350 with Quadrajet won't idle right. (1 Viewer)

[bikersmurf]

Last time I drove the 40, 2 weeks ago, it was running like a top. Filled up both tanks with gas, and gave it a good highway run. Even managed 17 mpg (US) on the highway.

Today, if seemed to require choke to keep it running even after warming it up. It sounds like a tractor at the fair at idle. Off idle, it seems to run ok, and it seems to have normal power.

I've tried to adjust idle mixture with no change.

Pouring a bit of liquid fuel system cleaner down the throat of the carb makes it run normal. At least until it gets too much and stats to stumble.


Any thoughts?
Bad gas?

I've tried the gas in both tanks,
The plugs were new before the last trip (about 3 weeks ago)

Could the Idle jets be plugged?

 

[RWBeringer4x4]

My first guess when my truck sits for a couple weeks then gets ornery is crud buildup somewhere.

When was the last time you cleaned the system? I'm running basically the exact same setup - PO had the idle set to about 1500RPM because it would die below that. Ran 2 tanks of of Chevron Techron through it, changed out the fuel filters, and was able to drop the idle down to about 850RPM, fires up nice, idles smooth almost immediately on warm days. We will see what happens as the temperature drops.

Only other thing I can think of is timing - what type of dizzy are you running? Something might have slipped causing a bad idle that's not as apparent when you're giving it gas.

PS - I would LOVE to know how you're getting 17MPG from your engine. I'm running a stock Gen1 350 targetmaster with a Quadrajet and HEI and the best I can get is about 8City/12HWY - and I'm not even dragging around 20-something extra gallons of fuel. What rear gears are you running? 3.73's or 4.11's?

 

[warpdriv]

Had a problem and I ended up being some stuff in the idle circuit. Pulled the idle screws, blew some low pressure air in there to dislodge the stuff, put them back in, started it, revved it and put my hand over the carb to choke it to suck the stuff out, and it ran great after that. HTH

 

[bikersmurf]

Dissy is the stock points distributor, with a Crane cams points conversion, lighter springs, and Acell adjustable vacuum advance. Got the carb from a friend, it's off a somewhat newer V6 Chevy, but I don't even know what year. Short dual 2" exhaust, Rams horns, Wolverine Blue racer RV cam, 3.70 gears, 33x10.50 BFG ATs. Motor is a Sept 69, 350 from a Bel Aire. Stock was 250 hp, now with dual exhaust, cam, and carb, I believe it has closer to 300 hp. Compression was around 195 across the board, last time I checked.

Truck weighs 4700 lbs.

Distributor has been fiddled with for years to get it to run well on regular gas.

17 mpg was on a straight highway run from Anacortes Washington to Vancouver BC at a fairly constant speed between 50-55 mph. I usually get 13-16, so the 17 somewhat of a surprise to me.

With 3.70 gears and 33s, 50 mph is about 2000 rpm. The motor seems very happy there.

 

[RWBeringer4x4]

Ah, I'm running 4.11's and 31's. 55mph sits around 2700 RPM. Have never checked compression either - only had the truck a couple months, and I have plenty of bigger fish to fry. Engine is running good after some fooling - that's good enough for me for now!

Sorry I'm not of more help with your issue but love the truck! I'd start with cleaning the fuel system, then look to the carb and fuel pump. Too bad you're on the other side of the country, sounds like we (almost) have twins!

 

[bikersmurf]

Had a problem and I ended up being some stuff in the idle circuit. Pulled the idle screws, blew some low pressure air in there to dislodge the stuff, put them back in, started it, revved it and put my hand over the carb to choke it to suck the stuff out, and it ran great after that. HTH

I'll have to give that a try. Sounds like a good step before pulling the carb to rebuild it.

I may also pour in some gas ling antifreeze... It's acting like it has got some moisture in it. Although I've not had this problem before even after sitting for months with an almost empty tank. (both tanks are almost full ATM)

 

[bikersmurf]

Ah, I'm running 4.11's and 31's. 55mph sits around 2700 RPM. Have never checked compression either - only had the truck a couple months, and I have plenty of bigger fish to fry. Engine is running good after some fooling - that's good enough for me for now!

Sorry I'm not of more help with your issue but love the truck! I'd start with cleaning the fuel system, then look to the carb and fuel pump. Too bad you're on the other side of the country, sounds like we (almost) have twins!

Mine is a July 74, I ran 31s and 4.11s for more than a decade. 33s are very nice, and about a 15% overdrive.

I may also have some plug fouling... A couple of them had some evedence of oil fouling before I changed them. Which is the down side of a 42 year old motor.

 

[POTATO LAUNCHER]

Fuel Filter in Carb Housing?

Have you checked filter behind the inlet? Might have gotten some bad gas and it plugged it and is restricting good fuel flow.
I had a similar problem when I had the QJET installed after I converted to SBC. Turned out to be the inlet filter and a bad base gasket. Doubt timing has changed, sure sounds fuel related to me.

 

[bikersmurf]

I agree that it is/was fuel related. I don't think I've got that filter anymore.

The problem seems to have resolved itself for the time being. If the problem recurs, I've got some ideas of where to continue looking.

Now I just need to find where I set down the mixture adjustment tool.

 

[Pin_Head]

Besides the idle mix, you also need to adjust the idle speed if it won't idle.

If turning the idle mix screw has no effect and it will only idle at high speed, you may have other problems, like a vacuum leak.

If it still won't idle, get Cliff Ruggles quadrajet book.

 

[warpdriv]

I'll have to give that a try. Sounds like a good step before pulling the carb to rebuild it.

I may also pour in some gas ling antifreeze... It's acting like it has got some moisture in it. Although I've not had this problem before even after sitting for months with an almost empty tank. (both tanks are almost full ATM)

Forgot to mention to count the number turns of the screw when taking them out so you can screw them back in the same number.

 

[srgould41]

I would so love to get 17MPG, or even 15. My 305 w/ Qjet, 700R4, 4.11's and 33's gets 12 always. Highway, wheeling, doesn't seem to matter.