Motor trouble - ever hear of this? (for the gearheads and I;m not one)

So_I_SkiSo_I_Ski Posts: 109 Baller
I own a 350 chevy block PCM, 4 barrel holly carb so not EFI. About a week ago the motor started dogging at anything over 2600 rpm. I can drive all day at 2600 or lower but anything above and about 7 - 10 seconds later it will stall out unless I pull back on the throttle. I can pin it and again it runs flat out but only for 7 - 10 seconds. I've changed the fuel filter, fuel pump, secondary rotor, checked and cleaned contacts in the distributor and rotor, cleaned the heat exchange, checked the impeller, put in a fuel conditioner (sea foam), sprayed in a carb cleaner and my buddy noticed that it was still misting gas into the carb as it was stalling. Seems like only some kind of ignition issue or maybe a faulty sensor shutting down the engine over 2600. Got a date with a mechanic sometime next week but just wondering if someone has seen this problem before or if anyone has any ideas. Thanks
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Comments

  • InthedayIntheday Posts: 137 Baller
    Condenser if it has one caused this on an old boat of mine
  • RednucleusRednucleus Posts: 238 Baller
    Your description sounds like fuel starvation to me - but that's all I got, sorry
  • jimskijimski Posts: 355 Baller
    Accelerator pump In the carb
    braindamage
  • HPskier1HPskier1 Posts: 48 Baller
    +1 for accelerator pump, did that on an old boat of mine. Rebuilt the carb and good to go or you can just do the pump.
  • Orlando76Orlando76 Posts: 994 ★★★Triple Panda Award Recipient ★★★
    350 PCM 4 barrel? Year? Although they do exist, rarely seen in the wild. Sounds like fuel, most likely the accelerator pump otherwise bowls are shutting off too soon.... but... you have fueling misting which means it is getting something.

    Now if you meant to say around about a 1992 351 PCM then it’s the Pro Tec Ignition going out. But I’ve never seen a PCM 350 from the days of the Pro Tec ignition to know what they used for spark on the 350. I’m not even 100% certain bow tie flavor was available in those short few Pro Tec years.
  • So_I_SkiSo_I_Ski Posts: 109 Baller
    Accelerator pump has two votes so that sounds promising so thanks for the input. It certainly acts like it's starving for fuel and if I let it stall out then it takes a minute or two to start again. And the year is 2006. It's in a Gekko that I bought new.
  • Orlando76Orlando76 Posts: 994 ★★★Triple Panda Award Recipient ★★★
    Really? Got a picture of the motor? Still can’t rule out ignition. Do you have a timing light and know how to use it? Have you taken distributor cap off? Ought to check timing and make sure it’s fully advancing and not a rusty spring.
  • TELTEL Posts: 279 Solid Baller
    Pull the pickup tube out of the gas tank clean the small screen on the end of the tube.
    Jody_SealISP6ballReallyGottaSki
  • 503Kento503Kento Posts: 4 New Baller
    Check your fuel lines, you might be sucking in air through a crack or loose connection.
  • PacManPacMan Posts: 51 Baller
    I would also say carb. Sounds similar to a problem with an 86 mc prostar my family had. Rebuilt the carb and a little tuning afterwards and everything's great.
    If your not having fun your not doing it right.
  • BraceMakerBraceMaker Posts: 3,487 Mega Baller
    Go with @TEL doesn't sound like accelerator pump to me at all.

    You said you can floor it and it acts normal for 7-10 seconds. The start of that would be accelerator pump then power valve as the vacuum dropped the secondaries should be mechanical on that carb.

    Then after 7 or so seconds the fuel pump starves and the level in the floats drops

    My old prostar would do this and every time in was crap in the spring inside the fuel tank pick up tube
    DWReallyGottaSkiRednucleus
  • WindsurfnutWindsurfnut Posts: 78 Baller
    There was a 5.7 HO PCM carb 315 around the mid 2000’s

