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Bogging down 79 Johnson 140 V4

csider

csider

Regular Contributor
"Here's the story / sympto

"Here's the story / symptoms.

Yesterday, at WOT after around 30 seconds the engine would bog down to around 3000 revs, before suddenly cutting back in again causing surging. On the way back in I also noticed a smaller surging (jerking???) from the engine at around 1500 revs as I approached the beach.

I don't think its a fuel problem as when it occured at WOT I got my passenger to squeeze the primer bulb (no effect) and I activated the choke solenoid (also with no effect).

Back home I tried testing the spark plugs with Joe Reeves excellent spark tester but could see nothing obviously wrong with any plug on engine turnover (good strong, snappy sparks, and painfull too according to my son who put his fingers too close).

Theres no obvious signs of chafing on the HT leads, and I can't see any tracking on the coils. I've also checked the earth/ground on the coils and all are clean. I've pulled apart the HT lead feed plugs - no sign of corrosion.
On the ingnition timing, the action is free and smooth. The fuel pump is working at turn over (fuel pumps into a cloth)

Any suggestions ?? an e-mail I could show "she who might be obeyed" saying buy a newer boat with a new engine would be good :)"
 
Further to my last I've ch

Further to my last I've checked over the HT coils with a meter and found a dodgy earth on one coil (wire broken in the insulation - sometimes OK - sometimes not depending on how you bend the wire).

I've also found the resistance between the primary coil and the post is 240 Ohms on three of the coils and 1.4 Kilo ohms on the fourth (not the one with the wire unfortunately).

I'm not trusting anything with this motor anymore so can anyone tell me what the correct resistance should be between post and primary wire.

All coils are Part number 582106 which according to Sierra Parts catalogue are compatable with the 581998 which was originally fitted.
 
"Have installed 4 new coils an

"Have installed 4 new coils and now the engine backfires, so I assume I've put primary wires in the wrong holes.
This has me confused as the Seloc manual has Orange from Starboard powerpack to coil 1 and Orange/Blue to coil 3.
Port powerpack says its both Orange and Orange/Blue to coil 4, which I know is nonsense, so I've wired it as the starboard powerpack

Any one out there know the correct wireing. I've tried swopping around the wires one side at a time, but it still backfires."
 
Suggest You try to put the low

Suggest You try to put the lower coils with terminals pointing forward to avoid spark-jumps to the cover latches which is a common problem.
 
Hi Morten.

All the coils ar

Hi Morten.

All the coils are fitted with terminal posts pointing forward. I'll re-wire the primaries tonight after work.

Thanks for the replies.
 
"Last night I swopped around t

"Last night I swopped around the primary wires and checked the rest of the plugs to the power packs. Checked the engine fired up and all OK.

This morning I took the boat to the beach and she started first turn of the key (promising).

Got away from the 5 knot area and opened up and she bogged down again after around 15 seconds of WOT.

Back in the driveway I flushed the engine and noticed the port side was running significantly cooler than the starboard side. I know this could be due to the stats, but could it also be due to the plugs now not firing correctly on this side of the engine.

So a couple of questions

1. Is it possible for a powerpack to be OK up to around 3000 revs, and then not OK above 3000.

2. If the stator was failing, this would affect all plugs wouldn't it ???

3. Could it be a perforated gasket around the carbs sucking air in above 3000 revs ??? (I dont think it is this, but I'm going to check the gaskets anyway). I've allready tested the fuel pump and this was ok (pumping fuel into a cloth on engine turn over).

4. I can get my hands on a high quality multimeter an oscilloscope to monitor the O/P of the power packs. what sort of voltage would I be looking for (50 - 60 volt spike ??? positive or negative going ???)

5. is there another way of checking the power pack (measuring resistance / capacitance etc.)

Good news is that the wife has suggested looking at a trade in........"
 
Further to my last have now ch

Further to my last have now checked the following
Sensor coil resistance
Port
a-b 34 Ohms
a-c 34 Ohms
Starboard
a-b 34 Ohms
a-c 34 Ohms

Sensor coil short to earth check - none found

Charge coil resistance test
Port
608 Ohms
Starboard
601 Ohms

Charge coil short to earth check - none found

Charge coil output
Port
150vac falling to 145vac
Starboard
160vac falling to 150vac

Unable to perform sensor coil tests as I don't have a CD voltmeter. Can a digital Volts Ohms Amps meter be used for this test ???

