New bike - 2 of 4 cylinders

I picked up an old beaten on 1982 KZ750 LTD (I think). It was not running when I got it. It would start on starter fluid but not on gasoline. So I attacked the carburetors.

I got them apart and they were atrocious. With a bit of work and a lot of ChemDip and GumOut, I got the things cleaned up. It starts! It idles! I drove it home (30 miles) and it kept running!

Now for the bad part. It starts hard. It idles rough. I idled it for a while and was mucking around trying to figure out why it was running so rough. I noticed an interesting problem. The passenger's side pipes were hot and the driver's side were cool enough that I could rest my hand on them.

I pulled the plugs and checked for sparks. They have them. The plugs looked black and slightly moist.

I had just gone through the carburetors and I verified that the float bowls are filling up just fine.

I sprayed carb cleaner into the outer one and it caused the engine to accelerate as expected.

I pulled both plug wires off (with plugs in position) and the bike would not start or idle at all.

As a relative newbie to motorcycles and especially to the KZ750, I hope you guys can shed some light. Thank you.

very nice post like this forum




envisionwebhosting web hosting reviews by envisionwebhosting
actualtests actual tests
actualtests ccna actualtests ccna
actualtests 642-813 actualtests 642-813
actualtests 1z0-052 actualtests 1z0-052
actualtests 70-640 actualtests 70-640

Which two aren't firing? If 1 & 4 or 2 & 3, the problem could be w the ignition, perhaps one of the coils.
I know you say you have spark, but I had a similar problem: spark, but intermittent firing on 2 cylinders, so....

Something you can try is to redo the spark plug wire connections at all points. The wires untwist from the coils & spark plug caps. On the coils unscrew the ribbed compression boots, then untwist the wires if they don't come off w the boots. If the wires have the white crusty oxidation, nip off the ends a tad (but not too much as they could end up too short). The connections become poor from oxidation.

I checked for spark in a darkened garage at night & it looked good to me, but doing the above solved the problem.
If they are the original spark plug wires, you probably ought to go ahead & replace them. Some say the stock coils aren't that great anyway, so you could replace those as well.

martin_csr wrote: Which two aren't firing? If 1 & 4 or 2 & 3, the problem could be w the ignition, perhaps one of the coils.

It is the two on the driver's side. I would guess that is 1 and 2, but I am not positive how the cylinders are numbered on this bike.

martin_csr wrote: I know you say you have spark, but I had a similar problem: spark, but intermittent firing on 2 cylinders, so....

Something you can try is to redo the spark plug wire connections at all points. The wires untwist from the coils & spark plug caps. On the coils unscrew the ribbed compression boots, then untwist the wires if they don't come off w the boots. If the wires have the white crusty oxidation, nip off the ends a tad (but not too much as they could end up too short). The connections become poor from oxidation.

I checked for spark in a darkened garage at night & it looked good to me, but doing the above solved the problem.
If they are the original spark plug wires, you probably ought to go ahead & replace them. Some say the stock coils aren't that great anyway, so you could replace those as well.

Good point, it is never a bad time to check contact with the coil and the quality of the wires themselves. I will bring my multimeter out to the garage with me and check the wires as well as visually inspecting the connection at the coil end.

Martin's suggestion is a good place to start. If you're still having problems after that, I'd do a compression test to see if you're within spec on all four cylinders. If you're low on your first two (they are numbered left to right), that could be the cause. If your compression all checks out, it may be a tuning problem with the carbs, depending on if you set everything back up after you cleaned them. You didn't say if you did or not. On the carb end, start with the "clear tube test" to set your fuel levels in the carbs correctly, that being too far off will cause you to be too lean or too rich to get ignition. Patton has a good write-up on this, but basically, get a piece of clear hose on your carb drain, let it drain and measure from how far up the fuel is in the tube, to the joint of the carb and bowl. It needs to be within a certain distance, depending on your carbs (need to check the spec in your manual for your specific bike).

Del_Herring wrote: do a compression test to see if you're within spec on all four cylinders. If you're low on your first two (they are numbered left to right), that could be the cause.

I should have mentioned this in the first post. I did a compression test and the first go, all except the left-most cylinder were fine (100+) and the left-most cylinder was 25. However, after I got it idling the first time, I re-did the compression check and the left-most cylinder was up to 100. I figured the cylinder must have gone dry as the bike was sitting for a while.

Del_Herring wrote: If your compression all checks out, it may be a tuning problem with the carbs, depending on if you set everything back up after you cleaned them. You didn't say if you did or not. On the carb end, start with the "clear tube test" to set your fuel levels in the carbs correctly, that being too far off will cause you to be too lean or too rich to get ignition. Patton has a good write-up on this, but basically, get a piece of clear hose on your carb drain, let it drain and measure from how far up the fuel is in the tube, to the joint of the carb and bowl. It needs to be within a certain distance, depending on your carbs (need to check the spec in your manual for your specific bike).

