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what's wrong with my carb?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 85chevy4x4, Jun 3, 2002.

  1. 85chevy4x4

    85chevy4x4 Registered Member

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    what\'s wrong with my carb?

    I've got an 85 chevy 3/4 ton 4x4. It has a 350 with the stock rochester quadrajet carb. It's a dog off the line and has no passing gear. If I floor it it slowly gets up to speed and has a bog right off the line. I checked all the vacuum lines and everything is good, new air filter, pcv valve, plugs, and wires. I know it has something to do with the carb. I don't know anything about it. What can I do to adjust it to run better? I'd like to get a new carb eventually but for now the stock one has to do.
     
  2. Blue85

    Blue85 Troll Premium Member

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    Re: what\'s wrong with my carb?

    How do you "know" that it is the carb? How is your timing? No passing gear? How about checking the TV cable. Carb should be the last thing to look at.
     
  3. 85chevy4x4

    85chevy4x4 Registered Member

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    Re: what\'s wrong with my carb?

    How can I adjust the timing? Do I just need to turn the distributor? I've got a timing light but have never used one before. What should it be set at and how do I do it? Thanks.
     
  4. Blue85

    Blue85 Troll Premium Member

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    Re: what\'s wrong with my carb?

    Not too difficult. First, find the timing mark on the damper cover. This is the big round thing underneath the fan, connected to the crank. It has a mark on it. Then locate the timing scale, which is stationary. It will show degrees BTDC and after. Clean these up so that you can read them. Connect the timing light to the battery terminals and put the clamp on the #1 plug wire. This is the plug closest to the radiator on the driver's side. Keep all of your cords out of the way of moving parts. You want to check the initial timing, so make sure that there is no advance happening. Find the vacuum canister attached to your distributor. Pull the hose off and put a screw inside the hose to plug it. Make sure that your idle speed is low.

    Now with the engine running, aim the light at the timing marks and pull the trigger. You will see the damper mark line up somewhere on the timing scale. This is your initial timing. A manual will tell you what this should be (usually 3-8 degrees Before Top Dead Center). You adjust it by loosening the distributor hold down bolt and turning the distributor.
     
  5. 85chevy4x4

    85chevy4x4 Registered Member

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    Re: what\'s wrong with my carb?

    I tried to do the timing last night. I found the mark on the dampner cover but couldn't find the stationary scale. I looked all over trying to find it and no luck. Where should it be at?
     
  6. Sandman

    Sandman 3/4 ton status Author

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    Re: what\'s wrong with my carb?

    If you have AC it can be hard to find. Look strait down between the alternator and the AC pump looking behind the water pump. You should be able to see the edge of it on the AC side. It is a tab that will hang over the damper. Hop this helps.
     
  7. 85chevy4x4

    85chevy4x4 Registered Member

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    Re: what\'s wrong with my carb?

    I don't have air conditioning, wish I did. I looked everywhere but couldn't find the mark. I tried timing it just by turning the distributor and it seemed to help a little, idles much better but still has a bog and if I really gas it and let off it backfires. Should the scale be on the bottom or the top of the motor. With the 6" lift and 35" tires it makes it kinda hard to look down through the top of the motor.
     
  8. Sandman

    Sandman 3/4 ton status Author

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    Re: what\'s wrong with my carb?

    The scale should actually be a tab that bolts on using some of the bolts that hold on your timing cover. If you dont have one, you'll want to get one. Any decent parts store will have a chrome one in their chrome section for a few bucks.

    Anybody have any ideas on the backfiring? Sounds real rich.
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: what\'s wrong with my carb?

    My mechanical advance was screwed up, and although changing timing did make a difference, it would still backfire through the carb going WOT from a standstill. Fixing the mech advance and resetting timing (by the tach and ear, I don't use a timing light) solved the problem entirely in my case.
     
  10. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Re: what\'s wrong with my carb?

    Okey Dokey. I like to run my timing FAST. I've got like 16 degrees initial w/ 64 cc vortecs and flat top pistons on 91 octane gas. I haven't had a ping even when I had the 195 stat, I am now at 180 because all the cool guys do that, hahaha.

