symptoms--leaking air

[leysathcj]

As I attempt to bring an older motor back to life, I'm curious as to what symptoms a fuel line air leak would create? I replaced the fuel lines and clamped connections as best I could but some seem a bit loose. What kind of engine operation would I expect if I'm sucking air?

 

[SpinnerBait_Nut]

Re: symptoms--leaking air

I am taking it your talking about the Evinrude so I will move this there.

 

[shipwreck]

Re: symptoms--leaking air

Tell Us What Year Model And Horse Power And Any Symptoms Your Are Have , Evrinrude 1967 Model 60733 60 Hp Example

 

[leysathcj]

Re: symptoms--leaking air

1977 Evinrude 70hp #70773S
rebuilt carbs, fuel pump and new fuel lines all the way to the tank; and the boat is running much better. Comes out of the water good and hits top end w/out any problems. What is curious is when I'm cruising along (regardless of rpm) the engine occassionly "kicks in" a little more. It's like I'm riding and everything is running well and then suddenly the she gets a little burst of power and I'm running even better. Perhaps I shouldn't be complaining but I guess I'd like to have that "little burst" all the time.
I fastened the fuel lines w/ nylon straps (using fastner gun) like they were originally but some are looser than I'd hoped. I can still twist the fuel line on the nipple, although they won't come off w/out cutting the nylon strap. Fuel line bulb is firm.

I'm running fresh fuel (87 octane) @ 50:1 w/ 6 oz SeaFoam per tank. No apparent fuel leaks from lines or pump. No apparent mis-fires when running but the occassional "sneeze" when starting.
Thanks for your help.

 

[F_R]

Re: symptoms--leaking air

You might be running on only two cylinders. When the third one fires, you get that extra kick. Running on two could be a number of causes from spark plug to ignition, to dirty carb for that cylinder, to water intrusion into that cylinder, to low/no compression. Can only guess without systematic checking it out.

Leaks in fuel line anywhere between the fuel pump and tank allow the pump to suck air instead of gas, causing a lean condition, or running out of gas. Leaks between the fuel pump and carburetor only cause a mess (or fire).

 

[leysathcj]

Re: symptoms--leaking air

I believe I have spark to all cylinders but will get a tester and verify. The boat is running pretty well which I wouldn't expect if one cylinder was out. Would I expect the sort of "pop" out of the hole and top end speed I'm getting if I was running on just 2 cylinders??

 

[shipwreck]

Re: symptoms--leaking air

imported_F_R
quote"You might be running on only two cylinders. When the third one fires, you get that extra kick. Running on two could be a number of causes from spark plug to ignition, to dirty carb for that cylinder, to water intrusion into that cylinder, to low/no compression. Can only guess without systematic checking it out.

Leaks in fuel line anywhere between the fuel pump and tank allow the pump to suck air instead of gas, causing a lean condition, or running out of gas. Leaks between the fuel pump and carburetor only cause a mess (or fire).""

my thoughts:
you maybe able to ground out the spark leads for each bank Or set of cylinders
in other would remove spark plug wire , ground the inside of boot to ground and start up the others to see if cylinder is running ( get spark) if see fires up and runs your gold.
i would check with , ( imported_F_R) to see if this is good idea , it is would i would do.

 

[jtexas]

Re: symptoms--leaking air

I have that motor in a '79 vintage, not much difference......on two cyl it will sound ok idling and moving slow, but just won't plane the boat (15ft fiberglass tri-hull) - I guess it might plane a smaller lighter boat......seems unlikely though.

And a hi-speed misfire gives you a very well defined "kick" so to speak.

Still, a cylinder drop test is easy enough: with engine idling pull, then replace, one spark plug lead at a time; if rpm's don't decline noticeably, that cylinder's not making power. Follow up with spark test.

Inspect the throttle linkages carefully. Make sure the throttle valves stay parallel...if one is a little loose it could be wavering. Same with the choke plates - they need to get open & stay open except when the choke is activated. Then check the spark advance rod - it should have a plastic (nylon?) ball-joint type of bushing at each end, if one gets broke, the spark advance will wander on you.

 

[leysathcj]

Re: symptoms--leaking air

Boat planes out fine (Glastron 15.5' tri-hull) and has lots of top-end speed but occassionly shows a-little-more speed and power so something is changing "for the better". If it wasn't for this "change" I would have assumed everything was operating fine as performance is pretty good.

Checked spark this evening and showing strong and steady blue spark at 7/16" gap. Will check throttle, choke plates and advance mechanism tomorrow as advised. Having recently rebuilt carbs, link & sync ect...I think throttle/choke are fine but will verify.

Had previously pulled spark plug wires at idle and found very little change (if any) on #1 and possibly another cylinder (can't quite remember). I'll do this again tomorrow also. Plugs new last season but perhaps I have a problem w/ one of these not firing up to par. Currently gapped to OEM specs. 0.040". I'm no mechanic but I can't believe I have 1-2 cylinders out as the boat is running to well.

Thanks to everyone for your advise.

 

[leysathcj]

Re: symptoms--leaking air

The throttle & choke linkages are fine; everything is working in sync and opening completely. The spark advance nylon ball-joint bushings appear to be ok; old but no apparent cracks or weak points. This plate appears to be moving freely.

I conducted another cylinder drop test w/ rpm decrease each time I removed a spark plug boot BUT I am getting quite a shock from the #1 cylinder (top) boot when I grab it w/ my plyers. The other 2 boots give me a much smaller, tingley shock but the #1 really "bites back". Looked for cracks ect.. and didn't see any. Wrapped wire and boot in elec. tape to see if it made a difference but did not. Plyers are handle-coated but don't know if they are truely insulated. I would estimate 10+ times the shock felt on boot #1 when compared to the others. 2 of the 3 coils showing a crack in the plastic coil covering but only signifigant shock from #1.

