Help needed to mod a 1980 Johnson V4 85hp

**spybot** · 06-15-2017, 03:10 PM

Hi all been reading this forum for a while now and had some really good ideas.
I have a 1980 V4 85hp Johnson. I want to tune her up to be a good fast not unreliable Loch (Lake ) Boat Engine
it will be going on my Dateline Bikini Similar to a Super Sidewinder.
So far i am looking at bigger carbs i have read that the 115 and the 85 are they same block and heads. The difference is in the carbs mainly in the throat diameter and jets.
I will have the ports done. I read about the " 9 page report " but i believe this was a 220hp v4.
I need as much help advice as possible please. I stay in scotland and trying to find anyone with info on moding a Johnson is near impossible.
I will look at lightning and balancing con rods crank ect ect but i dont want to push the motor to the point of a race engine and having to rebuild every few 100 hours. Just wanting a good fast lake boat.
I also want to try and dial out the chine walk im having with the old dateline. Possibly look at adding a pad or jack plate as the low pro sidewinder is almost the same hull.
So guys the floor is yours
Help if you can any advice gladly taken.

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**racer** · 06-15-2017, 05:21 PM

The nine pages was written for race type engines and too extreme for everyday type use.

**spybot** · 06-15-2017, 05:54 PM

Originally Posted by racer

The nine pages was written for race type engines and too extreme for everyday type use.

Is there any way that some of the ideas from this can be used to help in my quest ? Or should i just bite the bullet and go it on a trial and see basis ?

**olboatman** · 06-15-2017, 07:22 PM

I would think that any 140hp parts that can be used on that mota would be a good start. You may want to check to see if the 85 hp port timing could be changed closer to the 140s. I'm sure that some of the boys with v4 experience will chime in. Gary

**58Evinrude** · 06-15-2017, 07:33 PM

If that hull is the same as a Sidewinder I'm surprised you are getting chinewalk with only an 85 hp. I have had a Super Sidewinder and still own a Low Pro, both 16 foot. It took a 150 hp to get the SS fast enough to chine walk, at just over 60 mph. The low pro had a bit of chine walk at about 55 with a 115 on it, but I cured that by raising the engine on the transom.

**flabum1017** · 06-16-2017, 06:01 PM

Get rid of it and get a 2.4 or 2.5 200...............

**phillnjack** · 06-16-2017, 07:03 PM

leave the 85 as it is, the dateline bikini is a dangerous boat at high speed, they can and do blowout when you least
expect it.
dont try modifying the hull its a waste of time. and never go coastal with it.
the dateline bikini is a great looking boat, but thats it, its for looks only.
or maybe ok with a 50hp to keep speed down.
the bounty although looks almost identical is a totally different handling boat.

Here is my 1979 dateline bikini with its original 1979 70hp Volvo penta, even that at full speed was a bit too much for it.
on river and still water not too bad, on the coast a real nightmare of a boat.on the trailer looks great.

just keep it all standard and use the boat was it was meant for, upto about 40 with good pull away.
put a 15 pitch on it for ski-ing and a 19 for top end fun with 4 in the boat......

its like a glastron gt150 in that it looks a faster boat than it realy is, but back in the 1970's 40mph was
considered very fast for a family ski boat.

**FMP** · 06-16-2017, 07:16 PM

Really, that looks about as dangerous as a warm glass of milk

**spybot** · 06-18-2017, 02:20 PM

just keep it all standard and use the boat was it was meant for, upto about 40 with good pull away.
put a 15 pitch on it for ski-ing and a 19 for top end fun with 4 in the boat......

Hi philnjack
Thanks for the info on the dateline. I have had a bad chine walk at around 40 thats why i was thinking about the pad.
I put a set of trim tabs on her and that has seemed to cure the problem. All i want out of her is to be a fast ut safe speed boat for on the loch was going to attempt he coast but gave that a miss. She will only ever be in the loch. I dont know what prop is on her just not she maxed out around 35 to 40 (Dodgy speedo it started bouncing the needle) with 4 of us in her. I will not e towing any thing so should i be looling at a 19 or 20 even 21 ????
Any advise on these boats would be greatly appreciated as im totally new the world of classic speedboats. She is a 1980 model and has a 1980 motor.
Thanks for the tips on her and hopefully the advise on the prop

**71V153** · 06-18-2017, 02:24 PM

To 140-ize:

1 5/16 carbs.

Reed stuffers.

High compression heads.

Bubble butt exhaust manifold and chest.

**badbradviper** · 06-18-2017, 02:26 PM

Is there a link to the 9 page report

**71V153** · 06-18-2017, 02:28 PM

Need to know engine height, current propeller and RPMs before we can give you any prop advice.

**71V153** · 06-18-2017, 02:30 PM

Originally Posted by badbradviper

Is there a link to the 9 page report

It's on here, somewhere ...

**71V153** · 06-18-2017, 02:33 PM

Originally Posted by olboatman

I would think that any 140hp parts that can be used on that mota would be a good start. You may want to check to see if the 85 hp port timing could be changed closer to the 140s. I'm sure that some of the boys with v4 experience will chime in. Gary

Port timing's the same '78 up.

**spybot** · 06-18-2017, 02:38 PM

Thanks for that info 71V153
I will have the info needed for the prop next weekend (I only go to the boat at weekends. I possibly have the carbs and will search for the other items.here is a link to the report for brad
http://www.screamandfly.com/showthre...w-Thread/page2
Hope it helps others as well.