73 85hp rude Head scratcher

[wavrider]

Out on the lake today, did alot of idling. Noticed every now and then it would sound like a cylinder would stop firing, decrease in the rpms, then it would pick back up and fire again. Intermittent spark?

That is what I thought it was.

Back to the house after a great morning. Take the boat up to the shop.

Hook up timing light. All four cylinders are firing.
Pull the plugs do a compression check, all cylinders are in spec and within tolreance on variance.

Re-install plugs start engine up, starts easy idles good. Grab the insulated pliears and stat pulling spark plug wires.
#1 makes adifference, decreases rpm. re-install increases rpm.
#3- same as #1
#2- same as #1 and #3
pull #4, no diference in rpm, installed or uninstalled spark plug wires make no difference.

switched spark plug wires with #2 and traded wires on the power pack/amplifier assy. Now #2 coil will fire #4 cyl and vice versa.

Pull #2 spark plug wire no difference, pull #4 wire decreases RPM

So it is not electronic problems???

Only thing left is fuel, I guess. Carbs have been rebuilt, twice

Could it be a bad reed valve? not getting enough fuel to the bottom cylinder?

This is the same engine I posted about a few weeks back that had a miss and was sputterin misting on the bottom carb port side. I replaced a intermittent coil then and thought I fixed the problem.

I have never seen a cylinder have spark and pull the plug wire while running and it does not make a difference in idle speed, has to be fuel but where am I losing the fuel at idle speed?

thanks for the replies.

 

[patrick4266]

Re: 73 85hp rude Head scratcher

that is a head scratcher. i will be watching this post to see what they come up with

 

[Lou Eppell]

Re: 73 85hp rude Head scratcher

The slow speed jet that is located in back of the aluminum screw at the extreme side rear portion of the carburetor...... clean it manually with a .030 drill bit, then blow some air thru it.

Let us know if that cures your problem.

 

[ezeke]

Re: 73 85hp rude Head scratcher

You have two idle jets per carburetor, one on each side.

You most likely have an ignition coil going bad. They start by failing when they heat up, then get worse. Bad coils can kill a powerpack so don't fool with it, replace it.

 

[wavrider]

Re: 73 85hp rude Head scratcher

coils r firing,

this is a cold start at house in the barrel and it fires with the timing light, the spark tester, and holding the spark plug next to the block, but I have some more good coils I will swap it out just to be on the safe side.

I am watching the timing light light as the coil fires and pulling the sparkpluig boot at the same time, no difference in RPM, you can hear the spark jump when I go to put the plug wire back on the plug.

I will go through the carbs again and let you know what I find afterwards.

thanks for the replies and tips.

 

[jay_merrill]

Re: 73 85hp rude Head scratcher

When you swapped wires at the powerpack to accomodate the swapped spark plug wires, did you do so between the powerpack and the coils or did you swap wires between the timer base and the powerpack?

I think your problem is not neccessarily carb related. You could have either a bad powerpack or a bad sensor in the timer base.

 

[wavrider]

Re: 73 85hp rude Head scratcher

Swapped coil wires on the powerpack.

I will try to find time to swap sensor wires tonight if daylight permits.
thanks for the tips and pointing in the direction.

This thing is getting great spark.

That is why I am so stumped, if it has spark, it is in time, has fuel/air, compression is good, it should fire.

 

[Lou Eppell]

Re: 73 85hp rude Head scratcher

With the spark plugs out, at cranking speed, will the spark jump a 7/16" gap with a hot blue spark on all cylinders?

 

[tashasdaddy]

Re: 73 85hp rude Head scratcher

check the spark plug boots, could be arcing to the block. i've heard of some plug wire that have short boot, arc to the block, shortest resistance. you almost have to find it in the dark.

 

[jay_merrill]

Re: 73 85hp rude Head scratcher

Double Post

 

[jay_merrill]

Re: 73 85hp rude Head scratcher

Ok, here's what I get from the info you provided.

1. Before changing anything, pulling the #4 spark plug wire resulted in no change in rpm. This suggests that the #4 cylinder is the problem and it could be either fuel delivery or ignition. Since your problem seems to be intermittant, I suspect that ignition is the problem. That is not to say that you might not be getting intemittant fuel delivery but I think it is less likely.

