Topic: [solved] no throttle return - valves sticky

[gsgleason]

1975 CB750F.  I'm putting everything back together after a complete carb clean and rebuild.  Current issue is that the spring does not pull the throttle valves back into place when releasing the throttle control.  Disconnected the cables from the carbs and same issue lifting by hand.

I'm pretty sure I kept track of each carb's parts and get them back together in sets, but that may not be the case.

I soaked everything in simple green as per the advice on these forums, and it seemed to leave a funky residue on the carb bodies, which I cleaned off pretty well after the soaking, but possibly not good enough.

It's clear the issue is with the throttle valves not sliding easily.  I'm of course going to have to disassemble the carbs, but what can I do?  Everything is clean already.  How do I smooth the action of the throttle valves?

[Sporkfly]

Simple green does indeed leave a white residue. I follow any cleaning with Simple Green with soap and water. Anyway, you could maybe put some gas or carb clean in through the top of the carb. I suggest gas because it's meant to be used with any gaskets and o-rings in the carb. Carb clean could cause damage to internal things that aren't composed of metal.

[gsgleason]

I took the carbs off, disassembled, buffed the bore of each carb with 0000 steel wool followed by compressed air and carb cleaner.  When I put the valves back in, I tested each valve in each carb body, and found a better combination.  Save number 1 which sticks a little on the top, but is still better itself, their motion is much smoother.  Currently the throttle snaps back as long as it's not WO.  WOT sticks. 

The spring is discontinued.  The amount of stick is so slight that I think a little more spring would do the trick.

[mystic_1]

Is this your setup?



Have you greased the pivot points on the throttle lifter mechanism?  The chrome forks that lift the throttle rods.  Apply some light grease (I use spray lithium grease) where those forks meet the sync adjuster sleeves (#12) underneath the rubber boots (#21).  That may do the trick.

Otherwise, take your return spring off and go down to the local hardware store, you'll probably be able to find something suitable.  You may have to find one that is longer, then cut it down to size and bend the last coil out to form the hook.

cheers
mystic_1

[Jonesy]

I think there is a document in here somewhere (I can't remember) that outlines the Honda carb maintainance procedures. They recommend silicon grease for the bellcrank (where it meets the carb slides under the rubber dust caps) and light oil for the throttle shaft pivots.

If you still have the rubber sleeve over the return spring, remove it and clean the sleeve and spring. Reinstall the sleeve over the spring with a bit of silicone grease. Dirt can build up between the coils and become trapped under the sleeve. (HondaMan told me about this one when my throttle started sticking unexplainably)

[Johnny5]

Not to insult, but the sleeves arent installed backwards, are they? Dont know if that would cause sticking or not but worth a look to make sure.

[gsgleason]

Not to insult, but the sleeves arent installed backwards, are they? Dont know if that would cause sticking or not but worth a look to make sure.

By sleeve, do you mean the sync adjuster sleeve, or the throttle valve itself?  i'm not sure about the sync adjuster... I'll have to pull the carbs off again and look. 

[gsgleason]

I think there is a document in here somewhere (I can't remember) that outlines the Honda carb maintainance procedures. They recommend silicon grease for the bellcrank (where it meets the carb slides under the rubber dust caps) and light oil for the throttle shaft pivots.

If you still have the rubber sleeve over the return spring, remove it and clean the sleeve and spring. Reinstall the sleeve over the spring with a bit of silicone grease. Dirt can build up between the coils and become trapped under the sleeve. (HondaMan told me about this one when my throttle started sticking unexplainably)

This sounds like good advice, but I'm not sure I understand completely.  What's the bellcrank in the picture?  And the throttle shaft pivots, that would be the little springy mechanism that allows the metal rod that attaches to the throttle valve to pivot back and forth?  I need to lube that as well as where the big chrome arm contacts the sync adjuster thingies?

And about the return spring sleeve, I had removed it and cleaned it and the spring in and out during the rebuild. 

[gsgleason]

Is this your setup?



Have you greased the pivot points on the throttle lifter mechanism?  The chrome forks that lift the throttle rods.  Apply some light grease (I use spray lithium grease) where those forks meet the sync adjuster sleeves (#12) underneath the rubber boots (#21).  That may do the trick.

