• The Roadster Factory Recovery Fund - Friends, as you may have heard, The Roadster Factory, a respected British Car Parts business in PA, suffered a total loss in a fire on Christmas Day. Read about it, discuss or ask questions >> HERE. The Triumph Register of America is sponsoring a fund raiser to help TRF get back on their feet. If you can help, vist >> their GoFundMe page.
  • Hey there Guest!
    If you enjoy BCF and find our forum a useful resource, if you appreciate not having ads pop up all over the place and you want to ensure we can stay online - Please consider supporting with an "optional" low-cost annual subscription.
    **Upgrade Now**
    (PS: Subscribers don't see this UGLY banner)
Tips
Tips

Another BJ8 Misfire Question

CLEAH

Jedi Warrior
Country flag
Offline
BJ8 gurus, need your help. My car has developed a worsening misfire, a bit at idle, very bad at higher RPM's. I've been going through all the usual suspects--replaced the cap, rotor, condenser, points, disconnected the white and black wire from the boot switch, checked compression, looked at plugs. My numbers 3 and 6 plugs look fouled, and I suspect that is where the misfire are happening because all the other plugs look perfect. Compression at 180 in those cylinders. Newly rebuilt engine, and the carbs have been gone though.

But anyway, here is something I have not seen reported on the forum: When revving the engine and getting bad misfire, the tach dies. Rev to say 2500, and the tach needle drops and bounces up and down while the engine is misfiring.

I have not yet replaced the coil (my restorer is sending a new one). Thoughts?
 

EV2239

Jedi Warrior
Offline
On a BJ8 the tach is electronic and takes a feed from the ignition somewhere, so the fact that it falls suggests an intermittent connection in the area.
 

Bob_Spidell

Yoda
Gold
Country flag
Offline
A while back I heard there was a slug of bad condensers going around; if you got both from the same source you could have gotten two bad ones. The quality of points is suspect, too; not to be flip, but if you install a Pertronix unit you'll never have to worry about either again (NFI). I may have just been lucky, but my unmodified tach works fine with the Pertronix. Oh, and there were some bad rotors going around, too, but--in my personal experience--they fail outright.
 
OP
CLEAH

CLEAH

Jedi Warrior
Country flag
Offline
Agree with everything so far. Does anyone know where in the ignition system the tach picks up its signal?
 

4tecdog

Jedi Hopeful
Country flag
Offline
I should wait and fit the new coil it solved the problem for me, I think the tachometer gets its signal from the coil, I have known some GM engines lose spark due to a faulty tach could this be a possibility.
 

Bob_Spidell

Yoda
Gold
Country flag
Offline
Agree with everything so far. Does anyone know where in the ignition system the tach picks up its signal?

It HAS to be in series with the primary circuit to the coil. The pickup on the tach is inductive, and the signal is pulses of 12V from the timing mechanism (points or other). It's the only timed signal that isn't 15,000 volts or so.
 
OP
CLEAH

CLEAH

Jedi Warrior
Country flag
Offline
Thought I would update on this. After changing out essentially everything (points, rotor, condenser, cap, wires, coil, even the voltage regulator), it turns out it was the plugs.

I mentioned above that my numbers 3 and 6 plugs were sooty, so I replaced those. But the misfire reappeared (usually after the car warmed up) even though the new plugs from numbers 3 and 6 looked fine. We finally went from Champion RN9YC plugs to Autolite 64, and all seems solved.
 

Bob_Spidell

Yoda
Gold
Country flag
Offline
Just curious why you were running Champion RN9YC plugs; 12s are recommended, which are hotter running (this would explain the sootiness with the 9s)?

Did you fix your tach problem?
 
OP
CLEAH

CLEAH

Jedi Warrior
Country flag
Offline
Hi Bob,

Good question regarding the plugs. We really don’t know. Fresh out of restoration, the car was delivered to me with NGK BPR6ES plugs. It ran really well. The car needed to go back to the restoration shop for a bit of post-restoration fettling. The outside mechanic who does carb set-up and final adjustments was doing some further work on a problem with the carbs (ultimately determined to be a bad float), and as a part of the problem diagnosis, changed out the NGK’s. Why he put in Champion RN9YC’s I don’t know. When the car was returned to me, it was running fine on those plugs, until it didn’t. It never occurred to me that the plugs were not the “right” ones, even as I replaced a few of them because of sooting. Just did not register with me. My shop has since switched from their previously preferred NGK BPR6ES plugs to Autolite 64’s, which is what I now have in the car and it is running robustly.

I note that the NGK BPR6ES and the Autolite 64 plugs do not match (on the conversion charts) the recommended Champion RN12YC’s, but both result in excellent running.

