Backfiring Issues

I took my dad's 1981 KZ1000-J out of storage and I have been fixing it up for the past couple weeks. I have had it starting for a while but now I'm having issues with it spitting out the back of the carbs.

I have the air filter case off right now. And most of the backfire seems just misty gas but sometimes it spits out some smoke.

I don't think its gunk from the tank cause I just cleaned it with muratic acid. Are the carbs tuned wrong?

Could you guys help me figure out what's wrong? I'm new to motorcycles & KZ's. Sorry if I can't offer more technical data

If not already done, would assure valve clearances are to specs.

A too tight intake valve may allow combustion inside the cylinder to backfire out through the carb.

Good Luck!

not to sound like a noob but how do i do that?

Get a good shop manual, I'd first try E-Bay, then for a really good one go to www.repairmanual.com It might be $60 but it's the factory manual from Kawasaki.

I don't like the Clymer or Haynes versions, but if they have the valve clearance specs and they are easy to follow, I don't see why not in buying one of them.

The valve clearances are checked with a cold engine.Precision shims are used to adjust the space between the valve stem buckets and the cams. The buckets are a large diameter metal shim holders that will need a hold down tool,feeler gauges, and possibly a micrometer or vernier caliper to measure shim thicknesses.

A small magnet,machinist's scribe and plenty of patience and this chore can be accomplished.

ok well i looked at the service manual that i have and i understand now that it does look like the valve clearance.

you guys sure think its the valve clearance too? its an aweful lot of work and i'd hate to try and fix the valves only to realize that's not the issue :S

www.z1enterprises.com/catalog.aspx?pid=KZ1000-J1-1981-EN1 so i get my shims there. k. but i'll have to buy the $100 shim set cause I don't know which shims I need? :blink:

i found a feeler gauge on z1 but where can i find the valve lifter/hold-down tool?

but wait. how will incorrect sized shims make the engine backfire through the carbs? it leaves the valves open when the engine is firing?

and i don't think the engine was backfiring when my dad ran it 10 years ago but it is now. what would happen to the valves to cause them to do this?

www.z1enterprises.com sells the hold down tool, and feeler gauges can be bought at most good tool suppliers. You might have to use a conversion chart if the gauges are in imperial (English) markings to convert to Metric measurements.

The clearances might be within specs.

But won't know until measuring with a feeler gauge.

Measuring is the easy part.

Changing the shims is a little more involved, but not necessary if the clearances are within specs (i.e., don't need adjusting).

Incorrect ignition timing may also cause backfiring.

Good Luck!

roger. i'll grab a feeler gauge and measure the valve clearance and see if i need new shims.

And I'll do a Point Gap Adjustment and Static (w/ Ohmmeter) Timing Adjustment to readjust the ignition timing.

hopefully this will stop the backfiring
thanks for all the help

KZYoungBlood wrote:

...And I'll do a Point Gap Adjustment and Static (w/ Ohmmeter) Timing Adjustment to readjust the ignition timing....

'81 J model has electronic ignition without points.
Good to verify timing and proper functioning of the advancer by using a strobe-type timing light with engine running.

Am thinking the wrong manual is being consulted.

Good Luck!

haha yes i know i have the wrong manual. i have the 1977-79 KZ1000 service manual
i'll buy the right one soon enough. i feel cheap right now

this manual has details on how to do a strobe-light timing test. it will do no?

KZYoungBlood wrote:

i don't think the engine was backfiring when my dad ran it 10 years ago but it is now.

Sounds like a lean condition to me. Have you cleaned the carbs? At what RPM/speed does it backfire?