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  1. #31
    Join Date
    Mar 2008
    Location
    Bellevue, WA, USA
    Posts
    31

    Default "I just went through a similar

    "I just went through a similar scenario also! I changed props from 19 x 18 to 19 x 17 and now 19 x 16 to get the WOT up. It just kept getting worse on the starboard engine. Finally went to a professional shop and they found water coming out of one of the cylinders when doing the compression check! Turned out the riser had rusted through and was letting water drain into the cylinder resulting in rusted valves as well. After replacing all 4 risers on both engines and getting new reconditioned heads on the one engine, we had the pressure up to 150 psi on all 8 cylinders but still had low RPM (3500). So all the spark plugs, wires, distributor and coil was changed. This brought the speed up to 3800 RPM. Still not 4400, then we found out the new Mallory distributor had a cracked stator ring. So found an old GMC distributor and a new ECM and it went up to 4000. Finally, found out the tachometer was off by 400 RPM. Put a digital tach on and voila, 4400 RPM with 1/2 full fuel tanks (300 gal full) and empty water tank (100 gal.) and 19 x 16 props (3 blade Nibral cupped)

    With full tanks, only 4000 RPM can be obtained at 30 MPH. Hope this helps?"

  2. #32
    Join Date
    Jan 2008
    Location
    Groveland, MA, USA
    Posts
    139

    Default "I verified the (base timi

    "I verified the (base timing 12 degress bdtc) and that the advance was "working", i.e. it moved about 2-2.5" on the balancer from idle to 1600 rpm. I was too lazy to measure the diameter of the balancer but 2" advance on a 10" diameter balancer works out to about 23 degrees of advance. I verified the operation of the throttle and choke and warmed the engine up to 160 degrees. I removed and inpected all plugs, which all looked "good" according to my dockmate, a mechanic, unplugged the power lead to the distributer, opened the throttle and measured compression with a new gauge:
    Odd bank (psi): 132, 130, 130, 138
    Even bank: 134, 135, 140, 132.

    I was greatly encouraged by the compression values but at a loss on what to try next. Swapping the carburators seemd reasonable and only took about 1/2 a hour to switch the rochester q-jets. Before the car swap I recorded 4030 rpm on port motor and 3300 on starboard in calm seas. After the swap I got 3900 and 3400 in the river (fresh water trial; hurricane off shore). So no change from carb swap. IMPORTANT NEW DATA: My flowscan gauge only displays fuel burn for one engine at a time. There is a toggle switch to go between engines, but no indication of which engine is being displayed. I WAS CONFUSED when I previously reported that the weak engine burns more fuel. On the recent run the good engine burned 29 GPH at WOT and the weak engine burned 24 GPH. This may lead back to a fuel restriction. Its pretty simple to swap fuel lines and I'll try that next. I'll also check the engine mounted canister style paper fuel filters. There are new water seps. ahead of the final paper filters.

    Mako, I got the Marine 7000 DUI distributor for BB Chevy. The website is a little weak but see http://www.performancedistributors.com/marinedui.htm.

    I considered hooking up the timing light to each lead and look for a consistent flash but I had other things in mind. Will consider this test on another day, though. Since I have the same distributor on the other side I may have to swap them too, and see of the problem transfers to the other side. These are the types of definitive tests I'm focuing on. Could swap the wires, too, after the distributor swap.

    Rick, I completely agree that under a moderate load the "pull the wire test" will give much more definitive results. Believe or not I the same test occured to me independently when the suggestion to pull each wire first came up. I was thinking tie everything off twice and try forward gear at 1000 RPM (don't want to take to whole marina for a ride).

    Transmission is identical to the working side. Its looking like its about time to pull both props. and have them scanned, probably after the fuel line swap.

    It's a huge advantage to have one working engine right next door and an even bigger advantage to have you guys. I will get this thing fixed.

    Thanks so much for your help and time."

  3. #33
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default "ohhhhh, the fuel flow is [b]l

    "ohhhhh, the fuel flow is lower. Now, I'd think things like fuel flow issues, like you mentioned. Anti-siphon valve, filter, worn out fuel pump push rod; maybe in that order. A fuel pressure gauge would be definitive, but it likely is more work installing that than checking the possible culprits."

