New Boat / Terrible Hole Shot

[RIVERRUMMER 70]

what was the foil that was fitted on the cav plate ? just a normal plastic doel fin type or a nice drag plate type ?

MAKES NO DIFF WHAT IT WAS .....IT WAS THERE TO HELP THIS PROBLEM AND REMOVING IT MADE IT WORSE
THIS IS A NO BRAINER.
90 HP ON A 1500# BOAT NEEDS HELP EVEN IF ITS A GOOD MOTOR.
MOST THOSE FISH BOATS HAVE A BUILT IN FUEL TANK .....IN THE STERN.

[phillnjack]

if it has a big fuel tank and batteries at the back it will need a bit of help to get over the hump

I would put the plate back on after raising the motor as high as it would go, and definitely get a decent prop.
chuck some engine tuner down its guts and hope it bumps a bit of compression up.

definitely check out compression with a second gauge though, as it realy is low at just 100 to 105.

[stick]

I'll just put the foil back on for now and deal with it. Will fill the front livewell also and see if that helps.
The boat isn't holding water, but like most freshwater boats the fuel tank and batteries are in the stern. Someone told me that some of the older Javelin and Stratos hulls were stern heavy due to how the hull is designed.
I've ordered a tach. Once I get it installed, I can go from there.

[blacktruck]

The problem was pointed out and really simple, your motor isn't making much power, your compression is low. The foil and raising the motor won't help that. The motor height looks fine, you can play with it when the motor is running right. After a quick search, guys seem to run your boat around 46 mph to 49 mph with a 90 and 17' prop. So you're definitely running slow and losing tons of low end power. Fix that and problem solved.

[FMP]

Just to narrow it down and it has been done before, you did have the carbs wide open when doing that compression test? If you didn't and it test better at least you know a bit more.

[stick]

Just to narrow it down and it has been done before, you did have the carbs wide open when doing that compression test? If you didn't and it test better at least you know a bit more.

No
Didn't touch throttle. Removed the kill switch and spun it over for each cylinder. Cold engine.

[FMP]

First thing after dinner

[phillnjack]

Here is a vid I found of one of my old johnson v4 motors that compression was 100 at top left and 95 bottom left, 127 top right and 130 bottom right.

Lots of people will not believe this motor ran as good as it did, I owned the motor and could not believe the state of it when I took of the heads.

This motor ran ok , not 100% perfect but it got the 17ft boat out the hole and up on plane , but it had a bit of a ratlle to it between idle and 2,000.
it started absolutely brilliant for a v4 and sounded great on the trailer.

this is what one idiot tried telling me is a "Slight"gap between piston and bore . I think slight is a bit misleading.

but seriously you would not believe how good this thing ran in the condition of the insides. top is 100 psi and bottom is 95 psi.
I used two gauges showing just a 3 psi difference between them.

check it out https://youtu.be/X4Vs1b3Mzd8

[stick]

Update:
Got a tach installed and have got the boat out 4-5 times under various conditions and loads.
WOT RPMs with 2 people, 2 batteries, 8-12 gallons fuel is 5000 (choppy water every time, I'm sure rpms would be a smidge higher on glass/calm). Hole shot is a little better by filling front livewell, but I would like a little better.
I understand compression is low and the boat is probably wet, but it is what it is. The Johnson runs like a top. Fires right up, idles great, and no knock or rattles, so I'll run it till it quits.
Regarding the sluggish hole shot, would it be worthwhile to drill vent holes in the aluminum prop? I'm also not opposed to raising the motor, although that may not be best option with the AL prop.

[Flex]

Are your back decks glassed in? Or can you get in there to see if the foam is waterlogged? I would check there first. No telling how much extra weight some of the old boats are carrying.

Did you raise the motor up higher? I had a similar boat years ago with a 70hp. And it would run 41 loaded up and carrying me and a buddy and we are both 250+.

[phillnjack]

yeah vent the prop for better holeshot, it will work for sure.. not saying its going to fix the motor but will help a tired motor big time.
the vent size you will need is around 12 mm or just under 1/2 inch each hole ..

[stick]

Are your back decks glassed in? Or can you get in there to see if the foam is waterlogged? I would check there first. No telling how much extra weight some of the old boats are carrying.

Did you raise the motor up higher? I had a similar boat years ago with a 70hp. And it would run 41 loaded up and carrying me and a buddy and we are both 250+.

No way to get to foam without some cutting, but I'm sure the boat is heavier than it used to be. Haven't raised motor yet, but may at some point. I can get 38-39 mph so it's not all bad, but the with a heavy boat and a old motor it's a little sluggish getting on plane. As long as it runs, I'm going to run it. If it pops, I'll replace it.

[stick]

yeah vent the prop for better holeshot, it will work for sure.. not saying its going to fix the motor but will help a tired motor big time.
the vent size you will need is around 12 mm or just under 1/2 inch each hole ..

12mm at base of each blade I assume? I had a Stiletto on a previous rig that was vented like this from factory.
And I realize this is a band-aid 'fix', but I can't justify putting a $$$ SS prop on it.

[phillnjack]

ok lets start again
you have a worn out engine on a heavy arse end boat and have taken off the foil that helps get heavy rear end boats on the plane.
you also have a crap prop that will not bite like a stainless prop and wonder why it is not jumping up on the plane.

now first of all a vent in a prop is not a band -aid by a long way, its a way to get a prop to be a two-stage prop that even most big powerful motors have on them.
The foil will help a lot to lift the back end of the boat out of the water and only needs to be touching water until boat planes off, then it should be above water.


Unless you re-power or re-build the motor you need to
1 / sharpen the prop like a razor, ( you need all the help you can get )
2/ vent the prop or buy a smaller pitch (lose top end) ..venting the prop , even an alloy prop will give better holeshot, then act like conventional prop once on the plane.
venting just helps the motor get up into its powerband faster.
3/ fit the foil back on.
4/ make sure once on plane the foil is not hitting the surface of the water, if it is then raise motor bracket to get foil 1 inch above water on plane.
5/ keep as much weight as possible away from the back of boat
6/ give it a go with powertune to try and make compression come back and rings free for more power all round.

on top of all this make sure the carbs are sunced to each other, fresh fuel correct spark plugs with jump gap capable of atleast 7/16ths
check timing to make sure that is correct too.
any dings in the prop need to be filed or cleaned up, also check prop for run out and that all 3 blades are pretty much the same.


on the cheap you can get a 13 x 15 omc alloy or 13x 17 omc alloy, very different props to the old Michigan crap, and much better for your needs
if going stainless I would put a 13 x 19 Omc sst on it , vent it and hang on. again a cheap prop to buy seconhand on fleabay etc.

[Flex]

I have a 13 3/4x 17 and a 14x17 pitch I would sell cheap if interested OP.