    First off, we need to get you a good advance curve. Get a vacuum gauge and hook to somewhere that always pull vac, like that little tree on the back of the manifold. Keep speeding up the timing until the vacuum gauge reads its highest, then retard it around 1" or so. 12-16 degrees is also a good ball park figure too. Next go get the accel or Mr. Gasket mechanical advance kit, Summit sells these, they are identical kits because Mr. Gasket owns Accel. Also get the adjustable vacuum advance from accel, no matter what brand, they are ALL the same.

    Take the kit and put in the weights and use the medium and light springs. Leave the vac advance plugged off and go for a cruise on a real warm day. Listen for pinging when accelarating, its kind of a rattley/clanky noise that doesn't sound like a motor noise, but it is. Drive for a while then try to restart, if it kicks and struggles, get higher octane gas, or back it up 2 degrees and go for another ride. If it resarts fine but pings when accelrating, put in a heavier spring. If it runs great all around, you could speed the timing all the up to 16, but no more. Still good, put in a lighter spring and see what it does.

    Now we go on to the vacuum advance. It is only there for economy. A proper mechanical and intial timing will not need vac advance for performance. Hook the vac advance to a TIMED port. Well what is this? Unhook one of the vac lines of your carb, if you feel suction then it is a full vacuum port, not what we want. When you find that isn't sucking at idle, thats probably timed. Give the throttle a pull and see if it sucks, if it does its timed.

    Timed/Full vacuum is one of the most misunderstood things out there. Critics of timed claim that it starts pulling more vacuum when you open the throttle and will over advance the vacuum advance and cause pinging. This simply isn't true. There is a small little hole by the venturi on the primary that only gets exposed to vacuum when you open the throttle, so you get your vacuum to run the advance only when you are cruising. It pulls just as much as full only not at idle. You don't need all that advance off idle, you only want that little extra to keep the mileage up and plugs clean.

    But wait, I've got more to say, haha. Simply put in the adjustable vacuum advance and keep adding a turn of advance until that rattley noise comes and then back it up until it quits.



    Still not better? With the engine off, pull the choke open and have a peek down the carb. Give the throttle a pull and see if gas squirts out. If not, then the accelator pump is bad. Its that little deal on the front driver's side of the carb that kind looks like a little oil derik. It gives a little squirt of gas until the carb can catch up.

    If that works and it's still not better. You're power piston probably needs a little help. I've talked too much already, I can tell you how to check that if you need to know. PM if you want because I'm sure I make no sense on some of these things.
     
  11. 85chevy4x4

    85chevy4x4 Registered Member

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    Re: what\'s wrong with my carb?

    Excellent post. I felt like was ready my chiltons manual. I'm going to give it a try this weekend. The person that had the truck before me removed the scale for some reason. I messed with the timing going by ear last night and it's a little better. It starts much easier and runs just a little smoother but still isn't right. I have no passing gear. It bogs bad right off the line and seems like it catches 2nd gear way too quickly. It doesn't rev very high. If I'm going down the road and nail it to the floor, it slowy accelerates. I got beat by a ford escort last night in a drag race. Some kid with mom's old car and cut the muffler off and installed one of those chrome tips. It must have really made it fast. I just wanted to run over it. This truck needs help bad.
     
  12. Goober

    Goober 1/2 ton status

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    Re: what\'s wrong with my carb?

    Excellent description, Blazer_Boy!

    16 degree initial advance!?!??!!? Holy smokes!

    If you don't lock out any vacuum advance, that could give you over 60 degrees total advance !!! I'm sure the 91 octane helps but do you lock out any of your vacuum advance? How much total advance do you run?
     
  13. Blue85

    Blue85 Troll Premium Member

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    Re: what\'s wrong with my carb?

    Dude, you're describing transmission issues, not carb issues. By "no passing gear" do you mean that it doesn't downshift when you mash the gas? That's called detent or kickdown. Are you sure the TV cable is set right? It sounds like it is way too loose. If you get it loose enough, it will hardly even use 2nd gear, just clunk and then go into 3rd, so it starts off the line reasonably, then shifts and really, really dogs until you get up to maybe 40mph.
     