What I learned is to give attention to plugs along with all the other usual-suspect components when tracking down an ignition problem.

As for the tach going wonky, it only did that when it misfired. It is otherwise fine.
 

bob hughes

Luke Skywalker
Country flag
Offline
Plugs - they are a whole new world when it comes to running smooth, I remember replacing mine many years ago and a guy in the Self Fit shop could not match the old ones that I had, so gave me what he said was the Bosch equivalent. Well in no time at all I found out that they were not. Then I delved into the black art of sparking plugs and had my eyes opened for me. It turned out that the man gave me cold plugs when I needed hot plugs, one by one they sooted up and kept failing, they were ok when new or freshly cleaned. I then changed them out for a new set of NGK BP5ES and have had no trouble since.

:cheers:

Bob
 

Joe Schlosser

Jedi Warrior
Silver
Country flag
Offline
You cannot beat the NGK plugs for reliability.
 

why

Jedi Trainee
Country flag
Offline
Over the many years of forum reading, I have been impressed with number of posts of people with problems by using nonoriginal design ignition parts, distributors in particular. If the ignition system is properly installed with setting from the manual it will and does for everyone do just fine. Sometimes the reason for miss at high revs or starting from cold is there to be be found and rectified with a worn or misadjusted part. I would stay away from putting in new type whizzbang anythings in ignition systems.
Jay, '65 3000. Usual qualifier, I am referring to Healeys use for normal use as opposed to any form of racing.
 
Similar threads
Thread starter Title Forum Replies Date
CLEAH Found another number on my frame [BJ8] Austin Healey 6
D Another question 1967 BJ8 top installation,metal retaining strip Austin Healey 1
Y MGB Time for another puzzle piece.... MG 5
P Another beautiful Sunday Spotted 0
L T-Series Another brake prob. ? MG 12
T I added another TVR to the fleet. TVR 10
AngliaGT ANOTHER TR6,& an MGB Spotted 0
Rut MGB Another sad day! MG 10
T General TR Another trans popping out of 2nd Triumph 14
K TR2/3/3A Another electrical problem: Park light & 5ignal light on Drivers side are brighter than....... Triumph 3
JPSmit you won't likely see another Spridgets 4
D TR2/3/3A Another mystery part(s) Triumph 2
Hamish Racing Another 3 sisters spring with commentary Racing 0
K TR2/3/3A Another brake bleed question....... Triumph 17
Sarastro Another SoCal TR3 Spotted 1
7 Wedge Got another one! Triumph 3
Sarastro TR4/4A Another 50K TR4A Triumph 5
D TR2/3/3A Another mystery part Triumph 8
HealeyRick GT6 Another Satisfied Customer Triumph 3
nichola TR6 Another TR6 back on the road Triumph 1
Sherlock Another cruise night, more interesting British iron Spotted 2
D TR2/3/3A Another Carb question. Triumph 22
Healey Nut Another Use for J-B Weld Austin Healey 5
D TR2/3/3A Have exchanged one leak for another. Triumph 10
dbenichou289 TR2/3/3A Another exhausting thread Triumph 10
D TR2/3/3A Another mystery part..or two Triumph 14
John Turney Another Article to Criticize Austin Healey 5
tr6nitjulius TR6 TR6 made another list! Triumph 5
Lin Another Trafficator/Control Head Question Austin Healey 10
Rob Glasgow Can I find Another one as Good? Austin Healey 4
V LED light bulbs : One thing leads to another Spridgets 7
V LED light bulbs : One thing leads to another Austin Healey 2
Editor_Reid Bought Another One Austin Healey 14
tr6nitjulius General TR Triumphest 2019 another one bites the dust! Triumph 2
pkmh Yet Another Oil Question! Austin Healey 8
P TR2/3/3A Another Differential Question Triumph 22
Bob Claffie Spotted another AH Spotted 0
SherpaPilot TR6 Just Another TR6 Column Question Triumph 4
TomMull Post-War Other HERALD Simple Task turns into another project. Triumph 11
jackq Another building full of cars available. Other Cars 0
M TR2/3/3A Another TR3 Piston Ring Gap Question Triumph 1
Lin Another trafficator issue Austin Healey 8
B Another OD question Austin Healey 32
Elva164 Finally did another onboard video! Racing 4
Sarastro TR4/4A Another milestone: first engine start Triumph 8
RAC68 Another Discussion of Trans/OD Fluid Austin Healey 14
Y MGB Another question - this time on seatbelts.... MG 2
PC another one bites the dust... Restoration & Tools 0
AngliaGT Another MGB Spotted 0
J Another Healey back on the road....for now. Austin Healey 8

Similar threads

Top