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Is This Another Ht Lead Issue?


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#1 gozer

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Posted 17 April 2023 - 04:22 pm

I finally got the mk1 finished (apart from tyres) a couple of weeks ago. I rode it up and down the drive at the back of the house and all was good. Easy starting, nice even tick over, good acceleration etc. I left it for a couple of weeks until I could get the tyres. So, new tyres arrive and are fitted, go to start the bike, and it`s running like a bag `o` shite!

It seems to be running ok on the left pot but intermittent on the right. I had the plugs out to check for a spark and it didn`t seem to be firing at all on the right. Changed the plug and woohoo got a spark. put the plugs back in and crap running returned. 

It`ll start with choke but the merest whiff of throttle and it cuts unless you catch it just so and then it`ll rev, but you have to absolutely rev the balls off it to keep it going. The fuel was freshly bought when I put it in about 3 weeks back so I wouldn`t have thought that an issue but it is already looking a bit yellow but no rank smell.

Do you think that the firing issue is down to HT leads? I have checked it in a dark garage and I can`t see anything arcing out anywhere.

Any pointers from the oracles out there would be gratefully received./ :good:

 



#2 dablik

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Posted 17 April 2023 - 08:46 pm

Check your thermostat is not leaking ! if it is it will pool around the right plug and give you similar/same symptoms, has happened on a few bikes...

 

Edit...even a slow drip will nadger it.


Edited by dablik, 17 April 2023 - 08:47 pm.

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#3 fixitsan

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Posted 18 April 2023 - 08:07 am

Dirt in carbs (the one misfiring) ?


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#4 gozer

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Posted 18 April 2023 - 09:56 am

Check your thermostat is not leaking ! if it is it will pool around the right plug and give you similar/same symptoms, has happened on a few bikes...

 

Edit...even a slow drip will nadger it.

Thermostat checked and bone dry.

 

Dirt in carbs (the one misfiring) ?

Carbs cleaned to clinical levels and rebuilt with brand new jets etc.

The bloody thing was running perfectly a fortnight ago so I can`t see that standing for a couple of weeks  would bung up the carbs. It is misfiring / backfiring / spitting back through the carbs though.



#5 TDrummer

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Posted 18 April 2023 - 11:02 am

I'm no oracle and I would probably pay an oracle to sort it out.

Nonetheless, I'd empty all the fuel, pull, clean carbs, try to restart.

If it's running, get up to full temp, assess performance.

If won't start after carbs cleaned/fresh fuel, I'd replace ignition coil, keep testing. 

 

I did that on my 92 (truthfully, I paid someone to do it).



#6 AdamTDM

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Posted 18 April 2023 - 11:46 am

Try swapping the ignition coils, if the misfire follows the coil there’s your fault.


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#7 fixitsan

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Posted 18 April 2023 - 09:19 pm

Thermostat checked and bone dry.

 

Carbs cleaned to clinical levels and rebuilt with brand new jets etc.

The bloody thing was running perfectly a fortnight ago so I can`t see that standing for a couple of weeks  would bung up the carbs. It is misfiring / backfiring / spitting back through the carbs though.

 

I had a similar problem with dirt that was hiding somewhere in the system made it's way through to the float bowl somehow.

What about a vacuum leak ?


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#8 gozer

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Posted 19 April 2023 - 03:27 pm

Pulled all the bodywork this aft ready to do some mooching with the multimeter tomorrow. I can`t explain why I`m convinced it`s an electrical prob but I`ll test the coil and pickup coil just to be sure. I`ve got a spare cdi so I swapped that today and fed the carbs direct from an aux tank in case the pump was iffy but the problem is exactly the same. I`ll probably regret it by leaving it till last, but I don`t want to pull the carbs again unless I have to.

 

 

I had a similar problem with dirt that was hiding somewhere in the system made it's way through to the float bowl somehow.

What about a vacuum leak ?

Tried shooting some easy start at it while it was running but no evidence of leaks.

 

 

Try swapping the ignition coils, if the misfire follows the coil there’s your fault.

It`s a 3VD so only one coil, wasted spark type firing.



#9 Snowbird

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Posted 19 April 2023 - 03:58 pm

Switch the wires on the coil and see if the problem moves cylinder, the old 2cv's used to foul one plug and swapping coil wires would clear it till other side fouled, one side of the spark tends to jump a bigger gap than the other, I get it on bendix magnetos at work all the time.


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#10 dandywarhol

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Posted 19 April 2023 - 05:46 pm

I'd change the leads anyway - for under a tenner you'll have new wires. The wire is steel on Japanese bikes and corrodes at the ends where moisture can get in - copper core is the answer and while you're at it you might as well take the resistor out of the plug cap and put a bit of welding rod in place. Then you'll be sparking!  :pimp:


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#11 Rallyist

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Posted 20 April 2023 - 07:37 am

Check the plug cap as well I had one that caused an intermittent misfire


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#12 gozer

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Posted 20 April 2023 - 10:40 am

I`ll be checking the coil / leads etc later today. I`m just REALLY puzzled as to why it ran perfectly on multiple occasions and then started playing up instantly the first time I tried to start it after being stood in the garage for just 12 days!!


