Welcome to Club Hot Rod!  The premier site for everything to do with Hot Rod, Customs, Low Riders, Rat Rods, and more. 

  •  » Members from all over the US and the world!
  •  » Help from all over the world for your questions
  •  » Build logs for you and all members
  •  » Blogs
  •  » Image Gallery
  •  » Many thousands of members and hundreds of thousands of posts! 

YES! I want to register an account for free right now!  p.s.: For registered members this ad will NOT show

 
Like Tree15Likes

Thread: 350 running rich
          
   
   

Reply To Thread
Page 1 of 4 1 2 3 4 LastLast
Results 1 to 15 of 55
  1. #1
    JD323 is offline CHR Member Visit my Photo Gallery
    Join Date
    Jul 2020
    Location
    Pueblo West
    Posts
    19

    350 running rich

     



    Hello all!

    I'm working on a carbeurated LT1 for a friend and am having a heck of a time figuring out what's wrong with it. It's running way too rich and no matter what I do I can't seem to correct it. It's running a Holley Brawler carb. Timing is set at 32°, fuel pressure is right around 5 psi, spark looks very good. We're in Pueblo, Colorado so the first thing I did was change out the jets to 68 thinking that the altitude was messing with it, but that made no difference. It's pretty much immediately carbon fouling the plugs. Vacuum is way lower than it should be at 1000 rpm idle, we don't get decent vacuum until about 2500 rpm. Adjusting the primary idle mixture screws does absolutely nothing, when screwed all the way in there is no change in how the engine runs, and zero change on the vacuum gauge. When adjusting the secondary screws, it will stall out when they are screwed all the way in, but still virtually no change on the vacuum gauge. Even when adjusting the timing there is no change on the vacuum gauge. I'm using one of the ports in the front bottom of the carb to check vacuum and also run the vacuum advance. I was thinking vacuum leak, but I can't seem to find any anywhere. The fact that the primary idle screw adjustment makes no difference either way makes me think that it's an issue with the carb. I pulled the power valve today to look at it, but it looks fine to me.

    Does anyone have any suggestions as to where I might look next to try and solve this issue? If I left any info out that would be helpful, please let me know.

    Thank you in advance for any tips/advice!!

  2. #2
    36 sedan's Avatar
    36 sedan is offline CHR Member Visit my Photo Gallery
    Join Date
    Apr 2012
    Location
    american canyon
    Car Year, Make, Model: 36 Ford Sedan, 23 T Bucket
    Posts
    1,623

    Change the power valve it most likely has a bad diaphragm leaking fuel into vacuum ports making it rich and low vacuum.
    glennsexton and cffisher like this.

  3. #3
    36 sedan's Avatar
    36 sedan is offline CHR Member Visit my Photo Gallery
    Join Date
    Apr 2012
    Location
    american canyon
    Car Year, Make, Model: 36 Ford Sedan, 23 T Bucket
    Posts
    1,623

    4,692′!! You're gonna probably have to lean it out a lot.
    glennsexton likes this.

  4. #4
    JD323 is offline CHR Member Visit my Photo Gallery
    Join Date
    Jul 2020
    Location
    Pueblo West
    Posts
    19

    Thank you for the suggestions!!

    Right now there's a 6.5 power valve in it, do you recommend going with the same size? And where would you start as far as jet size to lean it out, is 2 sizes down enough?
    Last edited by JD323; 07-06-2020 at 07:24 AM.

  5. #5
    36 sedan's Avatar
    36 sedan is offline CHR Member Visit my Photo Gallery
    Join Date
    Apr 2012
    Location
    american canyon
    Car Year, Make, Model: 36 Ford Sedan, 23 T Bucket
    Posts
    1,623

    Until your vacuum stabilizes we won't know if the 6.5 will work or not, and the vacuum won't come up until the mixture leans (catch 22). Luckily, Power Valves are not real expensive, I would buy a couple different sizes, 8.5 to put in it now and a 6.5 incase it needs it later. Stick with the standard flow rates for now, with your altitude I doubt you’ll need higher flow rates.
    8.5 & 6.5 are linked below;

    https://www.holley.com/products/fuel...s/parts/125-85
    https://www.holley.com/products/fuel...s/parts/125-65

    With your altitude 2 Jet sizes smaller may not be enough, I would buy an assortment of #52, 54, 56, 58, 60, 62, 64;

    https://www.holley.com/products/fuel...s/parts/230052

    Tuning for this altitude is going to take some time and expense, be prepared to spend some bucks. Buy several sets of plugs, it'll probably foul a couple sets before we get it to run decent enough to dial it in.

