Carb Balancing Problems

[Ruby Racing]

I had to replace one of my carbs as it was damaged due to air screw being seized in place. I got a secondhand set (from Deefer666, thank you) and just used the one carb I needed, which was far left side of bike.


I have pod filters fitted and after switching the damaged carb thought I should balance the carbs. So bought a Morgan Carbtune balancer and tried to balance the carbs. Problem I'm getting is the carb I replaced is reading virtually off the scale and miles apart from the carb next to it or any of the others. I've adjusted the balancing screw pretty much through the whole range and I can't get it to come down. Have I missed something out? I've never balanced carbs before.


Also after swapping the carbs and refitting them the throttle cable is quite sticky in operation, that is if I let go of an open throttle it doesn't really snap shut.

[bandit]

Check the routeing of the throttle cable if it didn't stick before,recheck all vacuum pipes & make sure carbs aren't sucking in air where they shouldn't.
This is a good guide for carb balancing,


    http://fazerowners.yuku.com/topic/5398/HOWTO-Balance-your-carbs-inc-video#.Vl9kRNLhCW8

[Ruby Racing]

Thanks for the link. Very useful.


I didn't set the TPS before starting, would that make much of a difference?


I forgot to mention I also fitted a Dynojet kit (needles and main jets) and changed the fuel mixture screws as per their instructions (2.5 turns out on each carb).


As the problem carb is the second hand replacement I fitted, is it possible there is an issue with that carb? Maybe the diaphragm is damaged?


As the rod on the Carbtune is right to the top of the scale, is that indicating a lack of vacuum, or something else?

[darrsi]

Bike needs warming up before starting, and the TPS needs a check before AND after syncing the carbs.


Can't see any reason at all why the TPS could only knock out one carb though?


S'pose you could swap pipes over on 1 & 2 to rule out a sticky Carb Tune rod, or if it is indeed the new carb?
If everything is adjusted equally elsewhere then it would appear to suggest an issue with that carb i reckon.

[His Dudeness]

You've changed quite a few things in one go so it'd be hard for anyone to point to exactly where the problem is. There might be a carb guru on here but in general forums are good at helping with problems that occur regularly but this is an unusual one so collective experience might not give you the exact fault here. I doubt anyone's gone through this exact problem before so you might have to do some sideways thinking to get to the bottom of it. This one needs a bit of in depth knowledge on how a carb works to pin point an exact diagnosis which I don't have, I'm not a trained mechanic but I can make a semi educated guess based on some knowledge and logic (that's my disclaimer ) I think you've got two options 1 play it safe and put it back to the old setup and see if it's back to normal then change one thing at a time (slow method but should work) or 2 try the cunning fox method. think about how the internals of a carb works and how the changes you're making effects it. what is the gauge actually measuring? what causes the gauge to move up and down?

Here's my Fisher Price understanding of what's happening. As I understand it the gauges measure vacuum. The engine creates a vacuum in the cylinder as the piston moves down. That vacuum passes by the intake valve and up through the intake manifold and up as far as the butterfly valve in the carbs. At idle the butterfly valves are mostly closed but they are open a small bit so that a small bit of vacuum passes by them and draws a small bit of air through the air box and that incoming air draws fuel up from the bowl through the jets and that fuel mixes with the air and get sucked into the cylinder and that lets the bike idle with a closed throttle.

When you use the gauges you're connecting them into the intake manifold and measuring vacuum in each intake manifold. If you think about it there's an almost closed chamber up to the back of the butterfly valve and it's at vacuum pressure of that cylinder. When you turn the balancing adjuster screw what you're doing is forcing a screw to push down on each individual butterfly valve's linkage and opening or closing it a small bit. By turning the balancing screw in you're pushing down on the linkage so you're opening the butterfly valve. Opening the valve causes the almost sealed intake chamber to be a little less sealed so the vacuum you're measuring on you're vacuum gauge should drop. If you turn the balancing screw out you're closing the butterfly valve and sealing the intake chamber up more so the vacuum as shown on your gauge should go up. Yours is up off the scale so that suggests that the butterfly valve is totally closed so to test that theory you could try turning the adjuster in and keep turning it in until the gauge drops. It might drop or it might not drop on the gauge depending on out far out it is. If it does drop then you've pin pointed the problem but not the cause of the problem. You shouldn't have to turn one adjuster way more than the others so you'd have to ask yourself why is that one butterfly valve out so much compared to the others?

