Very very annoying problem with my KZ750

Hi,

first of all, i can guarantee this is my last topic for help since I'm asking alot of question on this forum and i feel bad because i can't contribute that much as you guys (not enough KZ savvy!)

I have an idle problem with my KZ750-R1 (GPZ) 1982 with mikuni BS34 carbs. I can't set it right!

I usually set the idle when the engine is warmed up (20 minute ride) to 1100-1200 rpm (lower than that its too rough).

everything is fine then after when i go into a traffic jam... engine want to stall i must always increase the idle then its okay it stays at 1200 rpm in the traffic then as soon as i clear the traffic i think the engine get cooler then when i come to a stop the engine rpm idle raise to 1500-1600 rpm !!!! and when i start it cold its the same high rpm

dear doctors what i can do (yes i try to avoid traffic jam as much as i can )?

I think my pilot is too rich but i can't never achieve the sweet spot ... either it backfire like a firecracker or it want to stall when hot (i did increment in half turns for the screws).

Each pilot adjustment screws are at 2 and half turns (kawa manual doesn't mention anything (factory how many turns) for the mikuni carbs).

any help appreciated... the engine stalled 2 times in the traffic today because i didn't increase the throttle manually !!

regards,
laurent

Checked valve clearances? Inspected mechanical ignition advancer for smooth operation?(it's behind a CD sized cover on right side of engine).

Ignition coils original? New sparkplug caps and wires?
Petcock clean?(fuel tank control valve).

Good compression? (125 PSI will run, 150 is better).

OK, #1, You'd better keep asking the questions or else... :laugh:

#2, Everything MFolks said, + It sounds to me like you might have a lean issue do to incorrect fuel levels. have you checked these, they're vitally important?

You really need to do a manometer vacuum sync, or else the bike could be erratic at idle, and cruise, and not really achieve max power till you do.

Are you running the stock airbox/filter/snorkel piece?
If so, then the stock 1 1/4 turns out on the mixture screws is fine. The mix screws really only affect the idle mixture, and not much else.

On my bike, if I dont pop the tranny into nuetral at a long light, it will drop the rpms right low, as the clutch is pretty old. Try it, just pop it into neutral soon as you come to a stop and let go of everything, then judge your idle. + sometimes the idle screw can move!

GL!

I had this same problem on my GS400 (Suzi), it would idle great if it wasn't hot out and the motor stayed a reasonable temp, but if it was hot and i was stuck in traffic and would quit after a few seconds if i didnt blip it a little.

I recalibrated my pilot screws just a little while before this to help with idling in general (before that it would not, i had to hold the throttle partially open), so it wasn't that on mine.

I started experimenting with other things and discovered that when I turned the headlight switch off, the idle revs would pick up and it would idle all day, even when it was hot. I guess with it being 33 years old and all the wires and charging system was getting weak or something.

I'm not saying i'm an expert and to go check your electricals, I'm merely stating my experience (just so this doesnt get taken the wrong way.)

#2, Everything MFolks said, + It sounds to me like you might have a lean issue do to incorrect fuel levels. have you checked these, they're vitally important?

You mean carb float levels ? yes i will check these you think the level is too low right ? hey btw do they have overflow tubes ? i can't find them on these mikuni (previous TK 26 on my kz550 had them)

You really need to do a manometer vacuum sync, or else the bike could be erratic at idle, and cruise, and not really achieve max power till you do.

I've already perfectly sync them last week (less than 1 cmHg) does playing with the idle mixture desync them ?

Are you running the stock airbox/filter/snorkel piece?
If so, then the stock 1 1/4 turns out on the mixture screws is fine. The mix screws really only affect the idle mixture, and not much else.

stock airbox with a k&n filter previous foam filter was scrap/teared

On my bike, if I dont pop the tranny into nuetral at a long light, it will drop the rpms right low, as the clutch is pretty old. Try it, just pop it into neutral soon as you come to a stop and let go of everything, then judge your idle. + sometimes the idle screw can move!

