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Thread: can't get above 70 MPH?

  1. #1

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    can't get above 70 MPH?

    Ok guys I have a serious question to ask.

    I did tune up of the truck and it runs and sounds a thousand times better than when i got it home for the first time.

    But one thing that is bugging the hell out of me is, when i test drove the truck down an old abandoned road I couldn't get the truck to climb above 70 mph!

    Now I admit that i don't drive above 65 as I am alergic to speeding tickets here in the south. But i would like to have the peace of mind knowing that if I ever needed to punch it, that I had the power to do so.

    main question is, is this normal for the stock carb? Is there a hidden governor that I am missing?

    will this change when I get the weber installed?

    Any advice on what is causing this, or way of fixing this would help incredibly.

  2. #2

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    I still think you have a vacuum leak, maybe in the advance for the distributor? My two cents.

  3. #3

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    Quote Originally Posted by royster View Post
    I still think you have a vacuum leak, maybe in the advance for the distributor? My two cents.
    But I don't any hissing that is evident with a vacuum leak...

    Would a vacuum leak cause the truck not to climb above 70 MPH? I've never heard of that happening before.

  4. #4

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    Do you know about the cigar smoke trick to detect vacuum leaks? With the engine off, you blow cigar smoke into the vacuum line, and watch for the smoke to seep out at the leaks.

    Two things: if it is a minor leak, you won't hear it at idle. At high rpm (highway speed) it would be most pronounced and of course, you wouldn't hear it.

    Inufficient vacuum could indeed cause the spark advance to not work properly and not allow higher RPMs. This is just a suggestion, Frank

  5. #5

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    Hmmm I guess I'll have to check that out.
    I will post an update later on today.

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    Shift into 3rd... (couldn't help myself)

  7. #7

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    Quote Originally Posted by LSR Mike View Post
    Shift into 3rd... (couldn't help myself)


    A Viagra joke in disguise. Good one, Mike. If your truck remains at 70 MPH for more than 4 hours, see your mechanic...

    Frank, as you know, my parts truck is a G63B 2.0. I never attempted to get it running, but in dismantling it, I removed that black spaghetti-covered carborator. Lots of electronic parts on there, and the number of vacuum lines on it boggles the mind. Perhaps the new Weber will solve the problem...I don't know, I'm no expert. In fact, I'm not much more than one of your cyber friends hanging around the garage tossing out ideas.

    Better than listening to crickets? I hope so

    I by no means endorse Scotty Kilmer, but this particular video was useful for me...perhaps it will help you.

    http://www.youtube.com/watch?v=zMok2y05jNE
    Last edited by royster; 03-21-2014 at 08:52 AM.

  8. #8

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    Well I swapped out all the vacuum lines for new ones and its still doing it. I will be changing the cap and rotor button next. I will post results.

  9. #9



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    Have you checked to see if it's getting wide open throttle?
    I know it's a dumb question but that is the first one I see. Put a broom stick / brick/ small child, on the pedal and then look down the carb. Then turn the linkage some more by hand. If it opens up more then you need to make an adjustment. You don't want the carb to keep the pedal off the floor. You want to have just a tiny bit of slack or you can bend the linkage with your foot. Thats why the end of the cable is on a slider mount by the carb. I guess I can make a video in the mechanics tips and trick section, since many You Tuber's like my electric choke adjustment explanation.
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  10. #10

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    Camoit's suggestion sounds better, except the small child part: a small child is likely to crawl off the pedal and thus give a false reading.

  11. #11

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    Quote Originally Posted by camoit View Post
    Have you checked to see if it's getting wide open throttle?
    I know it's a dumb question but that is the first one I see. Put a broom stick / brick/ small child, on the pedal and then look down the carb. Then turn the linkage some more by hand. If it opens up more then you need to make an adjustment. You don't want the carb to keep the pedal off the floor. You want to have just a tiny bit of slack or you can bend the linkage with your foot. Thats why the end of the cable is on a slider mount by the carb. I guess I can make a video in the mechanics tips and trick section, since many You Tuber's like my electric choke adjustment explanation.
    Ok I checked that out and there is just enough slack in the line so it is not taught. The last thing to check is the cap and rotor. It looks like the original factory one on the there so I will be swapping them out on my next day off and test driving once again .

