TOPIC:

Hey everyone, so i've been working on this 78kz1000 with vm26ss carbs for 2 months so far getting it back to tip-top shape after sitting for about 4 years. Here's what's happening:
1) It doesn't seem to be running on all 4 cylinders. If the plug wire is taken out of 4th cyl it doesn't effect idle. And 1st cyl barely changes anything also if taken off. 2)The idle seems to be very rich, plugs come out very black and the 4th cyl comes out slightly wet with gas.
3)I adjusted the timing(Dyna-S) as close to 100% perfect as I can get it.
4) I rebuilt the carbs and checked cam lobe gap which all checked out within range. The carbs aren't 100% synced but by researching it looks like I should wait to do that until the firing problem is solved.

Did a compression test which they all tested under 130 and if I put a little oil in the spark plug holes all the readings spiked. I guess the question is, is there anything this is all pointing to and/or where should I start?

A Compression spike with oil added indicates bad or worn rings. However, if you had consistent readings on all 4 cylinders, the low numbers could be a results of your testing procedure. Were the carbs removed or held wide open throttle?
Because your problem is with cylinders 1 &4, I would suspect a coil/spark issue. ! & 4 share a common coil. If possible, physically swap coils and see if the problem moves to 2 &3.

MDZ1rider wrote: A Compression spike with oil added indicates bad or worn rings. However, if you had consistent readings on all 4 cylinders, the low numbers could be a results of your testing procedure. Were the carbs removed or held wide open throttle?
Because your problem is with cylinders 1 &4, I would suspect a coil/spark issue. ! & 4 share a common coil. If possible, physically swap coils and see if the problem moves to 2 &3.

All of this plus check you voltage at the coils.

130 might be a bit down but on a bike that has been asleep for 4 years I would run a couple of tanks of fuel through it on the road and then retest. I used a bit of carb cleaner in the fuel and it helps free gummed rings.

Your CR will always spike if you add oil for a 'wet' test, much more noticeable than a car with bigger pots. Your high 'wet' test actually confirms valve seats , head gasket all ok.

I'd balance the carbs, you may be so far out that one cylinder is shut oiff at idle.

Also swap the plug leads and see of the fault transfers to the other cylinder - to eliminate ignition issues.

And clean the carbs.

Rule out the valve adjustment before going any farther.
Steve

and checked cam lobe gap which all checked out within range

he's done it already- one of the first things to look at agreed.

130 psi on a bike that has sat for the last four years is excellent compression. That's not the issue.

Most likely the issue is related to the carbs. Float needles sticking, fuel level too high, etc.

If the bike has been modified in any way that can throw a wrench in the works too, airbox delete in particular.

Cylinders 1 & 4 are both fired from the same coil. Install new spark plugs and swap coils with the 2 &3 coil and see if the problem moves to different cylinders.

As far as adding oil to the cylinders and seeing an increase in compression - that will ALWAYS happen - even on a brand spanking new engine, so I wouldn't place much faith in that as an indication of a compression problem. Take a look at the link below for a full explanation as to why this is true.

If you still believe you have a compression problem perform a leak-down test. If there is a compression problem it will help you identify where the problem is. remember -compression issues are not always piston ring related. Ed

www.kzrider.com/forum/2-engine/603190-kz...ild-questions#734187

MDZ1rider wrote: A Compression spike with oil added indicates bad or worn rings. However, if you had consistent readings on all 4 cylinders, the low numbers could be a results of your testing procedure. Were the carbs removed or held wide open throttle?
Because your problem is with cylinders 1 &4, I would suspect a coil/spark issue. ! & 4 share a common coil. If possible, physically swap coils and see if the problem moves to 2 &3.

If you add too much oil while doing the "wet" compression test, the pressure will go way - WAY up....never add more than 5 ml per cylinder!

Are you using the correct 3 ohm Dyan Coils and wires? If you are using the stock coils, the ignition will intermittently cut out, and you will eventually damage the Dyna S. My guess is there is a problem with carbs 1 and 4 - with the idle circuits.

Hey everyone thanks for the input, much appreciated. When I performed the compression test I got the engine up to temp and with throttle held open all the way and all plugs taken out tested it. I did another one today along with some other tests but for the comp tests they came out the same:
Cyl 1--136 Cyl 2--105 Cyl 3--145 Cyl 4--140
I know they isn't supposed to be more than a 10% between all readings so looking at this Cyl 2 is out of wack. I ran about 2 gallons of gas through with seafoam before starting any tests today and couldn't notice a difference between before and after. As MDZ and MadShad suggested I tested and swapped the coils but to no avail. They both read 3.8 ohms and cyl 1-4 still don't affect the idle if covered up at the carb intake. Not sure if these are completely safe for the Dyna and being a perfectionist i'll begin saving up to get the right coils. (Green Dyna ones I believe?)
Also taking up Tyrell Corp on his idea to balance the carbs because they might be the whole issue, I attempted to do so but with...Odd things preventing me. The needle at idle on all cylinders wouldn't go past 2 psi. The needle did however fluctuate rapidly between 2-13Hg on cyl 2&3 and between 0-10Hg on 1&4, which i'm not sure what to think there but i'll be researching a lot tonight. I'm almost 100% certain the cylinders all fire fine when revved up but at idle there's definitely a problem.
Also an important side note: I rebuilt the carbs a couple weeks ago and had ordered all parts from z1Enterprises but didn't pay 100% attention to the size main jets I put in, so the carbs are clean but I will be taking them off either tomorrow or this weekend to double check everything internally. As Nessism pointed out yes the factory airbox has been replaced with K&N pod filters, but they've been off during all these tests if that matters. I'll be posting up 2 videos of it starting and running in a bit, have to upload to computer first.
Thanks guys!

Some carb banks have a lead carb. Non adjustable. If not, bench sync them then choose one as the lead carb and match the others to that one. If your idle screw is in the middle position, you should be able to raise the idle when it falls and keep the motor running long enough to finish the sync. Last time I adjusted my needles, my lead carb showed 2 while the others were way up. It was popping as well. It can be a PITA but after a few tries I got them all close enough to run well at idle.
Steve

Compression = lowish but even and not problem - will likely improve with use and a thrashing.

vacuum guages showing inner bank running out of synch = needs adjusting, a couple of screw turns, easy.

plugs black, one wet = very rich mixture, recheck the carbs, filter(s), jetting, fuel level....modifictions by PO .

Some carb shennaigans to be expected on a bike stoodup for years.