Carb Experts...

[Yammer Dan]

O K Carb guys when did Yamaha move the Ignition Vacum from the #1 carb I think it is and where did they move it to?? What else is different about thesse carbs. I got a set from E-Bay claimed they were 83 but no vacum line nipple on this one. Again without a nipple is it useless?? (couldn't resist) Useless for my 83 I mean..

[hipshot]

dan. i thought the ignition vacuum, was on carb#2.?

sounds like you bought the WRONG set, or the seller, "mis-represented" what he was selling.

got any pictures?

just jt

[Yammer Dan]

Is #2 I think. No pics, I got a camera finally just haven't learned to use it yet.. How did I manage to post this twice??

[JPM]

O K Carb guys when did Yamaha move the Ignition Vacum from the #1 carb I think it is and where did they move it to?? What else is different about thesse carbs. I got a set from E-Bay claimed they were 83 but no vacum line nipple on this one. Again without a nipple is it useless?? (couldn't resist) Useless for my 83 I mean..

 

Those carbs should work just fine I'm thinking. I had a '83 and fitted a ignition box from a '86. I tried the vacum attached to the carbs and to the #3 intake manifold. I had the flywheel degree marked and found no difference in performance. While not exactly the same thing you want to do, still, the vacum box is the same si it should work just fine.

 

Joe

[Dano]

Dan, you gotta remember that the boost sensor goes before the carb(above) on an 83. 84 they moved it to the bottom of the carb. Maybe you got 83's but didn't remember where the sensor hose hooked up. Hope this helps. (Front left carb)

[Rocket]

How did I manage to post this twice??

 

You stuttered...... Now get to work on the scoot.

[Yammer Dan]

Is it the Boost sensor Rocket? As long as I give it vacum it should be OK? Could I tee it into The port where you Sync them???

[Yammer Dan]

Sorry Dan got a little mixed up there thought Rocket had posted something usefull. If that is the Boost sensor all I have to do is make sure it has vacum? Not sure if any more differences in the carbs I'll have to look at them. Guy posted them as 83 but guess not.

[Yammer Dan]

Got you Rocket!!!

[Dano]

Yea Dan, if they are 83 carbs, the vacuum port will be above the carb. Im not sure of the location, but probably on the boot that comes from the air cleaner or at the throat of the carb itself. I remember that there was a post on this on here earlier this year, I believe. Maybe Muffin knows. If you don't see a vacuum port below the carbs, then it's got to be above. You also have to use an 83 boost sensor on there too, because the vacuum is less above the carb than below. I think I'm wrong on that. It may be that it's positive pressure above, that's why you have to use an 83 sensor. It controls your timing advance curve.

[Dano]

Dan, here is the link that explains the difference. The nipple is located on the carb itself just above the throttle plate. The 83 TCI looks for zero vacuum at idle. Hell, just read the post!

http://www.venturerider.org/forum/showthread.php?t=16587&highlight=1983+carb

 

It'll save me all that typing!!!!!!! Probably what's giving you that crappy idle!

 

Dan

 

Found it by doing a search on 1983 carb, 1st post.

[Yammer Dan]

Where is Denden! He should be able to answer this one.

[Yammer Dan]

Looks like I have a set of 84 or later carbs and trying to put them on aq 83. Can this be done?? 83 needs to read 0 vacum at idle so it needs to hook to carb and not to intake. Would there be enough pull if I tapped into Air Box?? Going to have to look at this a little more.

[Rocket]

Yea Dan, if they are 83 carbs, the vacuum port will be above the carb. Im not sure of the location, but probably on the boot that comes from the air cleaner or at the throat of the carb itself.

 

Yammer, looking at the left front carb, you should see a small brass tube sticking out at an angle. It is just to the right of the main diaphram & about same level as the lower cover screws, in the main body of the housing. If it is in this location, you should have 83 carbs.

[Yammer Dan]

That's what I was saying Rocket. The set I got does Not have this tube. They must be for later than 83. Is there any way to use them? Can the vacum be hooked somewhere else on a 83? Is it the Boost Sensor that needs 0 vacum at idle? Am I back to trying the 83 set?

[pegscraper]

I'd bet the vacuum sensor is the same thing. The 0" of vacuum at idle idea is an emissions controls stunt. That used to be done on cars starting around the '70s before the spark advance was controlled by computers. It's called "ported vacuum". Prior to that the distributors were always run on manifold vacuum. Any car I ever had always got the distributor switched back to manifold vacuum. They run better. I'd say hook your vacuum sensor to one of your carb sync ports for a manifold vacuum source and be done with it.

[Yammer Dan]

That is what I was hoping. I should be able to hook it sync port. Only place it could make difference is at idle I think. With throtle closed not much flow going thru there anyway. Flow does not start till you open throttle.

[Yammer Dan]

Should not make much difference which side of throttle plate it was on vacum pull would not be there until throttle plate was opened. Is my thinking right on this? If I hook it to sync port will it affect anything?

[pegscraper]

Vacuum level is different than air flow. At idle with the throttle plates virtually closed, vacuum above the throttle plates will be zero and vacuum below the throttle plates will be at its highest. At anything higher than just off of idle speed, as the throttle plates start to open, these two vacuum sources will become almost exactly the same level and respond to the throttle opening in the same way.

 

No vacuum on the vacuum sensor at idle retards the spark advance and it makes the engine burn hotter at idle, supposedly burning a little cleaner. If you're in town with extended periods of engine idling, if you have a temperature gauge on the engine, you will see it running noticeably hotter. Late spark timing is also hard on gas mileage. Vacuum on the vacuum sensor at idle - advanced spark timing at idle - makes the engine run cooler, smoother, and gets better gas mileage in town.

 

This general principle of spark advance is true for any engine. In the '70s with the early attempts at emissions controls on cars, the vacuum advance on the distributor was run from a source above the throttle plates, and then run through a bunch of vacuum switches that would prevent vacuum from getting to it until the engine was fully warmed up, and until the transmission was shifted into third gear. On my cars, this poppycock was always pulled out and thrown away, and the vacuum advance was run straight to a port on the intake manifold, below the throttle plates, where it belongs.

[Yammer Dan]

Good explanation. So I'm going to tap into the sync port and it shouldn't have any effect on anything else? This one wants to run a little warm so it should help that also?

[pegscraper]

Nope, it won't affect anything else. And if I'm reading this thread right, the '83s are the only ones that had a ported vacuum source on the vacuum sensor anyway. Every year after this it is run from a sync port on an intake. Correct? Hook it up to the intake manifold, and it will be just the same as the later ones.

 

If you do a lot of in town riding where the engine idles a lot, you may notice it running cooler, because that's where the ported/manifold vacuum issue makes a difference. On the highway it won't make a bit of difference in engine temperature, because these two sources of vacuum are virtually the same at anything above idle speed.