  4. #34
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,824

    Default "Tom: In addition to Dave&#

    "Tom:

    In addition to Dave's list, I'll put on a few more specifics. I'd add the fuel pump, especially if it is original. if it turns out to be bad, I'd have a spare for the other side readily available. The other is a restriction/constriction in the supply line. A clamp could have given up letting some air in too.

    I bet your balancer is 8" in diameter. 2" on an eight inch balancer yields about 29deg of advance. If this occurs at 1600, the advance curve is too steep. I'd verify with the DUI guys what curve they provided and then set the timing at full advance and live with the retard at idle.

    another 'trick' that is viable on my setup, and don't know how your EH is done, so this may be mute. My spinon filters are right next to each other, on the same bulkhead. Exploiting that 'benefit' you ID'd of having a good engine, I can swap the feed hoses, or outlet hoses, pretty quickly. this enabled us to verify that one pickup was about 2" 'shorter' than the other....don't ask, it was one of those 'moments'."

  5. #35
    Join Date
    Jan 2008
    Location
    Groveland, MA, USA
    Posts
    139

    Default "Hi Mako: Yup, the fuel pum

    "Hi Mako:

    Yup, the fuel pump could be a weak sister. They are a little tricky to swap, so I'm saving that until I'm near the end of things to try. I'd like to test the fuel pressure on the affected side but I can't see how a gauge would connect to the output fuel line from the pump. It's a metal line with a special flared fitting that mates with the q-jet inlet under compression. There's probably some sort of adapter but I have no way of knowing.

    I'd appreciate feedback on the compression numbers for the affected engine, which was rebored and fitted with 0.010" oversize pistons and rings, if that makes any difference. So go ahead and weigh in, if you are so inclined. And don't hold back, I can handle the hard truth.

    Odd bank (psi): 132, 130, 130, 138
    Even bank (psi): 134, 135, 140, 132


    I've also considered an air leak in the fuel line at a hose clamp, spin on water sep., tank fitting, etc. There could also be an obstruction in the fuel pickup--fairly common. My spin on water seps. are mounted close to each other on a bulkhead, just like yours. I've already purchased some 3/8" fuel line and some hose barbs and will swap fuel lines after the water seps. This will rule out any problem with fuel the pickup, fuel line between tank and bulkhead, and water seps. Upstream between the water seps. and the fuel pump, the flowscan gauges and the engine mounted paper fuel filter elements can be found, and these will not be tested by the "swicth over". They seem like long shots, though. The paper filters were changed last year, and they are after the water seps. However I have new paper elements and will put those in place before the test run.

    The timing advance calculation was an estimate because I was down in the engine room with no RPM gauge and the 2" advance on the balancer was by eye. It could have been turning at 2000 rpm and the 2" travel could have been 1.5-2.5", i.e. the advance could be anywhere between 15-30 degrees. The distributor is new and I was trying to make sure it wasn't hung up. I'm the first to admit I'm a little unconventional and left to my own devices I sometimes do things that would make a trained mechanic laugh out loud. I have the identical distributor on the other side and could swap them, but it seems like another long shot."

  6. #36
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,824

    Default "Tom: On the compression nu

    "Tom:

    On the compression numbers, they may be a bit low from OEM but hard to tell without knowing who's pistons were put back in. To be honest, I've only seen one block that was bored to +0.010. Most go to +0.030 to ensure the bored is cleaned up and true. Good news is you still have some matrial left if needed.

    Sounds like your plan to find this gremblin is reasonable - a little time and you'll find it.

    Only other suggestion is get that toggle switch for the floscan labeled or reoriented to eliminate the 'which engine' issue."

  7. #37
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default "I think 135 +/- 5psi is f

    "I think 135 +/- 5psi is fine. I'd move off the compression, and perhaps rig up a temporary fuel pressure monitor. You would need to remove the steel formed line and replace with hose barb to flare adapters at each end. Something like 5/16" rubber fuel hose into a "T" and 10psi fuel gauge. Check out summit racing or jegs or PAW for the gauge. If you get something like 5-6psi of pressure at cruise, then you can eliminate the entire fuel delivery system, tank to carb."

