kz650 idles terribly

I had the chance to drain carbs 1 and 4 today. Each had very small bits of debris in there that I'm assuming are bits of rust from the tank. Should be safe to assume the carbs need to be cleaned now. After that, should I be looking at a fuel filter, tank liner, or both?
Random question, there is a portion of carb 2 that extends lower than the other three. What is that about?

The bike was professionally serviced last summer that included new O-rings and gaskets. Is it safe to reuse those now without purchasing new ones?

Random question, there is a portion of carb 2 that extends lower than the other three. What is that about?

A picture will help a lot to identify the lower part. Some carbs sets, ( one of the four ), have a acceleration pump mounted.

pa317 wrote: I had the chance to drain carbs 1 and 4 today. Each had very small bits of debris in there that I'm assuming are bits of rust from the tank. Should be safe to assume the carbs need to be cleaned now.

Yes

After that, should I be looking at a fuel filter, tank liner, or both?

Fuel filter yes, tank liner maybe. The tank may just need to be cleaned, or may need to have minor rust removed with acid bath and rinse. Liner only if rust is severe and ready to perforate the tank.

Thank you all for the help with this. Confidence to do this myself is growing (and saving me $$$ from taking it in). For the filter, does anyone know what size nipples a '79 kz650c uses?
And when you cut the main fuel line, do you make one cut and put the filter in there, or remove a small segment of the fuel line to adjust for the additional length the filter creates?

I used the Golan Super-Mini with 5/16" barbs (SKU 1222522 70-312G).

The original hoses were metric, but here’s what I use and it works perfectly. Goodyear 5/16" Fuel Hose SAE 30R7 (required 8") Part # 65123. Here is a link describing it - www.goodyearrubberproducts.com/2012pdfs/...wnloads/page0031.pdf I bought it at www.applied.com/apps/directory/storelocator?r=US&a=20853 Applied Industrial Technologies is nationwide, so there may be an office near you.

For clamping the hoses I use 5/16" spring clamps (see 1st image below). They are a million times easier and quicker to use than the screw type. Some auto stores sell them or they can be easily found on eBay.

I use a Golan Super Mini 5/16" fuel filter; see "70-312G 5/16 Barbed Fittings” at www.golanproducts.com/filters.html#filters-mini for specs. (See 2nd image below). They are not cheap, but one will last a lifetime; I got mine from ronayers.com. They use a stainless steel filter element that can be cleaned. They filter out very small 10 micron particles but still pass fuel at a rate of 6 gallons per minutes – MORE than enough for any bike. They are very small so they fit well under the tank. Also, I used a 5/16” stainless steel elbow to make the bend from the tank to the carbs so there is zero chance of the fuel line pinching (see 3rd image). I got it at a place that specializes in propane supplies.

I suspect all this seems like a lot of fuss over fuel delivery, but it works great, makes removing the fuel tank a 30 second task, and it will last for decades.

One word of warning – having tried numerous fuel delivery setups over the past 40 years the absolute worst product I found is Gates Barricade fuel line. Do not waste your time and money on it as it has an inner sleeve that rolls up like a loose sock and clogs the line when you install it. Ed

Thank you for the through descriptions! That really helps point me in the right direction. Although I'm not sure removing the tank will ever be just a 30 second project. My fuel petcock doesn't have an "off". Just reserve, prime, and main. For the people who don't have an off, what's your process look like for removing the tank? Do you syphon and burn off all the fuel before doing this work?

No fuel should be flowing in the main or reserve settings unless the petcock is faulty. If that's the case it might be flooding the engine.
Steve

SWest nailed it.

Your petcock is vacuum operated, and that vacuum is supplied by the suction drawn through the #2 carb when the #2 piston is cycling up and down. If fuel is flowing from the tank with the petcock in the "run" position and the engine shut off the petcock has a problem that needs to be addressed. Ed

Didn't know that. So if the petcock is in one of those two positions, I can disconnect the fuel line and fuel will not drip out?

Yes, you should be able to, but keep in mind that the engine's poor could be caused by a faulty petcock allowing fuel to flow through the vacuum line into #2 cylinder.

If it was mine I would put the petcock in the "run" position and disconnect the vacuum line. For sure not a drop of fuel should come from it. If fuel does drip from the vacuum line there is a problem with the petcock. Assuming no fuel drips from the vacuum line I would then disconnect the fuel line. Again, no fuel should flow from the tank. If it does there's a problem with the petcock. I wouldn't cut the fuel or vacuum lines because if fuel does flow you want to be able to reconnect the lines quickly. Ed

Sincerely, thank you to everyone helping with this. I'm learning a lot about this bike from just this thread. I have the Golan and new fuel line in my shopping cart, but that's going to have to wait until after my wifes birthday present gets ordered. Happy wife, happy life