New Carb, 86 k10 305

[BOWTIE]

Hi, new to the forum and new to carburetor engines. I purchased a 1986 k10 with 305 w/700r4. It currently has a Rochester quadrajet on it. I was having trouble getting it to run right. The primary choke pull off was missing so I installed a new one. Now the choke seems to be operating correctly. How many turns is a good starting point for the air/fuel mixture screws? And now I'm having trouble with the throttle sticking open. I'm guessing the throttle return spring needs replaced? And I need to adjust the idle screw. I was debating just getting a new carb. So the millionaire dollar question I'm having trouble figuring out is holley or edelbrock? Which cfm? Which model? And it has to be compatible for a 700r4. Any information would be helpful. Thanx

 

[firebane]

Fix the quadrajet and set it up properly. Will be the best carb you own.

Nothing like hearing the large secondaries of a quadrajet open up.

 

[Georgeb]

Fix the quadrajet and set it up properly. Will be the best carb you own.

Nothing like hearing the large secondaries of a quadrajet open up.

2X^

 

[BOWTIE]

I've had a few people tell me that they love quadrajets and through research I've done. It appears that someone has either rebuilt it or at least messed with it. So should I keep trying to tune it in or just say screw it and have it rebuilt? Some people tell me to go ahead and put bigger jets in it. Is there any good links to quadrajet tuning info?

 

[MikeB]

If I had stock engine with a Q-jet, I would stick with it. Nothing wrong with Holley or Edelbrock as universal carbs, but they are not designed for your specific application, will not bolt right up, and probably won't get the same gas mileage as your Q-jet.

Lots of good info here: http://www.cliffshighperformance.com/
I suggest buying his book. If you don't want to jump in that far, he will rebuild the carb for you.

Jon at the Carburetor Shop is another Q-jet guru: http://www.thecarburetorshop.com/

For less than the price of a new universal carb, both of the guys above will restore your Q-jet to like-new condition, and address a few known issues.

 

[BOWTIE]

Thanx man, I'll look into the links. See what I can figure out

 

[MadOgre]

I've had a few people tell me that they love quadrajets and through research I've done. It appears that someone has either rebuilt it or at least messed with it. So should I keep trying to tune it in or just say screw it and have it rebuilt? Some people tell me to go ahead and put bigger jets in it. Is there any good links to quadrajet tuning info?

If it were me and I were you and i had $ I would send it off to have it rebuilt by cliffs or someone. Personally I would do it my self but I have been messing with q-jets for 15 years or more.

2nd option would be to buy an Edelbrock 1406,1806,1826 carb. The only issues is that these will not mount to a stock GM cast iron intake with out an adapter and you also need to purchase an adapter for the TV cable and finding the correct brackets to run both the TV and Throttle can give you an aneurism!!!

TV cable corrector adapter bracket

You must be registered for see images attach

Edelbrock #8036 TV cable bracket which will only do the TV cable. It will not do both throttle and TV like they advertise which really pisses me off! So you have to find a throttle bracket that will mount to the back of the carb studs. I used the old single purpose throttle cable bracket that GM used in the 70s and notched the one end so it would fit the Edelbrock carb studs.

You must be registered for see images attach

This is how I did mine

You must be registered for see images attach

You must be registered for see images attach

Do not buy the universal TV/throttle brackets. They are completely useless junk.

 

[Joe383]

625 CFM street demon. The Q jet is my favorite carburetor if it is running rite but there a little complicated compared to something like an edelbrock for some one new to tuning carburetors. I have wanted to try the new 625 street demon cuz it kinda merges the edelbrock and Q jet in one carburetor but the cam in my new motor is a little too large for it. I have ran the 725 road demon and it is still my favorite carburetor to date out of all the aftermarket carburetors I have had over the years a 725 is too large for your motor and the street demons are probably just a little too much for your motor unless you went with something like the 575. A few other options would be an edelbrock 600 or a holley 570 street avenger. Do understand though that just about any carburetor you get your probably going to have to do a little adjusting on to get the best performance. I just put a 670 street avenger on my motor and have to put larger jets in the primarys and try a more aggressive pump cam or larger squirter for the accelerator pump. A wide band O2 sensor and a vacuum gage in the cab would be good gages to have in the rig for tuning and trouble shooting your carburetor.

 

[Georgeb]

When you say sticking open do you mean wide open or just a high idle? Since you had choke trouble and if its high idle I would look at the high idle cam first. With a 305 I doubt you will need bigger jets or different metring rods so a good rebuild will most likely suffice. As far as the idle jets go. Right or wrong I have been successfull with a vacuum guage on manifold vacuum. With the engine warm set the idle screws about one and a half to two turns out from bottom. Dont crank em tight just turn till you feel it. Start it up and set your initial timing around 12 deg with the vacuum advance unhooked. Now this is where I get fuzzy and some others here can set me straight. Hook the vacuum advance up to manifold vacuum and then get your idle down to around 500. Start turning the idle jet screws in a little at a time alternating from one to the other until a small turn on either makes the vacuum drop or you hear a noticable change in sound. From there turn them out one turn or so and set your idle back to the factory spec.

