76 k5 running rough with edelbrock 1406

[gethoht]

I have a 1976 K5 Blazer that I use as my plow truck for my mountain driveway. It's a sb350 with an edelbrock 1406 and a th350. I am having issues with it running rough. If it sits for a while it will start right up but won't idle well, i have to keep feathering the throttle to keep it running. If I just let it stall the only way I can get it to start again is floor the throttle and keep turning the motor over until it finally catches. It will start really rough and if I let off full throttle it will stall again, I have to keep it full throttle until it gets running smoothly. After it's running smoothly it will run for probably a minute or two until I have to feather the throttle to keep it running smooth. I have a fram inline filter and the filter definitely has fuel running through it. I've just replaced the fuel filter for the hell of it, and I replaced the fuel pump this summer. It's jetted for altitude(I'm at 9200 ft.) and I replaced the accelerator pump in the carb when I first got it as it seemed to stick. I've done a super preliminary vacuum check and can't find an obvious leak though I haven't used a vacuum testing kit to see what level it's at. The timing is a little advanced for altitude as well. I also replaced the plugs and wires last year.

I'm fresh out of ideas and am leaning towards taking the carb off to check float levels and make sure a jet isn't clogged or a needle isn't sticking.

Does anyone have any suggestions on how to proceed with troubleshooting? The problem seems like a fuel problem to me which would point me towards the carb but maybe there is something that I'm overlooking? Is there some trick to getting the 1406 to run right or am I looking in the wrong place?

 

[gethoht]

fuel pressure regulator perhaps?

I keep reading that the edelbrock 1406 likes low fuel pressure, something like 4.5 to 6.0 psi. I did replace the fuel pump this summer with some cheapo oreilly pump. Some people even recommend using edelbrock fuel pumps ($125!!!) because they don't pump over 6psi. Some suggest using a fuel pressure regulator but it seems like it would blow out the diaphragm sooner than later.

Anyone have experience with these carbs and has run into fuel pressure issues? Also how do you test fuel pressure. Most of the tester's I see are for fuel injected systems and have a schrader valve setup.

 

[paratrooper307]

Too high fuel pressure can be a problem for carbs, but it's likely your problem is something simpler, especially if this problem just appeared. If the pump were the issue it probably would have manifested as soon as you installed the pump. If you are worried about pressure, check and see what your pump is rated for. Many non-stock type pumps are rated for higher pressure and require a fuel pressure regulator for stock/street applications.

Rough idle, requiring throttle to idle, and dying is most often a vacuum leak. Even though you already looked this over, it wouldn't hurt to check again. I like to use a vacuum gauge and some starter fluid to pinpoint the problem. A vacuum gauge is worth its weight in gold for diagnosing a variety of problems, from leaking valves to bad mixture, incorrect timing, etc.

Even though you replaced your wires and plugs, check them for any problems. Never hurts to check timing again, either. I once saw a bad distributor hold-down bolt that allowed the distributor to shift and go way out of time. I had a bad plug wire that caused a misfire and rough idle. Take a look at the plugs for signs of a rich/lean condition. This may point you towards carburetor problems such as improperly adjusted mixture or a malfunctioning choke.


Best of luck with your troubleshooting!

 

[Magikal]

i run a 1406 also and the float level is temperamental. sounds like it is getting too much gas to me. Clue's you mentioned are

"If I just let it stall the only way I can get it to start again is floor the throttle and keep turning the motor over until it finally catches"
and
"I have to keep it full throttle until it gets running smoothly"

As mentioned, a vacuum gauge is invaluable. Personally, I would get it running and start spraying around the motor with starting fluid to find any vacuum leaks. Second, i would start it at night and pop the hood. any bad wires will be visible in the dark.

Its a long shot but blockage in the exhaust would give similar symptoms.