Cylinder #3 is all normal?

[liamstears]

Evening all

Did some bits to the bike today and to finish I decided to balance the throttle bodies

After doing it and having them all pretty close at idle the bike does seem smoother to ride and a lot of the vibration I had before has gone so seems to be running right but have a couple of concerns

Firstly I decided to remove all 4 sync screws and start from fresh as I think I messed it up last time I did it and noticed all the screws had a black liquid of some description on them, is this normal? I cleaned them and put them all back in fully then backed them all out about 3/4 before syncing

Syncs fine at idle but when revving the #3 cylinder doesn't seem to pull the same vacuum, it's pretty close up to around 3000rpm but as you get closer to 4000 number #3 seems to stay a lot lower than the rest, I did try spraying some Carb cleaner around the boots and hoses of #3 but couldn't find anything

Should also mention I recently had the local shop check valve clearances and was told all are in spec and the plugs were changed at the same time

Please see this video: https://youtu.be/7RAnf6V1bVQ

Is this normal? Or do I have an issue here? Appreciate any help

 

[FinalImpact]

Good observation!


I suspect a vacuum leak or a restriction. For KICKS swap hose and gauge at the bikes end trading 3 to 4 and 4 to 3 on the gauge side. This eliminates the gauge. Did the problem move to gauge position #4? If yes, it may be the restrictor. Move that restrictor to #3 but leave the hoses swapped from 3 to 4. Is it the gauge or restrictor?

Assuming it it not the gauge. Look the bike over. Use a syringe to suck or blow into the sync lines. If you can feel a difference swap lines and blow solvent into idle sync hose barb at TB.... verify all 4 do the same thing.
Verify Idle Air Control Valve hoses flow the same too. A hand held vacuum pump and gauge should help here more obvious than syringe pull test.

In short if you can't pin it down to a vacuum issue it goes back to engine health and or valve adjustment.

Think of the engine as a big pump. If it were spun by another force, the intake valve is open while the piston descends. This **basically** gives you the pulsed vacuum signal. In real life it is the crankshafts acceleration from combustion that makes the signal seen when the fuel burns on each stroke combined with the amount of "air leakage", if you will, which is the air the sync screws let in to allow the engine to idle. A controlled air leak.

All mechanical functions being equal, when a sync screw setting restricts volume to a cylinder, that cylinder can show greater variance.

If you set them all at 3/4 turn out, what does #3 look like at idle and 4k?

Verify the tool is not the cause by swapping as described. Then look engine over in detail. A tiny crack in a hose could do this. If true that cylinder has a source of air and will need less from the IACV. Find the leak!

Keep us posted as it seems to be off a good bit more than most. I would want to know why!

 

[TownsendsFJR1300]

Even at idle, #3 is barely in spec.

Is the RPM's shown about 1,300?

There's many a thread on it but IMO, I would do another fine tuning sync.

This will likely take longer than a reg sync so if you have a large fan, use it in front of the engine/header.

Generally, you adjust one cylinder, it'll affect another. So leaving #1 (base) alone, get #3 closer at idle.
Then rev and hold to 3-4K and adjust. MOST of the time, if the cylinders are super close at 3-4k, they'll be good at idle.

A couple of quick rev's in-between is important too.

Bottom line, get em close at 3-4 k and re-adjust at idle getting a happy medium in-between.

The more patient (thus the fan) you are, the closer you'll get em..



It should be noted, DO NOT adjust the butterfly adjustment screw(with the spring between cylinders 2 & 3)

 

[liamstears]

To be honest being a commuter I don't really have the time to pull it all apart and do all the diagnostics

Do you guys think just buying a set of used throttle bodies would be worth a shot? Can be picked up pretty cheaply...

 

[TownsendsFJR1300]

IMO, I would simply do a re-sync. Get #3 and #4 close. Someone may have dinked with the butterfly main shaft alignment screw (in the center)

If 3 &4 get and stay close, do the same for 1 & 2, THEN (pay attention to that "springed" screw setting) and see if you can get them all aligned up WITH the middle shaft, "springed" adjustment screw..


My Yamaha shop synced my old FJR (before I had the carb tune). They adjusted the one SPRINGED SCREW, NOT the air screw AS IT SHOULD HAVE BEEN.
The spring had white paint on it and it was very obvious they adjusted that. I put that back where it belonged and re-synced with the air screws...

 

[FinalImpact]

At least eliminate the gauge and restrictors as the source. It means lifting the tank....

Perhaps this will help...

From Final Impact Bike P O R N album...

 

[TownsendsFJR1300]

Any updates?

 

[liamstears]

Sorry busy busy as always, as I said before I didn't really have the time to pull it all apart and check everything over so I bought a throttle body complete from a local breakers for £30, changed it today and now my readings are normal and it balanced perfectly fine

Checking over the old throttle body the only obvious thing I can see is the extension for balancing on the number 3 cylinder looks a bit buggered where it enters the throttle body, looks like that could of been the problem and that alone would of cost me around £18 so the way I see it is I got it fixed for £18 and spent an extra £12 on a load of spares including 4 working injectors etc

Overall happy and all fixed, thanks for the help guys

 

[FinalImpact]

Sorry busy busy as always, as I said before I didn't really have the time to pull it all apart and check everything over so I bought a throttle body complete from a local breakers for £30, changed it today and now my readings are normal and it balanced perfectly fine

Checking over the old throttle body the only obvious thing I can see is the extension for balancing on the number 3 cylinder looks a bit buggered where it enters the throttle body, looks like that could of been the problem and that alone would of cost me around £18 so the way I see it is I got it fixed for £18 and spent an extra £12 on a load of spares including 4 working injectors etc

Overall happy and all fixed, thanks for the help guys

If you were not so far away I'd buy the TB assembly from you for my project!!!
Glad it is fixed and thanks for the Rep Point! :thumbup: