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  1. #1
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "All: This one's a myster

    "All: This one's a mystery to me, and I've got a pretty good engine background, so any insight would be appreciated.

    History: 1980 Welcraft Nova 250. Single merc 260/pre-alpha drive. Boat sat in a barn for at least 10 years before I purchased it (last sticker expired in '97).

    Following items were done as a matter of course before first time I hit the water:

    Ignition system: new plugs/wires/cap/rotor/points/set points/set timing.

    Fuel system: Remove q-jet, tear down, 2-day soak, rebuilt Q-jet. I knew she had sat 10 years so I tried to to a very thorough job cleaning out the carb, but I am human, so there is a possibility I missed something.

    Completely drained old fuel from tank. replaced water sep fuel filter, purged fuel lines, etc. Re-installed carb, with new fuel.

    Initial start had motor that would run fine at higher RPM, but wanted to die at idle--sounded really lean as RPM dropped off, and idle mixture screws provied no real help. All the classic signs of a vac leak with a q-jet (pissy idle, with man vac/RPM surging.

    Confirmed she was running lean by slowly closing choke plate manually, and the engine really liked the extra fuel. Hunted all over for a vac leak, including running around the base of the carb and intake/head interface with a propane bottle. No help.

    Out of frustration, I pulled the carb back off, looked all over inside for root cause. finding nothing, I raised the float level 1/4" to richen it up across the board (I know people are rolling their eyes, but this was a desperate moment).

    Overall, idle improved somewhat (like it will actually "run", though badly in Neutral @800 RPM. Idle mixture screws have a very MINOR influence on idle quality now. She's still running lean at idle, but off idle great--It was "good enough" that I was willing to risk sea trials, which have thus far proven successful (other than this niggling issue).

    Off idle/wot perf is actually pretty good (for an engine with 950 hours). Spinning a 4-blade 18" prop, With 4 people and half tank of fuel, I turn in 42 MPH at 4200 RPM WOT (on the low end, but not too far off the mark). Also, Fuel Economy is well within acceptable range.

    So, now if I can JUST make this thing meter fuel correctly at idle:

    Last observation--when actually got a couple hours not hauling kids around on a tube yesterday AM, I started trying (again)to sort this idle thing out.

    At base idle Neutral (800 RPM) looking down into the carb, fuel is spraying out of the main venturi on Port side (not really supposed to at idle), but nothing coming out of stbd main venturi. If I kick open the throttle to about 1500 RPM, neutral, I get some visible fuel flow through stbd side, (and lots more through port side).

    So now, here I am with a side/side issue fueling in the carb, and the whole system biased a little rich with the raised float. Off idle is OK, and performs quite well, even running only on the primaries, prior to the secondaries opening.

    Sure feels like an air leak, but I'll be darned if I can find it.

    Anybody want to take a stab at this one? Any ideas would be greatly appreciated.

    Thx"

  2. #2
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,521

    Default Well it sounds like you need t

    Well it sounds like you need to take apart the carb again and do a once over again.

    You either missed something or something??

    did you remove the emulsifier tube bank and look closely?
    The roschester 4 bbl are a very nice carb and should work very well so I would say you need to go back in.

    Did you put a vacuum gage on and see what your vacuum is and how steady it is or is not?

    You should be able to idle down to ~ 400 rpms with no issues if all is correct.

    What dwell and timing settings? Have you double checked?

  3. #3
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,521

    Default Oh Yah Did you put a good b

    Oh Yah

    Did you put a good base gasket in place?

    Raising the float masks the lean condition. You need to trace the idle circut carefully.

    I am at work but if I get a chance tonight I will look into the idle circut and see what I can find.
    I have many old kits and a few spare carbs laying around. Never can ahve enough spare parts.........LOL

  4. #4
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "K, Thx for the quick reply

    "K,

    Thx for the quick reply. A couple items: 1. Point gap set per spec (on high end of it, but in the spec, in case the wear block had any initial run-in) and timing subsequently set right at 8 deg BTDC after points gapped (done this before and been bitten by timing movement due to point gap).

