engine not running smoothly on idling

I recommend you buy a Clymer manual. You will note that they suggest doing tune ups in a specific order. There are very GOOD reasons for that order. For instance, if you start by synchronizing the carburetors and have a tight valve which lowers compression, the sync exercise will be a waste of time as when you adjust valve clearances, the vacuum will change making the sync wrong that you had previously done. BUY A CLYMERS. You could also buy a Haynes or factory service manual but the Clymers is easiest for folks who haven't been exposed to bike mechanics previously. Last, I personally would NEVER ride a bike I bought until I did basic maintenance and tune up but thats just me.

I've had a few bikes since 1994, newer though, and always by myself done routine maintanence and other things, such as changing oil, brakes pads, final sprockets and chain, clutch basket and plates, plugs, wires, fixing electrical stuff, swing arm, fork, etc. Also built myself a couple of spooked wheels for my Ducati Monster some years ago...

BUT I have never really been into the engine itself. Must admit I'm a bit scared of these things... Everything seemes som delicate.... :blush:

On this bike I've only checked, changed and adjusted things, such as plugs, oil, sprockets, rectifier, fork dust seals, swing arm, bolts, etc. Didn't want to touch the engine to much, since it runs really well on the road. But some small things are enoyning me...

Thanks to you guys I now feel a bit more secure regarding the engine, carbs, etc. and I will do it the way you have suggested.

Will let you know what's happening... And yes, I think I will buy a correct repair manual.

Thanks and hope you have a great bike season.

/Martin

Hi again

I've now made a compression test. What should the compression be? According to the old manual that I have for z650 -1976, the compression ratio should be 9.5:1. Is that the what I'm looking for?

Anyway, the results was:

#1,3,4 measures 135psi (9,5kg/cm2)
#2 measures 125psi (8,5kg/cm2)

So it seems that #2 has some less compression.
I put a few drops of oil in #2 and the compression rose to 10,5kg/cm2. According to the instrument manual this means that there is something wrong with the piston, ring or cylinder. If the pressure hadn't gone up there should have been something wrong with the valves.

I also checked the plugs again, and #3 and #4 looked perfect. But #1 and #2 looked very sooty. The temperature on the exhaust smoke is also a bit colder than that for #3 and #4, which is lukewarm. I will try to adjust the air screws to lean the mixture a bit.

- Is #2 still within limits would you say?
- Could this lower compression still be due to a vacuum leak in the manifolds? Or is it always something in the engine? I did a simple test with start gas, but with no air leak symptoms.
- Could the uneveness at idle speed be due to this lower compression on #2?

If it's okej to ride with this difference, I think I wait until next winter to take the engine apart... Is there anything I could try to get higher compression without taking the engine apart...?

/Martin

Not sure how carburetors can be sync'd by eye. They are not synchronized until you use a manometer to ensure that the vacuum levels are the same.

First, I would recommend you buy a Clymers manual which tells you which tools are required. They also suggest tuning the bike in a specific order. The reason for the order is that there is no point in doing some tune up steps to correct a tune up issue that should have been done first. For instance, if you sync the carbs THEN adjust valve clearances and find one of the valves has very tight (actually no) clearance, once the clearance is adjusted to spec, it will change the compression and hence the vacuum produced by that cylinder and make your carb tuning wrong.

Lots of folks on this site want to recommend very specific tuning techniques. I dislike doing this if the basics are not correct.

In general, the cam chain should be tightened (on a bike equipped with a manual tensioner) and valve clearances checked. Lack of valve clearance can make compression go way down because valves are held open. You have shim under bucket type valve train. The shims are used to adjust the clearance between the cam shaft lobe and valve. To adjust, you will need basic hand tools (wrenches/sockets, etc), a set of metric feeler gauges and spare shims. The shims on your bike are about the size of a dime and vary in thickness. Z1Enterprises sells a "kit" with a variety or you can do your checking and then order the shims needed. Anyway, a set of GOOD metric feeler gauges is critical. I use an old set of Craftsman where the thinnest blade allows checking minimum clearances. A shop manual will describe the method of checking and adjust clearances.

Once valve clearances are checked, check compression. If you have compression that is outside service spec, this indicates internal engine work needs to be done. If you have compression within service spec, you are pretty much good to go.

Sounds like you have a Dyna S? To adjust timing, go to the dynaonline.com website and download their detailed instructions. They are pretty good. Once you have verified timing, you shouldn't need to do it again. It would also be a good time to check coil voltages and for instructions on this and rectifying low voltages, you can see the tech article we have on our website under wg's Tech Stuff Index. The article is called Coil Repowering or something along those lines.

Last, the carburetors. I see lots of talk about do this or that but the first step is to adjust fuel level. You Clymers will describe how to use the SERVICE FUEL LEVEL spec and check fuel level and should have pictures of the technique. There has been plenty written in the carb forum on how to adjust fuel level using a clear plastic hose and inexpensive 1/4" plastic vacuum adapter. Next adjust idle mixture. You have either pilot mixture screws or air screws. The pilot mixture screws on VM carbs are underneath on the engine side. You need to allow the bike to warm/idle and adjust each screw for max idle speed. Start at about 1 1/2 turns out and turn the screw 1 turn either way. Sometimes, adjusting has absolutely no effect and this is NORMAL. Just leave this screw at 1 1/2 turns out. After the idle mixture is set, the carbs need to be synchronized with a manometer. This gauge measures engine vacuum and in your case, the opening of the slide affects how much vacuum pressure is measured. The bike is warm and idling and you will put vacuum hoses (connected to the gauge) on the four vacuum fittings on your carb holders. (by the way, I would replace the carb holders if you don't know their exact history) Having previously loosened the locknuts on the slide sync adjusters, you turn the slotted screw to adjust each carb in turn to make it the same as the others. In general, most vacuum gauges will show about 20-25 cm/in (hope the cm/in designation is correct... can't recall for sure) but anyway, most gauges will read between 20-25 when all four carbs have the same vacuum. Rev the engine to ensure that the setting stays the same and if it does, remove the vacuum gauges and recap the vacuum ports and tighten the locknuts while holding the slotted screws exactly in place. Last, go take a ride of a mile or two and then set the idle speed using the idle adjust knob.

I would also consider changing brake fluid and bleeding the brakes, checking the chain/sprockets for wear and alignment and checking the tires for wear and last, tightening every fastener on the bike. All these things are discussed in the Clymers manual. This stuff sounds like a lot of work but it is really a weekend project and once you have the procedures down, less than that.

At kz.info it says that the compression pressure for kz650 1977-1980 should be 155-185 p.s.i. (10-14 kg/cm2). This is what I measured on #1,3 and 4. The #2 was 8,5.

Is these figures to low or okej, would you say? Is 9,5 okej and is 8,5 okej comparing it to 9,5?

Thanks for your recommendations, wiredgeorge. I really appreciate it. Some of them, like checking bolts, brakes (pads, fluid, bleeding), sprockets and chain, tyres, forks etc. I have already checked. But the other stuff is great to know. And yes, I intend to buy the correct manual for my bike...

Yes, it seems that I have a Dyna S then. It looks the same on my bike. I also red your article on "Repowering ignition coils to get full power". When I get some money I will also buy some new manifolds, just to make sure there is no leaks. The ones I have now have been fixed, and even though I have made a test with start gas, one can never be sure.


/Martin