Engine help needed (Petrol)

[FullCircle]

We have a little Volvo MB2-A saildrive petrol twin that has been rebuilt. Its a sort of a hybrid Honda outboard 6hp actually, with a Volvo name on it.
The issue is that it will start sweetly and run, then after 5 minutes it mysteriously stops, and refuses to start again.
I have:
Tried choke in/out, throttle off/half/full on.
Plugs out and pull engine over to clear flooding
Renewed the plugs (again)
Gapped them
Checked for fuel - wet plugs! - New fuel last week
Tried a direct connection from tank (outboard 3 gallon with bulb)-no joy
Checked carb connections - choke is off, throttle is on idle stop, air intake is clear
Put plug on head to check spark - yep its there
Naughty bit - sprayed a whiff of Bradex in intake - still no start.

This is a CDI engine with a single coil, and the pickups are off the end of the camshaft.

Is it possible there is something that could be breaking down in the electrics after 5 minutes, not to return to normal after an hour?
Anything that a bank of lowish batteries could do in reverse to suck power from coils to spark?

Thoughts and musings would be very welcome. I have the hump with it all today as it has not been a happy year for engines.
Lynn says she doesnt mind me having the hump, but it wont last I am sure.....


Jim



<hr width=100% size=1>Our engine will never wear out - it only runs for 5 mins before packing it on again.

 

[silverseal]

For what it is worth I once had the same problem with a Ford Cortina... the garage not being able to find a fault when taken into them .. typical. The fault was a break in the winding of the coil. When cold the coil would work and as it got hot the winding gave way - no spark - no car. Worth a check to see if it is the coil

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[FullCircle]

Thanks Silverseal,
I have a spare coil in the back of the shed....
more more more....

At least Lynn is learning to sail on and off the mooring... a very natty finish downwind uptide with a 90 degree twist to knock off speed today. She looked delighted with the first time pickup.

<hr width=100% size=1>Our engine will never wear out - it only runs for 5 mins before packing it on again.

 

[Althorne]

Before changing the coil verify whether you have a spark once it stops and how strong it is, could save a lot of unrequired work. If it still sparks check out the float chamber in the carb' and make sure it's set properly or not holed and stuck on the bottom allowing continuos fuel to flow. If not come back and we'll try again.

<hr width=100% size=1>http://colvicownersclub.mysite.wanadoo-members.co.uk

 

[nickjaxe]

I had the same prob with a 5hp penta it was the coil breaking down when hot left it for 30mins ran fine till hot again and so on.

Nick.

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[FullCircle]

Re Althorne:
Thanks,
we do have a spark, difficult to see how strong.
The carb doesnt have a float, but is valved in some way. When I put the new plugs in, they werent very wet.
Besides, it runs perfectly (no fuel shutoff valve, so continuous supply) for 5-6 mins before cutting out.

Thansk for help, keep it coming....


Jim

<hr width=100% size=1>Our engine will never wear out - it only runs for 5 mins before packing it in again.

 

[Freebee]

is the petrol tank vent open and clear?

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[muchy_]

I once had this on old Capri. Turned out to be the condenser if I remember rightly. Also, it used to start ok and I'd run it round the corner to petrol station to put some petrol in and then it wouldn't start again for a while. My old Dad suggested putting some wooden clothes pegs on the fuel line in the engine bay. Put them on and it never did it again. Got to be wood though apparently.

<hr width=100% size=1>Is it the weekend yet?

 

[Colin_S]

As Mike suggests, check the fuel tank is properely vented. Easy test is to crack open the cap next time it cuts out. If you hear a rush of air in then you found your problem. You could also try runnig with the cap off to see if the problem still exists.
Is there an inline filter on the fuel? If so, that may be partly blocked.
Assuming you do it safely and are happy to give it a try, I would put a few drops of fuel down the carb to see if it starts. That will tell you if it's a fuel delivery issue.
Check the condition of the spark when it's cold so you have a benchmark for when it stops 5 mins later to check it again.
Also you could try unscrewing the plug caps from the leads and snipping off 1/4" as they sometimes corrode internally and start breaking down.
Has this problem existed since the rebuild or subsequently appeared?

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[supermalc]

As the plugs are wet, it sound as if it is the spark cutting out. With a rebuilt engine, it will have a higher compression. This requires a greater current to generate a spark. If there is a break in the coil, condenser etc. this could be the cause of the problem. It will appear to have a spark when the plug is taken out.

When changing components in fault finding, try to do one thing at a time....e g change the coil. If the problem still exists re-fit the old one before trying something else. Is it possible to borrow a coil to try, maybe better than trying to get your money back.

<hr width=100% size=1>Malcolm.
<A target="_blank" HREF=http://geocities.com/malcsworld/>http://geocities.com/malcsworld/</A>
Take a look at my boating pages.

 

[William_H]

As intimated spark plug leads can give trouble. If you have a multimeter you should be able to measure 10000 to 100000 ohms from the plug connector to the coil. or plug connector to ground through the coil. Otherwise it looks like a changing components job although I would try a new plug first if you havn't already done so. regards will

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[oldharry]

Could be any of the above. Or if you have a water cooled rubber exhaust pipe, check the state of the interior liner. These perish with age or overheating, and the liner goes all wrinkly, a piece breaks off and effectively shuts off the exhaust pipe, stopping the engine almost instantly.

The interior of the pipe should be smooth.



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[FullCircle]

Thanks to all, but dont stop sending
I have tried the fuel with the cap off the tank let alone just checking the vent.
The exhaust is loud and clear and pumping water sweetly (when running).
I have found all the values for coils, CDI etc and will apply those.
Will also replace bits one at at time

Jim
Who has spoken with the dealer who rebuilt the engine.....
Still with marginal hump like qualities.

<hr width=100% size=1>Our engine will never wear out - it only runs for 5 mins before packing it in again.

 

[copterdoctor]

Does this type of engine have an overheat cut out? If so look at cooling system or replacing the sensor.
This may explain why the engine starts again later.

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[chippie]

Is this a fourstroke? Valve clearances can tighten up when the engine is hot , reducing compression.
Check the washer in the fuel line connection to make sure it is not sucking air,however:
If the plugs are wet it must be electrical.

Is the spark strong and white when you check it after a stoppage?--Plug leads and caps are a possibility.

Keep us informed.




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[misterg]

No an expert, but these spring to mind:

How does the engine die?

Does it suddenly cut off? like you turned off the key?
-->Suggests electrical problems
Does it start miss-firing, or drop onto one cylinder?
-->Suggests electrical problems - possibly on the HT or plugs, or low battery voltage
Does it run intermittently? (like stricken WW2 fighter planes in the films)
-->Again, electrical ?
Does it just "bog down" and stumble to a halt ?
--> Almost certainly excess fuel or "breathing" related (ruling out partial siezure, because engine cranks OK)
Do the revs pick up just before it dies?
--> Fuel starvation
Does it "try" to respond to throttle movements as it dies?

More ideas...
You say choke is off - is it possible to verify this?
Air filter clean & un-obstructed?
Exhaust clear ?(as mentioned by others)
Presumably this has a diaphragm carb - is the diaphragm intact? Is the needle & seat completely clean? If a float chamber carb, check for dirt on needle seat, or groove worn on float needle.
Carb jets tight ? (CARE!)
Carb adjustment ? - shouldn't have moved by itself!
Got a fuel cut-off solenoid?
Fuel pump? - possibly a vapour lock, but pipe routing, etc. would have to be v. bad.

Having said all that, I stripped the carb of our Honda O/B the other week, and the problem turned out to be sealife up the exhaust....

HTH

Andy

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