• Hi Guest! Being a Paying Supporter is NOT a requirement to participate at BCF. However, subscribing will help ensure we can continue to serve the LBC community for years to come. If you enjoy BCF and find our forum a useful resource...Please consider supporting us by **Upgrading**
    (PS: Subscribers don't see this banner)
Tips
Tips

Tach jumping, rough idle.

Lionheart

Senior Member
Offline
The tach on my spit tends to intermittently lurch and jump about 500-1000 rpm above the actual rpm. It's much more prevalent at higher rpms.

Here's what I got:
Flamethrower coil
Pertronix ignitor
Otherwise, stock

Idle is a bit rough as well...was that way with the Stromberg, and is still that way with the single Weber 40DCOE. You can see the steering wheel shaking, even at 1000 rpm. Car runs good on the road, lots of pep.

Could this be indicative of a bad ignitor module? Could it be a bad tach?

Len
 

StagByTriumph

Jedi Warrior
Offline
I think you have an issue with the ignition.

Tell me, is it a 12 volt coil or a 6 volt coil, and year of your Spitty?

This is a just a s.w.a.g (Spitfire Wild Arse Guess) and I am probably way out in left field, but I often see 12vdc coils used where there is an external ballast resistor either in the harness or on the coil bracket - a 12 vdc coil needs 12 volts when the key is in "Run" to operate properly.

Am I wrong by saying that Triumphs mainly use 6 vdc ignitions that apply 12 vdc to the coil only during the starter cycle to enhance starting?? So what is happening is, you start up fine, but when you release the key, the ballast resistor is placed in the circuit and the coil is getting only 6 volts to operate the engine on. Low RPMs is when the engine needs the best spark to run smoothly.

Good test, use your old Lucas Coil and see how it runs.

If you decide to use a 12vdc coil, you have to loose the external or hidden ballast resistor so the coil gets 12vdc all the time.

Pertronix sales places automatically assume you are using an all 12VDC ignition system.

Second, older Smiths tachometers - say pre 1973 to be safe, do not like electronic points because it does not take the volts pulse to ground. The pulse pickup sensing coil in the tachometer does not see the amount of volt pulses to make the tachometer needle respond correctly. Those older tachometers need a second loop or wire run through the pickup coil on the tachometer circuit board.

Hope this helps ...
 
OP
L

Lionheart

Senior Member
Offline
Thanks Glenn.

It's a 77 Spit 1500.
The coil is running on full-time 12vdc.

I really wish I still had an oscilloscope, so I could view the breaker signal.
 

StagByTriumph

Jedi Warrior
Offline
Lionheart said:
Thanks Glenn.

It's a 77 Spit 1500.
The coil is running on full-time 12vdc.

I really wish I still had an oscilloscope, so I could view the breaker signal.

No local clubs have a SunTune?? /bcforum/images/%%GRAEMLIN_URL%%/frown.gif

So how about the plugs? Maybe locate a spark tester and stick that inline with the plug wire. You could have a dead plug.

Compression? Maybe a tight valve?
 
OP
L

Lionheart

Senior Member
Offline
I just put new plugs in it. They are ALL a nice cappuccino color.

I'll do a compression test tomorrow. I have no idea what the valves are like...it shows 85k on the odometer, and I have no evidence that there was ever any engine work done.

I just bought the car last August, so I'm still figuring things out. (This is my first 'proper' LBC...my first LBC was a 71 Plymouth Cricket...it's the same as a Talbot Avenger in the UK.)
 

StagByTriumph

Jedi Warrior
Offline
Well smoothing out running on the road, that is usually a quality of combustion. Yeah, do a compression check. What is running like under load like a hill? Oh right, you are in New Jersey /bcforum/images/%%GRAEMLIN_URL%%/frown.gif

Maybe check for vacuum leaks too, and pop the oil cap while idling to see what happens.

Weber's are a bit tricky to get right, but if you have a nice light brown deposit on all the plugs, that is a good sign the fuel is right, and no oil burning.
 