2. Assuming that the problem is ignition, the information prior to changing wiring around tells you that the problem could be pretty much anything in the length of the #4 ignition circuit - plug, spark plug wire, coil, powerpack or a sensor in the timer base. Any of the wiring inbetween could be bad too. I don't believe that the stator is the issue because you wouldn't be getting consistent spark to the other cylinders if it was.

When you swapped the #2 & #4 spark plug wires and the #2 & #4 powerpack to coil wires, you isolated the coil as a possible problem area because this change caused the #4 coil to fire the #2 cylinder. Since there was a drop in rpm when you pulled the #4 wire, you now know that the #4 coil is working when triggered by the #2 ignition circuitry. This leaves everything in the #4 ignition circuit that is "in front of" the coil suspect. At this point, I would say that both the powerpack and the timer base are possibilities.

3. If you switch the #2 & #4 powerpack to coil wires back to their normal position, and then swap the timer base to powerpack wires, you should be able to isolate the system further because you will go back to having the #4 switch in the powerpack complete the circuit to the #4 coil. If, after this swap, the #2 cylinder is firing correctly (remembering that you are now firing the #2 cylinder off of the #4 coil & powerpack switch, and the the #2 sensor), I would say that your problem is the #4 sensor in the timer base. If so, an ohms check of the #4 sensor should show it to be out of tolerence.

4. If pulling the #2 spark plug wire does not show a drop in rpm, indicating that the #2 cylinder is now the problem, this information suggests a bad #4 switch in the powerpack. This is true because we have already shown the #2 sensor and the #4 coil to be in working order.

In rereading this post, I realize that I have written what amounts to a "verbal spaghetti bowl." The information is sort of hard to follow, with all of the references to individual coils, sensors, etc., but you should be able to take things step by step.

After you fix the immediate problem, I recommend that you plan to replace all of the ignition system componets over time. What I found with my 1972 Johnson 65hp is that when one thing goes, the rest tend to follow pretty quickly. And, as has been said by others, one problem can actually cause the next one.

 

[wavrider]

Re: 73 85hp rude Head scratcher

Summarize.

I have eliminated the coils on #2 and #4 as not being the cause.

Paraphrase.

I am to swap the sensor leads coming from the pickup coils on #2 and #4 input into the powerpack.


I would also have to swap spark plug wires on #2 and #4 so the coil is firing at the correct time the amp tells it to fire? If I swap the input leads I would also have to swap output leads or swap sparkplug wires to have it fire the correct plug at the correct time?

I will try that this evening.

I think you are correct in the ignition,spark line of troubleshooting this problem,, yet I have spark all the time, maybe not enough spark?? How many pickup are there under the flywheel? Two or Four. I only see two. One pickup is for one bank and the other pickup is for the other bank. So if a pick up coil is going bad would it not effect two cylinders and not just one?


I do have a couple donor engines so I have a few ignition parts to swap around.

I went and picked up that over priced NAPA gallon of carb cleaner with soaker basket, the carbs will be clean as a whistle by the weekend.

 

[jay_merrill]

Re: 73 85hp rude Head scratcher

I am more familiar with the three cylinder motors of this era, but I believe that the coils you are looking at are on the stator and are the charge coils. If one cylinder on a bank is firing, while the other is not, the stator shouldn't be the problem.

The sensor coils should be located in the timer base, which is the part mounted inside and under the stator - its the one with the leg sticking out the side that is connected to the throttle mechanism via a rod. If your timer base is of the open, metal variety, I believe that you should be able to see the individual sensors. Timer bases on newer motors, and replacement units, are usually sealed so you can't see the individual sensors. This really doesn't matter though because individual sensors for the older units are not available to my knowledge.

