Help, Johnson 18hp is to slow!!

[hondarider188]

my 1960 Johnson 18hp is in my opinion to slow when at wot. i have used a gps yet but i would take a guess of about 10mph. i replace the coils/condesor's/points/plug wires/plugs then i have been running it with a new tank with new gas and oil. it runs good but every now and then it skipps a beat and it ssounds like a backfire but if i richen it in the high speed it stops and the same for low speed. i cleaned out he carb with brake cleaner and compressed air then cleaned out the needle(was sticking). then i just recently changed the gear oil, i blelieve it was the first time changed in like 20 years. but i have not yet ran it since then and the top seal on the venting srew is bad and oil is leaking out of it, so i will put a new o-ring on it. but could hte bad thick sludge (old oil) be causing drag? boat itss on is a 1961 feahtercraft cico ll with a V bow and a flat stern. the load is full 6.5 gallon tank with small tool box two average size, people 2 tackle boxes and poles then small clamp on 25lb thrust trolling motor wiht battery in bow. it also has a full steering and dash. so a dry weight for this boat is about 200lbs. when at wot the boat sits right on the edge of planing out and just plowing on threw if you go and stand in front of bow it just drops back down and slows down even more. and if you look in my restoration of hte obat you will see the hull and its shape heres trhe link
http://forums.iboats.com/showthread.php?t=506700

heres is the boat at feathercraft.net with all hte specs. on the last page of the catolog.
http://feathercraft.net/FCCatalog1961.htm

 

[fireman57]

Re: Help, Johnson 18hp is to slow!!

If your engine is running at the proper rpms at wot then it sounds like you might need to trim your engine. Did it used to plane the boat?

 

[hondarider188]

Re: Help, Johnson 18hp is to slow!!

i dont know about the rpms i dont have a tach. on it. and i tried trimming hte engine once and i moved it up one notch and i didnt notice a difference. so i moved it up one more and it just lifted the bow up more. hten there is only one more notch up and i havnt tried it yet. as long as we have had it it hasnt but since the last time it ran like ten years ago. and my dad says it runs better thatn when he had it ten years ago, but i never have asked my grandpa how it did before we got it. but from what i have read on this forum i should be going about 20mph. when i am running it at wot the water behind me looks almost like i am on a plane but just not quite and the bow never drops down at all. i think i forgot to mention it before but the prop is i htink stock as a 9X10p and it has a few little dings and what not. so i am going to file it smooth and see how it does. and dont worry about me filing it down to just a nub my dad used to do it to airplane props all the time so they would perform better. and i still think new gear oil will help it out alot letting it turn the prop over easyer. the old gear oil was just like a really thick sludge and took a while to drain out.

 

[lindy46]

Re: Help, Johnson 18hp is to slow!!

Yeah, that thing should be running like a scalded dog. Did you check spark with a spark tester? Did you torque the flywheel down properly? What is the compression?

 

[hondarider188]

Re: Help, Johnson 18hp is to slow!!

i did use a tester that just lights up nice and bright when it has good spark. and it has a bright blue spark. and the flywheel is torque down to 50# and i havnt used a gauge but it has really good compression. last time i ran it i did a 32:1 fuel mix but i found out it should be 24:1 so i will remix it. and i think i will gapp the spark plugs and points again. and i am running champion J6C's and Autolight 303's both are what engine says to recommend in it and a couple of other plugs but same brand so would a hotter plug be good to.

 

[fireman57]

Re: Help, Johnson 18hp is to slow!!

stay with the champion plug, don't use anything else.These engines were designed around them.

 

[hondarider188]

Re: Help, Johnson 18hp is to slow!!

even though on the front panel of the engine is says autolight two?

 

[fireman57]

Re: Help, Johnson 18hp is to slow!!

yes. I think that everyone on this forum has tried every brand of plug out there and Champions work the best in these engines. You might pull the prop off and make sure you don't have fishing line or weeds that are binding up your prop shaft. 50 footpounds seems awfully light. You might want to recheck the specs on it and make sure it is not sheared.

 

[wilde1j]

Re: Help, Johnson 18hp is to slow!!

Does motor have high and low speed mixture adjustments? If so, are you sure they are correctly set? Makes a big difference in power output.

