Length of the vacuumpiston-springs!

[sunyammer1111]

Hello together!

I must know the unloaded length of the springs in the vacuumpistons for the Keihin 755A.

Thank you very much!

Cheers Jan

[Placerville]

Courtesy of Alwing17

[sunyammer1111]

Thank you very much, Placerville. Thats awesome!!!

[Placerville]

You're welcome but, I just stole the image from another thread I remembered seeing. Image by Alwing17 posted by Whiskerfish.

[sunyammer1111]

Are you sure Placerville?

In my '75 there are 51mm springs mounted. By constant driving the engine stutters. Is that the reason for the unsettled running?

[robin1731]

Are you sure Placerville?

In my '75 there are 51mm springs mounted. By constant driving the engine stutters. Is that the reason for the unsettled running?

First thing to check is to make sure you have '75 carbs.

[sunyammer1111]

Hey Robin!

The carbs are 755A!

[ericheath]

I have 4 sets of 77 carbs. Two sets had the longer springs 67mm and two sets had the shorter springs, 51mm. The shorter springs ran rich and bogged a bit when giving a lot of throttle. The 75 carbs had an even larger main jet than 76 and 77, so I would guess that the vacuum overcomes the spring and lifts too early with the shorter springs. The economy with the shorter spring versions in mine was 37mpg almost any way I rode it. The longer springs could get in the 40's. I would look for the right ones. Octane has a suggestion on how to measure the springiness. I remember a few years back people talking about stretching them back out to shape, but the feeling was that you'd be pretty inaccurate.

[pistolpete]

Guys,

After hundreds of sets and some research, the standard 75 - 77 are 51mm (2.007") with 19 winds, .027" dia wire.
The standard 78/79 are 67mm (2.64") with 11 winds, .023" dia wire.

Pete

[Placerville]

...and the plot thickens.

[fish]

[quote="sunyammer1111" By constant driving the engine stutters.?[/quote]
allways start any repairs with the ignition system.
Check your point gap & timing

[ericheath]

The plot hardens. Wow, Pete, you would know. Alwing is pretty reputable too. Mine had the same number of winds, just considerably different lengths. Who's taking side bets? I have pic here somewhere of mine. Here:http://ngwclub.com/forum/viewtopic.php? ... b736fd5389

[pistolpete]

I know that we receive carbs that the spring length is all over the map. If it has 19 winds and it is longer than 51mm, someone has elongated them. I have a new carburetor for a 77 and the spring length is 51mm with 19 winds. As someone has stated before (I think it was Randakk), the length of the spring doesn't mean much as far as functionality is concerned.
I may be in error about who said it though.

Pete

[robin1731]

I know that we receive carbs that the spring length is all over the map. If it has 19 winds and it is longer than 51mm, someone has elongated them. I have a new carburetor for a 77 and the spring length is 51mm with 19 winds. As someone has stated before (I think it was Randakk), the length of the spring doesn't mean much as far as functionality is concerned.
I may be in error about who said it though.

Pete

I won't take credit for it but I have said it. Just like valve springs what matters is spring pressure at a given height.