Carb sync question

[DomP]

Am I missing something in all the carb sync guides,  I read them as wind out idle screw fully then set engine side gap using a small diameter drill bit (1mm).  This then means I can't bottom out the carbs though doesn't it?

[DomP]

I've read back through Kens suggestion that he fully backs out the idle screw then adjusts every slide until he sees them just start to lift off bottomed out position, sets them all the same then adjusts the idle crew to open all four up.

This enables full closure if needed during set up.   Is this a better method?

[McCabe-Thiele (Ted)]

That's pretty much what I did on my 500 however I found I ran out of thread on the stop screw to get it to idle  - the spring was over compressed. I ended up using Epoxy resin & a metal tab to build up the stop cam on the throttle shaft.

I've not put the carbs back on (again) as I need to sort out a couple of bowl threads. I'm having a Sabbatical from the 500 at the moment - taking out the 400 instead until my former  enthusiasm returns.🏍️🏍️🏍️

[DomP]

That's pretty much what I did on my 500 however I found I ran out of thread on the stop screw to get it to idle  - the spring was over compressed. I ended up using Epoxy resin & a metal tab to build up the stop cam on the throttle shaft.

I tried watching the German bloke on YouTube with translation on, hilarious but not much help🤣



I've not put the carbs back on (again) as I need to sort out a couple of bowl threads. I'm having a Sabbatical from the 500 at the moment - taking out the 400 instead until my former  enthusiasm returns.🏍️🏍️🏍️

That's pretty much what I'm finding Ted, I'm quite configured by the many and varied opinions on the distance between the bell crank and throttle cable as well

[McCabe-Thiele (Ted)]

On my 400 I went for a small gap IIRC it was 3/32" ( close to a small Pop rivett shaft) no issues with the throttle stop thread - it idles a treat - I set it at 1100/1200 rpm but I have enough thread that I can easily set it at below 1000 or until it stalls.

Avoids any hanging throttle issues on the 400, I'm guessing it will do the same on my 500.

[DomP]

I'll probably test my patience refitting the carbs tomorrow and see how it idles, hopefully an improvement on how it was, no3 carb float was at 23mm rather than 22 so that may have had something to do with it

[Laverda Dave]

I am losing my patience setting up my 400/4 carbs. They have now been off the bike three times. I have been using a 1.5mm drill to set the slides (from the engine side). I put the carbs back on the bike and one of two things happen, it will either rev it's nuts off at 300rpm (throttle stop wound fully out as is the fast idle screw), OR it won't tick over at all and if it does it runs like a pig and the vac gauges are miles out between the carbs even though they have been bench synced!
I'll take them off again tomorrow as something is obviously wrong somewhere but I cannot find what it is or are my carbs just worn out?

[McCabe-Thiele (Ted)]

I would try either 1 mm or go for the point where the lifter just starts to rise.
I used this as a guide https://www.vintagebikebuilder.com/cb350-400f-carb-rebuild-demonstration.html

I did not have a 1/8" drill  bit as per the vintage bike builder guide  so went smaller I think it was 3/32" but not 100% sure it might have been a tad smaller.

If you go for the point where the sliders just start to rise on each carb you could then check if there is enough travel in the
throttle stop screw for it to adjust up to 1/8.

[Bryanj]

1/8 is a bit big 1mm far better.
I back off the adjuster till the slides bottom then slowly open it till the drill just fits under one slide and adjust the others to suit

[DomP]

1/8 is a bit big 1mm far better.
I back off the adjuster till the slides bottom then slowly open it till the drill just fits under one slide and adjust the others to suit

That was my mistake, not using the idle to open them up to take the 1mm bit before adjusting all to suit.  I think I've got them right now, idle screw is nicely in the middle of its range and the throttle stop screws will adjust to meet.


*The only thing I've noticed is I seem to have too many threads showing on the adjusters, 4-5

[McCabe-Thiele (Ted)]

1/8 is a bit big 1mm far better.
I back off the adjuster till the slides bottom then slowly open it till the drill just fits under one slide and adjust the others to suit

That was my mistake, not using the idle to open them up to take the 1mm bit before adjusting all to suit.  I think I've got them right now, idle screw is nicely in the middle of its range and the throttle stop screws will adjust to meet.


*The only thing I've noticed is I seem to have too many threads showing on the adjusters, 4-5

I am slightly confused by you mentioning the idle screw & throttle stop screws.
I assume you mean the choke link screws.
I also found there was always one pair of links that had more threads showing on the adjusters. I even took it to bits to make sure that both sides of the plunger/springs were in place.

[Laverda Dave]

I'll try a 1mm drill today. To achieve the 56mm on the closing cable (the lower one) I found I had to rotate the bell crank slightly on the spindle, the adjustment bolts still sit on the flats of the spindle but that was the only way I could achieve the 56mm as stated in the Haynes manual otherwise it was 52mm.
I've watched so many YouTube videos of how to set these carbs up it has become confusing, everyone appears to have their own methods. One guy refuses to use four sync gauges and only uses one gauge with a separate manifold with tap offs!

[Bryanj]

Yamaha supplied the one gauge with rotary tap and i found it useless as adjusting one carb alters the rest

[DomP]

All back on and set to 1.5 turns out, no more hanging idle but smells very rich.  Could it just be that I need to get out on it and get some miles on it now?

[Bryanj]

Yes, get it all running then service at 500 miles