running rich? How to adjust?

[vtcruiser60]

84 FJ60 with 83K

I tossed up a question a while back and need a bit more clarification from the gods on the board. I believe that running rich can increased the temp of the engine. Is this correct?

If so, and I am looking to adjust the fuel mixture, which way should I turn the screw?

I have excessive heat in a engine, carbon on each of the six spark plugs, good timing, near perfect compression, and positive signals from a leak down test. The radiator is new.

In otherwords, I am trying to do everthing before replacing the headgasket.

So, will running rich increase the temperature and how should I adjust the mixture screw?

Thanks fellas...

 

[FJ40Jim]

Incorrect. Maximum combustion temp and maximum efficiency happen at the same slightly lean of stoich mixture.

The idle mixture screw is a fuel needle valve. Screw in to reduce fuel, back out to richen idle mixture. Note that the idle mix screw only has a notable effect on mixture at idle speed.

To adjust, set idle speed screw to 600-650RPM. Adjust idle mix screw to highest idle speed. If this moves idle speed above 650, then adjust idle speed screw back down below 650. Adjust idle mix screw to give highest idle speed. repeat as necessary until you've got an idle speed of 650 RPM or less, w/ mixture screw adjusted for best highest idle. As a final step, adjust idle speed, choke speed and AC up to your preferred settings.

Good luck!

 

[Cruisergreg]

If you are running rich above idle you may have a choke that is not opening all the way - check the cable adjustment. A float that is adjusted too high could also end up causing a rich mixture - see if the fuel level is roughly mid way up the sight glass.

 

[swank60]

Running rich above idle can also be a faulty/incorrectly connected air pump. Beat my head against the wall for 6 months trying to figure that one out.

 

[vtcruiser60]

I am much obliged and will report back with my findings. Thank you.

 

[vtcruiser60]

Just reporting back as promised.

I leaned out the carb and the temperature dropped a bit. Idle was off and my adjustment there helped the temp

BUT

As I was losing coolant from somewhere I took it to a shop and they discovered a crack in the block, about a foot long between the oil pan and exhaust manifold near the radiator.

My overheating issues are due to a crack.....

 

[lt1823]

Incorrect. Maximum combustion temp and maximum efficiency happen at the same slightly lean of stoich mixture.

The idle mixture screw is a fuel needle valve. Screw in to reduce fuel, back out to richen idle mixture. Note that the idle mix screw only has a notable effect on mixture at idle speed.

To adjust, set idle speed screw to 600-650RPM. Adjust idle mix screw to highest idle speed. If this moves idle speed above 650, then adjust idle speed screw back down below 650. Adjust idle mix screw to give highest idle speed. repeat as necessary until you've got an idle speed of 650 RPM or less, w/ mixture screw adjusted for best highest idle. As a final step, adjust idle speed, choke speed and AC up to your preferred settings.

Good luck!

Jim, in your experience, how many turns out/counterclockwise from all the way in would you set your mixture screw, provided everything else is working correctly? Would you say somewhere between three and four? I know this is a loaded question and may be specific to each vehicle but I didnt know if there was a ballpark number of turns.

Basically I dont want to run in too rich and gunk up the carb, but I dont want to run it too lean or too hot either and blow a head gasket.

I appreciate your help.

LT

 

[lcolon]

I setup my carb by having a bung welded into the exhaust pipe between the engine and the cat. With that, a wide band o2 sensor can be screwed into the motor to adjust the mixture at idle. This allows you to get it pretty much spot on. You can use an aftermarket o2 kit from amazon. Just add some wires to power the gauge while you are doing the adjustment. If you do use this method, make sure to plug the right vacuum lines to bypass the air intake (aka smog pump) from blowing air into the exhaust as that will screw up your readings.

https://www.amazon.com/ZHSYMX-Universal-Digital-Wideband-Ratio/dp/B0D3Z4ZMNC/ref=sr_1_2_sspa?crid=1CU86BHPX374T&dib=eyJ2IjoiMSJ9.UoDPYVnMJZSPP1qChOqyHjbtpLDL7_N1XLtEALAtkcPS_5eBBjAzKLmZcNfxrPaWPVnRJKd524MGX8kvf79axZbCBOn2F1vr0PHv4rwlfdrFsw3C4y2O1Hljmh5cxkMXpMXXdI7o-gwvaBOEWILfUxS8VLVs12HHKt-VkTj7FCjasyuJ7H6d667otcd15C1jHussdxLN7UqfPzlvDepYp3-VS4WRcqjLEf4W3ei5tCY.lgjE3xnE4Ee3eVLQy9pSAvkssNeaIsXKK0Cu9w4KF7w&dib_tag=se&keywords=wideband+o2+sensor+kit&qid=1736553135&sprefix=wideband+o%2Caps%2C172&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

Since I have to pass CA smog - this is very helpful...