Carb balancing and tuning

[splke 1,235]

Apologies if this is the wrong place

I am with a couple of friends restoring and rebuilding and my 2003 bandit. We are nearly done and and feel it will probably require the carbs fettling 

Anyone know of somewhere local to me that still fiddles with carbs please 

Leeds West Yorkshire? 

 

Thank you 

[Johnnie Mototrans 2,742]

Why not have a go yourself?

If the bike was running ok before being laid up then I would bet that the main issue will be modern fuel turned to a varnish or toffee like coating in the float bowls.

With a little care you should be able to remove the float bowls, floats and float valves.

Then a thorough blast with carb cleaner might be all that is needed. A couple of tins should only be about a tenner.

Reassemble and see if it runs.

If things really are a mess then Keyster rebuild kits are only about £25 per carb on the auction site.

This would allow you to replace all the jets and the float valves.

Just proceed with caution and dont force anything or mix parts from different carbs or play with the synchronisation.

The only other game changer would be access to a big enough sonic cleaner.

Do you have the carbs off the bike?

Are the rubber connectors ok?

 

 

 

[Andy m 23,473]

Try Startrite. Their passion is Norton their day to day business every Chinese commuter scooter. 

 

If you can reduce the carbs to a pile of bits I'll cheerfully run them through my ultrasonic cleaner for you. Its only big enough for single carbs mind so it the Bandit is a huge block I'd send them off. Makes a massive difference compared to spray cans and a tooth brush. 

 

Balancing is easy enough if it'll start, just get a set of vacuum gauges from the auction site and follow the instructions in the Haynes book. 

 

Andy

Edited March 24, 2021 by Andy m

[MatBin 5,080]

Synchronization sounds scary, but all it means is the slides all come up together, it's not that difficult for a competent person.

[Xactly 5,340]

7 minutes ago, MatBin said:

Synchronization sounds scary, but all it means is the slides all come up together, it's not that difficult for a competent person.

Or that the butterfly valves open together if the carbs are CV type.

[splke 1,235]

Thanks for the replies guys 

Yes we stripped the carbs and used a large cleaning bath replaced seals and gave a good blow with the airgun prior to refitting all seem to be operating OK 

Only problems I had prior to stripping was in really wet weather engine would stall which was getting worse each time. 

I will ring start right @Andy mand thank you I have used then for stuff before grans lads cheers

Might be OK when we get it back up and running should be in 2 or 3 weeks 

Edited March 24, 2021 by splke

[deecat 318]

Wet weather stalling ,I would look more towards the coils etc.

[davebike 943]

I would also ask what exhaust pipe  really open /loud  can / will make mixture rich low down add damp and you have a stall

As a rule open pipe need smaller idle jets and bigger main

[Johnnie Mototrans 2,742]

1 hour ago, splke said:

Thanks for the replies guys 

Yes we stripped the carbs and used a large cleaning bath replaced seals and gave a good blow with the airgun prior to refitting all seem to be operating OK 

Only problems I had prior to stripping was in really wet weather engine would stall which was getting worse each time. 

I will ring start right @Andy mand thank you I have used then for stuff before grans lads cheers

Might be OK when we get it back up and running should be in 2 or 3 weeks 

 

Sorry I was guessing where you had got to on the rebuild journey.

So you have already stripped and cleaned the carbs.

As long as they went back together with no mistakes and no settings altered then it should at least start.

Have you now tried to run the bike and experienced difficulties?

If so there are plenty of other things to check over before you post your carbs off for specialist attention.

 

 

[splke 1,235]

Not yet no but ilwith cv19 restrictions its been in bits for over a year and stood for 6 months prior to that. We feel it will probably need a tune and balance but won't know till we get it running. 

We replaced Coils and leads so hopefully it will be fine once complete and we can it will no longer be used for commute so should only be a nice sunny day steed up through moors and dales. 

[splke 1,235]

44 minutes ago, davebike said:

I would also ask what exhaust pipe  really open /loud  can / will make mixture rich low down add damp and you have a stall

As a rule open pipe need smaller idle jets and bigger main

It's pretty standard set up aftermarket end can but ran OK for years prior to wet winter of 2019

[Johnnie Mototrans 2,742]

7 minutes ago, splke said:

Not yet no but ilwith cv19 restrictions its been in bits for over a year and stood for 6 months prior to that. We feel it will probably need a tune and balance but won't know till we get it running. 

