Mikunis won't idle down

Hey Becker, the pilot Jet is a 17.5 ,from what I've seen when I had it apart everything is stock for an RS34-D21-K except for the main jets which are 127.5 Thanks for the test, I'll give it a shot when I get home from work tomorrow night. With all the mods that were done to the head(from what I am told), anything is possible.

Are all of the vacuum ports on the carbs/intake boots plugged? You said that it had a vacuum petcock but no vacuum line on it, if the corresponding port(s) on the carbs/boots weren't capped or plugged they would leak a lot of extra air into the cylinders.

You'll have to do some research on your carbs to properly distinguish vents from vacuum ports.

JakeB wrote: Are all of the vacuum ports on the carbs/intake boots plugged? You said that it had a vacuum petcock but no vacuum line on it, if the corresponding port(s) on the carbs/boots weren't capped or plugged they would leak a lot of extra air into the cylinders.

You'll have to do some research on your carbs to properly distinguish vents from vacuum ports.

Good call Jake. I had this problem initially. My bike had a vacuum petcock originally. The vacuum was supplied by the #3 carburetor which needed to be plugged. It caused me all sorts of problems before I got it capped. The port looks just like the vent on #2 and #4 except that it draws a significant vacuum at idle which the vents on #2 and #4 do not.

I wish it were that easy Jake, each carb has a vacumn port and they are all capped with rubber plugs and clamps, these are aftermarket carbs made for gravity feed as best I can tell, I did have the port on no 3 hooked up to the vacumn pump on the petcock for a while but in the interest of finding the source of this problem I capped it again.

Godfrey wrote: Hey MH the exhaust sprocket was slotted to get the cam degreed in correctly

So have you had a look to see if as you thought it is correct or off a tooth? Any chance the builder can come to you and re-check the degree/ lobe centers? Or do you have the tools Knowledge?
The mechanical out of the way, engine timing correct, then timing and as mentioned possibly still lean/ vacuum at carbs. Verify the Ignition with a good strobe light with advance feature so you can check total advance as well. There would be a chart in the service manual for stock timing curve. Maybe your builder has changed the curve some, changed the springs? Or even removed them for racing?

I still think it's in the carbs. Binding, not adjusted properly, etc.

I'm not familliar with your carbs, can you remove the caps (if it has them), operate to full throttle, then try to manually push down on the slides. If any of them move then you have some binding. Remove the idle adjuster completely and make sure all the slides fully seat in the carb body. Disconnect any throttle cables and operate the carbs manually.

Hi MH I bought the engine from a friend and the builder is also a friend. the advancer is stock cept for the dyna pickup. Its identical to the one from the 650 I took out of the frame. I know these things cause I hung around when they were messin with the engine. The builder went thru it several months ago, knowing I was gonna put it in the bike.Anyway I just did the test Becker talked about and when the choke was applied for a second the rpm started dropping, if left there it killed the engine, if pulled out and pushed back in again the rpm returned to 5 grand.

So richening it up is dropping the RPM, that would lend to believe it is getting a lean mix. This goes right back to the first couple of checks, air leaks, dirty carbs, slides to high, or maybe a pilot circuit that's to lean. That is why everyone has been pushing the tests for vacuum leaks.
You have already stated that you cannot find any "External" vacuum leaks. Are those slides reaching the bottom of the carb bore? They should be able to hit the floor of the bore if you have backed off the Idle speed knob and have slack in the cable. They should hit with a noise, solid on the bottom. And all 4 need to be set so that they have the same lift, starting with just cracking them open with the Idle knob, use a wire gauge drill or a paperclip to get them set. If the circuit is to lean then where are the mixtures screws set to? # of turns out from their seats?

Again, I have made various attempts with the mixture screws from 1/8 turn out to 2 1/2 turns out. In speaking with the builder , he says the engine was run with some restrictive oiled foam air cleaners which I do not have , so we suspect the idle jets are lean I ordered the next richer set, when they come in and they get installed we will go from there.

What air filters do you have on it now? K&N?

I suggest you bring the whole shabang back to the "builder" and let him sort it. An air filter isn't going to make your engine idle at 5k.

Godfrey-

My post might be of some interest to you; I've been working the kinks out of a set of these on my KZ1000. I think you may be on the right track with the pilot jets being too lean. I have 20s in mine and was told to START there, not at the factory 17.5s as these were way too lean and I think mine is too lean still at idle because I have the same issue as you, though not as drastic (I'm hovering at about 3K). I did a bench sync already and they are as spot on as you're going to get with the ball bearing method. My plugs tell the same tale of being lean at idle as well... If I only let it idle for a long time and pull a plug it looks to indicate a lean condition. No vacuum leaks on mine. And you're correct, these carbs are really made for gravity fed fuel bikes, though I'm sure you could use one of the vacuum ports that is on each of the throttle bodies to work a vacuum petcock.

After talking to a lot of people and looking at different setups, it just comes down to your individual bike with these carbs, regardless if someone has a similar setup or not. I've had a guy on my post tell me that he's running 125s on his 1000 and his is bored out to 11XXcc, whereas mine is only out to 1075... and that he thinks he needs 122.5s. He's probably correct for his bike, but after testing out the 145s and seeing the difference they made (and not at all "drowning" it out), I'm going to start with 132.5s in mine when they come in and go from there. Before all this, I started at the factory middle clip position on the needle and 120 mains in mine and my bike would fall flat on it's face after much of 1/2 throttle. Raised the needle up to the next position (richer) and it corrected A LOT of that issue, though still certainly not right. Tried the last position on the needle (Richer) and it got worse. Put it back to the 4th position, then swapped out my 120 mains for a set of 145s that I got the carbs with.... I figured I'd absolutely drown the bike out but to my suprise, while it's definitely too rich as indicated by stumbling, especially WOTing the bike at low RPMs and the plug condition after immediately riding the bike, the 145s overall make the bike run MUCH better than the 120s. I ordered a set of every size mains from 127.5s to 135s from Z1 Enterprises last night and plan on getting that straightened out. After that, I'm going to richen up my pilot jets to try and correct my high rev at idle issue. BTW, if you need jets for these carbs, those guys have the best prices I've seen so far; $1.72 a jet. All those sets of jets I bought with shipping only cost me about $32.....

Good Luck!

David