78 620, L20B foreign matter in combustion chamber.

[datzenmike]

Cold starts should be overly rich, this is what the choke is for. The choke should force a fast idle if adjusted correctly. Once warmed the choke/fast idle should should be off.

 

 

Often a lean mixture adjustment is hidden by the choke being on. (extra rich) Once the choke is off the lean condition asserts itself and it runs badly. Mixture adjustment and jets changes must be done with the choke off, engine warmed up..

[Atikin9000]

any ideas for a half working clicking speedometer?

 

Is it the cable?

[datzenmike]

Most likely.

 

The inner drive cable, the part the turns, is a small diameter but very long coiled spring. If it should catch on the outer sheath the drive end in the transmission will keep turning and the spring will just store the energy. When the spring frees itself the energy is released and the needle will jump to catch up. A speedometer the jitters or jumps regularly is like this. Naturally if the cable cannot free itself the spring will simply twist and break.

 

Use vice-grips to loosen the transmission end of the cable and pull straight out. Have lots of cloths ready or a container to catch the cable in and keep it clean. Once free pull the inner cable out and collect it. Have a care as it's slithery and oily and hard to handle. If the cable is dry, lube with a graphite powder or molybdenum grease. Inspect the outer cable for kinks or damage from catching on something. In this case it may be better to just replace it.

 

When installing the inner cable, twist it (both ways) with fingers and confirm the speedometer is engaged and jumps then engage the transmission end and tighten the nut. The end has a ferule and only goes in one way.

 

[Atikin9000]

Most likely.

 

The inner drive cable, the part the turns, is a small diameter but very long coiled spring. If it should catch on the outer sheath the drive end in the transmission will keep turning and the spring will just store the energy. When the spring frees itself the energy is released and the needle will jump to catch up. A speedometer the jitters or jumps regularly is like this. Naturally if the cable cannot free itself the spring will simply twist and break.

 

Use vice-grips to loosen the transmission end of the cable and pull straight out. Have lots of cloths ready or a container to catch the cable in and keep it clean. Once free pull the inner cable out and collect it. Have a care as it's slithery and oily and hard to handle. If the cable is dry, lube with a graphite powder or molybdenum grease. Inspect the outer cable for kinks or damage from catching on something. In this case it may be better to just replace it.

 

When installing the inner cable, twist it (both ways) with fingers and confirm the speedometer is engaged and jumps then engage the transmission end and tighten the nut. The end has a ferule and only goes in one way.

 

 

Thanks mike, I’ll have a look behind the gauge as well.

[Atikin9000]

I’ve been replacing dead bulbs all over the truck, and there’s a few spots that still don’t work.

 

I’m not getting power to the license plate light, and pass side side marker in the rear. And the cabin light comes on only once and a while.

 

Any ideas? wiring seems whole and all connected, fuses all look good and everything else works.

[datzenmike]

If the other marker is working then power is getting there. License, L&R side markers and running tail lights are all from the same wire.So bad bulb, bad socket or poor ground.

 

The door switches get rusty. Push then in and out a few dozen times to polish the contacts. You might even use a butter knife and un-clip them from the body and clean the rust off.to get a good ground.

[Atikin9000]

So it’s been a little over a month since I’ve messed with the truck, and I’ve run into this issue.

 

 

Loosing oil level slowly and it smokes.

 

 

I used 5w-30, which I heard is a bit thin, but I’m doubting the oil weight will make this much or a difference.

 

 

Smoke smells of gas only but it’s clearly blue.

 

 

 

 

I’m thinking it’s gonna he rings since I didn’t adress the bottom end when I got the head rebuilt.

 

Really don’t want to tear it apart again.

[kelowg]

Running overly rich well put some unburnt fuel into oil and/or  wash the cylinders. Or stuck rings from lack of maintence. Might ck carb jetting.

[datzenmike]

First, never run 5w anything. Get something with more ZDDP in it like 15w40 Rotella or Delo400 and change to a WIX filter. See if that helps.

 Make sure you are not over filled with oil. When you change it be sure to put in exactly 4 qts (or what ever is recommended) and read the dip stick to confirm it's reading correctly.

 

Place newspaper under engine at night and check for oil leaks in morning.

 

 

Do a compression test. 120 or lower indicates a tired engine.... but not always.
 

[Atikin9000]

First, never run 5w anything. Get something with more ZDDP in it like 15w40 Rotella or Delo400 and change to a WIX filter. See if that helps.

 

Make sure you are not over filled with oil. When you change it be sure to put in exactly 4 qts (or what ever is recommended) and read the dip stick to confirm it's reading correctly.

 

Place newspaper under engine at night and check for oil leaks in morning.

 

 

Do a compression test. 120 or lower indicates a tired engine.... but not always.

 

I’ll give a heavier weight a try, I did over fill it the first time and I used about 4 1/2 quarts but it wasn’t by much and since then oil level has gone down a bit, maybe 1/4 of a quart to half. And the oil level registers about 3/4 of the way on the dipstick.

[wayno]

You cannot over fill the engine with oil, it will smoke real bad especially on the freeway, it will make a cloud that will eventually get you a ticket.

I know all this because I got in a hurry one day and put to much oil in(about 1/2 quart too much) as I was late and had to get moving, it started smoking when I entered the freeway, then around 5 miles from my house it started missing, I could not find my spark plug socket so I drove to the customers house with it missing, did the job and then borrowed a spark plug socket from him and cleaned #4 plug as that was the one missing, the customer asked how I knew it was number 4 and I told him that is the only one that made no difference when I pulled the spark plug wire while it was running, I drove home and emptied a half quart out and all was good.

