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Why won't my Solo 210 start when hot?


Bob Moore
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Advice wanted please! Getting desperate for ideas to sort this Solo 210 I acquired a couple of months back, which had been unused for 20 years, sat in someones garage. (You may have seen my original posts asking for parts advice etc. It arrived minus the coil.) Been paragliding 15+ years and looking to get into power flying. I couldn't source the original coil anymore but 2nd coil I fitted a Stihl chainsaw coil that went in ok with a bit of fiddling and I had a spark. This is a magneto coil, ie no points, no battery necessary. I cleaned the fuel tank, did some rewiring, new fuel pipes, fuel filter, serviced the carb with new parts (done in twice now) . Woo hoo it started. I've had the 4 bladed prop off, rubbed it down , re-varnished, balanced it too! Super, it starts and runs well when started cold, and runs beautifully , picks up well, revs well. BUT, stop it and leave it for 10 mins and it won't start on the button. It's electric start. You can crank it forever but fuel is not getting into the pot. Drop a bit of petrol into the spark plug hole it will fire run again OK. I have tested crankcase pressure, good. When you are cranking it the crankcase pressure driven fuel pump that is part of the carb is pumping fuel. Carb is clean, jets are clean, I've dismantled it several times now and blown it with my airline. And anyhow, when running it runs beautifully. Pop off pressure I thought, this is the bit that opens the fuel metering diaphram and allows fuel in. Yesterday I replaced the fuel metering spring. £3. This can have an effect on running if it's weak. It started OK this morning revved up OK. Ran it 10 mins and stopped it . Went back ten mins later and cranked it with the electric start, wouldn't start. Dropped a bit of fuel down the decompressor vacuum tube which goes straight into the carb inlet manifold. (Incidentally I have had the decompressor off too and checked it!) Started no trouble. (Sorry this becoming an essay but I have been working on this reluctance to start when hot prob for weeks now.) I checked Pop off pressure with my home made device seems to be 12 lbs per square inch which should be OK and this runs beautifully anyway? The video is it running after my latest change, ie metering spring. I intend to train on this machine when I 'm happy with it, but I would like a motor that will restart when I'm in the air so that I can shut down and restart. A new carb is £81 Warbro WB32. Some people have successfully used WB 37. I am reluctant to shell out £81 and find the problem still exists and in any case, I find it hard to believe there is anything fundamentally wrong with the carb. It's a lump of metal with a few holes drilled in it and some diaphrams. It's cost me £160 to get this running OK (I got it for free.) £81 if it worked would still be a cheap motor. SO, please has anyone else got any other ideas as I think I've covered all bases. (And please don't say buy a new £3000 - £4000 xyz motor!) I am considering making a secondary priming device that I can operate while in the air which will inject a little fuel into the inlet manifold via the decompressor tube. That would be a fiddle but should work.
Edited by Bob Moore
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Thanks Cas but unfortunately no choke on this carb, that would be ideal.  I thought about removing the air filter and putting my hand over the intake, but I want to be able to start it in flight :(  Not easy to fit another butterfly either.  Injecting fuel is the easiest was to get it going.

 

Edited by Bob Moore
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my air conception has the system your thinking of fitting , it came  with a small strimmer type primer bulb ' but i also fitted a normal size primer bulb so i could primer it while harnest in . pipe for the extra fuel goes through the air filter neck . if you want a pic of it let me know .

cas .

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Thanks Cas that sounds the way go. Yes pics please. If you can't post here my e mail is bobtheflyer (at)gmail (dot) com 

 

My motor does have the primary bulb of course between the fuel filter and carb but I can't really reach that in flight.  Certainly not easily anyway.   I guess this is T joined in to the fuel line?

 

I think I've seen some motors that can be primed while in flight by blowing a tube too?

Edited by Bob Moore
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Check the needle valve in the carb is seating/sealing properly, if it isn't it will let the fuel run back down the pipe. Make sure no air is getting into the fuel pipe connections allowing the fuel to drain down. Failing that, you could try a non-return valve in the fuel line.

