Polishing next? A friend of mine modified a Yamaha RD250LC road bike back in the '80s. He installed 350 barrels, larger carb and jets, kept the 250 head for squish, added a copper spacer between the crankcase and barrels, ported & polished, and matched the parts so that the parts connected without mismatch. I think he called it pseudo blue printing. He upgraded all of the other parts such as brakes etc. I took it for a test run not thinking I would be able to detect a difference between a stock 350 and his hybrid. I was wrong! The thing flew and had so much power it was insane. All of us who rode it came back with a smile and smashed bugs on our teeth.
😂😂 yep I know about smashed bugs or dirt on teeth with motorbikes 😁 Love the 80s road bikes, especially the two strokes. Also used to ride around on my mates rgv250, that was awesome and another mate had a 350cc (think it was Yamaha) white and red two stroke that was fun to ride too. Cheers 🍻 Aussie Boat Guy 😎
Hi mate, Yep, it’s been so much fun 🤩 Still more to go too with the lower unit and props. Funny I had recorded all that stuff, didn’t think I had but it was on my phone. I will probably watch it another 5 times too 😂😂. I definitely go back to your vids too, way better than TV. Cheers 🍻 Aussie Boat Guy 😎
Hey aussie boat guy, i have a tohatsu 25hp 2 stroke and want some more speed have done the 30hp conversion, and a 15p powertech prop and have raised the motor, i also have some boyesen reeds i need to install. what else can i do to get some more speed, was looking at shaving my head but not sure where i can get that done and how much to shave off. Also looking at some cleavers. Anyways keep up the good work legend, would love to see a series of you modifying one of the tohatsu 25hps
Thing I like about this guy isn't he's just over the puddle, it's because he bored a prop out to fit a new center ... With a pharquen Battery Drill - it was then that I had this amazing thought "you have to be bloody kidding me and I subscribed to watch the disaster BUT - Whereas if I'd not used My Drill Press to accurately Center a Prop so some engineer thousands of years from now can see the expert precision but this Neighbour does it with a battery drill and it's not even a De-Walt ... and it works SHIT! ... anyway that's why I subscribed - boring out the center of a prop you intended to spin at high speed in water with a fucken battery drill ...
Hi mate, Thanks for your sub champ 👌 Yeah, it is amazing what you can achieve with hand tools and hand held cordless drills, grinders etc,. also the drill did centre itself in the bush as I was only skimming off the splines. if you are good with props you probably know that the rubber bushes themselves can be not centered themselves from factory, I have actually removed a factory bush and pressed in a new one because it was pressed in on an angle. ps: my 18v Makita is more powerful than my mates De-Walt 😂, I do like De-Walt too. You should put some vids out, seems like you are good at this stuff, could help some people 👍👍 cheers 🍻 Aussie Boat Guy 😎
what are you planing at? I did a minor port and a 9.8 carb on my 8 and im getting around 18MPH on the ocean ~15.6 knots with fishing gear/slightly fighting the ocean. havent tried in freshwater yet.
