75hp and 6mph video. What am I doing wrong?

[blk98gt]

This is an 1961 Evinrude 75 hp starflite that has been sitting for a very long time. We didn't do much to get it running but when we took it out yesterday it would not even get to 7mph (per gps). We have a new prop on it which is a 10 1/4"x 10 (no through exhaust). I know the prop seems small but that's what the motor came with originally. The boat is a 14' open bow and has been sitting in a dry garage.
Problem #1 is the boat wont break 7mph with 3 people.
Problem #2 is it has a clunk fairly well timed in the video at 5 20 34 and 48 seconds. Feels like someone hitting the boat with a small hammer like a gear miss.
Please help before I want to get rid of this motor.

Running- http://www.youtube.com/watch?v=H-aOUIpLoJM
Idle- http://www.youtube.com/watch?v=qN9YJ7NOHKk

 

[bktheking]

Re: 75hp and 6mph video. What am I doing wrong?

Sound like it's misfiring, did you check for spark and fuel as a starting point?

It also sounds like it isn't running on all cylinders.

 

[blk98gt]

Re: 75hp and 6mph video. What am I doing wrong?

To be honest with you, we did not check all cylinders for spark. We figured if it idled well that we had good spark.
Here is the idle:
http://www.youtube.com/watch?v=qN9YJ7NOHKk
I should say this is not a problem at very low rpm.

 

[coolguy147]

Re: 75hp and 6mph video. What am I doing wrong?

you clean the carbs. also have you changed your t stat and impeller? seems like it should pump a bit more water at idle unless it wasnt fully warmed up

 

[blk98gt]

Re: 75hp and 6mph video. What am I doing wrong?

I kept a close eye with an infrared thermometer on the temp of the heads. Never read above 140. The water was freezing cold so it probably didn't need much of it. It has a new impeller too. Carb rebuild will be my over the winter project. I guess on Wednesday I will do a compression test of all 4 cylinders and check for spark on all 4. Can you tell from the sound in those videos if its running on 2 or 3 cylinders or all 4? Even with 2 cylinders running I would expect little more speed.

 

[bktheking]

Re: 75hp and 6mph video. What am I doing wrong?

On a 4, if only one bank is firing they won't plane and do exactly what yours is doing, they run like a dog! My 83 did it 2 summers ago from a bad ground on a power pack. Easy to tell , the head on the left was normal temp, the one on the right was cool as a cucumber. To the trained ear you could tell running on muffs but I had it on them the day before and had no clue one bank was dead. I know what it sounds like now! And yes they will idle well with 2 or 3 plugs firing, they just don't have the same sound as with all 4. You sure can tell though when you take it out, full throtlle and it's like have a 9.9 on the back.

 

[lindy46]

Re: 75hp and 6mph video. What am I doing wrong?

Check compression, check spark. Does it jump when it misses? Is it Selectric shift? Could be popping out of gear momentarily.

 

[LongLine]

Re: 75hp and 6mph video. What am I doing wrong?

Don't overlook the simple stuff. (like I did once) Make sure your plug wires are all snapped onto the plugs properly. It's definitely not banging on all cylinders.

Tom B.
(LongLine)

 

[blk98gt]

Re: 75hp and 6mph video. What am I doing wrong?

Check compression, check spark. Does it jump when it misses? Is it Selectric shift? Could be popping out of gear momentarily.

I will check all that Wednesday. It is mechanical shift. It does jump a little like someone giving it a kick. What is weird is that thump is well timed around 13-14 seconds apart.

For now what I am getting from everyone is that I am not running on all 4 cylinders.

 

[blk98gt]

Re: 75hp and 6mph video. What am I doing wrong?

Is the glass bubble by the carb that holds the fuel filter supposed to be full to the top? Ours would only fill half way up while running. Could that be a problem?

 

[lindy46]

Re: 75hp and 6mph video. What am I doing wrong?

Sounds like you're dealing with several problems. The "miss" or thump is probably a worn clutch dog which slips and causes the motor to intermittently slip out of gear. It will only get worse. If compression is ok, then the other problem is probably engine not firing on all cylinders. Check spark with a spark tester, available at an auto parts store for about $10. Make sure you have at least 1/4 inch blue spark on all four cylinders. If ignition is all good, then it's on to the fuel delivery. That glass bubble will not remain full when running.

 

[blk98gt]

Re: 75hp and 6mph video. What am I doing wrong?

Sounds like you're dealing with several problems. The "miss" or thump is probably a worn clutch dog which slips and causes the motor to intermittently slip out of gear. It will only get worse. If compression is ok, then the other problem is probably engine not firing on all cylinders. Check spark with a spark tester, available at an auto parts store for about $10. Make sure you have at least 1/4 inch blue spark on all four cylinders. If ignition is all good, then it's on to the fuel delivery. That glass bubble will not remain full when running.

You think I could just put the spark plug tip up against the block and crank to check for spark?

 

[bktheking]

Re: 75hp and 6mph video. What am I doing wrong?

That's one way to do it but the spark tester for $10 can be adjusted to measure spark distance, much more accurate. You could see spark but it won't be any indication of good spark.

 

[yorab]

Re: 75hp and 6mph video. What am I doing wrong?

ahhh...the oil sheen of a Starflite. Ain't it beautiful! But seriously, I believe that your low speed circuit in the carb could be okay, but that your high speed circuit might be plugged a bit causing intermittent issues only above idle. A carb rebuild can be done in little time. Maybe you should do that to rule out a fuel flow issue form the high speed circuit since you say that you are going to rebuild it anyway.

 

[kenmyfam]

Re: 75hp and 6mph video. What am I doing wrong?

You need a basic health check of the motor before taking a stab at things.

Compression
Spark
Fuel delivery
Spark plug condition

Go from there.
Check the Top Secret Files at the top of page 1 of this section for more info.