hopped up the john boat

[Chevy1500z71]

been a while since i shared my little redneck creations with this forum,i pulled the john boat in the garage and cleaned it up a bit. as i was cleaning it i got to thinking, the 25hp johnson on  there is of the smallest hp rating that that particular power head is rated for, the largest being 35hp and the only difference is a larger carburetor. iv searched ebay from time to time for the proper carb with no luck. i gave up, the 35hp carb is probably in the ballpark of 33mm(probably smaller in reality), the one on there is probably around 28mm(also being generous). iv got a 34mm keihin off of my brothers 86 250r(he put a 39mm on it), its tuneable unlike an outboard carb and im basically dealing with a loop charged 500cc 2 stroke here, theres no reason i cant tune a 34mm carb to run like a champ on here and make an honest 35hp for next to free. i cut a peice of regular steel and tiged it to a peice of scrap exhaust pipe from an atv. i used a ruber adapter i found in the plumbing department at home depot, took an old chrome oil dipstick tube from a 350 chevy and bent it over to link the new carb to the stock throttle linkage using a peice of a  brake cable from a pedal bike, a leftover peice of summit racing brand braided fuel line from my truck, and a little bit of redneck enginuity. the pics explain the rest. lots of pics.







the manifold was about 35mm at the opening, so i lucked out there, pretty simple adaptation here.







how the throttle works with the new slide type carb, it used to push down a short linkage rod that went to the stock butterfly style carb. it just gets pushed down at some point through the timing plates curve, i set the throttle to move mush sooner in the timing curve to compensate for the extra air coming in. ill go over it with a timing light and tune it as well as the carb tomorrow.





and all finished up



the throttle is adjustable, i took a nut and drilled a small hole in it, i just feed the cable throuh the nut and tighen the set screw to set it, ill be replacing that huge bolt with a small set screw, remember, i did all this in a few hours and it needs to be cleaned up tomorrow.


old vs new



i also named the boat a while ago. if you have seen the boat, you'd get the joke lol, its a 14'x32" shallow gunwale riveted john with a sailboat longshaft 25hp johnson. the max hp rating is supposed to be 9horse, the transom is beefed up to say the least.







itl run about 30mph loaded to the max sitting 2" above the waterline with 3 people on board... it looks ridiculous, i actually have sunk it once in a pass. the boat started taking them over the side and filling up, if it didnt have that 25 horse i dont think i could have powered it through to some shallower water before it went under, need a new radio for it now. oh well, learned my lesson.

well im done whoring out pictures, tell me what you guys think? anyone tried anything like this before. still haven't ran it yet, tomorrow ill be firing it up and tuning it, might even get out and run it if the weathers nice(dont think it will be tho). i can never find any info on alternative carb swaps, maybe this can help someone searching google endlessly for info on this.

[NYRAPTOR]

Thats pretty freakin cool! keep us posted how it runs.

[Chevy1500z71]

started it up this morning with no main jet and it idled well, it even reved out but rich. so the needle jet is ok. threw a 230 main in becasue its the biggest i have and the biggest they make, runs great on it. it smokes a bit and pops on the down rev but thats exactly how it used to run, these things don't really like to be reved out under no load. all i had to play with was the timing curve adjustment and the throttle position per timing adjustment, im pretty much pissing in the dark here becasue i dont have a timing light at the moment but these omcs are easy to tune the timing, nothing like the old mercury tuning nightmares. i had to give it alot more throttle position vs timing curve which makes sense, and then i just dialed the idle in on the timing curve so that the timing sat where it used to with the old carb. it idles well and starts up good, it should be pretty close, ill have to get it on the water and start looking at the plugs and i should be in business. pretty pleased with how easily it was to dial in so far. as it sits its probably tuned just as good or better then from the factory, its not like these things were ever knows for butter smooth throttle response and smooth idles lol.

it revs out really quick, it sounds pretty healthy, i have a feeling iv got a lot more carburetor then even the 35hp models came with, cant wait to see how it runs.

[Chillinthemost]

Thats a cool mod. Do you have a tach? If it is truly making a significant increase in power you will need more pitch in the prop or chance over reving it.

[Chevy1500z71]

i do need to change the prop. i have a set of gauges, have a tach and a speedo, but the tach has never really worked well, it works when i run the boat in the driveway and always craps out by the time i get it to the boat ramp. im in the process of cutting a new dash panel for it so im going to rewire everything and get it all working, i need new switches and i need to get the live well working, i also put some cockpit lights in that i never wired in, i have some electrical work to do.

iv got more pics to come as i continue to get this project working. my brother tiged up a little reserve tank that mounts next to the carb so that the fuel pump will stop over pressurizing this carb and causing it to puke fuel from the overflow. i also made a new pickup with a return line for the gas tank since the new fuel system requires a return line to the tank.

