KZ650 Carbs "Spitting"

Hello! My name is Jon, and I'm the proud owner of a brand new (to me!) 1978 KZ650C2. The bike wasn't running when I got it off of craigslist, but after a quick cleaning of the carbs and points and some new plugs, oil, and a battery, she's alive!

However, since it has been running, it's making a "spitting" noise coming from the carbs when it first starts up. It's much more prevalent when the engine is cold and choked, but it also happens once she's all warmed up and unchoked. The P.O. replaced the stock airbox with some pods, but I'm unsure if the carbs were re-jetted or not. Some other symptoms have been bogging out when opening the throttle at idle, as well as once I'm going, it doesn't quite pull as hard as I would think it would above about 3k RPM.

I've sprayed some carb cleaner on the boots while she's running, and it doesn't seem like there's a difference in the idle, so I think that rules out that option. Are these symptoms of a lean mixture, which means I need to re-jet/re-synch? Here's a link to a video that I took earlier today of the "spitting" noise I mentioned earlier.



Thanks!

-Jon

Hello, Jon, and WELCOME to KZR forum!

We're glad you're here!

As to the spitting --- before further addressing carbs, would assure correct ignition timing, and also assure valve clearances are within specs (especially that intake valve clearances aren't too tight).

Good Fortune!

are you flooding out the carbs, the petcock looks like it's in the prime position.

I'm pretty sure (99%) that straight down is on, up is reserve, and in-between is prime for the petcock. Someone please correct me if I'm wrong though.

Patton, as far as ignition timing and valve clearances, this is definitely on the schedule for tomorrow. Do you know of any good guides on doing this? I've found a few here and on other forums, but if you know of any that are really great, that would be nice to know!

If it was mine I would replace the stock airbox & filter; ensure the carbs are squeeky clean and have stock jetting, put on new carb holders, and synch the carbs. At that point your carb issues will be behind you and you can focus on points, valve clearances, etc. Ed

Ed, as much as I'd love to throw the stock airbox and filter back in, the bike had pods on it when I bought it, so I'll have to find another somewhere.

On that note, does anybody happen to have their stock airbox or a spare laying around? I'm interested in buying!

Objective for points system ignition timing is for contacts on left-hand side points to begin opening just as the F mark aligns with the permanent case timing mark for outside cylinders 1 and 4.

And for contacts on right-hand side points to begin opening just as the F mark aligns with the permanent case timing mark for inside cylinders 2 and 3. (See image below)

When dealing with left-hand side points, just pretend the image numbers say 1 and 4 instead of 2 and 3.

Be certain it's the F mark and not the T mark.

This may be done statically (engine not running) with light bulb or ohmmeter. Then later fine tune dynamically (engine running) with a timing light.

Checking valve clearance is the easy part. Just measure with feeler gauge. Hopefully find gaps already within specs.

Adjusting clearances on KZ650 requires cam shaft removal to access under-bucket shims. Delicate job. Easy to bend a valve during re-assembly.

Good Fortune!

This image shows F mark for inside cylinders 2 and 3 where firing is governed by right-hand points. Just pretend the numbers are 1 and 4 (instead of 2 and 3) when dealing with the left-hand points which govern firing on outside cylinders 1 and 4.

This shows F mark for inside cylinders #2 and #3 where firing is governed by right-hand points.

Dagnabit! :pinch:

See following post.

Here's the advancer which is mostly hidden under the timing plate.

Good Fortune!