Fuel Injection or Carburetion ?

Engines, Exhaust and Fuel Systems

  1. 88_AHB

    88_AHB Well-Known Member

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    Hey everyone,
    I know this is a age old debate of fuel injection vs carburetion.Anyways I've been pondering of switching to fuel injection.I've searched around and done some reading on a few systems that seem fairly easily to install/operate.I've mainly been looking at Holley sniper and Fitech.

    The main reason why I've been searching is my current holley has had on going issues and yet its only few months old (600cfm).I've reset idle/air changed jets and yet still stumbles at about 1/4 throttle or so.Motor is a 318 with intake,carb,header,mild cam the usual.No obvious vacuum leaks,reset timing etc., thought of switching to a edelbrock 600. Anyways was curious to all that have made the switch to fuel injection. I know of the obvious pros and cons etc.
     
  2. AJ/FormS

    AJ/FormS Well-Known Member

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    Yeah a self-learning EFI system can get you past that stumble, but at what cost, compared to tuning the 600.
    Stumbles at 1/4 throttle usually point to simple tuning issues.By 1/4 throttle the mixture screws have long ago maxed out, and the transfers are also at full capacity. The carb is on the bottom of the mains, and the pump-shot is all used up.
    With an otherwise mechanically sound engine, you should not be able to make a stumble at 1/4 throttle.
    So then I gotta ask when does this stumble occur? Cuz there can be one of several possible scenarios; with different solutions.
    Does this happen:
    every time you leave the line accelerating with a fixed throttle position?
    Or does it happen with a moving throttle valve?
    Or is this a second gear deal when moving from one speed to another speed?
    Or are we in third gear going from a cruise to passing?
    or etc.
    What exactly initiates the stumble?, what sustains it? for how long? and can you drive thru or around it?
    Each of these may require a different solution.
    There are several to many guys here in this Forum who can help you thru this, and we do it for free. So, if you want help, we're here for you.
     
    Last edited: Dec 1, 2019
  3. Camtron

    Camtron Well-Known Member

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    Is it stumbling off idle, accelerating off a green light or when you’re cruising and try to get your foot into the gas? Sounds like an accelerator pump adjustment might be needed or perhaps a larger pump nozzle; if everything else is dialed in anyway. That’d be my first check/adjustment.
     
  4. Duke5A

    Duke5A Well-Known Member

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    I can help you with the fuel injection if you want to go that route. Personally, I'll never screw with carbs again. But if all you're looking for is to fix this part throttle bog then stick with what you have as this can be fixed with relatively little expense. To go fuel injection you'll be in for about $1500 by the time you get done. That is what I have into mine. Holley Sniper EFI 600...
     
  5. Aspen500

    Aspen500 Well-Known Member

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    That's what keeps me from going with EFI, the cost. One thing I found is, an A/F gauge is almost a must when tuning a carb. What I thought was fine seat of the pants as far as jetting, air bleeds, idle screws, etc, once the gauge was installed, I found it wasn't even close. It is an added expense but it was worth every dollar IMO. The AEM unit works great and is less money than the other brands.

    At one time, way back in the '90's, I had an Edebrock 750 and no matter what was done, it never ran right in all modes. You could get idle and WOT good, but then it would surge at P/T cruise or P/T tip in. Mess with jets and metering rods, springs, etc and then it was good at P/T but not at WOT, on and on. Bolted on an old OEM Holley off some very early '70's Mopar (don't recall what)I had sitting on the shelf and it ran perfectly as is. Just my experience with the Edelbrock's anyways.

    Make sure your ignition is good. The wrong amount of advance at the wrong time can also cause stumbling. A lot of carb issues turn out to be an ignition issue. Not saying that's what's wrong with your car, just something to keep in mind.
     
  6. Oldiron440

    Oldiron440 Well-Known Member

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    I had a friend who was a great carb tuner rebuilder he would tell me that half of the carb problems he looked at were timing.
    Not knowing what combination you have I'll give you the curve that mopar recommends. Basically its your initial timing at idle then full advance by 2500rpm, I've seen not having this cause a mid rpm stumble.
    I would check how much vacuum you have at idle and pick up a new power valve with a number half that of your idle vacuum. A blown or incorrect valve can cause a stumble. You will need bowl and metering plate gaskets get the blue ones.
    That's where I would start fixing a lazy timing curve and verifying the power valve by replacing with a correct part is a lot better than $1500.
     
    Last edited: Dec 1, 2019
  7. Oldiron440

    Oldiron440 Well-Known Member

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    I'd recommend picking up a Holley tuning book, the vac secondary 600 is a great carb to learn how to tune on.
    Summit has them and there not $1500.
     
