Outboard Top speed reduced ?

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munster1967

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Hi folks.
I have a dt2 Suzuki. I recently changed my sib from a 2.8 m slatted floor to a 2.5 m air deck model. I seem to have lost 2.5 km per hour top speed down from 11 kmph to 8.5 kmph. The spark plug was changed in the outboard because it wasn't starting and a Br6hs was put in instead of the original BR5hs.
Would the slightly different spark plug reduce performance. ?
 
No, not at all. The 5 would run hotter than a 6, useful if you run at WOT most of the time. If the jet became 'varnished' on the bore due to the lighter elements in the fuel evaporating, reducing the amount of fuel it could pass, the mixture would be lean and could cause piston damage.

A 6 plug would be slightly more tolerant of excess heat caused by a slightly lean mixture than a 5.

I suspect the different dinghy requires more power to reach the speeds you got with the previous one.

Our vee floor SunSport was slower than our current flat floor Talamex Superlight with the same Suzuli outboard.
 
munster1967 said:
Hi folks.
I have a dt2 Suzuki. I recently changed my sib from a 2.8 m slatted floor to a 2.5 m air deck model. I seem to have lost 2.5 km per hour top speed down from 11 kmph to 8.5 kmph. The spark plug was changed in the outboard because it wasn't starting and a Br6hs was put in instead of the original BR5hs.
Would the slightly different spark plug reduce performance. ?
Click to expand...
I very much doubt it . BR6HS is just one grade cooler, otherwise the two are identical but I notice that some older models, with coil and points ignition, were fitted with the hotter BR4H
 
rotrax said:
No, not at all. The 5 would run hotter than a 6, useful if you run at WOT most of the time. If the jet became 'varnished' on the bore due to the lighter elements in the fuel evaporating, reducing the amount of fuel it could pass, the mixture would be lean and could cause piston damage.

A 6 plug would be slightly more tolerant of excess heat caused by a slightly lean mixture than a 5.

I suspect the different dinghy requires more power to reach the speeds you got with the previous one.

Our vee floor SunSport was slower than our current flat floor Talamex Superlight with the same Suzuli outboard.
Click to expand...
Thank you. For the info.
 
I would suspect the new boat isn’t trimmed to run as efficiently. It could be bows up causing the stern to drag. Try shifting weight a bit forward now you don’t have a slatted floor
My 2.3m airdeck with 4hp will fly up on the plane if I sit in the bow. If I sit aft it plods along nose up making a big bow wave
 
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