'67 lurching/backfire when running

[yodel3]

1967 20hp johnson

starts fine
idles ok

Runs fine but every minute or so pops/lurches and the whole boat shutters. It feels like I hit a submerged rock or something. I assume this is a backfire. It is violent enough that I'm getting jittery about running it at all.

any guesses?

new points last year
key is good i think
new condensers
points gap .020

Thanks for your help.

 

[tx1961whaler]

Re: '67 lurching/backfire when running

Usually when somebody describes something like "feels like I hit a log", the is a worn clutch dog in the lower unit.

 

[asdasc]

Re: '67 lurching/backfire when running

Perhaps you actually hit a log?!

Or it COULD be a lean sneeze, although they aren't that violent typically. Try opening up your high speed jet about a quarter turn richer. If that takes care of it, it was a lean sneeze.

The clutch dog would be felt whenever you get above a certain speed under load, and if you throttle up from there it happens alot. I thought I had a bad clutch dog once but found that the two parts of the shift rod weren't connected right and it was so far out of adjustment that it was slipping.

I highly doubt it is actually a backfire. I don't think it would run if you were 180 out.

 

[coolguy147]

Re: '67 lurching/backfire when running

on the misadjustement inccident i had the same thing happen to me( shift rod) might need a carb clean if its a lean sneeze

 

[yodel3]

Re: '67 lurching/backfire when running

how can I tell if the shift rod is right?

 

[asdasc]

Re: '67 lurching/backfire when running

I am pretty sure that your 20hp is the same as my 18hp down below. If not, someone please correct me. About halfway down the leg on the right side is a vertical plate held on by 2 flathead screws (never remove a phillips screw). Pull the cover. Inside is where the upper and lower shift rods get tied together. In the end of each rod is a groove, which makes it look like there is a ball right at the end of the rod. The 2 bolts you see in the clamshell each go thru one of the shift rod grooves. Carefully, pull the bolts one at a time and using a flashlight while jiggling the shift lever make sure that groove in the rod is aligned with the bolt hole. Then put the bolt back in and snug it up. You don't have to tighten it down super hard, or you can strip it. The bolt going thru the groove holds it, not the clamshell force.

Good luck with it!

 

[yodel3]

Re: '67 lurching/backfire when running

thanks guys.

I reconnected the rods today. Hopefully that will help. they didn't look too far off though.

If the problem is the clutch dog, does that mean that the forward gear is also wrecked?

 

[asdasc]

Re: '67 lurching/backfire when running

Not always. Once you get it apart you will know for sure.

The key is to throttle way down before shifting into gear, and then snap it into gear, don't try to ease it in.

If you are adjusted right, you will be amazed how round the clutch dogs can be and still hold on tight.

 

[yodel3]

Re: '67 lurching/backfire when running

re-connected the shift rod just to make sure but I took her out tonight and shes still doing it. Ok at very low speed but throttle up just a bit and it happens instantly. I will remove the gears tomorrow and post pics.

If I do have to look for the whole lower unit, which years could I use for the 67? Most parts catalogs begin at 68 for some reason. Will that one work?

 

[asdasc]

Re: '67 lurching/backfire when running

I would search on eBay. Gears new would cost a fortune. I think most any lower unit from a Johnson/Evinrude 15/18/20 HP from late 50's to early 70's would fit. You can normally find them for $50-80 complete. It can be a crapshoot, but manytimes works out fine. New gears may be hard to find and very expensive.

 

[zinc]

Re: '67 lurching/backfire when running

Just my 2 cents worth.
I used to have a johnson 40 that did the same thing....
sounding like you hit a log or something.
clutch dog was worn.....soooo I flipped the gear set around,
forward gear and reverse gear are the same along with the clutch dog.
(forward gear was now the reverse gear and vice versa.
What started out looking to be expensive, really turned out cheap.
Hope this helps

 

[yodel3]

Re: '67 lurching/backfire when running

anyone with a second opinion on that? I suppose I will probably need to replace the whole lower unit ayway if it doesn't work.

I'll check it out today.

 

[asdasc]

Re: '67 lurching/backfire when running

Hmmm, looking on shop.evinrude.com at the 1968 18hp gearcase, they are different gears for forward and reverse. I do know that you can reverse the clutchdog, but I think I figured out that it is still putting the stress on the same edge in forward and reverse, so no gain. I could be wrong.

Interesting to note that while all 3 parts are still available, they price out like this:

Reverse gear: $65
Clutch Dog: $60
Forward gear: $500! No wonder they fail, they must be making them of soft gold!

 

[yodel3]

Re: '67 lurching/backfire when running

OK pictures can be viewed here:

http://picasaweb.google.com/danlaurajacobson/Gears#

as I understand it, my options are:

1. try a new clutch dog
2.try a new clutch dog and try to switch fw and rv gears
3. try to switch above without new dog
4 try to find entire lower unit.

looking at the pics, what do you think?

 

[asdasc]

Re: '67 lurching/backfire when running

What does the other side of the clutch dog look like? Better? If it looks better than this side, I would try to reverse it and see how it goes. Even if you just reuse the seals for a temporary test. Then if it works, you can pull it apart and install the new seals if it is leaking water.

 

[yodel3]

Re: '67 lurching/backfire when running

a good idea...

I put it back together that way. Maybe I can get it out for a spin tomorrow. I'll check back with results. Thanks for your help!

 

[zinc]

Re: '67 lurching/backfire when running

What does the other side of the clutch dog look like? Better? If it looks better than this side, I would try to reverse it and see how it goes. Even if you just reuse the seals for a temporary test. Then if it works, you can pull it apart and install the new seals if it is leaking water.

DITTO!