  8. Aspen500

    Aspen500 Well-Known Member

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    Yes, a tuning book on the carb is worth more than anything else. The DVD that came with my carb was referenced quite a few times, along with the manual that came with it. Not being an expert tuner by any means, it saved me a lot of hunt and peck type of stuff.
    I had a buddy (who is now no longer with us) who could tune a Quadrajet with his eyes closed and two broken arms, and it always amazed me. He'd drive the car, think a minute, change metering rods, or metering rod link, spring, and/or jets, etc, drive it, come back and maybe put a slightly lighter metering rod piston spring in or something and the car ran perfectly.
     
  9. 88_AHB

    88_AHB Well-Known Member

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    I haven't tried adjusting the accelerator pump at all that's a great point.This stumbling is mainly coming off from a stop,if I give it too much throttle at once it will do this and want to cutout "pop" under load.When going through the gears other that no huge issues that I've noticed,I still haven't driven the car a lot yet. My apprehension with this carb is that, I already had to return the last one to summit and warranty to this new one.I also thought there's no way two of them can be defective? Now i also thought somehow the power valve is shot already? Or wrong size for my application?

    The other reason why I thought of switching to injection is, summit gave the carb another year warranty with this one. So, If I wanted to make the switch I could probably get credit for it towards an injection system which is what the rep told me so around $350.One negative is the big hit on the price for injection,ive seen most systems are around $1k. Most don't include the pump,regulator etc. or other hardware needed.So figure $1500 like others have said here.

    This car did sit for some years, so i did drop the tank and flushed it and a new sending unit prior to this new carb.I can recheck my timing as well (been a few weeks since I have). I think it's initial timing is around 12 or 13 degrees haven't check total timing,also I have not hooked up a vacuum gauge to see where Iam on that. Also not sure if this is an issue or not, I know old carbed cars taking some "pumping" on the throttle to get started when cold. This thing is hard to start takes at least 5 -6 pumps or more cold start. Even once warmed up it takes a few to get going.Where I live on the west coast we don't get snow and don't have the harsh winters like most of you all. Maybe i'm just spoiled from injection on my daily driver Silverado lol.

    I thought these newer 600's dont have adjustable floats? Maybe someone can correct me or verify. Here's a link to the carb Holley Street Warrior Carburetors 0-80457S. Thanks
     
  10. Camtron

    Camtron Well-Known Member

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    definitely get a timing light and vacuum gauge on there. I’d start with the accelerator pump, make sure it’s adjusted correctly. That won’t cost anything if you already own feeler gauges.
    With your build on the engine, you may need a pump nozzle that’s a couple sizes bigger and I’d bet that gets rid of your stumble.
    I’m also rebuilding a extra edelbrock 1406 tomorrow. If you want to try it out, I’ll send it to you with a full jet and metering rod & spring kit to get it dialed in perfectly.
    EFI is absolutely the way to go if you have the money to do it. I would if I could afford it but, I can’t. So I play with carburetors lol
     
  11. Aspen500

    Aspen500 Well-Known Member

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    If the choke works correctly, it should start with one pump of the throttle, kick it off the high idle and go. If there's no choke, it will take more and then not run well until it warms up a bit.

    We do get spoiled with the EFI on the DD's where you turn the key, engine starts instantly and away you go, in any weather, at any temperature, hot or cold engine. Same if it's got rack and pinion steering, suddenly recirculating ball feels sloppy even though that's the way they always were, we just didn't know any different.
     
  12. 88_AHB

    88_AHB Well-Known Member

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    A lot to take away from here. Has anyone installed or dealt with megasquirt products?
     
  13. SixBanger

    SixBanger Well-Known Member

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  14. BudW

    BudW Moderator Staff Member

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    To start of with, I’m a Thermoquad fan and have something like 80-100 of 'em in my garage (some for parts, some to use). Only the early TQs are worth messing with. ALL TQ’s that came originally on FMJ’s are not the same as the early ones and take a lot of work to get to work well, whereas the older ones are almost bolt-on and have fun.

    That said, I’m now a fuel injection fan and can’t wait to get rid of the carburetors on both of my cars. Eventually my ’77 wagon and my ’86 Fifth Ave will get big blocks installed along with fuel injection.

    ‘My “plan” is to replace the 2-bbls on both cars with 2-bbl appearing FI units (not sure of brand, yet). I just don’t want to mess with changing out the intakes or worry about the transmission kickdown linkage - at this time. Once the big blocks are dropped in, then the 4-bbl appearing FI will take over and the rest of fuel system is already in place.
    BudW
     
  15. Oldiron440

    Oldiron440 Well-Known Member

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    Bud what do you consider early?
     
