mmurray70

Finally got my new engine running in my 48" woody. I got rid of the homelite and went with a 27.2cc stihl. Running much better now. Im really pleased with the new engine. Seems like it has really decent power. Its alot lighter and physically smaller then my homelite was too. I actually went back to the 280 prop and it spins it with much more rpm then my homelite could turn a 275 that was angled up halfway out of water! Heres a video: http://www.youtube.com/watch?v=syP3kc-NJcM

Still have a minor issue, my pipe tuning is off a little. It really rips the first lap or two, then once the pipe warms up it looses a little power. I cant go any longer without modifying the header I have now, and if i do its going to hang back over the transom a long ways. Should i make the header longer anyway or maybe go with a wet pipe to keep it cool and increase its tuned length? Any idea how much longer i need to go for being this much off (ie cold pipe working ok and performance dropping once its warm)?

martno1fan

Hi Mark she runs real good mate well done what header are you using now?maybe a wrap to centre will give you a bit more length without making the pipe hang too far over the transom,even a wrap forward header could work but you do lose a bit of power with those but might be worth a try.

bentley marshall

WOOHOOO that thing flys now makes mine look like a slug [&o] might have to look at a repower now

Dreamin Hemi

Great video. Looks very smooth on the water.

rigger freak

run's good, very nice place to run.

dwr9

The boat look like it runs great. How hot is the engine when you bring it in? It could be he pipe, but I doubt it. Is it water cooled or air cooled? Sounds more like an overheating problem to me. Doug

mmurray70

Not bad for a wood boat with a trimmer engine hey? I see people here everyday saying to just go and buy a zen and that youll never get decent performance out of a trimmer engine. I always wanted to prove them wrong.

Doug, the engine is fully modded and water cooled. It doesnt get very hot at all. Im pretty sure its the pipe. The engine gets a big boost of power from the pipe on its first lap but it just barely gets to the rpm where the pipe is really helping. It really winds out once in the video around the 17 second mark. So the pipe is on the short side of working properly anyway, by the time it heats up a little more its just tunned too high. Problem is worse with the pipe set shorter, doesnt really get the boost in power even with a cold pipe.

Its normal for pipes to change their tune as they heat up since the pressure wave travels faster in hotter air. I'm thinking a properly set up pipe will take a couple laps to get warmed up to really perform right. MX bikes are like this, they run like crap until the pipe warms up to proper temperature. I think its going to rip when i get that figured out tho. I cant believe im getting this much rpm with a 280 prop now. Im surprised, its alot better then I expected!

mmurray70

Heres some pics of the new powerplant...

martno1fan

Try a wrap to centre header that will give you a little more length.

y0ungbl00d

Sir, I'm new in this hobby and I'm trying to build a boat a bit like yours. I have a homelite engine and my problem is, what type of propeller should i get and how do I connect it to the homelite? Nice job by the way. Stihl really is a stronger engine than the homelite.

mmurray70

Thanks. Is it a homelite 25 or 30cc? Id say a Prather 275 or 280. My modified 25cc could barely turn my 275, i think a 270 would have been a little better (i didnt have one to try). A stock 25cc probably would have enough torque to turn a 275 and im sure a stock 30cc would have enough grunt to turn a 280. So it depends on the which engine you have and how its setup. Id say pick up a couple props and experiment with it.

You need a stuffing tube in your boat, i just used a 1/4" ID steel brake line. Then you use the flex shaft from your trimmer through this tube which connects to a prop shaft which runs through the strut at the back of the boat. Have a look for some pics. Lots of pics around of different strut setups.

y0ungbl00d

Thank you very much. BTW, mine's a 25cc.

mmurray70

Hey guys. Im going to run the boat again tonight or tomorrow to test a few more things. Do you guys think its any point to try my 275 prop considering its spinning the 280 with that much rpm in the video? Im thinking it would need to rev WAY higher with the 275 to match that speed and it may be pointless. Think its worth a shot or not?

martno1fan

Try it it takes 2 mins to change a prop and you never know till you try it ,other things you could try is a back cut on your 280 and removal of some tongue to let it spin faster .Try a back cut first,just file some material off the back edge of the blade to reduce its blade area .
Mart

jacob711

id say the 275 would be better, i have the same boat with a 28cc trimmer engine that i recently water cooled and done some engine mods to and running a tuned pipe and it is pretty much exactly the same performance as yours and i had a 280 prop on it and it was just like yours how power drops off after a few laps and it sometimes come back up but it would take the whole stretch of lake before it would get better again

but now i have a 478 on it and it is better but the power drops off if i don't keep at full throttle in the turns or if i take a turn to tight, i did also try a mates 275 and it was the best, the power never dropped off and it was quicker out of turns and in the straights it seemed the same or maybe a lil faster

do you mind if i post a vid and pics of mine

martno1fan

Another prop to try might be a x472 it runs great on my stock zenoah ,the new rmb props at whhobies might be worth a try too they have a 75 mm one and a x470/3 blader which might work ,its smaller diam but having the 3 blades might be ok to try?.I have one of the x472 ali props and theyre awesome,mine came sharp and balanced but theyre so lite you dont need to balance them to be honest.They also do brass too if you prefer.
Mart
[link]http://69.49.183.35/SearchResults.asp?Cat=37[/link]

mmurray70

Never had a chance to run it again yet. I made some turn fins and now im working on a set of trim tabs. Figure ill test it all at once.

