engine bogging down on freeway/high rpms

Ok, so i'm stumped again and you guys never fail me.

this is what i ride

1982 kz550a1
pod filters
straight pipes with home made baffles
pick up style ignition

new stuff
plugs,wires,battery,top end rebuild,clutch,igniter,carbs rebuilt and rejetted.


problem

Bike runs great until i get on the freeway,with heavy throttle it acts like it is starving for fuel or choking on it i can't tell witch.At stop signs the idle goes way down and almost kills the motor then comes back to normal.I had someone else re jet the bike and he said he drilled out the mains to the next size up 94?From my research of other threads i have learned what it might be but the list is so long it could be anything.Hoping some one can narrow the list of suspects for me.I think the carbs are over jetted other possibilities are vaccum leaks,bad coils,wiring issues,fouled plugs,bad plug wires,bad gas,venting/vapor lock

compression is good

valves are in spec

advancer is moving like it should

drilled hole in gas cap to make sure it is venting

carbs synced and all slides move together

Bike runs great around town with the exception of the idle at a stoplight.does anyone know what starting value the coils are?my coils tested 3-4 ohms and are the only thing i have not replaced as the bike runs.I have read they can fail under load and look fine while testing.I have sprayed carb clean on the intake and the motor does stumble a little,but i can't tell if some is getting in the engine through a pod from overspray or a leak in boot.Would a small vacuum leak cause so much trouble?

Frankly; without a real exhaust system I'm surprised it runs as well as you describe. Have you considered installing a conventional exhaust system? Ed

KZR member loudhvx has a motorcycle stuff page w a manual... links are in his signature.

Not sure what the problem is, but in regards to the coils you could check them to see if they're getting real hot to the touch by pressing firmly.

How well do you trust the guy who drilled out your jets? I'd pull them and see what you're working with. Nice bobber BTW. :evil:

thanks for the replies,as far as the exaust goes i have some clearance issues that prevent the use of a factory made exhaust system.The kz900 frame is wider than the kz 550 so the frame rail is right in the way of #1 and #4 exhaust ports so i had to mickey mouse it with what i had,also the bike is so low i can't run the pipes down under the frame as usual so im stuck with what i got unless i get somthing made all custom.The pipes seem to work well with some steel wool and washer baffles,quiet at a light but sounds like a modern sportbike when i get on the gas.

As far as the guy who did the carbs has really good reveiws on yelp and works for himself out of a shop so i assume he knows what he is doing for the most part.I feel like the bike is getting too much fuel,the plugs were really sooty so i got new ones and raised the clip on the needle to the top position (leaning it out) idle is way better but still can not get up to speed on the freeway.seems like if i loose momentum i can't recover that speed it just wont pull away and if i try to give more throttle it will bog like it is choking on fuel.


In my mind the suspects are

1.main jet too big

2.vacuum leak

3.coils and or wires intermittent failing under load

4.igniter/pick up coils failing.

Please help i want to go faster than 60mph!

I don't know exact rpm/speed this is happening, i don't have guages on my bike.

so after searching the internets,i realized that the steel wool baffles might be the problem creating way too much backpressure.I read on some auto fourums that cars have the same symptoms when the cat is clogged up and the engine can't breathe.I took all the steel wool out of the pipes and it looks like it heated up and melted causing too much restriction,witch makes sense to me not performing at high rpm.The problem now is i have open pipes and it's loud as hell.I'm going to take it for a test run after i deal with an exhaust stud that snapped off(doh!)I'll post results when i get that done.

Try going in your ignition timing cover and put some oil on the timing advance mechanism. Springs, under the moving parts etc. I have a stock set of pipes from a k1980 z750 that are chopped right after they go 4-2, I would be willing to part with them If i could figure out a way to use ebay or paypal or whatever.

really different looking bike like to see so other pic's really really digging that tank
pm me if you ever wanr to get rid of it

ok so the bike breathes a lot better now,noticeable difference in power.Still has the bogging problem at high rpm,i felt the coils and they are warm but not hot.I noticed the #2 cylinder exhaust pressure is weaker than other cylinders.Pipe is warm but noticeably cooler than others.Checked for spark and it is there but wouldn't call it a strong spark(not blue).Can one side of a coil fail?I have new plugs new wires so that's not it.Going to check float level tomorrow.Any easy definitive way to test for a bad coil?

Carbs sync'd...?
Valve clearances in specs...?

While driving @ steady throttle ~ 65mph, does she surge a little as if starting to run out of gas...?
@ 65mph, let go of the throttle to let snap shut, does she pop/back fire...?
In either case above, running lean condition...

For testing (actually any time for not a goood baffle), rid the steel wool...

Pop the plugs and review for lean conditions....

the new plugs are black and sooty,witch tells me im running rich.i get popping on decel but that doesn't mean it's running lean.When adjusting air screws does 1 turn mean 180 degrees or 360?haven't figured that out yet. :pinch: Icurrently have the needle set to top notch (leanest) and the bike has plenty of pep on the streets and seems to be happy also better idle.As soon as i try to go fast it seems like 65 is tops and it just won't drink any more fuel or make power.main jet too big?I may try third position from top of needle from what im seeing most recommend that setting.

mine was popping alot too, new petcock diapgragm, I fixed the popping for the most part. The popping is most likely the extra fuel in the exhaust burning.
the carbs may be lean if you have a free flowing exhaust and intake causing the cylinders to burn too hot, check the exhaust valve for white color. an easy way to check the valve color is to turn the engine(wrench at the crank) and look inside the spark plug hole.
I had this condition for a while, the inside of the exhaust was white, the exhaust valves were white, the floats were too low, and the k&n filter with the baffle free exhaust was running the fuel right out of the engine.