Need help CARB SYNCING!!!

Alright, I've had NOTHING but problems with my carbs ever since I first got the bike. With zero to little mechanical knowledge and experience, I dove right in to them not really knowing what I was doing.

With the help of XJBikes I managed to do a lot of work on my bike with very detailed and informative posts. Now I need help syncing my carbs. I've got an 81 xj650.

I learned today how to 'bench sync', which helped a lot with my high idling. I realized that turning the throttle screws while on the bike DID help lower the idle, but I noticed a stream of gas pouring from carbs 3 & 4. I pulled them off, which along with many of you, have probably mastered by now. Ended up doing a bench synch by eye without having consulted XJbikes first, which I would say helped quite a bit. I've ALWAYS heard about the vacuum test, carb synching, tuning, etc. but never understood any of it. I found a few handy links that I cant wait to tear into tomorrow for synching but im still a bit stumped. so here a few questions.


1) Does anyone else have trouble fitting the rubber boots (airbox > carb)? Are they all universal or are they specifically designed to fit the certain carb? I noticed that I have a hard time making a proper fit with these and from what I know, a small air leak can be really noticable.

Im going to attempt the 2 bottle sync tool some time this week, but there's a few things I dont understand.

2) Where do I hook up the 2 lines? I understand one goes on the engine > carb boot, but how about the other hose? fuel tank?

3) What exactly am I adjusting? Fuel mixture screw? Throttle screws?

4) Does the fluid have to be exact in each bottle?

5) Can I use something else besides ATF?

6) How do I 'read' the bottles??



Ill be asking more questions later on but if anyone can help me with the current ones I'd greatly appreciate it. To make things a little more interesting, I'll try to get some pics going

 

yes, those airbox-carb boots are a PITA. i find a little bit of WD-40 helps them go back in a little easier.

first off - if you have a stream of gas coming out of 3 and 4 - i think you need to check your float heights (search for float height clear tube method) and/or float needles/seats to make sure the bowls aren't over filling.

can't vouch too much for the 2 bottle synch tool - i tried to make a similar contraption but ended up buying a 4-stick vacuum gauge to do it "right" - i can tell you that, when you synch your carbs you are adjusting the butterflies (the same screws you adjust while bench synching) to match the amount of vacuum in all 4 carb-engine boots. there should be a little nipple with a cap on each of the carb-engine boots. (your petc*ck should be connected to one of them to provide the vacuum to open up the diaphragm and allow fuel to flow)

in your case, you have a 2 bottle tool with 2 hoses, each hose connects to a carb-engine boot.

i'm pretty sure you first synch 1 and 2, then 3 and 4, and finally 2 and 3. the carbs are "in synch" when you have the same level of fluid in each bottle (cuz both carbs are pulling the same amount of vacuum).

i'd imagine you can use any kind of fluid, but ATF fluid has 2 advantages: a)it's red so it looks cool and is easy to read and b)it's thick so it flows more slowly - the vacuum pull from the engine pulses in time with the valves, so a less viscous fluid (like red kool-aid) will bounce around more if that makes sense to ya. plus, if you accidentally suck a bunch of ATF into the engine, it shouldn't hurt anything (i don't think anyway).

it is strongly recommended that you check/adjust valve clearances before synching carbs - otherwise, if and when you do decide to adjust the valves, you'll need to synch the carbs all over again.

and, oh yeah, i'm assuming your engine says YICS on it, and if that's the case, you'll want to acquire or fabricate a YICS port blocking tool before you synch those carbs.

 

Thanks!

 

it doesn't have to be as long as a)you have a way to get fuel into the carbs (petc*ck on PRI) and b) that vacuum port is blocked off when you are not using for synching (shove a golf tee in the hose, hose clamp for good measure). it's pretty much impossible to adjust those screws while the gas tank is on the bike. you *might* be able to prop up the tank and reach in there, but if you can make a temporary tank with a long fuel line, it will be much easier.

that's a major bummer. checking valve clearances is pretty easy. correcting them is slightly more difficult. bigfitz's "airhead valve adjustment with PICS" covers the topic very well. you will most likely want to pick up an impact driver if you don't already have one. i'll defer to the experts as to what to do about your valve cover bolts - although i'd bet it's not as bad as you think. i have a hunch you can even fix it without removing the head. . . if you're compression is good, then you'll at least know you don't have any valves that are WAY too tight, but you can't really tell for sure without pulling the valve cover off and looking.

if you look at either side of your engine right by where the intake boots (the boots between the carbs and the engine) you will see a hex-head bolt. i think it's in the neighborhood of 12mm. those bolts are on either end of a straight passageway that connects all the carbs together. yamaha did this to improve mileage and emissions (and maybe even performance). thats the up side of YICS. the down side of YICS is that, since all the carbs are linked via this passageway, when you try to synch your carbs, an adjustment on any one carb affects the other three. in order to do a proper synch you need to temporarily isolate the carbs from each other. some folks claim this is unnecessary. . . but, some folks say otherwise. i've heard of stuffing a greased up t-shirt in there - but i don't think i would try that. there are plans on the internet (and maybe this site even) for a DIY yics port blocking tool. also, the user "chacal" here carries an extensive line of XJ parts, including a real YICS tool.

