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Old 04-27-2012, 02:06 AM   #1
jb0005
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Default hanging idle on gf55ii twin - walbro carb

i have a crrc pro gf55ii twin with a walbro carb, and since new it has had a problem with returning to a constant reliable idle. i have changed spark plugs and removed and inspected the seal where the carb meets the motor to check for an air leak, and found some oil residue, which suggested that might have been the cause. i refitted the carb and appiled some high temp silicone to ensure a good seal but the problem persists. when i start the engine for the first time for the day i allow it to warm up for a minute or two, then when i advance the throttle -even slowly- the engine bogs quite badly as if it is too rich, then clears up and reaches full power. i can then close and snap the throttle open a fast as i like with no problem at all, unless i let it sit for a minute or two at idle and the bogging problem re-occurs.when i do bring the throttle back to idle and leave it there,it returns to its set idle then climbs slighlty for a few seconds before settling back down. are the two symptoms related? do i have an air leak which is causing the hanging idle, but a rich mixture which is causing the bogging on power up after being left to idle.does this sound like it could have something to do with an incorrectly set needle lever?. like i said the engine runs fine at full power, has a mid range burble below half throttle, but has never stopped in flight. all help is appreciated
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Old 04-27-2012, 02:37 AM   #2
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Same engine simular problem. Carb setup. I found mine real touchy to the low speed needle. I contacted Chad at taildragger R/C and he helped me sort it out.
Try setting high speed first, peak rpm, then back off couple hundred, then the low speed.
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Old 04-27-2012, 05:08 AM   #3
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FWIW and without actually hearing the engine it's hard to tell what's going on, but from your description it sounds like you may be a touch on the lean side. Just a thought.
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Old 04-27-2012, 07:10 AM   #4
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Try richening the low speed just a tad until it stops bogging down when going full throttle.Low speed needle-leaning will idle better but will loose transition,richening will give better transition but idle will drop.
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Old 04-27-2012, 04:45 PM   #5
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I am pretty used to a Walbro, take them apart and reset them all the time...from your description I can't tell whether you are rich or lean. My advice is to seat each needle and back out 1 1/2 turns on each. Both needles affect the setting of the engine...they interact with each other...it is not like setting a needle on say an OS 60.

Start the engine and it should idle at those settings. Then...turn in the low needle until the engine speeds up and starts to falter. Note where that is...open up the needle until the engine again speeds up and then falters...(now you are too lean). Set the needle half way in between. Now go to the high needle...open the throttle full and screw in the needle until the engine screams and starts to falter...back out a 1/4 turn and the engine should sound solid. Now go back to the low needle...start to decrease the rpm...if the engine starts to 4 cycle screw in the low end until it stops...will not be much. Now decrease the rpm more...and watch for a 4 cycle... You do not want a 2 cycle engine to 4 cycle...they are not meant to 4 cycle. They are meant to 2 cycle and that is a smooth scream. You should have a pretty good setting on the engine right now....let it idle...if when you open the throttle it starts to hesitate (different than a bog) the engine is too lean...if it sputters or bogs it is too rich...make small adjustments.... I can tell you more if you want...or have more problems or your situation persists. daveyrt@gmail.com
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Old 04-27-2012, 06:21 PM   #6
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You have some great advice here. Most always goes back to the needle. The crrc 55 has a very smooth transitioning walbro carb. However the needles can be sensitive. Instead of half to full turns they take 1/8th turns If you need any more help feel free to pm me here
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Old 04-27-2012, 08:07 PM   #7
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I m wondering if the needle arm is set to far down and not even with the carb body?
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Old 04-27-2012, 11:04 PM   #8
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Also get rid of the idle screw if you haven't already
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Old 04-28-2012, 03:21 AM   #9
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thanks for all the advice,guys and if anyone has any more keep it comin'. i can get the engine to stop hanging on the idle if i richen the low needle about 1/3 of a turn from where it is(it is currently about 1.75 out). but this is definately too rich, as i ran with it like this for a full day and when i checked the plugs they were really black. the guy at the local mower shop who is very knowlegable on two strokes seemed to think that if i need to richen it this much to stop the hanging idle then it must be an air leak. he also believed that the fact the engine will initially come back to its correct idle then pick up rpm and idle high is also an indicatorof an air leak. i have also tried leaning the low end off and the hanging idle problem is the same. i will try some more needle adjustments this week to see if i can tune it out, but i get the feeling it could be some thing else.
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Old 04-28-2012, 08:36 AM   #10
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If you suspect an air leak,a simple way to find it is take your cowl off,get some Berryman carb cleaner,with engine idling spray the cleaner anywhere there could be an air leak,ie mating surfaces,bearings,etc,the idle will change if the cleaner is sucked into a leak.Good luck.
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Old 04-28-2012, 10:24 AM   #11
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+1

Where is your HI needle set? As previously stated, both needles have some effect on each other. If the top end is RICH, you can have the "surge" when you pull to idle because the hi circuit has excess fuel to clear. Now that you've stopped the BOG on the low end, lean the top down a tic at a time and be sure to check the plug to make sure you're getting a golden brown, not grayish white (lean), or black (rich) color. BTW, it is best to do this while flying as none of the engines cool well on the ground. Course tuning on the ground, fine tuning airborne.
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Old 04-28-2012, 10:37 AM   #12
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Also check to make sure your throttle linkage is working free with no binding. Seen that a few times
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Old 04-29-2012, 01:58 AM   #13
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thanks again guys for the ideas, i'll give them a try this week and i'll let you know how i go
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Old 04-29-2012, 10:03 AM   #14
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Hey bill...can you recommend a good twin cylinder that is not an arm and a leg....50 to 70cc... I noticed your 3w note and I know they make one...but I would have to give up my first born for one....now that I think of it............... anyway...any advice? And why are 3w's so good....?

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Old 05-05-2012, 01:57 AM   #15
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jb, let me know how you make out with setting up your 55.
Ran set my carb 1.5 low, 1.75 high. Starts great, runs great. Tweaked the low 1/8th leaner, and it idles fantastic. No hang whatever, and a very good transition. Still need to dial in top end, but it is performing great right now.

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