Yesterdays spark test showed an equally strong spark on all 3 cylinders w/ no decernable difference between them.

Should I switch the coils around to see if the "bite" is common to the coil or the coil location: or is there a reason why the #1 coil would shock so much more?? I think we're getting close...

Thanks a bunch..

 

[leysathcj]

Re: symptoms--leaking air

I moved coils around and severe shocking seems to be the one particular coil. I would think that this may be the difference between running well and running great. The engine is a 1977; should I be replacing all coils; the 2 cracked coils or just the one troublesome coil. Am I on the right track and/or any other suggestions?

I'm assuming a real marine tech has a tool to check spark-leak as my hair is still standing on end....

 

[HighTrim]

Re: symptoms--leaking air

Coils are a difficult thing to truly diagnose. If they are cracked, I would replace them, about 35 bucks with new boots, wire to plug connector and all. Which is good cause most ppl dont check inside their boot to make sure the spring isnt rusted or burnt from arcing. Have you tried pulling the plugs while running? Best to test a coil with an ignition tester, which you probably dont have. They should also be taken off the power head and tested on wooden or insulated bench top to prevent electrocution, lol.

 

[jtexas]

Re: symptoms--leaking air

Interesting......offering yourself up as a diagnostic tool.....might be some money in that........ ....if you have a manual you can measure the resistance of your plug wires, or run it at night to try and visualize any arcing.

A tachometer would really be helpful if you could get your hands on one, to see just how much RPM difference you get when it "kicks in". From your description it just sounds to me like the timing advances slightly. But hey I'm no expert.

Bet you've did this already......inspect the wiring coming from the stator for any weakness or frayed/missing/burned insulation......check for corrosion around all the grounds bolted to the engine block.

I bet somebody knows exactly what this is, but that person just hasn't read your thread yet..........hang in there.........

 

[darrklim2]

Re: symptoms--leaking air

imported_F_R
quote"You might be running on only two cylinders. When the third one fires, you get that extra kick. Running on two could be a number of causes from spark plug to ignition, to dirty carb for that cylinder, to water intrusion into that cylinder, to low/no compression. Can only guess without systematic checking it out.

Leaks in fuel line anywhere between the fuel pump and tank allow the pump to suck air instead of gas, causing a lean condition, or running out of gas. Leaks between the fuel pump and carburetor only cause a mess (or fire).""

my thoughts:
you maybe able to ground out the spark leads for each bank Or set of cylinders
in other would remove spark plug wire , ground the inside of boot to ground and start up the others to see if cylinder is running ( get spark) if see fires up and runs your gold.
i would check with , ( imported_F_R) to see if this is good idea , it is would i would do.

shipwreck - Just to let you know that you can quote someone by clicking the quote button in the lower right hand corner of someones post. then it will put the "quote" in blue like this so it is easier to tell what you are typing and what was being quoted.

 

[leysathcj]

Re: symptoms--leaking air

Are we thinking that the possible spark-leak from this coil may not be a factor? I guess I was thinking that the coil is operating sub-standard and the boats running ok and occassionly the coil functions fine and the boat runs better. I have a hand held tack which I haven't used during an open run but I'd estimate that the rpm difference between running good and running great is a couple hundred rpm; not a substantial amount.

Wires all look good and contacts are clean. I'll run it this evening to look for arcing.

Testing the wires may be beyond my capabilities but if you'd care to explain, I'll purchase the tools and give it a try.

 

[iwombat]

Re: symptoms--leaking air

Sounds to me like you've got a bad plug wire. Probably all corroded at the end just before the spring clip. Essentially making two gaps, one in the plug wire and one in the plug. Wire removers + you are a quicker path to ground.

When this happens, even small temperature changes in the material change the resistance characteristics. Conduct get hot, no conduct cool down, conduct get hot . . .

Try swapping just the plug wire and see if your symptom follows it.

 

[leysathcj]

Re: symptoms--leaking air

Plug wire seems to be a permanent part of the coil. Is it possible to cut off "plug" end and spice in new wire?

 

[iwombat]

Re: symptoms--leaking air

You can just pull them out of their socket with a little tenacity. You'll need a little lube to put them back in. Soapy water works fine.

I've got the same coils on my '77 85hp.

 

[Silvertip]

Re: symptoms--leaking air

You don't need a tester -- just a pliers with an insulated handle. Start the engine and pull one plug wire. If that cylinder is firing, the loss of spark should cause a drop in engine rpm, it will sound different and may even stall. Thats a good cylinder so reconnect the plug wire. Repeat on the next cylinder. If you hit one that does not stall or does not change the sound of the engine, that cylinder is dead. You are then getting intermittent spark on that cylinder under way and that's the extra burst you are feeling.

 

[leysathcj]

Re: symptoms--leaking air

I can't believe that it is this easy but IWOMBAT's suggestion may have cured my problem. I did pull the wire from the spark plug boot and inspect. No corrosion but I was able to re-insert the wire a bit further than it had been. It's hard to believe that a "close proximaty" connection is all that is required; no positive fastening of the wire and spring boot insert.

I connected everything and started the boat w/ muffs to conduct the "dead cylinder test" again; mainly hoping for a reduction in the spark-leak shock . Happy to report no shock found and engine idling smoothly. Tried a couple of times to make my hair stand up to no avail. Removed boot again to clean connections, re-inserted and applied elec. tape for added holding power. Will test run this weekend. If everything checks out, I may add some kind of adhesive instead of the tape to be certain wire stays in place inside boot.
Any adhesive suggestions??