Hesitation/bogging
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Hesitation/bogging

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    Default Hesitation/bogging

    I had the boat on the water for first time today with new engine. the timing isnt totally optimized - i need some stop bushings. so i could have timing as well as carb tune issues. that said, i havent touched the carb. it is a qjet, supposedly recently rebuilt.
    If i stab the throttle too quick, it will bog or hesitate. it also develops a bog above ~4000 rpm. any more throttle above 4k and it will bog till i pull back. any thoughts? can you even get jets for qjets anymore?

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    Shit Can the Qjet...

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    im cruising parts spam right now!!
    Im looking for a holley or edelbrock/carter... or maybe an old school predator!

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    Member MSCobalt220's Avatar
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    tune it first, Q-Jets rock when they're dialed in . You're just jumping around to the first thing you can change not knowing what is at fault . Timing first, fuel pressure/volume , then carburetor . Q-Jets are way better in the midrange than either Holleys or Edelbrocks when they are dialed . Admittedly , not everybody can make them work , it takes a carb guy to get it done . I just happen to have done a boat load of them over the years . I like em. Getting jets and metering rods may be a hassle, Edelbrock should have them. If I was changing out, the Holley is easier to dial than the Edelbrock .

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    Senior Member GT Jets's Avatar
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    Quote Originally Posted by slim pickens View Post
    I had the boat on the water for first time today with new engine. the timing isnt totally optimized - i need some stop bushings. so i could have timing as well as carb tune issues. that said, i havent touched the carb. it is a qjet, supposedly recently rebuilt.
    If i stab the throttle too quick, it will bog or hesitate. it also develops a bog above ~4000 rpm. any more throttle above 4k and it will bog till i pull back. any thoughts? can you even get jets for qjets anymore?
    Quadrajets are an excellent carb, the biggest problem is the spread bore which makes them tough to tune.

    I would look closely at the accellerator pump and make sure the secondary venturi butterfly (the one on top of the secondary venturi) is moving freely and that the choke linkage is adjusted properly, this holds out the secondaries and can cause all sorts of issues.

    There is also a rarely addressed issue on the secondary butterfly (top again) that can cause your high RPM dog out. There is a small spring in the linkage of this butterfly that has a funny, almost cheesey spring adjustment, this adjustment is the one that would be done with a secondary diaphram spring in a vac sec Holley (the Q-jet is a vac sec carb BTW). if this is mis-adjusted, it will stumble like a blind drunk..

    They are extremely tuneable and will flow killer CFM #s. (in the high 800's)

    I would look first into fuel delivery, your problem has running out of fuel written all over it....It does not matter what carb you put on it (with the exception of a teeny tiny something or other) this has to be fixed first.

    IMHO stay away from the Edelbrock carbs, they have good tuneability and are a descent carb for the price, but wont fix your problem and tend to need a lot of attention to work right, whereas a Holley will often times run right out of the box.

    To answer your "making the Q-Jet anymore", Edelbrock has the rights to the design and did (maybe still do) sell a bunch of them, mostly for OEM replacement stuff...

    GT
    GT


    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

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    Senior Member GT Jets's Avatar
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    Quote Originally Posted by slim pickens View Post
    im cruising parts spam right now!!
    Im looking for a holley or edelbrock/carter... or maybe an old school predator!

    Unless this thing runs in the high 6000's in RPM, step away from the Predator..................................

    GT

    BTW MSCobalt220
    GT


    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

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    Senior Member jetboatperformance's Avatar
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    Quote Originally Posted by Sangster View Post
    Shit Can the Qjet...
    Great carb for a 72 Olds 98 Tuna boat I worked with these in the 70's , sorry but have to vote it off the island Get a "Holley" type carb 750 (or better) DFDP Just my 02 Tom

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    Senior Member GT Jets's Avatar
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    Quote Originally Posted by jetboatperformance View Post
    Great carb for a 72 Olds 98 Tuna boat I worked with these in the 70's , sorry but have to vote it off the island Get a "Holley" type carb 750 (or better) DFDP Just my 02 Tom

    Got a Mercruiser Marine worked Q-jet on a Vortec headed SBC (355) and it made 326 HP at 5100 RPM with Iron exhaust manifolds. They do work, but they are touchy...

