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Decompression valve fitted, now doesn't start!


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So do you think by closing the internal decompression port and using the decompression valve instead I could get a few more horsepower eh? Now that does sound worthwhile...

Slightly off Tom's topic but in some ways relevant.  You may recall I acquired a Solo 210 a few weeks back. It had been in someones garage for 20 years and was minus coil. Long story cut short but I found a Stihl chainsaw coil that just about fitted , serviced the carb with kit and after some re wiring and other stuff, pipe work, fuel filter etc.  It starts and runs beautifully when cold.  Pick up from tickover to full revs is smooth and it sounds great.  Stop it and restart it a couple of mins later (it's electric start) and it starts without problem.

BUT ....  leave it 15 mins and you can spin it over forever and not get a cough. Prime it carefully to avoid flooding, nothing, prime it a bit more, nothing. Put a bit of fuel into the pot via the plug hole. Maybe, it fires, maybe not. If it fires it runs beautifully again.  I have tuned and retuned the carb numerous times. Run it for an hour, no problems. Plug is a nice colour.  But I want to know why it won't start after say 15 or 20 mins.

I checked the mag air gap again yesterday as sometimes the spark looks very weak after it won't start.  (Fouled plug?)  Bear in mind I had to botch the casing to fit this magneto. reduced the gap a bit more. (A thin business card gap.)  Ran it again today and it ran beautifully when first started, but 15 mins later, awful to start again.

There's plenty of compression and it's believed that this motor was barely used when it was bought 20 years ago.

I'm going to refit the carb again tomorrow and put a bit of gasket goo on gaskets to make double sure no air is finding it's way in though I'm pretty sure that can't be the case.

I'm wondering ...

 

1. Could it be something to do with the decompressor (hence posting this here)  I'd like to remove it and blank the hole, but my first careful attempt at unscrewing it didn't want to budge it. I assume it just screws into the head? Removing it would eliminate that as a source of trouble. Is there any way to test it?

2.  Horrible thought. It has been suggested to me that it might be the crankshaft seals. OK when cold and when running, but left for 20 mins and they go soft?  Doesn't make sense to me as it runs so nicely when first started. I've seen it suggested on a forum that to test the seals one should pour 2 stroke mix straight into the engine and see if it leaks. There must be an easier way.

3. But also, quite often after standing for a while the plug spark looks weak or non-existent (which would explain why it's reluctant to even cough with a drop of fuel in the pot.)  Could it be it doesn't like my mix? 50 - 1, or doesn't like the 2T I'm using. That seems more logical as when cold it's OK,  but after running and standing the residue of oil on the plug stops it firing? 

I've read up on pop off pressures for the carb and measured the gap between the body and canitlever, looks fine and there are no symptoms of poor running which would indicate starvation or too much fuel anyway.

Sorry this has turned into an essay but I just wanted to show I have explored LOADS of solutions!

Any suggestions welcome please. Everytime I retune the carb and fiddle with this I think I've cracked the problem and then the next day it's starts great. Run 15 - 20 mins. Rev it up, leave it sitting at tickover etc. lovely. Then I wait a while and I'm back to square one.

Has anyone ever replace the crankcase seals in one of these motors? And can you still find them anyway?  I couldn't get hold of the original mag coil after weeks of searching.

A complete strip down would give a job for the summer. I got the motor for free but have spent £150 so far!  Thought about a new carb, £60?  But I don't believe that it's where the problem lies.

cheers Bob

(Interesting to see you're still having fun with the one you acquired Tom ;) (

 

Edited by Bob Moore
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Yep, that's paramotors! Or at least that's old paramotors anyway! Can't help with this one i'm afraid, but do persevere - flying them is great fun! I've just found a new place to fly from here and have got permission and the weather's looking good for Wednesday and the motor is fully up and running...

Edited by tomarnold
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4 hours ago, tomarnold said:

Yep, that's paramotors! Or at least that's old paramotors anyway! Can't help with this one i'm afraid, but do persevere - flying them is great fun! I've just found a new place to fly from here and have got permission and the weather's looking good for Wednesday and the motor is fully up and running...

