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Old 29th June 2012, 21:21   #1
Tgo
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Default Throttle Position Switch of Thunderbird Twin-Spark UCE

Hello people. I need help in solving the stuttering problem I am facing with my 2009 TBTS. http://www.team-bhp.com/forum/motorb...xperience.html (Take 3 - 2009 Royal Enfield Thunderbird (Ownership Experience))

Let me describe what the problem is and what all has been done to get rid of it, till now.

>>
I noticed about a month and a half ago, that I could not get the bike rolling from stand still as the engine used to die. I thought this was because the engine doesn’t heat up. I could only manage to get the motorcycle rolling by releasing the clutch at high revs. I suspected that the carb overflows while the bike is parked.

Action: Did nothing, just turned the fuel tap to the OFF position before kick starting the bike. It worked sometimes but sometimes it did not seem to solve the problem at all. Even opening the throttle after idling made the engine stall. Continued like this for quite a few days when I realized that the problem was somewhat different and not related to an overflowing carb.

>>
I noticed that the engine stuttered, more like skipped a beat when the throttle was at around 20% open. I suspected that there is some water in the carb or it is somewhat choked and needs cleaning. I asked my mechanic to clean the carb.

Action: He cleaned the carb and claimed that he found some water in it. He said that he also checked the spark plugs and said that they need to be replaced. He had removed the spark plug adapter of the bigger plug saying that the current is leaking from it. He connected the HT cable directly to the bigger spark plug and said that the “missing” has reduced.

>>
I did not apply my brains then and took the bike for a trip to Madikeri we had planned for the next day. The missing was still present and happened at around 15-20% of opening of the throttle. Not before that nor after that, exactly at around 15-20%. By now I was sure of three things.
  1. The missing is not related to the carburetor needing a cleaning
  2. The spark plug adapter that he removed was not faulty as the missing should have vanished when he connected the cable directly to theplug
  3. The problem was related to the ignition timing of the engine.

I dropped off the bike for one last time at his garage saying that I am not happy with his job and that I want him to swap the plugs with some healthy bike and se if the spark plugs need a change. He did so and conveyed to me that the wiring has gone bad and that I need to change the whole wiring in order to get rid of this problem.

>>
I collected the bike in the evening and that’s when I realized that I had read about the Throttle Position Switch that the UCE engines are equipped with. I went through the service manual which I could only lay my hands on because of a fellow BHPian who had on his own mailed it to me the very next day I opened my ownership thread. Thanks a ton. But this is where the problem begins. The description in the manual for the TPS absolutely unintelligible. Please have a look.

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Old 29th June 2012, 21:31   #2
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Default My Interpretation

The way i understood what they are trying to say goes like this.

The Accelerator cable enters a junction box somewhere under the tank. Two cables come out of this junction box.

Cable A: Is directly connected to the butterfly valve pulley of the carburetor
Cable B: goes to the TPS

The mention of the figure 40% in the description makes me believe that the TPS cable should ideally be adjusted so as to actuate the TPS switch after the cable A has traversed a distance of 40% of fully open throttle distance. In other words, the TPS should be actuated after the throttle is 40% open. This I presume is designed in order to advance the spark timing after 40% throttle is opened. I have confirmed this layout on my TBTS and found everything from the JB to the connections to the carb pulley and the TPS are in place.

>>
The main throttle cable starting from the handlebar grip to the carb pulley has no play.
My idling speed is set as per the manual and is reflected in the tachometer.
These observations rule out the possibility of the problem originating from the carburetor or Cable A.

Now coming to Cable B.

>>
Opening the throttle slowly I observed a step increase in the load felt in the hand grip at say 15-20 % of travel.
I also noticed that the Cable B became taut at this point.
This makes me believe that the TPS is getting actuated at 20% throttle instead of 40%, thus advancing the spark timing much before than it actually should happen.

<<<< I believe that the course of action is simple now. I have to adjust the slack in Cable B to an extent that it gets taut at 40% throttle. >>>>


But I have two doubts before that.
  1. My Interpretation of the function of the TPS could be wrong.
  2. Is the TPS actuated like a switch (either ON or OFF) or is itprogressive (sort of like a fan speed regulator, you get more positions in between the On and OFF positions)?

I just wonder how ignorant these old mechanics are to the small and simple electrical details added in the UCE. Mine did not suspect the problem could be with the TPS, he might not have known that it existed.

People who have worked on the TPS and issues related to it may please shed some light on this. I get a chill though my spine imagining what damage this maladjusted timing can do to my engine and the main crank bearings. I want to get my bike running healthy as before.
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Old 29th June 2012, 22:54   #3
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Default Re: My Interpretation

Quote:
Originally Posted by Tgo View Post

But I have two doubts before that.
  1. My Interpretation of the function of the TPS could be wrong.
  2. Is the TPS actuated like a switch (either ON or OFF) or is itprogressive (sort of like a fan speed regulator, you get more positions in between the On and OFF positions)?


