troubleshoot suggestions re: two cylinders not firing

1979 KZ 650


I have spark on all cylinders, but after 5 minutes of running difficult, still cold on the left two pipes out. As suggested, I checked the carbs out, there is gas in all of them. I'm certain the two cold ones(both on the left side) are not hitting. Could you please give me suggestions of what I should check next or what might be the problem. Fuel is good. Thanks for the suggestions.

I am sure you know that electrical problems are suggested by problems on 1&4 or 2&3. Your problem suggests carburetors. Anyway, that is the SIMPLE answer... The more complicated answer is that as your bike heats, valve clearances close. If you have lost some compression due to lack of valve clearance, then the cylinders will quit firing.

Have you checked valve clearances? Compression with the engine warm?

If not, that is a good start to eliminate a likely cause.

Next, although you have spark and then don't have spark and the problem seems to not be hitting a single coil, what is the condition of your spark plugs? How about your plug wires/caps. I have seen quite a few bikes recently where the wires had poor contact within the coils. Do you have plugs/points?

Last, although you have gas in the float bowls, how much? Have you set the service fuel level in each bowl? I would do this with the carbs off the bike. I would remove the floats first, with the float needles and blow air into the fuel inlet and be sure air was coming out in equal amount on all four carbs at the fuel seat.

I think you had best do the things in the order I suggest as I put them in most likely to cause you problem order. Good luck!

I appreciate the suggestions..... sadly it leaves me feeling somewhat in over my head at this point. Do I need to take the bike to a "real" mechanic to check compression and valve clearance? Additionally, the bike seems to run hard regardless of temp.... I think the two cylinders are not firing right from a cold start.

I believe the problem shouldn't be the carbs since it was running fine last fall. This problem seems to have generated on its own during storage. I ran Sea Foam through it last fall..... could that have done something in the carbs to foul them somehow?


In answer to your questions, the plugs are brand new. The wires AND coils were brand new last fall from Dyna. The bike used to have points, but I put in a Dyna electronic ignition yet only static timed it last fall.... could timing cause the cylinders to not fire?


I'm sure I can follow the manual through regarding cleaning the carbs with air and checking the service level.... however I have heard horror stories about once apart never getting them to work right again or having to synchronize them. Is there anything I should be careful about or NOT do when taking them apart as you suggested?


Thanks

Well, if you are uncomfortable working on the carbs, contact me through my web site. I DO suggest you check valve clearances and compression. Given your obvious uncomfortable response regarding those items, I would guess they haven't been checked since you have owned the bike. To check compression, all you need to do is buy a compression tester at the hardware store. You have 14mm plug thread and could get a tester that screws into the plug holes but I would get one that has a rubber tip that press fits into any spark plug hole. A tester shouldn't cost more than about $20 - $30 I would guess. Anyway, remove your plugs. Hold the tested firmly in the #1 plug hole and either remove your carburetors or open the throttle all the way and turn the engine over with the starter or kicker. Turn the engine over a number of times so that the guage reaches its maximum reading and record the reading. There may be a release on the gauge to zero the reading. Actuate the release of press the air valve on the gauge tip to get the gauge back to zero and repeat for cylinder #2, #3 and then #4. On a 650, I suspect you should have ~140 psi to ~150 psi with no more than about 10 psi difference between cylinders. If you find compression down, or a variance between cylinders, put a teaspoon of oil in that cylinder and recheck. You can do this for each cylinder. If the compression pops up a lot higher, this indicates that your piston rings are not sealing. MOST compression problems are because the valves are hanging open a tad in the combustion chamber due to lack of valve clearance between the camshaft lobe and valve stem (retainer/bucket actually). To check this, remove your points cover. There are marks on your mechanical timing advance. T & F for both cylinder 2/3 and 1/4. There is a mark on the case at the 12:00 position. Align the T mark for 1/4 with the mark on the case. On your intake cam, there will be TWO lobes where you can now measure valve clearance. One lobe should be pointed up and the other pointed away from the bucket. The other two lobes will be in contact with their buckets. Measure clearance using a feeler guage. Sears sells a Craftsman feeler gauge where the thinnest gauge is .051mm. You will need one this thin in order to measure clearance. If you can not get that guage between the bucket and cam lobe, your valve is VERY VERY likely hanging open and spoiling your compression. If you can get the gauge in or a larger gauge fits between the lobe and bucket, record the value. It will be .051mm or greater in that case. Anyway, once the two intake clearances are measured turn the crank 360 degrees and you can measure the other two valves. Use a 17mm wrench on the inside nut to turn the crank and remember your plugs are still out. It is much harder to turn the crank with the plugs in. I think on your bike, you will repeat this process for the exhaust valve clearances (cam towards front of bike) using the 2/3 marks but you really should have a manual to confirm the exact process.

Honestly measuring clearances is easy once you have done it. If you find you have clearance issues and you probably will, the cams need to come out to replace the small shims under your buckets. I suggest that there might be a KZRider member in your area that would be happy to help show you how to do this or we can work you through the process as it isn't all that terribly hard.

The alternative is to take the bike to a shop. The main issue here will be that most shops won't work on your bike and those that will will tend to be not so hot. MAKE SURE you bring in all the shims needed as the not-so-hot shim will want to grind them to make them fit and not have or acquire the new shims needed. Ground shims tend to break up and will DEFINITELY damage your engine.

I went ahead and got the compression tester..... and ran it on the bike. I got a reading of about 90 psi in each cylinder. I haven't tried the teaspoon of oil trick yet... does it matter whether it is regular motor oil, or should if be the matching viscosity to the engine oil of the bike?

