[SOLVED]Engine break-in....stalling...overheating?

a bored over engine will run hot in the kind of temperatures u were mentioning ( I believe u said 97 f), mine did the other day and its set up near perfect, my temps were actually lower than urs ( about 90) i ordered and oil cooler for mine, like i said u may have more than one contributing factor to your problem
and when u find that holy Bible of motorcycle problems let us all know :laugh: :laugh:

a bored over engine will run hot in the kind of temperatures u were mentioning ( I believe u said 97 f), mine did the other day and its set up near perfect, my temps were actually lower than urs ( about 90) i ordered and oil cooler for mine

Well thats not good news! :ohmy:

An oil cooler will do nothing on idle (where i have my heat problem)... there only useful when air flow is available! fans maybe...

I'll check that out!

best regards,
laurent

Do the Clear tube fuel level check before doing any more jetting. You need to be certain that the fuel level is correct first, to low will lean your mix through the operating range Idle/ WOT.
If you bought the timing light, check to insure the ignition advancer is operating correctly, it should return easily and smoothly. There is a chart in the FSM as to how much advance per RPM. I agree with Tech9ine about retarding a few degrees, that will reduce some heat. The hole in the plate can be filled so it can rotate.
You can buy cylinder head temp gauges for Air Cooled engines, as well as oil temp. I believe most of those would show 340 as the top of the scale. We used to buy one that went to 500 max, but I can't remember the brand. Being stuck in traffic on a hot day with a Air Cooled bike is going to heat it up. Choosing a more flowing traffic route is a good idea.
Oh and that picture of your exhaust cam lobe, looks like weak spring pressure. It is not following the closing ramp as it should. When the valves and seats are cut, the valve sinks in the head, the installed height is greater causing lees spring pressure. Unless the valve spring is shimmed to compensate, the "Spring Installed Height" will be less. This means less pressure. An older spring would already be weaker. Were the springs checked for pressure or replaced? Valves weren't tipped, right, so I doubt Springs were correct either. Luckily, if you get ambitious, the springs could be changed without head removal. Just My .02

ELCouz wrote: ...recently built gpz 750 (now 810cc bored, wiseco kit) is stalling at stop...carb sync everything was great ... good stable idle at 1100 rpm mixture...good.

...first ride with the new pistons and valve job...Few minutes (15-20mins) of riding where perfect good idle at stop...highway did a series of WOT at 5 min interval. Throttle response was perfect... no flat spot! Then when i exit the highway and start to run in city.

Few red lights after that, engine died when came to a stop! (first gear fully pulled clutch) Started again in panic then had to play with the throttle to prevent it from dying!

Also when i played with the idle adjustment I've noticed the engine looked abnormally hot! i burned myself on the clutch cover !

Is the bigger bore which can cause overheating ? Is the bike really overheating ... how do we know ??

best regards,
laurent

But not for the Few minutes (15-20mins) of riding where perfect good idle at stop, would be even more suspicious of too tight set-up during engine reassembly.

After first starting a cold engine, and while idling with fan blowing on the engine, could also spray continuous steady water mist onto the engine to help determine whether the additional cooling allows the engine to maintain a steady idle.

Good Fortune!

you also may not notice ur engine running hot at highway speed, but it still may be, of course u would notice more at idle, but that doesnt mean that is the only time it is running hot, about the cooler, oil doesnt heat up or cool instantaneously, if it is cooler at speed, the rise in temp to bad levels will take longer when slowed/stopped.
but like I said u got more than one problem, Larry mentioned carb adj and he know his shit, start there and good luck

95% of carburetor tuning, especially more difficult with CV carburetors, is tuning the needle so it fuels properly through out the range for which it's intended to control the mixture.

You're right, 4 turns out on the pilot is probably too much. Generally if it likes that much pilot screw, it's asking for 1 size up on the pilot. Also, once you get past 3.5 turns out, there's not a lot of spring pressure to hold the mixture screws good and tight in some of those carbs.

IMO, I would lift the needle the last position available for starters and maybe jump one on the pilot if the extra lift on the needle doesn't cure it.

It's also possible that Patten's suggestion about tight bore job is correct. It's within the realm of possibilities....

I would put an accurate compression gauge on the hot engine and see what it reads. Remember, WOT when you check compression. It would be helpful to know where that's at.

Do you still have the factory oil cooler on the bike?

Do the Clear tube fuel level check before doing any more jetting.

That test never worked really well each time I've done it...don't know why but there is always a bubble stuck in the tube unless i play up and down with it but as said in the FSM... this will give false readings.

I'm gonna go directly to carb float measurements (I've ordered the tool so its gonna be easier!)

If you bought the timing light, check to insure the ignition advancer is operating correctly, it should return easily and smoothly.

Yes good idea..maybe it need some grease

Being stuck in traffic on a hot day with a Air Cooled bike is going to heat it up. Choosing a more flowing traffic route is a good idea.

