Rebuilt engine will no longer run well
 

OK, got a weird problem that I can’t seem to diagnose.

Background: I did a full rebuild of the motor and it was running well with likely 6 hours on it. A little hard starting but ran well one started… and was on my list to diagnose later. The next trip up I discovered a coolant link due to an exhaust stud leak from the coolant size. The weird thing was that the motor wouldn’t start as well. So I got a new manifold from MMI swapped the old one out, then noticing that the core plugs on the manifold had slowly leaked on to the carb. So I figured that may be part of the problem with not starting.

So cleaned up the carb, but did not rebuild it, and when I tried to start the engine, no joy. After many attempts, I finally tried only closing the choke halfway and opening the throttle about half as well and could get the motor to fire a bit but then promptly died. A few more attempts and no real improvement. I then thought that “well everything else on the engine is new, I’ll buy a new carb from MMI” and then rebuild the old one at my leisure. So when I put on the new carb, main jet 1.5 turn out from seat… on an the engine ran a tiny bit better, but would now die in 12-15 secs or when I released the choke.

I then checked pretty much everything, fuel gauge at the carb show 3.5 PSI, the polishing filter is new, I triple checked the distributor wires, made sure the carb was lubed and the advance was not stuck. The spark plugs are wet and black t and looks like it’s running rich but the insulated tip it a decent shade of brown (not tan). I checked the cap and rotor, no carbon traces and yes, I have lots of spark. I zero timed the engine three times and finally, with my engine mojo confidence greatly diminished… I even re-watched Don’s video on timing the engine, just I case I had a mini-stroke or something similar.

On the 2.5 hour drive home I was puzzling through what I could have missed and the only hail-mary I could determine was there was air leak I introduced somewhere… but that was an afterthought.

One thing about the engine that is not stellar is the distributor has a lot of slop in linear (up-down) shaft. But when I looked that the cut of the gears and rotation of the shaft, I determined the an slop would get "pulled down". Plus it worked well for the first 5-6 hours.

Other ideas of things to try? This my 3rd A4 and the first two I got to purr… but this one is vexing. ☹

Sounds to me like it's time for a test run off an auxiliary fuel tank. Having 3.5 lbs. fuel pressure doesn't mean much if the fuel is 75% water.

Recheck the choke adjustment to be sure it is all the way open\closed when you think it is.

ex TRUE GRIT

Neil--
Thanks! I haven't tried the aux fuel tank yet but the water separator filter was just serviced and there was no visible water in the gas when we replaced the tank. Also, using 87 octane ethanol-free, so less susceptible to absorbing water. That said, I'll next trip i'll bring my jerry can with the 1/4" spigot brazed in the bottom and some fuel line. With the McMaster-Carr flange fitting you turned me onto... it's a simple swap. ;)

John--
I adjusted the choke and made sure it was fully open and shut when working the lever.

All--
Any other ideas?

Double check your plugs. Yesterday my wife and I did 35.3 nautical mile day sail in 18 knts...friggin awesome sail until I fired up the engine. Engine ran rough the 100 feet to the dock. No 4 had no fire and wet with gas... Had fire at the wire...changed out 1 month old plug for another new one. No change. So I automatically think I have more going on. This morning, changed cap rotor and wires from my backup set. No change. As an after thought I pulled an old plug from my tool box and low and behold, it ran perfect again. So one failed plug, pulled one from new box that didn't work and an old one set her straight.

Sometimes the issue is a little around the curve.

Hope that helps.

OPSS issue maybe?

Mo--
I purchased a set of AL 437 plugs, just in case and have an new cap and rotor on the way with my spare new set of MMI plug wires. I might just bring up a disti from my newly removed engine.

Ando--
I don't think it's an OPSS issue since I can watch the oil pressure rise to 25 PSI during cranking and I get fuel pressure at the carb from the electric Facet pump, so I know the OPSS is sending voltage to the pump.

The plan now is bring pretty much a spare ignition system (disti, cap, rotor, wires, plugs) and spare fuel tank with 87 octane clear gas and all the fuel connections. Heck, I'll clean/rebuild the old carb as well.

Any other wisdom, thoughts, ideas, suggestions? The more the merrier. ;)

Have you done a thumb compression check? Seems unlikely to be the problem, but it's a quick and easy verification.

Any water in the oil? From the manifold or from the no-start cranking. Doesn't seem likely for it to run if the exhaust elbow is full of water, or if there's any in the cylinders. At least there's a way out from that problem though.

Just some ideas that I don't think have been mentioned yet.

S2S--
Thanks for the other ideas!

Yes, it passed the thumb test. I'll be bringing the old-school compression gauge up as well, otherwise I will need it. The murphy principle.

Oil is clean and clear. I'll bring some carb cleaner to check to see if I have subtle air leak.

OMG, I need to bring up the vacuum gauge! If I have a air leak, perhaps it could help.

Ron
I there a wire co joined from the starter solenoid at the fuel pump with the wire from the OPSS? This wire activates the fuel pump while the engine is being cranked bypassing the OPSS. This would get enough fuel to the carb for a brief run.
If yes there could be a problem with the OPSS - it's not closing when the key is in the run position which results in no fuel to the fuel pump. If yes to the co joined wire try bypassing the OPSS. The OPSS can fail in all sort of weird manners.


ex TRUE GRIT

GOT ANOTHER ONE
 

Run a wire from the battery to the fuel pump, bypassing the boats wiring and the OPSS. This will rule in\out a electrical supply problem to the fuel pump.

ex TRUE GRIT

John--

Thank-you! I didn't wire the starter solenoid 'r' terminal to the fuel pump. The pump normally seems to kick on after couple of seconds of cranking. I will take your suggestion and jumper from my ignition switched relay to the fuel pump for debugging... just in case.

There's no harm in bypassing the OPSS but your report of 3.5 PSI fuel pressure in the opening post pretty much eliminated it as a problem. Also in the opening post, the report of engine starting but dying quickly puts ignition problems low on the list of possibilities. Then there's the new carburetor. So what's left? Fuel, either quality or delivery hence my suggestion of an auxiliary tank test which addresses both. Has that been done yet?

Neil--

It could be fuel but I need to get back up there (Gig Harbor) so a 2.5 hour drive from Portland. I'll be able to get up there in a week... right now I'm just collecting all the parts that could possibly be "bad".

Sorry, the suspense is killing me. I'm not a patient man.

;^)


I *promise* to post an update from the boat when I get up there. ;)

Ok, Confessions of an idiot
 

Just got up to the boat yesterday and found the problem. In my enthusiasm to replace the leaking manifold i forgot to block the 1/8” NPT port immediately above the carb flange, causing the engine to run impossibly lean.

I found it by following the mantra of my high school electronics teacher, “Always begin debugging with a thorough visual inspection.” I did the spark plug wires, the coil wiring, checked for air gaps at the manifold gaskets, carb flange and then ran a mirror down both sides of the engine… and found that nearly 3/8” open hole in the intake passage. :eek:

I’M STOOOPID, with three ‘O’s (sigh)

I put a brass plug in the port and the engine immediately started. 20 mins later the idle and mixture is set and the motor is running fine…again.

Now it’s not all rainbows & puppies, the alternator is not charging… but that is today’s project along with tranny adjustments.

Thank-you all for the suggestions, your help and wisdom is always appreciated. :)

The alternator is toast. When I measured it output terminal, it would swing between 15.8, 15.9, 9.8, 10ish, 15.8, 16.0, 9.7, 9.9V ... over and over again.

Time to pull the proven old alternator from the former motor.