6hp Johnson Seahorse power issue

[gsh]

I had it out again today to adjust the low speed and used a length of PVC pipe to extend the tiller so I could stand in the center of the boat. Max RPM on a flat stretch of lake was 4,000 rpm. With just me in the stern it was 3,750 rpm.

The things in the boat were;
myself,
12 V battery & Minnkota 50 LB trolling motor (in case I screwed up the gas motor)
3 fishing poles and a tackle box (might as well have some fun after the testing)

All total it was about 300 lbs in the boat.

At this point, I'm thinking that when they rebuilt the carb they did a lousy job on it because I could barely keep it running at 700 rpm when it was on "SHIFT".

I'll get a puller and check the points and spark as well, but I plan on rebuilding the carb because I don't trust the previous work.

 

[gsh]

I just tested the spark with an adjustable spark gap tester and it jumped a 3/8" gap on both cylinders. I'm guessing that the spark is good.

 

[racerone]

Any competent shop would have done many of those carburetors.----Hard to think how they could mess up on yours.-----Ignition is not in need of any work here.

 

[gsh]

According to the shop, they changed the water pump. If the carb isn't the issue and the spark is good, could it be something they did with the water pump? Incorrect impeller or something?

As far as the carburetor goes, I have no idea who actually did the work. It could have been someone with very little experience with older motors or someone very experienced. It's hard to say. I may not have a lot of experience, but I'm rather meticulous when it comes to stuff like that and I've rebuilt several automotive carburetors from the late 60's and early 70s.

 

[racerone]

Nothing to do with the water pump.-----Those carburetors are elegantly simple .----So take it apart for inspection.----And does this motor have the original lower unit or one from 1965 or earlier ?---Pictures ?

 

[Chinewalker]

Check that the black lever on the rear of the carb is getting full throw. I’ve seen some of those with the arm that operated the throttle off the cam on the mag plate where the cam has worn a groove into the throttle lever. If the groove is deep enough, you won’t get full throttle at the carb.

 

[gsh]

Nothing to do with the water pump.-----Those carburetors are elegantly simple .----So take it apart for inspection.----And does this motor have the original lower unit or one from 1965 or earlier ?---Pictures ?

The motor is all original. Not really sure how many hours were on it when I got it, but apparently the previous owner was the original owner and took pretty good care of it. Aside from some chips in the paint and a little dirt, it looks almost brand new. His son said he'd use it to get to a spot on the local lake and then sit and fish. Then use it to get back to the dock and put it away for weeks at a time.

 

[gsh]

So I rebuilt the carb tonight and tested the motor. The carb rebuild was actually pretty straightforward compared to some mechanical work I've done.

After the rebuild I tested the motor to be sure I didn't make things worse. It runs at least as good as before, but if there's any improvement I won't know until it's under load on the lake.

I did take a video of the motor at 730 rpm in neutral and then I sped it up to 1130. The motor had warmed up for a few minutes and I adjusted the needle a bit as well.

https://youtu.be/nChPA_0v0AQ

 

[Tim Frank]

After all this I think you need a bigger motor !!!!

^^^^ +1.
There have been several threads in here on the same topic. You have to accept that you are really pushing the envelope with only 6 HP. Weight distribution and trim are absolutely critical. The prop may be just too deep and too much drag to get to the optimum RPM range.
You mention that your daughter is 60 pounds and can drive the boat. Send her out for a loop and watch what happens. (is she able to get a tach reading?)

I had the Evinrude equivalent on a 12 foot Thornes tinny. With my daughter alone in the boat it would fly....planed right out and drawing little water. With two of us not so much.
IMO your combo is right on the edge and the performance is not at all unreasonable. I think that the time you have invested chasing probable phantoms is not getting you anywhere. Much better to be on the water.

What has changed? Maybe a few extra pounds on the driver.......slightly different weight distribution (with such a fragile performance window you have zero room for a negative trend) ....and the motor is another year older.

You mention in post 1 that the shop changed the impeller and did the carbs. in a later post you mention that they ALSO changed the L/U oil.
Check for water ingress. I had a L/U issue on the 6 HP and it had a noticeable performance impact.

 

[racerone]

I gave the 7 year old grandson a 12 foot aluminum with a 79 model 6 hp.-----Did not take long to realize it was not big enuff.-----He now has a 1963 model 10 hp Johnson and it runs like a charm , trolls all day long too.

 

[gsh]

^^^^ +1.
There have been several threads in here on the same topic. You have to accept that you are really pushing the envelope with only 6 HP. Weight distribution and trim are absolutely critical. The prop may be just too deep and too much drag to get to the optimum RPM range.
You mention that your daughter is 60 pounds and can drive the boat. Send her out for a loop and watch what happens. (is she able to get a tach reading?)

I had the Evinrude equivalent on a 12 foot Thornes tinny. With my daughter alone in the boat it would fly....planed right out and drawing little water. With two of us not so much.
IMO your combo is right on the edge and the performance is not at all unreasonable. I think that the time you have invested chasing probable phantoms is not getting you anywhere. Much better to be on the water.

What has changed? Maybe a few extra pounds on the driver.......slightly different weight distribution (with such a fragile performance window you have zero room for a negative trend) ....and the motor is another year older.