    Went back and checked them once--I think things are right where they belong--no issues off idle, so dwell time doesn't seem to be likely culprit, and timing is dead on--good thoughts though--thanks for checking me on those.

    Per the orig post, ManVac was dancing around, though I'd have to go back and hook the gauge back up to quote the range of values... The only way I could get to a good value was to close up the choke, or take it off idle (like the idle circuit simply didn't want to meter fuel...)

    Got lots of experience with chevy small blocks, so concur with 400 RPM capability.

    Tell me more about emulsification rods..."

  5. #5
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,521

    Default I need to look when I go home

    I need to look when I go home but willget back to you.

  6. #6
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "K, I concur with your obse

    "K,

    I concur with your observation that raising the float did nothing more than mask the real issue--it was nothing more than a band-aid/big hammer so that I could make sure that other engine fundamentals were sound before trying to do a deep dive in the q-jet.

    Thx in advance for any help you can provide. I know the "fundamentals of operation" for the q-jet, but am somewhat handicapped by not having a detailed knowledge as to which passages are tied to which inside the body of the carb. I know that the idle circuit is fed off of the mains, so the problem could be anywhere from a main jet/metering rod on that leaner side, to some plugged passage between them, but that is where I get into trouble. I don't have the detailed knowledge of which passages to trace down, re-clean/verify.

    As it stands now, without that info, I could invest in another rebuild kit for the gaskets, tear it off and go through it again, and re-install with the same result. If there were a GOOD book that could take me through the level of detail I am hunting, I'd be happy to invest in it/have it as a resource--but I don't want to plunk down the $ for another book that will focus on basic rebuilding and "go-fast" mods when what I really need is the deep-dive details of all those passages and "who feeds what to who..."

    I look forward to your next post.

    Thanks again!!!"

  7. #7
    Join Date
    Aug 2006
    Location
    Calgary, Alberta, Canada
    Posts
    2,426

    Default Definitely your idle cicuit pl

    Definitely your idle cicuit plugged off.
    You should not see gas from your main venturi towers at idle. One side working and the other not means they need further cleaning.
    You need to tear her down again and blow each circuit and passage out with compressed air. They should blow free now that gas has been in the carb for a while.

    Last resort: Rebuilt carb.

    Rod

  8. #8
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "Concur that this very much ap

    "Concur that this very much appears to be a dead/plugged idle circuit forcing me to have higher idle air setting so that the main circuit meters fuel. I supposethat, looking at it from another point of view, a lack of idle fuel flow looks very much like an over-abundance of idle air/un-metered air. Same result--sad/lean combustion.

    Responding to the gasket question from K's earlier post, I have the thick gasket with the nylon inserts--the one that came in the marine rebuild kit--a big open hole with a thick perimeter. The one I pulled off originally looked very much like the upper face of the manifold--with individual holes corresponding to the four throttle plates--when I asked my marine parts source, they said that old gasket was no longer available, and hadn't been available for some time--no way to verify that, but a quick search of the web, didn't yield any of the old styly either...and all those claiming to be in the know say that newer one with the inserts is better to avoid vac leaks.

    As stated in an earlier post, I'll be happy to pull it and go through it again--just as soon as I know which particular passages to scrutinize at length and how to tell whether I have done a good job or not on the re-re-build.

    I know there are people in my area who can probably re-build these things in their sleep, having "been there, done that" over and over. The problem (at least it is a problem for mME right now) is that I'm one of those guys that feels that "need" to fix things himself (which often means I get to "fix" something more than once while I learn along the way...

    This isn't the first "situation" this boat has made me smart my way out of. Before she even hit the water, I was forced to think through how the cooling system worked so that I could get to root cause of why the engine wouldn't come up to temp--That one wound up being previous owner replaced exhaust manifolds/risers but failed to re-install the stainless plates between the two of them (guess he figured they were extra parts)...

