'81 90 horse V4; carb troubles

[100percentjake]

Hi all. Got a family heirloom Starcraft that has an '81 Johnson hanging off the back of it and I took a look at it this weekend and fixed a myriad of issues (battery cables, starter solenoid, incorrectly gapped plugs, intake plenum not properly affixed.

At the end of it the boat ran better than it has in decades for about 3 hours then became hard to start. I got it back to the dock and noticed that there was a massive amount of shaft play in the carb throttle blade shafts for both carbs, resulting in a large vacuum leak. This leak had also thrown off the sync of the carbs, so I pre-loaded the lower carb to bring it roughly back in sync with the upper and the engine would start, but idle at 1700RPM and was generally very unhappy.

These carbs seem to be a bit of a rarity, and don't appear to have any sort of distinct replaceable bushing for the shafts, leading me to believe my options are to either bore out the holes and machine some delrin bushings, buy another set of carbs and hope they are in better shape (haven't had much luck finding any) or buy the later style of 85+ carb with the adjustment screws in the throat, but then I'd have to get a new intake plenum as well which could prove difficult. Spraying carb cleaner on the throttle blade shafts with the engine running makes the RPMs jump significantly, so definitely a vacuum leak but I'm unsure if it is one that would affect runnability.

Anybody have some insight for me? This motor also appears to have two reeds stuck open on the bottom two cylinders, the coils are leaking potting compount, and it has NGK BH7S plugs which I believe aren't what are recommended. I have two weeks to get these carbs sorted before bringing them back down and putting them on the engine, so any help would be appreciated so I can get parts on the way.

Thanks for any advice.

 

[racerone]

Those carburetors are NOT rare.-----If it ran great then the throttle shafts did not wear out in 3 hrs ??---Did you install a new water pump impeller ?----Test the overheat horn ?---Mixing gas / oil at 50:1 ??-----Post the results of a compression test here.----Does spark jump a gap of 3/8" on all leads , yes or no ?

 

[100percentjake]

It ran better than it did previously, but I wouldn't say "great". It was far from smooth and bogged a little when snapping the throttle open and as the day wore on it refused to idle. Even after sitting, getting it started again was damn near impossible. Plug color looks good, though, albeit a little wet on the bottom two. Fresh gas was mixed 50:1, the engine pees but I'm not sure about the overheat horn. According to a mechanic that worked on it a decade ago it "has low compression in one cylinder" but mechanics around here are hacks for the most part and I'm guessing that low compression is a symptom of the cylinder not getting a full air charge due to blowback through the bad reed valve.
One of my guesses is that there was just a little bit of gunk that had "plugged up" the gap around the throttle shafts that worked free as we ran the engine; it was absolutely filthy.

Is throttle blade shaft play common, uncommon, worth worrying about, should I buy a rebuild kit, reed valves, used set of hopefully-lower-hour carbs on ebay, coils, and plugs and just do a full tuneup on the engine to "baseline" it? Even if there is a hole with low compression, if I can make it run like it did 10 years ago before being mothballed I'll be ecstatic.

I live 4hr from the boat and all i have with me is the carbs themselves so my ability to check on things is limited; just trying to get together everything necessary to get the boat back on the water before I go back down to the lake.

 

[racerone]

Guessing is the right term here.-----The reed valves have absolutely nothing to do with compression in the cylinder.-----Sounds like this motor has broken piston rings .----The MOST COMMON fault in these V-4 engines.-----Post your compression number here before spending any beer tokens on this motor.----If low compression in one cylinder , pull the cylinder head.----Lucky you if it is a blown head gasket.----Head gasket is cheaper than all the other work you are scheduling !

 

[100percentjake]

My 2-stroke experience is mostly limited to mopeds and dirtbikes but I assumed bad reed valves would show up as a low compression test because half of the fuel/air charge would blow back through the reeds instead of the transfer ports, leading to less compressible mixture in the cylinder itself.

Nonetheless, the engine had previously run for years with only 3 functioning cylinders and my goal right now is to get it back to that point as cheaply as possible, and what I am experiencing right now seems to very clearly be a carb/induction issue of some description. There is a bass boat with a junk hull for sale locally for $650 with an '80 Evinrude 90 on it that I may buy as a gamble to see if the engine is in better shape. If these Johnson motors are known for broken piston rings I'm not sure how far I want to go with this existing engine.

 

[racerone]

I am just going to step aside here.

 

[flyingscott]

I don't think you know how a 2 strk works. Maybe get the factory manual or watch a YouTube tutorial.

 

[100percentjake]

Alright well update now that I'm back with hands on the motor. Bought a set of carbs that don't have massive leaky shafts. Cleaned thoroughly, rebuilt with genuine parts. Replaced the reed valves. 3 out of 4 cylinders had absolutely hosed reed valves. New gaskets throughout. Put it back together and replaced all the fuel lines as the jostling from unbolting and re-bolting things had caused myriad fuel leaks. Got it back together, synced the butterflies and set the rollers and timing tower per a youtube video (factory manual would take a month to show up). New plugs, properly gapped. Bright white spark on all four coils. It'll fire up, fast idle, then slowly die. Won't idle at all. Tried a few times and pulled the plugs. Starboard bottom plug had water on it. The rest were still minty clean. Friend brought over a compression tester.

Starboard top: 75psi
Starboard bottom: 80psi
Port top: 85psi
Port bottom: 80psi

He also brought a camera that we stuck in the holes. Both starboard cylinders had some scoring in them. The hole that had water on the plug had a perfectly steam-cleaned piston.

I also found that the cables were adjusted improperly, with the idle lever cable propping the timing more advanced than it should be with the lever at idle.

So... I'm not sure this engine is worth pursuing any more. I had hopes I could at least make it run consistently poorly like it used to when this boat saw regular use but those compression numbers are atrocious and I'm unsure if the water is coming from the headgasket or elsewhere. I don't have the ability to do a leakdown test currently so I'm at a standstill.

Furthermore, it seems that quite a few pieces of the timing tree are worn out and have a lot of slop in them (plastic odd-shaped bushings) and those parts aren't available on boats.org.

I welcome any further advice. Might start looking for a trashed boat in Kansas where old 80s boats probably have seen less frequent use than here down on the lake and yank the engine off of it.

 

[racerone]

There is an old saying ( 50 years ago ) among experienced outboard people-----Most " carburetor trouble " turns out to be something else.-----So here we are.