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Solo 210 seize...bubbles in fuel line?


epurdy2005
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My solo 210 has seized 3 times now and I can't figure out why...Walbro carb that has been rebuilt, all new fuel lines, have done a leak down test, ....My main question is that i have a group of small bubbles that sit at the top of the fuel line before it goes into the carb while it is running. Sometimes the bubbles are there and sometimes they are not.Sometimes they move into the carb. But I don't see where it would be getting the air from? I've stuck a fuel line in another tank to try that and they are still there. Any ideas?

Thanks

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I would say it is sucking air in elsewhere as I know a few people that have air in the fuel line with no problems.

Air could be getting in through

bearing seals

crank case

inlet manifold

Head gasket

base gasket

Have you set the pop off pressure correctly when you rebuilt the carb?

Did you do a plug colour test after? what was the colour?

Are you getting max RPM?

Have you put a new prop on?

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Have not done the pop off pressure. I remember reading about it somewhere but you had to have a certain guage if i remember right? The color of the plug always looked good. Have not changed the prop.

I changed out the piston and cylinder twice . I put pressure to the case and it held air so I'm pretty sure its none of the seals there anyways.

I gave up and gave it to somebody else to rebuild

He changed all of the fuel lines and rebuilt the carb...I'm just worried that it will happen again cost even more money.

I just taught myself to fly and each time ended with an engine out so its getting frustrating. Thanks for the tips just wanted to see if there was just something weird out there that I am missing.

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There are 2 separate problems here - the air bubbles in the fuel line and the engine seizing. It is unlikely that a small amount of air in the fuel would cause an engine seizure, let alone 3 !

1 - There are several ways air can get in the fuel lines. The obvious causes are at each junction / connection point (tank, primer bulb, fuel filter or carb union) due to the type of tubing or hose clamp used - easy and cheap enough to check & replace. I had 2 inline fuel filters that leaked (square and round types) - thankfully they were clear and easy to spot a small stream of air bubbles entering. The primer bulb is the next likely culprit as they are not designed to work above the tank level and many microlight pilots have removed them due to problems with the check ball. I removed the bulb from my Walkerjet paramotor and it was easy to prime the carburettor simply by blowing down the fuel tank vent pipe, and it ran much better without it. Once fuel reaches the carburettor the primer bulb becomes unnecessary anyway.

2 - Engine seizure is due to either a lack of lubrication or overheating. Providing the oil/petrol and air/fuel ratios are correct then the engine should get enough lubrication. For temperature measurement a CHT gauge is invaluable - prolongued temperatures exceeding 200 degrees celsius will kill an engine. Spark plug colour is a good indication but you need to kill the engine immediately after a sustained climb as even a few seconds of idling will ruin the colour check. Make sure you are checking the porcelain colour near the base of the plug, not the exposed part near the electrode tip.

Overheating is mostly caused by an excessively lean air / fuel mixture (possibly by the gaskets as mentioned in other posts), but also by incorrect propeller sizing or reduction ratio, lack of cooling airflow over engine or other internal component problems. Is your weight / wing / motor efficient or do you need a lot of power just for level flight ?

Eliminate the potential issues systematically and you should resolve the problem.

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My adventure solo always has air in the pipe, I have never been able to eliminate it.

check plug colour, fuel mix, the L and H on the carb are set right

also did you gap the piston rings to the cylinder befor assembly? if not the rings will be oversized and will cause a seize every time

also the solo uses diffrent cylinders, look on the top of the cylinder, it may have a B or an A stamped on it, you have to get the right piston to match the cylinder, if not the piston will be too big for the cylinder and cause excesive heat and then a seize. the pistons are stamped up with the matching letter

my barrel is a B and I have an A/B piston. my last piston was a B

I was also informed there is an A piston so check the combo out. you could poss recover the old piston and rings you have, dont throw them away just yet.

also check the bore of the cylinder out, nothing stuck to it like a micro layer of aluminium from the previous seize in a localised area near the exhaust port? if so this will over heat every time in that spot.

nykersil lining ok? if worn in a part will heat up at that point every time.

ports inside the bore, no sharp edges?

nothing inside the crank case that keeps being thrown up each time? turn the motor upside down and wash it out with petrol just in case

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  • 3 weeks later...

