Stumbles shifting into 2nd while heavy into the throttle

[Quadrajet Power]

Cliff does have a year turnaround typically for builds.

I typically stay about 2-3 weeks turnaround.

 

[DoubleDingo]

It's a 2 week turnaround. That's what it took for mine anyway. You sure your not looking at cliffs?


Sent from my iPhone using Tapatalk

On their website it states a 12 month wait for a rebuild.

 

[350runner]

The link quadrajet power posted was suggested for parts unless you want to wait a year. Otherwise (quadrajet power) can build it for you

Sent from the dust in front of you!

 

[DoubleDingo]

I tinkered with the truck over the weekend. This is what I found out. I need to learn about these more modern carburetor's with the integrated choke, I have always had the divorced choke from the older models.

Anyhow, yes there was a vacuum leak, and yes the carburetor can use a rebuild. The make shift plug I made for the driver's side of the tee behind the carb that accepts the line for the cruise control wasn't sealed well. Added an actual plug for that. I messed with the choke a little bit in hopes to get it working a little better for the cold season. I need to find info on how to adjust a warm air integrated choke mechanism for fast idle, choke angle, etc. One thing I never knew was how much vacuum there is being drawn through the choke housing! I had the black part off and started the truck, it idled okay but I put my hand over the housing and it dang near sucked my hand into it. After doing that I put the black part back on and twisted it until it allowed the choke flap to have a small gap for air to get through, yet didn't cause it to close completely. And then I pulled the block off plate that I drilled holes in for the warm air tubes to poke through after the vortec swap, since the intake doesn't have provisions for the OEM warm air setup. I may need to add a bunghole on the driver's side exhaust and run the pipe up to the intake, since the warm air tube no longer extends down to the passenger side head, each tube is loosely poked through those holes. I added some vacumm tubing on the backside of the block off plate to hold them snugly in place and provide a better seal, and it worked a little. Need to figure out a better way to seal those.

Since the A/F screws don't work like they're supposed to, only the passenger side one works, I counted how many turns it took to bottom it out, and then returned it to its previous position. Then I bottomed out the driver's side one and backed it out to match the other side. That made it idle better.

This morning it fired right up with a tap of the key and idled fine with it being in the mid 40's and humid outside. It ran better than it did before but it still stumbled upon take off, so I know the choke has a lot to do with that. I feel if I can get the choke dialed in my cold issues will go away, and once I get all the vacuum leaks sealed up and the carb rebuilt, the other issues will go away.

 

[MadOgre]

Here is a link to my price list. I try to stay very affordable to help people keep a quadrajet instead of going to some auto store bolt on!!
I replace most of the parts inside and in your case, would resize the idle circuits to run correctly with your cam.

https://www.dropbox.com/s/6lkm20uzllc6rih/QP price list.pdf?dl=0

What does "most of the parts" mean ?

 

[MadOgre]

I tinkered with the truck over the weekend. This is what I found out. I need to learn about these more modern carburetor's with the integrated choke, I have always had the divorced choke from the older models.

Anyhow, yes there was a vacuum leak, and yes the carburetor can use a rebuild. The make shift plug I made for the driver's side of the tee behind the carb that accepts the line for the cruise control wasn't sealed well. Added an actual plug for that. I messed with the choke a little bit in hopes to get it working a little better for the cold season. I need to find info on how to adjust a warm air integrated choke mechanism for fast idle, choke angle, etc. One thing I never knew was how much vacuum there is being drawn through the choke housing! I had the black part off and started the truck, it idled okay but I put my hand over the housing and it dang near sucked my hand into it. After doing that I put the black part back on and twisted it until it allowed the choke flap to have a small gap for air to get through, yet didn't cause it to close completely. And then I pulled the block off plate that I drilled holes in for the warm air tubes to poke through after the vortec swap, since the intake doesn't have provisions for the OEM warm air setup. I may need to add a bunghole on the driver's side exhaust and run the pipe up to the intake, since the warm air tube no longer extends down to the passenger side head, each tube is loosely poked through those holes. I added some vacumm tubing on the backside of the block off plate to hold them snugly in place and provide a better seal, and it worked a little. Need to figure out a better way to seal those.

Since the A/F screws don't work like they're supposed to, only the passenger side one works, I counted how many turns it took to bottom it out, and then returned it to its previous position. Then I bottomed out the driver's side one and backed it out to match the other side. That made it idle better.