A possible cause is that when you joined the new carb into the bank of carbs you didn't line up all the linkages correctly or maybe you left something out like a spring or a spacer. I'd take the carbs out and inspect the butterfly valves. Is the one that has the problem closed more than the others? It could be a very small difference, you might need feeler gauges to see it. Next when you open the throttle and all the butterfly valves open is there any lag with the problem one? If there is then it suggests a problem with the linkage connection to the other carbs. So check the linkages make sure they're all lined up and all the springs are in place. Have a look at the manual to be sure you've got everything in place. It can be a bit fiddly getting all the little springs to seat correctly. That's why I don't split the carbs when I clean them.

To me a problem with the linkages causing that one butterfly valve to open differently to the rest seems to be the most likely problem, that's where I'd start but there could be other cause of it. Maybe due to the internal parts that you've changed out. The sticky throttle problem should be sorted too that could be causing all the butterfly valves to be held open but that would cause an equal problem across all carbs. The tps would also effect all the carbs not just one so that's unlikely to be the problem. You're looking for something localised to that one carb

[His Dudeness]

Just to add to that. The gauge is only measuring the vacuum that's in the intake manifold. Which simplifying it a bit is only effected by two main things the compression of the cylinder (which in your case you can rule out as a problem because you know it was fine before you did the carb swap) and how open or closed the butterfly valve is. The vacuum in that intake manifold can't be directly effected by adjusting idle mixture screws or the internal settings of the carbs BUT and it's a big but how each cylinder is running compared to the other cylinder and so how much vacuum that cylinder is creating compared to the other cylinders is most definitely effected by the mixture settings and all the internals of the carb in the idle circuit so it could be something in the idle circuit of that carb that's causing that cylinder to run differently to the others but I'd still be leaning towards the butterfly valve being out compared to the others. As I said though I'm just thinking out loud I'm not a mechanic so take all the advice with a pinch of salt and a waft of bullshite

[Punkstig]

Swap over the carbtune pipes to eliminate the instrument first!

[His Dudeness]

Swap over the carbtune pipes to eliminate the instrument first!

Definitely the place to start!

[Deefer666]

Is it reading high or low?

[Ruby Racing]

Thanks for the suggestions guys, especially the extensive post by His Dudeness.


I have limited time today, so here's what I've done today.


Firstly swapped over the hoses on the carbtune and I still get the high reading from the left/nearside carb. It's right at the top of the meter. So It's not the meter.


I've pulled the carbs off. I can't really see anything wrong, but bear in mind I'm new to working on carbs, so please treat me as someone with no knowledge.


I had a look at what happens when I turn the balancing screws and found something interesting. I'm guessing that moving the balancing adjuster screw changes the angle of the butterfly in just one of the carbs? Please confirm or deny this.


Looking at the original carbs, plus the replacement from the ones I bought from Deefer666 I can see that when turning the balancing adjuster screw for the two left/nearside carbs, the butterfly in the carb on the inside of the left/nearside carb moves, but the outer one doesn't appear to move. Looks the same on the other two carbs, just one butterfly moves.


However when I do the same thing on the replacement carbs, with my mangled carb on it, I see that the butterfly in the left/nearside carb moves, but not the one on the inside of the left/nearside carb! That confuses me, as it's the opposite of the other set of carbs. Surely the same butterfly would move? If only one butterfly moves when making adjustments between two carbs then perhaps I should swap the carbs back and just install the replacement carbs from Deefer666?


Hope that all makes sense.

[limax2]

As you observe the screw in between No 1 carb and No 2 only moves No 1 butterfly. Also between 3 and 4, only 4 moves.
The screw in the middle (between 2 and 3 carbs) moves 1 and 2 relative to 3 and 4.
The idea is you balance 1 and 2 to each other. Balance 3 and 4 to each other. Then use the centre screw to balance 1/2 to 3/4.
Blip the throttle a few times and thensome final tweaking is usually needed to get the best reading. I have not looked at the link that was posted so I am probably just repeating some of it!


The problem of one being way too much vacuum could be caused by a leaking diaphragm as that would stop the slide lifting. Easily checked by removing the top cover held by two screws. Also check that the slide is moving freely. You could swap the diaphragm and slide from your old carb or from one of the other spare spare carbs.   

[Ruby Racing]

Thanks Limax2.


So why is the butterfly in carb number 2 moving in my original carbs, but not in carb number 1? Have I installed the replacement carb number 1 incorrectly?


