HS6 problem

[Michel Higuet]

I'm making progress in detecting problems and here is one. There are plenty of videos to explain the SU adjustment, there are few on the different problems... :-)
The symptom: A stroke of the accelerator and the speed does not return to idle, the cause is the front carburettor, I have to push on the lever arm, it does go back a less than tiny fraction of a mm and the idle is there. I  removed the front carburettor to adjust the throttle disc but the problem remains, the "throttle clamping lever" has nothing to do with it, I could adjust this throttle lever so that it pushes on the lever arm, maybe a solution but that would mask the issue. This time I will dismantle the 2 carburettors to compare the closing of the throttle disc with the help of a light. To be continued...

[RogerH]

Hi Michel,

the spherical balls on the carb coupling rods can develope flat spots.  This can leave the throttle disc anywhere.

You can try rotating the ball so the flat spot is else where.

 

Roger

[BlueTR3A-5EKT]

 I still have a few NOS throttle rod balls.   The thread is the correct type (unf) unlike those which come from elsewhere (metric)  the thread is long so a nut can be used to secure them to the brass lever.   On the bell crank you may choose to reduce the threads length if the thread is ok in it.   

Price is £3.50 each plus postage.  PM if interested.

 

 

[Z320]

Hi,

both "tiny" coil return springs are missing?

Or they are different strong / long (my case)? I swapped them 1 -->2, 2-->1 for a test.

Ciao, Marco

Edited October 24, 2023 by Z320

[Michel Higuet]

7 hours ago, Z320 said:

Hi,

both tiny coil return springs are missing?

Or they are different strong (my case)? I swapped them 1 -->2, 2-->1 for a test.

Ciao, Marco

Symptom : from idle give gas, go to 3000  come back to 1500-2000 never go to 1.000, you could delink the clamping lever no change, you push back on the lever arm rear carb no change, you do it on the front carb you go back to 1.000 rpm. I see the lever arm going back a few but very few but seems sufficient. I need to make pics but I am busy with the starter motor.  

[Tr4aJim]

Michel, two things to check. 

When you move the lever on the front carb, is just the front carb lever moving or is the shaft moving with it? Normally the shaft and levers should move in unison, but the levers are frequently loosened to to adjust/balance idle between the carbs. Maybe it’s not tightened enough.

Second, is the throttle plate on the front carb installed with the bevel facing the right way?

Jim

[Michel Higuet]

On 10/24/2023 at 8:16 AM, Z320 said:

Hi,

both "tiny" coil return springs are missing?

Or they are different strong / long (my case)? I swapped them 1 -->2, 2-->1 for a test.

Ciao, Marco

I had already tough of a solution with stronger springs but not imagined a difference in the springs, on the pics all carbs have butterfly valve close but indeed here one is shorter and on the carb side who give the problem... They are different but because more extended I feel it pulls much more strength so it is not the problem  ( or... it caused a mark, blur in the venturi? ) . I still think of the butterfly valve ( but today I will fetch for a high torque starter ). 

[Lebro]

The springs in the top photo are there only to lock the idle adjustment screws in place, they do not return the throttle to idle.

The springs in the lower photo are the ones which should return the individual throttle spindles to idle,

where the position is determined by the screws shown in top photo. They look to me that they are not "stretched" enough - can they be shortened ?

Have you tried lubricating the spindle bushes, that can help.

Bob

[Z320]

Bob, you got me!

This springs are not really streched and look different, likely the left one is upside down.

I simply made both shorter to pull only some more, please compare with my photo above!

 

Edited October 25, 2023 by Z320

[Michel Higuet]

On 10/25/2023 at 9:49 AM, Lebro said:

The springs in the top photo are there only to lock the idle adjustment screws in place, they do not return the throttle to idle.

The springs in the lower photo are the ones which should return the individual throttle spindles to idle,

where the position is determined by the screws shown in top photo. They look to me that they are not "stretched" enough - can they be shortened ?

Have you tried lubricating the spindle bushes, that can help.

Bob

The two first pics was to show the butterfly throttle where on their rest position. So I bought a new spring and test them, feeble old 270 gr strong old 600 gr  the new one 870 gr. I used the two last but didn't change anything I suppose because at a moment I saw the problem on the front carb even his lever was way out the fork, the cause was the lever of the rear carbs via the shaft, I release it and the problem was gone. Almost no lateral play on this shaft on the contrary much play on the choke shaft, maybe I could measure and swap them.

The force of the spring doesn't change anything.

 

  

[Lebro]

Play on the choke shaft is not of any real consequence, the shaft is just a way of dropping the jets downwards. As long as the jets return to the fully up position when choke is released, and that the throttle advance cam is clear of the  contact on the throttle shaft then all is well.

Bob

Edited October 26, 2023 by Lebro

[Z320]

7 hours ago, Michel Higuet said:

The two first pics was to show the butterfly throttle where on their rest position. So I bought a new spring and test them, feeble old 270 gr strong old 600 gr  the new one 870 gr. I used the two last but didn't change anything I suppose because at a moment I saw the problem on the front carb even his lever was way out the fork, the cause was the lever of the rear carbs via the shaft, I release it and the problem was gone. Almost no lateral play on this shaft on the contrary much play on the choke shaft, maybe I could measure and swap them.

The force of the spring doesn't change anything.

 

  

With a close look and first thinking

and not acting you will find out most problems yourself.

[Michel Higuet]

15 hours ago, Z320 said:

With a close look and first thinking

and not acting you will find out most problems yourself.

Le problem was this : Even the distance between the two shafts ( 100.4 and 100 mm ) and the shorter shaft was at back ( 109.7 and 109.3 mm ) there was only a lateral play on the choke shaft ( > 2 mm ). So even the clamping lever was out on the front shaft the clamping lever of the rear carb via the tight shaft could grip and prevent the complete closing of the throttle valve on the front carb. Why? because in the 2 nuts protrude the end of the throttle spindle. I grinded 1 mm on each shaft and now I have the lateral play. Problem solved.

 

 

 

[Lebro]

Good news, well done for finding the problem.

Bob