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Level flight difficult on my Volution - is it the carb?


stuartasutherland
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Hi, I'm struggling to get smooth level flight on my Volution 1.

I might be going down 80ft/min then try to pull the smallest bit of acceleration (and I mean 0.5mm on the throttle trigger) and the revs just shoot up and I'm at 200ft/min up. Really tricky for low flying.

I have a new throttle cable so all smooth there.

I'm noticing some oil splattering around the carb - does it need a service? All the screws are tight. I've never taken it apart so would be worried to have a go.

Is it the tuning that needs adjusted?

Any help would be great. Does yours do the same?

Cheers

Stu

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Does it make a difference whether your arm is high or low? When mine was new I had a problem with the throttle where if you moved your arm down whilst holding the throttle, the engine increased revs quite dramatically, if you raised it they dropped - it made some flying (especially low turns) quite difficult. I adjusted the throttle cable as much as could be adjusted but the effect was still there slightly. I took it to the factory and they couldn't get rid of the last bit either (although it is usable now).

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Hi,

Just a thought but I think that your level flight cruise speed is just matching where the power band on the parajet is. At one second just below then it jumps into the power.

A possiable answer might be as easy as altering the trim speed of your wing to either speed it up and run the motor in the power band or slower and stay below that power band .

As I say just some thoughts hope they are of help...

Cheers Col....

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Power bands are due to mainly exhaust design and cylinder porting. Would be interested to know at what rpm it happens?

For an engine of that cc level fight depending on wing and AUW, the rpm should be 4500 upwards. Power bands shouldn't be in this range for our style of engines. Different for racing scooters and bikes that race flat out and change gear in a smaller width of power band, normally to the top of max rpm.

As Colin surgests you need to move out of that area.

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Hi Stuart

If you are trying lower level flying your beter of flying faster... As fast as you can and if you do have an engine out you have loads of energy to flair with... Full trim and use full speed bar then you can use the speed bar as a tool to climb and not have to use the throttle, start of using this technique high and get lower as you progress. DO NOT do it low until your ready

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Hi Stuart

If you are trying lower level flying your beter of flying faster... As fast as you can and if you do have an engine out you have loads of energy to flair with... Full trim and use full speed bar then you can use the speed bar as a tool to climb and not have to use the throttle, start of using this technique high and get lower as you progress. DO NOT do it low until your ready

If you just want to fly low (no fast comp type stuff) then fly on neutral trim.

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Hi Pete, I have been flying on neutral trim. My problem is the revs dont creep up as I squeeze the throttle, they almost jump up in steps. I don't have a Tiny Tach but they are significant jumps in excess of 1000rpm. Not all through the range but mainly where I want better control ie level flight.

It is not really an issue high up as I accept Ill always be climbing or descending.

My carb is leaking a bit of oil and I have some splattering around that area.

Is it easy enough to take the carb apart and change seals / gasgets?

Cheers

Stuart

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Stuart - I am 99% certain it IS the carb ..... the Walbro 37 is notorious for these symptoms (I've had similar) and particularly for a rough or 'dead' spot in the revs at the point where the high jet takes over from the low jet. A perforated diaghram, leaking gasket or worn needle tip on your inlet valve could all cause your symptoms.

It is very simple to strip and rebuild - just remove it to a clean area and take your time. No special tools required. Make sure you buy a full repair kit (about £11) that has all the gaskets, membranes, needle, spring, fulcrum pin etc to repair.

Also buy a tin of carburettor cleaner from any motor factor, to clean it thoroughly - especially the internal gauze filter which gets clogged. If you have an airline to blow it through then even better, but not essential.

Also, before you strip it down, count the turns on your high and low screws so you can set them the same after rebuild (initially) before making small adjustments to fine tune. It shouldn't take more than an hour to rebuild.

There are plenty of diagrams and guides to follow on the internet.

http://blueskyppg.com/index.php?main_page=product_info&products_id=123

http://tech.flygsw.org/walbro_tuneup.htm

http://www.aerocorsair.com/id27.htm

http://www.parajet.com/images/pdfs/Volution2Manual.pdf

Alan :mrgreen:

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That's the one - at that price there is no excuse for regular carb maintenance ... not sure why I thought you were in Canada though .... :lol:

Only other thing to note is you may need to set the fulcrum height by bending the metering lever a little bit after fitting the new needle. You can also adjust this by setting the 'pop-off' pressure, but this gets a little more technical and is not usually necessary.