As for swapping a timer base off of one of your parts motors, I have done that with temporary success but have found that replacing the unit with a new one, is pretty much something that you have to do at some point. What I may do, however, is to swap a bad sensor in one of my older timer bases with a sensor from another used unit that has a decent ohms reading when tested. This involves removing the bad sensor from the base, breaking the solder joint on the wire that goes to the common ground, installing the used sensor and then soldering the ground to the common wire. This isn't difficult and, if for no other reason other than having a spare timer base around, might be worth the effort.

According to the info in the following link, sensor resistance for your motor should be 38 - 42 ohms. The link also tells you how to do DVA checks on the motor but, since you may not have a DVA type meter, that info may be of marginal value. If you do the ohms check with a multimeter, be sure to use a range that will show a small difference in the recommended value and be sure to "zero out" the meter before taking the reading. There should be a small thumb wheel on the meter to adjust it.

"http://www.outboardignition.com/page34.asp"

The troubleshooting/isolation info that I gave you is based upon what I would do with my three cylinder Johnson. Given that there are a few differences in the four cylinder motors, however, I might be off a bit. I don't think doing any of these things will harm your motor though. As always, no ego here so if any of the folks that know the four cylinder OMCs want to chime in, I would say that would be a good thing.

 

[wavrider]

Re: 73 85hp rude Head scratcher

thanks for the replies and once again as always any advice accepted here.


I trying to remember the operation theory, hard to do with phone ringing and busy here at the office.

2 pick up coils drive the amplifier, located in the north south position under the flywheels.

Now experts please join in.

If one pick up coil drives the input to the amp assy is for cylinders #1 and #2 respectfully.

the other pickup coil drives the input to the amp for #3 and #4.

If this is in fact true, (which I can not remember the circuit and manual is at the house) then I can see where ignition can be problem.

#1 and #2 have a great steady almost as if it is a flashlight beam on the timing light.

#3 and #4 you can see the timing light fire as if on a v 8 thee is a noticeable delay in the light beam.

this could be a sing of weak pickup coil under the flywheel?

thanks again for the interest and replies

 

[wavrider]

Re: 73 85hp rude Head scratcher

I did not have time to do to many checks, daughter wanted to go shopping when I got home from the office so off we go.

I will try tomorrow.

 

[HighTrim]

Re: 73 85hp rude Head scratcher

Wav it sounds like you have faulty isolation diodes in your power pack.

I would get the ohmmeter out and check it out.

 

[wavrider]

Re: 73 85hp rude Head scratcher

After reading the manual and theory of operation, and eating three fudge brownies. ( daughter got to go shopping but had make brownies when we got back to the house)

I am thinking power pack also, I checked the spark with the plugs out of the power head, SeLOC manual says to have plugs installed when doing spark test to simulate operating conditions?

I almost bet a cold drink I do not have enough spark to fire the cylinder under compression, with plugs removed so engine can spin faster I get a nice blue spark.

Looking more and more like ignition in theory.

Yep I break out the DVM tomorrow and take a few brownies up to the shop ( if the kids leave me any that is) and do some OHMING and not the yoga type.

Let you know what I find. thanks for all the advice and Jay heck of string of spaghetti words but understood all of it, thanks for taking the time to write the advice.

 

[Lou Eppell]

Re: 73 85hp rude Head scratcher

With all of the wire switching as mentioned above, I've lost track of what's going on.

When you get time, put all the wiring back where it belongs. Physically switch the #4 coil with #3 coil..... that is actually move them.

Now, did the problem follow the #4 coil whereas #3 cylinder is now not responding?

Did you remove the spark plugs and check the spark to see if it is actually jumping a 7/16" gap?

 

[jay_merrill]

Re: 73 85hp rude Head scratcher

Admittedly, the wire switching is difficult and complicated to describe in writing, but it really isn't all that complex if you think through it logically. Additionally, he already knows that the coil isn't the problem, so physically switching two of them won't help.

Really, the best method of troubleshooting this problem is via a DVA type meter and it sounds like he has one. My recommendation now is to use it per the instructions in the maintenance manual.

 

[wavrider]

Re: 73 85hp rude Head scratcher

Tempted to call in and take the day off just to find the problem with this 85hp.

After all the advice and reading the theory of operation I am sure it will be a weak ignition part, but curious as to which one will be weak, powerpack or charge coils,