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justin666
08-05-2009, 12:57 AM
i've got a 81 kz650 that i ride pretty much every day. and its runs pretty damn good, except when i'm on the highway and i roll the throttle more than about 1/4 to 1/2 through the motor just bogs and i lose all power, and i'm pretty damn new to motorcycles. I've synced the carbs and got that bike going from a non running disaster, but some help on what might be going on would kick ass.

earz
08-05-2009, 1:04 AM
Will it ever pull through or does it continue to run shitty? Start with reading your plugs. if theyre black - you're running to rich. If white - too leam. You want a nice tan color. If they are tan-ish, and you have problems throughout the RPM's you may have a mechanical problem. I'd start with a compression test and depending on results - a leakdown test. Since it was a non running disaster, have you checked valve clearances?

justin666
08-05-2009, 1:07 AM
it doesnt pull through, it just bogs :(

i'll check the plugs and see what they look like

and no i havent checked the valve clearance so i'll take a look at that as well.
thanks

earz
08-05-2009, 1:09 AM
valve clearance should be 0.003 - 0.007 in (cold), but if it bogs all the time, I'd say you've got a carb problem. post up with your plug readings.

superflysnow
08-05-2009, 1:24 AM
What carbs are they? sounds rich... what happens past half throttle, does it open up again?

justin666
08-05-2009, 1:28 AM
it doesnt bog all the time, just when i get past half way through on the throttle, and its only in 5th when i'm going fast. it does great in every other gear and when i'm going slower.

justin666
08-05-2009, 1:30 AM
they are mikuni carbs. and what do i need to adjust if its running rich? it just loses power after half way through the throttle, and it doesnt get it back if i keep going. i have to just back off a bit. so right now the fastest i can go is like 65-70

earz
08-05-2009, 1:34 AM
what do you have done to the bike? is everything stock (i.e. airbox and exhaust)? It could also be a lean condition causing the problem. let me know what your plugs look like.

justin666
08-05-2009, 1:37 AM
its got 4 individual pod filters, theyre some shitty cheap ones and i'm getting some new ones that dont let as much air in, i can here those carbs sucking in air and sometimes it bogs a bit on the low end from too much air flow. i'm gonna try and pick up some uni ones this week, i thought maybe that could be part of why my bike was bogging at higher speeds but i thought id see what all you guys thought, being that youve got way more experience than i.

superflysnow
08-05-2009, 1:41 AM
x2 lets see em them plugs... take em out before you ride it and take a pic. put them in and replicate the problem then shut off immediatly! take em out and take another pic, with the mikunis you could be looking at float level problems which = easy adjustments.

Let hear about them pipes and intake too...

superflysnow
08-05-2009, 1:44 AM
are they foam filters... mx style and have you oiled them. if you can hear the air you aren't rich unless you are squeezing in at speed and blocking airflow... not likely though.

justin666
08-05-2009, 1:47 AM
its got a 4 into 1 kerker exhaust and the air filters are some cheap off brand

justin666
08-05-2009, 1:48 AM
the ones i've got arent mx style, they're like off brand k&n

justin666
08-05-2009, 1:49 AM
it bogs at highspeed the same way it does at idle sometimes when i can tell its just sucking in wayyyyy too much air. So i thought maybe it was just an air filter problem...

earz
08-05-2009, 1:50 AM
BINGO. I guarantee that your plugs are white. They are all going to flow about the same amount of air. The only way to remedy or tune your bike is going to be to rejet or reinstall the original airbox/airfilter.

