Assembling carbs

question for you guys, i’m assembling the carbs and i was wondering
A) how much light do you generally have shining through the butterfly when closed? I’ve got them all screwed on but some of them have a decent amount of line shining through
B) what are you tricks for holding the butterfly in place and getting the screws started while only having 2 hands haha i got them but damn there was some swearing.

 

forget the light, use the holes on the top of the carb throat. make the plates cover the holes the same, about half way and your good. now the idle knob should open/close them evenly.
if you hold the carbs throat up you should be able to balance the plates on the shaft, then a magnetic screwdriver should help

 

Halfway cover the holes?

 

This method beats using wires, paper clips or business card strips and is spot on.
Make sure plates cover the holes the same amount on each carb.
Halfwayish is about the "sweet spot" your looking.

 

The idle circuit hole. You will be adjusting the throttle plates by using the synch screws that are on the throttle linkages. Set #3 first (using the idle speed adjuster knob), then match the rest to it. (note that this is a different order than would be used for a vacuum synch).
Like so (the rearmost hole in the pic).

 

You can bench sync doing it this way in under a minute

 

I use the idle speed screw to:

set #3 at the back edge of the hole
Snap the linkage a few times
Adjust as needed

then set the other three to the back of the hole
Snap the linkage a few times
Adjust as needed

The back the idle speed screw out til #3 hole is half covered
Snap linkage a few times, adjust as needed
Fine adjust the remaing three to half
Snap the linkage a few times
Adjust if needed

Still only takes a minute or two to do it this way

 

hey guys,

I figured i would just keep this thread going rather than create a new one. carbs are back on, compeltely rebuilt. valves are in spec. i fired the bike up for the first time this afternoon. idled a little high tile it warmed up but then i had it idling without choke, turned it off and hooked up my vac sync tool to it. fired it up and BAM, rev'd straight to 5-6k RPM and sat there. just flying. messed around with idle screw, idle mixture screws, sync screws, nothing really had much effect on it. finally after about 30min of start/stop as i didn't wanna just leave it running at 6k i removed sync tool, put caps back on and figured i would start it again and see what it did. straight to 5-6k again. anybody have any ideas? intake boots looked good, EVERYTHING has been replaced in carbs, even throttle shaft screws. anybody have any ideas? i've sync'd quite a few sets of carbs in the past but this has got me stumped.

 

check to be sure you hooked the throttle cable to the correct location, not to the choke location.
make sure the throttle cable is not binding and has a little slack in it.
make sure the linkage is not hanging up on the cylinder head

make sure your vacuum hoses are tight and caps for port have clamps on them.

recheck carb to manifold connections for fully inserted to boots and that clamps are on correctly and tight.
do the same for airbox boots.

when you synced did you follow manual or start with carbs 3 and 4, then 1 and 2, then 2 to 3.

 

Verify that you put the airjets in correctly under the diaphragm.... large number toward the butterfly, small number toward the airbox

 

One item if you replaced butterfly seals , putting the butterfly plate can be slightly off ( don't ask me I know about this ) you may have to pull carbs and adjust position of plate ,recheck bench synch I like using 2 business cards cut in two, slide under plates adjust till there is a slight drag pulling on card this is usually very close .

 

never got as far as syncing it due to the rpm skyrocketing. cable is good. vac hoses were good, happened when connected to sync tool as well.

hmm interesting. it seemed to idle fairly normalish when warming up though.

yeah when i bench sync'd it it seemed good. if i have to pull them again i will make sure to check though

 

you can take a look at the sync setting with just the starter cranking a few seconds. not real close but you'll see a problem. might save you pulling the carbs again

 

Hi Guys,
I have same question as cg82 and imHo, the answer is still not clear. First start with the butterfly removed and peek up top, note 3 tiny holes( not 2)in vicinity of where top of butterfly contacts housing. #1 of these 3, ( maybe idle?) is 1/4" toward the Engine side and is not impacted by the butterfly position, as clearly shown in the pic in above thread. Cg82 and I, are asking about the other 2 holes, #2 & #3. These are 3 millimeters apart,and can seemingly be covered or contacted by the top of butterfly. So "our" question is
...when re-attaching the butterfly with my 2 NEW SSteel screws from Chacal(hoorah), should the top of the butterfly ( prior to synching) cover #2,#3? half of #2? all of#2 but not #3? blah blah
When "I" set the screws in the butterfly, the butterfly covered #2, and #3 not visible cause its behind or on other side of butterfly . My guess is, thats the pre-sync position. Look again at the pic above, you only see the #1 hole(irrelevant to the question)I will also add what do #2,#3 do? The butterfly almost seems to cover #2 hole exactly....leaving #3 to do some other function, since it's never closed or covered.
Thanks again for your help!

 

The rearmost hole (idle circuit) gets halfway covered by the throttle plate.
The forward hole in the photo is the enrichment curcuit outlet. There is no third hole on the HSC 32 carb that the throttle plate interacts with (and no #3 hole behind the throttle plate).

Inside your Carbs

 

The third hole (furthest from throttle plate) is regulated by the enrichment screw. It is something that should be checked when rebuilding the carbs to verify that a soft seat on the enrichment screws that the tip of the screw is visible and fully blocking the hole. Using the soft seat method damaged / corroded threads in the carb body can give a false positive that the enrichment screw has completely blocked the passage.

 

Oh...that third hole.
Mr. Dummy (me) checked his memory by picking up the wrong spare carb (a consequence of having more than one model of motorcycle in the garage).

The back two are both for the idle circuit, and having two helps to make a smooth transition from idle to main.

 

We are on the exact same track and I did soft seat the screws and of course they came through the small hole I would say a millimeter or two but that begs the second question if they're soft seated I'm assuming that the screw tip does protrude through the one or two millimeters and when I back it off two turns I'm assuming I'm not completely blocking off the passage. mine is an 81 xj750 should I be going more like 2 and 3/4 to 3 or should 2 and 1/2 be a good start? I've Been Around The Forum for a little while now but it's funny on YouTube it seems like everybody seems to think that if you wind that screw down that you're going to somehow break the tip and in my opinion the only way you could break the tip is if you had a small piece of sand stuck in the passage?
the tip is actually going to go through the hole and that whole screw is just going to hard seat itself and not go any further po sing little danger of breaking the tip unless you had something blocking the passage in my opinion.
As a sidebar, I would say the measuring of the fuel levels in the bowls is really difficult with fuel hose because it always wants to Kink as you're trying to make these hairpin turns with the fuel line so I'm going to come up with some contraption that will actually get that fuel line close to the two number two and number three bowls as those are almost impossible to get the tube depend up against , unless you guys have some particular kind of tubing that you used it a super flexible , the silicone tubing doesn't work that just disintegrates with the gasoline.
I am going to now bench sync with a guitar wire.

 

If the idle screw is tightened it will damage the seat that's cut into the carb, and that will alter the fuel metering (the metal gets distorted). You can also end up with the threads stripping out. The needle tip can crack and break off, but usually that's caused by dropping it on the floor (though ovetightening could cause a stress crack to form).

Don't tighten the needle. Soft seat only.