Finally power pack O/P test
Cylinder 1 28 vac
Cylinder 2 2 vac
Cylinder 3 27 vac
Cylinder 4 27 vac
(measured with high end digital meter)


No 2 spark plug now not sparking. I'm bloody positive it was last weekend when I used the J Reeves home made tester !!!

Am I looking at a new power pack ???
 
Swopped over power packs port

Swopped over power packs port for stbd and vice versa. Now power packs have an O/P on all 4 cylinders and sparks at all plugs again ?????

Trade in looking better and better
 
"Take appart all connectors, p

"Take appart all connectors, push out pins and CLEAN! (note possitions of pins before removing).
Check that the rubber connectors does not have any spark traces between the pins, if so change them. Even check that the female-sleeves are tight when putting the connectors together again. If pins are loose in the sleeves - problems like described. Use contact grease, but not too much!"
 
"Hi again Morten
Took the boa

"Hi again Morten
Took the boat out tonight after cleaning both port and stbd connectors, Deep cleaned (copper showing on pins and sleeves) and nipped tight the barrelled (sleeved) connectors onto the pins where possible.

Fault symptoms have changed slightly. I'm still getting bogged down after 15 seconds at WOT, and it still surges/cuts back in for a few seconds after bogging down for 5 seconds or so.

At engine speeds below 3000 revs the engine functions perfectly. Ran for over 15 minutes without incident. So replacing the coils has cured the lower speed jerkiness (is that a proper word ??), but still bogging down at high speeds.

My latest theory is that air is getting in between the block and the carbs and causing a weak mixture, this causes the engine to drop revs and bog down, the air being sucked into the engine reduces due to dropped revs and normal carburation and engine speed resumes for a few seconds before it happens over again.

Is this theory plausible ??"
 
"I think You have a carb probl

"I think You have a carb problem.
It should show on the plugs if You remove them and check.
It might be a float-valve sticking, incorrect adjusted, blockage between pump and carb (dirt) or air being sucked in somewhere. It might even be tank ventilation problem or sticking anti siphon valve?
I doubt there is a gasket leak between carb and block.
Start by taking the tank-end of fuel hose into a 20L fuel tank (no connector -open hose) to eliminate tank problem.
If You have a quick-connector at engine side -put the hose straight onto the VRO/fuel pump as next step.
Then its time for the carbs."
 
"Checked the plugs and all loo

"Checked the plugs and all look normal, though this could be because I have to motor in at 5 Knots for a few minutes and everything is working correctly at this speed.
I tried running without a tank connector into a can of fuel - no change.
Also tried bypassing the fuel filter/water sperator (new filter fitted 1 month ago by the way) - no change
Also tried conecting direct to the fuel pump from the can of fuel so there is only the manual prime pump in the line - still no change (no VRO on this engine).
Tomorrow night I'll strip down the carbs and hoses from the fuel pump"
 
"Whish You luck.
Use a white

"Whish You luck.
Use a white piece of paper when dismantling, and do it careful.
Guess You will find something blocking in the float-valve system/channels.
One way to pre-test is:
Turn the carb upside down and take off the float-bowl.
Take a rubber band not more tight than it holds the wheight of the float in closed position.
Attach the fuel-hose with bulb onto the carb and prime. Any difference in flow between the carbs?

If You are not afraid of fuel-spill You may even do a similar test with the carbs attached to the engine, just unscrew the drain-plugs and pump. Any difference between the carbs and You have the problem one. If You have a well assorted hardware store in vicinity, You may replace the drain-plugs in the carbs with nipples and plastic hoses to collect the spill and monitor more easily."
 
"Final report.
Took the carbs

"Final report.
Took the carbs and fuel lines to the carbs apart.
Found a small bit of rubber partially blocking the lower carbs float valve, probably came from the fuel line last time it was pulled apart and put back together again.
While the carbs were apart I cleaned them.
Put everything back together, link'd and sync'd and put on new fuel hose to both carbs.
Took to the water and tested at WOT for 5 mins plus - no problems.

Thanks Morten for your help/support."
 
[b]i was reading this and it s

i was reading this and it sounds like a problem i was having and it ended up being that i had a crack in my inline fuel filter ran good at lower speed but ...open it up and it would suck air . drove me nuts!!!! till i found the problem. good luck
 
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