It looks like your stock main jet is 92.5. Beings that you are in CO the air is much thinner and I would start by installing a 97.5 main jet. You may still need to bump it up a little. If your plugs are white, the best thing to do is remove your carbs. Remove the bowls and see what size jets are in it (the previous owner may have changed them). Take the main jet to your local bike shop and pick out the jets you need. I'm just guessing on jet sizes (I'm in MO @ 630' above sea level - compared to your 5300' above sea level).

superflysnow
08-05-2009, 1:52 AM
cool your only prob should be in the carb...

pull the plugs... just after the problem happens. if it is only on the highway in 5th gear at low rpms, that is when the motor should have the most load thus requires efficent fuel delivery. my guess is the float level is set too low in your carb, but it could be the jets... either way it is any easy fix

earz
08-05-2009, 1:52 AM
missed the post about the 4-1 exhaust. Better make that main jet size 100 or 102.5

superflysnow
08-05-2009, 1:53 AM
ha... rad two different diags... either way lets see the plugs

justin666
08-05-2009, 1:54 AM
hmmmm easy for you guys who know what the hell youre doing! ha. Alright, i'll check out switching out the main jet.

earz
08-05-2009, 1:55 AM
check your plugs first!!!

justin666
08-05-2009, 1:56 AM
and josh im not sure on the float level, i know when i first got the bike going it was pissing fuel like crasy and it was cause the valve needle was gummed up and wasnt even working, so once i took the float bowl off and cleaned up everthing it seemed to fix that problem. I need one of thos kawasaki factory tools to check the float level i think?

superflysnow
08-05-2009, 1:57 AM
x2!!!


and then...

http://www.mikuni.com/pdf/vmmanual.pdf

justin666
08-05-2009, 1:57 AM
and i WILL check on those plugs first! hahaha. i'll post up tomorrow on what they look like

earz
08-05-2009, 1:58 AM
a little help

KZ650 jet clean/replace (http://kz650files.kz650.info/adobe/650JetClean.pdf)

justin666
08-05-2009, 2:01 AM
this probably sounds like a retarded thing to say, but the main jet, theres one in each carb right? and will it be marked with the number of what it is?

superflysnow
08-05-2009, 2:03 AM
they wear off, but yes... right on the side. stamped

kevinhog
08-31-2009, 1:00 PM
fuck the dumbshit and just spend the money on a dynajet kit. They have been doing this so long that they know what all your jet sizes need to be for your set up and your elevation. They're like 150 bucks and your done. 1/4 to 1/2 turn of the throttle is your pilot jets, and I'm sure your mains are waaay off. You also need to make damn sure those things are really squeeky clean. It could be your pilots are clogged up especially if the bike sat for a while with fuel in the floatbowls. If you really want to get the job done perfect, google wiredgeorge. For like 230 bucks he rebuilds your crabs to like new condition and jets them for your situation. If you aren't too mechanically inclined that's probably your best way to go. Here's the link http://www.wgcarbs.com/ all your carb questions will be answered here and he even has a forum where he personally answers your questions.

djmfnk
08-31-2009, 6:56 PM
i personally like doing my carbs myself. its a great learning experience for a new rider to do the jetting themselves. do it yourself and you will appreciate the bike for what it is, not for what someone else has done for it. i have a kz with mikunis myself and i re jetted it until it was right. if you need anymore help let me know..

kevinhog
08-31-2009, 8:15 PM
this probably sounds like a retarded thing to say, but the main jet, theres one in each carb right? and will it be marked with the number of what it is?

I was just thinking this cat might be a little lost when it comes to carbs. So I gave him the best ways I could think of to get him un-lost. If he lived near me I would be happy tohelp him out and show him how to get it done. I know when I first started messing with carbs on multi cylinder motors, I fucked up more than I fixed.

justin666
09-01-2009, 2:10 AM
hey kevinhog, thanks for the suggestions and the advice. I've got a good friend whos been helping me with my carbs and helped me clean and re jet em. And i am glad i learned and did it myself, but it was really good to have some help from someone with some more experience, its not exactly the kind of thing you can just jump into and hope it works. haha

WOMPY
09-08-2009, 9:07 AM
If still having problems see wiredgeorge.com and his vintage bike forum. He will explain in detail more about your carbs and how to adjust.