You mention in post 1 that the shop changed the impeller and did the carbs. in a later post you mention that they ALSO changed the L/U oil.
Check for water ingress. I had a L/U issue on the 6 HP and it had a noticeable performance impact.

Nothing has changed in my weight since last year. The only thing that changed was I took it to this shop.

let's say you took your car to a shop and told them to change the oil, rotate the tires and give it a tune up.When you got it back the fuel economy was down and it could barely climb the hill at the end of the street.

Is that because you're fatter and pushing the power limit of your car, or is it more likely that the shop screwed something up?

That's what happened here.

I had the boat out last year for the last time in early October and it ran great. Top speeds around 10 mph. Then I stored it on a motor stand in my heated garage for the winter.

This March, I took it in or a once over before the season started and when I got it back, top speeds are around 6.5 mph.

If nothing else changed from October to April when I finally put it back in the water, what would you think happened?

 

[Chinewalker]

Any number of things could have changed. It doesn't take much to prevent a boat from getting over the hump, particularly if it was marginal to start with. My 14-footer with a 6hp will BARELY plane off with me in it, IF I place a full tank of gas ahead of the middle seat. If the tank is less than half full, it won't get over the hump. If the tank is aft of the seat, it won't go. You may have had a full tank placed a little forward of where it is now. Or you may have had a little less fuel in the tank, placed further back last year. Maybe last fall you were wearing a parka and boots, and this year you were wearing a tank and flip flops.

And, yes, it could be the motor. Not likely, as there isn't much they can change to take performance out of it without you being able to see what they've done. But it could happen. Maybe it sucked in a spider, partially blocking off one set of reed plates. Maybe a bees nest got made in the exhaust housing, partially blocking off the exhaust. Anything's possible...

 

[gsh]

The 3 gallon plastic tank placement is the same, I don't have spiders or bees inside my finished and heated garage. I was wearing jeans and a sweatshirt that day. It ran great last year, but this year it doesn't.

I'm heading to the lake right now to check if the carb rebuild I did last night changed anything.

 

[Tim Frank]

If nothing else changed from October to April when I finally put it back in the water, what would you think happened?

If I had not run it in 7 months before taking it to the shop I would not be able to determine whether it was something that resulted from the storage period or the shop repairs.
But based on the routine nature of the work, I would not be looking to shoot the shop. This is just as much a nightmare for the shop as for you....and the reason many shops dislike working on motors of this vintage.

You never said what the compression values were last year, but there may be lower compression this year.

You ignored the question about the tilt pin, and that could be a critical part of this.

You also do not seem prepared to accept how little needs to change to stop this set-up from getting on plane; that is where your RPM are going....like it or not.

So shoot the shop....and the various messengers in here, but first, seriously, let an under-80 pound person take the boat out and watch it from shore. Then put a second person in and watch the drop off.

If you want to be fair, reasonable, and open-minded....ask the shop if they could run it in a test tank with a test wheel and see if it gets full RPM. If it does ( my bet) you will apologise for wasting their time and graciously slide out the back door.

 

[oldboat1]

IMO, the motor sounds a little bit rough. If mine, I would put it in a deeper test barrel (more water), and see if it runs a little smoother and with higher rpm with a leaner air/fuel mix.

Are you speeding up the motor by opening the carb with the cam follower? It looks like you might be throttling up without moving the timing plate. (can be a little risky, and doesn’t test combined ignition and carb operation.)

 

[boobie]

I don't know if it's been asked or not yet, but have you checked the exhaust for being blocked or not ??

 

[Crosbyman]

sorry to ask…. has the ignition been checked out like…. clean points...timing adjusted with the VOM method

http://www.youtube.com/watch?v=ga1Cjymj6ms&feature=youtu.be

how is the water coming out of the engine steamy hot hot tolerable ??

how is the boat underside… clean or cruddy

tried new plugs ? ….j6c I think

tank vent open ?? tried a new hose ?? (some have inner lining chewed up by ethanol)

spay some fresh fuel in the carb while underway…. does it pick -up speed ??

 

[Willyclay]

tank vent open ??

Is the portable tank one of the newer-style, EPA-mandated, self-venting types? Other forum members have reported similar issues with them.

 

[gsh]

I don't know if it's been asked or not yet, but have you checked the exhaust for being blocked or not ??

The exhaust isn't blocked.

 

[gsh]

sorry to ask…. has the ignition been checked out like…. clean points...timing adjusted with the VOM method

http://www.youtube.com/watch?v=ga1Cjymj6ms&feature=youtu.be

how is the water coming out of the engine steamy hot hot tolerable ??

how is the boat underside… clean or cruddy

tried new plugs ? ….j6c I think

tank vent open ?? tried a new hose ?? (some have inner lining chewed up by ethanol)

spay some fresh fuel in the carb while underway…. does it pick -up speed ??

If the new carb kit doesn't solve the problem, points are next on the list to check.

The water coming out is not really hot. Just slightly warm.

The boat is clean and smooth aluminum. Just a standard gray patina.

It has new NGK plugs in it, but I'm trying to find some Champion J6J plugs for it anyway.

The fuel hose is new as of last year and is still in great shape. I don't use ethanol for my boat. I can afford to buy a few gallons of the regular gas and the motor was designed decades before ethanol fuel, so it makes sense not to use ethanol.

The tank is also new as of last year. I may try opening the cap to be sure it's venting and not getting vapor lock.