Truck feeling like it is under load?

[philo_beddoe]

Ok, will look into it. How about a pic??

[Eastonfrench]

Hey guys. Still chasing an acceleration issue. as long as i am easy on it, my truck runs great, however when I apply the accelerator too quickly the motor bogs down, and very rarely, it dies. It always starts right back up and my plugs arent wet or black so i dont think it is flooding. I think its the opposite: I think its getting too much air too quickly, resulting in a mixture too lean to run with much power. I have a new fuel filter, and new pump, so I find it hard to believe it isn't getting fuel enough, but I could be wrong.

How can I decrease the air to see if my hypothesis is correct? I know how to tighten the secondary air valve tension. Would that be where to start?

Am I headed in the wrong direction completely?
I've rebuilt the car. New accelerator pump. Fuel  Pump. Checked the vacuum and mechanical advance. I really feel like my fuel:air ratio is too lean on acceleration.

[SquareBodyBoy76]

I had the same issue on my '87 R2500. Check your intake gasket. You may have a small leak somewhere in it. Start the truck and let it idle, take a can of starter fluid or PB blaster and spray the line separating the intake from the head. If you use starter fluid, you'll know when you find a leak because the engine will pick up, whereas if you use PB blaster your engine will bog down. I did that and found a leak and replaced my gasket and it was better after that but I still needed a fuel filter but now it runs better than ever with no bog down. Hope this helps.

[Eastonfrench]

Square body- Thanks for the input! My dad tried that trick as well with no luck. But I may give it another try! The intake to motor gasket is the only one I haven't replaced so that could very well be it!
Anyone else have other things to try while I'm in there?

[Chisholmcody]

Also check all of your vacuum hoses with the same method stated above for vacuum leaks


Sent from my iPhone using Tapatalk

[zieg85]

Could be a bunch of things going on.  Timing at the point of acceleration, your accelerator pump on the carb, the secondaries on a quadrajet spring doesn't have enough tension and opens too soon, ( I had that problem on my race car), or too small of jets in the carb for the engine size (been there done that)

[bd]

Do the symptoms occur both cold and operating temp?

Is the hesitation instantaneous with throttle opening, or does it begin to accelerate for a quarter second before falling on its face?  Looking down the carburetor throat with a good flashlight and the engine not running, is there a good strong well defined stream of fuel with throttle opening, without any lag or dribbling?  Does the accelerator pump fully return to its up position with throttle closing and closely follow (remain in constant contact with) the pump lever?  Did you verify unhindered vertical movement of the primary power piston?  Did you check the fuel bowl cover (air horn) for flatness with a straight edge when you had it off?  What is the carburetor number and where did you set the float level?

[Eastonfrench]

Rich- It could be the secondary air valve spring is too loose, I may give that a try since its an easy, reversible solution. Do you, or anyone, have a way to tell how tight is tight enough? the way I did it was to (using a dental mirror) back the spring all the way off, and then slowly turn it until the tang on the spring just barely came into contact with the catch on the air valve, so that there is basically no tension when the valve is shut, but tension is applied the second it begins to open. Is that not correct?

bd- The hesitation is instantaneous.
Fuel stream appears to be fine.
 Accelerator pump is brand new, and quickly returns to its relaxed position after use.
Power piston is clean and has unhindered movement.
 I did not check the air horn for straightness.
Though I don't have the carb number on me, I looked it up and can assure you the float level was set to specs.

[bd]

Do you, or anyone, have a way to tell how tight is tight enough? the way I did it was to (using a dental mirror) back the spring all the way off, and then slowly turn it until the tang on the spring just barely came into contact with the catch on the air valve, so that there is basically no tension when the valve is shut, but tension is applied the second it begins to open. Is that not correct?

You set the air valve too loose.  There is a precise adjustment based on the carburetor number.  Instructions should have been packaged with the kit.  Post the carb number.

[Eastonfrench]

I was mistaken I did not simply turn it until contact. I did that, and then turned it in, but I am not sure how much. Maybe a full turn? I dont remember. How far was I supposed to? I could't find any concrete information regarding the amount of tension I was to put on the thing



The Carbuerator is a Rochester Quadrajet the info is

17080290
2049CYH

[bd]

From the 1980 Service Manual Section 6C4, M4MC Model Carburetors...

QuadraJet 17080290

• Float Level =  15/32"
  
  
• Pump Adj =  9/32",  inner hole
  
  
• Secondary Lockout =  0.015"
  
  
• Air Valve Spring Adj =  7/8 turn past closing
  

[jg1977c20]

def sounds like your secondaries are opening too soon -

[Eastonfrench]

Thanks gentlemen. I will give it a try and be back with the results.

[ScottD]

I had a similar issue with my 85.  I have a 350 with the stock quadrajet and the truck idled great, but had serious issues bogging out, shifting, basically ran like crap under load.  After changing the fuel filter and the vacuum lines, with no positive results I decided to buy a new carb. Since the motor is still basically stock I decided to try a rebuilt quadrajet from National Carburetor.  Price was $175 plus shipping.   Took all of 30 minutes to install and holy crap it was like driving a brand new truck.  I had fought that carb for 3 years and I'm just kicking myself because if I would have know that $175 could get you this much return I would have done it day one.  The carb looked brand new and the customer service was excellent.  Trust me, the results were amazing.   So, if you like me and using it for a daily driver now, but potentially looking to upgrade later, this is the way to go.  I decided that when I'm ready to turn the heat up, I will probably buy a different carb and intake, but for now I'm extremely satisfied with the performance and mileage that it provides. 

[VileZambonie]

I would ensure you don't have any kinked fuel lines or rubber hoses first before you go crazy. Check by the tank and going up to the carburetor first. Make sure you are running rigid lines