  12. #12



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    So how may miles are on it?
    What is the compression test come back on it?
    I don't remember how fast mine would go. But then again 70 is pretty darn fast in a death trap. It's fun to take people for a ride in my truck now. Because they think it's hauling ass. Just because it's loud, vibrates, and smell like hot engine and burnt fuel. Then you jump in a new car and it's all quiet and you are insulated from the speed and danger of driving. No wonder people drive like shit. They should put a big mettle spike right in the center of the steering wheel. That would solve all them problems.
    It could also have a coil going out. The higher the RPM the more demanding the spark is. It might be getting week after 30 years of service.
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  13. #13

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    here is what I did so far since I drove this puppy home:

    1. Oil change: used Delo 400, substituted one quart of that with Riselone. Added the ZDP addetive. used Purolator One premium filter (No shitty fram for me!)
    2. Changed all 4 spark plugs, using NGK v-powers. Gapped them to spec at .040
    3. Changed all plug wires one and a time as to not mess up the firing order.
    4. Used Lucas fuel treatment with every fill up (I noticed MPG and HP gain after the second fill up!)

    Here is the probelm check list so far.

    1. No Vacuum leak
    2. Throttle is not loos nor to tight.
    3. I will be swapping the distributor cap and rotor on Monday (my Day off) and speed test again.

  14. #14

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    Oh and the mileage right now is at 118,556

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    DO you have the right vacuum line connected to distributor so it advances correctly. Almost sounds like your distributor might not be advancing correctly. A good test is to remove the vacuum line at carb for distributor and remove distributor cap and rotor. Suck onto the hose end that removed from carb and make sure you see movement in the distributor. The advance vacuum mechanism in the dizzy should turn a bit at a reasonable vacuum as you test it.
    If you have the stock air cleaner also, make sure there is a vacuum line going to the heat riser flap on top of air cleaner housing and that the flap inside the air cleaner is fully closed after being warmed up.
    I had one experience with a car not getting to top speed and that was a 74 Toyota land cruiser. Though probably not your issue at all, but it's problem was a lack of oil being pumped to the head and we had to run a separate oil line to the rod tube. Very doubtful this is what is going on with yours.

    Camoit asked if your getting full throttle also, the cables may be fine but is it open carb flaps completely and is choke fully open as well when warmed up.

  16. #16

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    Quote Originally Posted by BradMph View Post
    DO you have the right vacuum line connected to distributor so it advances correctly. Almost sounds like your distributor might not be advancing correctly. A good test is to remove the vacuum line at carb for distributor and remove distributor cap and rotor. Suck onto the hose end that removed from carb and make sure you see movement in the distributor. The advance vacuum mechanism in the dizzy should turn a bit at a reasonable vacuum as you test it.
    If you have the stock air cleaner also, make sure there is a vacuum line going to the heat riser flap on top of air cleaner housing and that the flap inside the air cleaner is fully closed after being warmed up.
    I had one experience with a car not getting to top speed and that was a 74 Toyota land cruiser. Though probably not your issue at all, but it's problem was a lack of oil being pumped to the head and we had to run a separate oil line to the rod tube. Very doubtful this is what is going on with yours.

    Camoit asked if your getting full throttle also, the cables may be fine but is it open carb flaps completely and is choke fully open as well when warmed up.
    Hmm I guess I'll check the stock cleaner housing for that. And yes all the vacuum lines are going to where they are supposed to go. Now if it turns out to be the air cleaner, will an after market open air cleaner with K&N filter fix that issue. if I also use replace that hose with a K&N breather cap?

