Something weird with my throttlebodies

[gorbys]

Basically a copy/paste of what I wrote in my thread about intake rubbers but might be better to keep the two issues separate. 

So I've been having trouble obtaining steady idle as mentioned. Now I can get a steady idle but not a low steady idle. Like I set it at 1100, give it a few revs and now we're at 1900! Or it'll go down to 1100 again and then go lower and eventually die.... Its like there is no in-between and finding that sweet spot is super hard. 

 

So in anger while my idle was revving up I stuck my thumbs on the throttle linkage either side and pretty much forced it shut. And voila, low and steady idle... I let go of the linkage and it holds the low idle for a little bit then starts creeping up again. So there is definitely something going on with the linkage/throttle assembly as well... Anyone have some ideas ? 

It's like it won't stay closed enough 

[Isleoman]

On my modern bike it's usually the hand grip on the throttle tube is rubbing against the plastic housing.  Have to pull the grip outward till there is 1/16" clearance.   

Disconnect the throttle cables at the carbs and see if it idles smooth.  

[wraith]

Try disconnecting the throttle cable, might be a lot of old crud in the cable.

You've set the valves before balance the carbs I take it, think you said you had in your other post.

[gorbys]

12 hours ago, Isleoman said:

On my modern bike it's usually the hand grip on the throttle tube is rubbing against the plastic housing.  Have to pull the grip outward till there is 1/16" clearance.   

Disconnect the throttle cables at the carbs and see if it idles smooth.  

Good tip! I'll try that next time. 

11 hours ago, wraith said:

Try disconnecting the throttle cable, might be a lot of old crud in the cable.

You've set the valves before balance the carbs I take it, think you said you had in your other post.

Correct, I've also double checked them recently just to make sure. 

Speaking of balancing carbs I did try to balance the carbs earlier but that was before I knew about the air leaks. I assume I might need to do that again now if the air leak issue is resolved? 

 

[dago]

You're right you really should rebalance the carbs now the air leak is fixed

Edited August 7, 2022 by dago

[wraith]

Could be the reason for the idling being all over the place, just very bad balance carbs 

[gorbys]

10 minutes ago, wraith said:

Could be the reason for the idling being all over the place, just very bad balance carbs 

I'm not gonna rule out the possibility but to be honest this feels like a mechanical issue. Like if you manage to turn the adjuster to find that "sweetspot" it'll happily sit at 1000-1100 rpms all day until you touch the throttle. Give it a rev and it might settle down again but most times it'll hang at 1600 or 1900 or somewhere in the region. Sometimes it'll sit there for a little while and then come down. It's like the return spring is too weak or there's just some crud or other shit preventing it from closing those last few mikrometers... 

[wraith]

You need to start with a good base, carbs being balance right is the starting point. Un-balanced carbs can do all sorts of werd shit that can lead you down a completely different rabbit hole.

You will find out if there is something wrong, if the carbs keep going out of balance when you blip the throttle with the guages on.

Edited August 7, 2022 by wraith
Add a bit

[Reinhoud]

8 hours ago, gorbys said:

I'm not gonna rule out the possibility but to be honest this feels like a mechanical issue. Like if you manage to turn the adjuster to find that "sweetspot" it'll happily sit at 1000-1100 rpms all day until you touch the throttle. Give it a rev and it might settle down again but most times it'll hang at 1600 or 1900 or somewhere in the region. Sometimes it'll sit there for a little while and then come down. It's like the return spring is too weak or there's just some crud or other shit preventing it from closing those last few mikrometers... 

No vacuum leaks?

Engine tuned correctly?

[gorbys]

Last round with the starter gas turned out negative for vacuum leaks. 

Is there something I should try to lubricate on the throttle linkage assembly? 

I'll have some days off now so I'll look into the matter. 

I'm thinking rebalancing the carbs. 

Disconnect the throttle cable and see if that makes it close properly. 

Degrease and clean linkage and movable parts, lubricate. 

I assume I might have to revisit needle settings and idle screw adjustments too