Rebuild ???

What is the correct process for a rebuild?

Ooooh. A standard overhaul or performance? A comprehensive rebuild requires stripping down to the bare block and cylinder head, hot tanking both and a full inspection to ensure they are viable for reconditioning. The crank and cam need to have their journals inspected and a course of action for reconditioning as well (a light linish VS machining or replacing). A good machine shop will drill out the oil gallery plugs in the crank and supply grub screws to seal them back up as machining debris can get trapped in the galleries and destroy a new bearing in seconds on start up. IMO a cylinder head should always have the valve stems checked and a 3 way valve seat cut performed. If you have got the time, tidy up your own ports before taking the head in for work. The flywheel should be refaced as well or replaced (you'd be surprised how bad a flywheel can end up looking). The oil pump should be checked and a new water pump, thermostat, hoses and belts should be mandatory if you're going to do it right. Machine work costs money - if you can get the shop to supply all the internals and you assemble it yourself you will definitely save some cash. The 4G63 has some quirks to it. Look up ways to improve the life of the engine (upgrading the oil pump and derestricting oil galleries and oil returns in the head make a difference - most oiling failures take place in the forward half of the block and the earlier heads were prone to catastrophic damage from oil deprivation). Anything past that is in the realm of a performance build. High comp pistons, lightened rods, custom cranks and cams - these are serious coin.

I would call it standard overhaul. Its got 111K+ miles on it. I blew the head a few years ago and replaced it with a rebuilt exchange but since then it drinks gas like water and blows carbon out the tailpipe. Less than 200 miles on a 15gal+ tank. I wonder if I should rebuild the head anyway? The water pump is new since the overheat as is rad and belts but of course I'll go with new belts when I do it. I just want to have an idea I still need to use it for projects I hope to get done with the main part by august. How do ya know a machine shop is good? I do most of my own work because you can't trust people around here to charge honest prices or do honest work.
What does get the shop to supply all the internals mean?

Black smoke sounds like a bad carb setting. Floats sticking or Choke partially closed. If it is a Mikuni carb, it's time to upgrade to a weber and you will be much happier. No black smoke or gas sucking. Do a compression test also. These trucks don't have a problem doing 300k miles before rebuild. Try not to spend money unnecessary if you can. If your losing oil at all, valve guide seals can fix 90% of that.

Its not black smoke just carbon particles that leave a mark on the cement. It is a real Weber but I think it needs professional service or just replaced as I have rebuilt it many times with and without guidance to no avail. Compression test sounds right. I have come to suspect I did more than just blow the head gasket when it overheated even though the cylinders looked OK when I replaced it. Maybe I screwed up the balancer belt? maybe maybe maybe ?? :) It gets the job done it just seems a waste to be so young in miles and running so inefficiently.

Give it an oil flush, and try to tune it up. Hopefully if you have an overfuelling fault will make itself obvious. I would tend to think you are getting condensation in the exhaust (water). If it's a lot check your plugs, they normally indicate if you have a cylinder head crack/issue. It might be cold start condensation which normally indicates a healthy engine and tune :shrug: Dead valve stem seals are the biggest cause of oil consumption. If you have to do valve stem seals, give the head a once over. If you have overheated it be prepared to spend some cash sorting it out. If you can find a shop that will put it through an oven and press it straight, use them.

*if you are going to run a compression test, can you do an experiment for me? I have a theory that performing an oil flush will improve compression by breaking some of the build up in the piston ring grooves. Take compression numbers before and after the oil flush and let us know what you find. :thumbup:

I did the diesel oil flush last year. It was blowing carbon before that too. The CAT is hollow and there isn o emissions stuff on it, the last guy took it off. The head is new rebuilt within the last 1000 miles. When I blew it I just went ahead and bought the reconditioned head and got new bolts from Mitsubishi. It would be nice if there is something simple but you guys have helped me with rebuilding the carb and farting with the Distributor enough that I think the problem must be deeper or beyond my ability to see.
There are no signs of water in the oil. There is always a puddle of gas in the intake mani when I take the carb off. The cylinders looked good and felt smooth when I replaced the head. I saw no signs of cracks. ??????? I've got new pos battery cable and the link in the ground from frame to block that is apparently missing. and new wires (NGK) cap and rotor but with brass contacts. I don't want to install them unless I can figure out what the problem is. The plugs just don't look bad when I pulled them last year. ???? Could the distributor be causing this?

