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  1. #1
    Join Date
    Oct 2009
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    New Haven, CT, USA
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    Default Both engines not hitting WOT - '88 454's

    For the first time this season, I opened up both engines as I do every year. I was surprised that both engines only got to about 3,700 RPM's. The plot thickens a bit because I re-did my entire helm over the winter (all new gauges, wiring). Everything works flawlessly and the tachs on both engines appear to be accurate and are dead on with my synchronizer at cruise speed. My speed seemed to be in the ballpark but I need to check a video from last year to be sure. That's easy enough to rule in or out with my IR tach. If I selected the wrong cylinder/dipswitch would it be off like this? In past years, I've been right around 4,200.

    No dead spots or any other indication that there is an issue. I assume a fuel filter is something I would "feel" like I have in the past. I ask that because I have stretched out my Racor changes a bit. I was doing them every year and after cutting one open realized that I was throwing away perfectly good filters. I have about 130 hours and about 2.5 years on them now. I should probably just use this as a reason to change both.

    The other thing that comes to mind is my mechanical advance. I still have the original distributors on both engines with about 1,400 hours. It seems highly unlikely that both would stop advancing from one year to the next at the same time. Again, this seemed to be a pretty synchronized issue. I was planning on upgrading the distributors over the winter just based upon the age.

    What do you guys think? The bottom is still clean and same props.

    Bob

  2. #2
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    Default Re: Both engines not hitting WOT - '88 454's

    Bob:

    Since tachs are frequency to voltage converters, having the 'selector switch' set for less cylinders than you have should give you a 'high' reading, so I'd say the setting is correct....if the engines sound 'sync'ed' when the electronics indicate such, then I'd suspect its real.

    I'd doubt both filters suffer the same pressure drop - but if a common tank is used, the fuel may be suspect...???

    Advance could be an issue but, again, I'd doubt both mechanisms have suffered the same amount of degradation - easy enough to check though....

    how long has she been in the water, this year?

    maybe a piece of line has fouled both shafts??? a good visual is in order - and you can get a waterproof USB 'camera' for cheap nowadays - and most are small enough to function as borescopes as well.....

  3. #3
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    Oct 2009
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    Default Re: Both engines not hitting WOT - '88 454's

    Mark, yeah seems weird to me too. The fact that I'm getting almost identical readings on both engines rules out fuel delivery in my mind (separate tanks). I'm going to run it in the slip ans see if the engines get up over 4,000 in neutral and see if the tachs read that high. I have an IR tach and can double check what I see. The boat has only been in about a month and I dove under just the other day, all good. I use Propspeed and just wiped off some slime on the props/shafts, not a barnicle to be found.

  4. #4
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    Aug 2008
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    Fairport, NY
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    1,625

    Default Re: Both engines not hitting WOT - '88 454's

    Quote Originally Posted by bobct View Post
    Mark, yeah seems weird to me too. The fact that I'm getting almost identical readings on both engines rules out fuel delivery in my mind (separate tanks). I'm going to run it in the slip ans see if the engines get up over 4,000 in neutral and see if the tachs read that high. I have an IR tach and can double check what I see. The boat has only been in about a month and I dove under just the other day, all good. I use Propspeed and just wiped off some slime on the props/shafts, not a barnicle to be found.
    did you happen to measure speed of the boat?

  5. #5
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    Oct 2009
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    Default Re: Both engines not hitting WOT - '88 454's

    Dave,

    Yes, I took it out again yesterday and it's even worse than last week although the conditions were not great. I maxed out at about 3,500 RPM's and 20 knots which is about 5-6k lower than normal. Something is up so here is what I've done so far. It seems to be the exact same issue on both engines so I'm just focusing on my Stb engine for now to see if I can isolate the problem (and I have to disconnect and move a wetbar on the port side).

    1) verified that base timing is around 10 degrees. Waiting for UPS shipment today so I can check TA timing.
    2) verified that the advance springs were intact and that distributor rotates and puts tension on the springs
    3) changed my pre filter screen, Racor and carb filter. Also, just rebuilt this carb the other day.
    4) chokes are wired open on both engines
    5) verified that the engine will exceed 4,000 RPM's in neutral and that tach will read that high. Got to around 4,400 and pulled throttle back because I hate to run it that high with no load
    6) flame arresstors were just cleaned
    7) cap/rotor look good, about 225 hours and four years old
    8) plugs are two years old about 140 hours
    9) verified that the throttle cable aligns to the carb at WOT.


    Start up, idle and throttle up all have been and continue to be perfect. Not even the slightest feeling of an issue until you open it up. In a way, I'm glad it is happening on both engines as two common winter projects come to mind.

    1) as i mentioned in my first post, my tachs and all instruments and wiring are brand new. I've read that defective tachs can cause this type of issue which I never quite understood. Isn't the tach just an "output" of what the engine is doing? Can they actually create a running issue? Two defective tachs? Probably a long shot but maybe something else related to that work or wiring.

    2) I'm in the process of adding a Racor LG100 vent spillback unit on each tank. They install inline with the vent line. I have the STB side installed but not the port. In order to get the right pitch so fuel runs back into the tanks, I changed the vent line fittings on the tank from straight to a 45. The ID is the same compared to the straight fitting. I can't imagine how this would create an issue but it is a commonality between both engines. The first year I had my boat, I had a vent issue because the anti-siphon valves were getting clogged. I definitely felt that though because the engines were bogging down. I don't have that issue now.

