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Old 29 June 2005, 03:58   #11
DM
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Engine looks to be to low and with those doelfins at that depth, you'll get handling quirks.

First thing I'd try would be to remove doel fins and raise engine until antivent plate is a touch above the keel.

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Old 29 June 2005, 04:19   #12
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Phil, yep agree with the old man, ditch the fins and raise the engine. Also worth following Grahams advice and take a trip to Bill Highman in Worsely. Facinating place (think of car scrap yard only for outboard engines) and get a spare prop. That way you can eliminate the prop as contributing to the problem. When it was rebuilt it might be slightly out of shape adding to your problems. A spare is always good to carry anyway.

Good news is you don't need to cut the transom and with a couple of mates, a case of beer and a day at the seaside "testing" you should be able to solve this one.

Pete
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Old 29 June 2005, 15:39   #13
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Selva Overrevving

Thanks guys,

I'll give it a go & post the results.

However, I need educating (if you don't mind that is). In my very limited sense of logic, I would imagine that the further away the prop is from the air above it & deeper in the water, the less chance I have of getting air around it. Not that I doubt your wisdom, but I'm lacking insight in the science of props & engine positioning. Also, I don't understand how the plates can reduce the performance.

Someone once said to me that this stuff is a bit of a "black art". I'm starting to believe them! Or can you explode the myth for me?

Again, everyones help & input is very much appreciated.

(PS. I know, I sound thick but - the antivent plate, is that what the doelfins are attached to at the moment?)
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Old 29 June 2005, 15:46   #14
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Quote:
Originally Posted by Phil Robinson
Thanks guys,

I'll give it a go & post the results.

However, I need educating (if you don't mind that is). In my very limited sense of logic, I would imagine that the further away the prop is from the air above it & deeper in the water, the less chance I have of getting air around it. Not that I doubt your wisdom, but I'm lacking insight in the science of props & engine positioning. Also, I don't understand how the plates can reduce the performance.

Someone once said to me that this stuff is a bit of a "black art". I'm starting to believe them! Or can you explode the myth for me?

Again, everyones help & input is very much appreciated.

(PS. I know, I sound thick but - the antivent plate, is that what the doelfins are attached to at the moment?)
Yes the antivent or cavitation plate is what your doelphins are currently attached to. I would unbolt these and try it straight away without them as doelphins do funny things to ribs -they work on some applications but by no means on all!

Pete, would the prop bushing be a possibility or am I way off!!!!

regards

Alex
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Old 29 June 2005, 16:34   #15
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Pete, would the prop bushing be a possibility or am I way off!!!!
regards Alex
My thoughts too, if the prop has been repaired once already did they take the bush out before welding it up....who knows, but changing the prop would eliminate it as the problem.

Pete
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Old 29 June 2005, 16:46   #16
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[QUOTE=Pete7. Facinating place (think of car scrap yard only for outboard engines)
Hes got draws full of used parts , I could spend days in there.
Graham
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Old 18 July 2005, 13:19   #17
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Selva - another problem!

All,

Thanks for the many bits of advice. I tried the easiest thing 1st and did a bit of prop switching. I went down to a 15 from a 17 pitch. It worked!!!!
So that saves having to lift the lump up. Fantastic. Thanks to all.

However - I have another problem. The dammned thing won't run right. It stalls after a while on tick over, or when going from neuteral to in gear. I reset the tick over highish but not silly - no change. Starting is a nightmare. Having taken the plugs out, I see they're oiling up really quickly. A road mechanic told me that it can be a common problem in 2 strokes as the 50:1 mix is technically correct but not all motors like it. So I tried diluting the fuel mix a little & it got better. Also, the plumes of smoke reduced in size. Now, I've always been careful with a 50:1 mix, but I have a mate who swears by a 75:1 on his Merc 115 brown band. The mechanic says 75:1 wouldn't cause damage but I'm worried. Does anyone have any opinions?

If I screw this one up, the wife won't let me buy a 3rd engine!
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Old 18 July 2005, 19:14   #18
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Okay here goes. Phil you still need to lift the engine on the transom. Not difficult, 3 lads and a set of spanners and 15 minutes work. Don't lift the engine put the skeg on a wooden block and use the trailer to lower the stern of the boat then refit the bolts. Having lifted the engine try her at sea without the fins.

The starting problem could well be in the carburation. How old is the fuel ? lead free has a limited life. Fuel mixed with 2 stroke oil it forms a gum in the float bowls and jets which if left then sets to a varnish. Clean fuel doesn't seem to remove this but you could try a can of carb cleaner. If that doesn't work then the carbs & reeds need cleaning out. Stick with the 50:1 for now.

Do you have a rev counter? I think the 15" prop a little small, please keep a check on the max revs you can pull with that prop.
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Old 19 July 2005, 06:09   #19
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100HP on a 5m rib ? - that seems to be a lot of power ?

I'm not an expert tho' - just going by my own set-up - 4.7m Avon with 50HP and goes very nicely - max rating is 70HP....
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Old 19 July 2005, 06:34   #20
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Quote:
Originally Posted by Phil Robinson
Hi all,
I have a Selva S1400 / 100hp (1994) fitted to a narrow beam Osprey 5.5m rib (approx 1988)
its a 5.5m still plenty of ponies though!
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