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Thanks Savage, fuel doesn't appear to run back, no bubbles in the line and you can see it's still there.  The pump in the carb works too as if you hold down the metering diaphram while you are cranking it over fuel pees out of the carb.  Just doesn't appear to be going into the cylinder. Jets are clean too.

Amongst all the other stuff I did when I first got this motor that was unused for 20 years I replaced all fuel lines, cleaned the tank, new filter and new priming bulb which has a working none return valve too.  I have bitten the bullet and bought a new carb after someone offered me one on a Facebook group that they'd ordered but bought the wrong one. It remains to be seen if that resolves my hot starting issue. I doubt it but I might be lucky. It's another thing eliminated anyway.

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I had a Ros 125 which would never start from hot and I had to let it cool for 10 minutes before I could start it.The problem was the heat transfered from engine to the cab and the heat was vaporising the petrol. I made up a 12 mm nylon spacer to mount the carb, this seemed to help.

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3 minutes ago, kiwi k said:

GR002 we've already done that route on Bob thru FB 

 

Yes, apologies for a double post on Facebook but two forums grabs more attention and more people and did produce some other ideas. Unfortunately nothing I hadn't thought of or tried. Did produce a new carb at a good price though. Remains to be seen if it will make a difference though!

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Having a Solo 210 and a WB32, I had this problem when I acquired the engine some years ago. I always had to reprime my engine after I killed it, so fuel went back somewhere. And I also had to poke the diaphragm to get the fuel into the carburetor, often resulting in fuel pissing from the airfilter and flooding the cylinder, something was not right.
(but self proclaimed experts around me thought that this was the way to go).

I soon did a carb overhaul with new replacement parts, everything was well used inside the carb. Three things that I changed might have solved this for me.
First one was a new inlet needle with a fresh rubber tip. there was a visible difference with the new and the old one, not good.

4024d1280763220-leaking-carb-please-help-141_0707_16_z-keihin_fcr_carb_tech-float_needle.jpg 

Black tip is rubber and important the keep it tight. (just a sample pic)

Second thing was to change the diaphragm cover to a new one without an oversized drilled hole, since I believe that you shouldn't need to touch the diaphragm with your finger on a working unit.
Now I just have the small standard hole, and nothing that disturbs the diaphragm so the carb loses its pressure.
Try this, blow gently on the diaphragm when you have internal pressure and you will see why this is a big deal. Then think about it, is that something you want on your back when you fly?
I just pump the fuel with my finger-sized primer bulb. And with the right pop off pressure (adjusted with the walbro tool and a wet needle (might be the third step) you don't need much force to prime a wb32, just one or two fingers if you have the right sized fuel hose.

Also from Alex Varvs guide Pop-off pressure adjustment

Quote

1) Too high pop-off pressure leads to fuel starvation, hot engine, overheating   and even seizing, if the engine is run at full power for long periods of time.A good indicator of this will be of course a high temperature reading on the CHT, EGT or a very "clean" white-gray spark plug insulator. This is NOT an indicator that the oil used in the mixture is good and burns clean! It shows that there is TOO much AIR in the mixture and not enough FUEL. The combustion is done in excess of oxygen. Such a combustion generates excessive heat.

2) A too low pop-off pressure will cause a too rich mixture which is not really dangerous for the engine on the short run but will decrease its performance and cause too much carbon buildup. On the long run, the excessive carbon deposits may fragment, get caught in between the piston and the cylinder wall and cause scoring. If not detected in time, this deposits will sooner or later "load the spark plug" cause a short and an engine out.

Symptoms: engine flooding, difficult warm engine starts, rough mid range RPM,Lowered maximum RPM of the engine.

Hope this helps
//Casper

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Brilliant. I think that pop off pressure may explain why my new paramotor would not work properly last year.

From new it would run but not go to full power....all the symptoms of being too rich. After breaking the plastic safety cap off the high end needle, I started to wind it in. The problem was that I only got full power with the needle just 1 turn from fully in. Guideline is usually about 1 3/4 turns out!