    Thanks again for any/all info to help me through this fun!!!"

  9. #9
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,329

    Default "I've found that using a t

    "I've found that using a thick base gasket greatly improved idle mixture adjustment.

    After a year in the barn the gas turned to varnish. The liquid dried out long before 10 years causing the varnish to turn into a hard candy texture. That is what is blocking the idle circuits as stated above.

    Two day soak did not loosen the crud in the narrow cicuits. Try slow boiling the carb base on the stove for a few hours in a non-caustic, non-flammable detergent solution to soften the hard varnish. This cleaning may require re-epoxying casting plugs to prevent fuel leaks but will allow you to properly clean out all the circuits."
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  10. #10
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "Guy, Thanks for the sugges

    "Guy,

    Thanks for the suggestion.

    Not sure how I'm going to accomplish the slow boiling thing and still stay married...

    A few years ago, my missus offered me some pointed "guidance and counseling" about what tasks were allowed to be performed in the kithen after she caught me using the dishwasher to clean some grungy pieces of hardware. That Dish soap did a fine job, but she was rather unimpressed with my "creative" cleaning techniques.

    Do you suppose there is another option? Are the passages in question accessible to run something like a pipe-cleaner through them without screwing up metering orifi?"

  11. #11
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,521

    Default OK I looked at a book I have a

    OK I looked at a book I have and when you remove the top of the carb there will be 4 tubes hanging down. The two inner ones are IDLE air air tubes and must be clean and should be able to blow carb cleaner thru them.

    The way the idle circut works "basically" is the main jets at the botoom of the bowl supply fuel to the idle passages. The idle mixture screws meter that fuel.

    The idle air holes are visable from the top with the choke butterfly open. Did you remove the main jets and blow cleaner and compress air thru them?

    Did you blow air thru the idle air tubes?

    I agree the most likely issue here is the idle fuel passages have some shmeg stuck in them and are restricing fuel from getting up into the throttle bores.

    Sometimes soaking a carb can "backfire" because it disloges things and allows them to creep into places they may not normally get to. Carb rebuilders remove all the squelch plugs when they do a rebiuld and we do not so like I said to thorough of a cleaning can create problems instead of solving them.

    I would reccomend pulling the carb and working on it on a bench with WHITE clean towels and reclean and be especially careful on the cleaning of all tubes and passages. Almost every passage should have a out side so compressed air should find its way out. Take your time and look and observe each thing that is done.

    It is hard to really desipher a problem like this without the carb in hand. This is something that requires a bit of experience and first hand involvement.

    Good luck and let us know what if anything is found.

  12. #12
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,521

    Default Oh so you know if you do do so

    Oh so you know if you do do some kind of cleaning that destroys any of the squelch plug seals you can use good figernail polish to reseal. Most brands are impervious to gas. they usually only disolve in acetone!!

  13. #13
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,521

    Default That should have said FINGER

    That should have said FINGERNAIL POLISH My favorite is blood red!!

  14. #14
    Join Date
    Aug 2006
    Location
    Calgary, Alberta, Canada
    Posts
    2,426

    Default "Bill; The idle circuits need

    "Bill;
    The idle circuits need to be blown back from the point in the primary barrel throats where the gas exits, back to the bowl. This is not hard to do.

    The adjustable needles in the idle circuit control the gas admitted; the air is controlled by the primary butterflies per the base idle cam setting, with a small screw.

    If the idle jets are plugged, it won't idle.

    Rod"

  15. #15
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,521

    Default ROD S Thanks I got a millio

    ROD S

    Thanks I got a million things going on today and I could not put the idle controll in words.......Too much beer this weekend????

    I understand it a whole lot better than I can type it out in words. Ben rebuilding them for nearly 25 -30 years........I even have a throttle shaft reboring and rebushing set up to get the throttle shafts nice and tight.....

