Logo

New Jon Boat Problem? :-(

cody_stl

Member
Hi! New to the forum, first time posting here. Well, this is my first boat. I live in Central Missouri, so naturally I am striving to get a flat bottom Jet drive...but until I save that Money, I just picked up a 1970 14' V bottom jon boat with a 1975 Evinrude 25hp prop. I know it is a V bottom, but only the first third is the V, then it flattens out like a flat bottom...suppose they are all that way.

SO, the problem seems to be a fuel issue or an aerodynamics issue, I know aero has to do with air, but you catch my drift lol The boat with just me in it, gets up on plane, engine is humming at top RPM and we are cooking up the rivers pretty good. Everything seems as it should be. The guy who sold me the boat SAID that a 25HP on this short v bottom, pushes it pretty good. And I would say it is pretty quick.

NOW, add my father in the boat with me...and the boat most of the time seems as though it is only at 60-75% throttle...I have the tiller twisted as far as it will go, but the boat just won't get up on plane or get up in the RPM's. It seems as though something is holding the motor back, and the extra weight is just enough to keep it from cracking loose and getting up on plane.

What I have done so far is checked the fuel pump, seems to be pumping enough fuel, tho I have no baseline to know for sure. The timing is in order, and the points look pretty good. The carburetor I was TOLD was freshly rebuilt, and it does seem to be since the gasket on the bowl seems new. New spark plugs. And I have a tank of fresh 89 octane, so no old gas. When we got the motor, it wasn't running properly. After adjusting the points, new plugs, replacing a sheered off Keyway on the flywheel, and fixing the choke...it starts almost every time on the first pull now. Also, when the motor was mounted on the boat when we got it.. the anti cavitation plate was hanging about 2" from the bottom of the transom, and 5/8" or so below the keel, or V channel thing that runs down the middle of the boat. From what I had read, that was too low...so I added a 1" square piece of steel and raised the motor up about one inch. So now the plate is even with the keel, and about 1" below the transom. after running it today, It still seems as though even with the adjustment in height, the water seems to be riding at least an inch over the top of the cavitation plate...is it still too low on the boat? Are the fluid dynamics of the hull what is holding it back? I know it is riveted, should I try to smooth the hull out some, raise the engine more? Is there not enough fuel? LOL these are the questions pinging around in my head....it seems with just two adults of average size, this engine should be pushing alot better. I'm not sure how much I trust this guy....so maybe the carb does need some work. It just seems as though the engine is being bogged down.


Any help is appreciated
smile.gif
 
It really should be plenty of motor...truthfully the boat most likely is not rated to handle much more than 25 horse. The boat is riveted aluminum, so it is not very heavy. It currently has a 9x10 aluminum prop. Is there a better prop option for getting the boat to push more weight faster? My father was sitting in the nose of the boat...would him sitting in back make the difference?
 
Ummm SO I just drained my lower unit...and what came out looked like blackened water....no lubricating properties what so ever. What should I pour into the unit to eliminate the existence of the water before I fill it back up with gear lube? What could cause the lower unit to be full of what appears to be water??
 
what kim said above. you can take just the skeg off on that lower unit to check the prop shaft,bearings,gears and washers. there will be a groove in the skeg where it meets the the upper part of your lower unit that a seal sits in that looks like spaghetti that will need replaced(cant reuse it, ive tried lol!) and a o ring seal around the head assembley(part the shaft goes through before the shaft come out of the lower where your prop goes) that needs replacing after you remove the skeg. its pretty easy to check but if they are bad and you dont trust your ability then you can take it to get looked at. i will say this...finding just a used gearcase with the internals or without them will be a chore!! i looked for one for 3-4 years and finally got lucky and found a empty one for 100 bucks. i did see new ones but the oldest i seen was 1978 and they wanted 500 bucks for them empty. but you could probally find a 75 evinrude/johnson parts motor for a couple hundred bucks. and 75's are not the only year with the parts you need cross reference part numbers and id bet you have a couple years before and after thgat would work for ya. pm me and i can tell you where to check for a used lower if you want.
 
So, I just rebuilt the lower end as far as gaskets go, new impeller, got everything sealed up, and started it in the test tank. NO water coming out of exhaust relief. Something is wrong. I can't find out if I should have used sealer around the bottom of the impeller baseplate? Or what...
 
Ok, I got that fixed. Some RVT gasket and a lot of patience and she is spitting water like a champ. NOW I have to get the synchronization of the ignition/carb just right. Any pointers? I thought I had it synchronized right, but once I get the idle stop set to where I want it, so the RPM is low enough to shift, I recheck the synchronization and the roller is all ready past the marks on the cam when Idling! Which shouldn't be right...The manual I am using says that the roller should be center of the mark on the cam when the carb shaft begins movement....but my cam has TWO marks. So I am not sure if I should set the roller on the first one or in between the marks..it is a pain to try and get it right.
 
So I can set the idle properly. But the engine still has no power with a passenger in the boat. I am doing my best to synchronize the ignition with the carb...but I just don't think I know how to do it right. Once I think I have them synched, I set my idle screw. When I have my slow speed idle set, the roller on the throttle cam is PAST the second mark on the cam? Seems like at IDLE it shouldn't be past those marks on the cam all ready. Grrr. OH, and I checked cylinder compression...95ish in one and 85ish in the second. Is this good? Can't find the factory spec on what the compression should be.
 
Could the problem witht he lack of power with a passenger be related to a bad fuel pump? It pushes ok I guess with just me in it, when you add a passenger it dogs way WAY down. Could that be a fuel problem? Or do you think compression or ignition?
 