 

[hondarider188]

Re: Help, Johnson 18hp is to slow!!

what about a hotter plug would that work i know i will be doing a lot of trolling but what is recommend on a plug for it. and would J8C's be the next up for a hotter plug? and as for the flywheel 45-50 pounds is what i was told here on iboats. and the key on it has some damage and i thought that could be and issue from the start, i do have another key so will have to change them out but how exactly does the key come out and how does the new go in? then the mixture adjutments are pretty close to where they need to be so i dont think that just a touch off would make that much of a difference.

 

[fireman57]

Re: Help, Johnson 18hp is to slow!!

if the old key is not sheared or bent then I would leave it alone. If you do have to change it I use a high quality small screwdriver and a hammer to get in behind it to dislodge it. You might be able to grip it with a pair of channel locks if there is enough sticking out and wiggle it. If you low speed is set at a nice idle you can always fiddle with the high speed while someone else drives the boat. I would only use a hotter plug if I did a lot of trolling so it didn't load up my spark plugs. I'm not sure if your prop has the rubber in it or not. If it does scribe a mark from it to the lower unit. When you run the boat for a little bit a wot stop and see if the marks still line up.

 

[hondarider188]

Re: Help, Johnson 18hp is to slow!!

where exactly would i draw a line on the rubber and where is this all located on the prop and lower unit. and a picture would be nice if its not to much trouble.

 

[fireman57]

Re: Help, Johnson 18hp is to slow!!

just scribe a line on the backside of your prop where it meets the lower unit. You can use a sharpie if you like and draw a line on your prop and continue it on you lower unit. Basically you are drawing a line on both so when you run the boat you hope they stay in line. If they don't then your prop needs to be rehubbed. The rubber in it has broken loose.

 

[samo_ott]

Re: Help, Johnson 18hp is to slow!!

Yes, it should go around 20mph on that boat. Spun prop? Low compression? Running on one cylinder? Those are the standard issues.

 

[hondarider188]

Re: Help, Johnson 18hp is to slow!!

it is running on two cylinders and has good compression but for he spun prop i have know idea.

 

[kfa4303]

Re: Help, Johnson 18hp is to slow!!

Hi hondaraider. AS for the spun hub test, remove the prop and take a Sharpie and draw a straight, level line across the backside of the prop. Making sure you scribe across the inner/outer edges of the prop and hub. Now reattach the prop and run the motor up to speed in an attempt to induce the spinning. If/when the motor has run at WOT for a bit, stop the motor and remove the prop again. If the line(s) on the back of the prop is no longer continuous, then you have a spun hub. You may want to triple check the carb settings too. The lack of high end speed may be due to the hi speed needle being incorrectly adjusted. I agree that the 18hp should run you close to 20 mph, or so, under normal load. If the carb is ok, and the prop is ok, then you may need to look at the ignition. Coils can sometimes knonk out under load which can ruin performance at the high end while still giving surprisingly good low end performance (considering the motor is only running on one cylinder).

 

[hondarider188]

Re: Help, Johnson 18hp is to slow!!

k thanks for the help, it will be awile before i take it out for i am in the middle of repainting the boat.

 

[Bidget]

Re: Help, Johnson 18hp is to slow!!

I know I'm late on this, but I have one of these. mine's a 61 sea king 15 ( johnyrude ) When you make adjustments to the carb, are you getting a change in motor function? reason i ask, mine had some funky symptoms (everything perfect and still ran bad) then i took the carb appart for the 8th time and reallized the slow speed needle did not come to a point. It had siezed and broken off in the hole. "so that's why slow speed adjustments didn't do any good!!" it was hard to get out but with the hole cleared and the new needle installed, we got so cocky that we were on the other side of the lake before we spun the prop and had to limp home.

 

[kfa4303]

Re: Help, Johnson 18hp is to slow!!

Hi Bidget. Give this a read and see if it helps.


http://forums.iboats.com/showthread.php?t=167352

 

[hondarider188]

Re: Help, Johnson 18hp is to slow!!

thanks for the help guys and bidget it is never to late because i still havnt taken it out yet for i just barely got the boat finished and put back together. and the only thing i forgot was to install the bow light:facepalm:. but i will have to do it tommorrow maybe. and if you guys want to see the boat before i go to the lake and wash off all the paint just click on this link to my restoration thread
http://forums.iboats.com/showthread.php?t=506700