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Hessitation I can't seem to fix??

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Burt4x4, May 16, 2000.

  1. Burt4x4

    Burt4x4 3/4 ton status

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    Hessitation I can\'t seem to fix??

    Ok I know we have talked about this but I would like to run this by the gang to get more ideas....

    350/4speed/205, Edlebrock Q-jet 1901/4MV about 2yrs old with 15,000 +or-,Timing cain is about the same 15000 mile or so on it and timming is set to 4 btdc. MSD 8360 dist. w/vac advance. I have replaced cap & rotor,plugs,wires. I did the air to fuel mix adjustment to the carb using a vac gage( i'm not to confident i did it right[​IMG]??)I replaced all 3 fuel filters,checked for vac leaks none found,I do have an exahast leak from header gasket but don't think that madders.[​IMG]
    The hesitation is only off the line and then about 1200 rpm it feels like everything kicks in and my rig takes off down the road! Idel seems fine but I do have a cam in the motor so it runs like a camed motor blup,blup,blup....[​IMG]
    I am out of ideas ANY comments would be AWSOME!!
    Thanks

    Rock ON![​IMG] 72 K5 [​IMG] Led Zeppelin
     
  2. chevyfumes

    chevyfumes Court jester

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    Re: Hessitation I can\'t seem to fix??

    could it have anything to do with the tranny modulater or the detent cable and you just think it's the engine
     
  3. Burt4x4

    Burt4x4 3/4 ton status

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    Re: Hessitation I can\'t seem to fix??

    WHAT?? I have never heard thease terms before [​IMG]???
    My tranny is a manual SM465 4speed.....

    Rock ON![​IMG] 72 K5 [​IMG] Led Zeppelin
     
  4. Blazer1970

    Blazer1970 1/2 ton status

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    Re: Hessitation I can\'t seem to fix??

    Steve, have you tried running more initial timing advance? I think you could run a lot more (8 - 12 deg.??), and that might help (just watch out for detonation). That surge is also a characteristic of the Q-Jet to some extent.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  5. Burt4x4

    Burt4x4 3/4 ton status

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    Re: Hessitation I can\'t seem to fix??

    That is the direction I was thinking of. What the heck it's worth a try at this point![​IMG] I'll try 8 first then keep going if no change in heasitation. You think it's just someting with the Qjet that I get to live with??

    Rock ON![​IMG] 72 K5 [​IMG] Led Zeppelin
     
  6. 82K5

    82K5 1/2 ton status

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    Re: Hessitation I can\'t seem to fix??

    Did I read that right? You say you replaced all 3 fuel filters. Let see, you have a filter going from the gas tank to the fuel pump and one going from the pump to the carb? Where is the other one. Do you have 2 tanks? I dunno. I would think having more than one filter might give you some hesitation off the line. I am just guessing though. Just a thought. I got one fuel filter in my '82, should I add 2 more? I doubt it. Maybe someone has the answer for this.

    Phil in K.C.
     
  7. Burt4x4

    Burt4x4 3/4 ton status

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    Re: Hessitation I can\'t seem to fix??

    Ya I added an inline filter between the carb and fuel pump.
    But that thing has been there longer that this issue. It is one of thoes cleanable type of fuel filter(I just replaced the element inside of it).I am thinking of getting rid of the little paper one inside the Qjet, like you said three may be over kill especially now that I have a poly gas tank!
    hmmmmm, mabie my mechanical fuel pump is getting weak?????


    Rock ON![​IMG] 72 K5 [​IMG] Led Zeppelin
     
  8. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: Hessitation I can\'t seem to fix??

    Sounds like a bad accelerator pump to me. Engine off look down the carb and give the throttle a pop. You should see a stream of fuel shoot down each primary. If it dribbles or no shot the diaphram has poped off the plunger rod (Pretty common). That arm on the right side top (facing carb on engine) usualy green tint to it is the the actuator arm.
    If thats the case even with the engine at idle it you blip the throttle a couple of times it will have a dead spot for a second may even die.
    If this is the case $14 rebuild kit should fix the problem. could even do the repair without removing the carb from the engine. just need to take the top off and pull the plunger out and install a new one and new top gasket. be very carefull not to drop any screws down the carb.
    Also what sort of vac are you pulling at idle. that cam may be part of your problem if your pulling under 14 (stock should pull 18-20)
    For my next trick I will try to solve the nose up engine dies problem. :) doing some mods this week that I will get to test this weekend.