People who have worked on the TPS and issues related to it may please shed some light on this. I get a chill though my spine imagining what damage this maladjusted timing can do to my engine and the main crank bearings. I want to get my bike running healthy as before.
TPS is just an ON/OFF type for this particular model. So you could adjust the slack in Cable B as suggested, and check if the problem vanishes.
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Old 29th June 2012, 23:36   #4
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Default re: Throttle Position Switch of Thunderbird Twin-Spark UCE

I don't have much to contribute as far as the TPS is concerned, but in case that path proves unsuccessful, please have your mechanic check the ignition coil. I remember having the same issue on my old CI bike which was rectified by replacing the coil.
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Old 30th June 2012, 23:09   #5
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Default re: Throttle Position Switch of Thunderbird Twin-Spark UCE

Really grateful to have a quick and technically sound reply. I can't understand what the table's first column says? First row says Switch S1 and second one says something which I cannot read. So are there two switches? Or is it that only one actuator actuates two different switches at two different points in its travel from one extreme position to the other.

I am going to adjust the slack myself tomorrow morning. Will let you know how it goes. I will get the ignition coil checked if the problem doesn't vanish as GreaseMonk suggests.
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Old 1st July 2012, 00:24   #6
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Default re: Throttle Position Switch of Thunderbird Twin-Spark UCE

One of our members asked me for my thoughts on the TPS used on the Royal Enfields which use a carburetor.

Rather than giving him a direct answer I thanked him for asking me and suggested that he should see this topic for my thoughts.


As I understand it, the TPS changes the amount of advance the ignition system uses relative to the position of the throttle.

Most ignition systems including the ones on Royal Enfields will determine the amount of advance based on engine speed. The faster the engine runs, the greater the amount of advance (up to a point).

This is fine when the engine is lightly loaded and the throttle setting is small however when the engine is asked to produce more power by opening the throttle, the additional fuel/air entering the cylinder will burn much faster, often exploding rather than burning smoothly. This is commonly called a ping pr pink and it can have ruinous consequences if it continues.

If the advance can be reduced under large power demands the faster burning fuel/air mixture will have less time to burn before the piston reaches TDC so rather than creating massive pressures and pinging, its power can be used to drive the piston downward resulting in greater engine power without pinging.

To prevent this pinging under heavy throttle positions the Royal Enfield TPS switches to the "closed" position.

If you look at the photo in the post above you will see a chart with two graphs showing the amount of advance at various engine speeds.

The graph for the "switch open" shows that the advance to maximum occurs at 1900 RPM if the engine is lightly loaded. Above 1900 RPM the advance remains at 27 degrees before top dead center. This gives the best fuel economy.

This graph shows the advance when the motorcycle is being accelerated slowly with less than 40 percent of the total throttle rotation being used. (you are not trying to get home in a hurry or racing a Honda 250.)

The "closed switch" graph shows how the ignition advance is reduced when the throttle position is opened greater than 40 percent.
You decide to accelerate rapidly, open the throttle more than 40 percent and although the engine speed increases the maximum advance is greatly reduced.
This does not reduce the engines power but it does prevent pinging.
The amount of reduction in the advance is programmed to produce the greatest power safely based on the engine speed and the throttle position.

From this you can see that things like mis-firing, balky engine starting or poor idling has nothing to do with the TPS or its settings.

If your fuel economy is poor, it is possible that the switch is closing early or is stuck in a closed position.

If your engine develops a ping (pink) under hard acceleration, it is possible that the switch is not closing soon enough.

It is also possible that the switch is broken and fails to close or make contact internally, or if a wire in the wiring harness has become loose so that even if the switch is closed the ignition module will not know it.

Have a good day!

Last edited by ArizonaJim : 1st July 2012 at 00:28.
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Old 1st July 2012, 00:29   #7
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Default re: Throttle Position Switch of Thunderbird Twin-Spark UCE

Quote:
Originally Posted by Tgo View Post
Really grateful to have a quick and technically sound reply. I can't understand what the table's first column says? First row says Switch S1 and second one says something which I cannot read. So are there two switches? Or is it that only one actuator actuates two different switches at two different points in its travel from one extreme position to the other.

I am going to adjust the slack myself tomorrow morning. Will let you know how it goes. I will get the ignition coil checked if the problem doesn't vanish as GreaseMonk suggests.
Tgo, basically what it does is, change the ignition timing based on whether the switch is open or closed. So the bike is having two different sets of ignition timing, one set for throttle opening below 40%, and another set for throttle opening above 40%.

