backfire!

[Tarheel365]

i have a 91 zr750 zephyr and i'm getting lots of popping during 4-5k rpm. if i remain at that rpm it will keep backfiring. when i come to a stop the bike will idle lower then it did before. i normally keep it between 1500-1800 rpm but after the backfires it will drop to 1000 rpm im scared of it stalling at lights.

I haven't been riding much today but i was accelerating fast off of alot of lights.
i checked the battery connection and it seemed ok.

[nitrus]

sounds like a lean condition, take it in and have the carbs sync'd, and the pilot screw's adjusted.

[Coil]

That can be caused by a lean condition (as said before) and also by weak spark. weak spark meaning a weak ignition system. Check resistance in the wires, check coil...etc.

Worst case, it happened to me on a Yamaha. After it would heat up it did the same thing. Exhausted all possibilities and eventually found rear cylinder headgasket leaking BAD! What does that cause--------very lean condition.

Good luck

[Tarheel365]

anybody kno of good resistance for plug wires? i'm getting between 1.8-3.3 ohms

i'm sure its an electrical issue because i have a weak spark.

also my battery is at 12.4v at rest and when i turn the bike on it goes down to like 11v. can it be my battery?

[Quick 350]

Sounds more like a charging problem.

You should be getting some where in-between 13.5v & 14.5v at the battery when the bike is running.

With the popping problem at mid range RPMs sounds like the rectifier is on it's way out.

I think I've read a few other post on this same problem with the zyphyr.

check with the local dealer or dealer of your choice it may be a recall on that.

Good Luck!

Mike

[Quick 350]

If it was the battery it would read less then 12v with the bike off but still the voltage would go up when running.

Mike

[beerbaron]

The electric problem surely won't help.

Rectifier might be the problem for you might open you alternator and clean the contacts so that the brushes of the rotor have a better contact.

The connector of your alternator to your battery might also be bad, make sure you check your voltage as close as you can from the output of the rectifier.

I'd do all of that before going to buy a new rectifier.... as said a dear fried of mine: "If 95% of your bike runs fine changing this 95% won't make your bike run well"

BeerBaron

[Wizzard]

It could also be something as simple as your battery vibrating in its box . I know because I just went through this after buying a new battery cause the old one died of old age . It was a wee bit smaller and so sat loose in the box and vibrated itself and even bounced and shorted all my electrics out . Popping and sputtering , backfiring at hi RPMs led me to think at first that it was my air cleaners being dirty . After spending last Sunday going thru all the wiring , relays , etc. I isolated the problem and wedged in some cut lenghts of fuel line and viola , no problems since .
Just my 2¢ worth once again .
Kind regards, Wizzard

[Tarheel365]

i figured it out....
the wire ends wasn't making good contact w/ the cap. thanks all...now i have another problem........looks to be carbs though