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Outboard servicing.


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I have a little 2hp Suzuki DT2 outboard currently in a lot of pieces for a big refit, the reason for which is that recently she's been running a bit rough.

When I collected the parts needed from the service agent, he advised running on 96 octane instead of 91, and to use NGK plug BR4HS instead of the BR5HS. From the number the BR4HS is as slightly hotter plug.

I should add I assumed from his comments that I was running the wrong fuel/plug, but on checking later, I had it right.

Any ideas as to why the serviced agent would want to make these changes?

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Hi all, If the little suzuki had a history of oiling/fouling its plug due to prolonged low speed use then it could be a smart move to go a bit hotter plug ( hotter plugs have a longer heat path on the centre electrode so the tip runs hotter and can burn off oil/carbon) . There is a small risk going to a hotter plug(s) though (if one day you need max power for quite some time it can cause all sorts of trouble - detonation etc) so its possible the agent advised the use of 96 to help offset this...Hope this helps 

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  • 2 weeks later...

Thanks for the post Jim s.

I have found manuals online for the Suzuki DT2. One of the manuals says the engine should run on 91 octane with the BR5HS plug. The other recommends 95 octane and a BR4HS plug so I guess you can take your pick. Don't you just hate it when that happens? But it does explain the service agents recommendation.

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When it comes to petrol, the higher the Octane, the slower the Burn. It doesn't mean it is more volatile, which tends to be reverse from what many tend to understand when they think the number being higher may represent.
Chris, if you can get your hands on Amzoil products, get their Two stroke Oil. You get a really clean burn, need half the amount of oil in the mix than the normal ratio and it makes the little motor run much nicer and easier to start.
Amzoil actually developed a 2stroke oil with a 300:1 mix ratio, but decided not to market it because they could not see anyone actually accepting they could put in so little oil and not adhere to the ratio anyway.

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I have a 2hp Yamaha (looks just like the Suzuki) runs nicely but was a bit lumpy at idle, thinking it was too rich at low revs I dismantled the carburettor and found the fuel/air mixture can be adjusted. From memory there was a small circlip on the needle valve that had 3 grooves that gave varying mixture rates. Factory setting was the middle groove, I think I raised the circlip to lower the needle to get a leaner fuel rate and it now idles very sweetly.

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I've seen that adjustment on the needle valve Rafin but haven't touched it. In my OP where I said the motor was running a bit rough, that was because I hadn't looked at it all winter and the carb, fuel lines and tank needed a clean. Normally she runs very sweetly on the 91 octane. I figured that I might as well lift the head and clean out the waterways, decoke and check the tolerances whilst I was at it which meant getting some spareparts, and that was when the service agent recommended to run on 96 octane.

Interesting about the Amzoil Wheels.

Both online manuals stay to run the engine on 100:1 if using Suzuki oil, 50:1 if using other branded outboard oil. I don't thing that Suzuki are in the business of formulating their own oil - they may tinker with someone else's and rebrand it as their own - but it seems a huge variance in the fuel/oil ratio.

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The needle with the grooves in it gives most influence in the 1/4 to 3/4 throttle range - there should be a small brass screw upstream of the throttle slide that sets the idle to low speed mixture (it controls air into the idle circuit so undoing it say 1/3 of a turn would lean out the idle a bit) having said this if someone isn't happy adjusting their carb it might be worth getting assistance. Don't they always wait for the most inconvenient time to play up...

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Many engines happily run OK on 100:1, even if they are 50:1 designs. Except if you place them under high loads all the time, they can wear a little faster. A full synthetic OB oil usually can be used at 100:1 even if the engine is said to be 50:1 and the engine should still last well. the less oil, the less smoke and the easier to start and it idles a lot better. So it is worth buying a top oil quality and preferably a synth.

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