Good news, not giving up yet and I also have a couple of mates not too far away with fields. Haven't flown it yet though. As I say first off it runs really well, it's just the restart that bugs me!  Sometime soon I will get off the ground with it! I could do so now really I just want it to be right!

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2.  Horrible thought. It has been suggested to me that it might be the crankshaft seals. OK when cold and when running, but left for 20 mins and they go soft?  Doesn't make sense to me as it runs so nicely when first started. I've seen it suggested on a forum that to test the seals one should pour 2 stroke mix straight into the engine and see if it leaks. There must be an easier way.

 

Best way to test for crankcase leaks is remove carburetor and exhaust, make up blanking plates for holes then make an airline inlet easiest with an old plug, you need to pressurize them and brush over seals and mating surfaces with soapy water, and then you'll know if any leaks virtually immediately, and like previously said thats paramotors.

Just curious have you done compression check ?, or pulled motor down and done measurement checks ? on piston + rings ? and condition of barrel ?

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No doesn't drain back.  I fitted new pipes and filter plus new priming bulb so non return valve is good.  And I prime it carefully  till fuel runs out of the carb, then give it a go.

I read somewhere about testing crankcase seals by pressurising the crankcase, anybody know how to do this please?  It's one of the  things I haven't been able to check. I'm wondering if the seals soften when really hot and start allow pressure leakage?

Or I'm thinking a problem with the automatic decompressor just staying open or leaking and not enough compression in the cylinder. If I could unscrew it I'd fit a manual one like Tom. At least you have the choice of not opening it if you decide.

Edited by Bob Moore
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Thanks for that Kiwi K.  I figured last night that rigging a pump and gauge to the vacuum pipe might work, good to see that's what the tester used. I've got a foot pump with a gauge too. I've been reading up on methods and obviously testing is easier if the whole unit has been removed and stripped down but I don't want to go that far yet. I'll have a go at rigging something tomorrow but with the motor as is.    A hot/warm test would be the best really but any sign of a leak would be useful of course. 

 

Lots of other useful examples of tests linked on that YouTube video too. Thanks.

Edited by Bob Moore
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Bob in my experience i'd be surprised if it turns out to be pressure leak, sounds more like an electrical breakdown when warm. 

I know you did a cold compression check, but have you done it after warm when it won't restart ?

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Hi Kiwi K , haven't actually done a compression test yet. Hope to rig something today.

As far as electrics go hard to imagine it could breakdown as it's so simple. Just a magneto coil, HT lead and plug. No points etc.  Mix issue and fouling the plug I could imagine though.  

Anyhow, I'll try and do a crankcase test today. It has been suggested to me that a motor that has sat around for 25 years might well have poor seals anyway. We will; see. Fault finding is a process of elimination!

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Right.  I made a compression tester for the crankcase and tested yesterday. Positive pressure 10lbs a square inch held the pressure well.  Pressure testing involves taking off carb and exhaust and blanking off the ports and when I reassembled I used some blue Hylomar on the gaskets for a really good leak free seal.  Pressure tested the carb for blow off point which appeared to be OK, about 10 -12 lbs per square inch,  so I reassembled that.

Started it  this morning and it ran. That was a good thing!  And ran well. Tickover a bit faster now so dropped it down a bit , bit of carb tuning again, high end,  and it runs well. Stopped and restarted it ok after a couple of minutes.  I left it off for 20 mins as this was the problem I'd had, it had not wanted to restart after a longer period, even after priming.  This mornings test -  quick prime and it started and ran well. Maybe I have solved the problem just by making sure carb and exhaust were properly seated?  Who knows. Time will tell!

Thanks for all the input guys.

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Thanks Tom!  I didn't want to fly it till I was 100% sure it was OK. I'm now 99% and as long as my first test location has suitable close bomb outs I'll be happy. I'd still rather a machine with a clutch,  having spent a couple of hours last week with a mate (many many years a pg pilot) making his first few flights.  I reckon I'll be ok on the right day where I can reverse launch and keep the wing up.  And I haven't got a spare £2 or £3k to spend on another machine anyway!

