Carb bench synched, will run and idle slightly high

But when I hit the throttle = death.

I made sure the diaphragms drop smoothly. I need to know a baseline number of turns out from all the way in to start with on the idle/air adjustment screws. I did 2 3/4 turns???

The PO put pods on and he put caps over the 4 holes at top in between the carbs and intake that are on the boots.

I was able to figure this out on my 1976 honda but the whole diaphragm deal is new to me. no leaks in them and the rubber is nice and soft.

Main thing is that I have the choke cable unhooked and have to play with it to keep it alive at first(I suppose until it warms up which would be the function of the choke) but then I still have to play with it a little till I figure out the sweet spot with the large idle screw in the center of the carbs to get it to stay running at a slightly high idle.

OK novel is finished please help and thanks

 

What sort of petcock you got there ?
I would say your bench sync' is off the mark, move right on to a running sync'.

 

petcock looks oem. says yamaha on it. The tank may not be original?? i may be just flowing too much. here is a pic..81 xj750 seca.

also what in tha heck is a running sync? I cant get it to do anything but idle (sometimes lol) . We had it running the other day but after warming up we revved it a few times and then it tries to idle down and just stumbles to a stop

 

A "running sync" is when you block off your YICS, and using some form of manometer, vacuum sync the carbs to each other.

The manometer can be as simple as a long (6'+) length of vinyl tubing taped to a yardstick and partially filled with ATF, two baby bottles and associated tubing, a single vacuum gauge, a pair of vacuum gauges, FOUR vacuum gauges OR a 4-stick purpose-built manometer like a Morgan CarbTune.

You use a single or two-pot manometer to do "comparative" syncs; four gauges or a 4-stick manometer will allow you do do it all at once.

And yes, that's a Seca 750 tank.

 

Ok sounds all and well but before I get ahead of myself..
anybody know the number of turns out I need to start with on the pilot screws???

would being out of sync (but not badly out) really kill the bike with the application of any throttle at all?

I hope local shop has a YICS tool and I will defer to them on the actual syncing this time. I would like to drive it to them though. (dreamer?lol)

 

The reason I asked about the petcock, is that you said all 4 vac' ports were blocked off.

 

See that is why I asked the braintrust. There was a smaller hose running from the petcock to the second to left intake runner. I thought the PO was just crazy and it would dump fuel into that intake so I blocked it off too. was that a mistake?

was planning on just making a t fitting right past the petcock and connecting the two hoses.

 

That small hose runs from one of the vac ports, normally 2 or 3, to the small port on the petcock, that vac' line opens the petcock, might be why it wont rev or stay running.

 

I feel kinda dumb on that one but how was I to know. thanks for that save.
Now I need to figure out where to set my dang pilot screws because I know on any carb only minor adjustments to that could make a huge diff. Google isnt helping me with that query. thanks wizard and everyone for helping me along in this process of learning and elimination

 

Somebody else can correct me if I'm wrong, but I believe you should work on 2 1/2 turns out as a starting point.

 

2 1/2 is a good default, you set them right by using a colour tune, or by doing plug chops (getting the colour of the plugs to a brown paper bag hue.

 

ok I will try out those two things and report back

 

nifty looking bike, did you do everything yourself, or did you just aquire it this way?

 

bought it this way two days ago for 400 smackers

 

Sync and FLOAT LEVELS are both very important to proper throttle response.

You'll need to "wet-set" or at least "wet-verify" your float levels; even with properly sync'ed carbs one float way too high or low can cause your symptoms.

 

How about your valve adjustment? Will mess with the carbs synch.

And the checking the brakes on your newly acquired bike? may save your life.

Also if you add a location to your info someone maybe near by to help in person.

 

I made a couple of videos of it running and waiting for them to upload. Number 1-3 has a black plug and number 4 is tan. if I cover up two or 3 of the elliptical shaped holes on top of carb runner it will shape up. I am getting too much air for sure. The emulsion tubes seem to keep rising up out of their seated position??? the diaphragm pulsates up and down super fast when giving it copious amounts of fuel. I will check the floats with a clear tube I have and go from there.

will post vids in a sec

 

OMG!!!!!!! I broke it open and the floats are visibly out of parameter with each other at least. And the emulsion tubes were supposed to be held in by a washer that was on the other small screw that was holding nothing...AAAARRRRgh!

Well now that I am this far in it is there a way to set float level with it open???
The drain screws are seized and wd40 aint helpin. Wll have some vids in a little bit for you to hear.

 

They could be visibly out but stopping fuel at the correct point.

So you're missing the washer under the main fuel jets that hold the emulsion tube down? The tubes may well be stuck to the needles. I've seen it.

For the float bowl screws you'll need to get atleast one loose. Screw them down to a 2x4 and heat the bowl with a torch. The screw should then back out.