I've already tried that, no improvement i was thinking of a little bit of clutch drag but no ... it looks like the problem is not simple as that.

Good compression? (125 PSI will run, 150 is better).

from my last topic here it's
#1: 150 psi, #2: 121 psi, #3: 156 psi, #4: 145 psi

i will investigate this further this winter.

Ignition coils original? New sparkplug caps and wires?

still oem but i've checked the resistance values (what the kawa manual told me to check) and its fine

Inspected mechanical ignition advancer for smooth operation?(it's behind a CD sized cover on right side of engine).

Yes even before thinking to start it the first time i've got the bike ... they tend to stick i've lubed it ... maybe it need another grease shot!

Checked valve clearances?

it is not possible to check right now bike is my main transportation (winter i will do) since i will need the gasket kit (which anyway would be changed in winter) and a little risk to scrap my last month of riding... i know they might be off a bit hence the little clicking from the valve train if you really think this can play a role in the not so steady rpm (when hot or cold) i will endure this nightmare until its time to pull the plug

don't take it personally MFolks it just my previous experience during the motorcycle season whet bad last year with my KZ550... first i've started to check the clearance then i've sent the whole engine to be rebuild because of ... maybe this need to be checked... and this too (i was too paranoiac ) all this for a perfectly good engine... now i'm kind of guy .... if ain't broke don't fix it or don't go deeper than the problem is !

thank you for your precious time guys!

regards,
laurent

I had the same problem on my KZ650 It turned out to be intake manifolds were not sealing correctly onto the head allowing a vacumn leak. I took them off cleaned the sealing surface and applied some yamabond #4 to both surfaces, re-ninstalled and allowed it set up overnight. Problem went away.

Hi there!

I'm back from a non-stop (except for putting gas) 14 hours (700 miles) endurance ride up in the woody north of Quebec.

I'm very impressed with the KZ engineering. I've been pushing (testing) the limit of the bike half of the time. She always wanted more on the throttle even during the steepest hills I've encountered in my life.

Also, I've noticed that while the engine runs cooler (around 70F outside avg. temp) the idle was perfect all the time except when i came back to Montreal where the outside temp was around 90-100F. This confirm there's a problem with the mixture.

Really this bike... gained my respect and deserve the best mechanical maintenance i can give to her

In other word I'm very happy with my purchase !

BTW, i've noticed at around 300 km (~180 miles) the indicator show Empty but I'm able to fill only 11 liters (2.9 gallons) max!

Is the tank really 21 liters (5.5 gallon)? or it's just a very big reserve ?

regards,
laurent

There are many things that can cause that, but with the low comp and heat related idle speed, I'd at least check the valve clearances.

One very crude test you can do is ride on the highway for about 15-20 minutes at 65mph or above and then come to a stop. If it dies right away, but will restart and run normal after several seconds of slow riding, then I'd definitely check the valve clearances. Sooner the better. You don't want to ride a whole season with the valves not seating.

When the motor gets hot, the vlaves stretch and the clearance gets taken up. Then they don't seal. It only needs to cool a little bit after a hot run, the valves shrink back down, then they seal again. Warmer outside temps will cause it to happen more often. You won't notice a change while riding because the valves still close 99.999%, but it greatly affects idle.

Also, when you check the valve clearances, you have to release the cam chain tension before putting the valve cover back on, or you will stretch the chain or damage the guides.

Ok i will check the valve clearance today... i will do my own valve cover gasket then.

The valves expand that much with heat ???

Also, if the valve train is clicking this mean it have valvelash (too much clearance) thus the valves are not opening fully ?

If i understand correctly with times and miles... the valve gap from valve bucket to cam lobes increase and the the valves are not pushed enough (but will always seat) so a lost of performance occur right ?


How can a clearance be to tight with wear ?

Sorry I've seen 2 versions in this forum i don't know which is true.... valve clearance get tighter or looser with engine wear ?