But newer bikes are having potentiometric TPS i.e. it can distinguish more precisely the position of the throttle, say in steps of 5% opening. So in bikes with such TPS, there will be more than two sets of ignition timing.

In the graph which I posted, the X-axis refers to the engine speed and Y-axis refers to the ignition timing in DBTDC(Degrees Before Top Dead Center), the two lines refers to the two different set of ignition timing which I mentioned earlier. Since the bike is a carbureted version the ignition timing will be having an accuracy within +-2 degrees, where as in fuel injected bikes the ignition timing will be having an accuracy within 0.625 degrees or better.
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Old 1st July 2012, 20:51   #8
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Default Re: Throttle Position Switch of Thunderbird Twin-Spark UCE

@Tgo : Hi friend, I don't have any technical knowledge on the TPS. All I had was some trial and error adjustment method which you could read in the C 350 thread. But I have a gut feeling that the TPS in the 350s is not of a switch type. In a switch type tps, you should hear two audible clicks from the tps unit when operating the throttle. One when you starts to roll the throttle and another one near WOT. I think what we have is the resistor type TPS in our machines with TCI ignition systems.
http://www.team-bhp.com/forum/motorb...ership-61.html (RE Classic 350 - Initial ownership)
Just a few questions :
1. How is the cold start of your bike? Does it start without choke in cold climate ?
2. How much is your bike's fuel screw turned out?
3. What is your bike's FE ?
After finding out the number of turns, just turn the fuel screw 1/2 a turn to either directions and take a test ride with each setting and check whether the problem aggravates or diminishes. Doing a plug chop at the throttle position where your bike shows trouble will also help to identify the problem.
By the way, here is a great site on ignition systems
http://www.jetav8r.com/Vision/Ignition/CDI.html
Regards adrian

Last edited by adrian : 1st July 2012 at 21:07.
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Old 1st July 2012, 21:06   #9
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Default Re: Throttle Position Switch of Thunderbird Twin-Spark UCE

Quote:
Originally Posted by ArizonaJim View Post
If the advance can be reduced under large power demands the faster burning fuel/air mixture will have less time to burn before the piston reaches TDC so rather than creating massive pressures and pinging, its power can be used to drive the piston downward resulting in greater engine power without pinging.
Hi,
I think it is better to think that timing needs to be advanced for light load running, rather than needs to be retarded for full throttle running.

Goal is to see that peak cylinder pressure occurs slightly ATDC. For WOT, burn time remains essentially the same, so spark has to be advanced in terms of degrees, (not time) as the engine revs up. (In pre ECU days, in cars, the work of the centrifugal advance). This (ie timing at WOT) is worked out and set up first.

The engine will run fine (ie will not be damaged), but not optimally, with this timing at part loads also. The lower charge density of part throttle running takes longer to burn. So to get peak cylinder pressure at the same point in the cycle, timing should be advanced. (In pre ECU days, in cars, the work of the vacuum advance). In the case of Enfield, it is done by the TPS.

So the light load running timing (advance) is a correction applied to the base figure of WOT running, rather than WOT timing (retard) being a correction applied to baseline light load running.

Re: TGO's problem, I agree with you. TPS unlikely to be the cause.

Regards
Sutripta
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Old 3rd July 2012, 15:55   #10
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Default Re: Throttle Position Switch of Thunderbird Twin-Spark UCE

Now that I think of it. I was really wrong. I checked a relatively new TBTS yesterday. The TPS is actuated by cable B starting from the beginning of opening of throttle. All this while I thought it was supposed to be actuated (start moving) when the throttle is 40% open.

Thanks to Adrian for posting his experience with the TPS on his bike. Hoping that I have that awesome yellow line marked on my TPS pull rod which will rid me of going into the trouble of making all those stupid markings I made on the throttle hand grip.

Another problem is that, however much I tried to adjust the slack in the cable, it seemed not to budge much. Just a millimeter here or there. I think I will have to change the cable. Will let you know what I find.
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Old 3rd July 2012, 21:51   #11
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Default Re: Throttle Position Switch of Thunderbird Twin-Spark UCE

Hi everyone, I wish to add the following details regarding TPS adjustment. We have two RE service centers in Trivandrum. The Marikkar Motors and Arun Motors. The bikes that are getting serviced at Arun Motors have their TPS adjusted in such a manner that the TPS push rod moves the instant you roll on the throttle. On the other hand, the Marikkar guys never touch the TPS thing like they did on my bike where the TPS moves after 1/4th of the throttle is rolled on. The area service manager remarked that the TPS adjustment is different on each bike as it should match the carburettor jetting. Now considering the a fore said facts and the lack of clarity in the procedure described in the service manual, we are still in the dark regarding the procedure for TPS adjustment.