    Sounds fuel. Anti siphon valve in tank clogged/restricted?
    ReallyGottaSki
  • waterbeatwaterbeat Posts: 12 Baller
    Sounds like a fuel supply issue. Besides what others have mentioned above, there may be an additional filter concealed somewhere between the tank and the engine. Ran into this once on a Malibu where a filter was concealed behind the bulkhead in front of the tank.
  • LeonLLeonL Posts: 2,320 Crazy Baller
    First off, if the engine stalls at cruising speed it ain't the accelerator pump. (Note: acceleration). Some carbs have a filter at the fuel inlet. You didn't mention that.
    Leon Leonard Stillwater Lake KY - SR Driver SR Judge
    ReallyGottaSkiRednucleus
  • DWDW Posts: 1,968 Mega Baller
    Won't be the accel pump as noted, that should have dumped well before 7-10 seconds. Anti siphon valve stuck shut would cause a vacuum and restrict fuel flow, you can clean it with carb cleaner or brake clean. Dirty fuel filter, a restriction in the fuel line, clogged fuel tank vent (if a sealed fuel cap), are likely suspects but sounds like to checked those. Is there anything specific you could point to, did you do anything to the boat just before the problem started (maintenance, run out of gas, etc.).

    Debris in carb a likely scenario, you might also want to check the float level. You might have something on the secondary carb system not allowing fuel to be fed when the secondaries open up thus the mixture goes lean, the visual fuel mist test won't tell you that. So verify both bowls have the same amount of fuel in them. 2600 RPM seems a bit low for them to open but worth checking. Holleys should have a filter right at the inlet IIRC.

    What do you mean by contacts in the distributor, points or hall sensor?
    Tom351
  • JetsetrJetsetr Posts: 252 Baller
    Fuel filter, collapsed fuel line from tank not venting, dirty, plugged or restricted tank pick up filter, restricted fuel line...
    Easy tank venting check trick is to run with the fuel cap off...
    Not accelerator pump.
  • ReallyGottaSkiReallyGottaSki Posts: 39 Baller
    edited August 9
    I was 'arguing' with a guy who said the tank and fuel delivery wasn't he problem, said it was ignition because it fell on its face and had similar symptoms to yours at a higher rpm, and he didn't want me to take the tank out and dip tube apart.

    I squirted compressed air backwards the fuel line back into the tank, the rpm and duration the symptom reappeared became higher and took much longer to occur.

    So the tank got accessed, and the dip tube, screen and such finally got the proper attention

    Another troubleshooting method is to run the engine off a temporary/portable fuel source, like an outboard tank, but it has to have good flow available through its QD.
  • vtmechengvtmecheng Posts: 493 Crazy Baller
    Agree with everyone saying it isn't the accelerator pump, when that goes your engine will bog or die when you throttle up more quickly. The suggestions made from @BraceMaker down are good things to check. Keep us posted.
  • Keith MenardKeith Menard Posts: 513 Crazy Baller
    @Orlando76 I have an 2002 Gekko GTO fuel injected 350. When I was looking I noticed some out there that were newer than mine, but had carburated engines. Odd...but they exist.

    I had similar issues on a Camaro I had...it wound up being the screen filter IN the carb. No one ever checks that one...myself included. The other thing it can be is a collapsed bowl. Sometimes over the years the bowl will get a pin hole or something in it, so it will fill up with fuel and cause a lean out. If I had to guess in this situation...it would be that one.
  • 2Valve2Valve Posts: 167 Baller
    I vote for a fuel tank venting/pickup tube issue. One quick test that's been around for years on old motorcycles (non-fuel injected) is when the engine won't maintain a certain rpm, to open the fuel tank. If there's a sudden rush of air, you know you have a venting problem. Hope you get it solved.
    Keith Menard
  • Keith MenardKeith Menard Posts: 513 Crazy Baller
    @2Valve Yup...VERY easy test...just be careful not to take on water when you stop :)
  • BraceMakerBraceMaker Posts: 3,487 Mega Baller
    @2Valve - bees always the friggin bees.
  • So_I_SkiSo_I_Ski Posts: 109 Baller
    What a great site and what a great bunch of guys taking the time to offer possible solutions. Too many questions to answer directly but I did check that screen at the carb inlet last week and it was clean. There is only one fuel filter and a friend installed that a couple of years ago because it had no filter from the factory (odd). And I didn't do anything that I know of to precipitate this problem such as run low on fuel. Plus it came on in three stages. Started my holiday and all good for first three days. Then day four just up on plane and it died completely. Took a minute to start, then ran fine for two more days of skiing. Then cruising down the lake for 5 minutes and a quick brief drop in rpm and back up to speed without touching the throttle. Then I went home from our place on the lake for two days and when I came back, immediately headed out but only got about 2 minutes down the lake when it started dropping rpm and surging back up on it's own. This continued as I limped back to my dock. From then on as I tried different solutions it settled into that I described initially where I could drive it only at 2600 or lower which I did for the last 5 days of my holidays just to cruise out to where my buddies gather to ski on the second lake. Fortunately, half dozen of us all take our holidays at the lake at the same time and we all have tournament boats so my skiing was not interrupted.
  • vtmechengvtmecheng Posts: 493 Crazy Baller
    edited August 9
    Been thinking about this one. If the tank isn't venting at all then wouldn't it eventually stall even going slower than 2600 rpm? If it were venting some then he should be able to get it up to full throttle for a short time before causing a stumble and that time would likely increase as fuel in the tank decreases because the air is more compressible/expandable. From the description, the stumble happens more quickly. The vent thing is easy to test so he might as well but I have a feeling that won't be it.

