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TR4/4A Rich Idle

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Tim Tucker

Tim Tucker

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Hi All! Spark Plug TR4 (7-1-2018) (3).jpg
I have a fairly rich idle mix (black dry sooty plugs). The plug tips are tan to lean looking after running at speed. The car drives out great. I've:
Compression checked (warm,WOT): 155#, 160#,160#, 155#
replaced (TRF): pertronix electronic ignition (was running points), rotor, cap, wires, plugs (L87YC), and coil (FLAME THROWER)
verified static ignition timing: 4 BTDC
verified valve adjustments
VERIFIED THE ~.73" float adjustment for BOTH floats of each carburetor.
Verified good engine ground

I run 93 octane 100% Exxon

What have I missed? How big of an adjustment can I make to the floats (.73"+?) to lean the mix without starving the car at speed?

TIA!
 
3 more verifies:

Jets fully retracted when choke is off.
Idle nut positions from fully in?
Fuel level at the jet when viewed from the carb throat with air cleaners off?
 
My bad! I failed to mention I have Zenith Strombergs rebushed by Joe Curto 2 years ago. My distributor was rebuilt by Jeff at that time as well. I run straight 30W in the dashpots. The jet adjustments are set 1/2 and 1 flat leaner than the factory recommended starting point of 3 turns.
Thanks!
 
It's not unusual for the carbs to 'load up' if the engine is left to idle for an extended period of time.
After returning from one of those drives that leaves the plugs tan, how long do you let the engine idle before the plugs darken up ?
 
Tim Tucker said:
...(black dry sooty plugs). The plug tips are tan to lean looking after running at speed...
Click to expand...

I tend to rely more on the color of the tips than the body of the plug (near the threads). An if it is real important to know then a 'plug cut' is in order... drive at speed and when it is safe to do so cut the engine, depress the clutch and coast to the side of the road. Then pull and read the plugs.
 
poolboy said:
how long do you let the engine idle before the plugs darken up ?
Click to expand...
I'd say fast...the idle (~650rpm) seems to get rougher the longer I spend at stop signs. The car's "cold" drivability is better if I start it and immediately take off at ~1000-1500 rpm...luckily I can do this for ~1 mile. If I warm it the idle get rougher and it's drivability is rougher. On the return, I coast into my driveway to view the plugs with minimal idle time.
Thanks poolboy...you were a great help setting the TR6 ignition timing...many thanks for that!
 
When I saw 'tidentenn' I remembered you, Tim. Of course you're welcome !
I don't really know about fine tuning the mixture with the float level, only to say that if you see a puddle of gas on the bridge as soon as you shut down, you'll need to raise the float... I say 'raise' because the ZS carb would normally be upside down on the work bench when setting the height.
But I tell you what I'd be tempted to do is replace the fixed jets with the adjustable ones....Joe has them and he might cut you a deal since you're not completely satisfied with the current set up.
 
As promised, these pictures were taken after a 10 mile run with the jet adjusting screws three turns down (as stated in service manual) + 2 flats richer (down). I've ensured the should of the needles are flush with the air valve.
#1 plug #1 Plug 7-28-2018 (3).jpg #2, #3 looked the same
#4 plug #4 Plug 7-28-2018 (3).jpg

I'd say I'm still lean...the car had a bit of exhaust "popping" when accelerating from low speed in high gear in a later drive. What would be your next move? Keep going Richer on the jet adjustment?



 
I can't see much of the insulator on #4, but #1 looks the proper color to me....if you go richer a bit more, it won't hurt.
 
poolboy said:
I can't see much of the insulator on #4, but #1 looks the proper color to me....if you go richer a bit more, it won't hurt.
Click to expand...

That's what my plugs look like after doing plug checks. I thought that was sort of normal? I'm a little confused here when you say to go richer in the mixture. I thought black sooty plugs were an indication of a mixture that was too rich so would you not want go leaner? Just occured to me...I'm talking SU's not Strombergs.
 
Regardless of the make of carb, I still think the plug looks the proper color....but don't misinterpret what I said about not hurting if he goes a bit richer....That "bit" was more or less for Tim's peace of mind (if he needs it); certainly not to the point of sootiing up.
Also I noticed Tim went by the book setting for the ignition timing...which may or may not now be appropriate in this day and time for his particular engine...Timing also has an affect on combustion and spark plug appearance.
 
I have not had Stromberg’s since my Sunbeam in the 70ites—so just putting stuff out—I have seen bad oil rings leave black deposits--- I have seen distributors that do not return correctly leave black deposits—how does the car run and perform? Does this problem keep building up until a plug fouls out? I got say the tips look good. Maybe weak spark is not burning all the fuel. I guess what I am thinking is it might not be in the carbs themselves.
 
Sorry for the rich but let's go richer idea...sure doesn't fit the thread subject. In person they may look a bit lean. If I let that car idle they're black. That's my problem. All NEW ignition bits. Advance built distributor. Re-bushed carbs with TRF kits. I've missed something. The black soot is dry...would oil not be a wetter material?
 
ZS carbs and maybe SU's too, tend to load up when the idle time is extensive...
Maybe you've seen or read to clear them out by raising the rpms periodically when adjusting the carbs at idle speed before resuming the procedure.
Having said that, you may find that the fuel level in the float chamber needs lowering...that just adds to the loading up at idle scenario.
Overall, be happy with the mixture for the rpms you actually drive, not so much for the time you spend idling is my philosophy.
 
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