TOPIC:

Just wanted to take the time to say hi in the new members forum. I have a 75 kz 400 that is having issues running at higher rpms. Does not bog or sputter, just doesnt want to seem to rev past about 5k rpm. Its hard to explain but I have sorted out carb problems before on single carb bikes and this feels nothing like any of my past carb issues. The bike just does not want to go past 5k rpm?
Purchased the bike knowing it needed a slipping clutch replaced but now that the clutch is replaced and holding I am finding more problems...
Any ways I will be posting up questions after reading up on the forums. I will appreciate any help from experienced members.

-Jordan

Hello, Jordan, and WELCOME to KZr!

If not already done, would assure that the timing advancer is functioning properly, and isn't frozen in the retarded idle position due to rust, etc.

The advancer may require lubing, or disassembly plus cleaning and lubing.

If only lubing is needed, the weight arm pivot points might be accessible through the timing inspection window.

The advancer isn't supposed to look rusty, corroded and crudy as seen in this example:



A timing advancer that's non-functional because of being frozen in the retarded idle position will likely be evidenced by reduced engine power under load.

Good Fortune!

I will look into the timing advance mechanism. Also I have replaced the engine with a lower milage engine due to my previous engine had high miles and a lot of top end leaks. And the issue has stayed the exact same. I have two sets of carburetors and it is the exact same with both sets.
The bike has pod filters and aftermarket pipes so im trying to figure out if its related to jetting. Maybe ignition issues?
I noticed that the previous owner made a home made petcock and I am questioning if that is not flowing enough fuel? I am going to get that changed out for a stock one and see if that does anything.
i just question if it has to do with the carbs, it does not bog or hesitate, the bike just hits a wall around 5.5k rpm and wont rev higher and i know it should.
Thanks for the reply!

If not already done, would perform the so-called throttle-chop test and read the spark plugs. To diagnose fuel mixture at top attainable speed. If plugs indicate a too lean mixture, the reason might be insufficient fuel supply through the home-made petcock.

Good Fortune!

Where in Pa ya from? I lived in Erie most of my life,worked at Ge for 32 years before retiring in 09 and moving to Florida,,couldnt stand the snow and cold anymore,,sooo nice to be able to ride cycle year round,,welcome to kzr,,good people here

I live in mechanicsburg. It must be nice to be in flordia.. Its already getting cold in pa. Soon itll be to cold to ride. Ive been busy with work and now out of town, its killing me not being able to find time to work on my bike. But i guess thats what winters for.

Florida is great,,my parents moved down in 74 after selling their restaurant (glenwood diner),,i moved with them,,but didnt stay long and moved back to erie,,i always wanted to move back to florida,,but was job locked at GE,,be stupid to give up my seniority,,and i knew id never find the wages and benefits i got at erie GE,,but as soon as i got the chance,,i moved back to florida,,summers can get a bit to hot,,but winters are great,70's-80's,,im going to make a point of takin a nice ride thru the ocala forest to daytona beach on xmas and new years day,,lol

Stuck timing advancer is the first thing I though there, it is a maintenance item but rarely gets done. Clean and copper grease it, if you watch it with a strobe you will see it advance and back off as the rpms change.

Also a new plug, cap and 7mm plug lead plus cleaning the coil male spade terminals up would be good maintenace - but I don't think it is your problem here.

The not revving past 5k makes me think of ATU problems, marginal fueling or ignition would still usually rev up even if it ran really rough, like when a main jet is couple of sizes out, or your ht lead insulation is breaking down.

welcome!

Dumb question but is there a certain type of copper grease to get for the timing advancer? Im waiting on parts but will give it go this weekend. Thanks

If removed so the weight arm pivots are readily accessible, a good light-weight grease may be applied. Such as Molybdenum or Moll grease. Others may suggest favorites that might be better or more suitable for this application.

That said, I just use a drop of motor oil on each pivot, which seems to keep them adequately lubed for a very long time.

The oil is handy to use without much disassembly, because the pivots are usually accessible for receiving a drop of oil through the timing inspection window.

Good Fortune!

After checking the advancer, the next thing I would check are the slides on the carbs. Those carbs need at least one drop of oil on the sliding surfaces on the large outer diameter, and the small inner diameter. Without oil, and proper cover alignment, the slides don't move up and down like they should. This can limit the speed of the bike drastically.

Then of course, there are the other obvious things common to all bikes... coils, floats, petcock, etc.

If the bike is new to you, do a compression test and valve clearance check.

Thanks for all the input. I had time this weekend and replaced the fuel petcock and right off that bat that made a big difference. The bike revs up much higher it goes up to around 6-6.5k rpm and then sputters so thats good news for me. Its now acting like a bike that has jetting issues and that would make sense since it has 2-2 mac exhaust and pod filters.
I then took a look at the timing advancer and it was pretty corroded so I cleaned that up and got it greased. I already did the valves and they are all adjusted into spec. Next will be fine tuning the carbs and hopefully I can get those stock carbs to be happy with the 2-2 mac exhaust and open filters.
Any advice where to get good priced jets for those stock carbs? NOS ebay jets can be as high as 20$ bucks each. Factor in I doubt ill get it right first try and you get a ton of money in jets... oh well