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Old 02 February 2007, 13:04   #1
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does this sound allright ?


just replaced the middle piston and had rebored out to fit it, just got engine going now but it seems to be hunting around at idle we have used a color tune to set up the carbs and followed the manual to the letter , but i think it needs a fine tune doing to it.
please could you give me some advice as if to wether its sounding ok or whot ever as whot info i can get would be apreciated . cheers
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Old 02 February 2007, 18:01   #2
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Is there water coming out of the top exhaust?
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Old 02 February 2007, 18:19   #3
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You're not getting enough back pressure in that drum so it's going to sound odd-specially as one cyl has now got more compression than the rest.
You're not running it under any load either.

Try it on the water.
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Old 02 February 2007, 18:43   #4
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You just rebored the middle piston? Is that standard practice?

Hmm, if that's the case then you might well have some dificulty balancing the cylinders.

I would guess though that it's a combination of the lower compression and the fact that the middle carb will be out of balance as there is going to be more air fuel going into the rebored piston.

If your happy with the one cylinder rebored then the Carbs should be checked for balance.

Is that normal to have water comming out of he exhaust?
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Old 02 February 2007, 20:39   #5
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Quote:
Originally Posted by Hightower View Post
You just rebored the middle piston? Is that standard practice?
Shouldn't be but it's a cheap 'fix' for an old engine. I used to do it on aircooled 2-stroke bikes but they went bang so often it didn't matter anyway.

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Hmm, if that's the case then you might well have some dificulty balancing the cylinders.

I would guess though that it's a combination of the lower compression and the fact that the middle carb will be out of balance as there is going to be more air fuel going into the rebored piston.

If your happy with the one cylinder rebored then the Carbs should be checked for balance.

Is that normal to have water comming out of he exhaust?


I wondered about the exhaust water too.

Colourtune kits are utterly useless for balancing/tuning unless you can run the engine under load to balance it. The variance is too small at the throttle openings you use with no load.

IF you can find a test wheel it might help-or cut down an old prop to make one. This is roughly what they look like but the one in the pic below is for an old Chrysler which doesn't have a through-hub exhaust.
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Old 03 February 2007, 02:58   #6
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I agree. But you'll still have to balance the Carbs. Use a vaccum gauge connected to the carbs, or take it to the dealers (about a 30 min job)
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Old 03 February 2007, 03:06   #7
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I wonder if the carbs have take-offs for vacuum gauges?

Easy enough to drill/tap one if not I guess. Shame he's not down this way-I've got a set of gauges in the garage.
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Old 03 February 2007, 10:07   #8
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yes it kicks water out at the top dont all outboards do this its a selva, a big bag of bolts, the reason for only doing one piston is that i ordered a set of 3 in july last year and was kept waiting till november/december when selva said they dont do pistons for this engine any more so i oped for a bigger piston they had just to get the bloody thing going,still waiting for supreame marine in osset to bring prop back after 4 weeks ago ,
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Old 03 February 2007, 15:14   #9
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I wonder if the carbs have take-offs for vacuum gauges?

Easy enough to drill/tap one if not I guess. Shame he's not down this way-I've got a set of gauges in the garage.
Some vacuum gauges can be placed over the inlet opening of the carb and you simply hold it place.

Top car tuners can do it by ear. They hold a piece of tube near the opening and listen at the other end.
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Old 04 February 2007, 05:27   #10
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your all talking about the engine kicking water out of the top exaust tube but dont some of them do it my mariner ex rnli did, also a few other makes that ive seen on the net. when we rebuilt the power head we replaced all gaskets thermostat so every thing is compleatly new so i cannot work out why its doing it , the engine was run at up to 3000 rmp for a long time yesterday and we kept a eye on the engine temp with no noticible temp diffrence its keeping the block nice and cool, just sent vid to selva to see if they know if water out of top is ok , thanks for info received keep it comming as were all beginners ,cheers andy
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