Throttle pedal travel and vehicle performance

Discussion in 'General IH Tech' started by Rollercam, Oct 25, 2019.


  1. Scoutcamper

    Scoutcamper Farmall Cub

    Joined:
    May 23, 2018
    Messages:
    417
    Likes Received:
    163
    Trophy Points:
    43
    Location:
    Phoenix, AZ
    Maybe I missed it, but did anybody mention the possibility of a bad or wrong sized power valve?

    Took a quick look at the instructions for that carb, and it has several different power valve options, which are supposed to be matched to the vacuum the engine develops at idle.

    You can download the instructions and it has a section on power valve selection.
    https://www.jegs.com/i/Holley/510/0...MI6I6IuKTF5QIVCB6tBh02AgnZEAQYASABEgIPd_D_BwE

    Rollercam, do you have a vacuum gauge? If so, what does the manifold vacuum read at idle?

    With the motor off, do you get a good strong squirt of fuel in the throat of the carburetor when you fully open the throttle?

    -Josh
     
  2. Jeff Jamison

    Jeff Jamison Lives in an IH Dealership

    Joined:
    Oct 11, 2001
    Messages:
    7,561
    Likes Received:
    1,029
    Trophy Points:
    113
    Location:
    Aliquippa Pa
    Is your gas peddle bracket bent or cracked,it happens a lot at the pivot point.
     
  3. Patrick Morris

    Patrick Morris Lives in an IH Dealership

    Joined:
    Oct 18, 2001
    Messages:
    5,753
    Likes Received:
    735
    Trophy Points:
    113
    Location:
    San Diego, CA
    I don't think that's been mentioned. I imagine it would cause stumbling on acceleration though.

    That's why we keep mentioning the verifying of full throttle movement, even if everything looks okay at the carb. It's an important thing find out, or rule out. I don't know if bent foot pedal lever has been mentioned. Another thing to check. Also excessive carpet/padding under the pedal.
     
    Last edited: Oct 30, 2019
  4. Rollercam

    Rollercam Farmall Cub

    Joined:
    Apr 8, 2016
    Messages:
    77
    Likes Received:
    23
    Trophy Points:
    8
    I do not have a vacuum gauge, but I am trying to get with a mechanic friend this Friday to help me go through some diagnostics. We have already discussed things like using a vacuum gauge to set the idle mixture screws and help with possible power valve selection. checking the timing, check for vacuum leaks, etc....

    I believe the factory power valve in this carb (7448-1) was a 8.5. When we took the carb apart (it was remarkably clean), it had a functioning 6.5 power valve in it and 61 jets. The quick fuel technologies 2300 rebuild kit I bought (suggested on another post and owned by Holley) came with a 4.5 power valve. So, you can understand my confusion. Factory 8.5, previous rebuild 6.5, and new rebuild kit 4.5. We left the 6.5 in. We will check the vacuum at idle in drive and then calculate what size power valve is warranted. My understanding is that you wouldn’t use a 4.5 power valve unless. You were only pulling 9 inches of vacuum at idle. I am already assuming that the scout will be able to pull better than that.

    I talked to one of the guys at IH Parts America and he said he would not be that concerned about the 6.5 power valve that was in there unless I knew for sure it was giving me trouble. He said the 61 jets are what they would use in a 345 at 155 ft above sea level (where I am in TX).


    Sent from my iPhone using Tapatalk
     
  5. Rollercam

    Rollercam Farmall Cub

    Joined:
    Apr 8, 2016
    Messages:
    77
    Likes Received:
    23
    Trophy Points:
    8
    I will check the pedal and the arm for any cracking and see if I can tell that anything is bent.


    Sent from my iPhone using Tapatalk
     
  6. Rollercam

    Rollercam Farmall Cub

    Joined:
    Apr 8, 2016
    Messages:
    77
    Likes Received:
    23
    Trophy Points:
    8
    I plan to check for full throttle movement this Friday when I get an extra body to help me look at all of this. I just can’t seem to figure out how to clone myself.

    There is nothing but raptor lined sheet metal under the pedal. No carpet or floor mats. Raptor is thicker than normal paint, but certainly not thick enough to interfere with throttle movement.


    Sent from my iPhone using Tapatalk
     
    vince konicki likes this.
  7. Patrick Morris

    Patrick Morris Lives in an IH Dealership

    Joined:
    Oct 18, 2001
    Messages:
    5,753
    Likes Received:
    735
    Trophy Points:
    113
    Location:
    San Diego, CA
    Yeah. Sorry. I know you have several full plates there. The carpet thing was just spit-balling anyway. Winding down after a long day at the ol' office. Some of the reproduction carpet sets don't fit as tightly on the floor. Thought I'd mention it. Sounds like you have tons of clearance. Maybe you'll be able to verify plenty of throttle movement and other things an be focused on.
     
