Safer carburettor in a box?

Discussion in 'Inboards' started by tom kane, May 22, 2014.

  1. Ike
    Joined: Apr 2006
    Posts: 2,496
    Likes: 353, Points: 83, Legacy Rep: 1669
    Location: Washington

    Ike Senior Member

    Sounds like my Mercruiser 165. 1972 Vintage. It has a Rochester Carb that I had rebuilt last summer, but I am seriously considering either a new carb or a bolt on EFI. The current carb is a real headache.
     
  2. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 482, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Peter, I'll assume you need a R4/4ME which is really more CFM than you need on a marine small block with the cam duration and overlap typical of them. Of course, Edelbrock bought up the tooling, though have discontinued the Q-jet line, still sell replacement parts. Dare I say it, but the marine version of this carb, tends to leak at the bowl, because of weak attachment bosses.

    Consider the Elderbrock 1409 or Holley 80551 (both square bore instead of the spread of the Q-jet) as better replacements for the Q-jet. Both are 600 CFM, which is much better matched to a mild cam marine engine. Both have J tubes, sealed shafts, electric chokes and vacuum secondaries. For a good boost with these two carbs and not a lot of money, also consider the Weiand 8150 or Edelbrock 71014 intakes. They're available in non-EGR and will offer better breathing, particularly in the RPM ranges, where your boat operates.
     
  3. tom kane
    Joined: Nov 2003
    Posts: 1,767
    Likes: 48, Points: 58, Legacy Rep: 389
    Location: Hamilton.New Zealand.

    tom kane Senior Member

    I love modern marine technology. How do most EFI installed systems handle the crankcase and rocker cover gases there does not appear to be much info about it. I hate a stinky oily smelly boat. A fully functioning Marine style + carburettor in a box would have been handy 60 years ago.
    I have seen many top brand auto and marine carbs with all sots of ailments such as the brass fuel- in fitting coming loose from the carb body. In some cases just a straight piece of tube wth no means of locking to the carb body or fuel line. Twin clips no help there. Maybe I expect too much but I am happy to do it myself if I am allowed.
     
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 482, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    PCV systems haven't really changed, since going to the closed loop arrangement in the 70's. If you change your oil at regular intervals, it'll last a long time (the valve and baffle/breather). If not or in marine environments, it can clog with sludge and water. The valve is easy to clean, but being so cheap, it's often easier to just replace it. There's no difference between carburetor and EFI PCV systems. Blow by gases are handled the same way. The systems have become slightly more complex with newer engines since 2002, with blow offs and booster taps, but the system still works the same way. On race engines, the crankcase it plumbed directly to the exhaust, to relieve pressure, but this is frowned on by several organizations.

    You're right Tom, there are a lot of examples, particularly early applications where bowls and shafts weren't sealed, leak prone parts and fittings, but this has changed considerably, at least in the USA.
     
  5. powerabout
    Joined: Nov 2007
    Posts: 2,916
    Likes: 63, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    Par
    where can a q-jet leak at the bowl?
    One of my favorite carbs..
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 482, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Like most carbs of this era, they used pressed in plugs to cover passage drilling. The more common of these to have an external leak is the pump bore, just behind the vent pipe, in the top of the bowl. The Q-jet is pretty different, even compared to a square bore Holley, which also has it's share of issues, like transfer tube O ring leaks and warped body to bowl gasket weeping.

    Carbs have come a long way, but they're still not the way to go. I've changed my mind about EFI, having had way more carb'd engine experience, but I once thought epoxy was a fad too. If I was forced to use carbs, I'd probably find a way to bolt on, side or down draft Webers, instead of the typical 4V setups, found on most boat engines.

    I like Q-jets too, having had many and learning how to tune them right, but compared to a twin Weber setup or EFI, there's just no comparison. For example a single Weber 38 mm IDF will flow about 400 CFM, so two of these will answer any mildly hot rodded small block. Even a single 40 or 44 will do fine, both flowing near 600 CFM, depending on venturi. These Webers act much like fuel injection and are nearly as tunable. I've mounted four 44's on a small block and after getting the linkage sync's up, ran better than any other arrangement I've owned (trips, duel quads, etc.). Webers are cheaper then EFI and no electronics to play with, but they cost a fair bit more per CFM than a Holley.

