1972 FJ40 smells rich

[nacho]

I have adjusted the timing and set the points.
is there any easy way to adjust the carburetor on this truck?
i was told i should find a "four gas" detection device (which nobody seems to have) in order to dial in my truck.
also, not usre if carbon canister is worn out- looks original. would vacuum reading show significantly if the charcoal canister was "backed" up?
by the way, truck runs great!

 

[Splangy]

Does it only smell "rich" at idle? Is there black smoke coming out of the tailpipe? Is it a rich cumbustion smell or perhaps a gas leak?

I have adjusted the timing and set the points.
is there any easy way to adjust the carburetor on this truck?
i was told i should find a "four gas" detection device (which nobody seems to have) in order to dial in my truck.
also, not usre if carbon canister is worn out- looks original. would vacuum reading show significantly if the charcoal canister was "backed" up?
by the way, truck runs great!

 

[nacho]

i was told it was actually running lean but there is a strong exhaust smell all the time. shop told me they did not mess with carburetor adjustment, only timing and setting points

 

[Pin_Head]

Here is an odd ball possibility. The smog tech was bitching about my truck running really rich and stinking of gasoline while it was passing the smog test blowing normal CO and HC levels. Sure enough, it did stink of gasoline, but it wasn't coming out of the tail pipe. Turned out to be a loose spark plug.

 

[DSRTRDR]

checked whether the lines to/from the evaporative device are tight ?

 

[FJforty]

shop told me they did not mess with carburetor adjustment, only timing and setting points

It's nice the shop knows their limits, time to find an engine mechanic or will you do it?

 

[nacho]

is "evaporative device" the charcoal canister?
will check the spark plugs too.
is there a proper carb adjustement with air/fuel mixture screw?

 

[zags]

An engine that is lean at idle can have a "lean misfire" condition. The fuel mixture is too lean to ignite consistantly, sending the unburned fuel out of the exhaust. It may or may not idle rough. If it is not smoking, your shop is probably right about being lean, although it is kinda weird that they won't adjust the carb. Must be it is a bunch of kids, scared of carbs. You can adjust the idle mixture with a tachometer. (a dashboard type tach is not accurate enough) Adjust your idle mixture screw to get the highest rpm at idle, then re-adjust your idle speed. Repeat the procedure untill you end up at the correct idle speed. Be sure to check for vacuum leaks first of course.

 

[DSRTRDR]

is "evaporative device" the charcoal canister?

no, it's in the cab in the rear of the middle bench seat - there are lines to and from the tank that can easily get dislodged and will produce gas smell

 

[nacho]

i don't have an evaporative device- someone removed it.
thanks zags for carb adjustment advice. what is proper idle RPM?

 

[FJ40Jim]

what is proper idle RPM?

USA emissions legal= 650RPM
ROW = 500RPM

My truck= whatever I deem necessary (that's why it's adjustable).

 

[FJforty]

I'm sure everyone has their way, this is what I would do:
Put a vacuum gauge on there so you know the vacuum is good. Try to set the idle about the right speed and adjust the idle mixture screw, you should be able to kill the engine if you screw it in all the way. Search for how to adjust.
Next watch your plugs, check them about every 10 hours of driving. Adjust the float level so the plugs burn just off-white.

 

[nacho]

thanks for everyones input. i will check vaccum and adjust idle mixture screw (and idle).
i will also check float level

 

[bgray]

FJforty: It may be my ignorance on how the carb functions, but how does the float level affect the mixture; or were you just saying to make sure the float level is correct?

Thanks,
Brian

 

[FJforty]

The carburetor venturi effect. Search it up on the web. Simply put, air moving down the carb throat pulls fuel from the bowl, if the fuel level in the bowl is raised more fuel will be pulled in, if the fuel bowl level is lowered then less fuel. It really is that simple, if you are running rich then adjust the floats so that the fuel bowl level is lower. Make small adjustments, like 1/16 inch.

 

[FJ40Jim]

The float level has a very, very,very minor effect on mixture. The big thing that moves fuel through the jets is the difference between venturi pressure (low) and atmospheric pressure (high) in the float bowl.The head pressure of the 1" column of fuel above the jet is negligible. At higher power settings there might be 3 PSI in the venturi, and 14 PSI in the bowl. The Delta P at the main jet is 11PSI.

[math example]
Each foot of water exerts a pressure of .433 psi so 11 psi of pressure at the main jet = 11/.433= 25.4 feet of water column.

By comparison, the 1" column of fuel above the jet exerts .036PSI.

As a percentage, the small force of WC height in the bowl compares to the venturi pressure:
1"/25.4'= 1"/ 309"= .32%
[/math example]

That is why the mixture is tuned by changing jet sizes rather than fuel height. Don't expect to change the mixture even 1% by moving the float level up or down a few MM.

just sayin'