Help save my trip! Bike doesn't run when warm

Bjorn

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Hi guys,

I could really use some help fixing my bike. I plan on going for a trip next Friday with some friends. I've been building my bike for way to long and trying to get it running. Here is the situation.

Bike starts fine, runs strong for anywhere between 15 and 45min, after that it starts to misfire, stumble or hesitate. I notice this especially in the lower rpm range or small throttle openings. If I let it cool down for a bit, see runs for a while before it's back.

I really don't know where to look anymore. Here is what I've done so far or some background info:

-Got a new Speedo with voltmeter. Charging seems to be ok around 14,5v
-i suspected the coil. Changed it for an identical backups I had laying around. Measurements show similar ohm values between the 2 coils when cold. With it I replaced the plug wires, caps and plugs. Did not make a difference.
-then I thought it might be fuel related, because if I give it WOT it pulls through the stumbling. Although it's hard to be 100% of this in traffic.
I did not to anything to the engine/exhaust/intake during the build. Bike ran fine before. I cleaned the entire carbs, checked the diaphragms, all the jets, the choke (enriches) nothing weird found.
- bike has fuel in the tank
- cleaned the airfilters, they were dirty. Proper KN ones, been running them for multiple years.
-camchain play is ok. Valves were somewhat sloppy, redid those.
- bike has TCI ignition. Oem pickup, aftermarket replacement carmo TCI box.

Does anyone have anything to aim at? Time is ticking and I'm lost.....
 
Vent hole may be blocked as suggested by gggGary. With a blocked vent as the fuel is consumed a slight vacuum develops in the air space of the tank and eventually it becomes high enough to stop the fuel flowing. Next time it happens pull to the side of the road and open the petrol cap then close it and continue on and see if the problem is solved temporarily.
 
If not the fuel vent issue, then I'd be looking to the TCI, as Gary suggested. My stock one was acting in similar fashion. Fine cold, then quit. Mine was the stock system.
 
Gonna try the tank vent!

The TCI box is new and far away from the heat of the bike. I do happen to have the original TCI box . I know it doesn't advance the spark (that's why I got a replacement) but it does work. The bike is just not as fast.

What about that pick up. It is close to the heat of the engine....
 
Bjorn, I see you used the Carmo ignition. We do not hear much about them. I was going to install one on a Virago but it seems a bit awkward ordering via the UK at the time during Covid shutdown. Carmo also offers a repair service for the stock XS TCI. Have you noticed an improvement in fuel consumption or any other benefits since installing?

Thank you.
 
I once had a similar problem
Boyer Bransden Ignition
At highway little higher speeds .. Warm weather one cylinder dropped .
running home on one cylinder
When cooled down it ran perfect .
Not possible to fault finding on something that is not there
I had the Stock voltage regulator
I installed a voltmeter temporarily .And saw that it was charging to much
Replaced to an electronic regulator. And corresponding rectifier And the problem disappeared.
I used autoparts that I knew was working.

Perhaps riding with everything on high beam lights so that the voltage to the circuits are lover.
On the other hand the alternator works harder
I believe it was the high Voltage causing more electrical heat and thermal expansion shorting somewhere
Or the Boyer setup somewhere.
Regulator and rectifier is perhaps the cheapest to replace.
I do notice that the voltage appears to be correct in Your case
Just saying what it was in my case.
The thermal expansion can happen at many places.
 
Bjorn, I see you used the Carmo ignition. We do not hear much about them. I was going to install one on a Virago but it seems a bit awkward ordering via the UK at the time during Covid shutdown. Carmo also offers a repair service for the stock XS TCI. Have you noticed an improvement in fuel consumption or any other benefits since installing?

Thank you.

I like the box (only if it doesn't turn out to be faulty now haha)
You should not really see it as a upgrade over the stock system. It's not programmable or anything. Is a modern replacement in a different housing. Using modern components and a potted against ingress of water. For me it was a improvement because my original TCI box did not advance. Btw this came from carmo in the Netherlands (were I life). No lockdown here....

Btw
 
I once had a similar problem
Boyer Bransden Ignition
At highway little higher speeds .. Warm weather one cylinder dropped .
running home on one cylinder
When cooled down it ran perfect .
Not possible to fault finding on something that is not there
I had the Stock voltage regulator
I installed a voltmeter temporarily .And saw that it was charging to much
Replaced to an electronic regulator. And corresponding rectifier And the problem disappeared.
I used autoparts that I knew was working.

Perhaps riding with everything on high beam lights so that the voltage to the circuits are lover.
On the other hand the alternator works harder
I believe it was the high Voltage causing more electrical heat and thermal expansion shorting somewhere
Or the Boyer setup somewhere.
Regulator and rectifier is perhaps the cheapest to replace.
I do notice that the voltage appears to be correct in Your case
Just saying what it was in my case.
The thermal expansion can happen at many places.

