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When I first got my T150 I spent a whole summer chasing carb issues that resulted in plugs that looked just like yours. Turned out the problem was a bad ignition switch and the ignition system was running on about 6 volts. I don't know if that's possible with this modern electronic ignition, but it's simple enough to test for. (Put a volt meter on the hot lead of any one of the coils and see what you get.)

Lucas's law: 90% of all carburetor issues are electrical in nature.
 

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When I have a difficult to start bike I change the spark plugs wires and the connectors... it helps a lot.


Sent from my iPhone using Tapatalk
 

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Discussion Starter #43
  • the choke mechanism is working and is off
  • I checked the mix screws, they were all three between 2 and 2.5 out
- I did some measurements
Batt: 12.8V
I switched contact on.
Over the primary I measured 350mV.
Then I put the black lead on minus of battery.
On one of the contacts of the primary I measured 11.7V (during starting it drops to a value between 9.5 and 10V), on the other almost zero.


Looks all normal, I believe...
 

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Hoi Jan.
@ the problems you are dealing with, ... that you learn a lot.
That's the right attitude.
@ Is there a way of adjusting, without removing the carbs from the bike?
No that's all mess. ( the more often you put them away, the better you get at them) :oops:

Angle screwdriver I bought this from Louis but i still had to be adapt because the coolant pipe is in the way.( cil 1) from both sides.
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@ Don't have the tools right now to do a synchronisation again.
If you have three lower balls you can also do this yourself when the carburettor is out, if all three fall at the same time, the carburettor is perfect.
Take your time.

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@ Luckily I wrote it down. All 3 measured 17.5mm.
petrol supply needles clean ??
Yes, I think so.
Okay simple test gasoline is out there from supply hose is still on it , blow on it and see if they seal properly.
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Does this work ?
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WSC:
@(Put a volt meter on the hot lead of any one of the coils and see what you get.)
I did this as a good zero measurement ,with perfect engine,starts perfectly.
Battery = 12,56
lights off = 0,38
lights on = 1,17
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Perhaps Kehin.s law is: 90% of all electrical are carburetor in nature.:);)
We don't know sooner if we rule it out first.
 

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WSC:
It is another discussion I know but do it here anyway.
I read from you:
@ Low voltage at the horn is only the symptom of a bigger problem. (Why is there low voltage at the horn? And, where else is the voltage low? It's not the horn's fault!)
I am purely out of interest this measurement also done.

And found it baffling.
2.5 volt loss with light on. ( to the horn )
0,91 v light out.
I have several thunderbird, s all the same. Volt,s loss
I read you solution with relay, and what is the cause.
No problem at all for me , they are doing well. ( that was not why I did it)
Just out of curious ,and now plenty of time lockdown.
Learned something from you again.
So it is just structural,by design.
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The problem is the contacts in the ignition switch are overloaded. In addition, US bikes have the headlight wired always on, so the ignition swiith has to handle the initial surge, which is much worse than just carrying the running load.
 

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Discussion Starter #49 (Edited)
This doesn't look ok. (On all 3 carbs)
What can be the cause???
Still an assembly mistake made by me?



I allready did the blow test. Slide goes up when blowing.
 

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Jan, I understand that you want to do and learn everything yourself, but sometimes it is not unwise to get someone to help you further , otherwise you may stay in the same circle all the time.

@This doesn't look ok.
Hard to judge, they go all the way up when you accelerate ?

@ What can be the cause???
From here difficult to judge, all holes are clean, diaphragm works well ( its good you say ) than spring works well , butterfly valve works well ?

@Still an assembly mistake made by me?
I was not there so ?? hard to say.

Got the impression from the very short film that the engine starts wery well.
And good running at idle speed. ( with choke or without )?

Do that again , just let him run , turn the idle screw , something changes ?
Open the choke or close carefully , something changes ?
Play with this parameter, s what is happening ?

Is your air fiter, clean ?

You tube:
How does a CV Carburetor works - Quick and simple explanation.
 

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Discussion Starter #51
Yes, it is getting a bit frustrating at times. Don't have anyone in the neighborhood to help a hand... So I will have to succeed.:)

Yes, the filter is clean (it's a K&N filter that I cleaned and oiled)

I made a longer clip. The slider is really not staying stable, it's dancing up and down during idle running. I believe this is abnormal?
And engaging the choke is letting it run really wild in rpm.

And another clip where I use the throttle. It's going up, but still a lot of shaking. It looks that there also is a lot of delay on throttle response.


Don't know if you guys have any idea after watching these video clips.
Thanks anyway!!!
 

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In clip TBS-B the slide goes up upon opening the throttle but the RPMs don't go up until the throttle starts to close. That indicates either a lean condition or the engine is not warmed up enough. What is more troubling to me is the loud clicking/clanking noise and how the engine seems to stall momentarily each time the noise occurs. That sounds like your cam chain tensioner has gone bad or the timing rotor on the right hand end of the crankshaft has come loose or both. I would check into that before running the engine any more because either condition, loose chain or loose rotor, can cause a catastrophic failure that would be quite expensive to repair. I think your carbs are close enough for now.
 

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Discussion Starter #53
Hi Green,
I have a lot of backfire on the video clips. Plus I have a small opening in the pipes running underneath the engine. The pop is coming out there and my camera alters that sound a lot.
Just to be sure, I made a small clip. I had a backfire at second 3 and at second 7.
In real it's a loud pop, on video a very different sound.
I think (hope) you are referring to that noise?
 

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The bike won't accelerate correctly with the airbox off; it does go lean, but that's normal. The jetting is way off for that condition. The slides bouncing around at idle is also normal, especially without the airbox to smooth out the pressure pulses.
 

