VM24SS - How to Clean Enrichening Circuit?

Does the Mikuni VM24SS have an enrichening circuit? If so, would someone be able to describe how to clean it?

Then reason I would like to know is that I think I'm having a bit of trouble with the bike warming up on choke. I say think because I'm not sure if this is normal or not.

This past week, I did the WG coil mod, sealed the gas tank with POR-15, cleaned the carbs (as well as I know how), cleaned and gapped points, checked and adjusted timing and sync'd the carbs. The bike now perfectly, very smooth running and rock solid idle when warm.

The problem is when starting cold. It starts first kick no problem and immediately starts to idle at 2000, but then a few seconds later it starts to drop off and goes to around 1000 and doesn't sound very strong. It doesn't die but I can't lower the choke any or it will get worse. After about a minute or two of this I'll drive away and turn the choke off. Once warm it's perfect. My question is does this warm up sound normal? It only started acting like this the past month. Previously it used to start first kick and idle higher and stronger when on the choke. I could lower then as it warmed up no problem.

I'm wondering if the enriching circuit is clogged up a bit? Prior to doing all the above tasks I was getting some "silt" in the carbs from paint and primer that got into the tank from previous paintings. The gas was washing it away and it ended up in the carbs. I'm thinking this may have clogged things up.

I'm no carb expert, so when I cleaned them I removed the main jet, pilot jet and float needle. Cleaned them and cleaned the places they sit with carb cleaner. I know I'm not fully cleaning the carbs they way they should be done (still learning) but I'm unsure what else to clean. I couldn't determine where the enrichener circuit was.

The bike is a 1978 KZ650 D1 and is running Mikuni VM22SS. They have been rejetted to compensate for pods and slightly freer exhaust to 110 and 17.5.

Any help would be appreciated.

A couple of questions, please --
Are valve clearances within specs?
Are pilot adjustment screws located on the side
or in the bottom of the carbs?
Good Luck!

And a couple more --

Spark plug readings? How do they look?

Are floatbowl fuel levels correct (checked using the clear plastic tube method)?

May indeed be crud in the enrichener circuit. More on this to come.

Patton,

I have yet to check the valve clearances. I haven't done it before so I'll need to read up a bit on the procedure first. That is next on my to-do list.

Yes, I believe the pilot adjustment screws are on the side (again I'm a carb noob).

Spark plugs look good. They have been gapped to spec and look good, nice tan colour.

Yes, forgot to mention that in my first post, floats have been checked and are brought to spec using the tube method.

Thanks

It does sound like something is clogged.
Should be VM24SS carbs stock.

When I start cold and use the choke, she idles like yours with the choke all the way up.
As I lower the choke lever, the RPMs will climb (up to 4000 RPM or more) to about the mid point of lowering the choke lever, then the RPMs drop as I lower the lever even further.

You could try running some Sea Foam mixed in your gas to clean the carbs as you ride.
I usually add 2~3 oz. to a full tank.
Someone mentioned they added a 1/3 of a can to their gas and ran it through and it improved their bike's problems. I'm not sure about using that much Sea Foam in one shot.

Will now attempt to post excerpt from FSM (1977-1979 KZ1000) about Mikuni VM26SS enrichener circuit (FSM calls it a "starter system" while some folks just call it the choke. Am guessing your carb circuit is similar.

Clog may be anywhere in the circuit.

The pic shows choke in the "on" position (choke lever lifted) whereby plunger is raised so that the plunger tip and plunger pad (the soft material surrounding the tip) are removed from the fuel passage outlet and the #2 "plunger" is no longer blocking the #3 air passage. So both air from #3 passage and fuel from #6 passage move through #4 chamber into #1 carb bore.

Am uncertain whether #9 jet is removable (guessing "not" removable). But the jet must be clean and clear and the #7 pipe also clean and clear.

Can likely use carb cleaner cannister to blast through #3 while using finger to block orifice into bore, and thereby reverse blast from #3 to #9. And blast every other direction also, forward and backward. Wear protective goggles because the spray carb cleaner always backfires.

May also help to use a fine wire to clean the #9 jet and #7 pipe. A small guitar E string should work nicely.

Hoping the image is legible. There's a better image in the next post.[click on image for larger view]



Good Luck!

Edit -- See better image in next post.

This image comes out large enough to actually read. :laugh:

[click on image to enlarge view]

In the following post is an example of a typical side located pilot adjustment screw, this one being on a Mikuni 29 smoothbore carb.

These side located screws are AIR screws for the pilot circuit, with a beginning default position about 1.25-1.5 turns out from lightly seated. The pointed tip regulates amount of air allowed to mix with the fuel, thereby leaning or enrichening the pilot circuit mixture. They may be referred to as pilot circuit air adjustment screws. Turning "in" reduces air and thereby enrichens the fuel mixture. Turning "out" allows more air, thereby leaning the fuel mixture.

Bottom located pilot adjustment screws are different because they allow increasingly more fuel mixture as turned out further and further. And may be referred to as pilot circuit fuel mixture adjustment screws.

I've heard about some carbs actually having both types on the same carb -- but have no experience with them.

See next post.

This pic is courtesy of Z1Enterprises.com.

Wow, this is unbelievable information Patton. Can't thank you enough!

I don't think I can work on the carbs this week so I may try the Seafoam suggestion (thinks rstnick) to see it that helps any. If not, I should have time when I go on holidays in early September. I'll see if I can check the valves then as well.

If I remove the pilot mixture screws, does this then mean I'll need to resync the carbs?

Also, do these pilot mixture screws only effect the air/fuel mixture when the bike is idling?

Thanks again, really appreciate the help.

Also forgot to thank rstnick for correcting me on the carb name. I dont' know why I called it 22, must be getting old.

I've corrected the thread title in case someone searches for it at a later date.

HerrDeacon wrote:

Wow, this is unbelievable information Patton. Can't thank you enough!

I don't think I can work on the carbs this week so I may try the Seafoam suggestion (thinks rstnick) to see it that helps any. If not, I should have time when I go on holidays in early September. I'll see if I can check the valves then as well.

If I remove the pilot mixture screws, does this then mean I'll need to resync the carbs?

Also, do these pilot mixture screws only effect the air/fuel mixture when the bike is idling?

Thanks again, really appreciate the help.

Am glad to help, and you are very welcome.

Don't know how much the Seafoam might benefit, because it will only be working by running through the enrichener fuel passage while the choke is on, as no fuel runs through the enrichener circuit while the choke is off.

Removing and replacing the side located pilot air screws won't disturb the synched throttle slide heights (however the side located pilot circuit air adjustment screws will need to be again fine tuned after their settings have been disturbed, but without necessity of repeating the manometer operation). And please remember that the pilot air screws are part of the pilot circuit, and not part of the enrichener circuit, and really don't connect with the enrichener circuit. These are two separate distinct internal carb circuits (pilot circuit vs. enrichener circuit), each having its own separate air passage and separate fuel passage. However, both circuits are active at closed throttle position with the choke on, and when taken off choke, only the pilot circuit then remains active.

The pilot circuit (adjusted by the side located pilot air screws) is especially important at idle rpm, and is enhanced by the enrichener circuit when the choke is used in cranking a cold engine. The pilot circuit remains active until about 1/4 throttle as it gradually defers more and more fuel mixture control to the main circuit (throttle slides and tapered jet needles inside the needle jets atop the bleed pipes fed by the main jets). Much on-the-road operation is within the first 1/4 throttle where engine smoothness is particularly noticed during around town and lower speed riding, and quality of engine power and performance when pulling away from idle.

Good Luck!