Engine Performance problem
1981 Other Mitsubishi Models 4 cyl Two Wheel Drive Manual 200k+ miles
Was hoping you might have some ideas. I ´m a self taught hobby mechanic. I ´ve been travelling through some tough conditions in south america through the atacama desert, the los andes mountains to the amazon and beyond - more than 10,000kms. My vehicle for the adventure is a mitsubishi l100, which is very similar to the minicab models - its a chile/argentina specific fabrication I believe.
Its 2cyl 550cc!
OK. On my travels I have more or less worked on everything but now I ´m stumped.
The latest leg of my journey, it drives, but its rough and it wouldnt idle. Spark plug colour was perfect. I checked points and timing. I didnt have a timing light so I was doing it static styles but after having no results I lost faith in the static method and imported a timing light which showed it was running advanced by about 25deg. So I checked the points gap again, then retimed to just under 10deg. The built in time scale is 10 to -10 so I assume it needs to be in the usual 7-10 deg adv range. One mechanic told me to set it 20 or so. But I believe this was because we were at extreme altitude (the highest city in the world infact - bolivia).
I have rebuilt the carb numerous times. I believe it to be absolutely clean but I ´m stumped on the air fuel mixture screws. There are two (fuel and air pressumably - idle is another screw). I ´ve mucked around with them and can now achieve idle, but its way high. I ´m conscious of not applying too much idle and having a resulting problem with the mixture. There is currently hesitation on accel. Currently, after acceleration it will idle nicely, v high but nicely for about 10seconds and then drop further. If the idle is set lower the engine dies.
the other problem is its a little rough. A little misfire here and there, enough to be upsetting a 2cyl. I havent been able to sort it out in months of travelling (origially wasnt like this). Staring into the timing light it seemed ALMOST perfectly consistent (my way of trying to detect if its an ignition problem!).
On acceleration and high rpms the roughness is barely detectable - if at all.
I ´ve sprayed in search of a vacuum leak - nothing of note. Valves are set and even (but I dont know the official gap). I took an average of all, not tight, not flapping around noisily). I have had previous problems with the distributor. The metal bushing for the dist. Axel was sloppy causing the rotor to loose more than occasional proximity for a spark. When replaced, I had a normal idle but it was still a little rough.
There are leaks in the exhaust around the silencer chamber.
my current thoughts are the problem may lie with the carb, ignition system or lately I ´ve been thinking about compression. Haha! I think thats everything!
my plan now is to investigate the ignition system & distributor (i have replacements for all - not the dist.), Then on monday go in for a compression test.
Its helped me a lot just writing this down. I think I might have two seperate problems.
If you have any ideas that would be great. What would really help is if there is a way I can rule out the carb?
Saturday, July 3rd, 2010 AT 12:32 PM