TR2/3/3A Spark Plug cuts and diagnosing?

[karls59tr]

I did the plug cuts the usual way by shutting the engine off in fourth gear going about 50mph pulling over and checking the plugs. The electrode and insulator tips of the plugs look fine...tan color....and I understand that that is a good thing....... but there is black carbon sooty deposits on top of the plug above the threads. Some of the plug analysis sites say it could be an overly rich mixture. Does most of this get burned off after a high speed run or should I try adjusting the the SU mixture screw one flat at a time to see if it makes a difference? The front two cylinders seem to be getting more of the soot buildup than the back two so I'll try that carb one first. Any thoughts?

 

[Geo Hahn]

Like this?

I can usually do better on the TRs but this is my other British car (ZS carbs) and seems to be the best I can get.

Sorry no answer here - hoping someone has an explanation.

 

[karls59tr]

Like this?

I can usually do better on the TRs but this is my other British car (ZS carbs) and seems to be the best I can get.

Sorry no answer here - hoping someone has an explanation.

The plugs in the last two cylinders look like that. The plugs in the first two cylinders have much more carbon buildup.

 

[CJD]

You have to start with new plugs to get an accurate cut reading. The plugs in Geo's pics are very used and would have to be cleaned before doing engine cuts with them. Old plugs only give you an average for the time they were in service.

Unless you carry a cleaner in the car, you usually need a box of fresh plugs when tuning with engine cuts.

 

[karls59tr]

I did clean the plugs before doing the plug cuts. The plugs were fairly new and I cleaned them before the plug cuts..... "Before" I cleaned them there was substantial black sooty carbon buildup on the tops of the plugs but the actual insulators tip and electrodes appeared OK being the tan color except for one plug that was starting to blacken. Wonder if its an overly rich mixture but the car runs fine. One more thing....the inside of the chrome exhaust pipe extender is black and sooty as well. I was thinking of giving that a good cleaning to use a benchmark before I start leaning out the mixture. I'm a little bit leery about mucking about with the SU's seeing as how it's running so good otherwise!:confusion:

 

[TR-3rg]

Hi,

One thing I did that helped the color of my plugs was go to 20wt(3 in 1) oil in the SU dashpots. I had ATF in them and my air/fuel ratio meter was all over the place. The 3 in 1 smoothed out the mixture and the engine ran noticeably better. I run the Moss Rich needle and the AFR is typically 12:1, dropping to 10:1 when I get on it. The center of the plug and the electrode have a nice tan color. With the ATF, the plugs were black.

RG

 

[karls59tr]

Hi,

One thing I did that helped the color of my plugs was go to 20wt(3 in 1) oil in the SU dashpots. I had ATF in them and my air/fuel ratio meter was all over the place. The 3 in 1 smoothed out the mixture and the engine ran noticeably better. I run the Moss Rich needle and the AFR is typically 12:1, dropping to 10:1 when I get on it. The center of the plug and the electrode have a nice tan color. With the ATF, the plugs were black.

RG

TR-3rg Well that is most interesting because I'm running ATF in my SU's as well! I'm going to try the 3 in 1 like you suggested. Do you have an exhaust header on your car? The reason i ask is that apparently if you have an exhaust header it's recommended to use RH needles in the SU's. Any other mods done to your motor? I'm running a mild street cam and find I have to set idle around 1200 rpm or it runs rough.
What kind of a set up do you have to measure the AFR?

 

[Geo Hahn]

...the actual insulators tip and electrodes appeared OK... the car runs fine...

IMO - these engine tolerate a fair amount of variance in the state of tune and can still be enjoyable. There are worse things than running a tad rich, running lean for one.

 

[TR-3rg]

Hi Geo,

I have a 4 tube header. The cam was regound by the PO, I don't know what it is. Sounds like we have similar set ups.

RG

 

[Don Elliott]

Your photo gives me the impression that it's a very "hot plug". It is so far out the body. Mine are more tan but then they are much shorter out the body of the plug - i.e. more flush with the body.

 

[karls59tr]

Well here is an update. I regapped the plugs and put a new set of points in and put 3 in 1 oil in the carb dampers. I took off in fourth gear and did'nt hear any pinging! Went out on the highway for a 90mph run. Did the plug cuts and the electrodes and insulator tips looked fine. I'm just going to drive the car and enjoy it for now. Might try the RH needles at some point.
If I get ambitious:
A friend of mine has an O2 sensor and air/fuel ratio tester so I just need to install a bung in the exhaust for the sensor. Where would be a good location for it on a header.

 

[TR-3rg]

Hi,

I recommend installing the air fuel meter. I installed the O2 sensor on the collector, right before the flange. Its mounted about 2 O'clock so I have clearance with the frame and gearbox. If you install it down stream of the flange, it may leak and it will read incorrectly. If you go that way, you can buy header adapters that already have the bung installed. I have a Autometer Sport Comp 2 wide band O2 sensor.

The 3 in 1 oil I have has a blue label on it. Its marked SAE 20wt and "Motor Oil" as in electric motor oil. They have a version with a black label, that's not 20wt. The needles I run are the RH.

Good Luck,
RG

 

[karls59tr]

Hi,

I recommend installing the air fuel meter. I installed the O2 sensor on the collector, right before the flange. Its mounted about 2 O'clock so I have clearance with the frame and gearbox. If you install it down stream of the flange, it may leak and it will read incorrectly. If you go that way, you can buy header adapters that already have the bung installed. I have a Autometer Sport Comp 2 wide band O2 sensor.

The 3 in 1 oil I have has a blue label on it. Its marked SAE 20wt and "Motor Oil" as in electric motor oil. They have a version with a black label, that's not 20wt. The needles I run are the RH.

Good Luck,
RG

Thanks for the info. What is the ideal air fuel mixture for the TR3 with a header?

 

[sp53]

Nice call Don I missed that and that is not a stock tr3 plug. I believe they have ½ lengths. I do know what you mean about the front carbs having more carbon. I read an explanation on it once, but cannot remember. When tuning, I always remind myself that these cars were made when there was lead in the fuel and Chevron white pump gasoline was over 100% octane. Those plugs look good to me, but yes maybe a little browner, but again they are not stock tr3 plugs. When I see a sale at a big auto parts store, I often buy a few sets of Champion plugs and will do your test. I do ask for 1967 tr4a plugs because they are the same, and I do not want to confuse them about a tr3.
Steve