Do the simple tests.---Does the primer bulb go hard ?--------------Do you have strong spark on both cylinders ?----------What is compression like ?
 
Primer bulb is fine, great spark and new plugs, and the compression is 95psi in one and 85psi in other. I am starting to think that 90psi is LOW for this motor. Maybe the piston rings are stuck...maybe they need replaced. Wondering if I disassembled the motor to change the rings...what other parts would be required to be changed...bearings, gaskets etc etc.
 
The prop on it is a 9x10, which is stock for that motor I believe. And it is only a 14' aluminum boat...nothing heavy at all. It seems to push hard, and get up to plane and speed with just me...but add one more 180LB adult, and all bets are off....won't even get up on plane. If it is not the compression, I think it is still the synchronization. Getting the carb and ignition together. here is something interesting..I rebuilt the transom...it was about 3" higher than it was when I got the boat. Started with it at that height and figured I would trim it down as I needed until cavitation was gone and it ran right. Took it out yesterday, and it cavitated BAD...I mostly just putted around to avoid it and did some fishing. BUT, on the way back to the ramp, with me and my dad, I let it eat...and it got up on plane and was cookin right along, even though it was cavitating....weird. SO, I cut 1 1/2" off the transom last night and went again today..no cavitation, BUT would NOT get up and on plane again...surely it isn't THAT touchy when it comes to engine height?? The cavitation plate as it sits, is ABOUT 1" below the hull...yesterday, it was a lil less than an inch ABOVE the hull and would cavitate constantly.

I double checked my fuel pump today, it puts out good fuel. My carb is good. The points are gapped appropriate and are new. It HAS to be synchronization, compression, or engine placement on the transom. This is just starting to cost me a fortune in gas, nearest body of water with sufficient depth to test in is 35 miles away! Gimme some ideas, cause next time I go to the river...I'm taking every tool I own with me...that motor will run right...or will be a new structure for small fish to reside in :)
 
EvCamMArks.JPG These are the marks I am using to "Synchronize" the carb with the ignition. I THINK the marks I am supposed to be using are the marks shown on the cam, further to the right on the picture. BUT, why are there also 2 marks up above them further center in the picture? Coincidence?

Here is a link to the online manual I found http://boatinfo.no/lib/evinrude/manuals/1971-1989johnsonevinrude.html#/0 Only problem is it is kind of vague. And I can't make much sense of this part. Page 233 - 235 for those who would be kind enough to look at this and tell me what they think, or interpret it for me. Also, My engines designation in the book for that part is C-6...and the adjustment note for it is "Note 4" in the appendix, page 603.
 
K, I think it didn't post my first pic...SO...EvCamMArks.JPG I have been setting the synchro using the two small marks on the cam itself, pointed out by the arrow furthest right in the picture. BUT, there are two marks above the cam, pointed out by the arrow center of the photo. Also there is an arrow pointing out the cam follower/throttle link itself. Am I using the wrong set of marks to do the synchronization?
 
Photo07020346.jpgThis is what does not seem right....with the roller synched to the lower two marks on the CAM...and then my slow idle set where it idles nice and slow for good shifts...THIS is where the roller is situated. It seems like if the throttle first starts to open back at those two marks..my idle shouldn't put the follower this far up the cam. With it set at this, and in neutral, the throttle practically won't move either way, what with the idle stop screw stopping it one way, and the neutral position throttle stop stopping it the other way. Something isn't right I don't think.
 
Right. So it is NOT odd that after that, and after setting my idle, the roller is half inch past the marks on the cam, where the throttle began to open?
 
Yes, and the shear key is new too. The point gap we set at a "loose" .020, or.022 if you will. And yes the flywheel is torqued down appropriately.
 

Based on my experience 25HP is definitely not enough. Ihave a 13' flat bottom boat with 25HP motor. With fullthrottle it takes quite a while to get to up to plain with 2 full sized peoplein it. The motor struggles and develops the full revs only after it gets into full plain. So, if you do not get into plain your motor will be struggling. I actually stand up and lean forward to help in the process with the other personsitting forward. A V hull will give you a better ride but it does push morewater.
 
http://www.youtube.com/watch?v=eOOMEYHQsVA This is a spitting image of my motor and boat. This motor takes off hard and gets on plane fast...keeping it's RPM's up the entire time it is on plane. Mine lags in its take off, and most of the time the RPM's are not this high when it IS on plane..plus addd any weight and it prolly won't get on plain. This video is a grown man with 4 small girls...which about equals another grown man in weight... lol I am taking it to a local marine mechanic to have it tuned next week, hopefully with positive results.
 
Curious...I know it is too much motor...but how much is too much lol I just found a 1976 70HP Evinrude for sale cheap...I knowit is a lot of motor for this boat...but is it totally un do-able? I have a 2x8 transom that has three aluminium braces. And eventually would be using the motor on a different boat...but for the price I was thinking of picking this motor up. How much different would the weight of this motor be compared to the 25 I have now? For only $500 for the running motor with controls, I can hardly pass it up. Maybe even convert it to a jet for my next boat.
 
Update : Found the problme all along! Why the motor didn't make power, why it would not keep it's RPM's up, why it wouldn't push moderate weight. And the winner is....BLOWN HEAD GASKET! When I couldn't think of anything else, I popped the head off to see a big blow out in the gasket near the top cylinder. There was water in the cylinder. This explains the low compression, lack of power, and difficulty in setting the idle speed. I am replacing the head gasket and both exhaust housing gaskets for good measure. This should get this engine running properly....Finally :)
 
Back
Top