Would the 350 UCE guys mind posting the TPS settings in their bikes so that we could compare and analyze ?

My machines setting is as follows :
Standard 350 UCE
Fuel screw : 3 full turns out.
TPS : Okay.. as you know I monkeyed with it Currently it starts to move a bit after I turned the throttle (just before 1/8th of throttle) and the yellow line shows at WOT.
FE : 42 km/lr in city traffic
regards adrian

Last edited by adrian : 3rd July 2012 at 21:53.
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Old 3rd July 2012, 23:10   #12
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Default Re: Throttle Position Switch of Thunderbird Twin-Spark UCE

I seem to be in the biggest in the biggest fix of my life. Your post just above mine sheds some light on the other settings which also need to be set in order to work normally. As for the fix I am in...

I checked the TPS on my bike. The yellow line appears at WOT (Wide Open Throttle) but the pull rod starts moving after 40% throttle is opened. I haven't checked the fuel screw. Will do that tomorrow in daylight. But I am getting 40 km/L overall. It doesn't seem to change in the city or on the highway.

Now that you have mentioned the settings are different on bikes serviced in those two centers. I believe that the Fuel Screw needs to be checked. I request, like Adrian , other members may also spare some 5 minutes and put up their bikes' settings here along with the problems of misfiring or stuttering faced by them, if any.

Jim and Sutripta, I just want to rule out the possibility of this faulty TPS setting before thinking of other things that can be wrong. I appreciate your advice too.
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Old 6th July 2012, 12:13   #13
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Default Re: Throttle Position Switch of Thunderbird Twin-Spark UCE

I decided to drop my bike off at the RE Service Center at last, hoping that they would come up with a solution. To be frank I wasn't very optimistic as i hardly understand Kannada and explaining the problem to the mechanics was a different matter altogether.

I got a call in the afternoon that they have found that some piston in the carburetor has gone bad and asked for my confirmation to replace it. They had also found some rust inside the tank which could have caused this part to fail. They did the cleaning and changing and by evening my bike was ready. I collected it at 6pm and took a small ride to confirm that the problem was gone.... and yes, it was.

The part which had worn out. The blue coating on one side seems like some anti-friction coating (i could be wrong). It had come off on half of the cylinder.

Throttle Position Switch of Thunderbird Twin-Spark UCE-wp_000372.jpg


The scratched side. Its made of Aluminium.

Throttle Position Switch of Thunderbird Twin-Spark UCE-wp_000370.jpg


A close-up of the scratches.

Throttle Position Switch of Thunderbird Twin-Spark UCE-copy-wp_000366.jpg


I am down with Malaria and have rode just about 15 kms since yesterday evening. Till now, there has been no misfiring or stuttering at any position of throttle at any sane level of rpm (< 3500).

Part Cost: Rs. 537 + VAT.
Labour Cost: Rs. 350 For all check-ups and fixing this bug.

No adjustments were made to the TPS. So this message now becomes
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Old 25th April 2013, 15:14   #14
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Default Re: Throttle Position Switch of Thunderbird Twin-Spark UCE

I'm facing pickup/top speed issues on my BULL and suspect the TPS. I got a bullet 350 uce about a month back and after the 1st service I pushed it to the limit and was disappointed that it struggled to touch 100kmph figure whereas my previous bullet (2012 model, now sold) used to attain speedo indicated 120!! I checked the TPS and found that the pushrod moved at just 20% WOT whereas in previous bull, it used to move at nearly 50% WOT. Plus the mixture was a bit lean as indicated by the spark plugs (also its running on a freer flowing short bottle RE OEM exhaust). I changed the fuel mixture rich by about a turn but later while I was adjusting the TPS, I was confronted by a confusion:
1. I set the TPS adhering to the 40% WOT Rule but then in case I go by this, the yellow mark on the push rod is not seen at WOT as it remains 3-4 mm inside the TPS at WOT.
2. If I set it in a way that the yellow mark appears at WOT, then the pushrod starts moving at less than 25-30% WOT.

Please suggest which of the above settings should I go in for?? Keeping yellow line at WOT in mind or the 40% rule??
Please pardon me for an otherwise long post!!

Last edited by abhishek24x : 25th April 2013 at 15:19.
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Old 25th April 2013, 22:15   #15
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Default Re: Throttle Position Switch of Thunderbird Twin-Spark UCE

yellow line at WOT is the way to go.

Put everything back to stock setting and check the top speed. Ideally if a mixture is tuned rich the timing has to be retarded as rich mixtures burn faster.
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