hanging idle/revving

can improperly adjusted pilot mix screws ALONE cause a hanging idle and revving? the reason i ask is because i've put the valves in spec, rebuilt the carbs, bench synced, and attempted to vacuum sync at idle...any throttle at all sends it up to 4k and it takes a while to return and sometimes the rpms just stay high and won't drop. the idle set screw is fully backed out, the throttle cable isn't caught up in any way, i replaced throttle shaft seals, clunk tested, and now i'm out of ideas.

 

Vacuum leaks can cause some of that. Check your carb joints with an unlit propane torch and see if the idle picks up.
Did you polish the carb bores where the slides go? If you did not I would pull the carbs back off and see if they pass the clunk test.

MN

 

MN, i tried the propane test with no results, and i polished everything until clunk test was passed. the fuel level was set w/clear tube method and i replaced the vacuum boots/caps on top of each intake boot.

 

Did you sync with vacuum gauges yet? with block off tool?

 

that's where i'm at right now, vacuum syncing with a morgan carbtune, and the yics port blocked with the tool. i've got them synced up really close it's just the idle i can't explain...if i give it any gas it just revs and either doesn't come down or takes 10-15 seconds to do so. idle set screw is also fully backed out.

 

Ok when you cleaned the carbs, did you replace the throttle shaft seals? If so did you make sure the butterflys were seated properly in the bores when you tightened the screws.
If your idle adjustment screw is all the way out as you say, the carbs should be completely closed and the engine would not get any air to run.
Your going to have to pull the carbs back off and look them over. Also if you split the rack your going to have to set them on a flat surface and see how the alignment from carb to carb is. I like to set mine on a piece of glass before I tighten the rack screws. I know they are straight at that point.

MN

 

yes, i replaced the shaft seals. but i just went out and started it up and pressed down on the sync screws and the idle dropped. i noticed the new hose clamps i put on the intake boots were in the way slightly so when i moved those out of the way it helped ...no more hanging idle. BUT, i can still press down on the sync screws and get another 200 rpm drop so i guess i didn't align them correctly, seat the butterflies properly, and/or something else i missed.

 

Just "for a drill" ...

Loosen the Throttle Cable Slack Adjuster at the Throttle Grip
Snap the Throttles closed.

See it the Idle is still running high.
Press on the Linkage to see is something is stuck.

Also, ...
Anchor the Throttle Cable Sheath to the Frame.
A small "Saddle" of Duct Tape will keep the Sheath from moving.

 

It takes some precise "doing" to get the carbs lined back up dead-nuts on the rack again; I'm likewise thinking a bind in the overall mechanism.

 

rick, i loosened the cable and still have the idle problem. fitz, i tried realigning them with a glass plate based on some threads i found here and to no avail. what i did notice though is that carbs 1,2 are the ones not fully closing and when i looked closer i noticed that carb 2 does not have a set screw return spring on it's left side (left side if the carbs were on the bike and you were seated on it). i double checked with my pre carb teardown pictures and there wasn't one on before i took it off. so, it's either missing from the PO or not supposed to be there. the 2 carb body does have a post where the spring would go though. when i compared it to the other side...carb 3, on it's right side has this same post for a return spring, but no spring either. that side is returning shut just fine though. so, when i press down slightly on set screw #1, butterflies 1,2 fully close. another spring on the outside/left of carb #2 seems like it would give me the return pressure i'm lacking. hopefully i'm making sense. any thoughts?

 

i just looked through some carb photos on this site and am not seeing any springs on the outsides of carbs 2,3.

 

There should be a Throttle Shaft "Return Spring" on the INBOARD Side of each Carb Body.
This Spring is fitted around the protuberance on the casting that the Throttle Shaft is drilled through.
There is also a slot or an "Ear" which the Throttle Shaft Return Spring's curved end anchors to.

A "Main Return Spring" is fitted at the Inboard Side of No.-3.
When reinstalling this Spring, ... it has to have some pre-load applied before latching it under the Linkage.

1, 2, & 4 Each have a Sync Screw and Spring.

 

That's only one "plane." They have to be aligned both vertically and horizontally, so to speak. It requires TWO flat reference surfaces, one aligning them to the rack and the other at 90* keeping them in line with each other at the same time. I use two carpenters' levels; with one clamped in my bench vise.

It also does sound like you might be missing some springs. I don't have a rack of Hitachis other than the set that's currently mounted on my 650 to take a pic of for you.

 

This is all I got.
I put a RED Dot on the ones I could see.

 

what happens if you decide to operate a carb rack (Hitachi) without a throttle shaft "Return Spring"...

reason I'm asking is #4 returns back to rest under normal conditions (i.e. when not on the bike operating) and I'm having a balance issue on my rack trying to get them to balance evenly under a running vac sync.