TOPIC:

My Kz750 Twin backfires where do I start looking for the problem?

You start by providing more info

Backfires out the exhaust or the intake?

Backfires when?

Taken a look at the plugs? What do they look like (black/white/etc)

Checked the valve clearances?

Done a complete tune up?

What year 750 twin?

It backfires out of the exhaust, only when I let of the throttle and usually only in 2 thru 5 gear, but it seems to becoming more constant. Havent checked the plugs latley, havent checked the valves or done a tune up...it is a 82 KZ 750 Twin.

is it just a loud back fire or more of loud poping when you let off the throttle?

it might even be something simple like a headre leak. if you sucking air you will get a poping noise when you let off the throttle. or it could be the carbs.

Yeah the majority of it is loud popping after I let off the throttle. So do you think I should start with some new intake seals for the headers?

you can replace them if they look to be in bad shape. i got the thick ones in my 1000 and have had the header off many of times and reused them with out probs.

might want to check it might just be loose. just dont over tighten the header nuts. dont want to brake a exhaust stud.

bs1134 wrote:

Yeah the majority of it is loud popping after I let off the throttle. So do you think I should start with some new intake seals for the headers?

get a set of copper crush gaskets for the headers

where do you get copper crush gaskets?

click here

My bike was running pretty bad after getting stuck in traffic in this heat coming home from work. The engine got really hot and I was worried about possible damage. After, it was hard to start, backfiring through the exhaust, spitting back through the carbs, plugs fouled and a bit of smoking. Found the spigots for my header were all loose, I assume they stretched from the extreme heat and expansion. Snugged them all down, changed the plugs (next higher heat range) and gave it a good run to clean it out and it's been fine. I just have to remember to get a set of new plugs, proper heat range.

I would look at the exhaust to exhaust port seal first as mentioned above. I never realized before how a small leak there could cause so much trouble.

Just so you know, all the people so far seem to be describing different helpful suggestions that tackle problems that produce symptoms of leanness.

Backfiring/popping on deceleration is a symptom of leanness, so it could be any of the things suggested so far, or others.

The updated descriptions you gave are helpful in diagnosing the symptom, but can you tell us if you changed something recently that caused this, or did you just get the bike, or did it always do this? Etc.?

Ok, so i just purchased the bike in June, rode it a vew times, never riding it more than about 20 mi. in one day, it was completely stock and backfired in the same way. I sent out the gas tank to get repainted and put new 2 into 1 pipes on and thats it. Ive been trying to ride as much as possible, cause the previous owner said it had been sitting for a little bit. It just seems to be more constant now, popping after letting of the throttle. I know I need to get the Valves checked (who knows how long its been), and probably need to get a tune up and rejett. So thats about it, anything else I need to include that I might be forgetting to add?