Otherwise, take your return spring off and go down to the local hardware store, you'll probably be able to find something suitable.  You may have to find one that is longer, then cut it down to size and bend the last coil out to form the hook.

cheers
mystic_1

That is exactly my setup.  I'll look into some lube. 

I'm still concerned about the not-so-smooth motion on carb number 1 when I move the throttle valve by hand up and down.  I know I didn't have this issue when I took it all apart.

[mystic_1]

If the binding is only on #1, I'd personally pull that one carb out and examine it closely.  You may be able to spot rub marks where things are binding.  From what you're saying, it sounds to me like the throttle slide (#20) is binding, possible on the guide tab that keeps it oriented in teh bore.  Also possible that the throttle rod that connects the slide to the sync sleeve thingies (#12) is binding where it passes through the cap (#5).  Take it all down and test the parts individually.

Sounds like you're close.  Best of luck to you.

mystic_1

[Jonesy]

I think there is a document in here somewhere (I can't remember) that outlines the Honda carb maintainance procedures. They recommend silicon grease for the bellcrank (where it meets the carb slides under the rubber dust caps) and light oil for the throttle shaft pivots.

If you still have the rubber sleeve over the return spring, remove it and clean the sleeve and spring. Reinstall the sleeve over the spring with a bit of silicone grease. Dirt can build up between the coils and become trapped under the sleeve. (HondaMan told me about this one when my throttle started sticking unexplainably)

This sounds like good advice, but I'm not sure I understand completely.  What's the bellcrank in the picture?  And the throttle shaft pivots, that would be the little springy mechanism that allows the metal rod that attaches to the throttle valve to pivot back and forth?  I need to lube that as well as where the big chrome arm contacts the sync adjuster thingies?

And about the return spring sleeve, I had removed it and cleaned it and the spring in and out during the rebuild. 

This might help:



Here's the Service Bulletin procedures (sorry they are hard to read, not sure why they came out this way. The whole bulletin can be found at http://sohc4.com/tiki-download_file.php?fileId=18):

[gsgleason]

Jonsey,
     Thanks for pointing out this service bulletin.  I think this may be what I need.   Procedure B, number 14 is my issue.  The valves do NOT move under their weight alone.  None of them do.

I have more information.  The 4 throttle valves slide in and out by hand quite nicely without the carb caps, or even when they are loose.  As soon as the caps are tightened, the action becomes rough, as if the tightening of the cap and the throttle rod seal is putting sideways force on the throttle valve in a fashion that is causing excessive friction on one side of the valve.  Does that make sense?

It feels like the position of the throttle rod is not ideal, as if the rod is not moving perfectly up and down, like the rod is not in alignment with the hole in the cap.  Perhaps I need to loosen the screws that connect the throttle rod pivot thingy to the inside of the throttle valve and tweak the small amount of play I have to work with. 

Because the valves slide easily without the caps tightened, I think there is an alignment issue with the throttle rods (at least number 1).

One question, though.  In the bulletin, under procedure b, the first steps are as followed:

1 - remove carb assembly
2 - disconnect return spring
3 - pull dust covers back to expose throttle rod adjusters
4 - remove adjusters from each throttle rod
5 - remove carb caps

No where does it mention that the disconnection of the carb bodies to the large chrome piece that has the levers is necessary.  I've been removing that big chrome thing from the carbs in order to pull the throttle linkage from the rod adjusters.  It seems this suggests just unscrewing the throttle rod adjuster all the way with that big lever thing still in place.  Is this the common practice?

[gsgleason]

okay, after all that, it's much better.  I tweaked the position of the rod pivot thing that screws into the body of the throttle valve and lubed stuff with silicone spray.  Now it returns snappily when the cables are disconnected.  When connected, there is binding.

I already had new MP cables on the way.  I'll let you know how that goes.

[gsgleason]

Just wanted to report back.  Got the new cables (that come dry and have to be lubed - PITA!!) on and the throttle return is nice and snappy.  It's almost too snappy and takes some strength to hold the throttle in place.  =)

[mystic_1]

Glad you got it sorted.

This may help:



mystic_1

[dusterdude]

yep,you have found the happiness of the honda throttle return