    Change the Power Valve and start with #64 primary jets, don't mess with the secondary jets until you get idle and cruise under control. once you get it running you can start reading the plugs.

    No sense in looking at the plugs now, we know it's pig rich and they'll be black and probably wet.

  6. #6
    JD323 is offline CHR Member Visit my Photo Gallery
    Join Date
    Jul 2020
    Location
    Pueblo West
    Posts
    19

    Thank you for the detailed reply!!

    He actually has the 60-69 jet kit already. Power valves are on order, I'll update after I work on it this coming weekend.

    Is it ok to clean and reuse carbon fouled plugs, and if so, how many times before they just need to be replaced?

  7. #7
    36 sedan's Avatar
    36 sedan is offline CHR Member Visit my Photo Gallery
    Join Date
    Apr 2012
    Location
    american canyon
    Car Year, Make, Model: 36 Ford Sedan, 23 T Bucket
    Posts
    1,623

    Quote Originally Posted by JD323 View Post
    Is it ok to clean and reuse carbon fouled plugs
    Sure, if you don't want to know if your tuning did anything at all.

    Seriously, I warned you it's gonna get a little expensive.
    Dave Severson and cffisher like this.

  8. #8
    JD323 is offline CHR Member Visit my Photo Gallery
    Join Date
    Jul 2020
    Location
    Pueblo West
    Posts
    19

    No prob! Just making sure. These are what we're running for testing, any objections or suggestions? The engine is a mid 90's LT1, unsure of the internals.

    https://shop.advanceautoparts.com/p/...2756/5390532-P
    Attached Images

  9. #9
    36 sedan's Avatar
    36 sedan is offline CHR Member Visit my Photo Gallery
    Join Date
    Apr 2012
    Location
    american canyon
    Car Year, Make, Model: 36 Ford Sedan, 23 T Bucket
    Posts
    1,623

    Use a regular non resistor plug. Resistor wires are OK, but resistor plugs tend to give trouble

  10. #10
    53 Chevy5's Avatar
    53 Chevy5 is offline CHR Member Visit my Photo Gallery
    Join Date
    Jan 2005
    Location
    Doon, Ia
    Car Year, Make, Model: 53 Chevy 3100
    Posts
    2,325

    Keep listening to 36, the poor guy isn't getting any sleep lately, he's helping tune my carb too lol. Stick with his advice, he'll get you fixed up.
    cffisher, rspears and 36 sedan like this.
    Seth

    God cannot give us a happiness and peace apart from Himself, because it is not there. There is no such thing. C.S.Lewis

  11. #11
    DennyW's Avatar
    DennyW is offline CHR Member Visit my Photo Gallery
    Join Date
    Oct 2004
    Location
    outahere
    Car Year, Make, Model: 1934 Chevy Pickup Merc 422
    Posts
    1,157

    First rule: What is your vacuum at idle, warmed up, in park ???
    Altitude means less, thinner air. You have to lean the idle air mixture. Double check float level.
    Then, depending on vacuum, decide which power valve to use... That is all.


    ps:, you may have to also increase base timing to blend.


    I went from 600 feet where I live to Colorado Springs/Elevation
    6,035′ for my last 10 months in the service...
    Last edited by DennyW; 07-07-2020 at 09:25 AM.

