Brand new issue….won’t idle down?

[CHEWY1219]

So out for a ride today, and about 15 miles in, my bike starts acting strange and it won’t idle all the way down all of a sudden! Cables have zero obstruction, throttle snaps back as it should, etc. again, this started mid ride.
Got the bike home, took off tank, and still don’t see any reasoning behind this. Also perfect amount of slack in cables. Here is a short video of me starting the bike with tank off so you can here the idle….

https://youtube.com/shorts/FtKWEVWTgXs?feature=share

BTW otherwise runs solid, revs great.

Also it’s a 76 R75/7 with electronic ignition.

[gspd]

Did this just start happening after you installed that electrical stuff in your other post?
If so, make sure both cables are properly seated in their adjusters at the carb.
Make sure both butterflies are fully closing.

Revving that high means at least one of your carb butterflies is staying partially open.
A multitude of other things (listed below) can cause or exacerbate a fast idle issue, but none will over-ride a fully closed butterfly.

broken or weak return springs
sticking or kinked cables
vacuum leaks
holed diaphragms
sticking slides
ignition timing
timing advance sticking
choke malfunction

[Rob Frankham]

Had you done any work on the bike prior to going out? If you allow the vehicle to cool down completely does it idle reliably?

The thing that spring to mind is that, if you set the idle speed on an airhead with the engine cold, it will not return to a steady idle when the engine is hot (e.g. after riding a number of miles). The idle must be adjusted with the engine at full operating temperature... which means riding at least 10 miles before doing the final setting. There isn't anything unusual about this and it is common to all airhead (and a lot of contemprary) engines. Of course, if you do set the idle with the engine hot, the engine will die with the throttle shut when it is cold. This is also normal for engines of this era.

Of course, as GSPD says, there are a lot of other things that will contribute to an engine that won't drop back to idle but, in my esxperience a lot of such issues come down to this.

Rob

[CHEWY1219]

Did this just start happening after you installed that electrical stuff in your other post?
If so, make sure both cables are properly seated in their adjusters at the carb.
Make sure both butterflies are fully closing.

Revving that high means at least one of your carb butterflies is staying partially open.
A multitude of other things (listed below) can cause or exacerbate a fast idle issue, but none will over-ride a fully closed butterfly.

broken or weak return springs
sticking or kinked cables
vacuum leaks
holed diaphragms
sticking slides
ignition timing
timing advance sticking
choke malfunction

yes, it started after the electrical issues. This was my second ride after getting that sorted, and it started mid ride. I am 100% certain it's not the cables at least, I have checked them repeatedly.

I haven't tried starting the bike now that it is cold since we have not been home.

I have not touched the carbs since owning the bike (few months) since the previous owner did a solid service and she has been purring perfectly.

I'll start going down the list and update the thread as I find something!

Thanks guys!!

[CHEWY1219]

Started her up this morning cold, right back to high idle. Idle screws really didn’t help. Pulled them off the head…..seems like left carb will not shut fully? Idle screw didn’t move it.

Pic of left carb

https://ibb.co/zFCBr7J



Right carb

https://ibb.co/YchGVkC



Thoughts? I’m terrible with carbs!

[jagarra]

Butterfly on left card looks to be installed incorrectly. See how the previous mounting line on butterfly doesn't match the shaft.

[melville]

Found it! Your throttle plate has slipped in the shaft. Loosen both screws and move it around until you can get it all the way shut. Then tighten both screws while holding it shut.

There's a shot the threads in the shaft are stripped. It can be repaired:

https://www.forum.boxerworks.com/viewto ... 76#p130076

[gspd]

Found it! Your throttle plate has slipped in the shaft. Loosen both screws and move it around until you can get it all the way shut. Then tighten both screws while holding it shut.

The best way to do this is to fully back off the throttle screw and hold the arm closed while wiggling the plate around so it's centered in the bore.
Hold the carb up with a light behind it and center the plate so only a tiny crack of light is evenly showing when you look through it.
Maybe the plate was re-installed incorrectly at some point.
Be sure that the taper is facing the right way.
pics from snowbum below.

[CHEWY1219]

Ok I will try this tomorrow!! My main question is how could this happen all of sudden I guess? Wish me luck I will try to fix this and report back.

[CHEWY1219]

Found it! Your throttle plate has slipped in the shaft. Loosen both screws and move it around until you can get it all the way shut. Then tighten both screws while holding it shut.

The best way to do this is to fully back off the throttle screw and hold the arm closed while wiggling the plate around so it's centered in the bore.
Hold the carb up with a light behind it and center the plate so only a tiny crack of light is evenly showing when you look through it.
Maybe the plate was re-installed incorrectly at some point.
Be sure that the taper is facing the right way.
pics from snowbum below.

Quick question, and it may be really stupid, but by throttle screw you are referring to the idle screw, correct? I am brand new to Bing carbs as. Am used to Mikunis