Hi Jan,

I'm gonna try the original TCI box to see if that makes any difference. Also my bike uses the regulator and rectifier in one.

Would swapping it out make any difference? The Speedo has a voltage meter. And it appears to charge fine. Only when it starts to stumble I see the voltage fluctuating between 14,5 and high 12s. However I'm unsure if this is really the case or the misfiring has a weird effect on the Speedo.
If it is a charging problem, doesn't make sense I can let the bike cool and continue riding....
 
Only when it starts to stumble I see the voltage fluctuating between 14,5 and high 12s.
If that's the case then it very well could be a charging issue. Your replacement TCI box could see that as spikes. It might want a clean voltage and acts up with fluctuations.
On the other side of the coin... the misfiring shouldn't cause the charging system to fluctuate.
 
Outside the box.
Do you have a vacuum petcock ? Reason being, I once noticed years ago that if vacuum supply line (s) from the manifold to the petcocks are too soft when they get warm and soft the engine vacuum can collapse the tube ahead ot the petcock which then affects the petcock function.
Cutting off the fuel..
 
I just tested the tank vent on the bench since it's night over here. Kept it running for a few minutes, good stream coming from the fuel line. I can even hear air rushing into the tank via the cap. I think we can rule this one out.
IMG_20200906_232838956.jpg
 
If that's the case then it very well could be a charging issue. Your replacement TCI box could see that as spikes. It might want a clean voltage and acts up with fluctuations.
On the other side of the coin... the misfiring shouldn't cause the charging system to fluctuate.
Hmmmm.... I'm wondering out loud if the rotor could be failing. If it is the original, as in never had a rewind, it's a matter of when it will fail and not if. It will also be affected by heat.
 
If that's the case then it very well could be a charging issue. Your replacement TCI box could see that as spikes. It might want a clean voltage and acts up with fluctuations.
On the other side of the coin... the misfiring shouldn't cause the charging system to fluctuate.

Good point there!

I don't fully understand were the voltage comes from. I thought everything in the system is powered by the battery. Should that act as a buffer for the system?

The reason I find it hard to judge the voltage during stumbling is that it's mostly around or just above idle. Where charging isn't at its strongest anyways.

Or could it be a problem in the electrical wiring/batt itself?

Two years ago I had a intermittent electrical problems where on of the battery cells was failing due to vibrations. However it's wouldnt start at all during that. It was a non automotive batt, now I got a proper motorcycle batt in there since last year.
 
Hmmmm.... I'm wondering out loud if the rotor could be failing. If it is the original, as in never had a rewind, it's a matter of when it will fail and not if. It will also be affected by heat.
Yes that makes sense!

My stator failed me a couple years ago. Replaced that and kept the rotor since it didn't show any signs of shorting out.

Jeez, seems like every year something is failing on this machine....
 
If it's toast I'm out of the trip. There is no way I can have stuff rewound in days.

Still thinking about that battery voltage.

I was looking through some videos of the last few days of testing. Here is something interesting:
It's in Dutch but what's happening is that it started to stumble, I turn off the lights (low beam, this indication light is weird) and the engine is smooth again. See the video.


However today I tested during the day, never had lights on...
 
Hi Jan,

I'm gonna try the original TCI box to see if that makes any difference. Also my bike uses the regulator and rectifier in one.

Would swapping it out make any difference? The Speedo has a voltage meter. And it appears to charge fine. Only when it starts to stumble I see the voltage fluctuating between 14,5 and high 12s. However I'm unsure if this is really the case or the misfiring has a weird effect on the Speedo.
If it is a charging problem, doesn't make sense I can let the bike cool and continue riding....

I scratched my head when I had that problem as i mentioned
Hot I had problems
Cold ran perfect.

Hot machine you burn your fingers trying to locate the fault.
Cold it is not there .It is not possible to find not even Toyota could do it on a brand new car for a friend of mine

So I ended up replacing parts .As per Judgement ; If I remember correctly I bought a New Boyer system first
And then in the end found the Regulator.
So I nowadays have a tendency to go after the cheapest part first and .. Move up in the price range
If nothing obvious points to a certain Component.
Stators and rotors can give measurement values indicating if faulty at times.
But in my cases the charging voltage was not over 14 V if the alternator had problems.
But it can of course happen if not broken yet.

I would not immediately connect the stock TCI for testing because if it fries it is a costly mishap.
I have also had problems with the alternator.
Rewound 1 stator bought one replacement and one rotor.
Also expensive in relation to rectifier or regulator. ca 5 x more expensive.
The regulator are in my experience sensitive not the rectifier but since this is a unit. Well

To me a fluctuating voltage with a battery in -- indicates something wrong there
high 12 .s is battery with no charging aka shorted somewhere.
14 is charging ..
 
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