  16. Aspen500

    Aspen500 Well-Known Member

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    A properly set up TQ will work excellent. I remember working on them waaaaaaaaaaay back in the day. Seems I recall there's 21 external adjustments and they have to be precise AND done in the correct order. Mess up one adjustment and all the others from that point will also be off. Basically, as long as nobody ever messed with it, good to go (unless the composite main body is warped). Kind of like the Ford VV 2 bbl from the early '80's. If the adjustments were left alone, all was well. If someone messed with the adjustments,,,,,you're screwed! Only thing that went wrong with them was the variable venturi diaphragm failing and the metering rod sticking, there was no reason to touch anything else. The factory adjustments would never change on their own and the adjustments were made on a flow bench on each individual carb so it's impossible to do in the field (without a flow bench). Sorry, I'm starting to digress again, lol.
     
  17. BudW

    BudW Moderator Staff Member

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    ’72-74 and some ’75 TQ’s.

    The TQ numbers, I feel, are the best ones, as is (if set to factory specifications, that is) are:
    6138s, 6139s, 6144s, 6318s, 6319s, 6339s, 6340s, 6394s, 6614s, 9000s (these all have the smaller primaries, ie: small blocks)
    6090s, 6140s, 6165s, 6166s, 6320s, 6321s, 6322s, 6323s, 6341s, 6342s, 6410s, 6411s, 6446s, 6452s, 6353s, 6354s, 6455s, 6456s, 6457s, 6459s, 6460s, 6461s, 6462s, 6463s, 6488s, 6489s, 6496s, 6503s, 6518s, 6545s, 6615s, 6616s, 9013s, 9014s, 9015s, 9016s, 9017s, 9019s, 9020s, 9022s, 9023s, 9024s, 9025s, 9035s, 9036s, 9096s (these all have the larger primaries, ie: big blocks).
    Also, 9801s and 9811s which are over the counter carburetors – and have the smaller primaries.

    The above numbers are all considered to be the early TQ’s. The numbers below are the mid-range TQ’s.

    This second list is TQ’s that can be made to work OK – but not that well right out of the box. These are generally some ’75 and ’76 models (a couple were used on FMJ’s, but not many):
    Note: These are useable – but with the early ones still available, I highly recommend using an early one instead of these.
    9055s, 9123s, 9140s, 9152s, 9215s, 9216s, 9217s, 9218s, 9219s, 9223s (small primaries)
    9002s, 9004s, 9008s, 9009s, 9010s, 9011s, 9012s, 9034s, 9046s, 9047s, 9049s, 9050s, 9051s, 9052s, 9053s, 9054s, 9056s, 9057s, 9058s, 9059s, 9062s, 9063s, 9065s. 9066s, 9068s, 9069s, 9072s, 9073s, 9099s, 9100s, 9101s, 9102s, 9103s, 9108s, 9109s, 9110s, 9111s, 9112s, 9116s, 9117s, 9127s, 9148s, 9149s, 9150s, 9151s, 9173s, 9190s, 9211s, 9212s, 9213s, 9214s, 9221s (large primaries)

    All the other number TQ’s are the late design and are not worth messing with – except for possibly on a numbers matching car. Even then, I would keep the original carburetor in a box for the new owner of car and drive car with an early TQ.

    Note: most people will not notice much overall power difference between a small or large primary TQ. For a small block and 100% street usage, the small primary might be best and result in best fuel mileage.
    BudW
     
  18. SixBanger

    SixBanger Well-Known Member

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    Offtopic .Bud, how would your big blocks setup look likes on parts? Based on 440 or 426 hemi?
    It would be nice if someone get a multi point injection running on 440.
     
  19. Duke5A

    Duke5A Well-Known Member

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    Why go this route? You would be buying parts twice over. The 2bbl units are almost the same price as the 4bbl - about $1000. What I would do is swap to an iron 4bbl manifold and use the 4bbl injection kit on the small block with Lokar cables for the throttle and kick down. That way everything can be reused on the big block once you're ready.

    If you don't want to swing a cast iron intake around find a used Edelbrock and sell it when you're done. You'll be able to sell for what you bought it for.
     
  20. Oldiron440

    Oldiron440 Well-Known Member

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    Back to the TQs I've had very good success with the late Lean burn 440 TQs on both 440s, 340 and 360s. It took a little to get them fattened up but success none the less. I had one on a stock 340 with the Hemi grind cam, headers and 3.91 gears with a 4 speed running 12.10s. He pulled the 4 speed a put in a 904 with a mild converter and went 11.90s. Before any body squawks about the 904 being faster it was a small tire A body. I had a Cbody that I knocked 2 seconds of the ET using the stock 77 TQ. I had one on my 360 shop truck until a guy offered me stupid money for it, I always ment to put one back on but you know how that goes. It had a Holley 600 on it for years afterward.
    I quit messing with them around 1990 orso the accpump wasn't lasting because of the fuel or the kits in stock were old idk.