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The backfire at 7 seconds came back through the carb, you can see the flash. Not good.
 

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Jan I give one more time my opinion , do with it what you want.
I read you have mainly working on 50cc oldtimers.
Which is somewhat less complicated than what you are doing now.
As you see in your own videos, the petrol itself goes the wrong way,
As WSC writes , nothing is correct so , let alone that you can adjust something, or take a conclusion.

The assumption that Green01Sprintst do which the timing rotor has come loose , I personally think it is doubtful I think it will not start at all in my opinion or still run reasonably.

if you still want to check the rotor this is not so difficult, you will probably need a new gasket.( put grease on the new, perhaps you can use it again next time)

A loose cam chain tensioner I really can not judge on the basis of the videos.
But maybe has Green01Sprintst more experience with this.

But if you plan to check it out it is recommended to keep the chain taut, with attachment that you can make yourself. ( put on tensioner olso a new gasket.)

My story is now complete , if the TBS is all right once , you really have a very good engine I speak from experience.
Succes.
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Triumphjan, I mentioned the possibility of the rotor being loose because it happened on my Trophy 1200. The bolt had backed out almost 2 full turns allowing the rotor to flail around making all sorts of ugly noises and wreaking havok on the timing. The cam chain was slightly loose; the tensioner spring was sacked and around 4-5mm shorter than it should have been. I was easily able to get 2 additional clicks of tension on the chain. So yes, I have some experience with loose timing chains and loose rotors and I can say from recent experience that it can happen and it will cause problems with both ignition timing and cam timing.
 

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Green01Sprintst a completely understand.
The remark: But maybe has Green01Sprintst more experience with this.
Was also meant sincerely , therefore also the photos.
If you have had it yourself I understand that you warn Jan for it.

And it is easy to control.
if I had experienced it myself I would have certainly said just like you.
I have never seen or heard of it with a Thunderbird, in all those years.
And I know many.
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Discussion Starter #59 (Edited)
First of all, thank you all for the great advice, tips and help. Especially triumphjan! What a luxury with all those clear pictures.

About my experience. I have been working on and off on 50cc 2-stroke bikes a lot the last decade. I learned a lot over the years, especially for Flandria and Yamaha FS1. (You tend to "specialise" in 1 or 2 brands/types) Occasionally I worked on a 4-stroke (Honda Dax and CB125).
The experience you gain over the years, is the most valueable when troubleshooting a similar bike.
In the meanwhile I followed some evening courses on motorcycle mechanics. The TBS is my first Triumph ever, my first motorcycle ever, my (almost) first 4-stroke, my first liquid-cooled, my (almost) first multi-cilinder,...
I like wrenching on bikes, maybe even more than riding. But experience is what is missing here. I still have to learn a lot.
So I have made an appointment with a professional. Next Saturday we will have a look at it together. I can't wait to find out the cause of these problems. And of course, I will share it here.

About the worse scenarios suggested here (bad cam chain tensioner or loose timing rotor): I cannot state that this is 100% not the case, but I find this hard to believe. I don't hear any metallish noise or really bad sounds coming out of the engine. Only some backfire, with a very distorted sound on the video. Before the disassembly of the carbs, my bike was running fine once it was started. (I think the bad starting got solved by replacing the spark plugs and battery.)

It's hard to wait till Saturday... :)
So in the meanwhile, I did again a full dis/assembly of the carbs. I didn't notice anything strange.
This time I also screwed out the mixture screws. Only the screw and spring came out. The washer and O-ring didn't came out, but I could see they were there. I didn't try to take those out, for fear of damaging the O-ring.
Maybe it is best to replace these O-rings?

I doublechecked the membrane/diaphragma into the light: no tears.
I also did the blow-test on the atmosphere intake: slides go up and down smoothly.
I also did the blow-test on the petrol tube, while turning the carbs: they close off very good.
Butterfly valves are opening/closing smoothly.
I extra tightened the pilot jets. (they were hand tight, now I put an extra snug on it)
I turned the mixture screws out 2 1/4.
I visually checked the intake rubbers: can't see any rips.
I connected the choke cable and tested choke mechanism: works smoothly.
I connected the gas cable (what a pain in the ...!). I checked by using the throttle: works smoothly, cable doesn't hang and gas mechanism comes back easy.
I put the carbs back onto the rubbers as deep as possible and tighten the bands real tight.
I connected the fuel line.
I checedk to see if the 2 breather tubes are not pinched.
I connected the engine breather pipe to the air box.
I connected the airbox to the carbs and tightened them.
I also connected the aux box.
I checked the connections of the coils and plug wires.

Conclusion: still not running good. Off course. :)
Alltough I have the impression it runs a bit better. I think less backfires.
Idling sounds a bit better, but not always. (maybe synchronising will fix this...)
Engine doesn't want to stall as badly as before, when opening the throttle.
But the rpm's keep hanging after releasing the throttle.
I find it strange that I appearantly did nothing different than before, but the engine runs a bit better. But still not ok!
 

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This will be fine, great progress has been made.
Good reporting.
@I connected the gas cable.
I myself always do this on handlebar.

@ I put the carbs back onto the rubbers as deep as possible
very important (you can hear this well , if they fall into the rubbers)

@Only the screw and spring came out. The washer and O-ring didn't came out.
Is often so.

@ Maybe it is best to replace these O-rings?
Get hard over the years.

@ But the rpm's keep hanging after releasing the throttle.
Adjustment throttle on handlebar ,is good. 2-3 mm

@I find it strange that I appearantly did nothing different than before
cleaned, checked, securely fastened , it can be very small things.
 
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