Wits end again - 75 V4 115. Will an oscilloscope help??

[CamaroMan]

So - working on this motor for a customer.. So far all the DVA and ohms readings check out. Ive eliminated a faulty tach/rect/kill circuit.. I started getting small shocks near the pack- im wondering if the insulation has broken down causing cross arcing and grounding out the 300v wires from stator to Cap in the cdi pack..

Ive swapped plugs coils wires the works. Im getting random weird dips in the motor (see this video).

I also read this thread but couldnt find any conclusive thoughts from it..

Here I am taking readings from it running (turn on subtitles to see the readings):

https://forums.iboats.com/threads/using-an-oscilloscope-in-place-of-dva-peak-voltage-adapter.627812/

 

[Crosbyman]

if you install a spark tester... the ones that flash ... you may be able to see which plugs are misfiring . you can then focus on that circuitry.

plugs all good .. yes ?

 

[CamaroMan]

plugs good yes - i have an ignition analyzer with a graph and they all are kinda stable... but when it drops its not all the way down, like the whole system takes a hit, and its very all over the place.. shocks at the pack, dunno... been fiddling for hours, im trying to learn more than anything.. love hate is what it is...

 

[QBhoy]

No clue about these engines, but I’d put a meter across the ac side from stator before the rectifier/regulator and see what you have. Then a meter across the rectifier dc output and see. Then if both of them are all good…check what’s actually going into the battery. If that’s all good..run a jumper lead or makeshift earth cable direct from the battery negative to an earth on the block or around different earthing points around it. A bad earth or shorting like this can be a pain to pinpoint. You can easily get signs of shorting just about anywhere and everywhere you test or prove, around the whole system. I’ve been dealing with similar too.
Just a thought. When she’s running…try gently messing with the main loom and see if she’s getting affected.

 

[QBhoy]

Sorry. I see you’ve done some of that already.
Does it have power trim ? Electric choke ? I’d try operating each and see if that does anything. Trim motor could be shorting and affecting the whole thing. Can you unplug the non essential from the harness ? Could any relays be shorting ? Did you say the ht plug leads are showing stable continuity even when you flex them? Any signs of any of the earth wires in particular that is hotter than others ?

 

[Faztbullet]

Take a timing light and hook it to each org wire going to coils and see whch one/s are miss firing. You also need a DVA adapter as digital meter are to slow to catch a voltage flip. You should have seen the trigger voltage flip from + to-

 

[Crosbyman]

run the engine in total darknesss...see if you have arcing anywhere

 

[flyingscott]

That motor is definitely not running on 4 cylinders. Get a plastic pliers and pull the plug wires one by one. How clean are the carbs? Coils cracked?

 

[CamaroMan]

motor is def running on all 4- ive been analyzing the ignition graphs on each to look for oddities.. replaced all 4 carbs with oem ones yesterday - same issue. When i tried the open gap tester one of the fairly new sierra coils arc'd right thru the coil body to ground, and this was on a 1/2 gap- all new CDI components btw..

Is the upper crank seal dual lip? cos i sprayed some wd 40 under there while idling and i was able to stall the motor for the first time so have ordered a new one.. this issue is only really at idle, part throttle its pretty smooth..

Reason im asking is because the seal only had an inward facing / lower lip in pretty good condition (soft and not worn at any point), no upper lip facing out on top blocking a suction - so im wondering if the upper seal disintegrated allowing air to come in..

here is a video of it

 

[flyingscott]

what is your compression.

 

[racerone]

Motor seems to have electrical issues.-----Spme basic trouble shooting will find the issue.

 

[racerone]

If you think the upper seal is an issue, then replace it.----Post another video with the engine idling after a new seal is installed.

 

[ct1762@gmail.com]

those grounds do NOT look clean. wouldnt hurt to do a continuity check on all of them. not sure but if the powerhead isnt grounded, it might effect the pack. also very possible its coils as it sounds like cutting in and out on less than all cyls

 

[Scott Danforth]

rusty fasteners and green lugs means corrosion.

 

[CamaroMan]

I would imagine the seal would be double lip correct? When i removed the seal it only had one inward facing lip meaning the crankcase could potentially suck air.

I have run new extra grounds - no change Also removed sanded greased all surfaces and connectors - no change. ITS NOT THE GROUNDS.

New seal arriving 2moro - will upload once installed.

Spraying wd40 underneath the flywheel stalled the motor so im 99% sure.

 

[CamaroMan]

what is your compression.

120-130 on all 4- first thing i checked.

 

[racerone]

Well----I doubt the seal is the issue.