new kz owner having backfiring problems

Hello, I just Joined the forum today and am looking forward to it. i bought a 79 kz750 twin a few weeks ago, this is my second bike. I also have a 75 honda cb360t which is a lot of but i eventually started looking for something a bit bigger, and wanted another vertical twin so, naturally, the kz seemed to be the best choice.
I rode it to work the monday after i bought it, and it ran great in the morning, but later on my way home (my commute is 25 miles each way) i was about half way home when it started to pop and backfire through the exhaust and had no power. it was low so i switched to reserve and improved but still wasnt right, so i stopped and filled it up with fresh fuel (previous owner said he had not ridden it in a year and a half) and leaving the gas station it ran fine until about 15 minutes later it started to act up the way but worse. The next day i started it and it ran great, i took it out about 20minute ride from home -no issues. but when i started to leave for home again it was acting up right away and was essentially unridable, it wouldn't do more than 25mph. so i had my dad come with a trailer and pick me up.
i drained and flushed the fuel tank, and took the carbs apart and cleaned them and that didn't help. i fixed and cleaned some not so good ground connections and put a new battery in it. i cleaned the plugs, nothing made a difference. i ordered a new coil and also a factory service manual. There is spark to both sides, not sure if it is good spark though.
Sorry for the long post, but i really would appreciate your help
Thankyou

Is it stock?

If the exhaust or intakes have been changed or altered it might have issues that need to be addressed. Old story, someone buys an old bike and starts hacking things off and throws whatever cool looking ebay parts they can get their hands on at it. It then runs like crap in the long run and they sell it on.

Wait for the factory manual and check everything you can think of.

has kerker 2 into 1 exhaust, and is otherwise stock. I'll keep checkin things till i get it. thanks

Performance issues arising as the engine attains normal operating temperature can result from too tight valve clearance.
Popping during decel can result from too lean pilot circuits.
A timing advancer stuck in the closed position usually prevents proper performance at throttle positions above idle.

Fuel starvation for whatever of numerous poosible reasons may cause the reported issues.

Good Fortune!

Could be the fuel cap vent is plugged.

Also, if you have an inline fuel filter, make sure it is not the see-through type with a pleated paper element. The ones made for cars will stop flowing after awhile, even when clean. They require fuel-pump pressure to operate correctly.

thanks, i will look into that this weekend. it does have the see-through inline filters, is there a filter type you recommend?

I don't know what size line you have, but I use a couple different types on my 550 which uses 5/16 line (originally 7mm?). I tried a couple to see what works better or if there are any problems.

I use these:

www.z1enterprises.com/product/KL19-1271-1
These are a simple metal screen.
The ones I have worked really well for years and I haven't had any problems even with running ethanol.
But some have said there are versions of this out there that get softened over time.

[hr]

I also have one of these.

www.denniskirk.com/russell/5-16-in-inlet...p18116.prd/18116.sku
It has a replaceable element, but you can also just clean it.
Obviously it's not see-through, but will not soften. The only problem I've had with it is I did not tighten it enough once, and it started leaking a few days later.
The element is scintered brass.

www.denniskirk.com/russell/element-o-rin...0.p9859.prd/9859.sku

[hr]

I can't say which one I prefer. I like both, and haven't really had any problems with either. The Russel probably filters better, but I can't say that for sure. Neither one has really clogged since the 550 already has a screen in the petcock.

[hr]
This is the type I've seen get soft, turn yellow, and eventually break with ethanol use.

Check and clean the points and grease the advance.

Welcome,

JD

thanks, I just ordered a pair of the one at the top from z1. Hopefully, that will help and hopefully i can check into all these things, and report back this weekend, thanks for the help

Rule: when you buy a bike, remove air injection system. But I don't do that.
I only use clear paper (look like paper) filters. All other filters can let bricks go thru.

kztwin79 wrote: thanks, I just ordered a pair of the one at the top from z1. Hopefully, that will help and hopefully i can check into all these things, and report back this weekend, thanks for the help

So how'd it go?
Steve

I know 3 reasons for exhaust popping:
air injection system
exhaust leak
lean pilot adjustment/clogged holes next to throttle