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350 Won't Stay Running Under Load.

CheckmateFever

CheckmateFever

Well-known member
My summer has been a bust so far. In the spring the shop that takes care of my boat put a brand new SEI Alpha on the back of my boat. I picked it up, couple weeks before Memorial Day weekend, got to the lake and it fired right up with no problem. Idled fine, went into gear smooth, backed it off the trailer and idled out. When i tried to advance the throttle from idle (in gear) it died instantly. No cough or sputter, just like i turned off the key! That's all it would do, so i dragged it back to the shop. Three weeks later, now after Memorial Day, they call and say "it's running great, no more problems". Supposedly clogged fuel filter, also cleaned out the carb, and did a full tune up (to the tune of $400). Get back to the lake, the boat does the exact same thing, idled in gear fine, quits just barely touching the throttle forward. :brickwall: Took it back to the shop, mechanic is stunned, now after a couple more weeks diagnosed it as a worn out throttle cable causing it to trip the shift interrupt switch. So in goes a new throttle cable (and more $$$ too). Get back to the boat launch, guess what, still quits when advancing the throttle in gear!! Are you kidding me?? :brickwall::brickwall: Back to the shop, this time we put it in at their launch, he makes a few adjustments, and we take it out for a test run. Now, it would start to come up on plane, somewhat laboring, then quit just before getting on plane. :mad: Well at least that was an improvement. Does a couple more adjustments, still same deal. :brickwall: Leave it again, talked to him 2 weeks ago, said he's had it out several times and is pulling his hair out, never seen one act up like this. Ran every diagnostic test there is, everything is checking out good. Rebuilt the carb, gone thru all the ignition, so far hasn't figured it out. It revs and sounds perfectly fine while in neutral! Any idea's i can relay to the mechanic? They've been a good shop for many years, maybe not so much now all of the sudden, i don't know. Clocks ticking away on boating season, the frustration ship set sail along time ago!!
 
Sounds like it may be starving for fuel. If fuel filter was plugged as described, plugged with what? May need to clean out gas tank. Might be clogged fuel pickup/ strainer in the tank. Check that fuel lines are in good condition and not collapsing. Chedk fuel pressure at carb. Good luck.
 
Might consider an accomplished mechanic. Someone who has the knowledge and capability of actually tuning the machine. In your circumstance, the mechanic (or do we call him a technician?) should install diagnostic equipment onto engine and take her out for a whirl. You would have multiple meters and indicator lights hooked up for voltage, timing, spark, fuel pressure, amps, ignition, oil pressure and temps, the works. It doesn't take long to figure out what's going on without throwing parts and money at a problem. A well thought out, structured, logical approach to trouble shooting the symptoms will not fail. Seems to be a lost art these days. If your man did not have the engine 'wired for sound' how could you possibly know what was transpiring?
 
Jimway said:
Might consider an accomplished mechanic. Someone who has the knowledge and capability of actually tuning the machine. In your circumstance, the mechanic (or do we call him a technician?) should install diagnostic equipment onto engine and take her out for a whirl. You would have multiple meters and indicator lights hooked up for voltage, timing, spark, fuel pressure, amps, ignition, oil pressure and temps, the works. It doesn't take long to figure out what's going on without throwing parts and money at a problem. A well thought out, structured, logical approach to trouble shooting the symptoms will not fail. Seems to be a lost art these days. If your man did not have the engine 'wired for sound' how could you possibly know what was transpiring?
Click to expand...

Jimway, actually yes he did do all that, the thing looked like it was hooked up to a life support system... and again, as i was told, everything checked out! Don't get me wrong, i'm questioning the competence, but i've gone to this shop for over a decade now and they've never before now let me down. 2 other area shops did before them.

Flyby, that may be the best possibility i've heard so far, crap in the tank. The fuel line to the carb looked ok, not sure about the lines to the filter and pump.
 
Apparently he didn't do it good enough. This is simple. plumb in a pressure gauge at the carb. We have a water trap there also at the same time. We hook up indicator lights to the ignition etc to see if any safety devices or interlocks are causing grief. Vacuum, dwell, ignition output, hell, we even have a tailpipe sniffer to check A/F mixture (going fast costs money). Granted, I have been at this for a while and have amassed a bunch of cool tools but If you suspect a control problem unhook everything and run engine by hand. If you suspect fuel delivery problem, plumb in test tank. Hook up a timing light and see what happens when coming up on plane. If you have compression, ignition and fuel, it will operate. Spray some starting fluid into the carb when it bogs, if it comes back to life, you know which way to look. It just doesn't take that long to do this. I would like to hear that you have made it out on the water successfully.
 
Jimway, man i wish you lived closer to me and not a whole continent away! I haven't talked to the mechanic in a week and half now, i was out of town and busy but i'll be speaking with him either tomorrow or Friday. When i had it in the water one of the times, when i quit at the first slight advance of the throttle, i did try manually moving the carb linkage and it started to take throttle with out quitting. But no one was steering the boat so i had to back out of it. That made me think it had to be the shift interrupt switch, but i guess it was just the cable not adjusted properly. Quitting while coming up on plane has to be a totally different issue, correct? The boat ran perfect all season last year, only big change this season is the new SEI Alpha drive on the back....
 
If I could, I would so be there with a load of stuff (good stuff, that is). Very interesting that it would take throttle by hand sans the control. Bypass neutral interlock and see what happens. Get a helper to pilot vessel. Have your volt/ohm/dwell meter hooked up along with a timing light. I have little light bulbs with alligator clip leads attached to hook to coil supply and ground to see if power is interrupted at a glance. I'll use several volt/ohm meters to check voltage at various important locations. I have magnetic mounts for some test equipment, like an inductive timing light that can be run, hands off. With this equipment in place, a water test, we call it 'sea trials', can get underway. you will discover what is wrong in short order. And now, it is time for a short story. I helped a buddy buy a donor truck because his was developing a nasty noise from way down below. Got this screaming deal on a rear ended low mileage truck, 7.5 Ford. He swaps the engines out and goes to fire it up and it is all kinds of sick. they swap all kinds of parts back and forth and then call in the old guy. Now I had actually drove the donor truck and it ran perfect. I get over there and my buddy is all kinds of frustrated. Engine sounds terrible. I ask all of these questions, Sherlock Holmes like. He gets more frustrated. I'm sitting there in the garage looking at this new bag of rags. I can account for 23 of the 24 that were in the package. I know that he borrowed a lifting hook that I made that bolts on to the intake manifold. I ask him where the missing rag is. They all look at me like I'm an idiot. I pull my bore scope out of my bag of tricks and look down the throttle body. You guessed it, it is right there where they left it, in the intake manifold.
 
Jimway, got my boat back from the shop, and it's running pretty much normal again! Talked with the mechanic for a little while, can't pin point exactly where the issue was but it must have been something electrical. He went thru the main harness and other connections, cleaned and greased them all, and it started running just fine. Hopefully it will be trouble free the rest of the season! The new SEI drive is pretty noisy, but that's supposed to be normal for the SEI's.
 
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