Mysterious Carb Outlets - Help

Good Morning,

I have been working on a 1984 KZ750 (4 cyl) with the MIKUNI carbs since this winter and I am almost ready to have this thing certified. My last hurdle is to conquer these seemingly impossible carbs. This bike was running last year and the guy I purchased it off of ended up selling it for a steal when the starter stopped working. Prior to the sale, he had installed pod filters, a 4 into 1 exhaust and had the carbs fully jetted and synched.

First of all, a list of what I have already completed on this bike;
- Rebuilt starter motor
- Oil flush and change
-Brand new NGK BR8ES plugs (what he was previously running.. is this correct? I could not find the B7ES or B8ES recommended)
- Freshened up battery (with new distilled water to fill up the cells)
- The tank seems to have a red gel like coating inside which I initially believed to be rust but is actually some form of gas tank restoration treatment I assume

After the Initial carb clean in which I only pulled apart the float bowls (without actually removing the floats or the needles), main jets and pilot jets. At the time of initial cleaning I also replaced the float bowl gaskets. Once the carbs were reinstalled, the boots properly tightened, the pod filters on, and the vacuum line installed on the petcock I started the bike (for the first time in my ownership). The thing revved up to 5k RPM regardless of whether the choke was on or off.. It would backfire and spit nasty smoke out the exhaust and be very hesitant to return to idle. Once the bike returned to idle, any application of throttle would send it right back up to 4-5k RPM and it would hang there for a while after the throttle was let off before returning to 1300 RPM idle.

-This lead me to believe that the bike was running excessively lean either due to a blocked pilot circuit or a mass air leak on the engine side of the carbs.

At this point I decided I would bite the bullet and do a complete clean on the carbs. I grew up around lots of grease monkeys and have in return picked up a lot of their tricks to cleaning engine parts. I decided to tear apart the carbs from top to bottom removing every screw i possibly could and i boiled the carbs in 1 part lemon juice to 6 parts water for 2 hours along with the jets and the float bowls. I left out the diaphragms and the slides due to fear of melting them. After a quick rinse in soapy water and a thorough blasting with compressed air through all of the passageways with the choke on and off, they looked cleaner than I have ever seen them. This leads me to the critical part of my post and the question I am on here to ask;

On my carbs (MIKUNI), there is a primary fuel inlet that was attached to the tank at the time of purchase. Looking at the carbs now before reassembling them I see that there are 2 extra fuel inlets; one between the 1st and 2nd carb and the other between the 3rd and 4th carb where the primary inlet is located between 2 and 3. These inlets pivot unlike the primary one and were left unattached to anything upon purchase of this bike.
- What are these for?
- Will these cause leaning out when left unattached during operation?

Any help would be greatly appreciated!
Cheers,
Jeremy

Those are the vents. Connect tubing to them to keep water out & leave the ends open to atmosphere.

The vent tubing on my 81 650-CSR is routed over the airbox shoulders and fitted snugly between the airbox & side covers. There's a frame clamp for the left side tubing.

Thank you for clarifying what these are for. I will update on the status of the leaning out situation after I get them on the bike!

Cheers,
Jeremy

The carbs are back on and the bike still runs the same. I have the pilot jets out 2 turns like factory recommended. The main jets are 136 and thats as much as i know.

The bike starts and immediately revs up to 6000rpm, and the only way to get it back down is to kill ignition. The plugs are a very light grey which indicates to me that it is running excessively lean. The bike is on the side stand as it does not have a centre stand. Would this contribute to a problem? With the pods and the 4 into 1 exhaust what would my expectations be for the amount of turns on the pilot? I've tried 2 1/2 and it gets worse. I am inclined to try 1 1/2 and 1 turn but I am under the impression that this will make the bike run more lean.

You can check for leaks around the manifolds with a can of starting fluid.

braap.jeremy wrote: ...1984 KZ750 (4 cyl)...pod filters...Brand new NGK BR8ES plugs (what he was previously running.. is this correct?....

The "R" plugs are likely resulting in weaker spark due to adding resistance (via the plugs) in addition to the stock resistance component already in the secondary loop (which is usually resistor plug caps).

It's okay to run without any resistance component whatever in the secondary loop. But in any event, should never include more than one resistance component in the secondary loop, which single resistance component may be resistor cap OR resistor plug wires OR resistor plugs.

Unless already running solid metal core plug wires with non-resistor caps, would remove the "R" plugs and replace them with the proper NGK B8ES (which are usually readily available).

Weak spark causing incomplete combustion is sometimes misdiagnosed as a carb issue.





Good Fortune!