Sorry to not get back with you guys. I'm almost positive the engine itself is fine....my fuel line goes to the top of the carb and then makes a loop ino the carb.....I have a 3-4 in. spot with no fuel in it all the time when it starts to make the loop...then about 2 in. of fuel sitting in the line before it goes into the carb....Now when I run the motor and hit the throttle that 2 inch of fuel goes to about nothing until i back off the throttle...I even ran a different fuel line into a gas can. Its not getting any air from the fuel line...So where is this air coming from?Back from the carb?..Why won't the line fill totally with gas? I've tried getting rid of the loop in the fuel line and still the same thing.

Could the fuel pump not be pulling enough and always causing it to be lean?..The is boggling my mind. I wish i had another carb to see if that is the problem. I've had another person go through the carb as well though.

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Turn the inlet nipple on the carb to eliminate the loop in the fuel line. It will turn but be very very careful - owners risk and all that! If you are having the barrel refurbished, send the new piston with it so that it can be matched perfectly. Is the machine old? Bit of a long shot but check the pulse line is not gummed up.

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I have checked the pulse line and replaced it....I've looked at others and the fuel line is supposed to run with that loop there so I don't really want to change that. When I used the gas tank on the ground to see if it was a fuel line problem I had to use the electric start and carb to get the gas all the way up to the carb and it did it just fine..So I assume the pump is okay. I think I'm going to bight the bullet and buy another carb. With my luck with working on engines lately it probably won't fix the problem though.

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  • 2 weeks later...

Apologies for a late reply. Have had some head-scratching moments with blown pistons. Here's my findings which you may find useful. I found , with the variable timing CDI that the timing curve is still peaking max advance at approx 4000rpm and retards more and more as the revs increase. WOT is not a problem, but cruising, especially with a large prop would bring the rev range down to where its running at max advance (mid-range).

Mid-throttle seizures are often overlooked and more common inmodern equipment because of this. WOT its running great, but as soon as you lower the revs, bringing it back to max advance, and you have a lean mid-range condition, detonation can occur, followed by piston destruction in short order. As mentioned earlier, check the pop-off, even though the engine does not see the pop-off past idle. The paddle height and low screw all affect the mid-range. The lower the pop-off pressure, the more sensitive the low screw is to change and easily affects the litre per hour consumption. IMO

Please let us know when you have the problem resolved. Good luck.

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Apologies for a late reply. Have had some head-scratching moments with blown pistons. Here's my findings which you may find useful. I found , with the variable timing CDI that the timing curve is still peaking max advance at approx 4000rpm and retards more and more as the revs increase. WOT is not a problem, but cruising, especially with a large prop would bring the rev range down to where its running at max advance (mid-range).

Mid-throttle seizures are often overlooked and more common inmodern equipment because of this. WOT its running great, but as soon as you lower the revs, bringing it back to max advance, and you have a lean mid-range condition, detonation can occur, followed by piston destruction in short order. As mentioned earlier, check the pop-off, even though the engine does not see the pop-off past idle. The paddle height and low screw all affect the mid-range. The lower the pop-off pressure, the more sensitive the low screw is to change and easily affects the litre per hour consumption. IMO

Please let us know when you have the problem resolved. Good luck.

As an afterthought.................

The post above assumes the timing is correct. The units I have seen come more retarded. An engine straight from the manufacturer is more aggresive, great for showing the ladies your thrust, but it may well benefit if it is more retarded. (Badge and T-shirt fully on display) You will not really notice the lower output.

Instead of snapping the throttle open from idle, as usually suggested, try holding the throttle open at ¼ revs for a couple of minutes, then snap it open. This may help diagnose mid-range running. A plug chop can only give you an indication of how it is running at WOT and nowhere else in the rev range.

As usual, this is IMO.

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  • 1 month later...

We're having a similar case here in Western Australia

One of the pilots have replaced his carbi`s fuel lines and he start to see these bubbles in his fuel line

Shortly after that he seized his simonini mini 2 plus engine and here are some photos of it

14-2-11%20007.jpg

14-2-11%20009.jpg

Notes;

1- He didn't change his carbi setting in the last 30 hours

2- He didn't change his fuel mix

3- He didn't change his oil

----------------------------------------------------

He's thinking that the new fuel lines are a bit larger and they're not as tight as they were from the manufacturer and air can get sucked into it and that's the reason for the bubble

It makes sense as your engine is using the fuel to cool it self and by putting more air in the mix, you are leaning down the mix and over heating the engine.

You probably have a tiny hole in your fuel line which creates those bubbles and sucking the air in as you fly

Let us know about the result

Cheers

Idiot

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