I was sent another carb. Nearly the same result, but slightly worse...3/4 of a turn out.

I was sent yet another carb. Same result....3/4 of a turn out.

Engine went back to Polini. Came back with another carb on. And works. 

All carbs are identical spec.

I have lots of spares now!

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On 5/15/2017 at 22:07, cas_whitmore said:

my air conception has the system your thinking of fitting , it came  with a small strimmer type primer bulb ' but i also fitted a normal size primer bulb so i could primer it while harnest in . pipe for the extra fuel goes through the air filter neck . if you want a pic of it let me know .

cas .

Cas, thanks for the pics though any chance you could draw a diagram of the system, can't really quite figure it out from the pics. Sorry to be a pain!

 

Hi again Cas,

Thanks for the long and detailed reply.

I've serviced the carb twice and both kits had the new rubber tipped needle,  so hopefully that's OK.

Re the priming, for my initial cold start I think I have that cracked. I give the primer bulb a small pump until I see fuel run from the carb, one needs to press the top of the diaphram to do this, I thought it was the recommended way. Unless you do this fuel won't flow? But anyhow, little prime turn it over. It usually coughs and runs briefly. Then I give another short prime and it's away.

 

I'd seen the Alex Varvs pop off guide. Maybe I should get the proper tool as I just made something up and use a footpump with a pressure gauge.

 

I have read that most problems with these engines can be put down to pop off pressure.

I'll see how I get on with the new carb that should arrive in todays post!  If the issue still persists I'll make a primer that injects fuel into the inlet manifold as you had described.

Still not quite clear how it works though?

cheers Bob

Edited by Bob Moore
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Got it thanks, and I'd seen the small clear chainsaw type on e bay, that's way to go. New carb has arrived today, if I still have trouble I'll add a secondary primer. Or do you prime with that first when yo start?  The new carb I have only has the small hole in the metering diaphram cover too so I can't imagine how you'd press that anyway to prime?

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Thanks Cas, just fitted it.  Even cut a new gasket for inlet side!  Had to switch the pump plate  cover so spigot pointed the right way and switched low jet adjuster as the new one was just a screw head as opposed to an extended safer easy to use one.  Can't fire it up though as p.ssing with rain here in Devon.

 

Thanks for advice about priming.  If we get a break in showers I'll try and run it.

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It's a big misconception that you need to touch the diaphragm to prime a working carburetor. By drilling or using a bigger hole you just risk to lose internal pressure due to wind
from the outside. In worst case this makes it impossible to restart the engine without a new prime procedure, since the pressure will be gone as soon as the engine stops to suck fuel. A running engine helps to support a bad carburetor. But it won't help you when you try to restart in the air.

Remember why it have a diaphragm, to keep level with the atmospheric pressure. Even the smallest change in pressure will affect a diaphragm carburetor. And with correct pop off pressure it should be highly sensitive, and not something you want to poke every time you start your engine.

Walbro didn't design the cover plate just so users should make their own prime solutions. With a correct WB32 it should be just as easy to prime the carb as it is to push a key on the keyboard. And it should not piss fuel at all, since the inlet needle should be closed until the cylinder draws the fuel it needs.

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In a ideal world your right , but after your motors been in the shed for some time ' it's the quickest way to get fuel to the carb ' the alternative is to keep pulling the motor over . I'd rather press the diaphragm than damage the pull start mechanism. 

Cas . 

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If  the carb was gravity fed I would agree with you,  but this motor has the tank below the carb and depends on cranking and crank case pressure to pump the fuel. As Cas says, you could just crank it but all the advice I've seen re these carbs is depress the metering diaphram and pump till a little fuel trickles out of the carb.

 

PS  It started OK with the new carb. Still needs running up and trying when hot.  Tried it after stopping just once and it didn't want to go! But not a real test as I haven't properly tuned it yet.

 For the sake of a few quid I have ordered a small bulb primer and T piece.  I'm going to drill a small hole in the flange between the air filter and the carb and fit a tube. The secondary primer will be connected to that.

Edited by Bob Moore
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