Hi mate, i reached 38.5mph the other day. Keep in mind the motor has low water pickups and a surfacing race propeller on a 8.5ft aluminum boat Vids on the channel if you are keen to check out Cheers 🍻 Aussie Boat Guy 😎
@@25hpboatracerman awesome videos and great information. have you looked into kaboats? theyre flat bottomed with 4 fins but quite light and may be able to help with your top speed. I was getting 16MPH with gear on the ocean with my stock 5hp nissan/tohatsu and 13ish with a stock very abused 3.5 nissan
Hi mate, I think I’ve just came across a very old forum thread (10 year+ old) where you modified a johnson 9.9/15hp with twin carbs and low water pickups!! Was that you?? The guys name I think is Glenno on the forum. I have one of these motors and would love to see a video of you going the full 9 yards with one….. not just twin carbs but porting etc. out of interest, how comes you don’t tune those motors anymore/have videos of you tuning them? I know the tohatsu are very nice (I have a 9.8hp 2 stroke tohatsu now) and extremely light. I know some parts are not available but most parts are, ie… crank seals, bearings, pistons and rings, even if you have to buy aftermarket parts (I’m guessing you’re not keen on) basically, please please please do a 15hp 216cc full power build ON VIDEO, like, I would even pay towards the motor lol!!!! Oh yeah, and please say “YEAH” a bit more often lol
Hi Mate, Yeah, that was me 😂, wild build hey. I don’t really play with the Johnson 9.9 and 15 anymore as the gear ratio in the lower unit is so high unfortunately. Think it’s like 2.44 to 1 or something. the 9.9, 15 and 18 tohatsu are 1.85 to 1. From experience because of the gear ratio the Johnson gets about 65kph maximum with big mods and the tohatsu 18 will push 80kph without mods - both with nose cones and race props. Cheers 🍻 Aussie Boat Guy 😎
Hi Glenno!! Thanks for getting back to me, I’ve decided I’m going to modify one of my Johnson’s, I would love one of the tohatsu 18s but the johnson really is already a little heavier than I can comfortably keep lifting and carrying as I launch an inflatable without a trailer so a bit of a strain lol!! Out of interest, did you port your omc motor? What about mirror polished exhaust?? I’m thinking about doing exactly what you did but with a single bigger carb (bigger than the 15) and mild porting/smoothing blending the ports, polished exhaust and I will open up the reeds a little as you’ve done on your tohatsu build……….(learnt from the best!!!) to start with I want to do the low water pick up, I must say, the low water pickup on you omc build was COOL mate!!!! I’m not too fussed about if I’m as fast as or faster than a tohatsu 18 (too heavy for me) but it’d be awesome if I was even the fastest soft inflatable boat with a 15 on it! I must admit, I’m really quite fond of the omc 9.9/15 as I can get parts relatively easy and cheap secondhand and they are quite easy to work on and built tough. For what both my 9.9 and 15hp Johnson’s have cost me in total, I can honestly say it’s still cheaper than buying 1 decent 15hp 2 stroke short shaft Yamaha, tohatsu, mercury or mariner etc etc…… in the uk the 15hp 2 strokes in short shaft go for strong money if they’re decent. Would love any tips and any advice on what works modifying wise with one of these omc motors please glenno, particularly with the porting. There is quite ALOT of burrs around the factory port holes so can definitely be improved by just smoothing/ blending but what/how to do the ports size wise? Please please please tell me the full specs of your omc build and secrets for tuning my motor!! Cheered glenno and all the best, Steve from London!!!!
i think just doing the reeds and intake manifold alone would do most of the power gains. Most of these motors were same block and piston most of the time just different carbs and intakes to make different hp models. I have a suzuki 4 stroke that was a 4hp and made it 5hp just removing the throttle restrictor but im tempted to take the head off to port the crap out of it. I already have a heavier pitch prop for it
Hi mate, You are correct about the difference in hp models with outboards, the 4 and 5, the 9,9 and 15 etc etc. Unfortunately the 9.8hp is the same block as the 6 and 8hp and is already kinda squeezing most from the little block. The reeds and intake did make a difference but the porting, head and exhaust tuner plus big carb do add a lot as well. Ps: you probably have to pull your whole motor down to port it but be very carful as you port, it’s not just a matter of making the ports bigger, you need to shape them and enlarge in a very specific direction. Glad your tinkering with outboards too champ, it’s so much fun. All the best, Aussie Boat Guy 😎
Бро, приетсьвую! Подскажи пожалуйста, а выхлопную сделал конусом-это принцип резонатора? Дало прирост, проверял отдельно? Где можно посмотреть чертëж? Спасибо за видео, бро!)