I don't much like the design of the hand throttle and might modify it.  The kill switch is not easy to reach when holding the throttle with a gloved hand, especially my chunky heated gloves, and advice I've had is always be ready to kill the motor if you are needing to abort a take off.

One good thing about tinkering is you really get to know your motor.  I've read that a CHT is a useful bit of kit.  I guess I could use a mate's laser thermometer gadget to see how hot it runs,  though in the air I imagine cooling will be better than in my static tests as there would be better air flow around the motor.

Have you sorted your garage find now?

Edited by Bob Moore
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I flew it for the first time a couple of weeks ago, but when i landed to check the plug (to see if it was running rich/lean) the starter mechanism broke! I have ordered new parts but they haven't arrived yet, so i have fixed it as best i can so it starts. Going for a flight this evening. Will post a video if i can...

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  • 1 month later...

Hi Tom, bit of an update.  I now have a working and apparently reliable motor bought a couple of weeks ago.  This is an Adventure F3. It was minus starter motor but the motor from the old paramotor fitted so it's sorted.  I also took out a blanking bolt and fitted the vacuum driven decompressor from my original motor (the previous owner had burned out the starter motor) and it's starts easily and restarts.

BUT  I also acquired for free a more recent Solo 210 engine, electronic CDI ignition and believed to be OK., so to cut to the chase, I transplanted that into my original machine (which in many ways I preferred to the new one, smaller as it has a 4 blade prop and is lighter) but I want/need to fit a decompressor to that.  Way too hard to pull start without.  All the decompressor valves I've seen online appear to be 10 mm thread and the hole in the cylinder head is 8 mm.  What size thread is the one you fitted?  Did you find one with a smaller thread?  I could drill and tap the head to suit 10mm but if I mess it up it could be expensive, though on the bright size I actually have a spare big style later head too.  Also have a tuned exhaust but there's no space to fit it on either machine, and it adds weight. I'm only 69 kgs. Don't think I need the extra power.

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I took the head to a local lawnmower repair shop and they drilled and fitted the decompressor for me. But the easier option is to have a look inside to see if the inbuilt decompressor hole is blocked. All you have to do is use a 4mm drill bit to drill out the carbon and then it should be much easier to start. 

The big head and tuned exhaust are well worth having if you can fit them. I am 70kg so I get off the ground just fine with the standard solo 210, but it is nice to have the extra power when you launch in nil wind, plus having the ability to climb quickly is great partly just because it's fun but also for safety (if you find yourself stuck in sinky air or heading towards trees or something like that. My motor with the tuned exhaust is much more pleasant to fly plus the fact that it makes a much gentler noise. 

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Thanks Tom that's very helpful.  Was the valve they fitted similar to this? http://www.ebay.com/itm/DECOMPRESSION-VALVE-Fits-STIHL-HUSQVARNA-PARTNER-MAKITA-WACKER-DOLMAR-/140606126505  The other machine has a vacuum operated one now which is great.

 

I don't quite figure how the built in decompression works (if there is one)  I haven't seen any corresponding hole in the cylinder head?  I've seen pics, small hole in the side of the barrel and a hole in the top I think.

 

 

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I just took another look at my motors.  Two have the heads predrilled to take the original mushroom type automatic vacuum operated decompressor.   One is in use on the Adventure F3 that is up and running well.   My original motor (the 20 year old unsued one that I couldn't get to restart and  gave up on after spending £200 on it!)   had the hole in the side of the cylinder but blocked with a small allen screw which I guess means not used. The big head from the one that I was given with a tuned exhaust doesn't have a corresponding hole it to sit opposite the hole in the cylinder either.

 

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You have to take out the little allen screw first, then run the drill through the hole behind it to make sure it is clear. Then put the allen screw back in. Weird, but it works. Refer to this: http://www.geocities.ws/peaksclimbing/walldecr.htm

The other option is to fit the decompression valve, and yes, mine looks very much like the one you posted a picture of. It was for a Husqvarna 3120XP.

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