    Diging it in the dirt with my K5's
    Grim-Reaper
     
  9. 82K5

    82K5 1/2 ton status

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    Re: Hessitation I can\'t seem to fix??

    Yea, take that filter out of the carb, you don't need it. I use the Purolater inline between the pump and the carb. Just replace the element when it gets dirty.

    Phil in K.C.
     
  10. Mudzer

    Mudzer 1/2 ton status Author

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    Re: Hessitation I can\'t seem to fix??

    When you say "Off the line" does this mean when you actually accellerate using the Secondaries on the carb? (4 barrell) If so, this is probably what is wrong. Quadrajets maintain the proper amount of airflow into the secondaries by the means of an "Air Flap" above the secondary throttle plates (butterflies). This air flap is adjustable. If you are experiencing a bog when you "kick in the 4 barrels" you are probably getting too much air and it is hesitating. It is real easy to adjust it. You can make the adjustment while the carb is on the vehicle. Do the adjustments with the engine off. On the passanger side of the carb near the secondary air flap, there is a small straight-blade screw with an allen bolt set screw on the bottom of the casting. Find the right sized allen wrench and small straight-blade screwdriver. Next, mark the locatoin on the casting with your screwdriver for a reference point. Then insert the screwdriver into the screw. It is important to do this before loosening the allen set screw because the adjustment screw has a tensoin spring. Hold the screw and loosen the allen set screw. Turn the adjustment screw clockwise just 1/4 of a turn. Tighten the allen set screw, and put the air cleaner back on. Now do a test run. Repeat this until the hesitation is gone. I have used this trick on my old 12 second Firebird. I constantly adjust the air flap at the track to get my 60 foot times down. Same thing will work for your 4x4 if you want to make the air flap open quicker. Just loosen the tension on the flap to open quicker or tighten the tension to open slower. Keep in mind, this tip is only if you are having problems when you are entering the secondaries. If it is just an off-idle hesitation at the stop light, check the accererator pump on the drivers side front of the carb. You can also adjust the pump squirt by putting the linkage in the inner hole for less fuel and in the outer hole for more fuel. Good luck.

    <font color=red>Mudzer</font color=red>
    1978/91 K5 Blazer
     
  11. Burt4x4

    Burt4x4 3/4 ton status

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    Re: Hessitation I can\'t seem to fix??

    Ya Mudzer it's from a stop sigh or light not the secondaries. But a good reminder on thoes flaps!!
    Grim I hear ya! does the replacement kit you mentioned replace the acc pump with the spring? or just a pump and top gasket? I am using the hole furthist out on the acc pump lever.
    I think my vac never got above 15/16??
    Witch vac port should I be using? I had it hooked up to the front passingers side on the bottom!
    Thanks guys!![​IMG]

    Rock ON![​IMG] 72 K5 [​IMG] Led Zeppelin
     
  12. Emmettology 101

    Emmettology 101 3/4 ton status

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    Re: Hessitation I can\'t seem to fix??

    Did you put that carb on, or was it on the Blazer when you bouoght it?
    There is a spring adjustment for the secondaries(at least on regular Quadra toilets, I am not sure about Edelbrocks) and it is possible for the Secondaries to open pretty quick/soon even on vaccum secondary units.
    See how long it is taking for the Secondaries to open. They maybe opening reallysoon/quick and dumping too much fuel and that would cause you hesitation.
    If they are opening really soon, e-mail me and i will explain how to adjust them.


    Mike
    82 GMC Jimmy "Emmett"
    IN TOO DEEP Off-Road Club
     
  13. Burt4x4

    Burt4x4 3/4 ton status

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    Re: Hessitation I can\'t seem to fix??

    Are you refering to the top flap on the secondaries??
    I put the Qjet on there my self and it's been working for several years but I'm no guru when it come to tuning it so I would love to hear what your brain has to say! I checked your profile for an email but couldn't find one! Can you just post your brain here??[​IMG]
    Thanks Bro

    Rock ON![​IMG] 72 K5 [​IMG] Led Zeppelin
     
  14. Toad

    Toad 1/2 ton status

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    Re: Hessitation I can\'t seem to fix??