We replaced Coils and leads so hopefully it will be fine once complete and we can it will no longer be used for commute so should only be a nice sunny day steed up through moors and dales. 

 

Ah

So looking for someone to balance the carbs once you have it running again.

That makes a bit more sense.

I bought a set of gauges/ guages? yonks ago and enjoy setting carbs up immensely.

They weren't expensive and I have two pals to share special tool costs with.

I never remember how to do it so it's like learning a new skill every time.

Good luck

[Andy m 23,473]

This is why I stick to twins and avoid exhaust mods*:

 

From a Bandit forum:

 

"There are 3 sync screws located between each two carburetors on the butterfly shaft. They work just like on the Venture except the carburetors are all in line so there isn't a linkage from left to right. Just like on the Venture they're screws through sheet metal cams with springs on them.

 

"You'll probably need to pull the tank to get to them. In theory there should be enough fuel in the carbs to do a sync, but I generally use an axillary tank.

 

From the fiche it appears that the #2 (2nd from left) carburetor is fixed. You'd sync 1 to 2, then 3 to 4, then finally 3 to 2. It's really more intuitive than on the Venture because they're all lined up rather than the cross bike linkage (I always loose track of which screw is which on the Venture)."

 

So get it to idle any way you can and start fiddling. Anything that increases the idle continue until it doesn't then come back half way. Just keep going round and round until you have the fastest idle. Knock the idle back on the cable and Roberts your dad's brother. 

 

Definitely get an Auxiliary tank or at least enough hose to sit the bike tank on the bench. You don't want to be chasing your tail as the level in the bowls falls off. 

 

*The CL backfired yesterday and blew open a weld in the top silencer which of course upsets that theory! Idle went up but no power until 2500 rpm 😩

 

Andy

Edited March 24, 2021 by Andy m

[Xactly 5,340]

The process described is interesting; it seems more like adjusting a pair of Amals on an old Brit twin than doing it on a Jap multi. I would have thought that there would be four vacuum take-off points to which one would connect a balancer, then just adjust the screws to get the same manifold pressure on all four. Still, I’m not familiar with Bandits so I’m probably wrong, but surprised...

FWIW on my old T140V Triumph I used to use a couple of brazing rods inserted underneath the slide on each carb. By looking at the end of the rods one could detect minute movement in each slide and adjust them accordingly. When I bought a good old Carbtune mercury Gauge for the Moto Guzzi I had at the time I tried it on my Triumph - they were spot-on. These days it’s much easier to do with EFI, which also compensates for ethanol in the fuel, which has a different stoichmetric AFR to petrol and, on a carb engine, causes lean running, at least at 10% ethanol content.

[MatBin 5,080]

1 hour ago, Andy m said:

Definitely get an Auxiliary tank or at least enough hose to sit the bike tank on the bench. You don't want to be chasing your tail as the level in the bowls falls off.

 

Andy

Excellent advise.

[Tex 36,816]

There are two common methods of synchronising the four carbs on Jap bikes. The first type has one carb ‘fixed’ and you adjust the other three to match it, the second has them split into pairs so you balance 1 and 2 together and then 3 and 4 and finally you balance the two pairs. It’s not difficult and I would cheerfully do it for you, but we’re a long way apart..   

[Andy m 23,473]

1 hour ago, Xactly said:

The process described is interesting; it seems more like adjusting a pair of Amals on an old Brit twin than doing it on a Jap multi. I would have thought that there would be four vacuum take-off points to which one would connect a balancer, then just adjust the screws to get the same manifold pressure on all four. Still, I’m not familiar with Bandits so I’m probably wrong, but surprised...

FWIW on my old T140V Triumph I used to use a couple of brazing rods inserted underneath the slide on each carb. By looking at the end of the rods one could detect minute movement in each slide and adjust them accordingly. When I bought a good old Carbtune mercury Gauge for the Moto Guzzi I had at the time I tried it on my Triumph - they were spot-on. These days it’s much easier to do with EFI, which also compensates for ethanol in the fuel, which has a different stoichmetric AFR to petrol and, on a carb engine, causes lean running, at least at 10% ethanol content.

