Engine trouble - any ideas?

[crofty1984]

OK it's in a boat, but the motor's based on an old Buick lump.
I have a 1984 Sealine 22 with a 3.8ish litre Volvo Penta petrol V6 (AQ175A for them's wot no).
I've seen the engine run fine, but it cuts out after a brief time. Then it just plain old wouldn't start.
It's had new plugs, dizzy cap, condenser and points. It did run, but cut out, the plugs were a bit sooty, leading me to believe the (auto) choke was being left on.

Anyway, further inspection shows no spark any more, so I replaced the coil and now have bright blue sparks!
I cleaned up the plugs and put them back in. Fired up almost instantly - yay! Set it to 1900-2000 rpm fast idle as the book says, she sat there, then gradually struggled and died and wouldn't re-start. It did almost try once or twice. All this took about 30 seconds from first firing to death.

I don't think it's the choke any more, I've actually seen it disengage after a couple of seconds, plus, it wouldn't soot up and die in 30 seconds, surely?

I've taken the plugs out and you can literally tip them upside down and pour fuel out so it's getting fuel. There's definitely a spark there and it's happening at the right time and place, or surely it wouldn't run smoothly when it does run?

I've had it running for a max of 5-6 minutes, and restarted it half a dozen times before it died the first time (pre-my replacing the coil).

Now I think it could be the fuel. It's definitely getting there and there's definitely a spark, so why isn't it burning? I know the tankful's been sat in there for a least a year. Could it be that? It wouldn't surprise me if the previous owner accidentally shoved a gallon of water in there - he didn't seem to be the most methodical of people. Could it be that I'm lucky enough to pull through a slug of good fuel from time to time from the mess in the tank, but normally, I just get ste through?

This weekend's plan is to see if I can get it to run from a jerry can of fresh unleaded.

Any advice would be welcomed.

Thanks,
Dan

[ch427]

are you sure your points gap is correct?

[king arthur]

Water in the fuel tank? Common problem on boats, is there a water trap at the bottom where you can drain it off?

[crofty1984]

ch427 said:

are you sure your points gap is correct?

We gapped it to 0.40mm on the advice of someone that has volvos in his boat, which seemed about right.
Edit: just checked the manual. Says .43mm so that seems OK

Edited by crofty1984 on Monday 17th October 17:06

[750turbo]

Change the Condensor, should be cheap enough.

Also if the fuel is a year old, I would get the tank drained and cleaned.

[Rich1973]

Is it a carb, and if so, is the float ok? sounds like it could be overfuelling

[richardxjr]

If it is carbs, clean them and replace the fuel filter. Unleaded goes off in 2-3 months, you get benzine crystals (I think that's what they're called) forming in the small amounts of fuel left in the carb/s.

Been there done that. To avoid it, come winter turn the fuel tap off and run dry.

ETA must be time for a carb rebuild anyway: strip, clean, fit new internal bits and seals, refit.

Edited by richardxjr on Monday 17th October 17:21

[varsas]

crofty1984 said:

ch427 said:

are you sure your points gap is correct?

We gapped it to 0.40mm on the advice of someone that has volvos in his boat, which seemed about right.
Edit: just checked the manual. Says .43mm so that seems OK

Edited by crofty1984 on Monday 17th October 17:06

Actually it's not the points gap you want to set, it's the dwell angle, how long the points stay closed for over one revolution of the rotar arm. The book points gap should give you a near-enough dwell angle on a new dizzy. Get some wear in the cam of the dizzy (the bit which pushes the points out of contact) and the book figure might be way too big. On my landie the book says 0.36, but I actually have them at 0.15 to get a proper dwell angle, the car runs very badly indeed at the book setting. Measuring the dwell is difficult though, you can buy electronic tacho things which will do it.

If it where a gapping problem I would expect the engine to be difficult to start, and to misfire as it is revved.

When it is running is it firing consistently on all cylinders? If so I would tend to discount an ignition problem for now. I wonder if it's running excessively rich and is flooding the 'plugs? Any way to check the mixture?

ETA If it's very over-rich you could get bore wash (un burnt petrol washes the oil from the cylinders), which will lead to cylinder wear, so it's worth checking just in case...

Edited by varsas on Monday 17th October 17:30

[S1_RS]

Do you still have the originl condensor, if so try swapping it back in. With old school points & distributors I was taught to leave the condensor alone if it worked as it's not uncommon for replacements to be duff.

[ejenner]

Most basic test on an engine which won't run is the compression test. Have you done this yet?

If you're lucky enough to have an engine leak-down test kit then you can do that test as well, getting into the advanced stuff there though.

[Mr2Mike]

varsas said:

Actually it's not the points gap you want to set, it's the dwell angle, how long the points stay closed for over one revolution of the rotar arm.

Which is typically set by adjusting the point gap...

[kev b]

Is the air filter blocked? If not, I would clean out the carb, in fact I would be inclined to clean out the whole fuel system as a precaution as it has been left standing with horrible modern fuel in. If you do get it running then it may let you down due to dirt/water/blocked filter, maybe leading to a long paddle home.

[varsas]

Mr2Mike said:

varsas said:

Actually it's not the points gap you want to set, it's the dwell angle, how long the points stay closed for over one revolution of the rotar arm.

Which is typically set by adjusting the point gap...

Yep, probably should have said that! Closer gap gives higher dwell angle, bigger gap gives less angle.

[crofty1984]

Thanks everyone.
Plan so far is: Direct line from jerrycan of fresh fuel. If that fails, I'll get a-rebuilding the carb (I was going to do it over winter anyway) with said jerrycan.
If that works then I'll connect the tank up and if it fails again I know it's the stuff in the tank that's bad.

Who know's anything about Rochester carbs?