Well i do my possible to avoid traffic but sometimes it can't be avoidable...
Generally do air cooled overheat easily when properly tuned... i mean will stock motorcycle and well tuned survive in a lets says 30 mins intense traffic (foot by foot)? Personally I've never saw someone waiting on the side of the road because his Harley or big air cooled engine is too hot (Maybe it's different for KZ i don't know!)!

Oh and that picture of your exhaust cam lobe, looks like weak spring pressure. It is not following the closing ramp as it should. When the valves and seats are cut, the valve sinks in the head, the installed height is greater causing lees spring pressure. Unless the valve spring is shimmed to compensate, the "Spring Installed Height" will be less. This means less pressure. An older spring would already be weaker. Were the springs checked for pressure or replaced? Valves weren't tipped, right, so I doubt Springs were correct either. Luckily, if you get ambitious, the springs could be changed without head removal. Just My .02

Make sense...but for now that think will be on hold (money short)...at least no valve float at high rpm... trust me you will know it if it happens...i will be the first to brag here about my holed pistons :laugh:

After first starting a cold engine, and while idling with fan blowing on the engine, could also spray continuous steady water mist onto the engine to help determine whether the additional cooling allows the engine to maintain a steady idle.

Very good idea this way i could always tune correctly the engine leaving it for a long time without any worries about overheating it while on stand...

would be even more suspicious of too tight set-up during engine reassembly.It's also possible that Patten's suggestion about tight bore job is correct. It's withing the realm of possibilities....

I don't understand what guys are saying... tight bore job? I know piston clearance was set to Wiseco specs... about 2 thou.

You're right, 4 turns out on the pilot is probably too much. Generally if it likes that much pilot screw, it's asking for 1 size up on the pilot. Also, once you get past 3.5 turns out, there's not a lot of spring pressure to hold the mixture screws good and tight in some of those carbs.

Yes...that's why i'm gonna try with 42.5 pilot jet

I would put an accurate compression gauge on the hot engine and see what it reads. Remember, WOT when you check compression. It would be helpful to know where that's at.

Never checked while it was hot... i will check this

Do you still have the factory oil cooler on the bike?

Yes but i was looking to install a earl 10 or 16 row oil cooler...i can't find the tubing and fittings that could directly fit on my oil pan..i don't want to drill and tap...does anyone have a bolt on solution ?

ELCouz wrote: "That test never worked really well each time I've done it...don't know why but there is always a bubble stuck in the tube unless i play up and down with it but as said in the FSM... this will give false readings.

I'm gonna go directly to carb float measurements (I've ordered the tool so its gonna be easier!)"

It appears you are not performing the clear tube test properly. One end of the tube goes into the carb bowl drain hole. The other end of the tube is held above the carb bowl / carb body joint. There must be no plug in the tube. With the tube held this way when the petcock is turned on fuel will fill the carb bowl and the tube to the exact same level as a liquid seeks its own level. There can be no bubble in the tube because as the fuel rises in the bowl and tube it simply pushes the air out of the open end of the tube above the bowl/carb joint. Just keep the open end of the tube as high as you want above the bowl/body joint and see how high the fuel rises in the tube compared to that joint. It should stop rising 2.5 - 4.5 mm below the joint. Give it another try and you'll see what I mean. Adjusting the floats does not assure accurate fuel level; it will at best only get you in the ball park because the bouyancy of all the floats may not be exactly the same. The clear tube method is the only way to tell the exact fuel level in the bowls. Ed

ELCouz wrote: ...the Clear tube...test never worked really well...don't know why but there is always a bubble stuck in the tube unless i play up and down with it but as said in the FSM... this will give false readings....

Clear tube test must receive fuel from a float bowl "drain," not from an "overflow circuit."
An overflow circuit is NOT used during clear tube test.
Whenever fuel discharges through an overflow circuit, the actual fuel level inside the float bowl is already too high.

BS series carbs don't have overflow circuits, and the nipple on bottom of float bowl is a drain, which operates when the drain screw is loosened.

When performing the clear tube test, everything should be attached and set up already, with float bowls empty, and with the tube being held very steady against side of the float bowl, and then, with nothing else moving or allowed to move, shake or twitch, switch on the petcock to flow fuel. Hold your breath the entire time, and don't be swatting at any flies or gnats.

I'm gonna go directly to carb float measurements (I've ordered the tool so its gonna be easier!) --- But often fails to produce the correct actual fuel level, because the correct "float height" is whatever it happens to measure when producing the correct fuel level.
"Float height" isn't critical. "Fuel level" is critical.

...insure the ignition advancer is operating correctly...Yes good idea..maybe it need some grease --- Oil may be the better choice.
Imo, the reported performance history doesn't indicate an advancer function issue [engine runs okay both at speed and at idle, except when over heats at idle].

