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Solex 26FV carburettor problems for a Petter AS 3BHP

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Solex 26FV carburettor problems for a Petter AS 3BHP

Post by Pettercutter on Wed Aug 07 2013, 21:54





I have been having trouble getting fuel into the cylinder of the Petter A1 I am trying to get working and so have taken the carb apart. I found instructions for the carb, a Solex 26FV, online and it has no indication of a gasket in the joint I have marked "Gap" and on this particular one there seems to be a poor fit between the two halves. I made a new gasket for the top half that has a channel going around to connect the auxiliary jet to the venturi chamber by a circuitous route.



I made another gasket backed up with some red 'goop' gasket stuff for the part with the biggest gap and still had no luck getting fuel into the cylinder (it flows well enough into the bowl and the jet chamber). My question is has anyone experience of these carbs and is there an obvious fix I am missing? Should I get the two halves machined down? It seems very strange that there are there are only 2 bolts to hold the two halves together that put all their force onto the end with the float and not onto the crucial end with the venturi. Is this a design fault? The 2 machine screws with nyloks in the picture by the way are my own addition since the original thread in the aluminium casting stripped out and there was not enough 'meat' left to tap in for a larger bolt.

All suggestions gratefully received! cheers James


Last edited by Pettercutter on Thu Aug 08 2013, 15:59; edited 1 time in total (Reason for editing : changed title to AS from A1 and added 3BHP)

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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

Post by Foden on Wed Aug 07 2013, 22:09

A very common problem with the Solex carb! Ideally the two carb faces should be trued up, this can be done by rubbing them across some wet and dry paper on a sheet of plate glass unless you have access to a surface plate.

Pete.

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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

Post by matt86 on Thu Aug 08 2013, 05:48

As pete says a flat surface like a peice of glass. I have done using grinding compound, as at times the paper slips out as your working the carb around on paper.

Just down to what you find best, matt

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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

Post by Pettercutter on Thu Aug 08 2013, 15:57

Thanks for the advice guys. I did as best as I could and got both sides flat on wet and dry on glass. There is still the tiniest hairline crack (not visible with the naked eye) through which the fuel came out of when I tried to start the engine. Presumably since it was built with no gasket it is not expected to be a hermetic seal...

There was no ignition of the fuel at all but fuel did drip out of the carb and the bowl filled up fine. Is it possible to have too much fuel? The plug did not look wet so it seems fuel is not getting up there.

So now I am not sure where to go next. I have set up the timing so that the magneto clicks at TDC (with the keyway on the flywheel at the bottom and there is also a mark on the flywheel). There is a good spark (thanks to Matt aka Nutgone). The plug is a NGK B5HS.

All suggestions gratefully received. cheers James

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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

Post by matt86 on Thu Aug 08 2013, 16:30

Pettercutter wrote:Thanks for the advice guys. I did as best as I could and got both sides flat on wet and dry on glass. There is still the tiniest hairline crack (not visible with the naked eye) through which the fuel came out of when I tried to start the engine. Presumably since it was built with no gasket it is not expected to be a hermetic seal...

There was no ignition of the fuel at all but fuel did drip out of the carb and the bowl filled up fine. Is it possible to have too much fuel? The plug did not look wet so it seems fuel is not getting up there.

So now I am not sure where to go next. I have set up the timing so that the magneto clicks at TDC (with the keyway on the flywheel at the bottom and there is also a mark on the flywheel). There is a good spark (thanks to Matt aka Nutgone). The plug is a NGK B5HS.

All suggestions gratefully received. cheers James
what is the compression like ?
is the valve timing correct ?

yes you can have too much fuel but you have no fuel at plug which says the fuel isnt being sucked in . If you take the carb off and get a squirter bottle like a mr muscle and fill with fuel and squirt in the inlet manifold and crank over a few times . Then check to see if have a wet plug .

matt

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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

Post by Villiers on Thu Aug 08 2013, 18:18

There is a hole in the bottom of the float chamber that goes into the bottom of the jet tapping, is that clear? Also how far out is the mixture screw? Needs to be about 1.5 to 2 turns first off then wind it in/out to suit when running.

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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

Post by Pettercutter on Sat Aug 10 2013, 11:22

Thanks for the replies. There is no mixture screw as far as I can tell on this carb...

Compression seems to be good although I am no mechanic. Just seems to get harder to turn the handle on the compression stroke so assume that means good compression. Is there a more scientific way to guage this?

The hole at the bottom of the float chamber is clear. In fact fuel comes out of the 'mouth' of the carb and spills on the ground when I turn it over with the choke closed. I might try forcing the float down a bit with another washer in the fuel shutoff valve to see if less fuel in the chamber helps matters.


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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

Post by matt86 on Sat Aug 10 2013, 11:31

basic way of checking compression , roll flywheel back to stops ( oposite way to you crank it ) and by hand not with handle grab flywheel and fling it and if you can get the flywheel to bounce back you should be ok .

another way is to remove plug , slick thumb over hole but push thumb on well and when crank over if blows your thumb off you got compression . Laughing 

You going to have a go at the trick with the fuel spray into the inlet ?

matt

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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

Post by Pettercutter on Sat Aug 10 2013, 12:02

Hi Matt, yes I will try the spray trick this afternoon and see how we get on. Ditto the flywheel bounce...thanks

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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

Post by Pettercutter on Mon Aug 12 2013, 16:21

Smile 

I bought a new spark plug today and it worked...feel like a fool for not trying it before but the spark from the old plug seemed fine when I tried it. The old plug was a NGK B5HS and I tried it a NGK B6HS. Started with a single turn of the start handle...

Previously I had tested the compression as you suggested and got a good bounce back but when I tried spraying in petrol directly and got no combustion figured there must be a problem with the old plug in spite of the seemingly good spark.

The engine seems to over rev quite a bit and jumps around a fair bit so probably needs fine tuning but at least she starts. I will try and post a video soon. Thanks to everyone who chipped in with advice. Really appreciate t and biggest thanks again to Matt (Nutgone) for his amazing help on the magneto...the engine has never started so easily since we bought it in the 1970's. Now I just need to get it hooked up to the saw and start cutting wood for the winter.

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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

Post by Pettercutter on Thu Aug 15 2013, 14:12

I spoke to an someone today who has experience with old cars and he said that new sparkplugs differ from the old ones (such as the Lodge C14 recommended for this engine) in their not being glazed ceramic and that that can cause the phenomenom of them having a spark when viewed outside the engine (grounded to the magneto cover)  and then failing to spark when installed in the engine and under compression. Has anyone heard of such a thing as it certainly explains why I was not having any joy with the old plug in spite of a good spark? He also said that finding the old style plugs is getting harder and I was wondering if anyone knew a good source. cheers James

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Re: Solex 26FV carburettor problems for a Petter AS 3BHP

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