Theory Post... Running bike on 3 out of 4 cylinders

Hey y'all

So I'm on a trip on my 1980 kz550 and ran into some issues with fuel mileage. I filled up at the pump and filled 3.2 gallons to 60 miles. I am glad I decided to stop because I almost ran out! This alerted me to an issue. So today I stopped by a mechanic and did some testing. First, I thought the boot on the first cylinder spark plugs was faulty as it was falling off over and over. Then, I thought that the high tension lead was arcing because the previous owner did a messy job splicing wires. After patching the issue and switching leads, (1&4) the problem still persisted. Our solution to bettering the high tension lead did work however so hurrah!

I ended the day with a finger compression test (nobody seems to have posses screw in testerd to these spark plugs holes, are they 12 or 10 mm???) And could hold my finger down even as the bike ran on 3 cylinders. Bingo! Obviously this is the least desirable finding some 500 some miles from home. I can make it to a neighboring town where I have some friends--about 150 miles and might be able to get my hands on a compression tester. Regardless, I plan on riding minimally each day and only in the early mornings because I would like to get home and do not want to open the engine away from home. And this way, I will still enjoy a bit of a trip. I have ample time so I am not terribly concerned about riding 50-100 miles a day if I have to.

Here comes the question, a couple of beers in, I am thinking about unscrewing the throttle connection to cylinder 1 so I do no send gas through there and thus save on gas mileage. (20mpg on a 3.5 gal tank is less than ideal). I could see there being an issue with the exhaust affecting cylinder 2 but besides that I do no see why this would not be a terrible idea. What are yall's thoughts? Obviously this is not an ideal situation; returning home is the priority.

I have attached some pics for reference because it was fun to fix an issue that did not necessarily end up as an issue (the fix powered cylinder #4 when I switched the caps). Obviously it was not ideal to have electrical tape insulating spliced high tension leads.... Any thoughts, comments and questions are appreciated since I do have a distance to go and want to be as safe as possible for myself and the bike!

If one cylinder is not firing that problem should be corrected before you ride any distance. Think of it this way - if a cylinder is not firing but fuel (a lot or a little) is being drawn into that cylinder but not burned that unburned fuel will wash the oil off the cylinder walls as the piston goes up and down. The result will be that the piston rings will come in contact with the cylinder walls, and this can lead to cylinder wall (and maybe piston ring) damage. If you plan to ride the bike long distances the damage will very likely be severe enough to that cylinder that you will need to take the engine apart and repair it. If it was mine I would correct the problem before I rode the bike again rather than risk damaging the engine. Ed

With that bike you should be getting about 50 mpg, not 20. Definitely things not right.

You will not get better mileage by removing one cylinder. The amount of power required to propel the bike at any particular speed is the same, so you will just be revving the bike higher to get the same power from three cylinders that you would normally get from four.

How long since the last time you adjusted the valves? In case you don't know the valve clearance goes down with mileage and eventually compression will be lost and the valves will burn.

Regarding your coil wires, they should be fixed properly or the coils replaced. Typically the coil wires can be pulled out or screwed out of the coils. They fit down into a little tunnel with a spike on the end. You may need to dig out the wire with a pick tool but it's a doable project. The bike uses 7mm copper core HT leads which can be purchased at Z1 Enterprises and the like.

Valves were checked before my trip. About 600 miles ago or 3 weeks. They were on the tighter end of the spectrum but within the clearance. I've been riding in the southwest US and it has been getting hot and my pipes have been bluing a bit. It would not surprise me if the bike is running lean. Now, I suspect it is a valve issue but will know later today when I can do some compression tests. And yes, new leads definitely. I'm just not in the best physical location to address any problems.

Unfortunately I was in a remote town when I found the problem and am riding about 100 miles to get to a bigger town where I also have some friends.. hence the post and my question about disabling the throttle to 1 of the cylinders.

I understand that it's not ideal to ride and am planning to arrive before it gets too hot to mitigate issues but I think this is better than being stuck in a 400 person town. So far the bike is running fine-ish and I am about halfway there. I am happy for that. Who knows how happy I will be as a mechanic later though.

Not fun to be long way from home and get problems, on other «side» its exsiting riding a old classic bike on long trips when its working and you feel a satisfaction when things is working and you have worked on the bike you self!

Keep up the motivation!
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