For long I have been suffering from the engine overheating when I'm cruising on a highway in my Samurai. I've had this ever since I swapped the pulley fan with an electric one. The electric fan killed the overheating problem while idle, but brought in the heating at cruising. I replaced my engine with a good Japanese 1.6 G16A 8 valve, swapped in the carb and intake manifold from my old engine into the new one. The overheating was still there, but I also faced shortage in fuel supply at high load high RPM, especially when I climb a sand dune.
Driving on sand dunes really requires brutalizing the engine, especially when it is a small 1.6L engine.
I did the following to remedy the overheating at cruising, in the following order:
1. replaced the radiator with a new original Samurai radiator
2. replaced the thermostat with a Nissan thermostat that opens up at a lower temperature
3. adjusted the timing on the distributor to 8 degrees
4. put back the original Samurai transfer case (instead of the 6.5:1 rock crawler which I really don't need in sand driving) to keep the RPM lower
Nothing worked. The engine still overheated whenever it reaches 4000 RPM and stays there for a while.
So I decided it is likely that the problem is due to the engine running too lean on the Weber carb, which is calibrated for a 1.3L engine and I'm using it on a 1.6L. After taking advice from this forum, I ordered the rejetting kit from low range offroad, and started to play around with the carb jetting.
Here's a picture of the kit:
It was really interesting, and I learned a lot about carbs. I did the idle test according to the weber manual instructions, and found that I'm running perfectly ok on idle, which is expected since I had no idle problems. But I did benefit from one thing from this test. I got my mixture and idle screws adjusted properly, and now the car doesn't diesel anymore! That dieseling problem was driving me crazy for years, and turned out to be just the mixture and idle screws. I got my mixture screw at 1 3/4 of a turn out, which is within the weber specs of a maximum of 2 turns, so I did not need to do anything with the idle jets.
Then I started playing with the primary and secondary jets, and the air jets and pump jet.
This is where it got interesting. My stock setup was like this:
Air jets (air corrector): 160 (right), 170 (left)
Primary fuel jet: 140
Secondary fuel jet: 140
Pump jet: Single, 50
I thought since I am running lean, I should keep the air jets as small as possible, so I did not change the air jets. and I installed the largest fuel jets I have, to make it as rich as possible.
After some experimentation, the end setup I had was as follows:
Air jets: no change
Primary fuel jet: 155
Secondary fuel jet: 150 (the kit did not have identical jets, so I had to make them different)
Pump jet: Single, 55
I tried the double pump jet, but it caused the engine to cut off at 5000 RPM on third gear for some reason. I honestly have no idea what the pump jet is for or what it does, but I played with it nonetheless.
The result of the rejetting: The car now runs much better, has better power delivery and it seems to have stopped cutting off on load at high RPM, but I have yet to test it in the dunes. But IT STILL OVER HEATS AT 4000 RPM!
When I cruise at 4000 RPM, it overheats. It takes a bit longer to start overheating, but it does overheat.
I honestly couldn't bother taking pictures, so I found some pictures of a weber identical to mine in some other Toyota forum, which was really helpful in how to rejet my carb:
This is the picture of the float bowl:
The primary and secondary jets are at the bottom of the bowl, under the fuel, and the air jets are on the top. The pump jet is in front of the two air jets.
That is the richest I can get in this weber.
I wonder what will happen if I completely remove the jets, or probably drill them to make them even bigger?
Should I change the radiator to an Aluminum rad? Would that solve the problem? Or should I just fit a Chevy Lumina (Holden Commodore) 3.8L V6 and get an adapter from Marks adapters in Australia and completely change my Samurai to something different?