Truck is Sluggish/Choking between 45-60mph

[C4UC101969]

Today in the morning on my usual daily route to drop off my son in daycare, on straight flat road as i was getting to the 45mph mark it started to sputter, kind of holding back gasping for gas or air, so I let the gas pedal go let it slow down a bit and then again gradually speed up, it went past the 50mph mark without any sputtering or anything like that, it was normal once again. Then after slowing down and then speeding back up to the 45mph mark it began to sputter again and gasp for fuel or air, I let go off the gas let it roll for few seconds and then press the gas pedal and it goes once again past 45 without hesitation.

So on the way to and from my sons daycare it did that sluggish/choking on and off scenario.

I run on ethanol free fuel only with 91 octane, there was half a tank in the truck so the low fuel is out of question, what could it be? I am thinking the carb needs a good cleaning but would like to hear y'all opinion about this issue. Any suggestions would be greatly appreciated.

Its a stock 307 with three on the tree with 4 bar carb.

[FirstOwner69]

When did you last replace the fuel filter?

[67C10Step]

Sounds fuel supply related to me. Clogged filter or something starving the engine of fuel. At least that is where I would start.

[C4UC101969]

Thanks guys, I will check the filter then and hopefully this will solve the issue.

[71meangreenc10]

What brand of carb?

Smitty

[C4UC101969]

Originally Posted by 71meangreenc10

What brand of carb?

Smitty

It came off a donor camaro from the 80's as per previous owner who did full resto,

[71meangreenc10]

Q-Jet, Eddy, or Holley?

Smitty

[C4UC101969]

Originally Posted by 71meangreenc10

Q-Jet, Eddy, or Holley?

Smitty

I think its a rochester stock 4 bar carb from a donor camaro, see pic

[71meangreenc10]

Looks like a Q-Jet. As mentioned above change the internal filter and don't over tighten it or you can crack the carb housing. Also check your throttle shaft play to see if it is time for overhaul. There is a guy in Vail AZ that rebuilds and replates them to factory standards and I have his info if you want it. If the throttle shaft is worn that will cause a vacuum leak and possibly cause your symptoms.

Smitty

[HIGHWAY BY THE SEA]

Sounds exactly like my 68 did when the fuel filter was clogged. It would slow down if you pressed the gas, and speed up when you let off it.

I agree with all the fuel starvation comments above!

[C4UC101969]

Thank you guys, I will be changing the filter on Monday and will let you know if that is the issue, appreciate all the input on this.

[geezer#99]

While you have the fuel line off, put the end in a litre jar and crank it over. Should fill the jar pronto if the fuel pump is good.
Disable the power to the dizzy though. You don’t want it to start when doing that.

[dmjlambert]

Proceed with care. Be careful not to cross thread or strip the threads on the fuel filter inlet as it screws into the carburetor. Car parts stores carry the fuel filter, but they do not carry replacement inlet gaskets. They used to until a few years ago. There are 2 possible sizes of the fuel filter inlet gasket. That gasket is an order-online kind of part now.

There are 2 possible sizes of the fuel filter, short and long.

You'll notice there is a spring behind the fuel filter. There are videos on youtube showing how to replace it, if you like.

I have read it is a good idea to replace the gasket every other fuel filter change, and replace the filter yearly, so that is what I do. If you find yourself tempted to tighten the fitting more to stop a leak, stop what you're doing and get a new gasket.

If you have a leak at the fuel line side of the inlet fitting, there are copper flare gaskets you can get to eliminate the need to over-tighten that. On-line order item as well.

[HO455]

It is hard for me to express how right dmjlambert is without sounding like a real a22. Stripped filter treads have to be one of the top 2 or 3 reasons Q-jets get replaced. It is easy to cross thread the filter nut if you are not paying close attention to what your doing.

[Steeveedee]

Indeed. I've seen dozens of these over the years. It's the same ham-handed guys who strip oil drain plugs.

[C4UC101969]

Originally Posted by dmjlambert

There are 2 possible sizes of the fuel filter inlet gasket. That gasket is an order-online kind of part now.

If you have a leak at the fuel line side of the inlet fitting, there are copper flare gaskets you can get to eliminate the need to over-tighten that. On-line order item as well.

Where can I get all these gaskets, I would like to change them if I am already opening it up to change the filter. Thank you for the suggestion as well.

[geezer#99]

He means these in the link.

https://www.amazon.com/Parker-Degree.../dp/B077NHZ98C

Look here for gaskets, filters etc.

https://quadrajetparts.com/

[C4UC101969]

Originally Posted by geezer#99

He means these in the link.

https://www.amazon.com/Parker-Degree.../dp/B077NHZ98C

Look here for gaskets, filters etc.

https://quadrajetparts.com/

Thanks, I just grabbed them off the Canadian amazon and surprisingly they were for once cheaper than on US amazon I was shocked to see that, haha

[geezer#99]

Do you have line wrenches?
Like this.

https://www.amazon.com/Craftsman-Met.../dp/B007KHESG8

They come in standard sizes too.
Best tool to use so you don’t round off the tubing nuts.

Canuck tire should have some.

[C4UC101969]

Originally Posted by geezer#99

Do you have line wrenches?
Like this.

https://www.amazon.com/Craftsman-Met.../dp/B007KHESG8

They come in standard sizes too.
Best tool to use so you don’t round off the tubing nuts.

Canuck tire should have some.

Yeah I got those.

[dmjlambert]

The flare gaskets I used were copper, not brass. So they are probably softer metal. I got them at Grainger. Part number 5WRW3.


I'm not clear about how to tell the difference between the 7/8 and 1 inch inlets and I have not seen a picture of them side by side to compare them. I have heard the gasket fits on each one differently.

[C4UC101969]

Originally Posted by dmjlambert

The flare gaskets I used were copper, not brass. So they are probably softer metal. I got them at Grainger. Part number 5WRW3.


I'm not clear about how to tell the difference between the 7/8 and 1 inch inlets and I have not seen a picture of them side by side to compare them. I have heard the gasket fits on each one differently.

Thank you, I'll open up mine and see the correct size that I need and will order a few of them indeed.

[72c20customcamper]

If the carb is off an 80s Camaro it is may be a 1 inch gas inlet like my 77, it uses a nylon flat gasket. I just replaced it yesterday tried to use the old one and it was weeping a little. Got them at advanced auto pack of 10 various sizes but 4 for were correct for my rochester.