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Is 600 CFM too much for a 305??

Discussion in 'The Garage' started by diesel4me, Sep 21, 2004.

  1. diesel4me

    diesel4me 1 ton status Premium Member

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    I have an Edelbrock(*Adapt-O-Brock!)carb on my 79 C10 I just put the 305 in--the same carb was on the 250 six before this motor--its a model 1405,it seems like it runs great on the primaries,and when I just crack the secondaries open,but any more than 3/4 throttle you can feel it flatten out,and almost bog,back off the throttle and it goes much better,almost like its either getting too much air,or the motor cant handle that big of a carb--but the quadrajets they used on the 305's were often 800CFM! /forums/images/graemlins/confused.gifmaybe because they are vacuum secondary the rear barrels never open all the way on a Q-jet??. I disconnected the secondaries when I ran this on the six,it ran better that way,and I can understand that because it was too much carb for such a small cubic inch motor,but I thought the 305 would handle it fine--maybe because I have stock cam,no headers and a single exhaust it acts this way??.Maybe I should get a smaller carb like a 500 CFM,or re-jet this one??-the spark plugs look like its running perfect,nice greyish-brown color,not all sooty or carboned up.I'm beginning to think about putting my other holley two barrel "economaster"carb on it(its basically the same carb as a older 318 mopar)and see if that makes it go better,might get better mileage--but as long as I dont use the secondaries it runs well and gets decent mileage,so I'd rather not spend the time to re-do all the accelerator linkage and detent cable hookups again.Anyone out there have any advice?? /forums/images/graemlins/dunno.gif /forums/images/graemlins/ears.gif
    Also--how do I change my signature to refect the changes in my vehicles?? /forums/images/graemlins/ears.gif
     
  2. 84_Chevy_K10

    84_Chevy_K10 Banned

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    A 1405 should work fine on a 305. I had that setup for over two years.

    I'd suggest you check your ignition timing. 90% of so called carb problems are actually ignition issues.
     
  3. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    In a nutshell, no. Sounds like perhaps the float is not set correctly and you are putting way too much fuel into it when you hammer down. My carb is running kinda rich right now, but I know it's running rich. Also try the timing. I adjusted mine to the factory 4 BTDC, and it runs pretty well. BTW, I am running a larger than stock q-jet (don't know exact size 650 CFM + /forums/images/graemlins/dunno.gif ) on mine, and with the exception of it running slightly rich, it's great. Take it to a reputable carb shop, and have them set it up right. That's my plan.

    John
     
  4. diesel4me

    diesel4me 1 ton status Premium Member

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    I have checked and re-set the float level--it doesnt seem to be too rich,no black smoke from the tailpipe,or soot on the plugs--I also checked the metering rods to make sure they were not bent or stuck--nothing wrong there.I was wondering if the triangle shaped edelbrock air cleaner could be the cause(the one with the foam element and open top),letting too much air in??--I might try my stock air cleaner and see if that helps--as far as timing goes,I had to set it by ear,evidently this motor never had a "pointer" on it,but I advanced it till it pings pretty good with no real improvement,neither did retarding it,(this was a computer motor I put HEI in,maybe that is the cause??) and this carb ran this way on my 307 van motor as well,but I had a 4 barrel to 2 barrel adapter to the stock intake,so I blamed that--I think its the carb,either the secondaries are jetted wrong,or perhaps that air valve over the secondaries is opening too far too soon,but its not adjustable,its got a counterweight.Maybe its time to get a Q-jet before they crush em all?? /forums/images/graemlins/confused.gif I might be wise to check my fuel pump pressure too--its the original looking AC fuel pump on the motor--but it never seems to "run out of gas",it just feels like its holding back some,and you can feel it want to go faster when you back out of it.I'm not a carb expert,but I have been rebuilding them since my teens,so I'm not a dummy either--this one has me puzzled,I like the edelbrock and carter AFB carbs but this one seems to be a PITA--that reminds me--I have an AFB on my soon to be parted 74 K20-and that carb runs circles around this one--maybe my 1405 will be sitting on the 400 in my shed,and the AFB will run good on the 305--hhmmmmmm. /forums/images/graemlins/thinking.gif /forums/images/graemlins/thinking.gif--I'm open for more suggestions! /forums/images/graemlins/dunno.gif
     
  5. 84_Chevy_K10

    84_Chevy_K10 Banned

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    That triangular foam filter is one of the most restrictive pieces of crap on the market, not to mention that it will burst into flames if the carb ever backfires.

    Still sounds like an ignition problem. You need to set your timing correctly, not by ear. And if you have the wrong distributor it'll never run right.
     
  6. diesel4me

    diesel4me 1 ton status Premium Member

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    I never liked that air cleaner,it is a POS--glad I paid 5 bucks for it at a swap meet!--I was going to ditch it for the winter anyway,you really need the hot air pipe setup working around here when it gets cool and damp--the carb would frost up like a sno-cone with that edelbrock thing on it. I dont know about the distributor,I got it from a 76 305,(according to the casting ## on it)so as far as I know it should be close enough--I dont really want to convert my truck to a computer,the van is already in the crusher,its computer went with it!(I have the original distributor though)
    My friend has a 390CFM holley I could borrow,but I hate holley carbs--it might be a better match for the 305 though--I'll keep trying other things first,if all else fails I'll be swapping something different onto it.
    Anyone else have any thoughts?? /forums/images/graemlins/ears.gif
     
  7. 84_Chevy_K10

    84_Chevy_K10 Banned

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    If you get bored, change carbs. I bet you'll still have problems, which will prove my ignition statement.

    I'd check the advance weights and make sure they're moving. Some times they get rusted up and then they're stuck at full retard. You won't have any power at WOT unless you're getting the ignition advance you need.

    Find yourself a generic timing tab and get your timing set correctly, and check your total timing. Once you have the ignition system completely perfect you can concentrate on the carburator.
     

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