    On my Quadrajet (before I screwed it up) Grim helped solve about half of my problem. I had a small vacume leak. I swore up and down that everything was tight. I kept checking the bolts while the carb was on the motor. Did the spray around the carb base, no difference. I thougt it was all fine.

    One day I pulled the carb and checked everything. Screws on the bottom were tight and the gasket looked tight but I just happened to turn it right and saw a small gap when the light shone through. I took the screws out and put them back in and it helped a ton. Remember you can't check that part unless you pull the carb off.

    The rest of my problem was my metal fuel line was pinched a little. When I punched it from a stop it would hesitate, I think because it couldn't get enough fuel. Unfortunately I stripped the rest of the fuel inlet? And now I have a rebuilt carb.
     
  15. jimmyjack

    jimmyjack 1/2 ton status

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    Re: Hessitation I can\'t seem to fix??

    Burt, this may sound like a bit of a stretch compared to the other advice you've recieved, but check your battery. My blazer was getting horrible mileage, hesitated off the line,(practically stalled)and generally ran bad. My ammeter never budged but i had to jumpstart my truck one day after weeks of this problem, I went to Autozone, replaced my battery and it ALL went away. Mileage increased , hesitation stopped, and now it runs like a raped ape again. Like i said, it may be a stretch but you never know.

    Jim
     
  16. chevyfumes

    chevyfumes Court jester

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    Re: Hessitation I can\'t seem to fix??

    Sorry about that,I misunderstood, but just incase you should check the muffler bearings and jesus clips
     
  17. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: Hessitation I can\'t seem to fix??

    The kit is a complete rebuild kit and includes every thing but the float. The springs I don't remember. I think you reuse the old spring. All the spring does is return the pump. If you look at the carb if the silver rod under the pump lever is up than the spring is good. My truck poped the rubber off that pump a few months ago and the symptoms sound the same but with my Automatic if I stompted it I could get it to stall. If I Eased into it nice and slow and it was fine because you didn't get the big vac drop when the butterflies opened it could pull enough vac to activate the primary jets. Yours with that cam is going to have less vac to work with so my guess is it's depending on the pump more.
    Depending on the cam the 15-16 may be fine but it never hurts to check for a vac leak. As for one of the other guy finding the bottom plate was loose...yeah that happens. When it does it will let a vac leak happen internally and you may never find it with the carb on the truck. Check for the squirt first...that only takes 30 seconds. I think your going to find thats your problem.
    The vac port on the bottom passenger side is the one to use. That pulls vac off both sides of the plennum. It is actully connected internaly with the the line out the bottom center front for the PCV.

    Diging it in the dirt with my K5's
    Grim-Reaper
     
  18. bablazer73

    bablazer73 1/2 ton status

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    Re: Hessitation I can\'t seem to fix??

    being a retired drag racin fool, I wonder how "big" your cam is. as a cam gets bigger, the low rpm vacuum and performance suffers. If the rest of the truck is not supporting it, running in the same rpm range, there could be to much of a load on the engine at low rpm that the cam/engine CAN"T support. do you have the cam profile? lift, duration, and most imprtant lobe seperation? if not , do you remember what cam? I don't like q-jets! they are difficult carbs to dial in, and aftermarket parts are limeted. the secondary air door is adjustable through a screw on the side. the metering rods and jets may also need to be replaced to "fine tune" the carb. these aftermarket carbs are bench set to an "average" engine. the changes you make to an engine may not be the same as to what they set the carb to. Once agian I say I hate q-jets, they take a long time and patience to set up right. But on the plus side, when set up right, the are an excellent 4wheelin carb!

    your right. I don't understand the jeep thing!
     
  19. Burt4x4

    Burt4x4 3/4 ton status

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    Re: Hessitation I can\'t seem to fix??

    Thanks Guys
    I do not know the specs on my cam it was in the motor when I got my K5 back in 93. I was told the cam was an RV cam and thats all I know. This is a fairlly new syptom I have been working on so I think it is my Qjet or timming advance!
    I will do the things suggested and get back to ya all with hopefully an answer on the problem!
    again thanks you guys are AWSOME!

    Rock ON![​IMG] 72 K5 [​IMG] Led Zeppelin
     

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