Occassional dead cylinder

[TrueNorthist]

1985 J70ELCOS, aka a 70hp Johnson. After sitting for a month or so the engine clearly has dropped a cylinder and idles very rough. I replaced the spark plugs and performed some tests and eventually went for a quick shake-down run at a small but extremely busy lake which revealed a normal running engine. It hesitated a bit at first and was slow to climb out of the hole, but like throwing a switch she just snapped out of it and ran fine for an hour under all conditions.

Fast forward a week or so and at a different lake the engine again dropped a cylinder right away (I am fairly sure it is #3, the plug has a different fouling pattern than the others, with only half the radius of the plug fouled) This time I pulled the carbs and cleaned, blew out and synced them while inspecting the entire fuel system. I replaced a few borderline hoses but the carbs were fairly clean. I disconnected and cleaned and reinstalled all the ignition wiring and ran static tests on the coils which check out to spec. Running on the muffs I can easily jump a 1/2 inch gap with a crisp blue spark on all 3. Compression is 127, 124 and 123 from 1 through 3 and it is now idling very nicely, again on the muffs.

My question is: can the power-pack be the cause of this sometimes dead, sometime not cylinder? I cleaned all the connectors at the bus but do not yet have a DVA tester made up to check output.

 

[ondarvr]

Power packs can misbehave in many ways, but can be hard to trouble shoot if the problem is intermittent.

You cleaned the carbs and now appears to run better, I would pursue that angle a little more.

 

[jakedaawg]

I recently tested the entire ignition on a very similiar engine including key switch and isolating and testing blk/yel wire.

This engine had weak spark occasionally when warm. Not no spark, but weak on one cylinder.

Every single component that you can test tested out of spec but not very far out of spec, except the power pack. The only test for the pack is when diagnosing a coil. Basically you place a lead one place then another, if dva read x you replace the coil, if dva read y you replace the pack.

Long story less long: all ignition components were out if spec, but not very far out. Replaced pack, motor goes zoom zoom quite nicely.

Dont read too much into this. Packs do weird things but so do all components when they are just beggining to fail.

 

[boobie]

Do a cylinder drop test on it when it acts up and maybe you can find the problem cylinder.

 

[TrueNorthist]

Thanks folks, much appreciated. I will be putting the boat in the water on Sunday when the weather is a bit better. Good point about the ign switch. However the engine is indeed running better after cleaning and syncing the carbs so it is possible the problem is already sorted. (?) If it still acts up I will disconnect the ign switch and if still wonky I'll splash out on a new power-pack. No matter what happens it would be good to have a spare anyway.

Prior to my father giving me this boat he said from time to time, usually on the first or second run of the season, the motor would struggle to get the boat on plane and a fella at the local marina said to "pulse the primer" a bit, which apparently worked and it would run fine after that. Servicing the carbs should have sorted such an issue, I hope. The reed valves are in fine condition and everything else checks out on spec, so if it's still dropping a cylinder I reckon procedure then points to the power-pack. I'm also going to build a DVA adapter asap.

Thanks again. I will report any progress.

p.s. I maybe shoulda mentioned this used to be a VRO, which I deleted. The fuel pump leaked like a Bayliner at first but stopped upon tightening the case hardware. 31 years and perhaps 2000 hours was a pretty good run for that VRO system, but I figure it is wise to just mix the gas from here on out.

 

[TrueNorthist]

It took a while for the weather to improve enough to put the boat in the water and in fact never really did, but I decided to wear a raincoat... The motor is now firing consistently on all 3 cyls, but another issue has surfaced: Once up on plane for about 20 or 30 seconds it's as if there is a second controller that somebody starts yanking back and forth and gradually the boat falls off plane and will stall unless the throttle is reduced to idle for ~30 seconds or so. Once idled it will climb out of the hole smartly but... 20-30 seconds later -- about the time it takes to drain the floats I reckon -- it starts with the surging all over again. All plugs are showing identical fouling (minor and correct imo) and the motor no longer smokes like Camel Joe and idles smooth, starts right up and while supplied with fuel has a lot of power. However...

One thing I am not sure I mentioned, but before I did anything to this engine I simply hooked up the fuel line and pumped up the primer bulb and fuel was spraying out through the VRO fuel pump casing, so I snugged up the screws and the leaks stopped. I am beginning to suspect the fuel pump is the source of this "new" problem, in that now all 3 carbs are flowing fuel properly the fuel pump cannot keep up with demand? But before I go down that road I am going to buy a new fule line as all 3 of mine are in varying stages of decomposition. 2 Attwoods (rubbish) and a Sierra "long" (nearly rubbish) and all suffering from at least one idiosyncrasy. A new OMC or equivalent line or 2 will be a good investment regardless, but I am increasingly looking at the fuel pump with an eye towards rebuild or replacement, depending on which is the better choice. My fuel tank is also an Attwood so even it might be the culprit?

What say ye denizens of the deep? Am I on the right track, or have you experienced similar surging with a "deleted" VRO fuel pump that leaked and found a different solution? Can I rule out the power-pack now?

oh, and boobie, I will rig up a test rig and post results soon, however I did a monkey drop test and found disconnecting all three wires (separately of course) caused a drop, even when running very badly. But I will do another test now the carbs have been ruled out. Getting it to stay on the power long enough is a bit tricky though...

 

[Silvertip]

When the surging starts, try squeezing the primer bulb. If the engine picks up and runs normally as long as you squeeze the bulb, the fuel pump is the problem. If the bulb is being sucked flat, there is a restriction between the bulb and the tank or the tank vent is clogged. An ignition switch cannot cause just one cylinder to fail.

