Temporary Power Loss after Fillup

[PITBoat]

Is there a logical reason that might connect these two things, like anti-siphon valve or some such, or was it just a coincidence?

I filled up the gas tank today for the first time in many trips, and when we first powered up there was a noticeable shortfall in power. Starting and idling at the dock before that was normal. It seemed to rev normally in N too.

We messed around and started to pack it in a couple times and go home, but it began to smooth out after 5mi or so of running upstream from the dock and back, and it was normal for the rest of our time out, hitting over 40 once in roughish water.

It was really damp here this am, but the engine cover was on. The first manifestation was just power shortage, and it'd only do like 3,500 wide open; after we stopped and tried again, there was a noticeable continuous stutter or misfire with it too.

I'm gonna pull the plugs and look at them, maybe look at the inside of the dist cap again. I wanted to ask the question though, in case there is possibly something about the fillup that was the issue.

 

[dingbat]

Only if your fill up included some water off the bottom of the fuel tank.

Otherwise I would check to make sure the tank vent lines are clear. Seen them (low spot in vent line) fill with water after heavy rains

 

[PITBoat]

I blew into the vent - seems clear; I can hear liquid movement, and smelled mild gas fumes after that. Tried it with the cap on and off. We've had storms, but the vent and gas cap were under the tarp.

I did wonder at first about bad gas, and my son said that too, but what are the chances of that? Not likely.

 

[racerone]

Perhaps it is time for a complete fuel tank cleaning and new filter.----How old is the boat and when was tank cleaned last ?

 

[dingbat]

We've had storms, but the vent and gas cap were under the tarp.

Been there done that...

Long story short, boat was leaning in such a way that the recess surrounding the fuel cap was filling with water and leaking past the bad o-ring in the cap.

Was this a one time thing or an ongoing issue?

 

[PITBoat]

Boat's 32. Don't know about when or if on tank cleaning. I changed the fuel/water separator last season I think, but no other fuel filters that I remember. When I first put it on the water this season, I felt a slight hesitating that didn't even show up on the tach, but it smoothed out after a bit and has been fine since.

I checked the plugs and dist cap terminals (inside) this afternoon. All that looks good to me. I plan to have it out again later this week, so I'll see if that issue manifests again.

Yeah, my gas cap is right near where you step back into the boat from the small swim platform, so it's getting some water on it then; not ideal, but it seems to be sealing fine.

When I say it was damp that morning, I mean like everything dripping with dew. The windows on our house even, in a way that I haven't seen in I don't know when, so I do wonder if that could've been affecting the electrics until it all heated up a bit and dried off. The tarp was off the boat overnight. I know some old (land) vehicles seem more sensitive to that than others, like washing the engine off, and expecting it to run normally after that.

 

[PITBoat]

Some version of the same thing, but not as pronounced, when I had it out this week. I powered it up before the initial docking and loading everyone this time, and it didn't come right up to normal RPMs as it should have. It came up on plane and that, but was a little short (like not wanting to come up over 3,500 if I remember).

It cleared up fairly quickly this time though, so we boated with a full load and it ran fine (except for a brief bog on warm power-ups more often than not) and again hit over 40 at one point during some maneuvering around traffic, which woulda been straining for like 4100RPM or just a bit more (still a little short of spec, I know; 4,300ish is the most I've ever seen).

I'm gonna back the mixture screws back a half turn since I had put them in total of a full turn a few outings back (I felt it was running a little rich), at some point soon carefully file the points and recheck dwell angle, and have a look at the coil wire, since it wants to pop back out some instead of staying down inside the tower.

I need to run through the carb tuning steps, which I saw a good tutorial of on it still runs (can I say that here?) (Rochester 2bbl), but never have done. I don't know if it was rebuilt properly or not. I know the PO tried it, and had his shop redo it because he got something backwards.

I'm happy it does smooth out at least, for now.

I did notice an RPM gain when coming back to dock under partial power when I hit a shot of UP trim. That doesn't make sense to me as being related unless it had something to do with electrical power supply, or something binding in the drive, which I don't think on the latter.

 

[Lou C]

Well I can say that it makes sense to always go thru the ignition system first to rule things out, but I have averaged about 6 years between rebuilds on my Rochester Quadrajet 4bbl. The main thing is the cleaning. You need a real air compressor not just canned air. The gas cap, I’ve found that the rubber gasket on those cheap Perko caps dries out so I change them every couple of years. I always dump the fuel filter and have not found water in the gas for like over 15 seasons worth....

 

[PITBoat]

UPDATE: Before taking it out again this weekend, I lightly filed the points and checked the dwell angle and timing (just under 37deg and 8deg BTDC; spec is 39 +/2 and 6 BTDC. I dumped the fuel/water separator afterwards and it was full of clean gas.

On the lake, sometimes it had almost full power (up to about 4k and 40mph, which is still a little low), and sometimes not.

I'd set power at say 3,500 at what seemed like a lot of throttle and it'd run there for a while, then come up to say 3,750 on it's own. I'd pull it back to 3,500 and it'd run there for a while, then drop to say 3,250 on it's own.

So the issue is somewhat intermittent. This boat'll do 45 on a good day (and prob more if an expert tuned it), so even at best now it's coming up a little short, though we had a decent load out again. My son said the engine sounded different, and was "doing all kinds of stuff"; uncommanded RPM changes large and small is what I took that to mean.

I'm gonna check the coil next, maybe fuel pressure, maybe try to get the points gap closer to dead on, then ? I need to buy or make a screwdriver long enough to do the running mixture adjustment w/o losing a finger in the belts, but I don't really think that being off a little would cause this.

I'll update when/if I find exactly what's wrong.

A sidenote, I maneuvered the boat cold at low speed briefly before first docking, and idle was under 500, boat barely running there, but I noticed how easily it came out of gear like that. No surprise there I guess.

 

[Lou C]

Your ESA should be dropping the idle to approx 450 rpm. Mine shifts out of gear with 2 fingers...set idle in the water in gear at 600....
when was the last time the carb was cleaned?
Fuel pump is original?
Rochester carbs have a small inlet filter was this ever changed?

 

[PITBoat]

Carb was rebuilt within the last 4 years or so by PO's mechanic if I remember. I wouldn't be surprised if the pump is original; it seems like everything else was/is. My batwings had "Litre" on 'em too.

Small inlet filter... I looked at that fitting at the carb within the last day or two and wondered if there was a filter in there. I haven't touched it, so at the last carb rebuild was probably when it was changed. I'll open that up...

I think I put the condenser that I got the boat with, back in last summer after my first try at doing new points and condenser. That's probably 4 years old or so too... Can't remember if I left the new points set in or also put those originals back in (since my results with the new stuff was a hundred or 2 RPMs short of what I had before that).

That sounds about right on where my RPM is at idle, at least on my cluster tach (Equus?); more like 500 before it warms up a little; and I see it drop at the shifts. Once it warmed up a little the shifting was back to it's stiff-ish normal.

 

[PITBoat]

UPDATE II: I had it out for a good run today, and I think what helped was a new condenser. I did have one small uncommanded RPM drop from full throttle after 10-15min runtime, but otherwise it ran close to as good as I've seen it - 4,200RPM+ and 43mph+ all out.

Other stuff I checked/did besides above:

- Inline fuel filter (hard porous thing) - fine
- Coil resistance (a little higher than spec if I did it right; ordered another one)
- Sprayed oil off of both sides of (flapper in carb; can't remember the name) w/carb cleaner - didn't help (1500rpm test on the hose - seemed to be struggling)
- Running mixt. screw adjustment - didn't help
- Changed to new condenser and checked idle timing and dwell again (7, and nearly 38) - ran noticeably better on the hose last night after that, smooth at 1500 and revved well. Didn't completely like 2k once (mild audible misfiring), but it's had a low-mid RPM iffy spot since I've had it.
- Looked for anti-siphon valve; I only see a 90-degree fitting at the tank that might be where it is?

Also ordered a carb kit. Prob oughta get some plug wires too.
Boat still has the same gas, abt 1/2 tank, that brought this whole question on.

Thanks for input.