I have had this happen before when I added to much oil, I try to be more careful and not over fill it these days as I don't move as fast anymore.

[Atikin9000]

So went out today to start the truck in a while, it has been running fine and dandy lately, but today it decided to either run on 3 1/2 cylinders again or I have a wicked missfire.

 

 

Continued to run like crap even after warming up for 10 minutes. (Cold starts usually sound rough, so that’s why I thought it might need to be warmed up), so it wasn’t the choke, it’s super dark so i haven’t had time to do major checks.

 

One thing is, it did is clear up once or twice for about 2 seconds and then returned to that 3 cylinder sound.

 

I’m thinking ignition related, as I don’t think it would be intermittent if it was mechanical.

 

 

Thoughts and suggestions appreciated.

[Atikin9000]

borrowed a spark plug socket from him and cleaned #4 plug as that was the one missing, the customer asked how I knew it was number 4 and I told him that is the only one that made no difference when I pulled the spark plug wire while it was running, I drove home and emptied a half quart out and all was good.

I have had this happen before when I added to much oil, I try to be more careful and not over fill it these days as I don't move as fast anymore.

Didn’t even think of doing this, giving this tomorrow when there is some light.

[datzenmike]

For the spark to properly jump the electrode gap, IT (the plug gap) has to look like the shortest easiest path to ground. This would mean that if the electrode is contaminated with gas or carbon the spark will run to ground through this. If the outside porcelain is oily dirty or cracked the spark will take this short cut. If the wire back to the distributor or to the coil or a nipple is damaged, spark can escape to the block or valve cover and to ground. If the distributor cap is dirty or wet on the inside or outside or carbon tracked or cracked, the spark will use this as an escape path. If the rotor is dirty, wet or damaged the spark can jump to another ground. If the coil tower under the nipple is dirty, wet, cracked or carbon tracked the spark will jump to the negative terminal or the coil's metal case and to ground.

 

Carbon tracking is a burnt path on an insulator's surface where a spark has jumped across it and left a trail. Once burned, the trail is blazed and arcing is more likely to continue. Often it will run normally and jump to ground sporadically. It depends which happens to be the easiest path to ground. Engine load, weather lots of things can affect this.

 

Here's just one example on the inside of a cap.

 

 

 

They are often not easy to find.

 

 

Try starting up your engine in a dark garage at night and look for telltale blue flashes on the wires and cap. Rev suddenly to increase the voltage needed to jump the plug gaps. This will only work on outside visible sparks.

.

[Atikin9000]

Thanks mike, I’ll do some checks tomorrow.

 

My carburetor runs very rich as well, I’m hoping I just fouled some spark plugs.

 

I can’t catch a break with this thing, and it’s breaking me down.

 

Really need some motivating words hahah.

[datzenmike]

Is it really running rich? How to know? Poor ignition will allow un-burnt gasses out the tail pipe.

 

Causes...

Idle? idle mix screw not set right

 

Choke on or not shutting off properly.

Wrong jets? secondary mixed with primary? Rebuilt with parts swapped around.

Carb flooding... look at sight glass.

 

1/ Fuel pressure too high

2/ Float set too high

3/ Needle valve stuck or dirt preventing it closing

[Atikin9000]

Is it really running rich? How to know? Poor ignition will allow un-burnt gasses out the tail pipe.

 

Causes...

Idle? idle mix screw not set right

 

Choke on or not shutting off properly.

Wrong jets? secondary mixed with primary? Rebuilt with parts swapped around.

Carb flooding... look at sight glass.

 

1/ Fuel pressure too high

2/ Float set too high

3/ Needle valve stuck or dirt preventing it closing

I have that weird weber, and I’ve got it set to the best of my ability but you can see black out of the exhaust pipe and it some times backfires black with fire after shutting off

[Atikin9000]

Pull the plugs and read them. This one of the best methods to see what is going on inside the cylinder. They should be light brown or tan, even creamy colored. Black dry and sooty would indicate a too rich condition and carbon is a conductor that will leak high voltage to ground causing a missfire. Black oily could be oil fouled on one or more plugs.

 

I found this from an older thread too. I’ll be able to find out more tomorrow, thanks again mike.

[flatcat19]

If it's dark outside, take a spray bottle filled with water. Spray your spark plug wires. Watch for arc.

[datzenmike]

I have that weird weber, and I’ve got it set to the best of my ability but you can see black out of the exhaust pipe and it some times backfires black with fire after shutting off

 

Well that ain't right. Borrow or find a stock carb and swap it on. Problem solved it's the weber.

[flatcat19]

Or...just spend the couple hundred bucks and get a new Weber from a reputable Weber dealer.

[datzenmike]

I've lost track after 22 pages

[flatcat19]

TL; DR:

 

 

Buy a new carb. Buy a new cap, rotor, wires, and plugs.

 

Quit with the band-aid shit to questionable parts.

 

 

 

Report back when running like a champ.

[Stoffregen Motorsports]

TL; DR:

 

 

Buy a new carb. Buy a new cap, rotor, wires, and plugs.

 

Quit with the band-aid shit to questionable parts.

 

 

 

Report back when running like a champ.

I think after all this I would bite the bullet and buy a new carb too. For all the headaches of not finding the problem, and one huge smoking gun (that weird carb) the $350 for the new carb seems like chump change.

[racerx]

Weird carb? Meaning fake weber? Empi Crap? If so, spend that 350 or so and get it running or else, a year from now u will be diagnosing still. If real weber adjust accordingly...go on Pierce manifold tech page.