Dry sparkplugs

Moto Rumi technical problems or solutions
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martinasa
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Dry sparkplugs

Post by martinasa » Fri May 15, 2020 4:59 pm

Hi!

Just tried to start up my Scoiattolo for the first time today. The sparkplugs are dry and it seems no fuel reaches the cylinders. After some test to start it running fuel is dripping from the airfilter. The petroltap is working and I've tripple-checked the jets... Know the engine's supposed to have new pistons and cylinders and In the vespa world you could put the pistons on the wrong way and no fumes would enter the cylinder. Anything else you can recommend me to try?

BR

Martin

hugomez
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Re: Dry sparkplugs

Post by hugomez » Fri May 15, 2020 5:25 pm

Hi Martin,

I am not an expert but I would check that the float bowl is not stuck, or maybe one of the two jet is block. (Main jet or idle jet)

Greets,
Hugo
My little Formichino here: http://www.formichino.com/pictures1.html

Elie
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Re: Dry sparkplugs

Post by Elie » Fri May 15, 2020 10:19 pm

I think the two halves of the crankcase are leaking towards each other so that the pressure from one to the other goes at the wrong time relative to the position of the piston of the other

martinasa
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Re: Dry sparkplugs

Post by martinasa » Fri May 15, 2020 10:39 pm

@elie
Elie wrote:
Fri May 15, 2020 10:19 pm
I think the two halves of the crankcase are leaking towards each other so that the pressure from one to the other goes at the wrong time relative to the position of the piston of the other
Thanks for your answers...

Shouldn't it be leaking oil aswell then? Theres no oil-leak?

Hugo, what about the pistons?

Martin

Elie
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Re: Dry sparkplugs

Post by Elie » Fri May 15, 2020 11:11 pm

no no oil leak because it is a dry crankcase that only contains petrol oil mixture

martinasa
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Re: Dry sparkplugs

Post by martinasa » Fri May 15, 2020 11:19 pm

Elie wrote:
Fri May 15, 2020 11:11 pm
no no oil leak because it is a dry crankcase that only contains petrol oil mixture
No, got 1.1 l oil in the motor, if theres a leakage between the halfes should it be leaking oil aswell. Do You think the leak is in the oil seal on crankcase side. Whats the remedy in case you are right? Split it again?

Br

Martin

Lars
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Re: Dry sparkplugs

Post by Lars » Sat May 16, 2020 7:12 am

Hej Martin,

I don't think the pistons are turned the wrong way. That mistake is almost impossible to do. The Rumi pistons have a tall ridge on top, which fits into a cavity in the cylinder head. Turned the wrong way, the pistons would hit, and the engine would not even turn over.

I tend to agree with Elie that the most likely reason - if it is not pumping air as it should - is that the crankcase is leaky. Very common with Rumi engines. The oil you have in the engine is in the gearbox section. That may very well be tight (for oil), even though the crankcase section is leaking air/vacuum. To fix, yes, the engine will have to be opened again.

But before you resort to that, I would make some more attempts to get it started. For me, what usually works is to tickle the carb several times until fuel is almost seeping out of the exhaust, and then kick the starter forcefully with wide open throttle. Even a slightly leaky engine will usually try to start then. If you have spark, of course.

Best,
Lars

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Re: Dry sparkplugs

Post by hugomez » Sat May 16, 2020 12:58 pm

Hi,

But if the spark plugs are dry, doesn't mean that the fuel do not reach the cylinders?, otherwise they would get wet after failing the attempt to start the engine.
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Lars
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Re: Dry sparkplugs

Post by Lars » Sat May 16, 2020 1:26 pm

hugomez wrote:
Sat May 16, 2020 12:58 pm
Hi,

But if the spark plugs are dry, doesn't mean that the fuel do not reach the cylinders?, otherwise they would get wet after failing the attempt to start the engine.
Hi Hugo,
Yes,of course. But what I meant was that Martin should try some more to get the fuel into the cylinders. Flooding the carburetor a bit is one sure way to do it. Then see how the engine behaves.

It is very rare to see an engine that does not pump air at all. That usually means it has no crankcase compression at all. The crankcase is wide open. Hard to believe that Martin's engine woud be that bad. That is why I suggested for him to try some more.

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Re: Dry sparkplugs

Post by hugomez » Sat May 16, 2020 1:38 pm

Hi Lars,

Certainly is a good advise before try to start the engine to tickle the carb several times to be sure that fuel is achieving the cylinders, I also do it every time. If that solve the problem there was not a problem at all. Hopefully that is the solution.
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martinasa
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Re: Dry sparkplugs

Post by martinasa » Sat May 16, 2020 3:22 pm

Hi!

Thanks for all your replys! Went down to the garage and tried some more, think I had some ignitions before the battery ran out =) Really holding my thumbs that it will start eventually. It has been standing for at least 7-8 years so maybe it just need to run in for a while.

Got nice sparks but pretty shitty budget sparkplugs. The one I have is with a resistor, does that matter, and as I read in another post Lasse recommended BP6/7ES - that still stands?

