 that comes on a factory stock Zenoah will have throttle lag issues when the high needle is peaked for max power. So definitely worth taking Toms advice to check your engine and if its a 603, swap it to a 990 first before chasing other ideas.

-Jeremy
Whiplash-G
Helix 700G
T-Rex 450 fbl conversion
alot of planks

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09-17-2017 10:54 AM  66 days agoPost 9
3dorbust

rrNovice

Hudson Florida usa

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Zenoha carb tuning

That has been the debate for more than five years. Rebuild or buy a new one and yes they have come down in price. But are you getting a true walbro or a Chinese knock off that costs the seller 8 bucks? And even if you do get an OEM carb it may not perform like the original? Small changes are made all the time to save money so it's a chance you take. I'm glad you talked about this you must have some experience. So it's buy new get a good one and happy days or get a bad one and the nightmare starts. I have heard no it can't be the carb I just put a new one on more times than I care to count. So try to make someone believe there new carb is bad! I just know I can rebuild them so I like your point. I just want you to know carb manufacturers have to deal with the EPA and make most run lean via the main jet. They receive clean air credits for it which they trade for tax discounts. Performance is my only concern.

I know how Icarus felt

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09-17-2017 11:26 AM  66 days agoPost 10
3dorbust

rrNovice

Hudson Florida usa

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Zenoha carb tuning

I don't know what is best for others but I now replace new carbs on a scale I never thought I would. Yes diaphragm replacement is easy but not understanding what exactly is wrong and why. If you adjust your hs needle at full operating temp and at full load peak the engine then back off a bit you will safely get all the power that engine can make. No load adjustment means nothing.

I know how Icarus felt

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