Carb balance won't go

[Kenny Dave]

I can't balance my carbs. Picture below:

Link if it's too big: https://i.imgur.com/IBs756j.jpg
1-2 is out of balance with 3-4. Anti clockwise on the centre screw should help with that, but it doesn't. I've screwed it right out to where the screw is wobbling as it's lose in the seat. Turning it the other way Makes 1-2 bog and ultimately the engine stall.

I can't get 3-4 to shift at all, they're up at the top of the gauge always. They respond normally to throttle, coming down before easing back up. Choke brings 3-4 down a bit, and 1-2 isn't changed much. They looked roughly equal on the eye test before I put them in, just open on the tickover.

I can't get the tickover down below 2.5, I think I'm right out on the tickover adjuster too.

Any suggestions before I pull the carbs out and have a look to see whats up? Things to look at when I do? Bit of crap stuck under one of the butterflys I see as a maybe, can't think of anything else.

The background: carbs are a different set to what was in a week ago, cleaned. I balanced the old carbs only 3 weeks ago, no issues. I've got new spark plugs in. New carb inlet rubbers. Exhaust headers reseated. New coolant, new oil. Coolant rubbers and rad replaced.

Thanks if you can help, I'm having a bit of a mare over here, it never seems to end.

[Frasier]

Hi. I would do (I did) this, to avoid an endless suffering with the carbs:

0. while engine running spray brake cleaner around carb boots to check if they're airtight; idle should not change
1. order full seal, gasket and O-ring kit from [ https://www.litetek.co/ ]  (thai company, best quality and they have the proper sizes, quantities in their kit, and made of modern, ethanol infected fuel compatible materials (viton, etc.); don't buy from Yamaha!)
2. total carb disassembly, except butterfly + shaft
3. total cleaning with ultrasonic bath + compressed air, multiple times if needed, untill clean
4. check and replace every brass parts, which have signs of water (ethanol) erosion, or other damage
5. reassembly with new seals and new parts, put silicone grease on rubber parts while assembling
6. initial settings according to service manual (CO2 screw, etc)
7. carb balance, idle adjustment
8. success

[Kenny Dave]

Thanks that's a good common sense checklist.

This the repair kit you're talking of I think: https://litetek.co/Carb_Kit_Yamaha_FZS600_Fazer.html

I don't think it would do this with leaking fuel somewhere though. My issues are with the butterfly if it's staying open; I don't know why it would behave as it is if that isn't the case.

The settings: pilot screws are 2.5 out (I hope), what else is there to adjust other than balance and idle? Needle jets are all at the standard position (I hope).

I'm about to go and rip em out and see what's what. It's overwhelmingly likely I've done something stupid.

Update: had them off, checked everything. Can't see anything wrong. I have a spare set with seized pilot screws, which were good a month ago. So I put the removables from 3 and 4 from that into this set, switched the pilot screw for 1 & 3, and tried again. Exactly the same, 3 and 4 with the vacuum too high on the gauge, even with the tickover screw right out.

The butterflies are more open for 1 & 2 than 3 & 4. I'm starting to think it isn't the carbs, and I haven't screwed the spark plugs in properly or something. Or the carb rubbers I've got are spectacularly leaking. I didn't check with the carb cleaner or water spray, so I can try that tomorrow.

[Trebus]

I’d check from cold that all the exhaust header pipes get hot at the same rate. At least then you know you’re firing on all 4 and hopefully in the right order (dunno if it’s possible to get it wrong on these but we’ve all probably got the wrong lead to the wrong pot on something in the past). No air leak on your gauges?