BR

Martin
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martinasa
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Re: Dry sparkplugs

Post by martinasa » Sat May 16, 2020 3:25 pm

And, yes, will fix the seat and the lightinghouse as soon I can afford =)
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hugomez
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Re: Dry sparkplugs

Post by hugomez » Sat May 16, 2020 3:44 pm

Nice looking Scoiattolo Martin.

The NGK B7ES is perfect for that scooter and pretty easy to find.

Hopefully you will get it running soon.
My little Formichino here: http://www.formichino.com/pictures1.html

martinasa
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Re: Dry sparkplugs

Post by martinasa » Tue May 19, 2020 1:45 pm

Hey Hugo,

Remebering from another forum post that You said the UA15s carb was a bit tricky and strange and changed to a UA16S solved your issues, could that be the case here aswell?


BR

Martin

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Re: Dry sparkplugs

Post by hugomez » Tue May 19, 2020 5:57 pm

Hi Martin,

I don't recall saying that, but who knows, maybe if I see the conversation I can understand why I say that. Non of my Rumi mount a UA16s, never own one of those carburetors.

My Formichino and my Scoiattolo use the UA15s and no problem at all with them.

Maybe a good ultrasonic cleaning would be nice, if not just a proper cleaning of all components, and be sure that the jets are not block after so many years with the scooter in storage.

Just my suggestion.
My little Formichino here: http://www.formichino.com/pictures1.html

arthur lewthwaite
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Re: Dry sparkplugs

Post by arthur lewthwaite » Tue May 19, 2020 7:30 pm

Hello, when i worked on rumis years ago dry plugs and non starting was quite often seen, the reason was quite often the centre crankshaft seals allowing crank pressure/fuel to be pushed from one side to the other, new seals normally cure problem. This job entails spiting the crank in half. As long as crank was not worn /seal groove worn on shaft things were fine.

martinasa
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Re: Dry sparkplugs

Post by martinasa » Tue May 19, 2020 8:24 pm

Hi!

I read in the aforementioned post that u pressure tested your engine? Guess i can try that as well?

BR

Martin

Lars
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Re: Dry sparkplugs

Post by Lars » Wed May 20, 2020 7:47 am

Some of us do. I certainly do.
A pressure test is the first thing I would do if I saw the symptoms you describe. If the leak is bad enough, you don't even need a pump and a gauge. You just blow into the engine (with intake and exhaust blocked off), and you will hear and feel the air whistling out of the crankcase. If it feels tight though, you would need to pressurize to test more accurately. I use 6 psi.

Ren
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Re: Dry sparkplugs

Post by Ren » Mon Jun 22, 2020 9:18 am

Hi Lars,
When you pressure test, you block the inlets and exhaust, right?. Where do you apply the pressure?, The oil filler plug?
Regards,
Ren

Lars
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Re: Dry sparkplugs

Post by Lars » Tue Jun 23, 2020 7:27 am

Hi Ren,
No, in the spark plug hole. The flexible hose in the kit has a spark plug thread in one end, and connection the the manometer in the other. Keep the piston at the bottom when you test, so that the transfer ports are open.
Best,
Lars

Lars
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Re: Dry sparkplugs

Post by Lars » Tue Jun 23, 2020 7:51 am

Hi again Ren,
I should just add that the flexible hose I mentioned is taken from a standard compression test kit. The type of compression tester with different hoses for different spark plug threads. I then made up the connection from that hose connector to the pressure/vacuum tester.
Other users have made up a connector from an old spark plug, but I thought this was an easier way.

Here is a picture of the setup I am using.
Rumi Junior motor pressure test.JPG
Rumi Junior motor pressure test.JPG (96.18 KiB) Viewed 2203 times

martinasa
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Re: Dry sparkplugs

Post by martinasa » Mon Jun 29, 2020 9:22 am

Hi!

Thanks again Lars for lending me the stuff and sorry for not taking my time to test it before You needed the stuff back. When You are done with it I happily lend it again.

BR

Martin

Lars
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Re: Dry sparkplugs

Post by Lars » Mon Jun 29, 2020 2:51 pm

No problem, Martin. Any time. / Lars

UHJ200
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Re: Dry sparkplugs

Post by UHJ200 » Wed Jul 01, 2020 9:04 pm

The aluminium rings that the oil seals are fitted into sit in grooves in the crankcase, there are tiny little pins that hide in the bottom of those grooves in the lower half of the crankcase, that is what the notches in the rings are for, to locate the rings and prevent them turning.

The aluminium is soft and it is all too easy to get a seal carrier misplaced. What is worse is that you can still bolt the halves together and all might seem well but the pins will punch into the rings and deform it which in turn may well prevent the crankcase halves mating properly. Check carefully!

arthur lewthwaite
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Re: Dry sparkplugs

Post by arthur lewthwaite » Wed Jul 01, 2020 10:10 pm

Hello, all the aluminium housings in the centre of the crank are made to fit in the groove to hold the crank central to the crank cases. I have a crank that came out of the cases Hugo acquired from me that were Pat Guagenti (hope i spelt that right) that had a modification to the alloy housings. He machined the part of that held the seals and used 42 od seals on there own to locate between crankcase housings, so seal was held by crankcases not in seal housings. Obviously you had to make sure the oil seals were sitting back against modified sea housing when fitting crankshaft,

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