Hi all, I just bought a 77 toyota and it idles okay but once you get going it starts bucking. It has little power. I replapced fuel filter, plugs and wires, checked for vacuum leaks, adjusted timing. It always does the same thing. The accelerator pump looked okay, and it seems to be getting a good shot of gas. Is it possible the catalytic converter is causing this?

 

Lots of things it could be. Some easy things to check, starting with easiest:
Check that the advance on the timing is functioning - leave vac line hooked up and bring up the rpm's while watching timing light, should become more advanced as rpm's increase. If you have a delay light, I seem to recall total advance should be 32-36° at about 3000 rpm.
Valves adjusted properly?
Compression check on each cylinder.

Good luck and let us know what you find.

 

Thank you. The vacuum advance does seembto have suction, the valves on the other hand are out of my league right now though. Im worried to take it to a shop though, break the bank. I just dont dont the tools or space to do anything major right now.

 

Valve adjust on these engines is really pretty simple and the only tools you need are normal socket selection, a 10 or 12 mm open end wrench for the adjuster lock nut, and a flat head screwdriver. The only "specialty" tool is a set of feeler gauges, and those are cheap.
Get truck up to running temp, shut off, remove everything you need to to get the valve cover off, turn crank to to line up mark at either TDC or BDC. 2 intake and 2 exhaust rocker arms should be loose, check and adjust if needed, rotate crank 360° and repeat for the other 4. 22R is .008in intake side and .012in exhaust. Someone else should chime in if those numbers are the same for 20R.
I guess you never said what engine you have, I just assume 20R.

 

Its a 20r, is the feeler gauge for measuring the gap or what exactly do you measere when adjusting valves?

 

Yes, for measuring gap between top of valve stem and adjuster screw on the rocker arm.
Feeler gauge should "drag" a little when pulling it through the gap.
Gap is needed so that the valves can close all the way. Too tight and the valves don't fully seat when engine is hot and the metal expands.
Too loose and the valves don't open up as much as they should (less of an issue) and the rocker arms tend to make more noise when running.

On the distributor issue, having vac at the distributor is good, but I was also concerned that the advance module wasn't functioning. I've heard of them seizing up so that they don't do their job and advance the timing as the rpm's go up. Had my advance go bad years ago. Idled just fine, but as rpm's went up it had no power/fell flat on it's face.

 

20R Valve Clearance Specs - Intake : 0.008"; Exhaust: 0.012". IN millimeters if you have a metric feeler gauge set - Intake : 0.02mm; Exhaust 0.03mm. coleboy11 is right, there should be a very slight drag feel on the feeler gauge when the gap is adjusted correctly.
Be sure to recheck the gap after you tighten down each locknut as you go thru each one. Sometimes the screw can turn a bit when tightening down the locknut. Just try to hold the screw still with the screwdriver while tightening the locknut.

 

Also & BTW, correct timing for the 20R is 8 degrees BTDC, fully warmed up, at idle, vacuum advance disconnected from vacuum source & line to advance plugged. I use a golf tee or a properly sized nail for the plug in the vacuum line.

When you get around to adjusting the valves, It would be a great time & wise to replace the valve cover gasket, the two rubber "half-moon" plugs & the 4 rubber-backed metal washers. Here's a good set:
https://www.rockauto.com/en/moreinfo...sn=965&jsn=965

That item may also be available locally at your local auto parts stores.

 

Also, while you have the valve cover off, it's a good chance to replace the PCV and it's grommet. The valve may, or may not, still be good, and is easy to check. I can almost promise the grommet is bad, though. It doesn't take them long, and they get stiff, and brittle. Try to take it out of the valve cover, and it will frequently fall apart in small chunks. That's why you want to do it while the valve cover is off. It prevents a ton of small, stiff/brittle rubber chunks from falling down into the valve train. They do that, and finding them, let alone retrieving them is a royal bi&^h. With the cover off, they just fall out onto the ground, so a kid can sweep them up later

I would also check the EGR valve for a clog. They get clogged up over the years, and can cause strange problems.

Have fun!
Pat☺

 

I have a'74 (18R-C engine) & a '75 (20R) and they served me well, but both had intermittent stalling/no power problems that were fixed by removing a very small plastic screen just inside the fuel inlet. It's about 5/16" high and 1/4" wide, it filters the gas just before it hits the needle & seat. I have no idea why they installed this, there's an in-line fuel filter that is many times larger, and many times EASIER to service, it (the gas filter) is just before the fuel pump (on the 18R) and about on the same area on the other. I don't think you can access the screen through the inlet, (but maybe...) I removed the top of the carb, remove the float, and unscrew the needle & seat assy from under the top, it will be sitting right inside.

 

I have a'74 (18R-C engine) & a '75 (20R) and they served me well, but both had intermittent stalling/no power problems that were fixed by removing a very small plastic screen just inside the fuel inlet. It's about 5/16" high and 1/4" wide, it filters the gas just before it hits the needle & seat. I have no idea why they installed this, there's an in-line fuel filter that is many times larger, and many times EASIER to service, it (the gas filter) is just before the fuel pump (on the 18R) and about on the same area on the other. I don't think you can access the screen through the inlet, (but maybe...) I removed the top of the carb, remove the float, and unscrew the needle & seat assy from under the top, it will be sitting right inside.