cfm carb for Buick 350...places sell 600 and 650...is that enough?

Discussion in 'Small Block Tech' started by buicks, Aug 22, 2013.

  1. Fox's Den

    Fox's Den 355Xrs

    Gee, now I know why I use a Holley. Easy.
     
  2. buicks

    buicks Well-Known Member

    Maybe it would be clearer to say it bogs when the secondaries are called to be used, whether or not the secondary flaps open (wired shut or not). Since the secondaries down in the carb open either way. But then I would think a lack of fuel bog would happen if the secondaries were wired shut too right? The bog is worse with the flaps wired shut, and lasts longer too.

    I suppose I will call Cliff and see if he'll go over it again and what it'll cost me.

    ---------- Post added at 08:02 AM ---------- Previous post was at 07:53 AM ----------

    Both front barrels squirt when throttle is pulled, still not sure how to know how much tey should squirt, timing is at 30 all in at 3k rpm, it is a stock dist with lectric limited breakerless electronic ignition, it has the crane adjustable advance kit (springs), the vacuum line is plugged into teh lower drivers side port on front of the carb, mech advance was working well, fuel filter 2k miles old, car has not had debris probs with fuel.

    Heres the breakerless parts if you havent seen them
    [​IMG]

    Is there a way to know if the float bowls are the prob?

    ---------- Post added at 08:04 AM ---------- Previous post was at 08:02 AM ----------
     
  3. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I was reading back in the thread and saw you referring to the back choke pull off. That has nothing to do with the secondary air valves, just the front pull off does. Cliff is pretty good, so I can't help but think your problem lies elsewhere.

    Can you list your combination, cam intake, converter, gears, everything?
     
  4. buicks

    buicks Well-Known Member

    Good to hear the back pulloff isnt related.

    Cam stock 2bbl, intake TA stage 1 350, converter stock TH350, rear gear 2.56 ratio.
    Hooker headers, 2.5 inch dual exhaust, xpipe from jegs, flowmaster 40 series. I run 91 octane no ethanol fuel. Spark plugs gapped to factory spec.
     
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    OK, I need to know what your vacuum is at idle, fully warm. Is the transmission downshifting when you stomp on it? When was the last time you changed your fuel pump, and have you inspected your fuel line from front to back, including the fuel pick up?
     
  6. buicks

    buicks Well-Known Member

    Good thoughts.

    Tranny downshifts when stomped far enough that the cable stop at the pedal gets activated, but it does seem like I can take a 90 degree corner in 3rd way to easily.

    Fuel pump is 3 yrs old from Napa.

    The fuel pick up, isnt that in the tank? I've not dropped the tank in teh 10 years I've had the car. The fuel lines from the pump back have rust, the rustiest thing on the car. But dont leak.

    Where is the best place to hook up the vacuum gage, and does it need to be T'd in so no vacuum is lost? (sorry not used to vacuum checking)
     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Pick up is in the tank. Yes, you need to look at it at some point. Also there is rubber line at the fuel pump and back near the tank. You need to look at it also. If it is old and cracking, replace it. The pick up has a sock on it. It can become clogged over time.

    As far as vacuum goes, you need manifold vacuum. This is another source of confusion for many. I don't get why. With the engine running at idle, if you pull off a full manifold line from the carburetor or intake, it will hiss, very loudly, and there will be no mistaking it for a ported connection, which will have little or no vacuum at idle. You can tee it in to a line, or just connect the gauge directly to the port on the carburetor. It would only be necessary to tee it in if the line was powering something like the vacuum advance.
     
  8. buicks

    buicks Well-Known Member

    Thanks I will make time in teh next few days to check vacuum. What shoudl I expect to see for an idle number?
     
  9. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    I agree. This is why most people will choose this path, and I don't blame them. Though a pain in the ass sometimes, once you get the BS ironed out of the Qjet, you have a good carb on your hands, and it's the end result that you have to live with ultimately for years to come, so it just depends on whether it's worth it to you or not.

    ---------- Post added at 11:53 AM ---------- Previous post was at 11:09 AM ----------

    So the accelerator pump seems to be functioning, but the bog occurs later on. The secondaries opening up actually help resolve the bog (you said it's worse when they're wired shut), making it sound like a fuel starvation issue now, but only with the primaries.

