Keihin CV34 Throttle Advance Adjustment

Hi

I've been scouring around but I can't seem to find anything on this particular item, I'm wondering if anyone can point me to to some information on how, or if, there's any adjustment possible in the fast idle setting for the choke on the CV34 carbs.

Last year I did valve adjustments, and then carb synchronization on my KZ750-H2. Since that the bike's been running great when it's warmed up but cold starts are a pain, the main complaint being that I have to stand there holding the throttle open a little for a few minutes while it warms up. I had the carbs off for cleaning this week and I noticed that with the idle screw set where it was, the throttle advance cam that comes forward when the choke is on doesn't contact the throttle actuator, so the throttle doesn't actually move. It looks like I've been doing this little guy's job all this time!

But I'm not sure what I can do to improve this. The idle screw is set where it needs to be to get me ~1100 rpm when the engine's hot, but that setting is apparently beyond what the fast idle for choke wants to be. Is there a way to adjust that, or is this idle screw position a sign that something else is wrong?

Could post some pics? I have the same bike and carbs.
The choke lever rotates the one of the two choke shafts. 1st shaft attached to the choke lever is for choke butterflies of carbs 1 and 2. the 2nd shaft closes the choke butterflies for carbs 3 and 4. This shaft closes by the force of pretty weak spring and it opens up when the 1st shaft pushes it back.

Choke shaft has no relationship with the throttle shaft. They are independent.

I wonder if this might be a rare option? I don't see it in those picutures.

In the attached photo (it's not great, really hard to get a good angle...) you can see the linkage. Picture is taken from the front/engine/throttle butterfly side of the carbs. I painted a red line down the L shaped linkage that has a cam that rides against the choke actuator at one end and against the throttle adjuster plate on throttle butterfly shaft at the other. The little yellow mark is where it contacts the adjuster mechanism that you use in carb syncing between 2&3 carbs.

If I back my idle screw out far enough this definitely does start actuating the throttle butterflies when the choke is fully closed, it just sucks because if I set the idle where I want it this lever doesn't do anything anymore.

If you have a look at this file , the 4th page talks about the fasi idle mechanism, however the drawing doesn't look like mine, and it doesn't say anything about it being adjustable.

Sorry forgot to click insert on the image

Here it is from the choke/airbox side, The red line indicates the same L shaped bracket.

After a little more exploring it really looks like there is no adjustment on that linkage, it's very much fixed. This sent me further down the "something else must be wrong" path and I found my ignition advancer to be kind of gummy. It was still moving but not coming back to the end stops very positively. After a bit of cleaning and lubing it now comes back to the stop position with an audible snap.

This definitely had an effect on the test ride, I hadn't realized how much power I'd lost over the last year or so. When the bike was hot the idle was way up as well. With the idle screw re-adjusted to get me back down around 1000rpm I can now see that the throttle advance linkage is giving the throttle a nudge when it's actuated, so I'm guessing things are back to where they should be. Haven't had a chance to test a stone cold start yet though, so we'll see.

Keep us posted.

Tried starting from cold last night and it's still not great. Takes lots of manual throttle action with the choke between 3/4 and fully on to keep it running when cold. After about 30 seconds of that it'll will idle but only if I crank the idle screw in or hold the throttle open by hand. If I leave the throttle at that position the idle will slowly increase as the bike warms up, it'll very consistently rise, it'll get all the way up to 4000 if I don't intervene by turning the idle screw back down. Once it's warmed up I can turn the idle back down and it'll be rock solid, it'll hold steady at 1000rpm, running smoothly and reliably.

I'm starting to think I must have a vacuum leak somewhere in the carb boots, which is odd because they're new. Does it usually take some RTV or sealer of some type to get them to seal well? If not in the boots then where I wonder?

hi - when you cleaned them, how far apart did you take them? It sounds like maybe your diaphragms are not sealing well.

I only took the bowls off. I usually avoid taking the diaphragm caps off unless I've got a good reason because I'm always afraid of mangling them. But that's a good point, they're getting pretty old at this point.

When you get to a point where the bike is starting to exhibit issues surrounding dirty carbs.... my advice is to pull them and go through them. If your bowls were not exactly clean... think there are pin holes in your jets that likely have the same debris. If you go slow, and get them fully apart your bike and troubleshooting will thank me later.

Personally I have never disassembled the Keihin CV carbs, but I just took apart a set of Mikuni CV's off my FJ1100. The needle seat was cemented with varnish to the body, and I had to drill out the pilot jets to remove them. If I sent you a pic of the carbs prior to this - they honestly looked cleaner than your's But... there is a lot of nifty plastics protecting them on the FJ.

My diaphragms came out ok, and went back in no issue. They "should" be ok. And if you have trouble sourcing replacements people have repaired them with RTV and some versions of tape. I would replace if any holes or tears are found.