  12. #12
    36 sedan's Avatar
    36 sedan is offline CHR Member Visit my Photo Gallery
    Join Date
    Apr 2012
    Location
    american canyon
    Car Year, Make, Model: 36 Ford Sedan, 23 T Bucket
    Posts
    1,623

    Quote Originally Posted by JD323 View Post
    Adjusting the primary idle mixture screws does absolutely nothing, when screwed all the way in there is no change in how the engine runs, and zero change on the vacuum gauge. When adjusting the secondary screws, it will stall out when they are screwed all the way in, but still virtually no change on the vacuum gauge. Even when adjusting the timing there is no change on the vacuum gauge. I'm using one of the ports in the front bottom of the carb to check vacuum and also run the vacuum advance. I was thinking vacuum leak, but I can't seem to find any anywhere. The fact that the primary idle screw adjustment makes no difference either way makes me think that it's an issue with the carb.
    Hi Denny,
    Float levels was a good catch, I totally missed it. If the floats are too high it will spill into the carb's venturi and run way rich.

    Usually when you can shut the idle mixture off and make no difference it indicates it's getting fuel and air from somewhere else. While a vacuum leak can be a cause, usually it causes a lean condition not rich, this usually leans towards a carburetor issue. High floats or a damaged Power Valve diaphragm or gasket are likely suspects. The vacuum at idle is going to stay low until the overly rich condition is corrected, I suspect a damaged Power Valve issue, and it may be float levels as well.

    Mid 90's LT1 usually don't like as much total timing, 32-34° is usually max for their head design.

  13. #13
    36 sedan's Avatar
    36 sedan is offline CHR Member Visit my Photo Gallery
    Join Date
    Apr 2012
    Location
    american canyon
    Car Year, Make, Model: 36 Ford Sedan, 23 T Bucket
    Posts
    1,623

    A couple of caveats about Power Valves:
    Power Valves manage (control) the enrichment circuit in this type of carburetor. Their design is to add fuel under loads and WOT (this is the purpose of all carburetor enrichment circuits). With Power Valves the rating number on the PV indicates the vacuum level at which it opens and supplies fuel to the venturi boosters. Manifold vacuum holds the PV closed, as vacuum drops with throttle opening the PV opens and supplies the necessary additional fuel needed.

    Power Valves (or any carburetor's enrichment circuit) can be and should be used to tune WOT because the secondaries take a little time to activate before they can supply fuel. While Power valves come in different vacuum ratings, they also come in different flow rates, standard, high flow, 2 corner, 4 corner and stages (single or two stage), with the two stage adding a slight amount of fuel at medium throttle levels (usually not needed). PV enrichment circuit's passage restrictors can also be increased or decreased in size to further tune the circuit (not advised for un-experienced).

    Also, you will hear people say "Power Valves can not add fuel at idle because they are a venturi driven circuit (above throttle) and with the throttle closed there is no venturi vacuum to draw fuel up into the boosters". And this is true, EXCEPT, when the PV diaphragm is damaged or housing/gasket leaks. When this condition exist (damaged PV), manifold vacuum pulls the fuel through/past the PV into the manifold and adds fuel EVEN at idle. And JMHO, why it should be one of the first things checked when a rich idle condition exists.
    Dave Severson likes this.

  14. #14
    DennyW's Avatar
    DennyW is offline CHR Member Visit my Photo Gallery
    Join Date
    Oct 2004
    Location
    outahere
    Car Year, Make, Model: 1934 Chevy Pickup Merc 422
    Posts
    1,157

    That's another reason why I always ask what the vacuum is at idle...
    36 sedan likes this.

  15. #15
    JD323 is offline CHR Member Visit my Photo Gallery
    Join Date
    Jul 2020
    Location
    Pueblo West
    Posts
    19

    Finally got a chance to work on the truck again. I installed the new 8.5 PV and the 64 jets and new plugs. Still having the same issue though. There's no movement on the vacuum gauge when adjusting the idle mixture screws. I have the idle set right around 1000 rpm. I recorded a video of me adjusting the screws. I screwed them both all the way in and then back out 2 turns. It does seem like it's making more vacuum with the new PV, but I'm assuming that's because it's a larger size? Any ideas what to try next? Here's a pic of one of the plugs after about 10 minutes of running.

    https://youtu.be/YZ9MNaWyO1Y
    Attached Images

Reply To Thread
Page 1 of 4 1 2 3 4 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
Links monetized by VigLink