    Larry's on track. Assuming the carb is built properly, and Larry indicates that it should be, then the next logical step is a vacuum leak somewhere or fuel starvation due to a myriad of possible reasons: float level too low, fuel pump not feeding properly, fuel filter(s) partially plugged, pick up sump partially plugged, debris lodged up somewhere in a line, etc. resulting in less fuel volume to the carb...although none of those make sense if you factor in the fact that it rectifies itself with the aid of the secondaries.

    If there was fuel starvation as a result of poor delivery of fuel, the secondaries would only exacerbate the issue...

    It almost sounds like the primary jets are starving somehow, so that after the initial accelerator pump fuel surge, it struggles to get fuel and is worse without the secondaries.

    This points to the primary jets.

    This issue existed before the spacer, so the problem (as unlikely as some believe it to be) has to lie inside the carb itself.

    Just tossing in my 2c for thought. Whether I'm right or not isn't the issue, it's whether we can get your carb issue ironed out. The problem must be resolved.
     
  10. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    More than likely it is a pickup problem if the fuel tank and pickup are the original that are 40 + years old. I had a similar problem a few years ago with my 65 Impala with rust flake surrounding the pickup,although the tank looked solid on the outside,it was very rotted on the inside. You might want to check there,an old antena or some brake line tubing to probe the gas tank to try and feel for debris on the bottom of the tank.

    The way I fixed mine was a new tank and sending unit,hasn't been a problem since. A less costly,more labor intensive way is a tank sealer kit,I think Eastwood among others sells a kit,or a local radiator shop can do it for you(for a price) if that is what you need.GL

    Derek
     
  11. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    A stock cam with an engine in good shape should make 20" of vacuum, fully warm in Park/Neutral.
     
  12. buicks

    buicks Well-Known Member

    I'm really doubting the pick up is the problem because I have had no problem drawing alot of fuel and can go as fast as I want, and can rev a low gear up too, I just can't do it quick by flooring the pedal. I would also likey have orange gas or plugging up filters. But yeah it could be original parts in the tank.
     
  13. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Not saying this is the problem,but when it happened to me,it wasn't all at once. When the inside of the tank starts to rust over years and years of service,the inside will form flakes of rust on the inside of the tank that will slowly start to dislodge.(will dislodge at a faster rate on bumpier roads) If the car is ran with the tank rusty on the inside,new gas will get rid of any fuel dis-coloration that may of occured from sitting over the winter.(if its not driven in the winter) And as for your filters plugging up with this problem(if you have it)when the flakes let go they are to large to get sucked in right away,the more driving and fuel sloshing will eventually break down the flakes small enough to reach the filter.(ask me how I know)

    This might not be the problem right now,but it could be in the near future,something to watch out for on an old car.

    The more you decribe your problem,the more it sounds like the float isn't adjusted properly,as in like when you stomp on the gas peddle,the fuel bowl drains out right away,before the pump can refill it. Float set WAY to low,not a hard fix,there are directions in a rebuild kit on how to do it,or maybe you can find them online.GL


    Derek
     
  14. Fox's Den

    Fox's Den 355Xrs

    When I took my tank out the sock was sucked completely closed. It still flowed ok but when in the tank there could have been dirt there and when then fuel pump tries to pull the fuel dirt in the tank can easily plug the line if the sock is flattened like mine was. So this could be the problem with the fuel supply to the carb.

    I would look at the ignition system to make sure you are getting the proper spark to the plugs. Just as with no gas to the carb, no electricity to the plugs means the engine dies/bogs, do not overlook this. If you still have points look at the condenser.

    Most vacuum gauges work as fuel pump testers too, so make sure you get one.
     
  15. smar

    smar Well-Known Member

    After you check manifold vacuum 18-20... I would check to see if your vacuum advance canister is leaking down. Get/Borrow a vacuum pump and pump it to 15-20 in if it leaks down won't hold it then your advance can is gone. I've see it happen on just about ever make Gm. Ford... You have pretty much a stock set up so I'm assuming your timing is set up stock no re curving. If you take any stock set up that runs good then put a bad advance can in it will want to fall on its face under load. Just something else to check.

    ---------- Post added at 09:50 PM ---------- Previous post was at 09:20 PM ----------

    Also I must have missed it but did you post you ignition set up as crane *** 30 -3000 different advance springs. Just for Sh%%%s and giggles what is your timing set at idle. You have basically a stock engine with headers I think your advance cure is to aggressive. Now I'm not saying to set the base timing where Buick said to run it way back when but I would start at factory specs and then tweak it a little from there. Also are you running ported or manifold vacuum to your advance can with no emission's I would run it on manifold vacuum but then use pre 71' timing at idle specs (again as a place to start from) with the engine running pull the vacuum line off your dist. put you finger on it is there vacuum at idle if so its manifold if not rev the engine now do you feel vacuum then its ported.
     