I bought clear plastic hose last night so I will do the clear tube test as well. I don't yet have a manual for the bike but am bidding on ebay for one right now.

When you cleaned the carbs, did you completely disassemble them? Remove all the jets? Shoot carb cleaner and compressed air through ALL the passages? Replace the o-rings and gaskets? Verify that the jets and needles are the correct ones for your bike? Inspect the slide diaphragms for tears or holes? Are the carb holders between the carb and head in good shape, no vacuum leaks there? All these things need to be done/checked when working on old carbs that have been sitting a while.

Because your engine accelerated when you squirted cleaner into the carbs when the engine was running tells me you have adequate spark in that cylinder/s.

Get a FSM and keep digging. Let us know what you find.

TomW wrote: When you cleaned the carbs, did you completely disassemble them? Remove all the jets? Shoot carb cleaner and compressed air through ALL the passages?

Yes, yes, and yes. The pilot circuit was a pain to get to all of the openings, but I eventually got it squirting through nicely. There are only the two removable jets that I could find and I cleaned them and can see through them very nicely.

TomW wrote: Replace the o-rings and gaskets?

I am using the old float bowl gaskets and float drain plug o-rings. Are there additional o-rings and gaskets beyond these? They were all I saw. I found new float bowl gaskets on z1enterprises that I plan to buy. I wish I could find a source for the float drain plugs as those are not in great shape right now. I swear the P.O. must have been an orangutan and he stripped all the screws.

TomW wrote: Verify that the jets and needles are the correct ones for your bike?

The jets and needles are at least the same as the other cylinders. The jet sizes I have are a 62 and a 125.

TomW wrote: Inspect the slide diaphragms for tears or holes? Are the carb holders between the carb and head in good shape, no vacuum leaks there? All these things need to be done/checked when working on old carbs that have been sitting a while.

I did not see any tears or holes in the diaphragm and it does respond in a "cushioned" manner when I manually depress and release the slide. I sprayed WD and Carb cleaner around the boots and am not getting any response so they must be sealing reasonably.

TomW wrote: Because your engine accelerated when you squirted cleaner into the carbs when the engine was running tells me you have adequate spark in that cylinder/s.

Get a FSM and keep digging. Let us know what you find.

I will try and get my hands on the service manual as soon as I can.

Sounds like you got everything right in the carbs. Was the air box in place when you were running the bike? CV carbs need a good vacuum signal to operate correctly. Are the valve clearances in spec? A tight intake valve will cause a low vacuum.

TomW wrote: Sounds like you got everything right in the carbs.

Glad to hear that. I am a relative newbie to bikes and carbs, but they seem simple enough.

TomW wrote: Was the air box in place when you were running the bike?

The bike did not come to me with an air box. I am planning to put pods on it since I can get 4 pods for around 20 dollars on Amazon. I was hoping to at least get confirmation that the bike can run properly before sinking much cash into it.

TomW wrote: CV carbs need a good vacuum signal to operate correctly. Are the valve clearances in spec? A tight intake valve will cause a low vacuum.

I just found a download manual, so I will try to check the valve clearances soon, perhaps tonight. Is the only way to adjust them by replacing the shims? Is there an easy source for those shims?

In relation to needing a good vacuum signal, Pod filters are going to give you problems. You can get them to work on CV carbs, but you may spend as much on pods and jets as if you just got a stock airbox, because you'll need to jet it to run right with the pods or it'll end up really lean.

It is possible that it was already rejetted, since you got it without the box, who knows what the PO did. Might take a look at the jets in the carb and see if they're the same size listed in your manual. Should just be stamped on the top or side of them. If they're a higher number than listed as stock(richer), you may already be set up decent for pods. Otherwise, expect to spend some time jetting. I can find airboxes for about $50 for my bike, not sure on yours, may end up being cheaper to get the box.

On the initial low compression, you may have had a valve that wasn't quite seating right from sitting a long time, if it's doing fine now, I wouldn't worry about it.

For valve adjustments, it's all done by replacing the shims. Kind of a pain because you'll have to remove the camshafts to do it. I believe Z1 enterprises stocks shim for the KZ's. Some are a little harder to find than others, but give them a call. If you aren't sure, they'll be able to make sure you're getting the shims you need.

Do a forum search on CV carbs and pods. I'll think you'll find that the bike can't run well without an air box or pods with a lot of time and effort put into tuning. If it was mine I'd look high and low for an air box before putting on pods. Then when you get it running well, put the pods on and start your learning curve on jetting.
In the meantime double check valves, compression, ignition and timing to make sure everything is right. Carb tuning is the very last thing to do when trouble shooting a poorly running engine.

An engine needs 4 things to run well. Air, fuel, spark and mechanical integrity, it has to be put together and adjusted right. Do that and she'll run sweetly and fast. IOW get it to run well in stock trim before modifications are attempted.