    When I put the boat away last year it would get to around 4,200.


    thanks
    Bob

  6. #6
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    Default Re: Both engines not hitting WOT - '88 454's

    When the tach goes bad and impacts the ignition, think of it as a low resistance between the sender and ground terminals....these are functionally in parallel with the "points" (or whatever triggers the coil) - so instead of ON or OFF (which causes the spark), you have ON or 'mostly on' = no spark.

    I'd say you still have to isolate the issue as a fuel issue or spark issue....one easy thing, given your history, is to check the cap(s) and rotor real good for carbon dust/tracking....a white paper towel/rag....we used to see it on the old inline six cylinder outboards pretty often....easy fix. Take it off, remove the carbon rod/spring for the high tension connection, and was it out with hot water and dish soap. Let dry and reinstall. Same for the rotor.

    On the fuel side, the only 'easy' thought would be to check the anti-syphon valves again...could have crude in both. one test we used to use at the shop was to replace it with a 'pipe-stretcher' - an old valve with the spring and ball removed - as a temporary test. you could also just plumb a vacuum gauge into the 'extra' inlet port on the spin-on filter head. Any vacuum greater than ~4" Hg indicates too much restriction on the inlet side of the pump.

  7. #7
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    Default Re: Both engines not hitting WOT - '88 454's

    Mark, I have also read that temporarily running with the gas cap off will isolate a vent or anti-siphon valve issue. Do you agree? That was going to be my next step after checking the TA timing. I should have a spare cap onboard so I could do a quick swap and rule that in/out.

    I also replaced both fuel tank sending units over the winter. I was really careful about not allowing "stuff" to fall into the tanks but you never know. That could potentially point to the anti-siphon valves as I did both.

    Thanks, will do some more work and post back.

  8. #8
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    Default Re: Both engines not hitting WOT - '88 454's

    Quote Originally Posted by bobct View Post
    Mark, I have also read that temporarily running with the gas cap off will isolate a vent or anti-siphon valve issue. Do you agree?
    No.....removing the filler cap will bypass a clogged vent but won't do anything about a crudded up anti-syphon valve....you could actually use an outboard tank, temporarily, as a test, to be a surrogate for your regular tank....just make sure anything you discconnect is sealed up...no second chance when it comes to fuel vapor...and use the blower to keep the bilge fume free.....

  9. #9
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    Default Re: Both engines not hitting WOT - '88 454's

    ok, I'll just remove it and check/clean. One more thing I can check off the list, would be great if it is the issue!

  10. #10

    Default Re: Both engines not hitting WOT - '88 454's

    Another way to check for a fuel line clog is to temporarily Tee in a combination vacuum/pressure gauge between the water sep and line to the tank. The vacuum should not exceed 5 In-Hg.
    FL Panhandle

  11. #11
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    Default Re: Both engines not hitting WOT - '88 454's

    Good idea, I'm going to use this as a reason to add the Racor vac gauge (permanently) to my Racor housing. There is an extra fitting already. I removed the anti-siphon valve last night and it was spotless and the ball moved easily. So, fuel system from tank to carb is 100%.

    Will do TA timing next but really don't believe that'll be the root cause as the issue has effected both engines at the same time with simillar results.

  12. #12
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    Default Re: Both engines not hitting WOT - '88 454's

    good deal on the valves being clean....

    The racor gauges are way overpriced, IMO.....you can buy a decent liquid filled gauge for a lot less.....just make sure it will handle the environment and will tolerate gasoline....

  13. #13
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    Default Re: Both engines not hitting WOT - '88 454's

    I know, they're over $100! Thanks, I'll look around for an alternate version. Their was a post I came across on a Sailing forum that said just that.

  14. #14
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    Default Re: Both engines not hitting WOT - '88 454's

    $15-20 each, oil filled, with S/S case....I'm pretty sure you can even buy two Dwyer gauges for < $50, delivered....

  15. #15
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    Default Re: Both engines not hitting WOT - '88 454's

    I'll post a pic of the ones I got once they're installed, they should be here today (thanks Mark). In the meantime, I checked my total advance last night and made a very minor adjustment of about two degrees. The advance is definitely working and I'm at 32 degrees between 3,000-3,200 RPM's. I'm not expecting that to provide much of a change but have not taken it out yet. Will run with gas cap off temporarily to rule out venting issue next.

    I checked the (new) tachs last night and both are selected correctly via the rotary switch on the back. I might just temporarily install one of my old tachs and see what changes, if anything.


    Bob

  16. #16
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    Oct 2009
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    Default Re: Both engines not hitting WOT - '88 454's

    I did two tests today. On the off chance it was an air intake issue, I took it to WOT with my center and rear engine hatches removed. Then, I did the same test with both gas caps removed to test the vent system, again no change.

    I also dove under and looked at the running gear and bottom again. Just a little slime, really nothing else. I'm going to call Faria tomorrow and see if there is anyway my two (new) tachs could be the root cause. If this were happpening on one side, I might think I had a tired engine and dig in with a compression test, etc. It seems highly unlikely that this could be the case on both simultaneoulsy though.

    Someone asked if I had a cored hull and I do not so I would not attribute my issue to a weight change.

    What would you guys check next?

    Bob

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