1969 20hp tuneup help.

[Birdup]

Ok, I have searched the forum and not found the answers yet. So here are my questions. My 20 Model# 20R69B is slow. I don't have a tach but the rpm's sound low (1500-2000) at WOT. The motor is on a 15' aluminium jon boat and empty with one person I get 12mph on the GPS. My friend with a 25hp on a heavy 18' jon thinks its funny to do circles around me on the way to our fishing spots. <br /><br />I have a book on order and I have a lot of 2stroke motor knowledge, mostly motorcycles. <br />My first guess is that it has something to do with the timeing advance. It starts easy and idles with a little surge. But at WOT I have really low RPMs. I have not checked anything yet. I am going to do a tuneup on it but I don't know what I should look at besides points, plugs, and wires. I have the tools and the time so please let me know what you think I should do to keep that SOB from doing circles <br /><br />Thanks

 

[BF]

Re: 1969 20hp tuneup help.

Hiya,<br /><br />It sounds like it is only running on 1 cylinder. They can often start and idle surprisingly well on only 1 jug. You can try pulling 1 plug wire off while it's idling to see if it's running only on that one cylinder. <br /><br />Also I'd do a compression test before doing much else. If you know 2 strokes, you know you need compression, spark and fuel. If compression's OK, then check spark. Even if the spark looks OK, I'd pull the flywheel off and replace points/condensers, and maybe coils (depends how they look). I bought a 25 hp this spring. Seemed to run OK, but 1 coil was badly cracked... I replaced both and the rest of the ignition. With bad coils they can loose spark at higher rpms or when they get hot, so seeing a spark when you turn it over doesn't necessarily mean it's good enough.<br /><br />I got a factory service manual for mine off Ebay...really helpful. Is this a new-to-you motor or did it just start running like this one day?<br /><br />Brent

 

[Birdup]

Re: 1969 20hp tuneup help.

It didn't do this last year. It ran like a champ and now it's just slow.<br /><br />Does anyone know what the compression should be?

 

[Paul Moir]

Re: 1969 20hp tuneup help.

Even, within 10%. There are no published specs.<br />90psi or greater would be good, but that depends on a lot of things (warmed up engine, guage, etc).<br /><br />BF's got you on the right track. If compression's good, it's probably spark. Compare how far you can draw an arc off each - that often shows the problem. Coils like to crack from age and arc over. New ones are cheap.

 

[marinemech]

Re: 1969 20hp tuneup help.

look to see if throttle is going to wot inside of carb if not adjust so that throttle plat is level at wot (i think your moter has a link which pushes on the throttle arm to advance throttle usually routed under the flywheel attached to the throttle arm)<br />just a thought and good luck

 

[Birdup]

Re: 1969 20hp tuneup help.

Ok I checked the compression. 124 and 123. From what I've read that's some good compression. I synced the carb and roller cam according to the book. I then pulled the flywheel and looked at the points and coils. Everything loked brand new. The contacts on the points looked great and there were no visible cracks on the coils.<br /><br />I didn't have time to run it after the sync. I'll do that tonight. How would you check the coils? I don't want to replace them unless I have to. I have two new coils and a tuneup kit that contains condensors, new points and plugs. <br /><br />What about the plug wires should I replace those too?

 

[BF]

Re: 1969 20hp tuneup help.

Good news about the compression. Did you check whether it was running on 1 cylinder or not? If it is running only one 1, and you knew which one, by looking at the spark you might see a weak/absent spark and tell if the prob's in the ignition. Then you could swap ignition parts from one side to the other, one part at a time and see if the problem follows the part or stays on the original cylinder. That'd let you figure out which is the bad piece... <br /><br />But this is still this assuming the problem is loss of spark on 1 cylinder... might not be the case (?). Did you look for spark before pulling the flywheel? Kinda sounds like you might've got ahead of yourself a bit... you're doing link/sych and going through ignition all at once to solve the problem. But... it doesn't seem we know for sure whether there's an obvious prob with the ignition or not. It could run on 1 cylinder for other reasons too, like a leaky crank seal causing an air leak.<br /><br />If things look good and are working, I'd tend to leave them on (e.g. plug wires). But, since you don't know where the problem is, you'd better do some troubleshooting. It's more effective than just throwing parts on a motor without figuring out what the problem really is. As an added bonus, troubleshooting also ends up being cheaper <br /><br />tell us what you've found!

 

[Birdup]

Re: 1969 20hp tuneup help.

I pulled the plugs and they both looked a little wet. I think on top of everything else it's running a little rich. I am getting good spark to both plugs. I will put it in a tank tonight and see if the sync did anything. If it still has low rpms @ WOT should I pull a plug wire and check for the one cylinder theory?

 

[BF]

Re: 1969 20hp tuneup help.

Yes, that's what I'd do. Even if you get a good spark when you crank it over, it could be intermittent spark (=your idle surge), that goes away completely at higher rmps (=run on 1 jug, power loss, low rpms). Does it run better/have more power when it's cold? Electrical things (e.g. coils) often change when they heat up.<br /><br />If you have one, you could also stick a timing light on a plug wire, and while running it check the timing, and you'd also be able to tell if the spark fails completely (light would stop triggering). Repeat on the other wire. <br /><br />If you can determine that the ignition is good, then you can look elsewhere. <br /><br />good luck

 

[Birdup]

Re: 1969 20hp tuneup help.

I had put this motor away for the winter and used another but now I want to get this fixed. I have a tach and it is running 1800rpm @ WOT. I'm leaning towards the one cylinder theory. I have pulled the plug wires and it still runs. I replaced the point and condensors and still the same problem. <br />I will put a timing light on it tonight and see what happens. I'll also try to draw a long arc from the plugs too. <br /><br />Some one said something about a crank causing causing this? How do I check for this?<br /><br />Thanks guys this board has been great.

 

[Paul Moir]

Re: 1969 20hp tuneup help.

I don't think you'd be down that far with a leaky crank seal. Usually that causes a problem at idle and part throttle, not at full. If the fuel pump was leaking really badly then it'll flood out the cylinder it's connected to, but the primer bulb would never get hard if that was the problem.<br /><br />Can you pull either lead and still make it run?

 

[Chinewalker]

Re: 1969 20hp tuneup help.

If you pulled each plug wire off one at a time and the motor is still running, then your problem isn't ignition. That test tells you a couple things - both cylinders are getting spark, compression and fuel. <br /><br />Now, the question is, are you getting ENOUGH fuel and enough spark? Your compression test sounds good, so that piece seems to be in place. The other two will tell the tale.<br /><br />I would check all throttle linkage - is the butterfly on the carb flat and horizontally level at wide open? <br /><br />- Scott

 

[Birdup]

Re: 1969 20hp tuneup help.

The throttle linkage is fine and the butterfly on the carb is flat and horizontally level at WOT.<br /><br />How do I check for the amount of spark. I can put it in a tank and run it but what do I look for. Should put a meeter on the plug wires? Some one said that the spark should jump a gap of 1/4" Is this true. If so how do I check that. Do I just hold the plug a 1/4" from the block?<br /><br />I just found my timing light this morning so I'll try that too.<br /><br />Thanks for the help so far.