Misfire over half throttle?

[Fordmayhem]

Hi ! First post..

I am a new seagull owner, having purchased a 40 minus 1956-57.

She looks in good nick, however when giving her a wet test I have noticed that trying to take her over half throttle results in exhaust fumes coming out the carburettor and a loss of power. Is the cylinder reversing ? :s

Aswell as this, is it normal to see oil bubbling very very faintly from the head gasket when hot? Aswell as that I noticed oil coming from the top of the exhaust tube just where the screw is at the top.


I've put 2 videos together to hopefully help diagnose my problems

Cheers!
https://youtu.be/kUaYRvK09lg
https://youtu.be/AvPyrueVB4E

[Collector Inspector]

Lots of help here but I will start off aye.

I would start by removing the head and barrel. Inspect and use new gaskets when all OK to put back together.

Spitting out of the carb can also be attributed to either the above or an air leak in the crankcases.

What model is it?

If it is early with the wrong size carb it will also do the spitting out?.

Engine number?

If the correct carb is fitted..............clean and adjust as per SOS main site....or.......others will chip in I am sure

Once the mechanical symptoms/issues mentioned are sussed out then check all ignition from go to .......

Mechanical first.

BnC

[Collector Inspector]

Hmmm

Ignore the oil from the exhaust tube thing for now aye...

BnC

[Oyster 49]

Welcome to the forum! Some good advice from CI there. The reason engine is chugging at reduced throttle is that it is running a little rich. One you have sorted the head issue out we can talk you through tuning the engine. A little rich is better than a little though.

[Fordmayhem]

Hi thanks for the replies.

I'll have a look when I get time, may be a few days from now though.

The number is sjm3344.

I will need to have a look at the carb anyway to see what mixture ratio is being ran aswell. The man said 25 to 1 since he said this was a forty plus from 1970 I think he may not know the mixture. I've had a look at the faqs on how to identify these things so I should be good. Thanks! Will be back in a few days

[headdownarseup]

Welcome to the "Madness" that is seagulls.

Fuel mix on these old dears is 10:1 on anything made before 1978, but as yours is a mid 50's engine i'd stick with 10:1 for now.
Bruce and Adrian are right. Dont worry about the oily exhaust tube for now (quite normal until the motor has had a nice long run on the back of a boat)

Sort the mechanical issues first before you tune anything.
Start by stripping down the powerhead as Bruce (C.I.) has suggested and give EVERYTHING a bloody good clean, then inspect for wear.
Easy peesy, if you get stuck, one of us will jump in i'm sure.
Pics are always a good way for us to see what you're up against, so dont be shy.


Jon

[Fordmayhem]

Hello!

Back again, armed with Head and Base gasket along with some silicone gasket.

Had a look at the carb, yes it is indeed a 10:1. Villiers.

Took the head screws off(eventually....) and spark plug, picture as follows to what I found:











Cylinder looks good, rings look good, just dirty from what I can see.

[Oyster 49]

Looks entirely normal. Here's your list of things to do:

Clean water cooling passages using a small screwdriver to clean out rust etc.
Check gasket faces for flatness
Reassemble block and head
Clean and gap spark plug
Clean and gap points
Consider a new HT lead
Clean carb
Clean fuel pipe
Clean out tank
Replace gearbox oil
Run again, get to temp and run for a couple of minutes
Tighten head bolts again after cooling down.
If it is still running rich try adjusting the needle down half a turn and try again. Always better to be running a little rich than a little lean.

[headdownarseup]

Yep, not bad at all.
Clean everything before re-assembly and it should be good to go.
Not too much rtv on the head gasket though as it will ooze out, just a light smear and leave it to set for a few hours before you put the head back on.
Nice
Should be up and running again in no time.

Jon

[Fordmayhem]

https://youtu.be/RszlHUbXfqU

Here is the update. I've replaced both gaskets. Cleaned up pistol etc everything.
Now on 10 to 1. Actual smoke is leaving the exhaust now.
Feels a bit lumpy building up rpm, but can go WOT. Feels quite smooth at high rpm. I know my water bucket isn't filled enough... it went everywhere. Only ran for a few seconds. Next run will probably be on the water so I can make sure that the water pump is working.

Do still need to find some ep140 for the gears will have that soon.

Thanks!

[Oyster 49]

If you remove the prop for testing it makes less mess and the water flow into the engine will be better. It is entirely normal for a 40 to stop pumping water at tickover, but you will get used to that. Looks good though well done. Take it out for a run and have a look at the spark plug afterwards, if it is black and sooty then you are running a bit rich. The height of the needle can be adjusted up (Richer) and down (leaner) perhaps half a turn at a time to adjust. It sounds pretty good though.

Engines built after 1968 had slightly different bearings and can be converted run on 25:1. You just have to change the needle. The info is all on the main SOS site. John has the needles in stock.

It's always better to a little too much oil in the mix than too little of course, particularly if the engine is working hard. Use a good quality two stroke designed for outboards. These little motors are designed to be worked, not chugging around at low speed.

Fill the gear oil to just below the level of the filler, too much and it will start oozing out from the shaft.