  16. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    What year is your Buick, and what distributor part number?
     
  17. buicks

    buicks Well-Known Member

    Really? I was thinking I should have had all timing in by 2500. I recently moved my dist vacuum from manifold to a ported source and idle went quite a bit lower. But the throttle problem remained the same. I did this in this thread at the same time i hooked up the choke pulloff to vacuum. The vacuum cannister on the dist was replaced a year ago when the timing was set and crane spring set installed. The same bog problem existed before and after this was done.

    ---------- Post added at 08:06 AM ---------- Previous post was at 08:01 AM ----------

    How do you measure how much spark you are getting? If you read back a bit I have "breakerless electronic" not points. I have thought about replacing the coil but have no idea how to know if it is weak.

    ---------- Post added at 08:08 AM ---------- Previous post was at 08:06 AM ----------

    The car is a 72 Skylark
    The engine is a 69, dist should be 69 as well (Where do i see part number?)
    The heads are 72 oiled thru TA adjustable pushrods.
     
  18. smar

    smar Well-Known Member

    The timing all in at RPM... and how fast it comes in... are a must to know but for an engine with a hot cam, more comp, I'm not saying you won't benefit from changing your advance cure but as a control I would start with bringing your timing back to stock specs it's (free and easy) your engine being stock it should run just fine with this set up if it helps great if it does not you can at least put to rest any ignition problems. Also you got to put a vacuum gauge on it the gauge will tell you a lot like if your running lean, late timing, You want to see 18-20 in. (steady) no bouncing needle if its low and steady like 12-14 or something close to that then your timing is off if its low but the needle fluctuates then could be a vacuum leak. Most part stores sell them for 15-20 bucks.

    ---------- Post added at 09:31 AM ---------- Previous post was at 09:13 AM ----------

    Full manifold vacuum any nipple below the throttle plates Ported vacuum any nipple above the plates. But I thing Rochester carbs also have a full manifold port up high maybe on the back of the carb for the choke pull off I can't quite remember. Just for the hell of it is your choke opening up all the way and (staying open) after the engine warms up.
     
  19. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    Ok...

    Everyone needs to ask themselves what would cause an engine to bog under quick acceleration with a Qjet, and it's even WORSE with the secondary butterflies wired shut?

    If it was a result of float set too low, gas tank sock or anything involving fuel delivery to the reservoir, it would be WORSE with the secondaries working, not BETTER.

    This points to fuel that is somehow restricted to the primaries when they are helped out by the secondaries (either too much or too little). When's the last time you heard about a Qjet's secondaries alleviating bog instead of causing it? lol

    What if...the primary jets were too big for the CID being used? Would it take more to draw the fuel out under sudden throttle opening, resulting in a hesitation or sputter until higher RPM was achieved? Might explain the crappy gas mileage described earlier.

    Qjets were tuned specifically for the engine they were being used on. If the jets were too big, the 350 may not have the draw on them needed for them to function properly compared to a big block (if this is indeed so).

    IF the jets are feeding too much fuel, the secondaries would provide the air needed for the excess fuel. IF the jets aren't giving enough fuel (because gas can't be drawn out properly) the secondaries allow air and consequently fuel to offset the bog caused by the primaries.

    Just tossing that out there.


    Does black smoke billow out of the exhaust when you accelerate? Any backfires from exhaust? (or up through intake)
     
  20. buicks

    buicks Well-Known Member

    Yep, vertical flaps when warm. I will vacuum test in the coming days, possibly tonight. Also see pics of my carb a few posts back.

    ---------- Post added at 11:48 AM ---------- Previous post was at 11:44 AM ----------

    I don't notice smoke or backfires, runs great if you dont get on the throttle fast and hard. How do I test the accelerator pump to see if it is adequate, and how long to they last? This one was replaced when the carb was rebuilt about 2 years ago. If it is lack of fuel at initial jab of the pedal I suppose thats the number one culprit?

    edit to add, there may be some black smoke and popping sound only during flooring it to open secondaries, determined 9/28/13
     
    Last edited: Sep 28, 2013

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