TR6 Starter Relay = Low Engine Power Question

[fwtexasbj8]

This is a continuation of my Fuel Pump Priming post but with a new diagnosis! I have been digging into my problem and discovered I only have slightly over 6 volts on the positive side of the coil. All other coil checks seem to indicate the coil is good. I have traced the wiring into the coil back and found the white/yellow wire at the starter relay has only the same 6 volts. The power into the relay is battery voltage of 12.3 volts. Does the starter relay essentially power the coil and could a bad connection inside the relay yield a lower voltage and therefore rough running and no engine power?

As usual, I appreciate all the help

 

[Gliderman8]

The '74 TR6 had a ballasted system. The yellow wire is a resistor wire allowing the coil to work at approx 6 volts.
Make sure you have a 1.5 ohm coil or bypass the resistor wire to get 12v and use a 3 ohm coil.

 

[fwtexasbj8]

Thanks Elliot, so getting ~6 volts on the positive side of the coil is correct for my year? If so, it would appear the coil is fine. The ground wire in the distributor is a little suspect and I have ordered a new one to be sure. In the mean time, can I just connect the distributor ground connection to the coil to a good ground to rule that out? I have replaced the points, condenser, rotor, cap, plugs and wires and still cannot get it to run smooth and generate any power. The issue came on pretty suddenly while on a drive with everything working fine for years. I originally thought it was a fuel problem as the original issue was a lose fuel connection at the pump inlet but I have verified fuel is steady to both carbs. Do you have any advice on what to look for next? I am a little stumped right now.

 

[Gliderman8]

If you have a spare coil, I would try swapping it out to eliminate a bad coil. Is the clamp tight on the distributor pedal? Have you verified that you are indeed getting spark?

 

[fwtexasbj8]

Unfortunately, I do not have a spare coil to try. I have checked the distributor and it is tight and since it will idle, I had looked at timing and it is about 12 degrees BTDC so it is pretty good. When I checked the timing, I also connected my induction timing light to each plug wire and the strobe fires on each one so I think I am getting spark. Just to be sure, I pulled #6 and watched it spark but since it does not seem to affect the engine, I am moving back to a fuel issue. My next idea is to maybe pull the rear carb (I will start there as pulling the #1 wire does affect the engine) just to be sure fuel is getting into the float chamber and not clogged between the metal fuel tube and the float.

 

[TR3driver]

The starter relay only powers the coil during cranking. Assuming you checked with the engine not cranking at the time, then finding 6 volts (with the points closed) is both normal and a pretty good indication that you do have the correct 1.5 ohm coil and that the distributor was grounded while you were checking.

 

[TuffTR250]

Elliot says that the yellow wire is a "resistor wire" on the TR6. Sorry to change subject, but on my 1961 TR3A some PO cut off the yellow coil wire at each end and replaced it with a new white wire of the same gauge between the solenoid and the coil. I have not measured the voltage of the that wire at the coil nor the ohms of the coil, however I have the question as to whether that wire is supposed to be some some special type wire on the TR3A? I believe the coil is an original. Thanks!
Regards,
Bob

 

[Geo Hahn]

No Bob - the TR3A requires neither a resistor wire nor a ballast. The original wire to the coil would have been white and supplied full voltage at all times (cranking and running).

The coil is sometimes referred to as having an internal ballast but I think in fact it was simply designed to not require any ballast.

 

[TR3driver]

What Geo said. The external ballast (resistor wire) didn't start until 1972 for the TR6, and was not used at all on earlier TRs. It gets a bit confusing, as that means that early TR6 takes a different coil than later ones do.

"between the solenoid and the coil" Huh? A TR3A shouldn't have a connection between the solenoid and coil. The connection on later cars is only to bypass the ballast during starting, and obviously there is no reason to bypass something that isn't there. The TR3A solenoid also lacks the contact to power the coil, so it might pay to do some more investigation there.

 

[poolboy]

You don't have to pull a ZS carb off to see if there is fuel in the float chamber.
Remove the air cleaner so that you can see into the mouth of the carb.
If you have 73 thru 76 carbs, blow into this nipple while holding up the air valve.

If there is gas in the float chamber gas will bubble up around the needle thru the jet.
If you have earlier carbs, you won't have the 'red' nipple, so you'll have to blow into the float chamber vent represented by the brass lined hole in the carb's air box mounting flange also seen in the picture, although on the pre 73 carbs it won't be brass lined. The result will be the same..gas bubbling up thru the jet.
You can also pull or unscrew the float chamber drain plug depending upon which version you have, but that's not as easy, plus if there is gas, there'll be a lot spilling out.

 

[fwtexasbj8]

Thanks for the tip on checking the float chamber! I will do that tomorrow and hopefully, the result will give me a good clue as the cause. What I am wondering now is if the fuel pump screen outer plastic ring I mentioned in my Fuel Pump Priming thread that was partially disintegrated might have clogged the inlet.

thanks for the help so far!

 

[bobhustead]

Doug- You mention that pulling the wire from #6 plug does not affect the engine. Check compression in that cylinder and, if good, change the plug.
Bob

 

[TuffTR250]

Randall and Geo, thanks for the response to my question!
Regards,
Bob

 

[fwtexasbj8]

Here is the final update! First off, thanks for all the advice as I learned a lot more about the car tracking down this issue. I finally started to pull the aft carb and decided to start with the piston. Found the needle about 1/4 inches higher in the piston than the front. Was so far off the adjusting screw was completely unseated and pushed up in the piston. Not sure how that happened but obviously wrong. Also found no oil in the piston dampers. Even though the diaphragms were intact, the aft one was much softer and stretched out than the front. I replaced them both plus the o-rings in the pistons. I then reset the point gap, set the timing to ~8 degrees BTDC and set the carbs. Everything runs great again and it is back on the road!