low top speed?

SKIBUM1M · Jul 27, 2009

I have a 1966 johnson 60 hp on a 1990 15 foot larson and my top speed is only 17 mph according to my gps. I took the carburator apart and it was spotless inside. adjusted the points to .020". set the timing belt. new plugs, wires, coil. what else could it be? I should be getting about 35 mph shlouldnt I? any ideas would be very helpfull.

SKIBUM1M · Jul 27, 2009

Re: low top speed?

After setting the advance bar a bit longer i now have a top speed of 19mph.

Boss Hawg · Jul 27, 2009

Re: low top speed?

SKIBUM1M said:
I have a 1966 johnson 60 hp on a 1990 15 foot larson and my top speed is only 17 mph according to my gps. I took the carburator apart and it was spotless inside. adjusted the points to .020". set the timing belt. new plugs, wires, coil. what else could it be? I should be getting about 35 mph shlouldnt I? any ideas would be very helpfull.

Always a bit learly when i hear that statement

I had the same problem & rebuilding the carbs (they also looked clean) solved it

Just my thoughts - i'm a loooooong way from be a exspert

Good luck

swordfish25 · Jul 27, 2009

Re: low top speed?

Does it make any difference when you choke it? How new are the plugs? What is the compression?

SKIBUM1M · Jul 27, 2009

Re: low top speed?

i did rebuild it since it was apart. I just was saying there were no problems and no plugged ports in it.

kenmyfam · Jul 27, 2009

Re: low top speed?

Load weight, load distribution, water soaked foam, motor height, trim setting and condition of motor are all contributing factors to performance. Start with the ones that cost nothing to check out and work up from there.
Good luck.

SKIBUM1M · Jul 27, 2009

Re: low top speed?

Plugs are 2 days old, trim settings dont seem to have much effect, load is just me and my two girls (3 and 1 year old) bilge is empty but cant get to the foam to check till this winter when i put a new floor in it. I have not been able to compression test it yet since the schrader valve in my compression guage is shot. should i mention that once I did have it take off and it really went fast one day. then the next it was slow as ever. i would have thought it was fine except that it did give me a hint of what it could do. Should i try advancing the timing by moving the belt ahead a notch or two?

kenmyfam · Jul 27, 2009

Re: low top speed?

Sounds like a failing coil ??? from your last description.
Just my 2 cents though.

SKIBUM1M · Jul 27, 2009

Re: low top speed?

the coil did fail a while ago. a new one was $150 so i bought a $20 car coil and ran a coil wire thru the vent hole in the distributer to the spring in the cap and it currently shoots a 1 inch blue spark. this is what happens when you give a boat to an automotive mechanic. lol

green4themoney · Jul 27, 2009

Re: low top speed?

Hahahhahahahaha

SKIBUM1M · Jul 28, 2009

Re: low top speed?

ok did a compression test today with a new gauge. 100 to 105 on all cylinders using the rope to turn it over.

SKIBUM1M · Jul 30, 2009

Re: low top speed?

woo hooo i got 28 mph out of it today. I found a used coil and replaced my jerry rigged setup with the stock coil. I dont really understand why a 12 volt coil run off the battery would cause a 10 mph loss over the stock magneto coil but im not arguing. Now i just need a manual so i can do a link and sinc and a little fine tuning to try and get a little more out of it but today i am happy and so was my daughter who was riding on the bow like a hood ornament.

low top speed?

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