    Holley would be my vote, unless you're a broke ass boater like myself, in that case, tweak on the Quadrjunk...

    Hi Tommy!

    You working tomorrow?

    GT
    GT


    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

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    Senior Member jetboatperformance's Avatar
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    Quote Originally Posted by GT Jets View Post
    Got a Mercruiser Marine worked Q-jet on a Vortec headed SBC (355) and it made 326 HP at 5100 RPM with Iron exhaust manifolds. They do work, but they are touchy...

    Holley would be my vote, unless you're a broke ass boater like myself, in that case, tweak on the Quadrjunk...

    Hi Tommy!

    You working tomorrow?

    GT
    Workin on the homestead But always pretty close to the PC

    Dont get me wrong if all ya gots the QJ run it , but don't try to mix it up with a Cam of any proportions

  12. #10
    Senior Member GT Jets's Avatar
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    Quote Originally Posted by jetboatperformance View Post
    Workin on the homestead But always pretty close to the PC

    Dont get me wrong if all ya gots the QJ run it , but don't try to mix it up with a Cam of any proportions

    Wouldn't that apply to most vac. sec. carbs???

    I send you an e-mail Tommy, I have some needs and should be down sout in a couple weeks...Thanks!

    GT
    GT


    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

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    boats with fords wouldnt do that!

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    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    Quote Originally Posted by slim pickens View Post
    I had the boat on the water for first time today with new engine. the timing isnt totally optimized - i need some stop bushings. so i could have timing as well as carb tune issues. that said, i havent touched the carb. it is a qjet, supposedly recently rebuilt.
    If i stab the throttle too quick, it will bog or hesitate. it also develops a bog above ~4000 rpm. any more throttle above 4k and it will bog till i pull back. any thoughts? can you even get jets for qjets anymore?
    You may have more than one issue, so you may need more than one "fix".

    As noted before, Q-jets do work well when set up right, they just aren't as easy IMO to get right as a Holley is.

    Your worst nightmare is that sometimes someone rebuilds a carb, with very little idea what they are doing, and "improves it" wrongly.

    The idle-stomp on the throttle bog screams accelerator pump problem to me. Make sure you have full travel from the pump rod, make sure you get a good, full, strong squirt when the pump is activated, from virtually no throttle movement. Clogs can occur below the shooters, accel pump seals can leak, etc. Unfortunalely, the only fix for actual pump issues, is taking the top off the carb (internal pump).
    There should be a needle of some sort below the shooter, underneath it, in the fuel flow passage, it must be there, and must be free to move. They get cruddy or stuck and block off accel pump squirt sometimes.
    Sometimes it gets left out, by an "improver".

    A high-RPM bog or "deadness" sounds like the air flaps over ther seccondaries are opening too soon. If they are not stuck shut (making it pull rich like a choke) they must move freely, but only in response to the engine's needs. If you open them too soon, or (another "improvement") "mechanically", the engine has no use for that much airflow, and velocity falls, mixture leans because vac. signal at the venturi falls, and it bogs.
    Tighten up the spring and re-test, the engine will run much stronger, and just fine if they open too late, than if too early. You should not be able to tell when they open by any "engine feel", power delivery should be continual and smooth, any soft spots of "feeling the 4-barrels kick in, usually mens they are coming in too early.

    Best of luck to ya.

    I don't have a huge ammount of experience with q-jets, have dome a few, but a ways back, My holley seldom requires any attention once set, for years.
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
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    Well I am going to give the q-jet a look over and see if I can get it working, I guess give it the old college try. Apparently some local auto parts stores have q-jet parts so that isnt as big of a deal as I was thinking.
    Failing progress on that, I will be looking for a used holley. I am thinking a 750 DP would be about right size for a mild cammed 455 that probably wont see the sunny side of 5000 rpm. That size would leave room if I cam up the 455 later, or move to a little more aggressive BBC or BBF power.
    I see a ton of automotive holleys for cheap locally, is there a conversion kit to convert regular to marine? Is it just the J shape vent tubes or is there more internal differences on a marine carb?

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