Help! Engine bogging around 5-k rpms

Alright well no luck posting in the carbs section, I've got a '79 KZ400 B2 that bogs down around 5-6k rpms and wont go much faster than 50 mph (55-60 mph if I ease it up)

-Checked and replaced both vacuum valves(carb slides)
-Carbs have been cleaned thoroughly
-Points are correct clearance
-Motor runs smooth at low rpms

The right side exhaust was much cooler so I assumed it had to do with the right cylinder but nothing I've tried has helped!

Had a friend mention the coils maybe having something to with it? What do you guys think?
Thanks!

What are you using for air filtration? Ed

If not already done, would perform the clear tube test to check float bowl fuel level.

Good Fortune!

ed - Just using the stock Air fliter, looked pretty clean.

Patton - Ill see if can try that in the next day or two and let you know what happens

Some places to look at:

1. Original ignition coils,sparkplug wires & sparkplug caps? All should be replaced, as they are probably beyond their serviceable life. www.z1enterprises.com sells the popular "Emgo" coils to keep cost down, but if you want better coils, go with "Dyna" 2.2 or 3 ohm coils or "Accel" 3 ohm coils.

2.Replace the ignition capacitors, as they go bad from heat and vibration.

3.Check the operation of the mechanical ignition advancer with the engine off. It's behind a CD sized, right engine cover. Give it a twist, it should snap back, if not, make note of how it's assembled on the crankshaft & remove and lube it. Usually a dab of high temp bearing grease on the moving parts is about all it needs. The weight's,and the tube it moves on are the most important.

If you do upgrade your ignition coils & sparkplug wires, read this:

Ignition Coils And Sparkplug Wire Choices

What came with the bike, were ignition coils that even when new were marginal, add years of cooking under the tank in the stop and go traffic, and the coils will probably fail when hot.
Now, you have a choice on sparkplug wires:

1.Copper plug wires with no supression caps (the best choice, but will produce audio noise on Radio’s and TV’s). Not only do the copper core wires deliver better spark, they will also deliver a much longer lifespan - carbon core wires are prone to erratic spark delivery and early breakdown, & short lifespan.

2.Copper plug wires with supression caps (a built in 5000 ohm resistor, that can sometimes fail, (like what came with the bike).

3.Copper plug wires with no supression caps, but using resistor plugs(the “R” in the plug number).

4.Supression plug wires with no supression caps.

NEVER use resistor plugs combined with supression caps along with supression plug wires, as now there will be possibly three (3) sources of resistance in the secondary windings of the ignition coils, greatly reducing the spark energy.

Another choice is the Accel 3 ohm coils, with a similar, primary(small wire)electrical connection, using ring terminals as the Dyna ignition coils do. Whatever brand of coil you go with, make sure the primary wires will clear the mounting hardware, as the spacers come close, possibly blowing a fuse. Some riders have replaced the metal spacers with non conductive Nylon spacers, reducing the chance of an electrical problem.

7mm sparkplug wires will fit the stock ignition coils(if they have replaceable wires, indicated by screw off caps on the coils with ridges). The sparkplug wires fit into a port with a brass ”Stinger” that goes into the sparkplug wire or lead(the Brit’s. Canadians, and other countries call the sparkplug wires (“High Tension Leads”).

CafeKid wrote: ed - Just using the stock Air fliter, looked pretty clean.

Patton - Ill see if can try that in the next day or two and let you know what happens

That's good! You can rule out the typical pod related bog. Ed

Mmmm...Do you know the history of this bike? Have you been inside the carbs lately? My bike was running great and then started to have a stumble and hesitation at 4 k rpm. Would not pull past 5 k max. I checked everything. Number 2 cylinder was cooler than the rest, I used a spray bottle, not my hand, to see how fast the water vaporized. Finally, pulled the carbs to check the floats. Found the main jet had backed out and was sitting in the float bowl. I should have took a photo. Guess I didn't tighten it enough. Runs great now.
Any thoughts about using blue lock tight if it falls out again?

The BLUE Loctite is removable with tools, most of the RED Loctite is only removable by first applying high heat(usually 300 degrees).

MFolks - Hopefully tuesday or wednesday I'll have a minute to sit down and test the floats and if thats not the problem I'll go further into the coils, spark-plug wires, and plugs. Although I'd like to swap the wires and coils since I doubt they've been changed since they were first put on in the factory :laugh:. To the bikes defense everything so far looks like its in great condition though! But by ignition capacitors do you mean the ignition condensers? Or is that a different part? Thanks!

Ed - Exactly!

78z1Joe - Just cleaned out the carbs the other day so I dont think its a loose jet, thanks. Good to know about the loctite for future reference though!

Thread Locking Compounds
www.loctiteproducts.com/

Loctite #222MS PURPLE, low strength thread locker
For screws under ¼”.

Loctite #242 BLUE, Medium strength thread locker
For ¼” to ¾” bolts.

Loctite # 262 RED, High strength thread locker permanent
For up to ¾” bolts (can be loosened by 300 F heat).

Loctite #271 RED, High strength thread locker for sealing plugs, nuts and bolts (can be loosened by 300 F heat).

Loctite # 272 RED, High strength, high temperature(450 F) thread locker.

Loctite #565 Pipe Joint Compound.

Loctite #567 High Temperature Pipe Joint Compound

Loctite #6749 Primer

Loctite #515 Flange & Gasket Sealers



www.permatex.com/

Permatex # 24310 Low strength thread locker, PURPLE, fasteners under ¼” diameter.

Permatex # 22210 Medium/high strength thread locker, BLUE, ¼” to ¾” fasteners, surface insensitive (can be used on oily fasteners).

Permatex # 24210 Medium strength thread locker, BLUE, ¼” to ¾” fasteners.
Permatex # 27710 High strength thread locker, RED, 3/8” to 1 inch fasteners, may require heat for removal.

Permatex # 26210 Permanent strength thread locker. RED, 3/8” to 1 inch fasteners, will require heat for removal.

Alright so finally had an afternoon to check out the bike. Checked the fuel level with the clear tube test, fuel level looked a bit higher than normal so I'll see if I can open up that carb again and check the float, the tang, and the needle valve.
Although I havent been able to find the mm measurements in my service manual for the distance from the top of the floats to the side of the carb body.
Is it a pretty universal measurement for these bike or do they all differ?