Just let me know if you get stuck or need any further info, but these articles should have all you need for perfect, trouble free carburettor setting (Walbro WB series carbs are all pretty similar, regardless of model no.) :

https://www.pegasusautoracing.com/document.asp?DocID=TECH00038

http://tech.flygsw.org/walbro_tuneup.htm

http://www.footflyer.com/fix/motor/carburetor/walbro.htm

http://webspace.webring.com/people/bf/flphg/idle_adaptation.html

http://www.aerocorsair.com/id28.htm

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Is the throttle lever adjusted so when the engine is at max rpm, the lever is pulled back as far as it will go, so that there is no strain on butterfly pivot? If not, adjustment may put the lever in a position for better feel/control. This may not be your problem, but simple stuff first !

Hows the wrist ?

It was nice to see you all Saturday.

Carl

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Stuart - I am 99% certain it IS the carb ..... the Walbro 37 is notorious for these symptoms (I've had similar) and particularly for a rough or 'dead' spot in the revs at the point where the high jet takes over from the low jet. A perforated diaghram, leaking gasket or worn needle tip on your inlet valve could all cause your symptoms.

It is very simple to strip and rebuild - just remove it to a clean area and take your time. No special tools required. Make sure you buy a full repair kit (about £11) that has all the gaskets, membranes, needle, spring, fulcrum pin etc to repair.

Also buy a tin of carburettor cleaner from any motor factor, to clean it thoroughly - especially the internal gauze filter which gets clogged. If you have an airline to blow it through then even better, but not essential.

Also, before you strip it down, count the turns on your high and low screws so you can set them the same after rebuild (initially) before making small adjustments to fine tune. It shouldn't take more than an hour to rebuild.

There are plenty of diagrams and guides to follow on the internet.

http://blueskyppg.com/index.php?main_page=product_info&products_id=123

http://tech.flygsw.org/walbro_tuneup.htm

http://www.aerocorsair.com/id27.htm

http://www.parajet.com/images/pdfs/Volution2Manual.pdf

Alan :mrgreen:

Right Alan, I have a question.

I've been following this set of steps.

https://www.pegasusautoracing.com/docum ... =TECH00038

Section 5B mentions there are meant to be 2 gaskets but I only have one.

See photo with it still in the carb.

The other photo is what I have in the service pack.

So, should I replace like for like (the middle one) or add in the very thin one at the top (I think it is a one way flap) as shown in the guide (link above).

Many thanks.

Stuart

573364147c7a1_photo(7).JPG.ba9aeeef6cd76

573364147f10d_photo(8).JPG.688a413ce13b9

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OK, under the semi circular metering plate there should be a rubber diaphragm and a gasket ..... is it possible they are stuck together ?

You want the middle gasket from your kit photo, plus the thin diaphragm.

I have read a tuning tip somewhere that you can cut out the flap on the rubber diaphragm, but I would advise building it to standard spec before any further tinkering - it may be that this is a cause of your problems if someone omitted it previously - did you purchase the motor new or secondhand ?

This is a handy schematic / parts list: http://www.planetppg.com/content/WBseries.pdf

and some further info here: http://www.planetppg.com/Bing.html#WB37c

plus some tuning tips (although a different Walbro carb) here: http://www.geistware.com/rcmodeling/glowpower/gas_engine_tune_1.htm

Maybe Simon could edit the info and links together into a sticky section for Walbro carbs, since they are standard on many motors ? :?:

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PS - if you haven't already started rebuilding it, alloy wheel cleaner and a toothbrush will have the carb body looking all sparkly and new again.

The gasket mating surfaces can be cleaned with a nylon scouring pad and some carb cleaner (or petrol) - but not wire wool or anything that cold scratch it - followed by a final rinse and blow through.

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PS - if you haven't already started rebuilding it, alloy wheel cleaner and a toothbrush will have the carb body looking all sparkly and new again.

The gasket mating surfaces can be cleaned with a nylon scouring pad and some carb cleaner (or petrol) - but not wire wool or anything that cold scratch it - followed by a final rinse and blow through.

Hi Alan, thanks for all the advice. I've now built it all up again. I used Carb cleaner (got a tiny splash in my eye and the pain told me it should do a bloody good job on the carb!).

I used the paper gasket and rubber layer too - hopefully that will help things.

On the other side it was using the paper gasket and the rubber layer too, the guide said use the Teflon see through one so I went with that.

I'll run it up tomorrow and see what happens.

I'll let you know!

Thanks again

Stuart

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