 

[TrueNorthist]

I did as you suggest Silvertip and found all 3 primer bulbs kinda mushy, which is enough for me to consider them all hooped, but to be perfectly honest I was unable to really perform that test effectively while on my own. I am going to drag some innocent soul out to sea next time so I can do more such tests, but with a new fuel line for sure. I can say for sure the bulbs, such as they are, never went flat. I do not really suspect the tank but threw that in anyway, just in case.

 

[TrueNorthist]

BTW, sometimes a pic is worth a few bucks...

Please note I have installed a port for testing flow (!) plus all fuel lines are brand new. I also just borrowed a known good fuel line from a neighbor and the bulb firmed up nicely while priming.

 

[TrueNorthist]

Clearly buying a new fuel pump is darned near half-way to the cost of a used engine, so I'll ask another "get to the point" question: have any of you successfully rebuilt one of these VRO pumps? Can I even buy the parts? Or, is there a non VRO pump that I can swap in, or maybe an electric? Man I hope a new fuel line helps...

edit: I found a source for the info I was seeking, so thanks regardless. I can indeed swap-in a non-VRO pump assy and even lay hands on the various parts needed should I wish to keep using the original.

 

[TrueNorthist]

One further question if I may... Has anyone ever had success with installing a low pressure (~5psi) 12 volt electric fuel pump? I always wondered why a guy couldn't do away with the primer bulb etc and go with a 12v. Can the carb floats handle ~5psi continuous pressure? I can also source a 1.5 to 2.5psi max, better? I have traced a non-VRO fuel pump that will supply my needs, but I am tempted to try an electric just for the heck of it. One could be rid of all the o-rings etc and just permanently plumb the fuel lines.

Been done before?

 

[ondarvr]

The electric fuel pump can be done, but to do it correctly is a bit of a hassle, if not done correctly it can be a safety hazard.

Better to get the non VRO fuel pump, they work very and are extremely reliable.

 

[TrueNorthist]

Thanks ondarvr. I take it your concerns lay with leakage? I figure with such low pressure (4psi max) the fuel-injection clamps I am using should hold things together very nicely, but I would appreciate any warnings you might have. I reckon a 12v fuel pump actually eliminates several weak points: connections, primer bulb, one-way valves, pump diaphragms, springs, etc etc. Just one low pressure, 25gph solid-state pump on a simple relay that takes the load off the run circuit. Easy as pie?

Cheers

 

[jakedaawg]

We always used electric pumps on the race boats but they can not be reccomended for the casual boater. Yes its possible, but why not just delete the vro and go with a classic diaphram style pump. Its just so easy to do and they last for many years with good fuel and proper maintenance.

 

[oldboat1]

Think a VRO rebuild kit runs about $150, give or take, and a regular pump could be had for about half of that. Buying a used non-vro pump and rebuilding ends up about the same price as a new pump. Depends on what's in the budget.

Think you have the oil pump plugged and the harness disconnected, and pumping premix. Guess I might shop for a good price on a VRO rebuild kit, and simply go that route (JMO). Should give you the option of going back to VRO or sticking with premix, if that matters.

 

[flyingscott]

First thing I would do is take off the screw clamps and see if you cracked any of the elbows those are the wrong clamps. I would also get rid of that tee of the pump and get an elbow put in there

 

[TrueNorthist]

Thanks fellas. But let me give you one more thing to chew on... This engine is tired, very tired. Probably well north of 5000 hrs, all on the salt-chuck doing the bidding of a very demanding and mechanically unsound mind --? my Dad. The fact that it even runs is a testament to OMC, but at least the old fella followed my directions kinda well, which is paying off now I reckon. 30 years ago I told him to flush the engine anytime it was near fresh water and to rinse, dry then spray the powerhead down with Fluid Film twice a year. Also to use only quality, brand name oils and test the warning horns each time he hits the water. I will also put in a word for Lee's Marine in Lund BC, but I digress...

Back to that chewy thing. I cannot help but think of the potential effects of low compression on the fuel pump. I am probably wrong, but I suspect the pulse line to the VRO pump may not be delivering all that it once did and that a 12v pump will compensate for a weak and possibly faltering pump signal pulse, no? That is the other thing an electric eliminates, at least in my tiny mind anyway: the need for a pulse charge to drive a stiff, worn VRO fuel pump ?-- meaning tired reed valves etc will not lead an early (!) demise for this tired old girl! I am certainly not going to bother with anything more complicated than reeds at this point and maybe the 12v will tack-on a couple hundred more hours of zipping around the lake?

As always, thanks very much for the sound advice.

 

[TrueNorthist]

First thing I would do is take off the screw clamps and see if you cracked any of the elbows those are the wrong clamps. I would also get rid of that tee of the pump and get an elbow put in there

I wondered when somebody was going to say that! I can assure you the clamps have not damaged the fittings and the T was only there for testing purposes and has already been removed in favour of an elbow. Well spotted good sir! However it's not the clamps that are wrong imo, rather just what can happen when used incorrectly. In this case they are exactly what I need, but soon enough there will no longer even be any plastic fittings, nor even a filter up there. Most if not all of the shaped lines are hard and half disolved by alcohol and age, much like me, and it will be fan freaking tastic to not have to worry about it any more. And I sure do like the way they can hold a fuel line under pressure. When used correctly of course.

Cheers pal.

 

[ondarvr]

It doesn't take much to make the stock type pump work, I've seen some pretty weak and tired motors and the pumps had no problem keeping up. In fact I don't think I've ever seen where a stock pump in good condition didn't work exactly as designed and provide enough fuel. While an electric pump with all the correct safety considerations can work well, it's far more complicated with many opportunities for problems and failures.

 

[jakedaawg]

If the crankcase pulses are not strong eniugh to run the pumo i would be surprised if that cylinder would fire.