  8. #38
    Join Date
    Oct 2007
    Location
    Germantown, TN, USA
    Posts
    227

    Default "I purchased an inexpensive in

    "I purchased an inexpensive inline pressure gage from Auto Zone for about $10. It works just fine and is simple to install. If you have electric fuel pumps and filters, the gage helps to trouble shoot failure of pump, pluggage of fuel filters and kinks in the fuel line. Another thing that would be good, but probably not wise to install, would be a glass rotometer. With this you can see the fuel flowng (and any bubbles in it) and the quantity.

    Chuck Hanson"

  9. #39
    Join Date
    Jan 2008
    Location
    Groveland, MA, USA
    Posts
    139

    Default "Thanks, Chuck, for this infor

    "Thanks, Chuck, for this information and for your other post. I have mechanical pumps and it will take some engineering to make the connections, although I am probably overstating things.

    The fuel line connections at the pump and at the carburetor are compression-type with solid flared tubing in between and a brass nuts on both sides. For both connections, enormous force must be applied to the brass nut in order to make a compressive seal that won't leak. In fact a 5/8" wrench will round the nut before it seals, leaving a leaky fitting, so that vice grips must be used. I ordered a new fuel line--same exact issue no matter how carefully the fuel line was aligned and tightened. A marine mechanic had all he could due with vice grips to get a good seal at the pump connection, so its not just me, and I am naturally wary of fiddling with the connections. Seems like these connections should be the most positive and fool-proof possible, but they are not. I've tried fitting and re-fitting the lines, etc. and still must resort to vice grips and enormous force, probably enough force to break the aluminum carburetor inlet casting if its not held secure by a large wrench.

    I'd rather just try a new mechanical fuel pump; probably wouldn't cost that much more than the gauges and fittings for a fuel pressure test, but would be easier to install and better because then I'd have a spare. Mine are 24 years old already."

  10. #40
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,824

    Default "Tom: Those are called "

    "Tom:

    Those are called "inverted flare", not compression fittings. I'd incourage you to find a snap-on truck and buy a 5/8" "flare nut wrench". they aren't cheap but do just what is required. Also, get a good 1" wrench to 'back up' the fitting the fuel line nut screws into. I have to remove the vent nipple (yellow tygon line) to do mine.

    ps - the carb body isn't aluminum, but a softer die cast metal. You're right to be cautious"

  11. #41
    Join Date
    Jan 2008
    Location
    Groveland, MA, USA
    Posts
    139

    Default "Inverted flare", that'

    "Inverted flare", that's what I was looking for. Thanks, mako.

    I went out and bought a 5/8 flare wrench after my first fuel line connection got buggered up last year. Even with a new line and a flare wrench, the corners of the brass nut rounded off before it sealed. I had to resort to vise grips and what seemed like unreasonable force to stop the leaking on both ends of the line. Not at all impressed with that design...

    One of my carbs has the vent nipple and it is helpful to remove it."

  12. #42
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,824

    Default "Don't get a flare nut wre

    "Don't get a flare nut wrench, get a snap-on one. They make a variant of a combination wrench; the flare nut end takes the place of the box. that's the one I prefer. I've never seen a flare nut wrench that you could buy off the shelf do anything other than what you described. On the other hand, I've never seen a snap-on one do it. That's over a few decades of being around this stuff.

    If your not in a rush, you can find them on ebay. otherwise, stop at a local auto service provider and ask who the local reps are."

  13. #43
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default "I've gone to AN-6 fitting

    "I've gone to AN-6 fittings and have no issue putting on and off the fittings. Never had a leak. But, I did this because i changed carbs, and I found it so difficult/expensive to custom make a formed steel line and the double flare ends, I didn't even try.
    Still though, Tom must have a bur in perhaps the male side of the fitting, not fixed by the new fuel line. Once steel becomes scored or deformed, it will take a huge force to seal. I've used a Sears flare wrench on other model 350 without issue."

  14. #44
    Join Date
    Jan 2008
    Location
    Groveland, MA, USA
    Posts
    139

    Default "On Saturday I swapped fuel li

    "On Saturday I swapped fuel lines in preparation for another test run. As promised, I also changed the engine-mounted paper fuel filter elements. While lying sideways between the affected starboard engine and the hull, the loyal wife started the engine so I could check for a fuel leak after the filter change. No leak, but there was a very good measure of dumb luck. In the relative darkness of the bilge, a spark was emanating from a plug connection, #4 cylinder to be exact.

