1967 Johnson 80hp backfires when I mist fuel into carb

[BonairII]

My #2 and #4 cylinders are still giving me problems. Motor starts right up(on only 2 cyls, I think). I pull the #2 plug wire and engine doesn't stumble....same for #4.

I sprayed premix in the starboard carb throat(this carb feeds #2 and #4 cyls on the port bank) and the motor backfires(a loud "pop!"). I turned motor off and sprayed a little premix in both cylinders and reinstalled the plugs....restarted the motor with a loud "pop!" backfire.

What the heck could be causing this?

 

[Chris1956]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

Are the two sets of points set correctly?

 

[Sander]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

Is there a lot of carbon build up? Im sure you already did compression check. Have you tried sea foam?

 

[JB]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

This thread starts in the middle of a conversation, Bonair. Where is the beginning??

Sounds to me like you have either a sheared flywheel key or switched plug wires.

 

[BonairII]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

Just changed the heads/gaskets yesterday. Not much carbon at all. Set points today(per the manual) and did the link-n-sync per the manual.

Seems to smoke a bit out upper exhaust after the backfire. Pulled #2 and #4 plugs. Smoke came out of the hole for a few seconds when I pulled the #4 plug.

 

[jbjennings]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

I'm with JB on the switched plug wires, possibly even switched coil wires at the terminal strip.
JBJ

 

[BonairII]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

This is a continuation of my thread "Dropped 2 cylinders... AGAIN". Since I've been told to start a new thread when I have a new problem/question instead of adding new problems in one thread ...I started a new thread about the backfire.

Been having probs with the port bank of cylinders NOT running. I got all 4 cylinders to run one day a week or so ago...the next day I was back to 2 dead cylinders. Thought it was a fuel problem(cause plugs weren't wet after running motor with #2 and #4 cyls without plug wires attached.
Opened up intake and reeds looked ok to the naked eye. Dual carb has been off and inspected/cleaned/run fine wire thru orifices, pulled high/low speed jets 3 separate times.

Replaced all fuel line from tank back to motor...and all lines on the motor. All secured by hose clamps. Carb gasket in perfect shape.

Replaced both heads/gaskets yesterday (had bad spark plug threads in both). Plugs gapped at .030.
Did link-n-sync and set points today per the manual.

Manual doesn't give any troubleshooting help for a backfire. I was thinking maybe sheared flywheel key also(I've been reading every thread I can find on backfiring). Problem with that is that I got the #2 and #4 cylinders to work for an hour last week, so that would rule out sheared flywheel key........

Unless:
I've got a few problems going on at the same time and now the flywheel key sheared....adding a new problem(the backfiring).
I don't know if this rules anything out, but I checked belt timing marks on the flywheel with the crankcase per the manual and they are good.

BTW: The #1 and #3 cylinders have been running well consistently....if the flywheel key sheared wouldn't those cyls be affected?

I'm baffled

 

[BonairII]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

Here are a couple vids. One is of the motor 'hard starting' and then running. No backfire this time. Sprayed fuel into carb. 3rd spray killed motor...no backfire like last time I did this(earlier today)
http://www.youtube.com/watch?v=sDxERF8n6W0

2nd video is of me confirming timing. The continuity tone confirms closed points...point open(tone stops) as timing marks pass each other. So timing must be correct, i think.

http://www.youtube.com/watch?v=FYvCw8w9il4

 

[yorab]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

You could have bad spark plug leads. Try to switch #1 and #3 with #2 and #4 and see if the problem follows the leads.

 

[AlTn]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

have you tried an inductive timing light on each sparkplug wire while it's running to check for spark consistency and strength?

 

[BonairII]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

You could have bad spark plug leads. Try to switch #1 and #3 with #2 and #4 and see if the problem follows the leads.

I tried that a week or so ago and the prob didn't follow the wire...but just to be safe I'll try it again tomorrow.
At least now I know that the starboard carb is the one that feeds the port bank(read it in manual). Now I'll focus my attention on the correct side of the carb regarding fuel delivery.

After doing a lot of reading, the so-called "backfire" I had was actually an AFTERFIRE....and since I got smoke out of the #4 cylinder(I pulled that plug after the 'afterfire'), that confirms that my problem is def the left bank.

Now whether it's a fuel or timing issue, that's a toss up.

 

[Chris1956]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

You should be able to determine if you have a sheared flywheel key. Set the #1 piston to TDC with a screwdriver, and see if the timing marks on the flywheel align.

Does that motor have the two bbl downdraft carb? if so, a lot of them cross over the charge in the manifold, so the left bbl feeds the right side of the motor.

Make sure your points are clean, gapped properly and the wire connecting the points together isn't shorting out to the ditributor pully, by rubbing it.