Привет, брат, Отдельно я не проверял. Ранее мы тестировали более короткие и немного более толстые мегафоны на наших гоночных лодках и обнаружили, что более короткие и немного более толстые мегафоны не дают мощности в диапазоне более высоких оборотов. Спасибо, Австралийский лодочник 😎
Hi Mate, Good question 👍 I would say that adding the head is definitely worth it, it adds a heap of compression and gives more torque. The exhaust cover does help but the head is where you will notice it. Cheers 🍻 Aussie Boat Guy 😎
Hi mate, I can still run normal petrol from the service station but I make sure it’s 98 octane and I’m running normal two stroke outboard oil at a 50 to 1 ratio 50 fuel to 1 oil. fuel consumption has increased about 20% as my revs are about 1500 higher and it is running a bigger carburetor. in saying that I am covering more distance per hour too so may even out 🤷♂️ cheers 🍻 Aussie Boat Guy 😎
Hi mate, Thanks for your comments 👌 Unfortunately I didn’t keep my port map 😢😢 I know I could have gone bigger with the ports but I’m hoping it’s still reliable. Cheers 🍻 Aussie Boat Guy 😎
Hi another great video mate excellent motor mods. I was wondering how much difference these mods make to ease of starting and reliability. Have you noticed much difference with this 9.8 and the modified 5hp you did. Do you have estimates on power output on the 5hp and the 9.8 after modding. For instance would the modded 5 before the surface piercing prop compete with the standard 9.8. In your opinion. Cheers
Hi mate, Starting is just as easy as before modifying them which is nice, they both idle beautifully as well 👌 I did notice more of a difference with the 5hp I reckon. I don’t think the 5hp running full depth would keep up with a stock 9.8hp but I estimate it may be putting out about 7.5hp, but the speed comes from it being able to rev higher once surfacing. The 9.8hp I estimate being about 14hp and I’m not going to be able to see it’s full potential until it’s surfacing. It gps tested only 1/2 kph slower than a USA 15hp on my test boat. Cheers 🍻 Aussie Boat Guy 😎
Hi Mate, Not sure on the exact year model, most came out with a 20mm throat but a few came with the 22mm throat, I really haven’t noticed a difference in performance between the two. They also run slightly different jets. Cheers 🍻 Aussie Boat Guy 😎
Mate I'm going to do the same build with a flat slide and see how it goes . I'm trying to get a mad engine under a 6hp cowling 😂 you know the usual on the gold coast haha it's so fun 😊
Nice, that was kinda my goal 😁 Wait till the next few vids on that motor 👌👌 Lower unit mods are awesome too. I found it took all mods together to make the difference as the 9.8hp is already a tweaked 6 block.
Yes I see what you mean with the block sizing . I’d love to do a something like a motorcross cylinder in there on a custom case but the expansion chamber might be a giveaway 😂
Hi mate, Thanks, I appreciate your encouragement 😁 Yep, you guessed perfectly 👌 it gps read exactly 50kph on the dot. I’m hoping for 60kph or more 😁 Cheers 🍻 Aussie Boat Guy 😎
Hi. Wondering if you could advise me on my 15 Yammy. I've cleaned carb replaced plugs and get a stutter at 1/8 - 1/4 throttle when accelerating. Once she gets on plane it goes away. No fuel issues as I can run for 30min like that. Just confused at the stutter. Could it be timing?
Hi mate, Sone motors do have a splutter at that rev range no matter what you do. You could try fatten (more fuel) up the idle screw slightly and see if that helps, if not try lean it slightly and check the results. Many motors I have owned seem to have a miss at those revs especially if I am trying to run at those revs or take off really slowly. If I went full throttle past that rev range and then backed off to the speed I wanted it wasn’t very noticeable though. Cheers 🍻 Aussie Boat Guy 😎
Hi Champion, There is a lot that can be done to a 40hp Yamaha three cylinder two stroke, for starters you can put the 50hp parts on and have a 50hp. If more power is needed, you can get up near 70hp or more out of that powerhead with porting, carbs, exhaust tuner, high comp head. The porting is the science. Cheers 🍻 Aussie Boat Guy 😎
Thanks mate 👍 Oh man, so many hours, probably about 30hrs or more 😂😂 I actually didn’t count as it’s my downtime and hobby. There is more hrs to go on it too because I need to make a race gearcase for it then also modify props etc, so much fun 🤩. Cheers 🍻 Aussie Boat Guy 😎
Hi Mate, Good little motors but not much torque if the boat is heavy. Unfortunately I don’t have any insta or the like set up yet, I really should get onto that. You can message me here if needed. Cheers 🍻 Aussie Boat Guy.
