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  1. #31

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    compression test, 140PSI all cylinders
    https://youtu.be/5uM6L-mNBhE

  2. #32
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    even with all of the swapping of the fuel system pieces, I never read where you verified adequate fuel presssure at the carb's inlet....

  3. #33

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Hi Makomark.
    I didn't do a test on the pressure side of the fuel system. but I replaced the fuel pump twice and ran it with direct power disconnected from the carb and it pumps correctly. Also ran the fuel pump with a separate 5 gallon fuel tank and it does the same thing.
    I am pretty much 100% sure that the fuel pressure is not the problem.
    did you see the clip I posted with the engine noise?

  4. #34

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Has any one ever had a noise similar to the one I posted? anybody had a loose or cracked flywheel?
    Any advise?

  5. #35
    Join Date
    Dec 2011
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    San Jose del Cabo, MX, Osprey, FL
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    307

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    OK, so you have compression in all cylinders so that is good news. Anyway, it was a stretch to think that one bad cylinder could limit you to 2800 rpm, usually you can do much better than that. But if you have two bad ones, that's another thing. So be sure to follow Erich's advice about double (and triple) checking plug wire order. Turning two of those around would perfectly fit your symptoms (power loss and a knock) and is the sort of issue easy to do in new installations.

    It seems unlikely to me that you have issues with connecting rods, bearings, etc. Those should not limit your power (rpm) which is your major symptom.

    If you have compression, fuel, air and spark (at the correct moment) you should make power. You are not, so something is missing. I did not follow all your discussion on vacuum but there are some good articles on the internet about how to use a vacuum gage to trouble shoot. I think it is largely a lost art among many modern mechanics. And remember, your best source of information about what things "should be" is the sister engine that is running good (and it is also your best source of known good parts to swap out). Vacuum readings (while underway) every 500 rpm (1000,1500,2000, etc.) on both engines should yield some interesting clues. They should be the same at the same rpm. In your case they will diverge at some point since the same throttle setting is giving different rpms. But do they differ only above your 2800 rpm limit on the bad engine or does it also happen at lower rpm?

  6. #36

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Thank you CaboJohn
    I am headed to the boat right now. I will double check on the firing order.
    I ll post later tonight any updates
    Thank you for your help

  7. #37

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Firing order should be:
    LH (CCW flywheel) 1-8-4-3-6-5-7-2
    RH (CW flywheel) 1-2-7-5-6-3-4-8

    Worth confirming.

  8. #38

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    OK
    Just got back. I did double check the firing order and its correct.
    boat still does the same thing...I am completely out of ideas. I have never seen anything like this before.
    I am going to take out the intake manifold to see if there is something there. Also will check the flywheel.
    other than that, I have no clue.

  9. #39
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Quote Originally Posted by wellcraft33 View Post
    Hi Makomark.
    I didn't do a test on the pressure side of the fuel system. but I replaced the fuel pump twice and ran it with direct power disconnected from the carb and it pumps correctly.
    Sorry to be the 'broken record" but how can things be "ok" if you never measured the pressure delivered, especially under load??

  10. #40
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    Dec 2015
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    maplevalley WA
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Did you confirm true TDC on #1 cylinder with a piston stop tool?
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  11. #41

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Pulling the manifold may be premature. Low fuel pressure usually results in heavy surging at higher rpm which you do not seem to have. Still worth testing the pressure just to rule it out as the problem. Acting like insufficient spark advance at high rpm but you are assuming you have 30 degrees or so at 2800 rpm. Since MSTS has been deleted a bad MAP sensor is not a player (which may retard spark), but still may be worth checking the advance under load. Any chance your timing marks can be in error ? Might also check coil voltage under load just to be sure resistance is not increasing under some thermal load somewhere (wiring, ignition switch, CB). Just throwing stuff out there. The fastest route to a solution is targeted trouble shooting. Hang in there, we are all learning.

  12. #42

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Hello MakoMark
    I didn't actually connect a gauge to the pressure side of the pump because I have a steel tube from the pump to the carburetor, and don't have a way to connect a T for the gauge. I would have to get a flex temporary hose to do that, but this is what I did.
    I took the carburetor, steel tube, fuel pump, fuel filter and fuel housing from the good engine and put it on this one. Then I got a separate gas tank (5 gallons) and ran the motor from that tank. I checked the voltage at the pump and is good (13.25volts) I also ran the pump disconnected from the carb with the fuel going into a bucket and it pumps very strong. I think that should rule out loss of pressure from any fuel restrictions, plus all the components I mentioned are new.
    I will rig a hose to connect the gauge anyways and get the fuel reading later this week, just to have it, but at this point I really don't think the fuel delivery is a problem. I think my problem is in the intake manifold somehow. I ll keep at it until I find the problem.
    Thank you for all your input and help, I really appreciate it.

  13. #43

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Hello MulletWagon
    The reason I am looking at manifold is because I have changed just about everything else on this engine and still has the same problem, it acts bugged down has no power, like is only allowing fuel/air through two barrels, but then again, if you keep the engine at around 2000 RPMs, it runs the carb on 2 barrels and it does not miss, back fire, hesitate or anything. it actually runs very smooth and even at level, its only when you try to increase the throttle that the problem manifests itself.
    The fuel pressure, I have pretty much ruled out from all the things I posted to MakoMark,
    I checked the timing in neutral, and it advances to 30 degrees at 3000 RPMs. I haven't checked while under load, but I think if I get 30 degrees in neutral I should get it under load as well. As far as the timing marks, I am pretty sure they are right, anyways, if not you would hear the engine idle different. You can pretty much set the base timing by ear on these engines.
    I replaced the coil for a brand new one, but I will check on the voltage to rule it out.
    Thank you very much for your help

  14. #44
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Like Mullet, I'd say pulling the intake is not warranted....the vacuum readings suggest all is well there....

    you posted a few times the secondaries open fine....does this include the air valves on top of the secondary throttle plates? does the tension on the air valve spring feel similar to the other engine's carb? The air valve controls the fuel delivery in the secondary side of the carb. another thing to check is the secondary rods - they should have a two letter code on the shanks- they should be installed as pairs and be the same on both carbs.....