    The carb float could be getting stuck such that it can't replenish fast enough or it has a collapsed bowl. Also, did you replace the fuel filter that your friend installed or are you assuming the one he put on is still good after two years? If it's been a couple years you may want to pull it and see how things look in the tank while there.

    If all of these are good it's always possible that your ignition coil is starting to get weak but I feel they don't tend to go in this manner.
  • eleeskieleeski Posts: 3,810 Infinite Pandas
    Not sure what kind of boat you have but some boats have a check valve at the top of the fuel tank where it connects to the fuel line. That can fail and restrict fuel flow causing your problems.

    Some fuel tanks have a sock filter on the fuel pickup. If this is plugged you can get the same symptoms.

    My old American Skier had both a sticky check valve and an inlet that would intermittently plug up. Similar issues even with the new ZO engine. Running on outboard style 5 gallon tanks cured the problem. I removed the stock tank and will clean the tank and bypass the sock filter in the tank (unless I can figure out how to service it) - someday. Blowing out the sock filter didn't solve the problem but something popped for sure indicating that there was a filter there and it was plugged. Bad design when one can't service a filter - but the boat is 40 years old.

    New boats sure are nice...

    Eric
  • BraceMakerBraceMaker Posts: 3,487 Mega Baller
    @eleeski I still wish we had those in ski boats. Hauling the gas in cans anyway!
  • teammalibuteammalibu Posts: 772 Crazy Baller
    edited August 9
    Try running on a clean fuel supply directly to the carb. Eliminate fuel supply issues!
    Mike Erb Cedar Ridge Canton Miss.
    Horton is my hero
  • So_I_SkiSo_I_Ski Posts: 109 Baller
    @vtmecheng yes the first thing I did was replace the fuel filter that my buddy had installed plus checked the thumb sized screen entering the carb. So I was too busy today to try anything but tomorrow morning I will go with Bruce's suggestion and pull the fuel tank pickup tube and check it for debris. Spoke to a merc tech today who had also stopped by to visit a mutual friend and he suggested the primary coil as the possible culprit. So replacing that might be my next trick. After venting or fuel supply hiccups and then the coil, it sounds from you guys that I might be into carb issues but those are beyond my pay grade so I will wait for my appointment with the monkey wrench mid next week. Unless one of guys wants to fly up to beautiful BC and go skiing on a remote lake that Andy Mapple described as one of most beautiful settings he had ever skied on when we had him up here coaching about 6 years ago. He skied at noon each of the three days and ran from 28 thru 39 off at 34 and never missed a ball. He went out on his road bike at the end of each day and said he was in the best shape of his entire life. All lean muscle and I think he said he weighed 178. What a loss.
  • JetsetrJetsetr Posts: 252 Baller
    A float in a carb that sinks cause the engine to run rich, not lean...when it sinks it holds the needle and seat open flooding the engine...usually fuel will run into the engine thru the bowl vent.

  • So_I_SkiSo_I_Ski Posts: 109 Baller
    @Jetsetr thanks for that explanation. So if I understand you that would align with my symptom when I let it die instead of pulling back on the throttle. Then it doesn't want to start for a minute or so because it's flooded.
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