Calling SOLEX-perts.

[GrowingLad]

Hi Guys,

I've got something strange going on with my engine. Volvo AQ115 (Petrol)

If I start her up from cold and leave her ticking over everything seems to be just fine...If I've been running for a while and then come back down to tickover...i.e. coming into a marina or getting ready to load her back on the trailer the engine will cut out and I notice last time it backfired once/twice. To start back up I have to turn it over for about 10 to 15 seconds and give it a bit of gas to get it going. Normally unless I haven't started it up for a few weeks it tends to start pretty quickly. If I keep the revs at around 1500 it doesn't cut out but if I bring it down to tick over it will cut out pretty quickly.

I need to double check the tickover as I'm not 100% sure the rev counter is exact but normally tickover is around 900-1000 mark. Basically I have it to the point that when I engage forward or reverse the engine has enough revs not to die....as I mentioned, from cold everything seems fine...it's when the engine has been running at higher revs for a while and then comes down to tickover it dies.

I stripped the carb down last summer and gave it a good clean out, put it back together using a new service kit.

I need to check the timing (It's got an electronic distributor) Spark plug gaps and valve gaps but have the carb at home to double check.

Now, I know what a carb does but I won't pretend that I know what exactly each part does.

I understand that the float stops any more fuel being pumped into the bowl when not needed and the accelerator pump gives it an extra bit of fuel.
I'm having a read through the manual to see what each mixture screw extra does but I've noticed some holes in the main body of the carb but it seems as though I'm "missing" a hole in the gasket. I put a thin screw driver inside the tubes and noticed that there was some **** down inside.

So, my first question (of many) is what do these holes/tubes do?

As you can see the hole that was circled is now covered by the gasket.

 

[Thistle]

Could be a number of things. Have a look here for some ideas.

 

[2Tizwoz]

This link is to the Volvo site owners handbook

Carburettors can wear around the spindle on the butterfly valve and the resulting air leak can weaken the mixture so that idling becomes a problem.

The adjustments for idling and timing are in the manual and will need checking before you start playing with the carburettor adjustment.

 

[elton]

The symptoms remind me of a problem I had with a Solex carb on a car. Everyone was baffled. I eventually traced the problem to air being drawn in around the throttle flap pivot spindle thing. I replaced the nylon bushed and bingo! I traced it by spraying WD40 at various places on and around the carb until I detected a change in the sound of the engine

 

[elton]

Carburettors can wear around the spindle on the butterfly valve and the resulting air leak can weaken the mixture so that idling becomes a problem.

Blimey! I reckon you and I are the only people in Britain who know this.

 

[Thistle]

M'luds, you'll note that the leaking spindle bushes and the WD40 detection method referred to in the link I gave above. Common problem with old Solex carbs but not the first thing you'd think about if you're not familiar with them.

(Though I'd guess that there will be a fair number on here who had vdubs in their youth ... or still have them in their second youth!)

 

[GrowingLad]

I think you chaps might be on to something!

Hi Guys,

That's what I love about this forum...the amount of knowledge that is available and so willingly given is amazing.Thank you!

So, I've had an investigation:

Now, I've crudely taken a look at the butterfly, there is a tiny bit of play and if I remove the nut and washer and blow air is leaking very slightly through the spindle (I will confirm this with the WD40 method when it's back on the engine).

Annnnddd It's a lot worse when the butterfly is in the tick over position NOT when it's opened up a bit.

Now...I got to thinking, it seems fine whilst the engine is started from cold and it appears to happen once the engine has been running for a while. Could it be that the heat from the engine and the difference between the metals of the carb base and the spindle mean that due to expansion the gaps gets worse?? Or is that a bit pie in the sky?

So, there aren't any bushes to replace..what now...is there something I can do to improve matters or do I need to search out a new carb base and butterfly?

Thanks again, when I read your replies this morning I felt better that my pain had been suffered by others

Cheers,
Simon.

 

[oldharry]

Whoa! You say you put a screwdriver down some of the holes and find C***? Then thats your problem, it needs a thorough clean out. There are aerosol sprays to do this, which need to be squirted through all the various tubes and openings. Otherwise take it to a local Motorcycle workshop where they will do the job properly, soaking it overnight and then cleaning with a high pressure airline. Do this BEFORE you start buying new parts, then see if you have a problem still.

If it was running OK last season, then it is unlikely that wear has caused such a major problem in so short a space of time. Spitting and refusing to tick over when warm suggests a weak mixture - what are the plugs like after a run? They should have an even biscuit brown colour on the centre electrode. If they are dry but blackened with soot, the mixture is too rich. Black and wet, oil is getting past the rings. Dry but uneven burnt appearance the you have weak mixture.

Weak mixture can be throttle wear, but that builds up slowly. It can also be caused by air leaks in the manifold, between the carb flange and manifold, or incorrectly seating gasket on the carb. Far more likely a blockage in the carburettor, or possibly a sticky float valve. Could also be a blockage in the fuel feed, or faulty fuel pump not delivering fuel. Check the float valve cone. If there is a 'step' where it meets the valve body it will stick causing fuel starvation, and needs replacing.

Check that the carburettor flange is exactly flat. If it has been dropped or bumped it can be out of true causing major air leaks in the manifold. It can easily be flattened again by grinding it back with wet 'n dry paper wetted with oil on a true flat surface. I have saved
more than one obsolete carb this way.

 

[GrowingLad]

Hi Harry.
I did strip everything down and soak in carb cleaner..what could come off has been taken off, service parts have been replaced and everything looked to be okay...I'm not actually sure what these holes (circled in red) do, any ideas? Everything else looks to be clean and good.

From tick over at cold the engine runs smootly, when opened up the revs build responsively, when reved everything is smooth..only problem I have is tickover once the engine has been running for a while.

I'm going to fit the carb again and give the inlet manifold and various parts of the carb a spray with WD40 to see if I notice a change in engine sound.

Yep, next job when I'm down at the boat is to double check valve clearence, plugs and timing.

Problem was the boat was in parts until two years ago and everything only got put back together last year..I don't have any prior experience of how things run before now.

Thanks,

Simon.

 

[macnorton]

It could be the lift pump? check the fuel supply pressure hot vs cold.

 

[Trundlebug]

From the symptoms you descibe, your problem sounds most likely either a weak idle mixture and / or timing slightly too advanced. I know you're about to check the timing, but the fact that it starts and runs OK from cold would indicate it's probably not that.

Therefore I can only think that the idle mixture is too weak. If you try greasing the throttle spindle with normal LM grease it will serve two purposes, it will seal any minor leaks and also prevent further wear.

I'm not familiar with Solex carbs I'm afraid, but the holes you ringed in your photo look like jet tubes or air bleed tubes to me. I don't know how much adjustment you can make to the idle mixture but if poss you need to richen it a bit. If no adjustment is possible, check if the extra hole that was blanked off and is now open is allowing excess air in at idle speeds? That may be the cause of your problem - you may need to blank it off again? Also, always best to blow out all the tubes with an airline after cleaning, just to make sure nothing is blocked. It could be a blocked idle jet not allowing enough fuel through at idle speeds.

Note: if you richen the idle mixture too much, the engine will "hunt" and go thrum thrum thrum rather than hold an even purr.

Hope this helps a bit - sorry I don't know Solex's more intimately.