Odd no start issue

[a Aron]

I have a 88 MMM with the g63b. Bone stock. From time to time the truck will just crank and not fire up. It will roll start though. It doesnt do it all the time and there isn't really a pattern. It does kind of smell like fuel when it does this. Any ideas? Is it just flooding out?
Also I cant give the truck more than 30-40% throttle. If i give it any more than that it falls on its face and blows black smoke. Think a diesel "rolling coal" . I have tuned the carb with a dwell meter and it didn't change much. So I had a tech at work tune it (I worked at mitsubishi at the time, he has been there 20+ years) and it ran pretty the same. I cannot find any vacuum leaks, I have cleaned the carb very thoroughly and it runs exactly the same. My next thought was to replace the 02 sensor, but I wanted to get opinions first. I am leaving for boot camp in just a couple weeks and I would like to get these issues sorted out before I leave so the truck doesn't give my dad any issues while I'm away.

[BradMph]

Is your cat clogged up? If it is throwing so much black suet out the exhaust like that and you can't give it too much pedal before it wants to die kind of make me think that the cat or EGR canals are clogged. On earlier G63B motors, the recirculating goes through intake through a sub valve near bottom of a stock carb and then through the head into the #4 exhaust port where it dumps. This canal can get so clogged up by carbon that if it was a heart valve it would have a heart attack. One way to clean out the canal in the head is with a coat hanger, but this usually requires removing the intake to clean or inspect. If you live in a state that no longer needs to inspect your truck, maybe a weber conversion is the best bet. It can save you money and give you a lot more power in long run and get rid of that 28 year old Mikuni. You can clean these all you want, but it still isn't going to be right.

Another thing could be the timing. How long has a belt been replaced, could it of jumped a tooth. They usually last 60k-80k before they need replacing. One other item might be distributor advance, but if it has vacuum, it should be ok. One way to check is remove vacuum tube and suck on the end that was connected to carb and watch the action of distributor. You should see the weights move under the cap.

What you have is also a hard item to diagnose until it finally takes a crap and stops completely. But, knowing the age of the truck it could be a few things. The cat has many little holes that the gases go through on the way out the exhaust. They are smaller then the size of a pencil and could restrict the exhaust causing it to be constipated in other words. Your truck pushing black smoke is raw fuel, so something isn't right. Check plugs and see how they look. This will tell you a lot about the internal engine condition along with a compression test.

Check your compression also, does it burn oil. How many miles are on it? we already know how many years are on it, lol.

[camoit]

Bad coil. timing correct, choke not opening fully.

[a Aron]

It has about 190k on it. The timing belt has 6-8k miles on it, and I checked the timing and it is correct. If the cat is plugged, can I just delete it? I think I have read that you need it with the stock carb.
I will pull my spark plugs and see what they look like. It has a new coil on it as well so I doubt that is the issue but i wont rule it out just yet.

[pennyman1]

check the hoses going into the box on the drivers fender - bet there are cracks or holes in the hoses - that will cause the fall flat throttle under load issue.

[mini max]

I am having the same type of issues. Hover my truck is a 1990 3.0L, ecu clicks, fuel pump turns on, engine will roll over and sputter, then turn and turn. Doe it every month or two. Runs fine or weeks then no start. seems to do it more when there is moisture I.e rain, puddles.
Any thoughts would be more than helpful and appreciated. Than you!
Truck is currently not starting in a parking lot with restricted access. trying to avoid having to tow it out because it will be a major headache