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    try and drive it with out the air cleaner and see if it helps before you spend money on that.
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  18. #18

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    Quote Originally Posted by camoit View Post
    Have you checked to see if it's getting wide open throttle?
    I know it's a dumb question but that is the first one I see. Put a broom stick / brick/ small child, on the pedal and then look down the carb. Then turn the linkage some more by hand. If it opens up more then you need to make an adjustment. You don't want the carb to keep the pedal off the floor. You want to have just a tiny bit of slack or you can bend the linkage with your foot. Thats why the end of the cable is on a slider mount by the carb. I guess I can make a video in the mechanics tips and trick section, since many You Tuber's like my electric choke adjustment explanation.
    What he said ^

    These trucks are not the most powerful (or thrifty on gas for that matter) What they do well is just keep on running- Energizer Bunny type running. They just keep on running with minimal fuss.

    On the interstate 70-75MPH you have to keep your foot on the floor just about.

    I remember many years ago I took in on the highway to see what it could do.

    I think I just barely got it over 80 after 15 minutes of trying to push the gas pedal through the floor. Must have come up on a downslope.

    26 years and 346,000 miles later it runs the exact same way.

    What they give up in power they more than make up with in heart.

    Can't kill 'em...

  19. #19

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    Ok I checked for wide open throttle and it is correct. i swapped out the cap and rotor, and while I was in that area I noticed the PCV was clogged so I swapped that too.

    Still same issue. can't climb above 70 . I guess i'll just have to live with it till I swap out the carb for a weber...

    other than that the truck runs better than ever, no popping or ruff idle. MPG is good and gets up to 45 mph in a snap.

    I'm thinking the stock carb's secondary is the issue and I am not rebuilding this thing!

  20. #20

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    My G63b 84 model ram 50 hits 85-90 easily on a flat road LOL. Gotta love a mikuni that is not computer controlled. And of coarse mine only has 33,000 miles on it. I could'nt dream of a weber as I have california emissions.

  21. #21

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    Quote Originally Posted by Kaos731 View Post
    Ok I checked for wide open throttle and it is correct. i swapped out the cap and rotor, and while I was in that area I noticed the PCV was clogged so I swapped that too.

    Still same issue. can't climb above 70 . I guess i'll just have to live with it till I swap out the carb for a weber...

    other than that the truck runs better than ever, no popping or ruff idle. MPG is good and gets up to 45 mph in a snap.

    I'm thinking the stock carb's secondary is the issue and I am not rebuilding this thing!
    Wise choice.

    Rebuilding a stock carb would be as useful as probing for toe jam.

    IIRC I got mine up to 85 or so.

    Top speed is higher in 4th as opposed to 5th. LOL

  22. #22

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    LOL 85?! The speedo goes all the way to 115! This is false advertising if you ask me.

    My goal is to make the truck use the full scale on that speedo! Weber , Headers, and magna flow muff should help with that, or get close. (I hope)

    oh and this is an automatic with overdrive, so it is a 4 speed.

  23. #23



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    My old 2.0 and 2.6 would hit 100 pretty easily. I think you have a problem somewhere.
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  24. #24

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    I have the same thing happening only it takes me a short bit to get to even 45, just has no power. and I got up to 76-78 earlier today but any kind of hill at all and I was dropping to 4th in hopes of staying above 55.then hope for down slope to get back to the speed limit. im feeling a 4g63t swap will be a must when I get my fall school loan. ive had mine for 2 days and I admit I love the thing but my friends golf cart could yank me around the yard probably. maybe a locker and some 4.10 gearing would help us. honestly I see the weber as a waste, if we cant get up to speed in a reasonable time now a carb swap isn't going to do much if anything other than throttle response in itself. my .2

  25. #25

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    OH Shit wait I just thought of something..
    Since I have automatic this truck should have a torque converter if I am not mistaken.

    Could the torque converter be going bad, to cause this issue?

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