'78 35 HP Seahorse not running full power @ WOT

Hello,

First post on the forums. Have gained quite a bit of knowledge lurking on the forums but really havent had any q's until now.

Motor is 78 johnson seahorse tiller w/ electric start. Seems to be a fairly common and dependable motor. Owned the motor for 3 years or so and it has ran good until this past week.

Fishfinder has logged speed at around 20 MPH or so at WOT in the past.

Problem:

Motor not running at full power. Motor is now running at around 8 mph at WOT instead of 20+.

Symptoms:

Motor ran find last time out on boat.
Motor began to ran fine then once i hit WOT it bogged down to around 8 mph or so.
Turned throttle down, opened back up, went up to high speed then bogged back down to 8 or so.
Did this around two or three more times.
Now the boat will only go 8 mph at WOT.


Ive tried pumping the bulb and this doesnt help one bit.

Gas is fresh and new.

Spark plugs were replaced around 6 wks ago (could they be bad already?)

Motor is shooting out water at a steady stream.

Motor starts fine, idles fine, runs fine and seems to do okay at 8, just doesnt have full power!

Any ideas what this may be?

Looking forward to responses. Hopefully I can save myself some $$!

Thanks

Re: '78 35 HP Seahorse not running full power @ WOT

bump

Re: '78 35 HP Seahorse not running full power @ WOT

clean the high speed jet just not with carb cleaner stick wire through it to unclog
like electric wire three strands should do it, while your at it rebuild carb

Re: '78 35 HP Seahorse not running full power @ WOT

confused ..are you still at WOT when it drops to 8mph..or does the engine it self drop rpm's also....

if the engine drops rpm's....may be time for a cab rebuild and cleaning....get a bread tie wire and clean out all the orfices even under the welch plug...put all the new parts in...but make sure you wire.. spray.. and blow out the jets and orfices....

now if you motor is still running the WOT rpm's and it just slows down drive wise..you may have a spun prop......

what is your RPM's when your doing 8mph.....

Al

Re: '78 35 HP Seahorse not running full power @ WOT

The engine drops rpms... just sort of bogs down to 1/2 power or so. The first couple times it would open back up and try to go full power then would bog back down and do the same (rpms drop), now I open it up and rpms wont go all the way up and it just hangs at around 8 mph @ WOT.

Hope this helps.

Al-53 said:

confused ..are you still at WOT when it drops to 8mph..or does the engine it self drop rpm's also....

if the engine drops rpm's....may be time for a cab rebuild and cleaning....get a bread tie wire and clean out all the orfices even under the welch plug...put all the new parts in...but make sure you wire.. spray.. and blow out the jets and orfices....

now if you motor is still running the WOT rpm's and it just slows down drive wise..you may have a spun prop......

what is your RPM's when your doing 8mph.....

Al

Click to expand...

Re: '78 35 HP Seahorse not running full power @ WOT

you could be running on one cylinder as well...pull the plug wires off the plugs one at a time, if no change to idle or wot...that cylinder has no spark...to test fuel side...at wot spray some fuel mix in the carb throat..if it picks up...it needs more fuel....if it bogs..fuel mix is probably ok...these tests will give you a starting point

Re: '78 35 HP Seahorse not running full power @ WOT

check spark, compression, and check carb linkage, it may have slipped and you are no longer sync'd, quite a few times the set screw loosened and my motor wouldn't run right.

Re: '78 35 HP Seahorse not running full power @ WOT

I have heard of this problem a bunch whist browsing this forum.
I had the same problem this spring with my 1982 evinrude 35hp.
I did a fuel pump rebuild kit and it didnt fix it.
I got a OEM manual off ebay and removed and cleaned out the carb and did a carb rebuild kit before I put it back on. I also put all new fuelline whilst I had it apart. I also noticed that I was missing an O ring at the connector from the fuel tank to the actual outboard.
I cleaned everything pretty well with carb cleaner. I did not mess with the little lead shot deal under the cap on the top side of the carb. Thats about it.

It run good now.

I never did identify the specific problem.

Hopfully this helps any.

I had no prior experience with outboards but the OEM manual helps a bunch.

Re: '78 35 HP Seahorse not running full power @ WOT

I had a similar problem with my 1977 Evinrude 35 HP. The bottom line is, I replaced the "fixed high speed jet." The high speed jet was partially blocked after having some bad gas (water in the gas).
This is what I did........after viewing this forum:
I knew I had new plugs and spark.
1. Removed the starter to get access to the carburetor.
2. Cleaned and rebuilt the carburetor.
3. Replaced the squeeze bulb on the gas tank.
4. Replaced the gas connector from gas tank to the motor, (This resulted in new "O" ring and all other parts in the connector).
5. Replaced a hardened hose from the "gas connector" to the fuel pump.
6. Rebuilt the fuel pump. Tested the fuel pump with plastic hose and bottle. It worked great.
7. Replaced a hardened hose from fuel pump to carburetor.
8. Replaced the "fixed high speed jet" ($8.00) at bottom of carburetor bowl. I used an extractor to remove the old high speed jet. I put oil on the tread and installed the new high speed jet.
After the rebuild, the motor ran great. I wanted to share this with the readers. Thanks to all the help I initially got from this forum.