Three problems, possibly related 82 KZ750e

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.

Start simple. Check your timing first. For the revving, oil up your throttle cable and linkage to make sure it's not just sticking.

If that doesn't sort you out, then start looking at things like valve clearance and wiring. Save your carbs for last.

Good luck!

Oh, and I've got an '81 KZ750. I've never considered it a slow machine.

l0g1c wrote:

Start simple. Check your timing first. For the revving, oil up your throttle cable and linkage to make sure it's not just sticking.

If that doesn't sort you out, then start looking at things like valve clearance and wiring. Save your carbs for last.

Good luck!

Oh, and I've got an '81 KZ750. I've never considered it a slow machine.

Thanks for the ideas, I was hoping the last thing to attack would be carbs. I have a feeling the previous owner never had any valve adjustments. Sorry about the slow machine comment, my bike before this was a CBR and significantly faster. I like my KZ better though and it still has more power than I really even need.

:laugh: No offense taken. I have a feeling you might be surprised when you get that old girl running right.

Hello,

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.

Robert

I'm saying check the timing too. Sounds a lot like the issues I had with my kz250 recently. I had just changed the points and forgot to reset the timing...checked it and it fixed the issues. Definitely start there!

~Clutch

First, understand that stock 750 -4s are pretty fast bikes. I would do the following to establish a solid baseline before playing with other stuff. 1) Install new carb holders. The idle symptoms you describe sound like there is a leak between the carb holders and intakes on the cylinder head. You can check this by idling the engine as low as it will keep running and spraying carb cleaner around the mating surfaces of the carb holders and head. If the idle changes or the engine dies it confirms my suspicion. 2) Replace the original airbox and air filter. The problem you describe when you open the throttle sounds like the mix is too lean . Rather than monkey with the internals of the carbs, I would simply replace the airbox/filter and see if the problem goes away. You should be able to pick one up cheap on eBay or a recycler. If you get the bike running like it did before someone started changing stuff on it you will be surprised how much power it has. Ed

GPz550D1 wrote:

Hello,

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.

Robert

Thanks. I had wondered if the airbox could be part of the problem. Not sure if it should have been rejetted (like a k&n) or not. Thanks for the ideas, i can't wait to get this thing purring.

650ed wrote:

First, understand that stock 750 -4s are pretty fast bikes. I would do the following to establish a solid baseline before playing with other stuff. 1) Install new carb holders. The idle symptoms you describe sound like there is a leak between the carb holders and intakes on the cylinder head. You can check this by idling the engine as low as it will keep running and spraying carb cleaner around the mating surfaces of the carb holders and head. If the idle changes or the engine dies it confirms my suspicion. 2) Replace the original airbox and air filter. The problem you describe when you open the throttle sounds like the mix is too lean . Rather than monkey with the internals of the carbs, I would simply replace the airbox/filter and see if the problem goes away. You should be able to pick one up cheap on eBay or a recycler. If you get the bike running like it did before someone started changing stuff on it you will be surprised how much power it has. Ed

Thanks for the idea. I will go out and get some carb cleaner tonight. Also you said to replace the airbox. Are you saying to go find a original airbox or just replace the existing air filters. Thanks for the ideas!!!

clutch wrote:

I'm saying check the timing too. Sounds a lot like the issues I had with my kz250 recently. I had just changed the points and forgot to reset the timing...checked it and it fixed the issues. Definitely start there!

~Clutch

Thanks Clutch, I called a shop to get the timing adjusted, just waiting for my "time slot". Pretty sure messing with timing is a bit over my head. I do think it has something to do with it since the previous owner never did it. Thx

I think he means to try finding the stock airbox and install it with a new air filter.

Robert

l0g1cand 650ed. I 100% agree, I have no clue the real performance of this bike. Mine obviously isn't running upto par. I had assumed these are just slow crusing type bikes. Now I really can't wait to get this thing purring. Thx again for responding to my post.