Will it spit wet carbon after you've got it to full temp and driven it? I would still tend to think the engine is fine and it's only condensation. Check to see your choke mechanism is fully opening as well. The Weber is a less restrictive carb than the Mikuni and maybe you need to have a less restrictive exhaust system as well to match the flow (I have looked up the carbon phenomenon and all indicate that this is a normal occurrence or may be a sign of a partially closed choke or restriction in the exhaust)

The Choke is open when I have to start it with the air cleaner off. The CAT is clear I can see through it and the pipe from it back is new 2". Any restriction would have to be in the exhaust manifold. Could the rebuilt head be the problem? Never checked to see if it spit carbon after it was up to temp. It's generally after It sat for a week or more and I start that it does it.

If you are experiencing cold weather you will get a fair amount of moisture in the air on start up. Enough to cause the carbon spitting. Also the moisture in the air will condense on any surface it can come in contact with like the element in your air filter - it will literally pull droplets of water straight through it and down the throat of the carb.

No condensation in the air cleaner. This happens in all weather hot or cold.

Could it be the head?

I don't know :shrug: My initial search indicated that the carbon spitting you are experiencing is normal. I'll give you a theory - the exhaust system was fouled before the head went out. The exhaust was lined with carbon and after you went through the head and put it back together it began running cleaner (may even be from the cat being gutted and reinstalled). The moisture in the exhaust gases is getting contaminated by the carbon and it's slowly being purged out.

Thakns Geez. I have to haul wood to build a couple things with it in the nest few months but as soon as i can I will try to work on it.

Well I looked at the choke this morning and when I loosened it I was able to open it more so I did. It started right away and I don't see a streak out behind it. So you were probably right the first time on the carbon Geez. Gas mileage is still awful. Starting with zero on a full tank I have 77 miles on the trip odo and its down below half tank. It was never great but since the new head its been awful. I had a 73 caprice that got better mileage than this! :)

The jets might be clogged up. You can try blasting it with carb cleaner and performing a 'purge'. With the air filter off and the engine running, cup your hand over the throat of the carb and try to starve it of air (don't let the engine stall and die completely - and don't stick your face over it either...safety first). The sudden increase in internal vacuum sometimes is enough to force debris in the jets to come loose and clear themselves. If the jets are fouled it prevents adequate fuel atomisation which won't cause it to run rich by itself but won't burn clean either.

This carb is old and it has oddball jets. I forget what the are right now but two of them are identical and they are supposed to be different. I mentioned it in the thread Pennyman and others including you I think, helped me rebuild it. I also think the thing was seriously abused before me and I may have screwed it up too since I had no idea I had no idea what I was doing when I first rebuilt it on my own. I may have to just bite the bullet and get a new one with a brass float. If that fixes things with the mileage I'll be over joyed.

Methinks it is time your retired this junk carb and got another one. As long as the unit you buy is complete, the auto choke + secondary throttle vac actuator appears to be functioning and the throttle shafts aren't frozen or have excessive play it is a better starting point for a rebuild. Do a basic '3 part' breakdown of it - fuel bowl/top cover and auto choke: carb body/venturis: throttle plate. Work over a tray, use a piece of cardboard as a template so you can keep track of what screws came from where and keep the high risk components in a zip lock bag (fuel bowl float and pin, brass float and ball bearing, enrichment pump spring etc) Make sure you give each of the individual parts a thorough clean with carb cleaner and compressed air (if you have access to a compressor) Don't pull it apart right down to air bleed jets and disassembling the auto choke mechanism unless you have to. Being patient and observant will go a long way.

*tip for disassembly - give the whole carb a spray of WD40 and allow it to soak. Wipe off the excess. Then as you remove all the screws and disassemble the carb, place the screwdriver tip into the screw heads and give the handle of the screwdriver a tap with a hammer. This will 'break' the threads and make it easier to undo the screws. The number of times you will experience a stripped screw head will decrease (EVERYBODY has destroyed a screw or 2 taking these things apart...)