Carb Help

Discussion in 'Technical' started by im devestatingly handsom, Mar 16, 2008.

  1. I have a chevy 305 with a 4b carb. It was running great, until right after I left for a 400 mile trip. I can't seem to figure out what's wrong.

    I was cruising and I noticed it was making a lot of popping noises, especially in the exhaust. If i let off the throttle it runs fine, or if im very very light on it ( going 45 mph in a 75 isn't too exciting, or safe ). It has nothing to do with the secondaries, i presume it's the vacuum pressure.

    I stopped at a shop and a guy decided instantly it must be a metering rod. Well he was right, we pulled them out and one was badly bent and was obviously not moving. Of course there was no way of getting one till i got home. So i got new ones and replaced both with the exact spec ones that were in. Now it runs better, i can get it up to speed no problem, but if i have the throttle open for more than a few seconds it starts doing it again increasing with the rpms until it almost won't accelerate. It is almost a rev limiter (sounds like one too). It usually will get up to 6000, but it starts this whole gurgle crap around 3500...
    Im going to take apart the carb and replace the jets, but everything looks clean inside. Not to mention its 10 degrees out and i really am not looking forward to taking out my carb right now.

    I was just wondering if anything else could be causing this, even not carb related, and what i could do to fix it.


  2. almost sounds like its running lean on the high end.
  3. #3 im devestatingly handsom, Mar 16, 2008
    Last edited by a moderator: Apr 25, 2016
    that's what i thought. i replaced the metering rods and springs, to much much richer ones, but it didn't change anything. i took apart the whole carb replaced the jets and checked everything i could... nothings wrong. I have it running richer than ever and it makes no difference.

    the sound right after the first burnout is very similar to what i hear, except mines higher pitched...
  4. sounds like a sticky float or the fuel pump might be giving up
  5. could either of those still be the problem if the fuel line is always full, along with the "fuel holders on each side of the carb" ( not sure on the technical name)?

    its been at a shop for three days and i just got it back. they had no clue either. only way to go would be a new carb they said. they also said that i'd just be best to just stick with the carb instead of buying a new one for $400. Problem is.. i can't give more than half throttle and would have a hard time reaching 75 mph.

    it is running very very lean at 1/2 throttle to full, and it also happens when secondaries are disconnected. metering jets, rods, springs are not the problem. Timing is right on, idle mixture, idle speed is good. I fixed the exhaust leak but that didn't change a think. I am stumped.
  6. Yes, either could still be the problem if fuel is getting to the carb.

    The float bowl is the "fuel holder" in the carb, it might be stuck where it doesn't keep a large enough reserve for heavy throttle. Sometimes tapping the side of the carb with a rubber mallet can free it up.

    When the fuel pump starts to go bad it can usually supply enough fuel for light throttle for a while, constantly getting worse until it won't even do that.
  7. I bought a new fuel pump. i figured it was worth a shot and definetly cheaper than a new carb. i installed it and successfully bent the rod going to the cam. i am going to pick up a new one tomorrow. any advice on how not to bend it other than making sure it's all the way back? i did the best i could about keeping it as far back as i could and still bent it...
  8. When you place the fuel pump rod in the engine put a decent amount of wheel bearing grease on the pump end of the rod. then push the rod up until it sticks to the upper wall of the houing. As soon as you start the engine it will fall down into place and the grease will liquify as the engine warms.

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