Problems with Z900A4

[sprint]

Hi

I am having problems with my UK 76 Z900A4.

I restored it a few years ago and up until a few months ago had been running fine. It is in standard build with original 4 into 4 pipes, carburation, air box etc. It is however, fitted with a Dyna S electronic ignition.

The problem is as follows:

Bike starts and ticks over smoothly and without any problems and on gently acceleration pulls away. However, if you suddenly open the throttle or try to go for a fast acceleration the engine will more or less die and splutter, etc and will not improve if you hold it at that throttle position. Close the throttle and open the throttle gently and it will pick up. All plugs, NGK B8ES were black and sooty, see attached, No 1 on left.

The carbs had previously been stripped and cleaned with carb cleaner and an air line and float levels set and I have also done the relay mod which did improve the previous problem I have with sooty plugs. I removed the float bowls and jets in situ and they were all fine. Run the bike again no change.

So I decided to fit some hotter plugs, NGK B7ES. For around 40 miles all seemed fine but then I noticed that all pots were not firing properly. Completed the remaining 20 miles in that state.

On the return journey on closing the throttle and at low speed it started to backfire on No 4, as reported form somebody who was following me. It then cut out on occasions on at least one pot and misfiring. And the problem of the engine dying on fast acceleration or opening the throttle fast from a steady speed remains.

On getting home I found that on tickover both No 3 and 4 pots were misfiring, but No 1 and 2 seemingly OK.

Removed the plugs, see attached, to find that No's 1, 2 & 4 less sooty but No 3 still very sooty. Have removed the jets on No's 3 & 4 and they are still both clear.

Coils seem OK and can jump around 8mm and there is no indication that there is a problem specifically with No's 1 & 4 or 2 & 3?

Don't feel that there is a problem with the electronic ignition, but I have no way of checking that beyond seeing that the coils spark.

Have done a cold compression test with all between 120 & 130 psi.

Air filter has only done around 5K miles and does not look dirty.

I have run out of ideas and would appreciate some suggestions?

[z1bman]

i would say its a faulty ignition coil

[sprint]

i would say its a faulty ignition coil

Thanks for the reply.

However, as indicated that being the case I would expect the same problem with No's 1 & 4 and No's 2 & 3 as they use the same coil?

[Pigford]

i would say its a faulty ignition coil

Thanks for the reply.

However, as indicated that being the case I would expect the same problem with No's 1 & 4 and No's 2 & 3 as they use the same coil?

Not necessarily - if the ignition was weak, there may only be enough power for 1 x decent spark at a time and the plug/lead with the least resistance would fire whilst the other of the pair, may not.

[johny brando]

Hi

I am having problems with my UK 76 Z900A4.

I restored it a few years ago and up until a few months ago had been running fine. It is in standard build with original 4 into 4 pipes, carburation, air box etc. It is however, fitted with a Dyna S electronic ignition.

The problem is as follows:

Bike starts and ticks over smoothly and without any problems and on gently acceleration pulls away. However, if you suddenly open the throttle or try to go for a fast acceleration the engine will more or less die and splutter, etc and will not improve if you hold it at that throttle position. Close the throttle and open the throttle gently and it will pick up. All plugs, NGK B8ES were black and sooty, see attached, No 1 on left.

The carbs had previously been stripped and cleaned with carb cleaner and an air line and float levels set and I have also done the relay mod which did improve the previous problem I have with sooty plugs. I removed the float bowls and jets in situ and they were all fine. Run the bike again no change.

So I decided to fit some hotter plugs, NGK B7ES. For around 40 miles all seemed fine but then I noticed that all pots were not firing properly. Completed the remaining 20 miles in that state.

On the return journey on closing the throttle and at low speed it started to backfire on No 4, as reported form somebody who was following me. It then cut out on occasions on at least one pot and misfiring. And the problem of the engine dying on fast acceleration or opening the throttle fast from a steady speed remains.

On getting home I found that on tickover both No 3 and 4 pots were misfiring, but No 1 and 2 seemingly OK.

Removed the plugs, see attached, to find that No's 1, 2 & 4 less sooty but No 3 still very sooty. Have removed the jets on No's 3 & 4 and they are still both clear.

Coils seem OK and can jump around 8mm and there is no indication that there is a problem specifically with No's 1 & 4 or 2 & 3?

Don't feel that there is a problem with the electronic ignition, but I have no way of checking that beyond seeing that the coils spark.

Have done a cold compression test with all between 120 & 130 psi.

Air filter has only done around 5K miles and does not look dirty.

I have run out of ideas and would appreciate some suggestions?

Definitely electrode centre's are showing now running too hot with those B7ES plugs ! But certainly a good move just to try them ......& clearly instantly ...it seemed to run better & make a difference in the first 40 miles...perhaps then the new plugs just started to get too hot & break down as a result.. ignition electrical components tend to do just that with heat. As your aware there are numerous possibles culprits & even more possible combination factors that can show up.....that said with the limited available info it certainly seems either just too rich OR showing too rich due to incorrect or incomplete combustion due to ???? Try to initiate only ONE change at a time & then try the bike under load ! each time .....then move on ( as numerous combined changes will leave you not knowing what the route cause really was .... it's an elimination project aye ! ) Where assuming (please check first ) that your mixture Air Screws are all about 1.5 turns out & your battery & charging system are functioning correctly here ..low voltage can cause ignition woe's so ensure all's well there & your battery is taking & holding a charge correctly & is consistently over 12 volts & is charging at 13.5 v or more .
Clean & gap refit old B8ES plugs & then first try running with no air filter " see if there is any general improvement " ....could be the old paper element is just restricting flow ? due to perhaps just old age ?...they may look clean but doesn't always mean that there flowing enough fresh air . Then try as another simple quick experiment changing the plug caps from another known good source ( beware resister plug caps & some certain plug types ...do not work well together ! ) Assuming you still have the OEM ignition set up... I'd then try swapping both the Advance & Retard unit ( ensuring it first rotates-operates smoothly & freely & the points cam is fitted correctly !! ) and then fit the points plate Assy & re-time it & test ride again. If the issue then still persists ....best go back to the carbs ,as it most likely is there ( go deeper within them & don't forget to check choke plunger seals ) I hope this might be of some help to you & I expect there will be others along to help & chip in too . Good luck . Johny. B.

