Throttle not "snapping back"

[imtaylors]

First......welcome to the forum imtaylors



This is an excellent suggestion from G because at a stroke it will confirm if your problem is due to the carburettors or the cable/s & throttle assembly . You can potentially eliminate unnecessary checking and concentrate your attention where the problem lies

If the throttle shaft return springs haven't been reassembled on the correct carb (they have different strengths on BS38s and may have on your BS34s ) or haven't been assembled on the shafts with the correct number of pre-turns then that could cause a slow/ weak throttle return.

Your carbs are presumably BS34 . it might be necessary to add some additional spring/s to the throttle shafts to compensate . Your original return springs will have lost a lot of their spring strength over the years and aftermarket replacement springs may give little improvement.

I attached a strong coil spring to my throttle shafts and the throttle shut down is now nice and snappy

I have posted a few photos, lemme know what you think!
Hopefully these photos do some justice. And hopefully show you clearly what the issue may be.

 

[imtaylors]

Hi imtaylors and welcome,
Yes, please post photos.
Your posts keep saying CARB, singular.
When the bike left the factory it had two of them.
If a dreaded PO has been messing with it, anything is possible.

Sorry about that! Yes, I have two carbs. Here are a few photos

 

[imtaylors]

There should be a rather large coil spring around the casting that the butterfly shaft sticks out of .....

Both carbs should have one .....

I have posted a few photos in this thread! Please let me know what you think the issue may be!

 

[yamageddon]

yamageddon, I would think that your replacement spring would be putting extra stress on your shaft and the bores, causing extra wear on both. Just something to think about during the future of that carb.

Scott

The replacement spring is not very strong. My guess is that it's even lighter than an original coil that supposed to be on it. I think the radial forces on the shaft will be of the same amount by opening the throttle. I don't know if an original spring takes away some of those forces. Unless it functions as an extra 'bearing' that gives strength or support on the radial movement of the shaft. But you might be right that it gives a little more support. Dunno if it's negligible? . Nevertheless...if I'm able to find an original one it's mine
Thanks Scott!

 

[yamageddon]

Sorry about that! Yes, I have two carbs. Here are a few photos

View attachment 114977 View attachment 114978 View attachment 114979

I very much like that coil spring...it's beautiful! If you want to get rid of it?

 

[peanut]

Sorry about that! Yes, I have two carbs. Here are a few photos

View attachment 114977 View attachment 114978 View attachment 114979

don't forget to put the rubber covers back on the inlet vacuum spigots

 

[TwoManyXS1Bs]

Imtaylors, pull the throttle cable end out of the slotted holder.

Then, while holding that end with your left hand, manipulate the grip throttle with your right. Should be easy then to figure at which end is the problem...

 

[peanut]

Imtaylors, pull the throttle cable end out of the slotted holder.
Then, while holding that end with your left hand, manipulate the grip throttle with your right. Should be easy then to figure at which end is the problem...

yes that is what needs to happen.......Gary and I have already suggested that posts #3 & #10 but as yamhageddon hasn't mentioned a sticking throttle since I guess we had assumed that that problem is now fixed ?

I had to fix an auxillary extension spring to my throttle shafts to get the snappy return I wanted so I think the new replacement aftermarket torsion springs are not up to the original Yamaha spec

 

[yamageddon]

yes that is what needs to happen.......Gary and I have already suggested that posts #3 & #10 but as yamhageddon hasn't mentioned a sticking throttle since I guess we had assumed that that problem is now fixed ?

I had to fix an auxillary extension spring to my throttle shafts to get the snappy return I wanted so I think the new replacement aftermarket torsion springs are not up to the original Yamaha spec

That's correct peanut. I didn't have a sticky throttle but just a lazy one due to the lack of an original coil spring as I found out here.

 

[imtaylors]

don't forget to put the rubber covers back on the inlet vacuum spigots View attachment 114981

of course not!

 

[imtaylors]

Imtaylors, pull the throttle cable end out of the slotted holder.

View attachment 114989

Then, while holding that end with your left hand, manipulate the grip throttle with your right. Should be easy then to figure at which end is the problem...

Okay I will go ahead and try that! Thank you so much

 

[imtaylors]

First......welcome to the forum imtaylors



This is an excellent suggestion from G because at a stroke it will confirm if your problem is due to the carburettors or the cable/s & throttle assembly . You can potentially eliminate unnecessary checking and concentrate your attention where the problem lies

If the throttle shaft return springs haven't been reassembled on the correct carb (they have different strengths on BS38s and may have on your BS34s ) or haven't been assembled on the shafts with the correct number of pre-turns then that could cause a slow/ weak throttle return.

Your carbs are presumably BS34 . it might be necessary to add some additional spring/s to the throttle shafts to compensate . Your original return springs will have lost a lot of their spring strength over the years and aftermarket replacement springs may give little improvement.

I attached a strong coil spring to my throttle shafts and the throttle shut down is now nice and snappy

Also, where have you bought your aftermarket springs? Because that very well may be the issue!

 

[peanut]

Also, where have you bought your aftermarket springs? Because that very well may be the issue!

Here is a link to a online calculator if you are interested in checking your springs but I don't know where you'd obtain the spec for the original springs fitted by Yamaha.
http://www.tribology-abc.com/calculators/t14_4.htm

I have to confess that I have long since forgotten all that I learnt about Youngs Modulus and Poissons ratio etc back in 1980 )

I have never experienced any problems with my throttle return because I made sure that I re-fitted all the original parts correctly and also made sure that everything was working properly however I do prefer a sharp instant ,throttle response so I made various modifications to my bikes including fitting an extension spring to the throttle shaft .