  8. Patrick Morris

    Patrick Morris Lives in an IH Dealership

    Joined:
    Oct 18, 2001
    Messages:
    5,753
    Likes Received:
    735
    Trophy Points:
    113
    Location:
    San Diego, CA
    Maybe automatics run different. but in my experience, 9 in of vac at idle would mean a bad vacuum leak somewhere, or a really funky cam or cam timing. With that carb at your elevation you should see around 18-20 in of vac on a healthy, stock IH engine.

    Regarding the power valve it's certainly easier to know what you need by driving the truck with a vacuum gauge hooked up. This, by the way, is also where fully available throttle opening comes into play. Let's say your accelerating up a freeway onramp, in third gear (or whatever an automatic does), if you floor the gas pedal doing this you would hope to see vac needle drop to near zero inches. like 1-2 inches. One thing this tells you is that your throttle is opened as much as it can. If you only see no lower than 6-7 inches when flooring it going up a hill, it means the throttle isn't opening enough.

    This also shows where those various power valves would kick in. You would probably find that you want it to kick in in that 10-7 inch range, but that's a guess. 4.5's a bit low I think, for a heavy vehicle like a Scout. You would want fuel enrichment earlier than that for sure.

    Anyone else, feel free to correct me if I got any of this wrong. It's just what I've learned from my own experience.
     
  9. scoutboy74

    scoutboy74 Lives in an IH Dealership

    Joined:
    Mar 10, 2004
    Messages:
    6,652
    Likes Received:
    1,125
    Trophy Points:
    113
    Location:
    Daze Crick, Jefferson
    They shift differently than a manual, but an auto trans has no bearing on manifold vacuum at idle. A tachometer would also provide some useful feedback, such as...the engine doesn't rev beyond 2500 rpms in Park or while driving, etc.
     
  10. Rollercam

    Rollercam Farmall Cub

    Joined:
    Apr 8, 2016
    Messages:
    77
    Likes Received:
    23
    Trophy Points:
    8
    I have an autometer tach (in fact all the gauges are round autometer gauges). It will rev up as high as I am comfortable going in any of the three gears (i.e. I have always shifted “manually” to the next gear it prior to revving it to its limit). It will rev as high as you want in park.

    I hope to have a solution or at least more answers Friday evening.


    Sent from my iPhone using Tapatalk
     
  11. Patrick Morris

    Patrick Morris Lives in an IH Dealership

    Joined:
    Oct 18, 2001
    Messages:
    5,753
    Likes Received:
    735
    Trophy Points:
    113
    Location:
    San Diego, CA
    Apologies. When I read the original question I was thinking accelerator pump, not power valve. A bad accelerator pump/diaphragm will certainly cause a stumble.
     
  12. scoutboy74

    scoutboy74 Lives in an IH Dealership

    Joined:
    Mar 10, 2004
    Messages:
    6,652
    Likes Received:
    1,125
    Trophy Points:
    113
    Location:
    Daze Crick, Jefferson
    Well...hmm...the plot really thickens with this revelation. If you can max out the rpms in Park...that right there should rule out any thought of a mechanical or physical restriction that could limit the throttle linkage from opening fully. Beyond that, being able to reach full throttle under load in all forward gears would not be possible if the linkage was being restricted in some way. So now we seem to be circling the wagons in on a central question. How fast or hard is the engine capable of propelling the vehicle to a reasonable road speed, from a dead stop, on a level road surface? And this would seem to now be more a question of overall engine and transmission health than anything else. Maybe a link to a YouTube video of you revving a warmed up engine several times and then taking us for a drive where you just put that hammer down and get some on a level road. What's the top speed that you've driven that thing at?
     
  13. RDC279

    RDC279 Farmall Cub

    Joined:
    Oct 18, 2019
    Messages:
    49
    Likes Received:
    35
    Trophy Points:
    18
    What is timing set at?
     
  14. 1975IH200

    1975IH200 Y-Block King

    Joined:
    May 7, 2007
    Messages:
    3,205
    Likes Received:
    493
    Trophy Points:
    83
    Location:
    Western North Carolina
    OK, thanks.
    Does this scale accurately represent your tach-o-meter scale ??
     

    Attached Files:

    Last edited: Oct 31, 2019
  15. Rollercam

    Rollercam Farmall Cub

    Joined:
    Apr 8, 2016
    Messages:
    77
    Likes Received:
    23
    Trophy Points:
    8
    Sorry, I just now had an opportunity to get back to this thread and read through everything.

