Seagull 40 plus starts fine, runs until warm then fails

[Revoli]

Hi

Problem: Seagull plus 40 engine starts every time when cold, runs for a while then once hot starts to slow and at best chugs along finally stalling.

My faithful old seagull has suddenly developed a fault which I am struggling with. This was working fine after a rebuild in the winter, plenty of grunt, no problems until last weekend power just dropped off and now she is just spluttering along. Fortunately I was just returning into Marina when this happened. Ignition is villiers mkII type. Checked points (.20). Checked and replaced spark plug (.35) Champion D16. Checked fuel. 25:1 same as usual, fresh batch a month or so ago. I wondered about the HT lead as this was not replaced but cannot see how the symptoms described would fit with faulty HT lead. Any thoughts on this? All gaskets were replaced with genuine Seagull gaskets from John at SOS and seated with appropriate sealant during rebuild. Block was stripped, degunked and was found to be sound. Points cleaned and checked. She runs fine for a while suggesting spark is good, at least initially. Something happens once the engine becomes warm with engine revs going from very good to chugging along once warm. I have tried shutting the fuel off to simulate a leaner mixture but this made no difference.

I am running in a tank with water at correct height (as always do without problems). Engine has not been submerged, cooling water runs fine, completely cleaned out in rebuild). Carburettor cleaned and reassembled but made no difference. Engine always flushed out. Stored in a nice dry garage. I have been through the service manual and cannot spot anything else obvious.

I am looking for advice as to what to try next.

[Charles uk]

What is the sparkplug gap, & is your measurement metric or imperial?

[Hugz]

I always thought the Mk2 magneto was the wipac not that it changes anything. I usually run the D16 at 20thou. Did you tighten the head bolts down after you have run the motor for a while? Define "spluttering along".... missing, 4 stroking, not revving out? Wonder if you have water at the bottom of your tank. Easy to check, disconnect fuel line and let a bit of fuel run into a glass jar and observe. Also can you spray some WD40 in the carb when it is running to see if it revs up if it does it is probable a fuel problem, though if it runs fine at start up unlikely. Also while it is running can you spray WD40 around all joins to see if the revs change (leak).

Not to alarm you but I had a century that did the same to me and it turned out to be a hairline crack between transfer port and bore that opened up when heated. I needed a seeing eye dog to notice and the only way I knew something was amiss with the block was that I replaced it and everything worked again.

The only thing that has changed is your rebuild so I would be looking at head gasket leak or similar. How often have you used it since the rebuild? The screw in HT mag connection sometimes corrodes and the coil can breakdown but I'm thinking it is not that.

Is the motors name Oli? ie Rev oli. Maybe a name change

[Horsley-Anarak]

Could be a coil problem I would say, check the resistance, good youtube vid
https://www.youtube.com/watch?v=KT8rk5QWgS0 Doug knows his stuff.
http://www.villiersparts.co.uk/ignition.html

"Villiers fail" can also be the condenser that is hidden under the points box, I have had a couple that have run well cold but just died when they warmed up, then started again when cold.


H A

[Collector Inspector]

Did you check the mating surfaces on the crankcase halves. They have to be flat ie no high or low spots.

What did you use to seal the case when putting back together.......

BnC

[Revoli]

Gaps stated are imperial so should read 0.020 for points and 0.035 for spark plug although also tried .020 which is recommended in the service manual but I noted John at SOS recommends .035 and have tried both. No change. The ignition is the MkII type as shown in the service manual for a plus 40. It's a WIPAC not Villiers, me being stupid, the carb is Villiers seagull one with the plastic float chamber. I know there is a spark and it must be decent as she runs fine when cold but thank you for the excellent video, I now know how to test properly .

By spluttering along I mean the revs fall right off even with throttle wide open. There seems to be quite a bit of discharge through the carb each cycle. I need to check this to see if it's just oil or an emulsion with water. If it is and the tank is clear of water could this be a sign of water getting into cylinder?? I did draw some fuel out of the tank just to flush the fuel pipe and it looked clean but will check again.