OP
L

Lionheart

Senior Member
Offline
I did a compression test today. Here's what I got:
143
140
140
146

They all rose about the same; taking about 3 comp strokes to build the majority of the pressure, and a few more to max out.

I don't have a leakdown tester, so didn't test that.

I realize that the tach jumping and the rough idle may or may not be connected. If they are, then it's ignition-related.
Is the Pertronix Ignitor prone to this type of failure?
 
G

Guest

Guest
Guest
Offline
Worn-out end on your tach cable? Try going back to points and condenser and see how she runs.
 
OP
L

Lionheart

Senior Member
Offline
TR6BILL said:
Worn-out end on your tach cable? Try going back to points and condenser and see how she runs.
This is an electric tach car (at least I think it is...you got me wonderin' now). I believe the original ignition was an optical breaker system. I'm not really sure about that, but in the box of extra parts that you always get with an old car, there is an optical pickup and rotating assy.

I would install an aftermarket distributor in a heartbeat if they didn't cost $300.
 
Similar threads
Thread starter Title Forum Replies Date
G Jumping Tach MG 4
Joe Reed MGB Tach slow to wake up...why? MG 6
Lin Tach drive housing for BT7 Austin Healey 4
HealeyRick Tach Trouble Spridgets 2
W Tach wiring problems Jaguar 12
Marvin Gruber BJ7 tach cable location. Austin Healey 3
E TR6 ā€˜74 Tach Triumph 7
PAUL161 T-Series Lazy Tach MG 3
boxofparts MGB busy tach on 1979 MGB at 75 mph MG 3
J Speedometer Tach Correlation 1965 Austin Healey BJ8 Austin Healey 3
J 1965 BJ8 Tach Austin Healey 3
longbridgehealey Alternator conversion and tach Austin Healey 9
Healey Nut Mechanical tach drive Austin Healey 2
Healey Nut Mechanical tach drive assembly Austin Healey 4
S TR2/3/3A grounds the tach and speedo dash lights Triumph 1
S TR2/3/3A tach cable lubricant Triumph 4
Drone Dog BT7 tach question Austin Healey 8
5 Tach Drive Generator for a Bugeye Spridgets 2
I Tach help Spridgets 3
Marvin Gruber BJ8 tach Austin Healey 9
Superwrench Tach not working Austin Healey 6
JimTR4 TR4/4A Capping off redundant tach cable connection Triumph 0
Z TR4/4A Tach and Speed inner gaskets Triumph 13
W Use of original Tach Spridgets 8
A Need help wiring my tach Spridgets 11
Patrick67BJ8 Tach Hookup Instructions from Nisonger Austin Healey 23
S TR5/TR250 tach problems Triumph 2
J Hunting tach and back fire TVR 8
B Longbridge 100-6 Tach Cable and Speedo Angle Drive Questions Austin Healey 7
M Tach generator gearbox Spridgets 6
M Strange Healey Tach Austin Healey 9
steveg Checking Healey Mechanical Tach at idle Austin Healey 3
busybrit Tach stops when flashers are turned on !! Jaguar 3
busybrit Electrical tach issue on Aston Martin DB5 Other British Cars 2
AngliaGT What Goes to the Left of the Tach? Spridgets 3
S TR2/3/3A speedo and tach until the weather gets better Triumph 3
J How can I tell if I have a negative ground tach? Austin Healey 5
E TR4/4A Speedo v Tach cable Triumph 2
rjc157 tach goes crazy Austin Healey 8
Sopwith_Camel tach-less Spridgets 11
B Lazy Tach Austin Healey 2
J Tach drive housing eccentric Austin Healey 14
G MGB Tach and speedo rebuild. MG 3
Schroeders T-Series TF Tach Calibration - DIY? MG 3
Darwin Spitfire Help wiring up a tach Triumph 9
5 Tach Drive on Bugeye Austin Healey 10
C Tach stops when panel lights are switched on Austin Healey 5
Patrick67BJ8 BJ8 Tach Won't go past 2400 rpm Austin Healey 5
Mowgli81 RPM / TACH not working. Austin Healey 4
mt10flyer TR2/3/3A Tach and Speedo acting up. Triumph 8

Similar threads

Top