    I am not sure how high a 345 should rev, but I am afraid to take her much over 3000 right now. Maybe I am being too cautious.

    Unfortunately, the guy that was going to help me with everything today, was unable to make it. He is going to come first thing Monday morning and we will try tinker on it a bit before I have to head out of town.

    However, I was able to adjust the throttle cable a bit and get more movement and range of motion out of the throttle pedal. I also changed the plugs to some NGKs and put back on the carb that the guy cleaned up a bit for me. It still has the 6.5 power valve in it, but I may up that if the vacuum reading warrants it.

    We will be checking timing on Monday. I have no idea what it is set at right now. We shall see.


    Sent from my iPhone using Tapatalk
     
  16. scoutboy74

    scoutboy74 Lives in an IH Dealership

    Joined:
    Mar 10, 2004
    Messages:
    6,652
    Likes Received:
    1,125
    Trophy Points:
    113
    Location:
    Daze Crick, Jefferson
    Maximum sustained rpm for a 345 is 3800 rpms. By sustained, that means IH built them to run at that for a full duty cycle over the natural life of the engine. Granted, they sound like they're turning 6k and about to fly apart at that speed, especially if you're used to driving more modern and civilized vehicles. Typical 727 shift points in drive with a properly adjusted TV rod will happen around 2500 rpms under normal/moderate acceleration. A light foot will allow them to happen sooner, while a lead foot should make them happen later.
     
  17. Scoutcamper

    Scoutcamper Farmall Cub

    Joined:
    May 23, 2018
    Messages:
    417
    Likes Received:
    163
    Trophy Points:
    43
    Location:
    Phoenix, AZ
    Couple more questions for you, Rollercam...

    First, just to recap, your original description of the problem was

    "It starts fine, appears to idle well, stumbles a bit off-idle until it is warm, but then runs fairly smooth. However, when leaving a stoplight or starting from a standstill, I can put the pedal to the floor and the scout moves like a snail (i.e. a guy on bicycle could probably beat me to 25 miles an hour). I am not expecting a race car by any means, but I am just wondering if this is normal or not. Top end speed seems to be there. I can hit 65-70 (that is about as fast as I want to go right now on this suspension) and the engine feels smooth and steady.... I think it is running rich and has even “desieled” a few times when I turn it off. It has stalled on me twice at idle and I can smell raw fuel strongly under the hood and it acts flooded, yet, I am not sure if it died from not enough fuel or too much fuel because the under hood fuel filter seems nearly empty when this happens."

    Background questions-
    - Did you ever have it running well since it's been back together, and now performance is down?
    - You mention that fuel filter looks empty- do you have one of the clear glass or plastic filters? Where is it on the motor?
    - Are you running the stock mechanical fuel pump or an electric pump?
    - You mention getting it back together recently- In detail, what (if anything) was done to the motor?

    Specific mechanical questions-
    - Do the advance weights under the distributor cap move freely, and do they both have springs to pull them back in?
    - Is your vacuum advance hooked up, and is the vac line good?
    - Do you have the correct carburetor gasket style with a heat shield under the fuel bowl? Couldn't tell for sure from your pics.
    - Are you seeing any overheating? Flip side, is the engine getting up to operating temp or just warming up a bit so it's not on cold?

    I'm going to repeat the suggestion you pull each spark plug, one at a time, and look for visual differences to see if any cylinder(s) are acting differently.

    Your description of an empty-looking fuel filter makes me wonder if you might have fuel boiling off, or an inadequate pump. Fuel boiling off can cause flooding and dieseling as pressure forces fuel into the bowl and past the seat.

    Your description also reminds me of what happened to my '77 Chevy Nova WAAAAAY back when I was in college- also a Holley 2bbl. I had an accelerator pump go bad, which eventually caused a backfire which blew out the power valve, at which point I fiddled with the mixtures screws and timing until it idled and ran somewhat smoothly, but it had exactly the kind of gutless performance you describe.

    -Josh
     
    Dan DJ likes this.
  18. INT77345

    INT77345 Farmall Cub

    Joined:
    Feb 3, 2009
    Messages:
    298
    Likes Received:
    47
    Trophy Points:
    28
    Location:
    DENVER
    my bet is part of whats going on is your under timed..... at 5,400 feet im timed at 12 before top dead center and my vacuum at idle is 18 in your near sea level. a good running engine timed correctly will be a higher idle vacuum then mine at altitude. read the post about "power timing" and if you have a timing light start your initial timing at 5 degrees before top dead center then "power time " from there

    remember all you need is air, fuel and spark in the right quantities and at the right time. you will get it solved, have fun on the journey.
     

Share This Page