Edited by gozer, 20 April 2023 - 10:40 am.


#13 Bjørge

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Posted 20 April 2023 - 11:01 am

I had a leaking tank cap causing repeated intrusion of water causing trouble like this. Rubber in cap seal was stone hard.


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#14 gozer

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Posted 21 April 2023 - 10:54 am

I checked all items in the ignition system yesterday and every reading was in spec. Cleaned all connections and made sure they were tight, put it back together but the soddin` problem is still there. I guess it must be a carb issue after all.

It won`t start without choke even if I`ve managed to get it warm. then it constantly coughs and farts and spits back through the carbs. Even the tiniest whiff of throttle, and I mean anything that just takes the slack out of the cable, and it cuts out immediately, unless you just happen to catch it and then it won`t keep running unless you`re absolutely thrashing the balls off it.

It`s absolutely doin` me feckin`  swede in now seeing as it ran perfectly at first and started this malarky for no apparent reason. :angry:

I`d be really grateful if there is a carb wizard out there who could tell me what I should be paying specific attention to when I pull the carbs to pieces.

Ta very muchly.



#15 Snowbird

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Posted 21 April 2023 - 10:57 am

An airline with a fine nozzled blow gun helps no end when clearing carb passages, poking with bits of wire can cause further issues if not careful.

Can't advise any more as never had TDM carbs apart or even off for that matter.


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#16 fixitsan

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Posted 21 April 2023 - 01:32 pm

""It won`t start without choke ........................ then it constantly coughs and farts and spits back through the carbs.""

 

Sounds like too lean for sure.

 

Out of interest when it only runs on the left cylinder, is that with the bike on the sidestand, leaning over to the left ? If so, does it change when you lean the bike to the right, in which case I'ld be looking at the fuel pump. I had a tiny piece of dirt in the fuel pump once, preventing the rubber one way valves to seal properly whcih meant pumping wasn't at full pressure


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#17 curlylegend

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Posted 21 April 2023 - 09:09 pm

""It won`t start without choke ........................ then it constantly coughs and farts and spits back through the carbs.""

 

Sounds like too lean for sure.

 

Out of interest when it only runs on the left cylinder, is that with the bike on the sidestand, leaning over to the left ? If so, does it change when you lean the bike to the right, in which case I'ld be looking at the fuel pump. I had a tiny piece of dirt in the fuel pump once, preventing the rubber one way valves to seal properly whcih meant pumping wasn't at full pressure

 

Or an air leak ?



#18 Studley Ramrod

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Posted 22 April 2023 - 02:27 pm

It's soooo difficult to diagnose a problem without being there.  I'm happy to go over the carbs if you pay for postage.

 

The coil could be breaking down, it can pass the multimeter tests but still break down at low revs. A fully charged battery is a must too, like 12.8v not 12.5v.


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#19 gozer

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Posted 22 April 2023 - 03:00 pm

 

Sounds like too lean for sure.

 

 

 

 

Or an air leak ?

 

It's soooo difficult to diagnose a problem without being there.  I'm happy to go over the carbs if you pay for postage.

 

The coil could be breaking down, it can pass the multimeter tests but still break down at low revs. A fully charged battery is a must too, like 12.8v not 12.5v.

What is absolutely twisting my melon man is why it has suddenly started doing it out of the blue as it was running and riding perfectly when I put it all back together. It was started many times for checks and carb balancing etc but it hasn`t been in use, only ridden up and down the drive at the back of the house. It was then parked up for 12 days until I could get some tyres and then the first time I tried to to start it this problem appeared.

That was what convinced me it was electrical as I know leccy bits can give up the ghost at the drop of a hat, but every thing is giving good readings and yes, I made sure the battery was fully charged and it is brand new. I may get another coil if I see a cheap as chips one.

Diagnosis at a distance is nigh on impossible and thanks for your kind offer of giving them the once over Studders and I might come back to you on that, but I`m not frightened of pulling them to bits again. I was just hoping to be pointed at exactly what I should be paying attention to. I`ve rebuilt many a carb in the past and never had anything like this before. For now I`m going to follow the concensus that it`s down to a lean mixture and give the carbs another smack with a Brummie screwdriver!  I`m still hoping someone might look at this thread that has had this exact prob happen to them and tell me what it is but I`d still be grateful for any suggestions (careful now!) along the way



#20 fixitsan

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Posted 22 April 2023 - 05:02 pm

 

Or an air leak ?

 

Yup, I suggested that already, need to make sure all the vacuum takeoffs are attached or blanked off


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