Three problems, possibly related 82 KZ750e

yes and they affect both idle and mid-range on Keihin CVs. on Mikuni CV carbs the filters can block the choke(enriching)openings too. on both Keihin and Mikuni CV carbs the the filters can restrict the air flow to the diaphragms.

l0g1c wrote:

...I think top speed is 120ish, though my speedo only goes to 85mph.

I've heard the same for top speed....and have the same issue with the speedo!

hoghaterkaw wrote:

yes and they affect both idle and mid-range on Keihin CVs. on Mikuni CV carbs the filters can block the choke(enriching)openings too. on both Keihin and Mikuni CV carbs the the filters can restrict the air flow to the diaphragms.

:ohmy: Definitely something to think about when considering pod filters over the stock box!

as to the motor not returning to idle, you likely have an air leak. on our old bikes that is mostly from cracked rubber carb hangers. but make sure the throttle snaps shut and make sure the throttle cable is not kinked, pinched or has a sharp bend somewhere between the grip and the carbs. you didn't say if your bike has an aftermarket exhaust. if it does have an aftermarket exhaust, the mid-range loss of power is due to to the jetting being too lean or you may need to raise the jet needle.
the back firing could be from a too lean of a mixture.

this thread needs to be moved to the carb forum.

Sounds like you may be experiencing a lean mis-fire. This can be caused by a number of things including removing the stock air box. If the more experienced here on this forum concour with this diagnosis, they can direct you on how to enrich the idle/low speed circuit of your carburetors. It is not too difficult to do and often can be done by adjusting the pilot air screw or idle mixture screw, whatever your carburetor is equipped with.

try this simple test.duct tape.tape up 1/2 of your air filters and if it runs better and returns to idle faster you are lean.someone may have suck the filters on without rejetting.you may have to readjust idle speed down after you tape

hoghaterkaw wrote:

as to the motor not returning to idle, you likely have an air leak. on our old bikes that is mostly from cracked rubber carb hangers. but make sure the throttle snaps shut and make sure the throttle cable is not kinked, pinched or has a sharp bend somewhere between the grip and the carbs. you didn't say if your bike has an aftermarket exhaust. if it does have an aftermarket exhaust, the mid-range loss of power is due to to the jetting being too lean or you may need to raise the jet needle.
the back firing could be from a too lean of a mixture.

this thread needs to be moved to the carb forum.

Thanks again for all the info. Its suppose to be nice out this way tomorrow and I am going to take a real good look through the bike. I will take the air filters off and look to see if they are blocking those holes. Maybe i will take some pics or video and post it on here. That would probably answer a few things that I don't know what to look for. My bike doesn't have aftermarket anything... except those air filters. I thought maybe it needed a different jetting cuz of those. I saw that it does with the K&N. I might just pick up a stock airbox, like someone suggested in a earlier post. Thanks again for the ideas and suggestions.

meNmyKZ wrote: "How fast top speed can these things go? I can't see getting over 100mph without some wind protection or flaring. On my CBR, 130-140mph was comfortable, on this bike, I feel like I am brushing death at around 90"

Depends on which model you have. My KZ650C1 will run at just about 120mph and my friend's GPZ750 (back when he owned it) would walkk away from me when I was flat out. If your bike is handling funny (not Ha Ha funny)you may need new shocks and and a fork oil change and maybe new steering stem bearings and possible tires. Sounds like a lot, but none of these are a big deal, and if you plan to explore the top speed of this bike they are worth doing. Here's some specs on the '82 750 GPZ. In '83 the standard model had the same specs as the '82 GPZ.

750 Specs

Nebr_Rex wrote:

Sounds like you may be experiencing a lean mis-fire. This can be caused by a number of things including removing the stock air box. If the more experienced here on this forum concour with this diagnosis, they can direct you on how to enrich the idle/low speed circuit of your carburetors. It is not too difficult to do and often can be done by adjusting the pilot air screw or idle mixture screw, whatever your carburetor is equipped with.

try this simple test.duct tape.tape up 1/2 of your air filters and if it runs better and returns to idle faster you are lean.someone may have suck the filters on without rejetting.you may have to readjust idle speed down after you tape

Thanks for the post, I will try that tommorro also. I am curious, does "LEAN" mean to much air and not enough fuel? And being "RICH" is the opposite? Am I correct? Thanks again for the "tests" to perform. mucho gracias!

650ed wrote:

meNmyKZ wrote: "How fast top speed can these things go? I can't see getting over 100mph without some wind protection or flaring. On my CBR, 130-140mph was comfortable, on this bike, I feel like I am brushing death at around 90"

Depends on which model you have. My KZ650C1 will run at just about 120mph and my friend's GPZ750 (back when he owned it) would walkk away from me when I was flat out. If your bike is handling funny (not Ha Ha funny)you may need new shocks and and a fork oil change and maybe new steering stem bearings and possible tires. Sounds like a lot, but none of these are a big deal, and if you plan to explore the top speed of this bike they are worth doing. Here's some specs on the '82 750 GPZ. In '83 the standard model had the same specs as the '82 GPZ.

750 Specs

Awesome. I love the line "if you plan to explore the top speed of this bike they are worth doing". Well I totally planned to buy this bike to drive slow, cuz I figured when I bought it, it would be slow. After driving it a bit today, through the country roads, and after hearing all your responces, I can say that idea is tossed out the window. It is a pretty fast machine. Kinda surprised me a couple times, especally when i gunned it through a dip in the road and in first it brought the front tire up. Made my hair stand up. I have a feeling this summer is gonna be a fun one. Thanks for the post and info.

Sorry if I keep posting unrelated questions, I just don't want to start a million threads. But is there anyway (such as drilling the muffler) to make it louder? Is that bad thing to do to stock exhaust? Would i need to get new pipes to make it sound a lil "tougher". Thx

meNmyKZ wrote:

Ok, first off I would like to thank all that reply. Now I will explain the bike and its set-up. 82 Kz750e, 11000 miles, appears to be all stock except for the air box has been taken off and each carb has its own air filter. And its not the K&N ones, they are the ones that you see on ebay for about $30 for a set.
Heres the problems. When it is warming up, and sometimes even when its warm, the carbs "backfire". Not with flames or anything, but you can hear it and see a bit of smoke or vapor come out of the carbs. Its not the same one everytime, its random. Happens about once every 4-8 seconds. Sometime twice in a row. I can also tell a loss if power from that cylander not firing. Mostly only at idle.
Second problem, when i drive it and go to stop, it will idle at 4 grand til i rev it up a bit, then it wil go back down. Happens almost everytime and I look like a massive tool reving up my 82 KZ750 at stop lights.
Third problem, when i open it to full throttle it pretty much losses. Especally when I get on it trying to get on the expressway. Not so bad in 1st and 2nd, but the rest are really noticable.
If ya drive it normal it drives good and runs good. I am not looking for a performance machine, just something fairly reliable. I don't even plan on driving it hard, but i can tell these problems need to be delt with to make it the slow reliable machine I am looking for. Thx to all for the ideas of what is wrong.

I have the exact same issue when I stop at a red light...(Ya, I know I have a mega-power 650 beast...and I am just too proud not to rev it up at red lights) I just had the bike re-gasketed and tuned up including a workover of the carbs... points and condensor the whole she-bang...new cables so there shouldn't be an issue there... are there things that would cause these issues as related in this (750) post that would be causing this besides (NEW GASKET HANGERS)? Thanks so much!