Additionally, I think that I probably didn't warm the bike up long enough, I only warmed it about a minute if that. I think it is good that all the cylinders are within the same limit, but I will re-try when I know what oil to put in it.



Finally, the brand new spark plugs on the two cold cylinders look new still while the brand new plugs on the hot 2 cylinders are black already. Clearly, they are not firing without a doubt.

It is very strange to have an ignition problem on the two cylinders you mention, since they should not both feed off the same coil and ignitor pick-up circuit. If I were you I would double check to make sure that you have the plug wires going to the right plugs. One coil should feed #1&4, and the other should feed #2&3. If that is wrong, then look at your wiring diagram to make sure you are getting things wired correctly.

If you are miswired, fix that first, then start looking at the coil, or the pickup for the two cylinders that are not firing.

Thank you for thoughts, however, I have spark on all 4 plugs regardless of whether they are set up backwards..... and the bike was running fine beforehand. This is the dilema, that I have sparks flying but no ignition. Which is what led me to ask, can timing be an issue, can the strength of the spark be an issue. WiredGeorge ran through what I believe is going to be the problem. I am waiting for his reply as to what type of oil(if any) can be dropped into the cylinders during compression testing.



**... assuming my little knowlegde overall though, is it possible that if the coils were set up wrong somehow, that two of the cylinders wouldn't fire even though they are getting spark?

Post edited by: b4schroer, at: 2006/05/24 14:39

Oil in the cylinders... First, did you open the throttle completely whilst doing the initial compression check? Please confirm that you did. If you did, then one teaspoon of regular motor oil (10W40) will do. Put it in only one plug hole and test, then do the next. If you pull oil in all of them and turn the bike over, the oil in the three cylinders where you DON'T have the tester located will turn into gushers. Don't ask about how I know this hehe

Anyway, if you DID check compression with the throttle open and you find that compression jumps from about 90 to say 140 psi, then you can guess you have a sealing issue with your rings. If you find it doesn't jump up all that significantly, say it goes from 90 to 100 psi, then I think it is time to look at valve clearances.

You have buckets on the top of each valve. If there is no clearance between the bucket and cam lobe, The cam lobe will depress the bucket. This in turn pushes the valve open just a tad and spoils compression which in turn spoils combustion. Checking the clearance is relatively easy so let's work toward that step after finishing with compression testing.

One last thing... I don't recall if you have an OEM points or electronic ignition. Please confirm. In any case, one more easy thing to check is the wiring. Note that on your coils there are two smaller connections (not the plug wires). I think of them as one being the power for the coil and the other the firing signal. This is a little bit of a misnomer BUT works for what I need you to look at... Each coil will have one wire that is the same color on both coils... probably red or yellow/red. This is the "power wire". The other wire will most likely be black connected to one coil and green to the other. These are the "firing signal" wires. The green wire SHOULD be connected to your right hand coil as you sit on the bike and the black to the left. The green wire makes that coil a 2&3 cylinder coil and the black makes that coil a 1&4 cylinder coil. That is, the 2&3 coil should fire the 2&3 cylinder spark plugs and 1&4 coil should fire the 1&4 cylinder spark plugs. Once you have located the coil with the green wire; hopefully on the right as you sit on the bike, ensure that the two plug wires coming out of the coil go to the 2 and 3 spark plugs. The cylinders and hence their associated spark plugs are numbered 1 through 4 and left to right as you sit on the bike. Make sure that the wiring is correct.

I did NOT open the throttle completely, I followed the directions in the box which said to open the choke all the way. I'm sure my choke doesn't match full open throttle. So I will re-check with open throttle and warm the engine up further.


Thank you for the answer RE: oil type.



I have a Dyna AFTER MARKET elec ignition. The bike was originally points...... I will re-check the wiring.


Short story. Last fall some guys tried to steal my bike... (I have a secret switch to prevent that) In doing so, they pried a knife or screwdriver down into my ignition switch(key). They also screwed with the wiring, I believe after they couldn't figure out how to start it. It is possible they could have re-routed my wires... since the coil wires have plugs at both ends. I will check. Thanks







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Quick check found the green wire on the LEFT side coil when sitting on the bike. While the right coil was fed by the black wire. Should I switch them, or just make sure the green corresponds with the right cylinders?

Post edited by: b4schroer, at: 2006/05/24 15:21

I think good news, at worst, progress anyway. So I warmed up the engine considerably. Checked compression in each cylinder and found them roughly between 125-140 psi. This is a slightly low book value, which gives std compression to be between 156-185 psi.

I then put in oil and re-checked each measurement. Each cylinder went above 150psi, one of them maxing at about 162.



Additionally, I found the coils to be fine with the way they are hooked up, except that as Apeman had thought(thank you) I should be sure they were wired to the right plugs. And they were not. On the cold side, the two wires were in the wrong plugs, so when the attempted theft occurred, they must have played with them or switched them on purpose.... and I just assumed they were in their appropriate positions since I hadn't touched them.


So all four cylinders are now firing, which is awesome..... however, I am still wondering what the diagnosis is regarding my compression. Whether that is typical for a 1979 bike, to have a little less compression, or whether that is a bad sign and I need to replace some stuff. Thanks so much for the help, and thoughts.

My pleasure to help out. I love it when a problem starts to get solved, and the bike starts running like it should. Now you are close enough that some fine tuning should put your bike into near perfect running condition.

I leave to others whether your compression is a problem. It sounds okay to me, but then I dont't have the high standards that some around here have (such as our drag race experts). To me, if it goes like mad on the highway, and easily crests the hills, then I must have good enough compression.

Fantastic thread guys. I am having similar problems on my 79 650. Hopefully following this will help me too.