This morning it fired right up with a tap of the key and idled fine with it being in the mid 40's and humid outside. It ran better than it did before but it still stumbled upon take off, so I know the choke has a lot to do with that. I feel if I can get the choke dialed in my cold issues will go away, and once I get all the vacuum leaks sealed up and the carb rebuilt, the other issues will go away.

What type of cam did you install? if it barely lopes then you should be fine with the stock idle circuits and could probably just use a good carb cleaning overhaul.

If it is a lopey cam then yes an *********** of the idle tubes will help.

The problem is a lopey cam has less vacuum at idle and thus less sucking force to pull fuel through the tubes so if you enlarge them it helps out with the fuel delivered at idle.

So to compensate you turn the idle speed screw to get it to run but this means that the throttle plates are now opened enough that it kills the suction to the idle ports below the throttle plate and now you are running from the off idle circuit making the idle mixture screws ineffective.

A big enough vacuum leak can cause the idle mixture screws to do the same thing because there is too much air entering for the idle mixture to make much of a difference.

Also you may / probably have leaky fuel well plugs which just compound the problem.


As for the choke you can retro fit the hot air housing with electric choke components.

For simplicity sake you can remove all the choke linkage and wire the valve open and if you still have problems when the engine is at full warm temp you can rest assured that it is not choke related.

 

[Quadrajet Power]

What does "most of the parts" mean ?

It would be wrong to say "I replace all parts", as some original, removable parts don't wear and need replacing, such as float fulcrum, check ball screw. Read my price page linked above and you see what all I replace new. Much more than a "kit" provides.

 

[Quadrajet Power]

I tinkered with the truck over the weekend. This is what I found out. I need to learn about these more modern carburetor's with the integrated choke, I have always had the divorced choke from the older models.

Anyhow, yes there was a vacuum leak, and yes the carburetor can use a rebuild. The make shift plug I made for the driver's side of the tee behind the carb that accepts the line for the cruise control wasn't sealed well. Added an actual plug for that. I messed with the choke a little bit in hopes to get it working a little better for the cold season. I need to find info on how to adjust a warm air integrated choke mechanism for fast idle, choke angle, etc. One thing I never knew was how much vacuum there is being drawn through the choke housing! I had the black part off and started the truck, it idled okay but I put my hand over the housing and it dang near sucked my hand into it. After doing that I put the black part back on and twisted it until it allowed the choke flap to have a small gap for air to get through, yet didn't cause it to close completely. And then I pulled the block off plate that I drilled holes in for the warm air tubes to poke through after the vortec swap, since the intake doesn't have provisions for the OEM warm air setup. I may need to add a bunghole on the driver's side exhaust and run the pipe up to the intake, since the warm air tube no longer extends down to the passenger side head, each tube is loosely poked through those holes. I added some vacumm tubing on the backside of the block off plate to hold them snugly in place and provide a better seal, and it worked a little. Need to figure out a better way to seal those.

Since the A/F screws don't work like they're supposed to, only the passenger side one works, I counted how many turns it took to bottom it out, and then returned it to its previous position. Then I bottomed out the driver's side one and backed it out to match the other side. That made it idle better.

This morning it fired right up with a tap of the key and idled fine with it being in the mid 40's and humid outside. It ran better than it did before but it still stumbled upon take off, so I know the choke has a lot to do with that. I feel if I can get the choke dialed in my cold issues will go away, and once I get all the vacuum leaks sealed up and the carb rebuilt, the other issues will go away.

That hot air choke will pull a good bit of vacuum, so try to seal up that intake tube. You can adjust the fast idle with the small flat blade screw facing front of truck on passenger side of carb, under the choke system. With choke set, adjust that screw to set fast idle speed.
If you need to adjust your choke, to make sure it opens all the way when warm, you can loosen and turn the black mechanism until it's adjusted correctly and then re-tighten.
I convert a bunch of these type to electric choke systems. You have to block the vacuum since it isn't needed anymore and connect to a key on power source.

 

[MadOgre]

How do you clean the idle tubes and how do you seal the fuel well plugs ?

 

[Quadrajet Power]

How do you clean the idle tubes and how do you seal the fuel well plugs ?

I use a chemical dip, then ultrasonic system for general cleaning. The idle tubes are always measured and cleared from blockage with gauge pins. Resized with micro drill bits and pin vise. Pulled and changed/modified/replaced as necessary. (especially after a big reman shop ruins them).
Well plugs, unless they are bad leakers, are molded around plugs with light hammer and sealed with a special marine epoxy I mix.