 

[BonairII]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

You should be able to determine if you have a sheared flywheel key. Set the #1 piston to TDC with a screwdriver, and see if the timing marks on the flywheel align.

Great tip, thanks! The #1 cyl appears to be at TDC when the marks align cause the piston starts going down just as the marks pass each other.

That's a relief, really didn't want to have to pull the flywheel.

 

[Tim Frank]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

A few Qs:

1) Is this motor new to you or have you had it a while.
2) If not new to you, has it always run OK since you got it or has it always had problems.
3) I haven't seen any compression values....but you have changed head gaskets. Was that because of compression issues or just because...?

 

[BonairII]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

A few Qs:

1) Is this motor new to you or have you had it a while.
2) If not new to you, has it always run OK since you got it or has it always had problems.
3) I haven't seen any compression values....but you have changed head gaskets. Was that because of compression issues or just because...?

I've posted a handful of threads on diff issues with the motor. I've had it a month or so. Wire harness was burnt(PO had a fuel leak and small fire). Got the wires replaced. Got it running. Dropped in water and found out only cylinders running(drop test). Only was doing about 24 mph on my 16' Glasspar.

Two weeks ago, I got all 4 cylinders running and ran it around for a bit. http://www.youtube.com/watch?v=rwG-jkAaBA4

Compression was 90psi across the board(hopefully higher now with swapped head and new gaskets-haven't check it yet). Both heads had a cyl with stripped spark plug threads, so I swapped head from an identical parts motor I have.

 

[Chris1956]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

Is the distributor timed with the flywheel properly and synched with the carb(s)?

 

[Tim Frank]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

Is the distributor timed with the flywheel properly and synched with the carb(s)?

Chris, OP had a long thread about just this, and I believe that he got it done right.
If you have a minute check => http://forums.iboats.com/showthread.php?t=511599

 

[BonairII]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

Checked compression today just to be sure I installed the heads/gaskets corrrectly. It was still 90psi across the board.

Tomorrow I'm going to have my son turn the motor over with the starter and hold some flat cotton discs over each cylinder hole to see if I'm getting fuel to all cylinders.

I'm going to check spark again with my adjustable spark tester. No money for a timing light at this point.

Chris,
I did the link-n-sync per the manual, but I'm going to do it again to confirm I did it correctly. Once again, I'm confused by the instructions

A couple probs with my link and sync:
- When I line up the roller shaft with the scribed line....the butterflies aren't completely closed. They are darn close to being closed(prob 1/16th" or less open). To completely close them the roller would be a tad left(1/8th-1/4 of an inch) of the scribe mark, but still in contact with the cam. there is no way to manipulate the cam or adjustment screw so that the roller is on cam scribe line AND the throttle is completely closed.

-In the instructions(see pics) the manual says that the butterflies should start to open when the roller shaft "reaches" the scribe line. Isn't this a bit contradictory? In the first part of the instructions it tell me to line up the roller/scribe line....theen it goes to say to that when the roller "reaches" the scribe line(implying that the roller starts BEFORE the scribe line.

 

[yorab]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

I was a bit confused with this as well the first time. In my manual (which is a few years earlier than yours), there was some ambiguity as far as what part was what. The same part was referred to by two different names in various paragraphs.

Anyway, you need to align the "Scribe Mark on Cam" with the center of the "Shaft" shown in Fig 3-24. Hold the parts in that position and loosen the "Adjusting Screw". It may help to have an extra pair of hands, but it can be done solo. Because the "Throttle Arm" is connected to a spring, the arm will rotate until the butterflies are completely closed. This occurs after you loosen the adjusting screw. Then, while still holding the scribe mark in alignment with the center of the roller shaft, tighten the adjusting screw. At this point, your roller shaft should remain in alignment with the scribe mark, while at the same time, your throttle butterflies should be closed and just "at the brink" of opening. When I adjusted mine, I found that the scribe mark was slighty off, but it made no discernible difference.

 

[BonairII]

Re: 1967 Johnson 80hp backfires when I mist fuel into carb

Update:

I got tired of all screwing around with my motor.....and went back to basics.

I pulled my carb and put on my "backup carb". My primary carb is suspect at this point.

I pulled all plugs, and wires completely off, checked them for corrosion etc and reinstalled the wires being careful that they went to the correct cylinders.

I also pulled my points and condenser and replace them with new parts(they just came in today). I confirmed again that points were set correctly.

Had my son turn the motor over and held a small piece of bunched up t-shirt over each cyl hole. I smelled gas on every hole, so I'm at least getting some fuel.

Hooked up my spark tester and set it to approx 7/16ths....and got great blue spark on all cylinders.

Hooked up my portable fuel tank and had my son fire it up. It started immediately and seemed to run pretty smooth.

I drop tested all cylinders and the RPMs changed on every one.

Gonna drop it in the water tomorrow...and test it further (fingers crossed)