Generally do air cooled overheat easily when properly tuned... i mean will stock motorcycle and well tuned survive in a lets says 30 mins intense traffic (foot by foot)? Personally I've never saw someone waiting on the side of the road because his Harley or big air cooled engine is too hot (Maybe it's different for KZ i don't know!) ! --- Not "easily," and usually will "survive," but likely over-heat, for instance when crawling along and foot paddling bit by bit on A1A at Bike Week in Daytona Beach during 98 degree temps. Not unusual for any model bike to be seen pulled off and being allowed to cool. Harleys are even more susceptible due to decreased air exposure of rear cylinder.
Especially hard on any fresh re-build before the engine has "broken in" and "loosened up" a little.

tight bore job? I know piston clearance was set to Wiseco specs... about 2 thou --- Good. Hope that's accurate, and that correct size rings were also fitted, and with proper end gaps. Would also heed Wiseco's cautionary instructions as to "break-in" speeds and extended idling sessions on a fresh top-end rebuild.

Yes...that's why i'm gonna try with 42.5 pilot jet --- Imo, a slightly rich carb pilot circuit might help a little toward holding down the idle temp, but a too rich pilot circuit will cause its own problems.

...looking to install a earl 10 or 16 row oil cooler.... --- as known, oil cooler is meaningless absent air flow.

Good Fortune!

Well I am watching this thread closely, cause I just about have the identical problem,kz750 engine with a Wiseco 810 kit. I agree with most peoples assessment here; very good information.I changed plug heat range to a B9ES and the bike seems to like it, actually can ride farther before the idle starts tryin to die on its own. I just put the plugs in yesterday so haven't pulled them to see how they are burning yet. I do like Larry's suggestion about raising the needle a step or 2, lol I've been so focused on the idle bein the problem, I never considered that the engine maybe running lean on the road, and heating up, but it makes sense, and Bravo is right too , the oil once hot isn't gonna cool down instantly. I'm no expert here but I was under the impression that gpz750 engines already had an oil cooler installed and the pans were built with a place for the fittings to attach on the front left hand side? Anyway I'm off to raise the needles in my flat slide carbs a step to see if it helps.

Clear tube test must receive fuel from a float bowl "drain," not from an "overflow circuit."
An overflow circuit is NOT used during clear tube test.
Whenever fuel discharges through an overflow circuit, the actual fuel level inside the float bowl is already too high.

No no no ... i get air sucked from my drain screw... they are in bad shape! (and they don't come in the complete carb rebuild package...at least no from Z1enterprise !)

Do you really think i will be dumb :silly: enough to plug that on the overflow ... you also have a clear picture in the FSM that the guy connect it to the drain :laugh:

Remember i did the wiseco pistons job myself...why i would be dumb enough for the rest :silly: :silly: :silly: hehe i will take that as a compliment :whistle:

BS series carbs don't have overflow circuits,

I have 2 unconnected barbs that are the level of the float bowl... i asked last year about that seems to be the overflow.. just they don't have tubing attached to it.




These carbs are not mine (just to show i'm not crazy :pinch: ) but they are the same... you have the fuel line in the middle then 2 other barbs between a set of 2 carbs... don't know why he connected them but barbs are there

Hope that's accurate, and that correct size rings were also fitted, and with proper end gaps.

They came in the kit... if wiseco supply the wrongs rings with their overbore piston kit... i think Houston we have a bigger problem ... the guy who work for CVT-Tech (who did the whole machining job and valve seats) had access to my pistons and rings anytime ... he even refused to do the job unless i ship them the piston kit because of size difference that on paper (specs).

They are not cheap (labor) though!

Yes...that's why i'm gonna try with 42.5 pilot jet --- Imo, a slightly rich carb pilot circuit might help a little toward holding down the idle temp, but a too rich pilot circuit will cause its own problems.

I will increase to #42.5 from #40 because it's the next size...i check step by step going to #45 in one shot maybe too rich especially when i'm nearly ok (well not too far because i have no flat spot or no popping when riding except on big compression... that's normal especially with a freeflow pipe) carb settings... so i will avoid dramatic change like skipping jets sizes.

...looking to install a earl 10 or 16 row oil cooler.... --- as known, oil cooler is meaningless absent air flow.

It's easier for me to put a fan on the oil cooler than the engine because of space restriction... header almost touch my wheel guard on my front fork!
I know the engine is not oil cooled but i think it could help...better than nothing i think.

. I'm no expert here but I was under the impression that gpz750 engines already had an oil cooler installed and the pans were built with a place for the fittings to attach on the front left hand side?

Yes they all came stock with a tiny oil cooler but fittings are not standard... on the oil pan the connector is just 2 flat surface with a o-ring and holding everything with 2 bolts... no threads to screw a adapter or anything standard for the tubing...

..insure the ignition advancer is operating correctly...Yes good idea..maybe it need some grease --- Oil may be the better choice.
Imo, the reported performance history doesn't indicate an advancer function issue [engine runs okay both at speed and at idle, except when over heats at idle].

My advancer is already lubbed to the max with oil...i was thinking maybe grease because in the FSM bible they show place to grease on the advancer.

Anyway you are right Patton for the advancer... it's not sticking...just want to die at low rpm less than 1500 rpm else i would have timing problem below 3000 rpm

I'm happy to see it help someone else at the same time...that's why forum exist, to archive discussions

have a nice ride guys,
laurent

the two other 'barb" are vent lines not overflows