how it basically works now is the main fuel line from the tank feeds the fuel pump, the outlet on the fuel pump goes to the little reserve tank mounted under the cowl, the reserve tank has 3 fittings, and inlet from the pump, a return to the gas tank, and a fitting on the bottom to feed the carb. what this does is create a non pressurized gravity feed effect on the carb since thats what it was made for, it cant handle the direct pressure from the fuel pump like the oem carb can. this will effect my tuning so i need to run it one more time with a working tac before i decide on my prop, right now im thinking 2 pitches deeper and add a cup. with this 4 blade prop im running the extra rpms really feel like i get alot more lift on stern of the boat, i think the 4 blade will work out fine so im going to have ti repitched rather then a new 3 blade, i know a 3 blade will go faster but i feel like the 4 blade really keeps the ass out of the water alot better in almost any situation.

i appreciate the interest and compliments guys, ill keep the thread updated with pics as it progresses.

[LakeMaryKid]

Awesome! That is a crazy lookin boat! I bet it will scoot with that motor.
Here is my 14'x72" mirrocraft with a 30HP johnson.


-Curtis-

[Chevy1500z71]

Awesome! That is a crazy lookin boat! I bet it will scoot with that motor.
Here is my 14'x72" mirrocraft with a 30HP johnson.


-Curtis-

sweet setup. wheres that at? im moving up to the lakemarry area in a few months to go to school, still dont know if im going to bring the john boat up or leave it back at my parents house.

the new fuel system setup is about done, ill grab pics when i can. the golf cart decided to break, iv got something in the works with it, building whole new custom swingarm/engine mounting plate setup that will swing off of some heim joints and have coil over shocks instead of leaf springs... thatl be another thread coming soon lol. iv been getting my moneys worth out of my welding class, my crappy mig welder doesn't touch the equipment im using in there to build this stuff.

[LakeMaryKid]

That's the St. Johns river. You ought to bring it. LOTS of places to fish around here. What school?

-Curtis-

[Chevy1500z71]

great to here ill have some good fishing up there, ill have to bring the boat. im Seminole state college. im doing the 2 year automotive program.

now that this thread has been brought back up i dont think i ever posted the finished product, its been running great, i just took it out earlier today. still running a bit on the lean side, iv been drilling out the main jet, they dont make one big enough.


need a return line now, the primer ball doesnt really get hard anymore since it just passes through the catch tank, kind of an unsure feeling pumping the ball now but it works good.

i just found out this motor is a crossflow after looking at the pistons... im pretty disappointed, i normally make fun of cross flows. thought for sure this thing was a looper, o well, i cant run pipes now lol.

[LakeMaryKid]

Cool deal. I'm majoring in Construction Management and Supervision there. They have a great automotive program! Let me know when you get up here, we'll get together and do some fishing and riding.

[Chevy1500z71]

cool, ill let you know.

[gearhead400]

Thats awesome, I love how you just put it together with random crap laying around, thats the best! 

[Chevy1500z71]

lol, you dont know the half of it man.

 thats pretty much how my projects are born, if you look over the boat half of those parts are free from various junk boats that people dump at the local riding spot. all the rod holders, steering wheel, steering box, deck latches, cleats, bow light, stern light, and throttle(or at least what my homemade throttle is built from) were all striped from junk boats. even the 1/2" pt for the deck up front was free. the transom is built from 2 road signs, more of the free 1/2" pt and parts of a craftsman creeper(the square bar), the trim tabs are built from a  road sign as well and the support bars for them are 1/2" square bar from a broken old craftsman creeper.

the hull itself was purchased from a freind for $20. the outboard was obtained pretty much for free, someone dumped a billy goat brush mower on the empty lot next door, thought it was junk becasue they couldn't get it to run, i got it running pretty good and repainted it and a guy traded me 200 bucks and the johnson for it, of course the Johnson was in "unknown condition" but it ran fine. i just get lucky with these projects. iv got more money in gas, registration and hardware then anything else.

wait till you guys see my golf cart thread, if i ever get it home from the welding shop at school ill get pictures, lets just say ill be walking out of my welding class with at least 100lbs of free steel lol, iv got coil overs and a link type setup that should yeild me something like 10" of travel with a swing arm, its pretty cool. itl be another thread.

[MedicMudder]

That boat is verykoooolll you will have a blast with it.I noticed a Fire Helmet in the background,who is the Firefighter in your Family?? I am
a Lt. with Jax Fire Rescue.

[Anoriginal]

This is one of the best threads on this site in a long time. I've enjoyed it and look forward to more posts/threads like this.  

[Chevy1500z71]

thanks, im glad you guys enjoy it. ill have another thread soon for golf cart upgrades. i dont really post on this forum as much as i used too but i know my little projects are always a big hit on this forum, especially the golf cart.

medicmudder, my dads the fire fighter in the family. i was going go that route too but i decided id be better suited as a mechanic.

[MedicMudder]

Thats cool you will prob make more $$$$$$ fixing broke stuff, not a lot of $$$$ in  Fixing sick folks  Good lluck in school