@@25hpboatracerman I’m currently not getting any spark when I got the motor I was told it just needed a cdi box so I put one on it and still no spark coil packs ohm good what do you reckon it could be
Could be a few things. Those old mercs run pulser coils I believe under the flywheel, could be those, also try pulling it over with the cover off at night in the dark as you may see a spark earthing somewhere (a leak in the circuit). Could be wiring issues or kill switch earth or leads or spark plugs. Could also be the new pack you’re trying if it’s second hand. Fix by eliminating things. Cheers 🍻 Aussie Boat Guy 😎
Why not pop an AFR gauge on then you can tune it perfectly. Also EGT are a cheap great addition as EGT will tell you of danger before it’s to late and they tell you good info as well . Just absolutely a must in 2stroke world. Love my EGT.
@@25hpboatracerman you'd need to drill and tap into the exhaust tuner somehow like the big boys do with the v4/v6 motors. I have also installed them on the exhaust side of the cylinders. just gotta get the depth absolutely perfect for each cyl. not too hard.
Hi Champion, Correct 👌 Check out my other vids on that motor, it now has low pickups and running with prop shaft above waterline. cheers 🍻 Aussie Boat Guy 😎
Hi mate, I had a stainless steel hub machined. I made three identical blades, made a jig to hold them straight at the correct angle then welded them on. was a lot of work and would not do it again. cheers 🍻 Aussie Boat Guy 😎
I have the 8 HP version of one of these, it's only used as an emergency get me home motor. So wouldn't suit being a little racer. But i might cut the the head at some point. What is a good starting point for how much to skim by? bearing in mind I'm starting with an 8hp. Also what are the prop fitting options on these is it limited to Tohatsu/Mercury, any other other brands fit? Thanks in advance
Hi mate, Prop fitting is only Tohatsu/Mercury unfortunately. As for shaving your head, you can take a fair bit off the 8hp head as it’s a low compression head to start with. You can basically keep shaving it until your about 1mm off the squish band on the outer edge, an easier way is to just buy the 9.8hp head and bolt that on. Cheers 🍻 Aussie Boat Guy 😎
@@25hpboatracerman @25hpboatracerman Appreciate that thanks. I have the machinery to do myself so will do so. I was going to aim for about 145 PSI, I had a mercury V6 a while back and from memory that's what I skimmed them to. I'm in UK and can get 99 RON gasoline
That channel is a compression relief for starting (from factory) Doesn’t really affect too much a high rpm. I’ve done duel carburetor setups in the past, they look cool for sure but I really didn’t gain any speed. Cheers 🍻 Aussie Boat Guy 😎
A little help mate. In the title specifications does not have an apostrophe. Words need to ‘own’ something before having an apostrophe, such as Outboard’s specifications, you see the outboard owns the specifications.
Now he's taking you through the Obvious in Porting a 2 stroke Obvious if you know how a cam works on a 4 stroke - Timing open sharp and timing closed sharp and it's going to idle like an old lady push starting an electric wheel chair - it likes 7000rpm
Hi Mate, The outboard I modified actually idles really well and top end is great too. if I was to raise the port roofs a heap more I would have a poor idle but power band would be in the higher revs - like 8500. it’s ported for 6500 to 7500 so pretty mild. cheers 🍻 Aussie Boat Guy 😎