[sprint]

Hi

I am having problems with my UK 76 Z900A4.

I restored it a few years ago and up until a few months ago had been running fine. It is in standard build with original 4 into 4 pipes, carburation, air box etc. It is however, fitted with a Dyna S electronic ignition.

The problem is as follows:

Bike starts and ticks over smoothly and without any problems and on gently acceleration pulls away. However, if you suddenly open the throttle or try to go for a fast acceleration the engine will more or less die and splutter, etc and will not improve if you hold it at that throttle position. Close the throttle and open the throttle gently and it will pick up. All plugs, NGK B8ES were black and sooty, see attached, No 1 on left.

The carbs had previously been stripped and cleaned with carb cleaner and an air line and float levels set and I have also done the relay mod which did improve the previous problem I have with sooty plugs. I removed the float bowls and jets in situ and they were all fine. Run the bike again no change.

So I decided to fit some hotter plugs, NGK B7ES. For around 40 miles all seemed fine but then I noticed that all pots were not firing properly. Completed the remaining 20 miles in that state.

On the return journey on closing the throttle and at low speed it started to backfire on No 4, as reported form somebody who was following me. It then cut out on occasions on at least one pot and misfiring. And the problem of the engine dying on fast acceleration or opening the throttle fast from a steady speed remains.

On getting home I found that on tickover both No 3 and 4 pots were misfiring, but No 1 and 2 seemingly OK.

Removed the plugs, see attached, to find that No's 1, 2 & 4 less sooty but No 3 still very sooty. Have removed the jets on No's 3 & 4 and they are still both clear.

Coils seem OK and can jump around 8mm and there is no indication that there is a problem specifically with No's 1 & 4 or 2 & 3?

Don't feel that there is a problem with the electronic ignition, but I have no way of checking that beyond seeing that the coils spark.

Have done a cold compression test with all between 120 & 130 psi.

Air filter has only done around 5K miles and does not look dirty.

I have run out of ideas and would appreciate some suggestions?

Definitely electrode centre's are showing now running too hot with those B7ES plugs ! But certainly a good move just to try them ......& clearly instantly ...it seemed to run better & make a difference in the first 40 miles...perhaps then the new plugs just started to get too hot & break down as a result.. ignition electrical components tend to do just that with heat. As your aware there are numerous possibles culprits & even more possible combination factors that can show up.....that said with the limited available info it certainly seems either just too rich OR showing too rich due to incorrect or incomplete combustion due to ???? Try to initiate only ONE change at a time & then try the bike under load ! each time .....then move on ( as numerous combined changes will leave you not knowing what the route cause really was .... it's an elimination project aye ! ) Where assuming (please check first ) that your mixture Air Screws are all about 1.5 turns out & your battery & charging system are functioning correctly here ..low voltage can cause ignition woe's so ensure all's well there & your battery is taking & holding a charge correctly & is consistently over 12 volts & is charging at 13.5 v or more .
Clean & gap refit old B8ES plugs & then first try running with no air filter " see if there is any general improvement " ....could be the old paper element is just restricting flow ? due to perhaps just old age ?...they may look clean but doesn't always mean that there flowing enough fresh air . Then try as another simple quick experiment changing the plug caps from another known good source ( beware resister plug caps & some certain plug types ...do not work well together ! ) Assuming you still have the OEM ignition set up... I'd then try swapping both the Advance & Retard unit ( ensuring it first rotates-operates smoothly & freely & the points cam is fitted correctly !! ) and then fit the points plate Assy & re-time it & test ride again. If the issue then still persists ....best go back to the carbs ,as it most likely is there ( go deeper within them & don't forget to check choke plunger seals ) I hope this might be of some help to you & I expect there will be others along to help & chip in too . Good luck . Johny. B.

Thanks for the very detailed response and suggestions.

1. I have a Dyna s electronic ignition fitted which uses the original mechanical adv/ret mechanism, which I believe to be functioning OK.

2. All the air screws are between 1.5 and 2 turns out.

3. Battery and charging OK and as previously advised I have done the relay mod (to connect battery voltage directly to the coils) when I first re-built the bike.

4. I have NGK resistor plug caps fitted and they all check out at around 5K ohms.

5. Primary coil resistance around 5 ohms and secondary resistance around 25K ohms and they create a 7 to 8mm spark, so they seem OK?

6. Bike has been running for some 3 years without problems so it is something that has developed over the last few months.

Will do as you suggest about cleaning and re-fitting the B8ES plugs and remove the air filter and see what difference it makes. But with the B7ES plugs fitted No 3 was still very sooty and as a result I checked jets again which are all clear.

At the moment I am not sure as to if it is an electrical or carb problem? There is a bike garage not too far away that has a DYNOSTAR Model 70 Dyno so if all else fails I may take it there as they should be able identify as to if it is a carb or ignition/electrical issue?

[z1bman]

have you got a colour tune to see exactly what's happening as regards the mixture settings