Poor Running ?

[Mr Ex]

Never heard of a Z tacho giving a misfire before, just one unit failed in 28 years of working on zeds!

Mark I've had a rev counter bounce about more than once when a fault with the ignition.

The blue wire to the coil goes to the terminal with a blue dot at the side of it.

900ss you need to do a plug chop to check how the mixture is burning & post pix up here for "us" to see. In my early days of Z ownership I had a misfire that was puzzling & the plug tips were yellow, it turned out to be a blocked fuel filter!

 

[SKiddell]

If the rev counter dances then the problem must be in the low tension side of the ignition

not necassarily true (but highly possible)

The rev counter is an analogue device, directly measuring engine rpm via current pulses to the coil (or distributor pulses on later tachos), if the fault were on the high tension side this would cause the engine to falter/stumble which in turn would be picked up by the tacho possible showing up as discribed, (try pulling one plug lead on and off at a few thousand rpm and watch the tacho dance)

There's a lot of talk of the tacho possibly causing this fault but I'm with Mark (260TT) on this one, the tacho is a non invasive device, measuring a result (dont blame the messenger....the tacho being the messanger) and is unlikley to create the effect unless the continuity of the coil voltage (which on early tachos passes through the coil) is interupted by a bad connection (30 years of oxidisation).

Think Occam's Razor (and no before any one says it, Gillet don't make one)
"The explanation of any phenomenon should make as few assumptions as possible"
In other words, when your done screwing around its nearly always the simplest thing thats at fault, or as Homer Simpson would say...."Dohh!!"

Failing that then its time to perform that age old ritual that most Z owners fear, loath and detest.....the opening of the wallet ceremony.......go buy your self some rolling road time, and kill 2 birds with 1 stone, diagnose the problem and check your power output at the same time..

 

[Mr Ex]

not necassarily true (but highly possible)

The rev counter is an analogue device, directly measuring engine rpm via current pulses to the coil (or distributor pulses on later tachos), if the fault were on the high tension side this would cause the engine to falter/stumble which in turn would be picked up by the tacho possible showing up as discribed, (try pulling one plug lead on and off at a few thousand rpm and watch the tacho dance)

There's a lot of talk of the tacho possibly causing this fault but I'm with Mark (260TT) on this one, the tacho is a non invasive device, measuring a result (dont blame the messenger....the tacho being the messanger) and is unlikley to create the effect unless the continuity of the coil voltage (which on early tachos passes through the coil) is interupted by a bad connection (30 years of oxidisation).

Think Occam's Razor (and no before any one says it, Gillet don't make one)


He still needs to do a plug chop first to see what that tells us.
"The explanation of any phenomenon should make as few assumptions as possible"
In other words, when your done screwing around its nearly always the simplest thing thats at fault, or as Homer Simpson would say...."Dohh!!"

Failing that then its time to perform that age old ritual that most Z owners fear, loath and detest.....the opening of the wallet ceremony.......go buy your self some rolling road time, and kill 2 birds with 1 stone, diagnose the problem and check your power output at the same time..

He still needs to do a plug chop so we can see what's happening & what direction to go in.

 

[Wyn]

Guys pull the low tension wires off your coil and connect them around the other way....maybe the coil polarity is wrong. Worth a try.

I tried that today just to see, but that made the prob twice as bad, like it wouldn't even rev proper Also tried disconnecting one of the 2 wires on the neg? side of the coil, but it wouldn't start like that so I just put it back as be n tried some new needles I had brought a few weeks before. Ran out of time but it runs worse now then it did before lol so tomorrow will be spent re adjusting the carbs just to see if I can get it running any better
Still atleast the suns out

 

[twoforty]

Can you borrow a set of known good carbs from another nearby Z owner...just to rule them out?

 

[Wyn]

I had a misfire that was puzzling & the plug tips were yellow, it turned out to be a blocked fuel filter!

Strange that cos I tried some new BPR7ES -11 plugs today n noticed the tips of the old plugs had yellowed, but I put that down to fuel?

 

[Wyn]

Can you borrow a set of known good carbs from another nearby Z owner...just to rule them out?

I do now have set of 45's that will be going on soon, but just making sure I have all the bits in place before I try fit them
In the mean time I like to try get it right on me ol SU's before I open the next can of worms lol

 

[twoforty]

Sounds like you may have worms in your SU's!!