  15. #45

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Building a temporary fuel pressure checking assembly is a no-brainer (I actually did it). Just need some flexible fuel line the same diameter as your vacuum gauge, two "inverted flare" fittings with hose barbs, a tee with barbs and you are good to go. All the hardware is readily available at a car parts store. The assembly completely replaces the steel fuel line. It will allow you to safely monitor pressure while underway. Like you, looking forward to finding the problem !!

  16. #46
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    Dec 2011
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    San Jose del Cabo, MX, Osprey, FL
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    If you are correct that the spark and the fuel supply to carb are not the issue, then the limited power makes it sound like restricted air flow. Have you swapped air filters with the good engine or tried taking the filter off when underway? Have you looked into the carb underway at full throttle and insured the secondaries are open?

  17. #47
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    Dec 2015
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    maplevalley WA
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    100% wrong especially on marine applications. Before you do anything else confirm you have proper TDC on #1 cylinder and then adjust base timing. It is impossible to earball ignition timing you may get lucky but until you confirm it your putting your engine at risk for permanent damage. Detonation is the #1 killer of marine applications.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  18. #48

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    https://youtu.be/2mXrzaFfOHc

    thats the engine running. I have since replaced that card and it does the same with the new one.


    https://youtu.be/Kvv90yRU-NY
    Here is the engine at idle today.

  19. #49
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    looks like the air valves open ok...

    you may want to revisit the ignition system secondary parts.....I'd say swap cap and rotor as well as ohm out each plug wire (with the wiggle test)....I've seen more than one bad wire in a 'new set'.

  20. #50
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    flywheels, manifolds???
    Stop replacing stuff.

    1. What is the fuel pressure at WOT/loaded?
    2. What is vacuum at WOT?
    3. What do the spark plugs look like immediately after test 1,2? Yes, you will need gloves and its a pain to work on a hot engine, and you really want to do this before you idle back to the dock.
    4. You said 30 degrees max. You did see a change of about 20 degrees from idle, correct?
    Last edited by diver_dave; 09-01-2017 at 07:23 PM.

  21. #51
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Do a cylinder drop test.....
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  22. #52

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    What happened?

  23. #53

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    I basically gave up.
    I am using the boat like that.
    top speed is only 15 knots, and the right engine is maxed out at 2500 RPMs.
    It does not mis,backfire, bogs down or hesitate. idles and runs smooth, just lacks power and won't rev past 2500.
    I have checked and replaced just about every system there is.

  24. #54

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Could this be too-tight stuffing box or bad cutlass bearing? If it revs to max in neutral, then seems like something it impeding it when in gear.

  25. #55
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    Dec 2015
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Have you done a cylinder drop test? While idling pull a plug wire and then put it back on. The engine should respond the same with all 8 cylinders. It can be tricky in tight places be careful of moving parts and use insulated pliers to avoid getting bit. You normally notice the difference putting the wire back on.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  26. #56
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    You should replace the packing in the stuffing boxes every other year. Does the stuffing box get hot? If the packing gets hard it can cause excessive wear on the shaft, if you have not serviced the stuffing boxes now would be the time to eliminate that variable.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  27. #57

    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Thank you all for the input
    The boat was pulled out of the water to drop in the new engines, the shafts were taken out and aligned and I replaced the hoses and packing in stuffing boxes as well as the cutlass bearings on both sides. Also painted the bottom. So I can pretty much rule that out.

    I have not done a cylinder drop test pulling the wires one at a time, I will do it next week and post results. but I have replaced all the spark plugs, all the wires, the complete distributor and the coil. All new.
    I am thinking I have some kind of electrical issue that perhaps is dropping the power to the distributor while on a load. I have to see how I check that. Is there any way that the alternator could be causing this? I may switch harnesses from one motor to the other to rule out the harness.
    In the mean time, I have been running the boat as is, its runs slower, but its pretty smooth. I have taken 3 mechanics already and non have been able to figure this out. It maybe something very simple that I am just missing, but so far, its a mystery.

  28. #58
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Do both stuffing boxes drip while running? From what I was reading the boxes should not drip when static and have a slow drip when in gear. Is there a notable difference in engine rpm between engines when you shift into gear? Pull both throttle cables and measure the throw from slow to WOT. Possible throttle cable sticking or has bad bushings in the control. It takes alot less throttle opening for the engine to rev up without a load. Just throwing stuff out there you will eventually figure it out. With the engine off put the control at WOT and look down the carbs and see if the butterflys are fully open?
    Last edited by kimcrwbr1; 10-08-2017 at 01:00 PM.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  29. #59
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Anything “loading” a BBC is going to dissipate a tremendous amount of heat. Engine should be good for some 300 x 750 Watts! A tight stuffing or cutlass will soon be sacrificed��

  30. #60
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    Default Re: 454XL, lacks power and won't rev past 2800 RPMs

    Quote Originally Posted by diver_dave View Post
    Anything “loading” a BBC is going to dissipate a tremendous amount of heat. Engine should be good for some 300 x 750 Watts! A tight stuffing or cutlass will soon be sacrificed��
    2X that!!!

    the 'drop test' mentioned can tough on some engines.....We found it is best to do it in gear....so that means another set of hands (& eyes) which is always a good idea from the safety perspective....

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