    Peter, if you stick with the Q-jet, make sure the ID number starts with a "1", which designates it as a modern version. They're easy to pick out of a pile as the choke is self contained (no intake tube). The metering rods and hangers will also be a give away.
     
  7. powerabout
    Joined: Nov 2007
    Posts: 2,916
    Likes: 63, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    165 came with a 2 barrel
    only the very old 200 inline 6 came with a 4 barrel, 250 cubes is fine with a 4 barrel though.
    Still get an old q jet from a marine engine but as Par says get one with an electric choke.
    EDIT or a modern marine 4 barrel
     
  8. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 482, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I assume V8's with outdrives, other wise it's cheaper with an outboard. They have small 4 barrels, from 390 CFM through 550. 390 CFM will be fine for a 250 with a typical marine cam, assuming volumetric efficiency in the high 70 to low 80% area. The 165 and 181 4L will run better with a 38 MM Weber though.
     
  9. powerabout
    Joined: Nov 2007
    Posts: 2,916
    Likes: 63, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    where did outboards come into this conversation, now I'm confused?
    what has a small 4 barrel?
    a q-jet is over 700cfm ( 2 different models)
    pressed in plug on the outside of a q-jet, dont remember that sure inside but that leak goes into the engine I think hence they made a very good marine carb?

    Todays trivia
    OMC have made 2 4 barrel outboard carbs, one common one not so,
    (side draft of course).
     
  10. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 482, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    When I need less then say 200 HP, I look to outboards, not I/O's, simply because of the ease in hookup, maintenance, etc. Its mentioning was only in this regard.

    The Q-jet came in several CFM requirements, most where 675. The plug I'm referring to is on top of the bowl in the top cover, just forward of the bowl vent, often partly hidden under the pump lever. If it leaked externally, it would roll off the top of the carb, onto the manifold.
     
  11. tom kane
    Joined: Nov 2003
    Posts: 1,767
    Likes: 48, Points: 58, Legacy Rep: 389
    Location: Hamilton.New Zealand.

    tom kane Senior Member

    Safer carburettor in box?

    Not trying to change the subject but just as a mater of interest one of the first Crossly internal combustion engines had an exhaust pipe 60 ft long to help it breathe.
    The Induction and Exhaust systems are an interesting study both in Classical and Quantum (the study of sub-atomic particles behavior) Mechanics.

    I experimented with a long 8 foot flexible induction (gasoline resistant) tube so a carburetor could be fitted anywhere in a boat or auto.
    The flexible tube gave automatic adjustment supply of fuel air to the motor by increasing or decreasing the diameter according to the throttle opening and the high or low manifold pressures. I ran an Austin 1960 auto and a boat quite a long time on several different models. The flexible tube can be fitted in a metal tube if you wanted. The evaporation of the fuel keeps the induction tube at a cool and even temperature. There are many aspects to consider.
    The motors could run at very low RPM like a steam engine and quiet because the long induction tube gives high volumetric efficiency with the ramming effect over 100%.
    I did not have trouble with the fuel condensing out of suspension or the carburetor freezing. most problems can be overcome. Back-firing was induced and no problems resulted because of the ramming effect of the long tube.
    There were no problems at shut down such as dieseling or with fuel still in the tubes, no different to the normal motor.

    It was quite interesting watching the fuel and air in the see through induction tube at different throttle openings and RPM.
     

    Attached Files:

    Last edited: May 26, 2014
  12. Ike
    Joined: Apr 2006
    Posts: 2,496
    Likes: 353, Points: 83, Legacy Rep: 1669
    Location: Washington

    Ike Senior Member

    This is the carb when I first got the boat. I will have to get some pics of what it looks like now. All the hoses and fittings have been changed and that filter is gone.

    [​IMG]

    [​IMG]
     
  13. Ike
    Joined: Apr 2006
    Posts: 2,496
    Likes: 353, Points: 83, Legacy Rep: 1669
    Location: Washington

    Ike Senior Member

    Here is what it looks like now

    [​IMG]


    [​IMG]

    [​IMG]
     
  14. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 482, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Looks like a GC model. Toss that mechanical choke, especially if you'll need it a lot.
     

  15. gonzo
    Joined: Aug 2002
    Posts: 15,247
    Likes: 949, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    The easy fix for the leak on the plug next to the vent pipe is epoxy.
     
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.