Good idea about the diaphragm swap. However would first like to resolve the inconsistency of the butterflies opening if possible. From what you say carb number 2 butterfly should not move when adjusting the balance between number 1 and 2. Except it does!

[limax2]

Thanks Limax2.


So why is the butterfly in carb number 2 moving in my original carbs, but not in carb number 1? Have I installed the replacement carb number 1 incorrectly?


Good idea about the diaphragm swap. However would first like to resolve the inconsistency of the butterflies opening if possible. From what you say carb number 2 butterfly should not move when adjusting the balance between number 1 and 2. Except it does!

Having studied a set of carbs on the bench I am struggling to find an answer to this.
I agree the butterfly thing needs sorting before bothering about diaphragm that is probbably o.k. anyway.
First check again that the butterfly adjuster, springs and anything else between 1 and 2 are a mirror image of that (undisturbed) between 3 and 4. This to make sure you have not missed something when fitting number 1 to the rest.
Does it all look the same on your spare carbs between 3 and 4. I'm fairly sure it will be as I don't know of any changes made in that area.
I don't want to insult you obvious talents but will mention that putting pressure on the adjuster between 1 and 2 can move both butterflys against the pressure of the spring opposite the middle adjuster. (The same does not happen between 3 and 4 because of the idle stop. The middle adjuster moves 1 and 2, leaving 3 and 4 against the idle stop thing).
Keep us informed and I will come back if I can come up with anything else.

[limax2]

For what it's worth here is a picture of the adjuster and springs between carbs 1 and 2, looking from the air filter side.
Number 1 on the left. The bit between the adjuster (at top) and the bottom spring is attached to No 1 spindle. Adjuster and bottom spring seat is attached to No 2 spindle. The top spring is just to hold the adjuster at the set position.
I guess if No 1 butterfly was fully closed (or some how stopped from fully closing), then screwing the adjuster down would open No 2 and also 3 and 4 at the same time. If you think that is a possibility you could try screwing the idle adjuster (on flexible cable going to bottom centre of carbs) in to partly open all the carbs and see if No 1 to 2 adjuster still moves No 2. It shouldn't.

Details

[celticdog]

The problem of one being way too much vacuum could be caused by a leaking diaphragm as that would stop the slide lifting. Easily checked by removing the top cover held by two screws. Also check that the slide is moving freely. You could swap the diaphragm and slide from your old carb or from one of the other spare spare carbs.

+1 for a vac leak!

[Ruby Racing]

For what it's worth here is a picture of the adjuster and springs between carbs 1 and 2, looking from the air filter side.
Number 1 on the left. The bit between the adjuster (at top) and the bottom spring is attached to No 1 spindle. Adjuster and bottom spring seat is attached to No 2 spindle. The top spring is just to hold the adjuster at the set position.
I guess if No 1 butterfly was fully closed (or some how stopped from fully closing), then screwing the adjuster down would open No 2 and also 3 and 4 at the same time. If you think that is a possibility you could try screwing the idle adjuster (on flexible cable going to bottom centre of carbs) in to partly open all the carbs and see if No 1 to 2 adjuster still moves No 2. It shouldn't.

Details

All sorted!


Thanks for everyones help, especially the pic you posted Limax2. When I put the "new" carb number 1 onto the others carbs I just jammed them together, with the result that the tab of the adjustment lever from carb 1 was in the middle of the spring that should have been below it, as per your photo, so that the screw at the top contacts with the tab.


It was a bit of a fiddle to get the tab in the right place and the spring jumped out more than once. About 6 times!!! In the end I put the spring in position then put the carb back on and used the two long bolts that connect all the carbs to pull it in slowly. Once it was just pushing against the side of the spring I managed to flick it underneath with a screwdriver.


The reason I didn't spot it was because the breather tube lies right in front of the adjuster, so in the photo Limax2 posted it would obscure the screw totally.


As for the throttle not snapping back. I think I had managed to cross over the two cables underneath the fuel tank. Fixed now.


And the Carbtune works properly now and I've balanced the carbs so she's so much better now. Not spot on, but it's my project bike and everything will be coming apart again soon. Just need to ride her to see how she runs with the pods and the Dynojet kit fitted.


Thanks again folks.

[limax2]

Well done, glad you got it sorted out  .
I know what you mean about the breather pipe, because I moved it out of the way to take the photo  [size=78%].[/size]

[His Dudeness]

Nice one.