I will
- check fuel tank for water
- Tightened head bolts as these had not been tightened post build. No torque settings in the manual I notice so guess work.

If that does not work I might be into taking the head off again. Don't really want to as would disturb the nice new copper gasket.


Thanks for the replies so far.

[headdownarseup]

Check the fuel mixture screw in the throttle slide. You have the manual there so should be easy for you.

At this point it's possible you might be running too lean or rich in the carb giving you the same symptoms. ( what you describe as "discharge" through the carb). Chances are that the powerhead as you describe has been apart recently and rebuilt, so possibly NOT a leak or anything that you've done in the rebuild process, but more of a set-up issue.
By all means check ALL of the fuel side for cleanliness and security. Can't do any harm.

Jon

[Revoli]

Update.
Fuel tank is fine, no water present.
Starts fine and runs wonderfully suggesting spark, gaps etc fine. No discharge from carburettor. After about five minutes of running or so start to get a discharge from carb, definitely an emulsion like mix of water and oil. White in appearance. Eventually grinds to a halt. I did tighten the head bolts as far as I dared, diagonally of course.

Before I do anything else thought I would seek advice/opinions. My guess is water in the cylinder. I could remove the head and visually inspect but may not see much if it's a hairline crack. I could try reseating the gasket with some sealant but I guess these are use once items. Might be worth trying before getting another. Beyond that all I can think of is a new block. I did remove all the gunk out of the water jacket with electric drill and frayed cable which may have been the straw that broke the camels back I suppose. Thoughts appreciated.

[Revoli]

Did you check the mating surfaces on the crankcase halves. They have to be flat ie no high or low spots.

What did you use to seal the case when putting back together.......

BnC

I did visually check and used steel rule where possible. Cleaned with thinners. Used vtech vital red silicone gasket maker rated at 650 degrees F to seat.

[Revoli]

Check the fuel mixture screw in the throttle slide. You have the manual there so should be easy for you.

At this point it's possible you might be running too lean or rich in the carb giving you the same symptoms. ( what you describe as "discharge" through the carb). Chances are that the powerhead as you describe has been apart recently and rebuilt, so possibly NOT a leak or anything that you've done in the rebuild process, but more of a set-up issue.
By all means check ALL of the fuel side for cleanliness and security. Can't do any harm.

Jon

That sounds it might be worth a try. If I understand you correctly you suggest checking the needle setting in the carb and adjusting to make weaker or stronger? I will dissassemble and check it is currently in the factory standard setting flush with top of throttle valve piston. Will then try adjusting weaker or stronger by adjusting screw one complete turn above piston then one turn below and test result of each. I suppose it is possible that the emulsion like discharge seen through the carb is atmospheric moisture and oil as it's very humid currently but I might be clutching at straws there

[Revoli]

Interestingly weakening the mixture (screwing one whole turn below top of carburettor piston has improved things. Gone to one and a half. This is way out of kilter with the factory preset but seems to work. Still running very lumpily (ie revs go up and down without change of throttle or raising/lowering control arm) so not perfect but that I suspect is normal for a Seagull of this age? Discharge reduced. Maybe the mixture is the answer. I read that running too lean a mixture is bad for the engine so reluctant to go much further. Any of you seasoned Seagul officianados consider a slightly lumpy rev rate normal or am I being too picky.

[headdownarseup]

By the sounds of things you might be onto the cause of your troubles.
You are correct in that the factory setting for the needle jet is FLUSH with the top of the slide. However the manual does suggest that 2 full turns down from flush is still within limits. Not really worth going too rich with the mixture as it will make things worse (4 stroking)
Worth remembering here that not all seagulls will present the exact same symptoms. Fuel requirements are just one possibility. Block specifications/condition are quite another depending on how much this engine has been used over the years.

