The Hardy Motor Boat Owners Club Message Board | Engines | Prop size for a Suzuki DF70T on a Family Pilot/Rev Limiter Issue

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Message board > Engines > Prop size for a Suzuki DF70T on a Family Pilot/Rev Limiter Issue

Message 7 of 7
Posted by member Steve Pickthall on Monday 9 August 2010

I was the person who wrote the original mail re suzuki prop size if anyone wants to discuss I am here ...

Message 6 of 7
Posted by member Andy Mcmullan on Monday 2 August 2010

Hi There was a very informative and detailed post on the forum a few years ago from an owner who had this engine and had experimented with props. I had look back to find it and it seems to have fallen off the forum radar. I think once posts get to a certain age they are no longer displayed. Maybe the webmaster could help you there? Digging into the memory banks, I think 13 x 13 was found to be ideal by this poster. I have a 13 X 15 on my 98 Pilot on a Yamaha 80, and it revs to about 5900 with my normal load which is just about ideal with max revs rated at 6k for my engine. The fact that yours is hitting the rev limiter at 3.5k sounds very strange. Do you know what speed the boat is doing at these revs? If it is planing and the motor doesn't sound laboured and is reving out ok then maybe the rpm reading is wrong on the tach. If 3.5k is a true engine reading then the boat will be struggling to plane at these engine revs. It might be worth trying to get the Suzuki people out on the water for an engine test as running the engine on the hose attachment without a load on the prop may not truely reflect what is going on with the motor. Cheers, Andy

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Message 5 of 7
Posted by member John on Monday 2 August 2010

If you search Google for 'Prop size calculator' there are several which may help. One such is http://www.vicprop.com/displacement_size.php Hope this helps

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Message 4 of 7
Posted by member Webmaster on Monday 2 August 2010

Postings are removed after a long period of inactivity. However Suzuki 70hp 4 stroke Prop Size is still on file and has been re-instated for interest at the end of engines

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Message 3 of 7
Posted by member Bob Pollock on Monday 2 August 2010

Steve/Andy/John/Webmaster, Thanks for your help. Engine should rev to 5800rpm. At 3400rpm it is showing 8/9 knots on the GPS, and Andy is right, the rev limiter kicks in at 2800rpm when on a hose. Personally I think it is an electrical issue, although we have eliminated all the usual suspects, leads batteries, coils, etc. Now found a faulty microswitch which prevents the engine from being started in gear, which may be the culprit. Will try replacing that then run the boat in the water connected to the diagnostic to see if that cures the fault or we can identify what is happening at the point the rev limiter kicks in. The local engineer has also sourced a diagnostic ECU from Suzuki -keeping my fingers crossed it is the microswitch! I'll let you know how I get on. Usefull information on optimal prop sizes for when I get the engine running. Brilliant website and great to know there are people out there willing to help. Regards Bob

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Message 2 of 7
Posted by member Steve Hook on Saturday 31 July 2010

Hi Bob....Matching a prop to a boat/engine is very much trial & error. a prop should be fitted that allows the engine to achive its max revs..in your case probably around 6000rpm but look in the tech spec of the engine to see its max rpm..your 15in pitch prop should not prevent your engine going above 3500rpm. Why is the limiter kicking in? what rpm should it operate at? Give Suzuki UK technical a call to discuss..Good lock & keep us posted Steve

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Message 1 of 7
Posted by member Bob Pollock on Friday 30 July 2010

Hi, I have just bought a Family Pilot which is fitted with a Suzuki DF70T. The engine runs sweetly to 3500 rpm at which point the rev limiter kicks in. As soon as you drop to 3400 revs it runs sweetly again. Been to my local Suzuki dealership and nothing is showing as faulty on the diagnostic. Could it be a prop issue - fitted with a 13.5/15 prop, or has anyone encountered a similar problem? Thanks Bob

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