[Frasier]

When I bought my Fazer last year, the biggest problem was with the fuelling / carbs. It was somehow rideable, but very far from good.When I'm saying: rebuild it to avoid suffering, then I mean suffering = what you are doing now. You try to solve your problem, but who knows what's in a 20+ years old carb?
I decided to rebuild the carbs according to my list. Man... the rubber O-rings and seals were crumbling, cracking, they were hard, because of ethanol fuel and age. Brass parts were pitted because ethanol fuel absorbs water, water corrodes everything.IMHO the only solution is using those ethanol resistant viton seals (yes, you found the proper one on the litetek site), and replace brass parts beyond acceptable. I noted which jets needs to be replaced, and ordered them, but my sligthly pitted jets are still in the carbs now. With the cleaned, resealed, synchronised carbs the bike purrs like a kitten, totally worth it. I'll replace the jets later just for the peace of mind.If you know your carbs surely OK, then you can avoid a rebuild, but the Fazer is a simple bike; only a limited number of problems are possible: wrong valve gap, leaking carb boots, bad carbs. Maybe some ignition problem, but improbable.Let us know when you'll solve your problems, I'm curious!

[Kenny Dave]

It has to be either the carb bodies, or something other than the carbs. Because I've flipped everything but for the offending cylinders, 2 and 3. I'm going to do a quick sense check on other stuff, then order a couple of carb bodies this afternoon.

Thanks for your efforts, I do appreciate this place a lot.

[Kenny Dave]

Update: switched carb bodies, no change. They have the parts from the carbs that worked ok. Diaphragm, valves. Anything other than the bare bones.

Also checked: sprayed around inlets and both sides of the carbs all cylinders with easy start to see if it races, it does not. Also tried with a water spray the other way. Tried on the spark plugs too. Float heights seem correct also.

It's 3 and 4 running hard even when the tickover is right down. I get 2.5k on the tickover with the adjuster not even touching, and the balance screw taking 1&2 right up. 3&4 still flying.

The butterflys are completely closed for 3&4 and it still does this. I thought maybe something to do with the choke, but I have changed them with changing the carbs.


I'm at an absolute loss as to what to go after.

[Mike_2002]

Might be a stupid question, have you checked the throttle cable slack?, re the tickover.Also have you swapped the carb balancer to different positions?

[BBROWN1664]

swap the carbtune pipes around

1&2 to cylinder 3&4, 3&4 to 1&2 and see if the problem is still visible on the carbtune as it appears now. i.e. prove its not the gauges causing a non-issue

[unfazed]

Update: switched carb bodies, no change. They have the parts from the carbs that worked ok. Diaphragm, valves. Anything other than the bare bones.

Also checked: sprayed around inlets and both sides of the carbs all cylinders with easy start to see if it races, it does not. Also tried with a water spray the other way. Tried on the spark plugs too. Float heights seem correct also.

It's 3 and 4 running hard even when the tickover is right down. I get 2.5k on the tickover with the adjuster not even touching, and the balance screw taking 1&2 right up. 3&4 still flying.

The butterflys are completely closed for 3&4 and it still does this. I thought maybe something to do with the choke, but I have changed them with changing the carbs.


I'm at an absolute loss as to what to go after.

I have come across this a few times and the reason I fund in the Fazer

1. The slide needle Nozzles had fallen out and the owner didn't notice it missing and/or had fitted the nozzle upsidedown. This allows fuel to be dragged up through  the main jet by engine vacuum.

2. The main jet O-ring was perished  and again allowed fuel to be dragged up through  the main jet by engine vacuum. (this you said was replaced by a Viton O-ring)

3. The blank jet in next to the main jet was not tightened full an fell out and again allowed fuel to be dragged up by engine vacuum.

[Kenny Dave]

I have solved the problem, and it was something that wasn't moving when I moved the bits between the cylinders: me. I am an idiot and don't know how vacuum gauges work.

I thought I did, and was sure, and it made sense. What I should have done is just ramp the revs up and turn it the other way to what I thought, and it got there. The gauge went down on 1&2, then went back up. I'm still not sure wtf is going on with them, but I guess I've learned something: when you're stuck, just have a fiddle and see.

What I was faced with was the level low on 1&2. Turning clockwise on the centre screw caused 1&2 to bog and the engine to die. So I didn't go further with that, wanted to turn them out more. What I needed to do was turn the tickover right up, and then turn the centre screw clockwise, which brings down 3&4. I was thinking 3&4 were running hard, 1&2 were not as they were dying. Still not a clue what is actually happening, but it's all sorted and balanced anyway.
Thank you for the suggestions, I do appreciate it. Even if I was too dumb for it to be any of the sensible suggestions given.