True, there might still be a hairline crack within the block somewhere. Only more testing in the tank will begin to show this. (perhaps a bit easier to remove the block/cylinder in 1 component from the crankcases, less to dismantle that way without having to re-do the head bolts and joint again)

I remember back to when i was refurbing one of my LS's which presented similar symptoms. Fine when cold, but as it warms up it would sputter to a stop with loads of "discharge"coming from the carb inlet cowl.
Small increments of adjustment to the mixture screw were all that was needed. (no more than 2 full turns from flush)

As a general rule of thumb, what you're trying to achieve here is a motor that runs with a bit of 4 stroking at below say half throttle but as the revs increase above half throttle the 4 stroking reduces significantly. (not quite screeming, but crisp sounding with no bogging)
At this point it's probably worth putting the motor on the back of a boat for a proper long run.
Then go and check the condition of the spark plug again. Wet and oily might suggest the mixture is still a tad rich. Dry but with greyish/brownish deposits all over and you're pretty much there.

Trial and error some of this.

If the motor has a good strong spark with adequate fuel flow (as yours has) then that's half the battle won. The rest is down to fine tuning.
I reckon you're almost there....

Suck it and see

Jon

[Revoli]

By the sounds of things you might be onto the cause of your troubles.
You are correct in that the factory setting for the needle jet is FLUSH with the top of the slide. However the manual does suggest that 2 full turns down from flush is still within limits. Not really worth going too rich with the mixture as it will make things worse (4 stroking)
Worth remembering here that not all seagulls will present the exact same symptoms. Fuel requirements are just one possibility. Block specifications/condition are quite another depending on how much this engine has been used over the years.

True, there might still be a hairline crack within the block somewhere. Only more testing in the tank will begin to show this. (perhaps a bit easier to remove the block/cylinder in 1 component from the crankcases, less to dismantle that way without having to re-do the head bolts and joint again)

I remember back to when i was refurbing one of my LS's which presented similar symptoms. Fine when cold, but as it warms up it would sputter to a stop with loads of "discharge"coming from the carb inlet cowl.
Small increments of adjustment to the mixture screw were all that was needed. (no more than 2 full turns from flush)

As a general rule of thumb, what you're trying to achieve here is a motor that runs with a bit of 4 stroking at below say half throttle but as the revs increase above half throttle the 4 stroking reduces significantly. (not quite screeming, but crisp sounding with no bogging)
At this point it's probably worth putting the motor on the back of a boat for a proper long run.
Then go and check the condition of the spark plug again. Wet and oily might suggest the mixture is still a tad rich. Dry but with greyish/brownish deposits all over and you're pretty much there.

Trial and error some of this.

If the motor has a good strong spark with adequate fuel flow (as yours has) then that's half the battle won. The rest is down to fine tuning.
I reckon you're almost there....

Suck it and see

Jon

Many thanks for your invaluable advice. Might just let it run in the dustbin for half a tank once the wife is out and I stop getting noise abatement notices from her. Duly noted about the plug colour. I reckon I can go a bit leaner. I suppose so long as the plug is tending towards black rather than brown the mix is rich enough not to do any damage long term. I would like to be sure I can get an hours burn out of it before committing to the boat. Don't fancy being halfway across the Solent, needing an engine and getting stuck. Whilst I have oars it's a mugs game and the old ticker might not be too pleased either.

[headdownarseup]

No matter how often (or not) i intend on using a motor, i will ALWAYS give it at least 30 mins in the bin before i commit to open water.
Why tempt fate! If it's gonna have a tantrum it's better on dry land than in the solent...

Ideally the best way of testing a seagull is on the back of a boat doing what it does best. When you get back to shore, quickly whip the plug out and see the colour of the plug. This alone should be able to tell you a lot about what's going on inside your motor. It's old skool mechanics after all.

Keep us posted

Jon