74 620 l18 engine bogging and backfiring

[Nas]

So while all this was going on ( http://community.ratsun.net/topic/18370-620-wont-shift/ ),

My truck was starting to bog and back fire.

It has just been fully tuned, and everything seemed in place under the hood, so I was really shocked.

It was raining, dark out, I didnt have a flash light or tools on me, and it was a lil too late to be calling friends for advice, so I just said fuck it and started walking home.

I needed to clear my head and think anyway.

 

But tomorrow, I have to face the music.

 

Anyone have any ideas of things I should check that might be causing this?

 

Stock l18.

Stock carb.

new plugs, wires, filters, etc.

[freaky510]

are your points burned up??

[Nas]

are your points burned up??

 

I'll check those. Thanks!

 

Btw...the "back firing" I mentioned didnt sound like other cars Ive heard back firing....shotgun like.

This sounded more like a bottle of champagne popping off, or the sound of a potato gun, if that makes sense.

[datsunaholic]

Sounds like backfiring through the carb, which is often caused by the points not firing correctly. Either because the cam rider wore down (and the "modern" points I've seen seem to last about 3000 miles before the rub block wears off- I could get 30-40,000 miles on the old OEM style) or because the dist shaft bushings finally wore out causing wobble, which fires the points almost randomly. When they finally do fire, you get that "thwump" sound out the intake and a huge stutter.

 

Oh, and a wet dist cap will do that too, moisture gets in and it causes arcs, which fires the wrong plugs out of sequence or just arcs to the dist body.

[datzenmike]

Makes sense to me. Sounds like a carb backfire. The air filter mutes it.

 

Trouble with all new stuff is that a bad part could have been installed or installed incorrectly. You could start by checking that but bad ignition usually backfires... out the tail pipe.

 

I don't think electrical. I suspect the carb is running lean. Was it near freezing? Or close to freezing rain? If so it may have been carb icing, in which case it will run fine the next day.

[Nas]

Awesome info, guys.

No, it wasnt freezing cold. Its been staying around 50 degrees in seattle lately.

But there is a chance that there was moisture in there because I had the hood up and was looking around earlier in the day, plus its been raining non stop.

[datzenmike]

For any moisture that might have gotten into the gas or condensation in the tank. Go to Wall Mart paint dept. and buy a liter/quart of methyl hydrate. It's the main ingredient in gas line anti freeze. Except that for $350 you get 10 doses instead of one or two of those little plastic containers. Every time you fill up just squirt a 1/2 cup in the tank. Gas and water won't mix, but methyl hydrate will mix with both and will dilute and carry the water through the carb and 'burn' it and get rid of it.