 

Ill buy some fuel line so I can extend my tank higher so I can work on the carbs. I dont think I'll be touching valves yet, I dont think there's anything wrong with them. I cant remember if I've seen that hex bolt, but I bought a parts bike that had an unfamiliar screw just south of the 4th plug hole.

Starting to sound like a pain in the ass, haha

 

1 everyone does, there's a tool that helps a lot, i think the 2 inner ones are different from the 2 outer ones, silicone spray helps spin them so they fit right, there's mark on them where the clamp goes, mark to the top
2 2 hoses go to 2 vacuum ports 1/2, 3/4, then 2/3, none go to the tank, run it on prime
3 between each carb is a screw that adjusts each idle speed in relation to each other
4 no, but each bottle should be less than 1/2 full so nothing can get sucked in the engine
5 i use water
6 when the fluid quits moving from one bottle to the other your golden, regardless of the levels

 

Just wondering but I didn't think the 81 xj650 had a YICS motor. They didn't come out in the 650's until 82. Even then for a while in 82 they did make some non-YICS 650's. Somebody correct me if I am wrong. It has been known to happen to me once or twice.. maybe a few more times........

 

Im riding an 81 xj and the previous owner swapped in an 82 YICS. which is the one with the black YICS valvecover.

 

My 2 cents worth............I know that in Oz the '81 xj650 was not a YCIS motor,may have been different in the States tho, .......cheers, murray

 

Here are my 2 engines, I noticed once is plugged and 1 has a screw in the engine block.

The one Im trying to tune is the one with the plug, and all the silicon. Looks like I dont need the yics tool to sync??

 

i ain't sayen nutten

 

It looks to me that both of those engines are YICS.

 

It's not the screw...It's teh bolt below it.

 

Damn. I was hoping that I wouldnt need to bother with the YICS tool.


Im going to avoid all controversy about the YICS tool and sync them without


Off to buy vacuum gauge supplies tomorrow. Hopefully the 1.5 inch plumbing couplers are cheap at P auto for some new intake booties. Once I get some progress going Im sure I'll have much more to ask

 

You gots two YICS engines there amigo!

 

REALLY don't mean to start something with this!!! I didn't use YICS tool. As well as my bike is running, it has to be pretty goshdarned CLOSE...

skillet
BTW who knows? maybe it would run that much better if I used the tool

 

There's obviously 2 large groups of users who are both for and against the YICS tool

 

Here's what I've got done between work. Finally got around to make the 2 bottle tool, it was very fun and only cost me about $10. I set it up with 2 black zip-tie markers with negative vacuum pressure to set over night and see if theres any vacuum leak. will have to buy more hose and 2 couplers tomorrow so I can mount it to my carbs and begin synching



wish me luck!

 

There's a synch tool in that pic?? I didn't see it.

 

You seem to have made a hybrid of the "baby bottle" and the "2 tube" Manometer, and to prove that it's a bit "wrong", your level isn't level even when not hooked up.

In fact, the top tubes seems to reflect the exact difference in the bottom.

To fix- - the longer tubes end at the top of the bottles(cut them),
These tubes remain dry.
If those are 8 OZ bottles, only use 7 OZ (plus what's in the transfer tube)

You could also just use a 2 tube rig, and not use the bottles. (this requires baffle/restrictors) Good luck

 

silly dilly where are you located?

 

Southern Alberta.

The only reason they aren' even is because I sucked the ends giving them a negative vacuum pressure over night to see if there's an air leak. Whether they are supposed to even out during negative pressure, I dont know. but when released they even out perfectly.

Not the YICS tool... the bottle sync tool.









Worked excellent! Needed to do it a few times but I've definitely noticed improvement. Idle is spot on, I can crank the throttle and it will very effectively race to high rpm then DROP back down to idle. Didnt think it would be that easy!

all I need to do now is colortune my plugs and I'll be summer set.

 

Bushy wrote:
There's a synch tool in that pic?? I didn't see it.

I had to look again to see the tool also. Don't feel bad Bushy. lol

 

ha-ha. I got it now

 

Sillydilly, did you have to fiddle a lot with the adjusting screws? Were your fluid level changes relatively responsive?

I've heard the levels can take a long time to change and therefore it's easy to end up over-adjusting the screws.

 

the first time I over adjusted so badly that the bike no longer ran and I had to bench synch.


Second time over, I did it in 1/4 turn intervals. I started the bike, watched the tubes, shut it off and turned the adjusting screw 1/4 in. started it up... if it got better, i'd turn it again. if it got worse, I'd do 1/2 OUT. fine tuned it that way... trial and error. Dont over spin the screws it shouldnt take much. and once you over adjust it your bike probably wont run