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Technical Rochester BC with cheap air cleaner idle problem

Discussion in 'The Hokey Ass Message Board' started by 1pickup, Aug 4, 2018.

  1. 1pickup
    Joined: Feb 20, 2011
    Posts: 1,437

    1pickup
    Member

    Found the reason for my too fast idle on my 250 chev with dual carbs. Chinese air cleaners. I bought the cheapest ones I could find on eBay (I know, that's the problem). What are you running, or what did you have to do to get the idle down on yours? My Idle screws are backed all the way out. It tends to run on, after shutting the key off. Never did this when I had mis-matched carbs (one manual choke & one automatic), but now I have 2 BCs & it idles faster. Took the air filters off, & it idles much slower. Did a search, but probably wasn't using the right terms. Ideas?
     
    chryslerfan55 likes this.
  2. Deuces
    Joined: Nov 3, 2009
    Posts: 23,753

    Deuces

    You get what you pay for..... :rolleyes:
     
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  3. 1pickup
    Joined: Feb 20, 2011
    Posts: 1,437

    1pickup
    Member

    ^^ Thanks! That was very helpful! ^^
     
  4. BJR
    Joined: Mar 11, 2005
    Posts: 9,817

    BJR
    Member

    Obviously the air cleaners were too restrictive and causing the car to run rich. When you take them off it leans out the mixture and it idles better. Like running with the choke on a little.
     
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  5. 1pickup
    Joined: Feb 20, 2011
    Posts: 1,437

    1pickup
    Member

    Yes, obviously. I guess I need to state things clearer. I know the cause, now I need HELPFUL suggestions. I will also state, that I don't want to spend huge money for a low buck car. Just wondering what everybody else uses, or if they modified the cheap ones to work somehow. What type are you using, that seem to work well & don't cost more than the car?
     
  6. Pics of what filters you have now ?
    Maybe different elements will solve your problem.
     
  7. BJR
    Joined: Mar 11, 2005
    Posts: 9,817

    BJR
    Member

    How about putting a taller filter in them? This is where a picture of what you are starting with would help.
     
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  8. 1pickup
    Joined: Feb 20, 2011
    Posts: 1,437

    1pickup
    Member

    images-2.jpeg images.jpeg
    Paper element. Just cheap Chinese junk. Didn't think they would be so restrictive. Is there less restrictive paper elements that you guys use? Or did you just splurge for some high dollar thing that I don't know about? Still not sure why it worked on the mis-matched carbs either?
     
  9. 54vicky
    Joined: Dec 13, 2011
    Posts: 1,599

    54vicky
    Member

    if it is a low buck you obviously must not care about motor ingesting dirt simple do not put filters on it.would you use sandpaper to wipe your butt?after all it is paper.good filters have a reason for cost research and reputation
     
  10. BJR
    Joined: Mar 11, 2005
    Posts: 9,817

    BJR
    Member

    Look at the surface area of the louvers on the element covers. Now compare it to the round opening of the top of the carb. Does it let enough air in? It doesn't look like it. Plus if that small element gets a little bit of crap in it think of how restrictive that will be. I think you need to get a filter with a bigger diameter for starters, and no restrictive cover over the element.
     
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  11. Even without the filter element, those are crap.
    Throw them away.
     
  12. I've run those same air cleaners on a tripower with no issues at all. You may need to look at the filter element themselves.
     
    XXL__ likes this.
  13. The louvres are to small and not opened up enough
    Try making the louvres wider and bigger

    If you f’up that marvellous Chinese chrome just paint them

    Remove the junk paper element and try foam compressor elements for more air flow

    You can also make velocity stacks out of cheap chrome tail pipes and stuff some steel wool mesh or foam in them
     
  14. XXL__
    Joined: Dec 28, 2009
    Posts: 2,117

    XXL__
    Member

    I have the non-louvered version and Chinese (Mr. Gasket) air filters on my significantly hotrodded 250 (major head work, roller cam, etc.). No issues here. I feel like we're missing info at this point.
     
    firstinsteele likes this.
  15. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    When you say 'idle screws' do you mean idle speed screw or idle richness screw? Sounds like an odd vacuum leak. With filters off the air enters thru the top and kinda idles - we know it really won't 'idle' because the idle screw is backed out so that means something else is going on as well. With filters on the air enters via vacuum leak below the throttle blades causing it to run lean at higher rpm. If you idle richness screw is the one backed out then thats a vacuum leak right there. But, bein an hot rod and all it I might be wrong, just a guess.
     
  16. 41rodderz
    Joined: Sep 27, 2010
    Posts: 6,540

    41rodderz
    Member
    from Oregon

    Maybe missing the point but if you have all that work, parts and money in your engine why wouldn't you want the best or better filter set up you can use? Just wondering.
     
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  17. Joe H
    Joined: Feb 10, 2008
    Posts: 1,525

    Joe H
    Member

    You can't have to much air filter, all on a 250 inline.
    Yours are just big enough for a lawn mower!
     

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  18. Terrible80
    Joined: Oct 1, 2010
    Posts: 785

    Terrible80
    Member

    I would think restrictive air cleaner= low idle. Choking off air. How does less air raise idle? Or you just couldn't turn it down and Get a correct idle?

    Sent from my LG-TP450 using The H.A.M.B. mobile app
     
  19. 1pickup
    Joined: Feb 20, 2011
    Posts: 1,437

    1pickup
    Member

    Idle speed screws are backed out completely, so they are not touching the little cam thing. I don't know the technical terms. Thanks @VANDENPLAS for the good suggestions. And, thanks @oj. I will look for leaks. I realize what these are, but hoped they wouldn't be a hinderance. First plan was to make something a little different, but it was too easy to click a button & have these show up at my door. I did rebuild these carbs, & I'm no expert. They seem to work good until the filters go on.
     
  20. Joe H
    Joined: Feb 10, 2008
    Posts: 1,525

    Joe H
    Member

    Check here for filters by size, FilterBySize.aspx Once you click on the filter you want to see, it will give the CFM it's made to work with. A stock 1970 Camaro with a 250 used #42083 air filter, 2" x 9.718" and 65 CFM capacity. Yours are likely less then 4 or 5 cfm each!
     
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  21. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
    ALLIANCE MEMBER

    I'd agree that the air cleaners are a bit restrictive but a restrictive air cleaner SHOULD slow the engine down because it isn't allowing enough air into it rather than speeding it up.
    I've done a lot of tunes ups on engines with restrictive stock air cleaners that I had to raise the idle speed after putting the air cleaner back on but have never had to lower the engine speed because the engine speeded up because of the restriction.
    You have another and bigger issue going on with the carbs/intake that the air cleaners are bringing out when you put them on. No restriction =it runs fine / raised restriction it speeds up is just flat backwards to what it should be if the engine is actually set up right.

    You could cut a couple of metal disks out that would replace the chrome bells to lower the air restriction to see if that changes it. but it won't fix the original problem.
     
  22. XXL__
    Joined: Dec 28, 2009
    Posts: 2,117

    XXL__
    Member

    The assumption in your question is that the filters I'm using are somehow inferior. I haven't found anything in their functionality to indicate that.
     
  23. Petejoe
    Joined: Nov 27, 2002
    Posts: 12,264

    Petejoe
    Member
    from Zoar, Ohio

  24. bobscogin
    Joined: Feb 8, 2007
    Posts: 1,771

    bobscogin
    Member

    54vicky likes this.

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