Some sage advice would be greatly appreciated. I already have 2 anchors. I don't need a 3rd
Raw fuel from carb
Moderators: John@sos, charlesp, Charles uk, RickUK, Petergalileo
Raw fuel from carb
I have a SilverCentury Plus with Amal carb. This summer managed to get it firing up 1st pull most of the time and running well (enough) for long periods. I have 2 queries, however. First is what is the likely cause of neat fuel being sprayed out of the air intake? This is most noticeable when above half revs. The second is dissapointing power output (thrust) when compared with my Merc 4hp 2 stroke. The Seagull should be much better for my 16' displacement sailing cruiser and certainly 'feels' more appropriate. Could the 2 issues be related in any way?
Some sage advice would be greatly appreciated. I already have 2 anchors. I don't need a 3rd
Some sage advice would be greatly appreciated. I already have 2 anchors. I don't need a 3rd
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Charles UK
There are 2 possibilities that spring to mind on this question.
1. incorrect inlet timing, inlet port open too long.
2 Piston rings very tired, allowing some blow back on the compression stroke.
It's unlikely you've moved the inlet port, so try a compression test, there is not usually enough crankcase compression on a century for the pulse to start from there, so it's probably coming from the top of the engine.
Centurys seem to run OK with compressions ranging from 45lbs to 75lbs.
1. incorrect inlet timing, inlet port open too long.
2 Piston rings very tired, allowing some blow back on the compression stroke.
It's unlikely you've moved the inlet port, so try a compression test, there is not usually enough crankcase compression on a century for the pulse to start from there, so it's probably coming from the top of the engine.
Centurys seem to run OK with compressions ranging from 45lbs to 75lbs.
Thanks, Charles.
Can't imagine how the inlet port timing could have been altered during my ownership.
Low compression due to worn bores/tired rings does sound likely and would account for both my concerns. If that is the case not sure what options are available.
Running on 25:1 would mean lower viscosity in the fuel/oil mix and that could be a factor in an old engine, I guess.
Gummy rings not expanding to the cylinder walls is a possibility, I suppose. Oversize rings? Are they available? Any other solutions?
Can't imagine how the inlet port timing could have been altered during my ownership.
Low compression due to worn bores/tired rings does sound likely and would account for both my concerns. If that is the case not sure what options are available.
Running on 25:1 would mean lower viscosity in the fuel/oil mix and that could be a factor in an old engine, I guess.
Gummy rings not expanding to the cylinder walls is a possibility, I suppose. Oversize rings? Are they available? Any other solutions?
Oversize rings aren't available - but new rings are; contact John at SOS.
But the problem may be that they're gummed up.
If you part the block from the crankcase you'll be able to tell quite quickly - if they're stuck in the grooves they need freeing off carefully, and the offending gunge removed.
New rings are not expensive.
But the problem may be that they're gummed up.
If you part the block from the crankcase you'll be able to tell quite quickly - if they're stuck in the grooves they need freeing off carefully, and the offending gunge removed.
New rings are not expensive.
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Charles UK
Not sure I agree with the other Charles with regard to removing the head, I always remove them.
I think I have broken 3 or 4 head bolts out of the 15 to 20 heads I've removed, if you have stainless head bolts it's never a problem, plated steels ones can be a problem if the threads were drilled & tapped right through into the water jacket as the ends of the bolts rust & expand.
The only way to assess the condition of the water jacket requires head removal.
But Charles is right on a ring job, after a very low compression test you might as well leave the head on if you've good water flow.
I think British Seagull when they had a service department ensured their continuite of work by casting "do not remove" onto the cylinder head ensuring it was sent back to the factory or to an authorised service center for head removal.
Broken head bolt removal & retapping is well within the competance of any small engineering workshop with a mill & a 5/16 BSF tap.
All the cylinder needs is a light hone & a new set of rings, John Williams must have heaps of them.
But for a Century to wear the rings this badly the whole outboard must have done a considerable amount of work, a complete reconditioning might be the order of the day if your planning on using it for more than a sunny sunday put put up the river.
I think I have broken 3 or 4 head bolts out of the 15 to 20 heads I've removed, if you have stainless head bolts it's never a problem, plated steels ones can be a problem if the threads were drilled & tapped right through into the water jacket as the ends of the bolts rust & expand.
The only way to assess the condition of the water jacket requires head removal.
But Charles is right on a ring job, after a very low compression test you might as well leave the head on if you've good water flow.
I think British Seagull when they had a service department ensured their continuite of work by casting "do not remove" onto the cylinder head ensuring it was sent back to the factory or to an authorised service center for head removal.
Broken head bolt removal & retapping is well within the competance of any small engineering workshop with a mill & a 5/16 BSF tap.
All the cylinder needs is a light hone & a new set of rings, John Williams must have heaps of them.
But for a Century to wear the rings this badly the whole outboard must have done a considerable amount of work, a complete reconditioning might be the order of the day if your planning on using it for more than a sunny sunday put put up the river.