Hello everyone,
Im a recent boat owner but long time 2 stroker (ive rebuilt many 2 stroke motorbikes in my time). I was never interested in boating until I was offered a boat fairly cheap with an engine that needed TLC. Now, after a fair few hours I have a working engine on a pretty neat boat.
Now, I want to try and get the most bang for my buck.
I've done quite a bit of research and have come to the following conclusions (along with questions). But first, a little about my boat and motor
So my questions:
PHEW! Long post. Sorry about the wall of text. I believe the prop and hull repair would bring me most power, but any small thing I can do to help is great.
Many thanks for your help! Much appreicated!
Im a recent boat owner but long time 2 stroker (ive rebuilt many 2 stroke motorbikes in my time). I was never interested in boating until I was offered a boat fairly cheap with an engine that needed TLC. Now, after a fair few hours I have a working engine on a pretty neat boat.
Now, I want to try and get the most bang for my buck.
I've done quite a bit of research and have come to the following conclusions (along with questions). But first, a little about my boat and motor
- 3.93m (12' 11") runabout. Width at transfom is 1.55m (5' 1") and length from bottom of hull (centre rib) to outer most part of hull is 0.820m (2' 8"). Not sure if that measurement is needed though!
- Fibre glass. Low profile and fairly light (max 4 person capacity)
- 50hp Mariner (inline 4) 2 stroker. SN is 6453200 so going by the internet it is a 1983 or 1984 model. Mercury made.
- Main purpose of the boat is for cruising. Top speed is more important to me than quick acceleration
- I was hoping to do some skiing from it too (two ski's. beach start, considering the small engine) but after some reading up I feel that the sort of prop and tuning I am hoping to do will render the boat/engine fairly inadequate for skiiing. No problem for me. Id prefer the speed
- I am getting about ~120psi per cylinder. Not the best but not bad either. I am not up for rebuilding the top end any time soon (or at all!) as its just not worth the $$
- I tuned it recently and replaced the carby floats and main needles (they were worn)
- Currently, I am getting 50km/h (31mph) with 2 people in the boat (each weighing about 80kg's [176lbs]) at WOT with ~5500rpm.
- The existing prop (3 blade, aluminium) has scuff marks and some dings. I want to change it but dont know what to change it to. I cant find the existing figures on it so have no idea on the pitch or diameter. My reading up has said I should change to a slightly higher pitch (or highest pitch possible) for higher top end speed. Is this recommended? If so, which prop should I go for?
- I have read somewhere that changing to slightly larger carbies will help with more power (I can understand why). During my repairs of the engine I bought a set of 2nd hand carbies that are off a Mercury with a higher HP rating, but the carbies still fit the same block. I am still yet to do my research on them, but assuming they are bigger carbies (im fairly sure they are) could I replace my existing ones for these and hope to get a performance increase? It really is at no additional cost to me and about an hours worth of work.
- The hull has chips in the bottom. I read this will add noticeable drag to the boat. I have fibreglass putty and a new orbital sander. I read 600grit paper should be good for this sort of hull. Can someone confirm this is OK to do? I also read that sanding in the direction the water will flow helps too. But does it help so much that I need toss the orbital aside and do it all by hand?
- What is the recommended fuel octane level for this engine? Living in Australia we have access to 92, 95 and 98 octane fuels. Im currently using standard unleaded fuel (95 octane) but am happy to increase it to 98. But dont want to damage my engine as this is a cooler burning fuel and drier.
- I looked in my workshop manual and cant find an oil filter fitted to this motor. Is there one? If so, is it worth it if I change it to a high flow filter?
- I removed the inline fuel filter beside the hand pump on the fuel line (this was extra, not needed) but there is still the fuel filter in the engine and then another gauze/filter at each carby. Im obviously not going to remove these, but is there a high flow alternative I could use? Especially when considering ill be putting on bigger carbies. Would I also need to change to better reed valves (ie. Boyesen) to allow for better fuel flow?
- I have replaced the spark plugs with what was recommended by the manufacturer. However, would I get a performance increase if I fit it with high performance spark plugs with 1 heat range designation higher than manufacturer specs?
- The motor has a Hydrofoil attached to it. I read a few people saying to get rid of it. Should I? Its a fairly small (light) boat so perhaps this isnt such a good idea for me.
Many thanks for your help! Much appreicated!
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