1988 Mighty Max 2.0 California Version Looses Power/Engine Bogs Out on Freeway

1988 Mighty Max 2.0 California Version
The Problem > It will start and run, rev and idle (after warm up) with no issues. It will drive ok at low city speeds for about 20 min. Taking it on the freeway, it will act like it run out of gas. Sometimes the engine dies outright but it will be able to start right back up. Other times I am able to keep it running by holding in the clutch and revving the engine or just putting in the clutch and the motor will idle but bog out if you give it gas. After about 1-5 min of this, it will start to drive ok at low city speeds for 15 or so min then will start to die out anyway.

Work done to try to fix this issue (and other repairs as needed)
· Rebuild the carb
· Replaced Cap, Rotor, Spark Plugs and Wires
· Replaced the Fuel Pump
· Replaced all/most vacuum hoses (there could be a hidden one I missed)
· Found the EGR valve stuck ½ open and cleaned it so it is working
· Found the gas tank had a pressure leak around where the gas gauge bolts on and made new gaskets
· Cleaned the gas tank to make sure it does not have debris in it
· Replaced the gas cap
· Replaced all the gas lines and replaced the fuel filter
· Found a wire running from the coil to the heat sink on the coil that has a few strands left and replaced it.
· Replaced the coil and heatsink
· Checked the distributor vacuum advance, they both move when a vacuum is pulled on them
· Removed and checked the electronics of the distributor and made sure it was in spec on the multimeter
· Checked/cleaned the PCB valve
· Replaced the Alternator
· Checked the electronic choke and it is moving and locking open when everything it warmed up
· Replaced the Oxygen Sensor
· Replaced the water pump (started leaking)
· Replaced both timing belts (I was in there anyway)
· Replaced the Catalytic Converter

WOW

1) Does your truck have two catalytic converters..? You made sure that both are not plugged..? My truck had a cat inside the exhaust manf..!
2) Did you get sat results on any compression test..?
3) The distributor has 3 timing adjustments for advancement A) Initial B) Centrifugal C) Vacuum Test them with idle rpm set use a laser tachometer...
4) Mikuni carburetor A) Test needle seat for leakage B) Set float adjustment C) Test the vacuum diaphragm that opens the secondary throttle plate
5) Load test the battery & coil...

I'm thinking not enough air or fuel is reaching the combustion chambers at higher speed & load and the exhaust must not be plugged (Muffler..?)
I had to replace the cracked cylinder head on my truck to solve combustion gases blowing water out the tailpipe & loss of power...
Keep at it and eventually you will fix the problem; the habit of testing before buying parts is worth the study & effort...

P.S. Follow torque specs and check tightness of all fasteners under the hood including electrical connections grounds etc. exhaust manifold nuts intake manifold nuts (my truck had 3 missing nuts on the old head) carburetor bolts, etc. etc. Install & test using all new filters in the intake casing one for air & one for blow by... Disconnect the vacuum going to the air intake duct warm up valve on the casing snorkel end remove the hose and cap it off at the vacuum source under the Mikuni carb... It will default to stay open without vacuum supply and should allow more cold air into the intake especially if it has a leak which causes it to default to closed which causes hot air to always be supplied to the intake (it happened to my truck)...Good Luck...

You deserve :thumbup::thumbup::thumbup:

Only 1 Catalytic installed
Still looking for my compression tester
Distributer adjustments?!?!?
Carb has tested ok
Battery is newish and holding a charge. New coil and stuff

Just finished replacing all the vac lines with new blue ones.
I had a PSI gauge that I desided to attach it in line. Ran the truck and it would bunce from 0-2.5 psi and when revving the motor, it dropped to 0-1 psi. It did not stall out so the next question is if it should be that low on the gas psi?

Are the fuel pump-to-carburetor lines routed correctly? One outlet port is restricted. If it's connected to the float bowl inlet, the fuel flow will be low (should be 2.7-3.7 PSI). That might cause the low pressure and drivability issues. Also, got a vacuum gauge? It's a good diagnostic tool. Here's a sticky to go with the gauge:
http://www.mightyram50.net/vbulletin...ngine-Problems