    The aforementioned loyal wife shut down the motor and promptly located a spare wire that came with the new DUI distributor last fall. It wasn't long enough, but she identified another wire on the #3 cylinder that would reach, unplugged the longer wire and replaced it with the spare, then connected the longer wire to the coil where the bad wire had been removed, and routed it to me. (Editors note: Stuck in an awkward position, I made no contributions to the repair).

    Took the old girl out for a test run (the boat, not the wife). Starboard engine spooled up to 3900; previously it would only turn up to 3200-3400, with 3200 more typical and 3400 a good run. Port engine turned up to 4100. Pretty close. Top speed was 24 knots with a fuel burn of about 30 GPH per side. Backed it off to 3200 RPM cruise for a while. Throttle positions appeared even. This was new. At cruise, both engines burned 16 GPH at 19 knots at 3200 RPMS. Not bad for a 33 Egg harbor, a beefy 18,000 lb boat. Declared the problem fixed, by my wife of course. I worked on it for 3 years; she fixed it in about 5 minutes (my only contribution: barking at her from behind an engine).

    The failed wire was burnt up pretty bad inside and around a linear cut at the right angle boot. It was a new wire and its hard to believe I tore it when I installed the DUI distributor last fall. Could have been a latent defect, I suppose, or maybe heat from the exhaust manifold. It was a little tight and maybe it was up against some hot metal. Doesn’t much matter now.

    Thanks for all the help and support. Its comments like the following that will keep people coming back to the board for a very long time indeed:

    “I think 135 +/- 5psi is fine. I'd move off the compression”--Diver Dave

    or maybe this one:

    “Don't get a flare nut wrench, get a snap-on one. They make a variant of a combination wrench; the flare nut end takes the place of the box. that's the one I prefer. I've never seen a flare nut wrench that you could buy off the shelf do anything other than what you described. On the other hand, I've never seen a snap-on one do it”--makomark."

  15. #45
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default Bad wire. Impressive find and

    Bad wire. Impressive find and thanks for the report!

  16. #46
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,824

    Default Glad you found it...make sure

    Glad you found it...make sure you note the details in your log so you may fix it faster next time these symptoms recur.

  17. #47
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    15,263

    Default Just changed a bad wire on my

    Just changed a bad wire on my as well; it got too near the exhaust mnifold where it attaches to the head (and is HOT!)

    Good idea to do a check of the wires now and then.

    Jeff

  18. #48
    Join Date
    Jun 2009
    Location
    Lusby, MD, USA
    Posts
    3

    Default "I'm baaaaack, but not wet

    "I'm baaaaack, but not wet. Yet!! I have (recent purchase) a 40', 1983 Silverton with 454's. I just made a trip down the Potomac River from Wash., DC to Southern Maryland. About 140 miles. I could not get more than 19-20 MPH @ 3200 RPM out of either engine. The RPM seems to be low. Am I right or wrong? The boat ran strong, consumed a whole bunch of gas and 'felt' like it should be faster.........Any suggestions out there?????"

  19. #49
    Join Date
    Jan 2008
    Location
    Groveland, MA, USA
    Posts
    139

    Default "Most common problem is the me

    "Most common problem is the mechamical advance in the distributors. Connect a timing light and see if you are getting full advance (approx. 26-30 degrees) should be all in at 2500 RPMs. Also could be ignition fault (coil or wires), fuel restriction, etc."

  20. #50
    Join Date
    Jun 2009
    Location
    Lusby, MD, USA
    Posts
    3

    Default "Thank you, major-tom. Guess I

    "Thank you, major-tom. Guess I have to go to work now! Have a great day"

  21. #51
    Join Date
    Jun 2007
    Location
    mississauga , ontario, canada
    Posts
    63

    Default also double check your RPM gau

    also double check your RPM gauges ..make sure they are correct ... i had similar problem and both gauges were off by 1000 RPMs I used the timing light with the rpm build in to diagnose the problem...And then instead replacing the tachs i had the flowscans installed..

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