 

[grolls]

I do now have set of 45's that will be going on soon, but just making sure I have all the bits in place before I try fit them
In the mean time I like to try get it right on me ol SU's before I open the next can of worms lol

I think you'll find the car just didn't like going north......I can understand that!!

 

[moggy240]

grolls....... i got my mates car started ,you was right it was the points

 

[Nigel Brook]

Sounds like you may have worms in your SU's!!

Still convinced this is an ignition/wiring problem.

 

[twoforty]

Yeah you would think so but he seems to have replaced every component....also the carbs have been messed with.

Still convinced this is an ignition/wiring problem.

 

[Nigel Brook]

Yeah you would think so but he seems to have replaced every component....also the carbs have been messed with.

Carbs problem will usually just cause the motor to run rough, not normally a complete cut-out at x revs.

 

[twoforty]

That depends on the problem, sure it does sound like ignition but it could also be fuel starvation, unlikely but possible.

 

[Mr Ex]

I think you'll find the car just didn't like going north......I can understand that!!

Wash yer mouth out.

 

[Mr Ex]

Strange that cos I tried some new BPR7ES -11 plugs today n noticed the tips of the old plugs had yellowed, but I put that down to fuel?

Plugs should be BPR6ES I tried 7's & they where prone to foul up when starting from cold & that causes a misfire but the rev counter stays steady.

Yellow tips sounds like it is running weak.

 

[Wyn]

Still convinced this is an ignition/wiring problem.

As am I
Well I found out why it was running so poor on the new needles I had just fitted
Seems the new fixed type needles I had brought are actually shorter then the old spring type, (well no one told me lol) so it must have been running way to rich lol. So after readjusting the jets yet again I got it to run ok
After that I looked at the fuel flow from either carb feed. Using a glass jar (approx 400ml?) and counting it would fill within approx 20/25 secs on each, so imo there’s deffo no fuel supply prob.
Then I tried all new connectors on the coil n dizzy and cut out the old connection where the old ballast resistor was just to be sure, but the misfire was still there afterwards
So after another 10 mile blast n giving it large I got it misfiring at 3k in 2nd at one point, but change up to 3rd n it would then miss at 4.5+ again, so fook knows what’s up. Maybe it’s the temp gauge after all lol
At the end of the day a mate popped round to lend an ear. Stationary and on the throttle it would still misfire so its gotta be electrics
Aiming to get it on a rolling road next.
Till next time

 

[Nigel Brook]

As am I
Well I found out why it was running so poor on the new needles I had just fitted
Seems the new fixed type needles I had brought are actually shorter then the old spring type, (well no one told me lol) so it must have been running way to rich lol. So after readjusting the jets yet again I got it to run ok
After that I looked at the fuel flow from either carb feed. Using a glass jar (approx 400ml?) and counting it would fill within approx 20/25 secs on each, so imo there’s deffo no fuel supply prob.
Then I tried all new connectors on the coil n dizzy and cut out the old connection where the old ballast resistor was just to be sure, but the misfire was still there afterwards
So after another 10 mile blast n giving it large I got it misfiring at 3k in 2nd at one point, but change up to 3rd n it would then miss at 4.5+ again, so fook knows what’s up. Maybe it’s the temp gauge after all lol
At the end of the day a mate popped round to lend an ear. Stationary and on the throttle it would still misfire so its gotta be electrics
Aiming to get it on a rolling road next.
Till next time

Just a long shot. Have you checked the alternator leads and the voltage regulator/cutout?

 

[Wyn]

Just a long shot. Have you checked the alternator leads and the voltage regulator/cutout?

No and no.
Never gave it much thought as the car cranks fine, even after a 2 - 3 week rest, so I'm assuming its charging fine. There is one spare short o/e wire coming off the back of the alternator loom, but it looks to go no where?

What I am thinking next is how I can make the simplest ign circuit to do away with any of the cars own loom?

 

[Wyn]

Plugs should be BPR6ES I tried 7's & they where prone to foul up when starting from cold & that causes a misfire but the rev counter stays steady.

Yellow tips sounds like it is running weak.

Tried 6's - 7's and now 7-11
All run the same without obv low rpm misfire/ non start prob

Think that covers that