    Just hard to discribe...........MONDAY!!

  16. #16
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "Thanks K--I really appreciate

    "Thanks K--I really appreciate it.

    This book that you looked at. Would you recommend it as a resource I should purchase? Like I said earlier, I THINK I have the smarts to knock this one out, if I have the proper resource materials in hand to review.

    Concur with the clean towels/work area, that is how I approached it before. Easy enough to repeat that part.

    Tonight is grass-cutting night, but tomorrow night I'll go down and pull off the carb and start this process. If you think that the book you refer to would help, maybe I can also grab that as well between now and then.

    I'll look VERY VERY closely at those idle pickup tubes. I certainly will get back to you at the end of all this and post any results/lessons learned.

    Thanks again.

    Bill"

  17. #17
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,521

    Default My book is for automotive and

    My book is for automotive and is over 10 years old.

    It really does not have what you need. This is just a case of a missed passage with some stuff in it. No need to reaserch the carb any further.

    You could probably find a source online thru google

    I bought the book for some other reasons to do with modifications but it has some basic descriptions that I was looking at.

    Initally I was confused/forgot (monday) with the 2 bbl that has the emulsifier tubes and bleeds you can remove.

  18. #18
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,329

    Default "Are the passages in quest

    "Are the passages in question accessible to run something like a pipe-cleaner through them without screwing up metering orifi?" I've read somewhere to not use wire or similar; could damage orifi.

    A gas grill w/a side burner will work. A camp stove w/a propane tank also works; even a hot plate will work. Take it to a radiator shop. Most have hot tanks w/ultrasonic cleaning which should break all the crud loose.

    Lestoil liquid cleaner will soften any hard paint like substance. Start w/boiling water and detergent and soak carb parts until it cools.

    Last week I cleaned my Mercab circuits w/Sea Foam "Deep Creep" cleaner in a spray can. It is an impressive product. I used the spray tube to spray it into the tiny openings and then let it soak a hour; blew it out w/compressed air and tube nozzle to get the pressurized air into the tiny holes. Repeated the process. I used it in the jets and power valve since they would not come out. Also the metering rods; placed the comp. air tube over metering rods and blew out the crud.

    Carb has never run so good w/thick gasket.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  19. #19
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "Thanks to all. I think I&#

    "Thanks to all.

    I think I've got some pretty clear direction. And some extra motivation now that I have a sort of "support net" off of which to bounce these questions. I'll go back in there and do it right this time.

    Thanks for the Sea Foam tip as well... Whatever it takes to get the crud out of there.

    Big picture wise, I shouldn't really be that surprised. The carb was absolutely CAKE up with grungy stuff inside. I was thorough about the jets and rods and MOST of the passages, but I simply dropped the ball on clearing out the idle circuit--goes back to what I said about sometimes getting to "fix" things more than once...

    Will advise results later this week, perhaps."

  20. #20
    Join Date
    Aug 2006
    Location
    Calgary, Alberta, Canada
    Posts
    2,426

    Default "Kg; No worries, been there d

    "Kg;
    No worries, been there done that too.
    Maybe NOT ENOUGH beer this weekend? I hate it when that happens.

    Bill;
    I have a Q'jet service manual (dated 1973; Yikes!)in jpeg format I can email you offline if you like? It shows lots of detailed views including the whole idle jet system. Its about 7.5 mb.
    I originally downloaded it off this site.

    Let me know.

    Rod"

  21. #21
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "Rod, That would be most ex

    "Rod,

    That would be most excellent! Sent you an e-mail directly. At your convenience, you can respond to the account from which I sent it. Thanks for that!

    Assuming this upload works, thought I'd include a pic of the "Hillbilly Nova" as she looked when I first got her home Memorial Day weekend. Note the industrial trailer...