Thank you for your help guys!


laurent

99% of the time, the valve clearance goes down. This is because the valves wear into the seat. This makes the valve stem effectiviely stick up farther. This reduces the clearance. I'm not 100% sure that there aren't other mechanisms (like the stems actually stretching permanently) that contibute to the loss of the clearance, but I can say, they almost always get tighter.

The valves don't expand that much, but if your clearance is zero, then any expansion will result in loss of seal.

The problem is this bike sat for some time so you haven't really had a continuous monitor of how it runs.

Normally the first sign of valve clearance issue, assuming all else is fine, is the bike will stall right after a hot highway run. Usually the bike will start right back up and a few seconds later it will idle just fine and won't stall unless you get it real hot on the highway again.

As the problem get worse, it will stall more often. Eventually, when the clerance gets near zero, the idle will get rougher as the temperature outside goes up. If you turn up the idle to mask the problem, the problem can go undetected for some time, but the bike will run rougher and rougher.

If it is ticking, then some of the valves may have clearances that are fine. Not all valves wear the same. It usually ticks a little louder after adjusting the clearances.

I've made a couple gaskets myself, but it takes a long time. The whole job takes a long time if you take the time to clean and polish the gasket surfaces. After that I put on a new gasket with a super thin layer of anti-sieze. Then the gasket comes off like new everytime. I've used some 3 or 4 times without having to scrape one bit.

I hate to see you do all the work of checking to find they are fine, but I don't think there is any other way to know.

Thank you that clear a lot of confusion i've had.

The problem i can see... if the valve gap is too tight i have to buy thinner shim , install then put the cam again then remeasure then rinse and repeat until i find the correct gap ?

This could be costly (shims aren't cheap)!


regards,
laurent

ELCouz wrote:

Thank you that clear a lot of confusion i've had.

The problem i can see... if the valve gap is too tight i have to buy thinner shim , install then put the cam again then remeasure then rinse and repeat until i find the correct gap ?

This could be costly (shims aren't cheap)!


regards,
laurent

After you have the valve cover off, you don't have to disassemble anything to measure the gaps. But you'll need to take things apart to find out what shims are in the buckets that need to be changed.

If this is a daily driver, you will have to do some extra work to put it together while you wait for the shims. If you knew what shims were in place now, you wouldn't even have to mess with the cams until your new shims arrive.

If you think the original shims are in there, someone may know what the 750's generally started with. For example, on my 550's, I know that most came from the factory with 2.55 and 2.60 shims. My memory may be wrong, but I think the 650's had 2.60 to 2.65 shims in them from the factory. So you'd be safe to assume the 750 has shims in that range if they've never been changed. You could try to order a few shims in the approxiamte range, but then you are spending more money than you have to. It's a tradeoff time vs money. If you don't think the shims are roiginal, then you'll have to pull those particular buckets to see what you have.

It saves a bunch of work if you know what shims are in there to start with, so obviously you want to write down every shim to keep records for next time.

You should only need to change the shim once unless the existing clearance is actually less than zero. But make sure to spin the crank forward and measure the gaps again or even 3 times. Sometimes the gap will vary if it's right near the cutoff of one feeler. If you can't spin the bucket while the lobe is pointed away, the clearance is less than zero. You'll have to put in a temporary smaller shim to measure the gap. That's extra work, but if you put in a temporary shim based on assuming the gap is about zero, you may get lucky and the temp shim will be the right size to be permanent. If you can easily spin the bucket, but can't get a gauge in, just assume it's zero.

Because most of the shims started in the same range, you typically need a lot of the same size shims. For this reason, a shim kit is not really what you want unless you plan to do several bikes for years to come.

