Re: Case 448 project tractor...
I just got this project tractor running, but no matter what I do, I CANNOT get it to run right. It's starting to drive me nuts!
First, I'll list whats been done, then I'll describe what its doing.
WHATS BEEN DONE:
Engine: Onan B48M -- looked pretty good, so thought I would try to get it running rather than rebuild it right away.
Compression: 130 on drivers side, 105 on passengers side.
Valves: Valve job done two weeks ago, valve lash set.
Carbeurator: Newer style "DD" series, with diaphram type fuel pump on front side. Rebuilt last week, with complete "dd deluxe" kit -- including new fuel pump diaphram. Carb body not soaked.
Points/Condensor -- both replaced last week. Point gap lightly sanded, cleaned with brake cleaner, gap set at .021.
Fuel line and filter -- new filter (came with carb rebuild kit), line replaced all the way back to tank. (Fuel line was leaking / allowing air bubbles into the line.)
Spark Plugs -- new.
WHAT ITS DOING:
Completed everything listed above, ran great for the 15 minutes I drove it around the yard. Ran at all throttle positions, running great!
Went to do some work with it the next morning (had a case hydro vac/cart hooked up), thats when the trouble started...
Idled good, but overall got progressively worse after about one hour running time, started running terrible at higher RPM's, mild backfiring, would lose power, acted like it was running out of gas. Two times it just quit -- I guickly opened the hood, and the fuel line/filter was empty (no gas in the line, tank was full).
It's getting plenty of gas, or I should say, there is plenty of gas available in the tank and line.
Messed with the carb adjusting screws. Low speed screw works fine, adjusted it to best position. Main/high speed screw (brass screw on back right side) seems to work normally from around 0 to 1-1/2 turns out, but going from 1-1/2 turns out to 4+ turns out, doesn't seem to change anything.
Blew out main port 5 times with carb cleaner, port seems wide open / no obstructions, carb cleaner shoots heavy stream into throat of carb. The nozzle where cleaner shoots out into the throat of carb looks a little deformed, did not look examine as would need proper instrument to inspect.
Carb. main adjusting screw -- still no difference after 5 times with carb cleaner.
Motor is running worse by the hour --- was running fine 0-1/4 throttle, Now it starting hard, and it's loggy / terrible response at throttle lever. Higher RPM's are terrible. Acts real loggy across the entire RPM range. Increasing throttle shoots mist of gas straight verticle from within the carb throat. Mild backfiring at high RPM's, open throttle all the way, backfiring gets worse.
The more load I put on the engine (like engaging mower deck) causes more backfiring.
Let motor run at any continuous rpm -- low rpm not bad, anywhere from 1/4 to 3/4 rpm motor "hunts" / has a miss, seems like one cylinder might be cutting in and out, inrease to full throttle --- backfiring starts, so did not run past 3/4 throttle.
I can't figure out what might be causing this, but whatever it is, it's getting progressively worse. It seems like I've fixed the most common causes, but I might be missing something?
At this point its starting hard, and acts like it hardly wants to run.
Any help will be greatly appreciated.