VM26 carbs with Accelerator pump-Won't idle down.

Thanks for the report.

Am unfamilar with the billet aluminum advancers that have no springs and do not really advance. (The pic has not yet come through). Am wondering if this might be drag race oriented with only max advance available, akin to an oem advancer locked in the full advance position.

If reduced spark advance isn't available for low rpm idle, it wouldn't be surprising under that circumstance to find a refusal to idle down to the desired steady sustained 1000-1200 rpm, even with perfect carbs. Am likely missing something here, because that's way too simple. :laugh:

Anything's possible, but I don't suspect removal of the aluminum plugs and lack of 0-ring on the pilot air screw to be an issue, but could be wrong. If not already tried, could dab silicone for temporarily seal over the area previously covered by the aluminum plugs, and see if that makes any difference.

Good Luck!

You must have 26's that have the pilot down stream,and under the throat.These tune easy most of the time.Did you sync them?Sometimes they are so out of wack,slides are a little open,even with the idle speed screw removed.
If you go further than drop in cams,stock carbs don't like that either.Stock advance makes it worse.

Bingo on your discription of the billet advancer. Just like welding the stock advancer to full advance, just lighter.

I had a stock advancer on the engine when this problem started and put the billet advancer on in hopes of curing the problem. Of course the race engines have much higher compression and wildly difference cam lobes and cam timing so I guess that could make a difference.

I've used the billet advancer on dragbike for years and have never had a problem with the engines idling down. In fact the engine response both coming off idle and idling down is, normally, much better with the aftermarket advancer. Of course my race engines have much higher compression and wildly difference cam lobes and cam timing.

I thought about the silicone solution but have been trying to find some small plugs to fit in the holes and then silicone around them. I've not be able to find the right plugs...

Again, Your suggestions are most welcome and appriciated.

Buzz

Z Krazy,

The carbs have been sync, the cams are stock as are the cam sprockets.
A completely stock KZ900 engine with new rings, fresh valve job and all tolerances within Kawasaki specs.....

Only thing not stock is the iginition advancer which is billet aluminum and does not retard at idle.

Thanks for the input.

Buzz

For the record, in January 1974, the automatic timing advancer was modified with timing @ 1500 rpm set at 20 degrees btdc (instead of the earlier 5 degrees btdc @ 1500 rpm), which "automatically" advanced to 40 degrees btdc @ 2350 rpm.

Am thinking one of these would cure the low rpm idle problem.




Good Luck!

The 26s used in this case come from a 79 KZ1000B LTD model and have an accelerator pump and air cut off valve. They DO have air screws on the sides and should not have any orings on these air screws which sit deeply into the wells they screw into. I suggest these three things:

1. Get rid of the billet timing advance and put a stock advance on.
2. Go back through old posts and look at how I suggest bench sync be performed and bench sync the carbs.
3. Go to hardware store and buy a new return spring with more tension.

Thanks for the input Wiredgeorge. All of your suggestion will be given a try this weekend. I picked up another stock advancer yesterday and it's in like new condition. I bench the carbs again.

Didn't think about the spring sagging or bouncing....thanks!

Thanks to everyone for the information and suggestions.....

Buzz

Bench sync carbs will get ya in the ball park, and afford sufficient leeway in the idle thumbscrew adjuster needed during subsequent finer manometer syncing of each individual carb slide on a running engine.

Manometer sync on running engine fine tunes each individual slide height and pilot circuit mixture at low idle rpm.

There are some excellent existing threads on manometer sync technique.

Good Luck!

The reason I suggested he bench sync is not for fine tuning. If someone uses a large object to bench sync, like a nail or something and each of the slides are set the same but too HIGH, then the idle screw will not be able to lower the slides sufficiently to put the idle into the correct range. The bench sync has nothing to do with "ballpark" settings but is crucial for setting the slides to where they can completely close and open sufficiently with the idle screw. Bench sync is not done to "synchronize" the carburetors which should be done with a manometer but to set the slides height adjustment so that they can be in the appropriate range of up and down movement.

I gotta agree with welding the advance unit.When running cams with CV carbs,I remove a spring of the advancer,so it stays full advance when running,but goes back to F when starting.79 with air cut valves?Air leaks?Plugged pilots?
These things cause it do fade out and quit at idle,as long as the idle speed screw is not screwed all the way in.
I think you are dealing with two problems.

FSM terminology uses phrase "Initial Synchronization-Mechanical" to describe getting the throttle slide heights equal, and the phrase "Fine Synchronization-Vacuum" for "fine adjustment of carburetor necessary for smooth engine operation requiring the use of vacuum gauges." Perhaps being overlooked, but I don't see the term "bench synchronization" being used in the FSM. However, "bench sync" is commonly used when referring to what the FSM calls "Initial Synchronization-Mechanical."

Then along comes Sudco 4th edition recommending only "mechanically synchronizing smoothbore carbs" therein described as being performed "with the carburetors on the work bench." Sudco discourages vacuum synchronization of smoothbores (for various reasons), but am thinking many of us intentionally ignore this particular advice from Sudco, and achieve rather good results via vacuum syncing the smoothbores. Works for me.

In the quest for best idle rpm performance, the point intended with the "ballpark" reference is to urge continuing with the "Fine Synchronization-Vacuum" (manometer or vac gauge on running engine) and not stopping after the bench sync "Initial Synchronization-Mechanical" stage (which may alone dramatically improve idle performance).

Where the slide heights have gotten beyond any semblance of being relatively equal, they are imo often not in the synchronization ballpark. :lol:

Good Luck!

For reference, here is the parts diagram from kawaski.com for the 1979 KZ1000-B4 LTD carb. (No o-ring on pilot screw)

The pump assembly is shown in the following post.

[Click on image to enlarge view]