Engine Surging Up Hill Only

[gstuck3]

I did search a but didn't find an answer. I have a 74 Jimmy, stock Q-Jet carb, TH350/350cid. It normally runs pretty good. It recently started to "surge" when going up hill. It did it last Thursday and again today. It surges, spits and sputters really bad, almost to the point of stall, and did stall once, but only when going up hill. It did it today while going 50 mph. When I got on level ground it started to run right again. When I got home shortly after, I let it idle a bit to make sure it would run. The exhaust smelled "funny" so I put my face to the tail pipe. It burned my nose and eyes.(lean?) Shortly after, it started to smell like it usually does (a little too rich). Any Ideas? I don't know very much about Carbs but I assume that is the problem. It did the same thing back in the summer but I thought it was vapor lock or something(120 deg. in the desert). It has a new fuel pump. I did drop the tank about three weeks ago to install my shackle flip.

George

 

[AV8]

My Suburban did that real bad, turned out it just needed the fuel filter changed.

 

[darkshadow]

sounds dumb but check your ATF level in your tranny.

if it is low you can get by fine, but up hill it starts to suck air, and make it surge and run like crap.

elemanate the easy stuff first

 

[SubYuman]

I concur

Fuel Filter!!!

 

[Jagmeister]

I had a very perplexing problem like that with my 350 SBC powered Jag. Drove me nuts but I finally tracked it down to the gasoline blend. Lived in Iowa at the time and the ethanol blend offered higher octane and was actually several cents cheaper per gallon than the plain stuff so that's what I always bought.

The Jag had a real problem dealing with all the engine heat from the 350 (not much airflow through the engine compartment) and in the summer I could not run the ethanol blend because it had a lower boiling point and just got too hot under the hood. That's probably not a likely problem with a K5 but the symptoms were exactly the same. It would stumble and nearly die when going uphill.

Definitely check the fuel filter as mentioned, it's the likely culprit. It is located inside the carb right at the fuel inlet. Remove the fuel supply line and you will see it.

You might check to make sure your fuel line is not passing too close to the exhaust manifold or other major heat source.

 

[gstuck3]

Someone else told me it could be the Float Needle sticking. Could that be it? The ATF level is good, or was a week ago, but I'll check it again. I changed the the fuel filter about 3000 miles ago when I replaced the fuel pump. However, I did let the tank run low for a while so I could drop it easier when I did the lift. It could have got some trash in the line. The line is not close to the engine any more. I moved it away from the block when I thought it was vapor locking in the Summer.

 

[Jagmeister]

Float needle... well... seems unlikely, but what if the float was partially "sunk" or not adjusted properly? That might do it.

What happens if you go to wide open throttle on the straight and level?

One other thought... How thick is the gasket/spacer between your carb and the intake manifold?

 

[dyeager535]

Mine acted very similar, typically going up hill at a fairly high rate of speed (60-70MPH) which increases the demand for fuel over flat ground cruise. Finally stalled on me one time, but once I got it started, it was the last time.

If you get it to stall on you again, coast off the road, don't try to restart it, pull your air cleaner, and hit the throttle. Watch the primaries to see if gas is shot in when you work the throttle. If you don't see any, then you've got a dry float bowl which is likely to be a float issue. A sunk float will provide too much fuel, so you'd still have fuel when you work the throttle.

Fuel filter should not be the cause if it's stock...the fuel filter in a Qjet unseats/bypasses if it stops flowing enough fuel, but you certainly couldn't hurt anything by checking to make sure that it's installed correctly, and replacing it if it's obviously been in there awhile.