Breva 750 throttle return

[GonzoB]

The throttles on my '07 Breva 750 don't return home completely

They almost get there, but stop in the last couple of mm of movement. I can force them closed with the twistgrip, but if I blip the throttle and just let the twistgrip snap closed, the throttles stay open a bit. The revs remain at about 1200 until I force the twistgrip closed.

I've done all the normal things:

• check that the cables move smoothly
• lube the twistgrip
• check the freeplay

I'm wondering if there is something in the throttle body I need to lube. The bike had sat mostly unused for about 12 years before I bought it.

Any thoughts?

Gonzo

[Muzz]

The "open" cable set a bit too short?

Adjustment are a wee bit awkward to get at.

[GonzoB]

No, the cables are fine. Even with visible excess slack at the throttle body end (independent of the twistgrip situation) it doesn't go home unless pulled by the return cable. If there were not enough slack in the "open" cable I figure it would never go home.

Oh, and the fast idle mechanism is well clear.

I'm wondering if a spring is broken, or something.

Gonzo

[guzzisteve]

If they are not clean, clean them and the air passage for bypass. I seen them so nasty they would stick, springs on the side get gooey too. Make sure linkage arms are free.

[malik]

At one time the 2TB V7C (same as the Breva) had a sticking throttle. Found it was caused by the oil breather fouling the throttle body control rod rose joint on the RHS. Re-routing the breather tube & cable-tying it out of the way solved the problem.

The only other throttle cable problems have been a lock nut at the cable's throttle body end loosening itself, and a broken strand on the pull cable. I ended up replacing the cables at 158,000km, spent a bit of time getting the pull and return adjustment right, and has been untouched since then (now at 214,000km).

[malik]

PS. I've heard that it is possible for the butterflies in the bodies or their axles to wear with use. It is easier to clean them out and check for wear with the throttle bodies off the bike. So next time you have them off .......

[GonzoB]

Steve and Malik,

Thanks for your suggestions. The breather is well clear of the linkage. It's unlikely to be wear in the shafts, as the bike hasn't done 5,000 km yet (it had sat unused for many years). So it seems I'll have to wait until I next have the tank off, and give the TB's a clean-out.

Can you unbolt the linkage assembly from the bottom of the TBs without having to do a major re-tune? I won't have to take the tank off to get at that.

Gonzo

[guzzisteve]

The crossbar should have 2 screws under ea TB. Good time to clean & lube all the pivots on throttle plate. They shouldn't be too dirty at that mileage.
You might check the choke screw on the throttle plate, it has to have play also.
If you remove the crossbar you may have to resync the TB's

[malik]

I've only ever taken the whole assembly off as a unit - the support bracket covers the Screw of Doom, the top screw connecting the bell housing to the block. Less chance of me mucking something up. It requires STRENGTH to squeeze in the manifold rubbers in to move them into the airbox, and once all the manifolds are off, it's a juggling act to manipulate the assembly so as to get it out past the frame sections. In spite of appearances it does come out, and it gets easier the more often you do it. Getting it back in can be equally frustrating. Hands of a leprechaun & the strength of Hercules would be an asset, and I've neither. But it is easier to work on once on the bench.

I'll be familiarising myself with the techniques once more in the very near future, I've another clutch job and then an engine & clutch next up.

[Muzz]

I've only ever taken the whole assembly off as a unit - the support bracket covers the Screw of Doom, the top screw connecting the bell housing to the block.

That one really is a bear Mal!   However, it can be done.  When I do the gearbox I leave all the injectors etc. on; I use a hex as found in one of those multi bit sets you get with the holder that has the 1/4" square drive.  With the aid of numerous extensions and a universal you can JUST squeeze in under the crossbar.

As an edit, I was forced to do this (getting to Gonzo's problem and the cross bar) because on one of the little screws holding the cross bar Luigi must have emptied his entire bottle of Loctite on it and it just would not shift.  All I did ultimately was wreck the head of the screw.  Trying the hex screw and the extensions seemed a more preferable try than removing the entire throttle body set-up.

[GonzoB]

OK, so I tried undoing the nut on the bottom of the right throttle valve. I got the nut off, but was unable to get the lever (with the linkage attached) off the shaft. Is it heat-shrunk on? Do I need a puller? I lubed the shaft where it enters the throttle body and gave up.

Gonzo   

[GonzoB]

And here's the embarrassing bit...

Remember I said I'd checked all the cable play? Well, I had... Well, almost.

I hadn't checked the play in the cruise control cable. It was a smidge too tight.

The problem is now fixed. Thanks everyone for your help.

Grovel, grovel.

Gonzo

[malik]

All's well that ends well. AND along the way you learned a bit and became more intimate with your bike. It's a winner.

[Muzz]

All's well that ends well. AND along the way you learned a bit and became more intimate with your bike. It's a winner.

Yup. Most of us have been there,done that.

Good gnus Gonzo.

[GonzoB]

Hey, now I've got engine braking back! Cool.

Gonzo

[cee2cee]

Glad you got it fixed.  You are going to really enjoy your Breva. I have a 2007 Breva750 with 34,000km on her and not one problem..