TomZ

iTrader: (2)

Hey folks,

Ran the boat pretty hard yesterday afternoon coming back up the Potomac. Oil pressure stayed consistent (which is always good), temp stayed right at 160* (another plus), and the motor seemed to perform very well. I ran it for probably a 45 minutes at speeds between 4200 and 4800 with some brief slow downs to cruise at under 4000 while dealing with the rules-of-the-road.

Anyway, by the time I made it to the no-wake at Alexandria (about a 25 mile run from where I was), I noticed that the motor sounded a bit different. The idle wasn't as choppy as it had been and I could tell that it was missing slightly (maybe even loading up a bit). Also, I could hear a hissing sound that seemed to be at about camshaft speed. It wasn't down on power too much though I didn't erally push it from that point (seemed to still pull like a train once out of the no-wake area). I went back to the marina to pull it out and found someone using the ramp so I had to wait my turn. While trying to motor around the motor stalled out when going from forward to reverse. It was a mother to start from there, though she did restart (seemed flooded to me). The motor sounded the same as it always did though while trying to start (meaning, it didn't sound like an engine would that was down on compression in one cylinder, etc... which is what was really worrying me, with the hissing noise and all).

So based on the above, and the fact that I have the "black transom" syndrome, I'm thinking that I might have fouled a plug. I think my coil was having some trouble lighting it off at high speed so again I think it's plug related.

Any quick ideas or things to check out? I have not done anything with it since yesterday. I loaded the boat on the trailer and then headed straight over to my folks for my birthday party and then dragged it back home afterward. By then it was too late to do anything else so I cleaned up the boat real quick and went off to bed.

Any thoughts or suggestions would be appreciated!

Thanks!

NObaja

Had a similar situation a few years back, it was a broken valve spring. Also check for a broken rocker stud.

The black transom sounds like carb tuning issues.

What's your setup?

TomZ

iTrader: (2)

It's a 383 Chevy.

10.3:1
Comp XE 274H
Vortec heads with big valves
Performer intake
750 Q-Jet.

I didn't hear any tapping that would indicate a broken rocker or stud... just the hissing a poor starting. If the plugs didn't show me anything then I was going to yank the valve covers off for a quick look.

Now, just for curiosity sake (and because I'm a worry wart), what would a holed piston sound like? I have had no detonation problems since removing all the old gas and I'm running very conservative timing (32* tops). But the hissing erally bothers me. The motor does seem a bit rough off idle but smooths out as power is increased so I eally doubt it's anything like that, but still I think mentioning it is good.

Vinny P

The best suggestion I have for you is to run a leakdown test. That will tell you right away if there is an internal problem.

John B

Hissing..... have you checked for a vacuum leak? Did insulator blowout of a spark plug?

Griff

Sounds like a vacuum leak and or carb problem that created the condition. An easy way to check fro a vacuum leak is to get some aerosol carb cleaner. Spray it in quick spurts at different places on the outside of the carb. If the rpm goes up when you spray it on a spot, thats where the leak is. Also spray it on the intake to head area if you don't find a leak near the carb.

TomZ

iTrader: (2)

Thanks guys!

I'll probably have a look at it tonight as long as it doesn't rain.

rws

iTrader: (3)

Check Ignition timing, my friends boat suddenly lost power last week and the culprit was a loose distributor.

Rob

jr

Tom, you didnt mention. What kind of speeds you were you running when you were running hard.

I had mine out this weekend and spanked it abit. She sounds really nice. I have a cruise of about 40 at 3000. Around 4200 I was at bouncing at 55-60 on the speedo, which is pretty accurate but I didnt have my GPS. I ran it up to 4800, no secondaries yet, and my speedo pickup flipped up because of the speed, but I was around 65. Those things scream. Ya gotta love SBC's. But I'm still afraid to run them too hard for fear of having them come apart again.

My boat looks somewhat unassuming but sounds fast. I had a punk on a modified wave runner pull up along side while I was cruising at about 45-50. The look on his face when I nailed it and the boat just took off was priceless.

Personally I would check for a cracked plug. Also what jets are you running. I checked mine and they are 68's on the front for the 409's. I didn't check the rears but they aren't coming on anyway. But I get a very light dusting of soot, after running 80 miles over a couple days. I still need to put a set of plugs in and read them at a high cruise and see how rich things are.

TomZ

iTrader: (2)

Jeff,

I'm still running into issues with props and the fact that I need to spin it to at least 5500 to really make it sing. I have not had it that high yet...maybe 5k or so. Anyway, cruise with my 17P is 33 on GPS turning about 3200 RPM. I have the same problem with my depth finder and speedo pickups getting smacked up when I get into the upper 40s. I still don't have the tune down right so about 50 is all I've been able to get out of it. It's possible, too, that I'm over cammed. Lift and duration are great but the LSA could stand to be a little wider to broaden the torque curve. I haven't seen the dyno specs from this combination other than the peak numbers. Can you run that stuff through the Desktop Dyno again for me?

I love my motor, too. I had the same thing happen with a jet ski the other day on the way back. Too much fun! My boat starts to get a little freaky though at higher speeds so when she gets up to 50 it starts to be a handful.

Here's something cool though... we went tube riding behind her on Sunday... man what a blast. I wanted something a little more special from it and decided to unhook the tube and go a drift while my buddy ran the boat to and from me (about 50 yard away from me in a protected area so I wouldn't get squashed by approaching boats). Talk about music to the ears! I'm going to make some changes here and there that'll help the performance appearance some... though the sleeper image has been really cool!

Thanks for the advice. I'm goign to mess with it tonight if it isn't raining.

Later!