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188 igncarb argument needs closure

B

bobber

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"I need a conflict settled bef

"I need a conflict settled before spending the cash;

188 merc was propped WAY wrong when we got it (17 was spun, he put a 23 on it). With new prop, have bad misfires, stuttering, cut-outs and some backfiring under full throttle at load, and unbelievably takes just as long to plane. Problem seems to kick in at about 2000 rpm - first 2k are quick and she jumps from a stop to 18mph and just stays there. For what feels like forever.

Pulled plugs on starbd - 1 and 4 are tan and perfect, 2 and 3 are sooty and wet looking (not water).

The argument is : Brother thinks it's a carb/fuel prob, I'm thinking plug wires or possibly even cap/rotor (although they both inspect visually OK), as if it were fuel problem, all 4 would/should be 'wrong' together.

It eventually does get up and hits spec. WOT RPM, but I'm not getting any younger, and the backfire/misfire can't be doing her any good.

560 hours on motor btw, and idles like a purring kitten - no heat isuues, fresh gas, no oil loss or increase, starts in under 1 sec cold, maybe 3-4 hot.

Loser buys, so I hope I'm on the right track."
 
"may want to get a compression

"may want to get a compression tester out to settle this one. If it says what i'm afraid it will, both of you lose."
 
"Thanks! (Although I woul

"Thanks! (Although I would prefer one of my listed options).

I have that on the list as well, but the low end is extremely strong and the problem onset is very sudden - almost like it's over or under-advancing on the timing. Also, once she's on plane, you can cut her back to 1/2 throttle (just to maintain plane) and nail it and has great acceleration - just dogs real bad in the mid range. (2-3k)

Even with the 23 on, it was (obviously) very lugged, but there was no missing or backfiring - just slow to plane and WOT was only 3200-3400 depending on load. Nonetheless, I'll check it and stand by for other input (which I'm hoping to be less catastrophic)."
 
I say plug wires. Clean the p

I say plug wires. Clean the plugs and switch the wires; 1 to 2 and 4 to 3 and see how it runs. Get rid of the 23P prop.
 
"After re-reading, it could be

"After re-reading, it could be both issues. The misfires could be due to the timing advance weight/spring mechanism being rusted/damaged. 2000 rpm is the right range for that to be easily noticed.

The center plugs could appear 'rich' is the float is old and a bit absorbant. this may cause a slight increase in the fuel level in the bowl and this excess may only be enough to color the plugs on the 'close' cylinders.

Either way, its time for some methodical diagnosing. Let us know what you find."
 
"Well after a run to Autozone

"Well after a run to Autozone to borrow their compression tester (which is a complete POS btw), and having the Jebus scared outta me most of the day, I have some relief. The compression isn't stellar, but it's pretty even, and oddly enough, the best compression is on #3, which was the worst looking plug. The one they loaned me was impossible to get past lightly finger tight as the hose swiveled on a flat flange too small to wrench, but they all hit +/- 120-125 even with that leaky rig, and 125ish with a few squirts of oil in each. She's 34+, so if she wants to burn a LITTLE oil, I'd allow that, especially vs. one or two REAL low cylinders.

Can't water test until after the weekend - I have a trip to guide leaving in the morning, but for the money, plugs and wires is going to be our starting point. I'd do the swap test, but she runs fine on the hose and even under load up to a certain point, so it may be moot. And yes - the 23 is on craigslist, I have a 19 spare (other boat) on her now, and the 17 will be done tomorrow, so between the prop and plugs/wires I am progressing with crossed fingers.

For the record, the 2,4,6,8 are all in great shape (plugs), and compression is pretty even, but ranges slightly higher than starbd at 125 to a bit over 130 dry, so I'm leaning electric vs. fuel for the time being.

Thanks for the input guys! This site is the best thing since sidewinders and ratcheting wrenches."
 
"[b]" Brother thinks it&#3

"" Brother thinks it's a carb/fuel prob, "

Ayuh,... Your Brother is Right,...
It's going Lean under load..."
 
"Just so you understand a bit

"Just so you understand a bit more,

The center plugs always tend to run a bit richer than the outer plugs. Simple gravity. the fuel source is closer there fore more fuel in a shorter period of time.

That bieng said when all is not just right then the center plugs closest to the carb will look wetter.

One way to do a check for cylinder loss is to get a very very thin and sharp test light and when the boat is under power with someon else driving. clip one end of the test light to ground and STICK the thin sharp end directly into each spark plug boot where it exits the dist cap and short each one to ground and listen/feel how the engine runs. If there is no change then you have pin pointed a problem cylinder(s) and can diagnose what is causing the failure from there, (fuel, wires, plugs, internal)

This is a quick and dirty check but do not over puncture the wire boots so as to cause a issue, just a simple proping action."
 
"I have this in another thread

"I have this in another thread, but wanted to drop it here too in case someone else is following.

Why I didn't notice it before is beyond me, but while taking the carb down to clean, noticed that the choke was ALWAYS wide open. Even stone cold, the butterfly lever wasn't even touching the spring - it was apparently 'adjusted' to straight up and down - more visually appealing, but hardly functional. For giggles, put the spring part in the freezer for an hour and checked it - it still wouldn't touch when installed where it was.

Timing & dwell set back to factory spec, and (now) choke is right. Correct prop back from the shop and on. New plugs and wires. Sea Foamed intake side, thoroughly cleaned carb and bowl/jets/pump. Water test Wednesday. Fingers crossed."
 
"Well wanted to check back and

"Well wanted to check back and relay the final synopsis.

SOMETHING - whether prop change, new plugs/wires or tearing down and scrubbing the carb ... worked.

Hit Pend Oreille for 4 days and the old girl ran flawlessly. Gas mileage went to hell in a hand basket, so I'm leaning towards the carb not giving her enough gas (lean) prior. Planes right, runs right, stays cool and idles perfect. Still don't know which problem was the main contributor, but all those things needed to be done, so it all ends well.

Oh - and I did the carb work, bro bought the plugs and wires - seems like a fair settlement.

Thanks to all!"
 
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