 

I swapped the washer around to the correct spot and she runs a million times better. However it is slow to idle down and still dies after a few pumps on the throttle. Seems as if I give it a twist and it takes a second to rev up.

I used left hand drill bits after heating the screws up and just ate away most of the screws. So, where would I get new screws if I just drill these on out?

I know it can be done because honda carbs that are pretty similiar can be done that way. I know someone has done it before by setting the first one with the tube method and then using a ruler and a flat peice of bar or something.

I just need that baseline number.

Or an idea of where to get new screws. P.S. I will drill a hole in the side of the float bole and put in a clear peice of glass or something cuz this is crazy cuz. lol

 

Oh does the regulator need to be grounded? charging system is next.

 

No wiring diagram close by here at the office. So I can't help there.

XJ4ever has all the parts you need. Click his logo in the top right of the screen.

 

The problem with "wet-setting" only one and then dry-setting the other three by comparison is that the range of adjustment is ONLY 3MM. And that's +1/-2 (or vice versa) so you're dealing with a level with ONE whole millimeter tolerance one way and TWO millimeters the other.

Setting them dry will not guarantee that they all maintain the same tolerances; they have to ALL be wet-set, or at least wet-verified.

(This is one of my early "XJ lessons" learned the hard way; trust me.)

 

Well I am smart enough to listen and hear. So Would it be a bad idea to just drill these suckers out and tap em for some actual bolts form home depot??? something with a head on it for future maintenance.

 

They'd have no seat to seal against. The actual screws have a pretty good length of taper on them.

 

NO, actually you do need real drain screws because of the "sealing" portion.

However, you can buy not only original replacement screws, but a variety of AFTERMARKET drain screws with oversized heads from our resident parts source, XJ4Ever.

Click the logo/link in the site banner, PM member chacal or send an email to info "AT" XJ4Ever.com. Len will hook you up.

 

OK here are a couple of videos. I fixed the emulsion tubes.

http://s114.photobucket.com/albums/n257 ... CN0906.mp4

http://s114.photobucket.com/albums/n257 ... CN0907.mp4

Washer where it should be.

 

I hate to say it but,

EEWWWW.

Those carbs gotta come apart and get properly cleaned or you're gonna beat your head against the wall for a good long time.

You can see bits of crud and "encrustation" of those jets.

You wanna RIDE this bike or f* with it forever?

Slow down and do it right; or it will slow you down for you.

 

I'd take those babies over to the church.
http://www.xjbikes.com/Forums/viewtopic/t=14692.html

There are a few other write ups too i think rick and fitz have ones with really good picks and lots of great info.

Also there's an entire thread on drain screw removal somewhere around here.

 

While you are ordering all the other bits for those carbs do yourself a big favour and buy four of the internal hex (allen key style) drain screws from Len at XJ4ever, they are the best thing since sliced cheese.

Your journey is only just beginning

 

I just rebuilt my carbs...what does it mean to set the float levels?

 

See this picture i posted up this morning,

the carb that is together has at the bottom the float bowl installed, the other 3 don't.
Well, inside that float bowl or chamber is what is known as the float, which is either metal or plastic and is sealed against petrol getting in and it's hollow so it floats in the petrol. On the bracket that holds the float in place in the carb body or float chamber there are two metal tangs that can be adjusted with a flat head screwdriver to adjust the level at which the float floats in the petrol, and this setting is known as the float level, and it's usually measured from the base of the float chamber to the top of the float when it's in position.
In the manual for the bike it lists the height at which the float level should be set for the correct operation. Too high or low will mean either not enough petrol in the chamber or too much, in which case petrol will overflow or starve the carb.
That's a basic idea, hope it helps.

 

The floats control the level of fuel in each carb just like the float in your toilet cistern. It must be set accurately and the best way to do this is by testing it with a piece of clear tube connected to the drain port. You adjust them by bending the tang on each float, but it is a painstaking process to get rigtht, so take your time and do it properly.

 

Yamaha did post a tech report in 1980-1. I will get you the link but it is 17.5mm or 21.5mm. I finally found another thread on here that went into some detail. I still have more than enough time to fiddle with it cuz I am in the middle of the church right now

 

Ok when using a micrometer the setting for my carbs sans gasket should be 17.5mm . I had one in spec the other 3 were 15-15-13.5. no wonder. I of course do plan on wet setting them to verify everything.

Starter went out and I found a new one for 111.00 shipped so I have to save up for that before any more tuning can occur.

 

I did a ton of searching on the forum and found alot of references of the clear
Tube method. What I didn't find was an explanation of how to do it and what I'm looking for. Can anyone please explain it to me better?