 

The vacuum gauge method is more accurate and it will almost certainly have take off points, the brazing rod idea less so but would get you a starting point. Just a case of what kit you have. Back in the day gauges would have been beyond the means of most, so bikes like the CL don't have take-offs. The rod and speed methods still work as well as they ever did. 

 

The CL starting point is by ear, let go of the throttle and hope you hear one tap as the close not two. I used to have a rubber cup thing you could put over the carb mouth for when they had no tapping. I won't be drilling into the throttle bodies to fit them. 

 

Andy

[splke 1,235]

2 hours ago, Tex said:

There are two common methods of synchronising the four carbs on Jap bikes. The first type has one carb ‘fixed’ and you adjust the other three to match it, the second has them split into pairs so you balance 1 and 2 together and then 3 and 4 and finally you balance the two pairs. It’s not difficult and I would cheerfully do it for you, but we’re a long way apart..   

thank you shame that 

[Xactly 5,340]

3 hours ago, Tex said:

There are two common methods of synchronising the four carbs on Jap bikes. The first type has one carb ‘fixed’ and you adjust the other three to match it, the second has them split into pairs so you balance 1 and 2 together and then 3 and 4 and finally you balance the two pairs. It’s not difficult and I would cheerfully do it for you, but we’re a long way apart..   

I’m familiar with the former, balancing three to the reference carb.

[Defender 3,834]

21 hours ago, splke said:

Apologies if this is the wrong place

I am with a couple of friends restoring and rebuilding and my 2003 bandit. We are nearly done and and feel it will probably require the carbs fettling 

Anyone know of somewhere local to me that still fiddles with carbs please 

Leeds West Yorkshire? 

 

Thank you 

Whilst I can't recommend anyone local to you, as it's not my area, in my opinion if you want to have it done properly and right first time, get it set up on a chassis dynamometer/rolling road, it's not cheap but is worth it in the long run for both bikes and cars with carbs etc.

Edited March 24, 2021 by Defender
Correction.

[splke 1,235]

Well the day came and we got her running but not great

 

we messed about till we killed it (fuel leak) really odd as it seemed great initially but steadily got worse in the end it would only run on choke so i am guessing the bowls got shitty (maybe from dirty pipes)and jets ended up getting blocked !

we sent bike away to  a chap up york road who knows his way around bandits and carbs so hoping for the best , maybe next week eh ? 

[Slowboy 20,358]

If you got a fuel leak from the carbs, that sounds like crap in the tank. I’ve had a similar problem in the past and went to the trouble of completely draining the tank, getting two good handfuls of granite chippings (or washed gravel of a neighbours drive😁) and sloosh (technical term) the tank about for 20 minutes or so then draining it of all the rocks. Leave it to dry in the sun for a few hours. The slooshing can be much shorter or more effective if you have a couple of old towels or blankets and a concrete mixer to shove it all in.

 

Don’t forget to remove the fuel tap before putting the granite/gravel in, use gaffer tape to seal the fuel tap and petrol cap holes

 

 

Edited May 28, 2021 by slowboy

[splke 1,235]

Just to revisit this 

I've had carbs set up and refurbed cleaned etc 

Still not right though runs OK till warm then on idle the thing is all over the shop from 1m

.2k to 3.5 k revs 

Video of idle

Checked all fuland breather pipes refurbed fuel tap and removed online filter 

Going  round twist and a little here 

[Johnnie Mototrans 2,742]

That could be one or more float valves sticking but I now wonder if the electronics are playing up.

Revs jumping about like that seems almost like the advance is randomly going up down and sideways.

Check the connections on the ignition circuit to make sure they are all corrosion free and make solid contact.

If not then I would probably try to hunt down some second hand parts and start swapping one thing at a time.

Just how clever are the electronics?

Is there a lambda sensor anywhere in the mix?

Good luck.

 

[splke 1,235]

11 minutes ago, Johnnie Mototrans said:

That could be one or more float valves sticking but I now wonder if the electronics are playing up.

Revs jumping about like that seems almost like the advance is randomly going up down and sideways.

Check the connections on the ignition circuit to make sure they are all corrosion free and make solid contact.

If not then I would probably try to hunt down some second hand parts and start swapping one thing at a time.

Just how clever are the electronics?

Is there a lambda sensor anywhere in the mix?

Good luck.

 

Thank you not sure about a lambda sensor on a 2k3 model? Will check connections though it's pretty sound till warm tho.