  14. 85chevy4x4

    85chevy4x4 Registered Member

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    Re: what\'s wrong with my carb?

    I have no kickdown or detent at all. It doesn't downshift at all. It's got the auto 3 speed with a 400 turbo. It makes that clunking sound you are talking about. How do I adjust the tv cable? I have no idea where or what it is. This sounds like it's my problem.
     
  15. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Re: what\'s wrong with my carb?

    The 400 does not have a mechanical kickdown or TV cable. It used vacuum modulation to time shifts and an electrical kickdown switch under the gas pedal to control kickdown. You may be getting weak vacuum signal to the tranny or the kickdown may not be correct. I have not worked with too many 400's as I prefer other autos (although the 400 is an excellent stock tranny and will last a long time if properly maintained). Somebody who has dealt with these more will probably be able to help you more than I will.
     
  16. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Re: what\'s wrong with my carb?

    If you hook the vacuum advance to full vacuum when you do what he's describing, you won't have any vacuum advance at WOT. It gives you the initial plus whatever mechanical advance you have (say 15-20 degrees). The cool thing about that is, your engine runs cooler when you're just cruising because of additional timing at part throttle. Also, you'll get better fuel mileage at a cruise.

    He knows what he's talking about. I suspect he needs to put more of that 16 degrees in his mechanical advance and take out some initial for more detonation resistance, but he has the Vortec heads that are VERY detonation resistant compared to other iron heads.

    What he's describing is a great idea and I'm doing it for my '84 before I drive it again (I've got the kit already). I plan on using FULL vacuum though and putting all of it in the curve. Vacuum advance should ONLY be used to smooth your idle and advance your timing at cruise. Stock vehicles have way too much vacuum advance, and that's why you use the adjustable canister.

    I'm doing something similar to his, but I expect to run about 12 initial, vacuum advance to smooth the idle (8*) and the rest in mechanical (for a total in the 32-34 range.
     
  17. Blue85

    Blue85 Troll Premium Member

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    Re: what\'s wrong with my carb?

    OK, who put the 400 in? Perhaps something was done incorrectly, or maybe the vacuum cable or vacuum modulator is bad or hooked up wrong?
     
  18. 85chevy4x4

    85chevy4x4 Registered Member

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    Re: what\'s wrong with my carb?

    My tranny is original as far as I know. Where is the vaccuum cable or modulator located at?
     
  19. Blue85

    Blue85 Troll Premium Member

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    Re: what\'s wrong with my carb?

    Oh, yeah, 3/4-ton. I was thinking it was a Blazer. Sorry.

    The vacuum modulator is sticking out from the tranny, with a hose that runs up to the carb or intake manifold.
     
  20. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Re: what\'s wrong with my carb?

    Yeah, I'm kinda special because I spend alot on gas and got a great deal on heads /forums/images/icons/laugh.gif. 16 degrees intial is quite a bit for some applications. If you feel a little nervous about doing that much, then 12 would be excellent too.

    So...I have 16 intial + 20 mechanical + whatever vacuum. I haven't really checked the vacuum to be honest, its only there for mileage for me. I was told when I was learning this stuff to run full vacuum for the vac advance and was having problems. I was blaming my poor carb. When you romp on it, engine vacuum decrease, along with off the line advance the can was giving and I was falling flat on my face.

    You want a smooth start and no pinging at very light throttle when setting the initial. A little more throttle or rapping it and their should be no pinging, thats the springs job. Then throw whatever little extra you can with the adjustable vac advance. All you do is stick a little allen wrench in there and give a turn to lessen the amount of advance.

    84 Chevy K10 up there is right about 16 being quite a bit. If I was having problems starting I would have to change some things. I would probably just back up the initial a few degrees, but really skilled people can reshape the mechanical weights so they allow even more advance.

    I would say you can't go wrong with 12 degrees and a light and medium spring. Tell us what happens if you time with the vacuum gauge. If it still stinks off the line, try advancing it until it pulls its highest reading.
     

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