Z1 enterprises have the 13mm shims you want, and they are by far the fastest at sending out shims. I haven't dealt with a better company than them.

www.z1enterprises.com/catalog.aspx?pid=KZ750-R1-1982-EN1

Also, you will need a suction cup or magnet to pull out the buckets. I use a suction cups so they don't scratch. Plus I think they can pull harder. They need to be about 1 inch to 1.5 inch in diameter. Get several as some can be finicky. Someitmes you can get them at a drugstore or department store for hanging things on in the bathroom or kitchen.

The numbers on the old shims are hard to read, so you'll want a really good caliper or cheap micrometer.

And since we're covering everything, you'll probably want to print this out and have it handy:

#200 = 2.00mm = 0.0787in.
#205 = 2.05mm = 0.0807in.
#210 = 2.10mm = 0.0827in.
#215 = 2.15mm = 0.0846in.
#220 = 2.20mm = 0.0866in.
#225 = 2.25mm = 0.0886in.
#230 = 2.30mm = 0.0906in.
#235 = 2.35mm = 0.0925in.
#240 = 2.40mm = 0.0945in.
#245 = 2.45mm = 0.0965in.
#250 = 2.50mm = 0.0984in.
#255 = 2.55mm = 0.1004in.
#260 = 2.60mm = 0.1024in.
#265 = 2.65mm = 0.1043in.
#270 = 2.70mm = 0.1063in.
#275 = 2.75mm = 0.1083in.
#280 = 2.80mm = 0.1102in.
#285 = 2.85mm = 0.1122in.
#290 = 2.90mm = 0.1142in.
#295 = 2.95mm = 0.1161in.
#300 = 3.00mm = 0.1181in.


0.00mm = 0.0000in.
0.01mm = 0.0004in.
0.02mm = 0.0008in.
0.03mm = 0.0012in.
0.04mm = 0.0016in.
0.05mm = 0.0020in.
0.06mm = 0.0024in.
0.07mm = 0.0028in.
0.08mm = 0.0031in.
0.09mm = 0.0035in.
0.10mm = 0.0039in.
0.11mm = 0.0043in.
0.12mm = 0.0047in.
0.13mm = 0.0051in.
0.14mm = 0.0055in.
0.15mm = 0.0059in.
0.16mm = 0.0063in.
0.17mm = 0.0067in.
0.18mm = 0.0071in.
0.19mm = 0.0075in.
0.20mm = 0.0079in.
0.21mm = 0.0083in.
0.22mm = 0.0087in.
0.23mm = 0.0091in.
0.24mm = 0.0094in.
0.25mm = 0.0098in.
0.26mm = 0.0102in.
0.27mm = 0.0106in.
0.28mm = 0.0110in.
0.29mm = 0.0114in.
0.30mm = 0.0118in.
0.31mm = 0.0122in.
0.32mm = 0.0126in.
0.33mm = 0.0130in.
0.34mm = 0.0134in.
0.35mm = 0.0138in.
0.36mm = 0.0142in.
0.37mm = 0.0146in.
0.38mm = 0.0150in.
0.39mm = 0.0154in.
0.40mm = 0.0157in.
0.41mm = 0.0161in.
0.42mm = 0.0165in.
0.43mm = 0.0169in.
0.44mm = 0.0173in.
0.45mm = 0.0177in.
0.46mm = 0.0181in.
0.47mm = 0.0185in.
0.48mm = 0.0189in.
0.49mm = 0.0193in.
0.50mm = 0.0197in.


0.000in. = 0.000mm
0.001in. = 0.025mm
0.002in. = 0.051mm
0.003in. = 0.076mm
0.004in. = 0.102mm
0.005in. = 0.127mm
0.006in. = 0.152mm
0.007in. = 0.178mm
0.008in. = 0.203mm
0.009in. = 0.229mm
0.010in. = 0.254mm
0.011in. = 0.279mm
0.012in. = 0.305mm
0.013in. = 0.330mm
0.014in. = 0.356mm
0.015in. = 0.381mm
0.016in. = 0.406mm
0.017in. = 0.432mm
0.018in. = 0.457mm
0.019in. = 0.483mm