Dirt in Carbs?

[krusty]

Checking my manual it shows 1984-1990 2 turns.
1991 on 3 turns.
My bike is 10/90, 4AY (3XW) so which applies, 2 turns or 3.
That said, 2.5 turns would be a starting point.

[Arnie]

IF it were as simple as 2 turns or 3 turns out, then for your bike it would be 3 turns.
HOWEVER, those are merely starting points.  Yamaha set the mixture individually for each cylinder using an EGA.
If you or the PO has changed the relative positions, then you have to start somewhere and 2 or 2.5 or 3 is a starting point.  You'll need to do a "blip test" to fine tune (assuming you don't have an EGA)

Also, unlike the Kehin carbs on the Honda, these are mixture screws not air bleed screws.  They control how much additional mixture is allowed into the engine at idle.  So, further opening allows extra air & fuel both into the engine.

Arnie

[krusty]

The bullet has been bit. I've had the carbs out, cleaned them, reinstalled and synched. A few points noted in the process.
First off, I used the above recommended method off removing the rear sub-frame bolts and tilting it back. I couldn't move it very far but enough to make the job much much easier.
With airbox removed I took out the airfilter. Hmmmm. PO has done regular oil & filter changes (according to his log book) but has neglected the AF. It's done 40000ks since it was last replaced (whoever last replaced it had written the klms on it with a marker), the foam was disintegrating and paper filthy. Also noticed the airbox had been out before because the crankcase breather was not attached (it still isn't).
With the carbs on the bench it wasn't long before I had all the boowls off. Except for brown sediment in the bottom of the bowls, they were very clean looking. Then I pulled the pilot jets and found the cause of the idling problem. Although not totally blocked there was enough crud to cause my problem. The pilot jets only have the one hole in them, unlike some that have extra holes in the sides. I soaked them overnight in solvent and then gave then gave them some time in an ultrasonic cleaner. I also removed the main jets and they were perfect. I also checked jet sizes and they were all stock.
Jets and cleaned up floatbowls were all reassembled and the carbs and airbox refitted. I happened to have a few spare airfilters left, from some that were given to me a few years ago, so one of them went in.
No problems putting everything back together and, on restarting the bike was it again idling properly BUT it now had an obvious rattle that indicated synching was needed. This was all a couple of days ago.
Today I resynched the carbs. It all went smoothly (under an hour all up) and now the rattle has gone and it idles just like it should.
Will give it a test ride in sometime this week and I'm confident all will be well.
Thanks to you guys for your info and advice with this job that I was a little apprehensive about tackling.
I now have the confidence to do the carbs on my 1100 that hadn't been touched since 1998.

[movenon]

Now you are on the right track .  Never trust what a PO has done. Don't think the "Yamaha" shop knows everything either.  No substitute for knowing yourself  Best you become the expert on your bike especially with the older bikes.  
George

[Pat Conlon]

^^^ +1 to what George said.

My experience (years ago) with the service dept at a local (now out of business) Yamaha dealer proved that the kids know very little about the workings of our CV36 carbs..

Lesson learned, never again..... It was 17 years ago and thinking about it still pisses me off   Got to let it go....

[krusty]

Today I plunged into doing the carbs on my 1100. Happy to say all went well. Pretty much the same story as the 1200. Nothing untoward was found. The carbs were very clean considering this bike had stood for 15 years before I bought it last year. With everything buttoned back up I took it for a 20klm run and all is good, only needed slight adjustiong of the idle screw.
Something I just remembered, the mixture screws were wound out three turns but the book says 2 turns. I reinstalled them with 2 turns. I'll do a sych on it later as its running pretty smooth at the moment. Have been running Valvoline Injector and carb cleaner in it since I've been riding it.
Before and after pics of the bowls.