 

[DoubleDingo]

What type of cam did you install? if it barely lopes then you should be fine with the stock idle circuits and could probably just use a good carb cleaning overhaul.

The cam I put in is a Crane Cam 3896929 Blueprinted 300hp 327 cu. in. Cam with an RPM range of 800-4500; Duration: Int. 195*/Exh. 202*; Lobe Separation: 112*; Gross Lift: Int. 0.390/Exh. 0.410.

If it is a lopey cam then yes an *********** of the idle tubes will help.

The cam idles smooth, definitely not a lopey cam.

The problem is a lopey cam has less vacuum at idle and thus less sucking force to pull fuel through the tubes so if you enlarge them it helps out with the fuel delivered at idle.

So to compensate you turn the idle speed screw to get it to run but this means that the throttle plates are now opened enough that it kills the suction to the idle ports below the throttle plate and now you are running from the off idle circuit making the idle mixture screws ineffective.

A big enough vacuum leak can cause the idle mixture screws to do the same thing because there is too much air entering for the idle mixture to make much of a difference.

I am thinking the various little vacuum leaks are causing the problems with the idle mixture screws.

Also you may / probably have leaky fuel well plugs which just compound the problem.

I have a feeling the well plugs are okay because it fires right up after sitting.


As for the choke you can retro fit the hot air housing with electric choke components.

For simplicity sake you can remove all the choke linkage and wire the valve open and if you still have problems when the engine is at full warm temp you can rest assured that it is not choke related.

I had the black part of the choke turned enough to keep the choke flap completely open and it ran like crap until it got good and hot. Still had a miss, but I believe that was coming from the vacuum leaks. I forgot to mention I also tightened the carb to manifold bolts about 3/4 to a full turn.

Well my intended answers in between your questions didn't preview right, hopefully they will display correctly when I post them. Nope, they didn't, some of your stuff got italicized.

 

[DoubleDingo]

That hot air choke will pull a good bit of vacuum, so try to seal up that intake tube. You can adjust the fast idle with the small flat blade screw facing front of truck on passenger side of carb, under the choke system. With choke set, adjust that screw to set fast idle speed.
If you need to adjust your choke, to make sure it opens all the way when warm, you can loosen and turn the black mechanism until it's adjusted correctly and then re-tighten.
I convert a bunch of these type to electric choke systems. You have to block the vacuum since it isn't needed anymore and connect to a key on power source.

I will adjust that screw and see how it works out. Right now the fast idle is just the normal idle when it's cold. I think there is something missing from inside the warm air housing. Is the spring supposed to be loose, meaning not attached in any way to choke arm? Or is there a hook or something that grabs better to the choke mechanism/arm inside the housing? When I pull off the black part with the spring inside of it, that is all there is inside, so I think it's not fully controlling the choke flap. To me, there should be something on the end of the spring that gets a better hold of the choke arm inside the housing. I have no problem running a warm air choke setup, I just want it adjusted properly so I can drive the truck while it's cold outside without issues. Once I can get all the stuff to rebuild the carb, I can get a better working choke too.

What is the adjustment screw for on the top of the choke housing? The one where the red arrow is pointing in the attached pic.

 

[Quadrajet Power]

You are correct. Inside the housing there should be an arm that attaches to the center shaft with a screw. The choke element end should go over this arm and then it would open and close the choke flap with engine heating. I am including a picture.

The red arrow points to the primary choke pull off adjustment. It just adjust the positioning. You shouldn't need to mess with that.

 

[DoubleDingo]

It has that arm in the housing. What is the list of parts for one of these hot air choke systems? Is it just that arm and the spring, and then the adjustments are the fast idle and choke flap? I have never in all my years, seen this type of choke setup tore apart, so I don't know what is missing if anything is. One thing is certain, I am wanting to rebuild this carb so I can better understand it, not just for adjustments but for the inner and outer workings of it.

I did a search for my carb number and got nothing, I guess my carb is just an odd ball like I am...lol...

 

[DoubleDingo]

Did some more research and found some info on my carb. Some sources say it is M4ME, but as it sits it's a M4MC. For me to rebuild it myself and replace old components, I am looking at $200+-. That doesn't include switching it to electric choke. That will take it over $200. But it is needed.