Stumbles shifting into 2nd while heavy into the throttle

[DoubleDingo]

Carburetor guru's I need some input about this issue I am having. I haven't drove the truck much after I got the engine back in it, so that may be part of the problem. I do add at least 10 gallons of 91 octane each time I start driving it again, and sometimes just fill it up and cuss the oil company that steals my $80-$90.

Okay the problem I am having. You can hear a mild miss at idle. Timing is set to 10* btdc, and the vacuum advance is per the factory set up, so it is probably ported. It has all the factory emissions stuff installed. When I first fired up the truck after stabbing the engine, the mixture screws didn't cause the idle to change at all so I couldn't adjust the A/F mixture. I ran some Motor Purr in the tank and a couple days later the mixture screws were doing their job again, but still not right like they were before. The truck seems to run well down the road, and for the most part it accelerates okay, but I can tell it's not running at peak performance. I added a mild cam while the engine was out, so that and the engine being resealed is the only difference. This stumble issue didn't happen before the cam swap and engine reseal. When I go to take off from a dead stop or even rolling start with a lot of throttle, it takes off fairly decently even with the mild miss, but as soon as it shifts into 2nd gear it literally falls on its face like it died, but then it picks right back up again and takes off.

What do you guys think it is? I was wondering if it may be the choke flapper closing and/or opening because the guts of the choke are not all there. Or maybe something internally in the carb? Or possibly a vacuum leak, or maybe one or more of the check valves are no good. Before I put it back in I sprayed carb cleaner in all the ports but not with the nozzle spraying full force. Also sprayed carb cleaner over the entire outside, inside, topside and underside of the carb except I didn't take it apart to spray in the bowl area. Something isn't right and it is really bothering me.

 

[350runner]

"Falling on its face" is usually a vac leak issue.there's a lean spot that is the cause of the fall.

Sent from the dust in front of you!

 

[Quadrajet Power]

Hi Shane. I'm new on the board, but not new to the carbs.

What carb are you running? A quadrajet?

When you changed the cam, you change the vacuum structure for the engine, and that can require some internal calibration changes on the quadrajet for it to be it's best. Especially the idle circuits. You probably had to turn up the idle screw to keep it idling, and may be getting nozzle drip and rich condition at idle, which is why the idle mixture screws are working.

On the shift to second, that could be several things. May be running out of fuel and not recovering quick enough. I use a high flow needle/seat to keep the bowl full.

Also, I would just remove all the choke components, including the primary flap. Have to grind the back side of the screws before removing though or they will snap.

Hope this helps. Keep that truck on the road!

 

[DoubleDingo]

"Falling on its face" is usually a vac leak issue.there's a lean spot that is the cause of the fall.

Sent from the dust in front of you!

I may be able to locate the leak, it may be from the cruise control lines, they were not changed when the PO had the hoses redone. I'll check there first. And maybe that will get my cruise working again.

 

[350runner]

Awesome Mark is right as well. If your idle screw is turned to far you are not running off the carbs idle circuit, thus the reason the a/f screws are non functional

Sent from the dust in front of you!

 

[DoubleDingo]

Hi Shane. I'm new on the board, but not new to the carbs.

What carb are you running? A quadrajet?

When you changed the cam, you change the vacuum structure for the engine, and that can require some internal calibration changes on the quadrajet for it to be it's best. Especially the idle circuits. You probably had to turn up the idle screw to keep it idling, and may be getting nozzle drip and rich condition at idle, which is why the idle mixture screws are working.

On the shift to second, that could be several things. May be running out of fuel and not recovering quick enough. I use a high flow needle/seat to keep the bowl full.

Also, I would just remove all the choke components, including the primary flap. Have to grind the back side of the screws before removing though or they will snap.

Hope this helps. Keep that truck on the road!

Yeah it's a stock rochester q-jet. I believe I did have to turn the idle screw to get it to idle, it's been a few sleeps since then. I can't remember if I had to turn the idle down or up, but it needed to be adjusted for sure. Sounds like a carb rebuild may be in order. If I remove all the choke components, won't it affect my cold starts in the winter? It already runs like crap with the flap not knowing whether to be open or closed when it's cold.

After I installed the vortec heads I drove up to mom and pop's and after I adjusted the carb I had him check my cooling system for pressure leaks. Anyhow, afterward, I let it warm up without the air cleaner assembly on the carb, and he looked at the flap and it was almost closed. The truck ran fine that way whether it was cold or hot outside. He mentioned it not running right closed like that so he opened the choke can to see what was inside. I haven't seen this type of choke before so I don't know what a functioning one looks like. So we adjusted the black part to hold the flap open, and since then it is horrible on cold days until it gets hot.

 

[DoubleDingo]

Awesome Mark is right as well. If your idle screw is turned to far you are not running off the carbs idle circuit, thus the reason the a/f screws are non functional

Sent from the dust in front of you!

Good stuff here guys. I have a direction on what to check first.

 

[Quadrajet Power]

yea, sounds like a rebuild time.

That carb, I think has the hot air choke, with canister on the side. You can convert those to electric to help the operations. Something to consider.

If you build your carb yourself, make sure you get good parts, and not a parts store kit. Those are crap these days. I recommend cliffshighperformance.com for good quality parts.

good luck.

 

[Skweegle89]

Or let ^ do it. He did a great job on mine.


Sent from my iPhone using Tapatalk

 

[DoubleDingo]

Yep it has the hot air choke, and with vortec intake the hot air tubes don't have the inside horseshoe-tube that extends down to the passenger side head. So the hot air is coming from the belly of the aluminum intake.

I just remembered I may have another 80's non-computerized q-jet sitting around that has an electric choke on it, will have to dig around for it. I may slap that one on to see if anything changes. I rebuilt it a few years ago.

Those look like really good carb kits. Thanks for the link.

 

[DoubleDingo]

Or let ^ do it. He did a great job on mine.


Sent from my iPhone using Tapatalk

How much did he charge?

 

[Skweegle89]

I didn't have a core for him to rebuild, and he added an electric choke to mine. So yours will be a different case, but he does way more than just put a store bought rebuild kit in it. You can look at his website quadrajetpower.com for a price list or just shoot him a PM and I'm sure he can tell you.


Sent from my iPhone using Tapatalk

 

[DoubleDingo]

I didn't have a core for him to rebuild, and he added an electric choke to mine. So yours will be a different case, but he does way more than just put a store bought rebuild kit in it. You can look at his website quadrajetpower.com for a price list or just shoot him a PM and I'm sure he can tell you.


Sent from my iPhone using Tapatalk

I checked it out, looks to be a 12 month wait for a rebuild if they do it. I can get on the call list. First I am going to try and locate that other carb I mentioned and see if it will work since it was rebuilt. If it works better I will run it in the interim until I can get the other one rebuilt. And I need to get some rolls of vacuum hose and replace and reroute some lines to make it look and function better.

 

[Quadrajet Power]

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

 

[Skweegle89]

I checked it out, looks to be a 12 month wait for a rebuild if they do it. I can get on the call list. First I am going to try and locate that other carb I mentioned and see if it will work since it was rebuilt. If it works better I will run it in the interim until I can get the other one rebuilt. And I need to get some rolls of vacuum hose and replace and reroute some lines to make it look and function better.

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