[C10Mike]

So recently i've started to think that my truck has been running on 7 cylinders instead of 8. For some reason ever since it started getting warmer and the weather has been ****y/rainy. My truck idles real low around 600rpms. I had my truck set to idle at around 808ish rpms and the idle wasn't smooth the hood would shake and stuff, but now that its idling at like 600rpm the idle is real smooth the truck doesn't shake, i just get some clutch rattle. BUT after i beat on the truck a little once its at operating temperature the truck will sometimes rev its self up.. like a little blip.
I dont know how to describe it. it would be idling at 600 and then for a split second or if im coasting in neutral it would blip the throttle to like 700 for a split second. Any idea as to what it can be? i have a HEI distributor, and i think im gonna replace my spark plugs and get a new cap and rotor.

So today I went out and started seeing if i was getting spark to all cylinders, I hooked up the timing light to each wire and it would flash. So then i took off the plug wire for Cylinder 8, i did not notice a difference in idle, so obivously this cylinder was not firing. So i took out the plug to see if it would spark, and it did. But the spark was a redish color so i cleaned it and opened the gap a tad more and the spark turned a good blue/white. Put it back in, but it did not change a thing. So then i started removing more plug wires to see which cylinders were firing. So turns out that when i pulled the wires off spark plugs 2,8,3,5 There was no difference in idle. Odd. I then took a spray bottle and started spraying water on my headers. On the primaries for cylinders 1,7,4,6 the water evaporated instantly. on the remaining cylinders it took a while for the water to fully evaporate. Im sort of stumped, the truck seems too have too much power for it to only run on like 4 cylinders you know?

Motor is a stock 350 with a small small small cam.
im going to buy new spark plugs tomorrow and a compression tester.
spark plug gap should be around .45 for a sbc right?

Edit: i printed out one of those pictures that shows which wire goes to where.. and i compared it my setup and it doesn't match up..

[LATECH]

cylinder 2,8,3 +5 all share the same side of the intake manifold.They all could be running lean due to a sticking intake valve on any one of the 4 cylinders.or broken valve springs. Could also be a big vacuum leak on that side also, may be hidden, like between the intake and head on the inside of the crankcase rather than to the outside.
could also be one side of the carb is just flat plugged up.Plugged booster siphon... etc .
You are wise to start with a compression test.

[C10Mike]

Originally Posted by latech

cylinder 2,8,3 +5 all share the same side of the intake manifold.They all could be running lean due to a sticking intake valve on any one of the 4 cylinders.or broken valve springs. Could also be a big vacuum leak on that side also, may be hidden, like between the intake and head on the inside of the crankcase rather than to the outside.
could also be one side of the carb is just flat plugged up.Plugged booster siphon... etc .
You are wise to start with a compression test.

The one thing that confuses me though, is i dont feel any loss in power. It still spins in first, and at the bottom of second gear. I'll pick up new spark plugs and a compression tester tomorrow from summit racing.

I also dont think it runs lean. I smell too much gas when it idles.

[Ron Golden]

I think one barrel of the carb isn't getting fuel at idle.

Ron

[C10Mike]

Originally Posted by Ron Golden

I think one barrel of the carb isn't getting fuel at idle.

Ron

Thats a possibility, i bought it used off a neighbor for 60$ I dont know anything about carbs though lol.

[EOD Guy]

Is the carb an Edelbrock 600 cfm?

[C10Mike]

Originally Posted by EOD Guy

Is the carb an Edelbrock 600 cfm?

Im not sure its either a 600cfm or 650cfm

[EOD Guy]

left hand side of the base (looking from front bummper) 1406 is 600 cfm.....my opinion JUNK! I had one same issue cept mine would rev to full throttle and spin the tires finialy got tired of it and purchased the Thunder 650 CFM...... supposed to be a good one we'll see........ waiting on my new fuel pump.