 

[fussfeld]

i think it boils down to using what you're comfortable with. But, since it sounds like you're almost there, why not try getting the Q-jet right?


You could get a brand new holley 4175 which will bolt right up (has spreadbore pattern), but i hear they are not as good as the q-jet in terms of mpg.

 

[MadOgre]

When you say sticking open do you mean wide open or just a high idle? Since you had choke trouble and if its high idle I would look at the high idle cam first. With a 305 I doubt you will need bigger jets or different metring rods so a good rebuild will most likely suffice. As far as the idle jets go. Right or wrong I have been successfull with a vacuum guage on manifold vacuum. With the engine warm set the idle screws about one and a half to two turns out from bottom. Dont crank em tight just turn till you feel it. Start it up and set your initial timing around 12 deg with the vacuum advance unhooked. Now this is where I get fuzzy and some others here can set me straight. Hook the vacuum advance up to manifold vacuum and then get your idle down to around 500. Start turning the idle jet screws in a little at a time alternating from one to the other until a small turn on either makes the vacuum drop or you hear a noticable change in sound. From there turn them out one turn or so and set your idle back to the factory spec.

OH I missed it being a 305 in that case Edelbrock #1400. The Demon carbs are good if you can find one for 350 cubic inches and less like that 575 or what ever. Stay away from the Holleys they are not a very good carb overall IMO.

As for the Idle tune, Just do one side at a time. Realize though that this only affects idle and some part throttle situations. It is not going to substitute jet calibration.

That said The quad jets are very forgiving carbs when it comes to jets. Unless it came off a big block it should be fine for jets and rods. A lot of guys like your buddies really don't have a clue how a Q-jet works. So don't go off their advice or you will probably end up ruining your carb!

The jets and rods are probably fine and it is smaller issues causing you grief. If the choke assembly was removed it is probably because the last guy who owned didn't know squat! And did the red neck thing and just ditched it cause he couldn't figure out how it works!

If the throttle is sticking open it could be because your linkage is rusty or binding or from the throttle shaft having gum and debris stuck in the bore or the throttle plate is warped and the shaft is binding in the bore. In which case the throttle shaft bore is probably worn and is allowing a vacuum leak which is why you are having issues with idle quality.

 

[BOWTIE]

Ok, well I did some more tinkering and and greased up the throttle assembly and seems to be operating smoothly. So now I don't have those hanging rpms, when the throttle is pressed and released. I set the fuel/air mixture screws out 4 turns from bottom. And now I have hesitation in throttle response like it is choking itself out before acceleration. And when the rpms do rise it is puffing out black smoke. Which means too much fuel. One piece of info I forgot to add was the guy who owned it before me install new plugs wires and distributor. So it hit me that maybe he just slapped the dizzy on and didn't set the timing. U had trouble being able to see the timing marks with the timing light, can anyone explain or show the best angle to see the timing marks? And I also was wondering if someone could show me the correct vacuum ports to hook up the vacuum gauge to when tuning the fuel to air screws. I tried the vacuum line directly above the driver side fuel to air screw and didn't get any vacuum reading at all.

 

[MadOgre]

K first screw the idle mixture screws all the way in GENTLY to not tighten them just go to all the way in then back out 2 full turns. That should help some at least. 4 turns is way to much.

The balancer has a little groove in it for the timing mark so get a screw driver or something and clean that little groove out good then you can use some white out or something in the groove to make it visible. You just need the mark to contrast the balancer so if the balancer is black and you get the groove cleaned to shiny metal it should contrast fine so that you can see it well.

Stand on something (SAFELY) so that you can look straight down at the timing mark. You should be looking straight down from the front of the engine when adjusting the timing. The vacuum advance on the distributor should be plugged as well as the vacuum port from the carb that is used for the distributor.

Usually its anywhere from 5-700 rpm that you want the engine at when checking the timing. If you need to adjust it. just loosen the distributor hold down bolt just enough so that you can turn the cap with one hand but not so loose that it moves by itself. Then one hand on the distributor and one on the timing gun check the timing while adjusting at the same time till you get it right then quickly shut off the engine and tighten the hold down bolt. Then recheck the timing to make sure it hasn't moved on you.

A stock 350 will do 4-6 degrees before TDC with an aluminum after market intake usually 8-10 degrees before TDC.

And make sure the vacuum advance is hooked up to full manifold vacuum. So any vacuum port that is below the throttle plates at the bottom of the carb.

For the tuner I would use the rear port that feeds the brake booster.

 

[MadOgre]

Also if you lubed the throttle linkage and bores with something like WD40 go back and clean all that out with carb cleaner because the oil/penetrating fluid will actually collect dirt and particles that will gum everything up.

The carb doesn't need lube it just needs to be clean.

 

[Quadrajet Power]

Send me your email address and I will email you my basic quadrajet tuning instructions. Sounds like you are getting close with it.