    Hillbilly Nova

  22. #22
    Join Date
    Aug 2006
    Location
    Calgary, Alberta, Canada
    Posts
    2,426

    Default Bill; I sent you the pdf by e

    Bill;
    I sent you the pdf by email. Sorry I earlier said it was a jpeg; duh. It's a pdf file.
    Let me know that you get it OK.

    Rod

  23. #23
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "Came through fine. Thanks

    "Came through fine.

    Thanks a bunch! I'm already getting smarter (well...ok, that might be a stretch)...

    Seriously, THANKS!"

  24. #24
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,521

    Default Rod S send it to me also pleas

    Rod S send it to me also please.

    Contact me thru email
    I wouls like to see this also.

    All though I think I have seen enough first hand but its all good.

  25. #25
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "Rod, Thanks again. I pri

    "Rod,

    Thanks again. I printed it out, and tonight, it's getting hole-punched and going into a 3-ring binder, then to the magazine rack in the bathroo.... I mean "library"... so that I can review it at length.

    Thanks again!

    Bill"

  26. #26
    Join Date
    Aug 2006
    Location
    Calgary, Alberta, Canada
    Posts
    2,426

    Default "Kghost; Sent the manual to y

    "Kghost;
    Sent the manual to your email address.
    Hope it gets there OK.

    Cheers,
    Rod"

  27. #27
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "All: I believe I have root

    "All:

    I believe I have root cause as to lack of idle fuel flow.

    Tore down again and this time pulled out the idle pickup tubes. That was quite a chore but it was worth it, I think.

    Narrow portion/orifice area of BOTH tubes were completely caked/cloggged with crap. Pretty sure it had no chance of getting any fuel that way. So they are out and openned up. Leaving them soak overnight in cleaner before blowing them out one more time. Also blew out the associated passages connecting those pickup tube reservoirs to the primary jets in the main body. At least now it should have a fighting chance at flowing fuel at idle.

    To be honest, even with the manual you sent me Rod (thanks again for that, by the way!) it is a good thing that the q-jet book by Ruggles that I ordered arrived today.

    Had he not provided significant warnings/encouragement to pull those tubes and clean them (and some good advice on how to do it), I'd have put that thing back on the boat, had the same problem, cursed myself at length and then sucked it up and ordered a rebuild.

    Knowledge in hand is a wonderful thing--and thanks to you guys for being a part of that.

    Last question: IF POSSIBLE, can you describe how much is too much slop on the primary shafts?"

  28. #28
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    3,521

    Default "Thats a tough one without act

    "Thats a tough one without actually feeling it.

    If there is too much slop it will act like a vacuum leak.

    I have special tool/drill and bushings to fix such a problem, I purchased it from a carb shop out of California several years ago.

    I would not be too concerned at this point and just try to get it running as good as possible.
    Unless this motor has a ton of hours on it it should be fine."

  29. #29
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "Just to be clear, the tubes I

    "Just to be clear, the tubes I am refering to are the ones pressed into the main body of the carb that carry fuel upward from the resevior just after the main jets. The metering orifice in the tip which hangs in that resevoir were absolutely plugged. The only way I could get them open was a wire. Initially upon reading the two pages of warnings in Ruggles' book I poked down into there with a very thin wire. I noted where the wire stopped on the first side and thought "That's not far enough to have actually made it through" I poked into the second side and felt the wire get stuck in something (felt almost like poking a stick into the dirt)--I thought "That aint good at all, and now I absolutely have to pull them to know for sure what is going on." It's a good thing I did--cost me abut 45 minutes to get the pressed in caps to come out of the carb body, but I'm calling that time well invested, since I'm pretty sure I got root cause now. This is the "Ah-ha!" that I was looking for..."

  30. #30
    Join Date
    Aug 2008
    Location
    Detroit area
    Posts
    32

    Default "Engine at 950 hours. 1000 h

    "Engine at 950 hours. 1000 hours is only half a ton, right?

    ;-)"

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