Jacob, Yes go ahead and post whatever you have. What port timing are running on your engine? I still kinda think the loss of power after a couple of laps is a tunning problem. Im still thinking its mostly the pipe length. I mean if it has the power to turn the prop on the first lap, it should be able to do it anytime. I guess overheating could be another possibility too like doug said. My water jacket barely even gets warm, but i guess its hard to tell the temp of the cylinder thats underneath. Im gonna keep an eye to the temp of the remaining fins below the water jacket on the next run.

Ill give the 275 a shot tho. Not sure if my engine is going to wind out enough to really take advantage of it but ya never know.

martno1fan

Mark have you got your needles locked off so they cant vibrate and loosen?,if not take a piece of silicone tubing stick it on one needle then bend it over and put it over the other this locks them off.Might be worth trying just in case your needles are moving a tad which could account for the loss of power etc.
Mart

jacob711

heres a few pics of mine and i was going to get a new video but it kept stalling but i fixed that and then the the solder joint between flex and ferrule broke[:@] and the camera batteries went dead lol i will try again tomorrow

mods are as follows on my engine timing durations are 170ex (also widened 4mm) 145in (also widened 3mm), stock transfers, lightened piston, .015 squish clearance, fins removed from flywheel, walbro wa-82 carb (15.8mm bore 13.5mm venturi), and water cooling

the pipe length is what is causing the power to drop off on mine but it is adjusted out as far as it can go, as for it running good at first and then dropping off when warmed up i would think it is the way the pipe reacts to different temperatures

alloutcustom

Love your build, did you buy the engine used or in the trimmer? I work at true value and ive been planning out my "true Value" inspired build. I wanna use as much stuff from true value as i can. I was also wondering what pipe that is. Im assuming you made your own mount. How did you? Thank you for any help/tips.

mmurray70

Jacob thats very similer to what im running. Im using 165 exhaust timing, 145 intake, 22.5 blow down, widened all ports, 0.018 squish, lightened piston with boost ports added, only running one ring, and i put an angle on the leading edge of the crank weight to force fuel/air through the transfers, also using a 13.something mm venturi carb too. Also I had to switch to a homelite coil to eliminate the rev limiter and I set the timing at 30 DBTDC.

You should defenatly rework your transfers if their stock. You need to raise them since you modified the exhaust, and increasing area helps a bunch too. If you break through the casting up top (theres very little room) a little JBweld should do the trick. I've used some industrial stuff from Devcon that worked great but I would imagine JBweld would be fine too.

Post up some video soon! I'll do the same on my next run. Still working on trim tabs...

jacob711

i was thinking of opening up the transfers a bit because they are quite small but i wasnt sure how the engine would hold up with too many mods, with the transfers left stock on my engine and the modified ex timing the blowdown is 27 which is a little high but it seems to run ok, i am running the standard coil and it doesn't have a rev limiter,

i may do more engine mods later but at the moment it is a handful to drive, one thing that is really starting to annoy me is that the bow runs really low in the water in turns and if there is any chop in the water when turning the bow usually dives under a little bit and flips the back around and the motor sucks a little water and sometimes stops, i have tried adjusting the trim tabs way up and tucking the rudder in and out and using a turn fin and using no turn fin and using heaps of positive angle in the strut but i can still never get the bow to ride higher in the turns, in the straights it is fine though

mmurray70

Yeah the front is a little low in the stock woody. I did a 3d solid model of the boat and made some changes to each frame until I got what i wanted. I raised the front and sides a little, and went with a nice curved deck. Mine handles ok i guess. Cant really complain too much. Up until now I havent had any trim tabs or turn fins. Hoping to be able to dial it in a little better now. Sometimes it gets a little unstable in turns. I did flip it once on a rough day.

If your engine is gulping water while running just make a deflector. There was a post here a little while ago about how someone made one for a rigger. Id defenatly look into that. Injesting water with a high reving, high compression engine is not a good combination.

jacob711

ok i got a chance to get a video today, sorry its not very good but it was getting dark and there were ducks in the water so i had to slow down at the far end and there was an 8yr old manning the camera lol

i didnt get a chance to make any adjustments so it wasnt running very good but like i said it was getting dark and there were houses nearby so i didnt was to piss them off

http://www.youtube.com/watch?v=-aypgRLYvfg

FHHOBBIES

That 8yr old camera man did a perfect job! Nice project, gotta love Stihl.