 

http://xjbikes.com/Forums/viewtopic/t=3 ... rt=30.html

page 3. the meniscus doesnt count and the level should be 2-4 mm below the rim

there is a pic about halfway down

 

Thanks for the link. I read it and have a couple questions. First I have my carbs installed already so will this method work?

Second, in the writeup it says this "Attach the Tools and tie the Vinyl Hose to the Upper Rail so the Hose rests along side the Bowl at the Screw and Washer.
Level the Rack.
Fill the Bowls and Open the Drains.

Carefully determine which Carbs need an adjustment.
If one or more are OK ... select the BEST one to use for "Measuring"
Drain Carbs
Remove Bowls."

When I open the drain what am I look for....a certain flow rate, no flow at all, measure the amount of gas that comes out, what exactly?

Thank you for your help.

 

ok well I guess it wasnt clear enough. So in great detail...
you will prolly have to take the carbs off of the bike...
remove the drain screw allowing the fuel to empty out of the bowl.
insert clear tube into drain hole.
bend it up and tape it to side of carb.
refill float bowl.
watch as the level of fuel in the clear tube rises.
when the level of the fuel stops rising take the measurement as shown in the picture in the above posted link.
remove float bowl and adjust float as needed.
re-install float bowl.
retest using the clear tube.

At this point if all is well and measuring within spec...remove clear tube and reinstall drain screw. button it up nice and tight and move on to next carb.

wash rinse repeat.
good luck

 

Awesome I finally get it now thanks....off to the store for some clear tubing!

 

Carbs should be off the bike, level on all planes, for the clear tube measurement.

 

A Picture is worth more than a Thousand Words.

The Picture of your Carbs tells me that they need to be Cleaned a lot better than they are in that shot.

Since the amount of enjoyment you want to receive from owning a Motorcycle is wholly dependent upon the degree of Fine Tuning achieved; cleaned Carbs in perfect working order is what your goal must be.

Regroup and become detail-oriented in the work you do those Carbs.
Tooth Brushes
Pipe Cleaners
Small Nylon Paint Brushes ... cut "Short" ... to let the Bristles scrub-off residue.

Replace nasty fasteners.
Scrub and refinish the Piston Bores.

Protect your hard work with a Gas Filter when you're done.

 

ONLY to "verify" and ONLY if you can get the front of the bike propped up so the carbs themselves are level; plus the bike has to be dead-level from side-to-side as well.

The problem is, if any of them need adjusting, the rack's gotta come back off anyway. Much easier to pull the rack; "fixture" it level, and do the whole thing on the bench.

 

I pulled my carbs back off yesterday and checked/ adjusted the float level. I pulled out my service manual and found that the level is different from the writeup that is linked earlier. On my 700 it says to be 1mm +- 1 mm from the top of the bowl. Does this vary from model to model? The writeup says to be about 3 mm? I went with what the manual says and reinstalled them and it's running great now! Thanks all for the help.

 

Yes, the spec varies from bike to bike, the 550s are different from the 650/750s, Mikunis different from Hitachis, etc.

It's good you followed your manual. Forum members often forget (or don't realize, if they have only one "flavor" of XJ) that there are all sorts of small differences like float levels, spark plug gap, oil capacity, etc. While there are occasional errors in the books, that isn't one of them.

 

Cool I was worried about flooding because of the difference but I guess I'm fine then thanks for the confirmation.

 

Oh my bejeezus!. I have cleaned and cleaned. I have checked jet sizes. I have done a serious bench sync. set the floats dry at 17.5mm as per my haynes and verified wet 3mm as per haynes. I can only crank it and it will only run if the choke is "ON".
I totally unscrewed the idle screw to where there is no contact and she is still idling fairly high.
(1) Can they be synched while not idling??

(2) I can revv on it all day but it takes a long time to get back down to this high idle. the diaphragm drops smooth and fast. In my opinion that is telling me it is taking a while to burn off the extra fuel in the bowl ie floats set too low allowing too much fuel in bowl.

(3) wont run without choke on ie not getting enough fuel ie floats set too high not allowing enough fuel in bowl.

obviously # 2 and 3 are contradictory to each other so is there a way to verify what carbs I have. I cant find any markings like hitachi or mikuni or model #'s any where. Do I just have tunnel vision?

 

DOH... I never tried the pilot screws after setting them at 2-1/2 turns out. I might try and go in 1/2 a turn and see.
thoughts??

I have always been an EFI guy.I have more experience tuning and tweaking on an LS1 than I ever will on a carb.

Oh and by the way. I may be hard headed as all get out and argue you down about something till I actually follow your advice but I really do appreciate all of your help and patience.

 

If you turn the PMS in you are going leaner & 1/2 turn adjustments is way too extreme, just a few degrees at a time, ONCE you are sure what you are trying to achieve.

 

thank you for that sir.will do