COMPRESSION TEST ADVICE AND SPARK PLUGS TOO

I ran my kz1000 1978 A2 standard model after increasing main jets in the carbs from #105 to #120, pilots from #115 to #120, raised the needle up by lowering the needle clip to position 4 (down one notch).

I rejetted because the prior owner had not changed the stock carb jetting despite doing the following mods to the engine:

- 1137cc kit
- hotter cams
- removed rearmost section of air intake, the stock air filter remains
- Gerex electronic ignition
- 4 into 1 Kerker w/street baffle

I haven't checked valve adjustment yet, but had some time today and did a compression test, and here are the results:

Cylinders #1, #3 and #4: 140psi
Cylinder #2: 138psi

So that's just fine.

Now, here are the 4 spark plugs in order, cylinder #1, then #2, then #3, then #4. NOTE: cylinder #4 is sooty, "carbon fouled" because I discovered the choke plunger on #4 carb was stuck open, needed some lube on its shaft. #4 plug will look fine now, since jetting and compression are the same on all cylinders.

SO WHY is the bike not feeling like a very powerful 1137cc with hot cams, it feels torquey up to 3000rpm then just feels like a regular kz1000 from there. No 'pulling my arms out of the socket' rush.


Spark plug, cylinder #1:


Spark plug, cylinder #2:


Spark plug, cylinder #3 (it's blurry, looks *exactly* like #2):


Spark plug, cylinder #4:

Could be the stock carbs don't flow enough to feed the extra displacement sufficiently to get full power out of it.

If you have a couple running rich it will make it bog down.

Plug #1 actually looks a little lean, #2 looks rich. Quite a range, looks like the carbs need cleaning/balancing.

definitly needs more carb to get the most out of it i'd be looking for 34 or 36 flat slides or at least 33 smoothbores that should liven things up. you definitly need more air flow for that big of a motor.

bountyhunter wrote:

Could be the stock carbs don't flow enough to feed the extra displacement sufficiently to get full power out of it.

If you have a couple running rich it will make it bog down.

Plug #1 actually looks a little lean, #2 looks rich. Quite a range, looks like the carbs need cleaning/balancing.

I've never had a hot rodded motor like this and never thought about the limitations of carbs, thanks for the tip.

One of the first things I usually like to check is points condition and timing, but this has an electronic ignition -- in your mind is there anything timing-wise that could be happening with the electronic ignition?

The timing has a specific advance curve it's supposed to follow, shows in the factory manual.

timebomb33 wrote:

definitly needs more carb to get the most out of it i'd be looking for 34 or 36 flat slides or at least 33 smoothbores that should liven things up. you definitly need more air flow for that big of a motor.

Thanks TB33 -- as a stopgap measure prior to 'investing' in a bank of bigger carbs, I *may* try this:

- switch to individual pod air filters
- go bigger on the the main jets/pilot jets/needle clip
- and go to a less restrictive 4-into-1 pipe

This kz1000 '78 came with a 'Kawasaki by Kerker' 4-into-1 system. I remember this from back in the day. Kerker was hot-hot-hot back then and Kaw decided to leverage the Kerker name and licensed and sold these 4-into-1 systems that sounded as quiet as a stock kz1000, only thing in common with the Kerker we were all buying back then was -- the look and the Kerker name.

This system is like a condom put on a REAL Kerker pipe. It's so quiet even churchgoers will snicker.

I will try maximizing the amount of air and fuel these stock carbs are pumping and use a less-restrictive exhaust. If the rotator cups in my arms are still in one piece after this I'll consider the bigger carbs.

Does it make sense? I figure, with the flat slides or smoothbores I'd STILL need to go with a less restrictive 4-into-1 anyways, why not try this.

cleaning the carbs, going to a hotter plug, are the jets too big, ie. too much fuel?

I thought a good performance pipe was supposed to lean you bike out a little?

Anyways, avoid pods and keep the stock airbox if possible. Maybe try a K&N with some tweaks to the air srew?

Good luck

Something makes no sense???? To go to a 1135 on a 78 motor there are a lot of engine modifications required. Such as re-sleeving the cylinders, and boring the cases to accept the new cylinders. For a motor of that size the stock 78 head will not flow enough to supply the cylinders (after all it was made to supply a 900). So first question is, is the head stock or not? Next thing is!!!!! Why in the He** would someone leave a stock set of 26mm carburetors on an engine which had so much other effort and money put into it???????? I would get rid of those carbs and get a set of more modern BS34s off of eBay, for about 100-150 bucks. This way you do not have to spend the money for smoothbores and get the flow of 31mm CVs. I did that on my 1150 and it runs like a raped ape.
kzrider.com/index.php?option=com_kunena&...ew&catid=4&id=332289

after looking at the plugs, I tend to be leaning towards a bad or weak coil, 2-4 do not look the best with 4 beaing the worst,
have you checked the voltage to the coils and poss checked the coils to see if it may be going bad.
That in itslef could lead to a miss fire under load thus not getting the power feel you should have

BSKZ650 wrote:

after looking at the plugs, I tend to be leaning towards a bad or weak coil, 2-4 do not look the best with 4 beaing the worst,
have you checked the voltage to the coils and poss checked the coils to see if it may be going bad.
That in itslef could lead to a miss fire under load thus not getting the power feel you should have

I agree I would definitely check the spark.

Another thing that I just thought of is; On my 76 900 which has the same carbs, I had a similar problem. What it wound up being was the plungers for the inrichening system, mistakenly called the CHOKE. The seats did not seat all the way and after a couple of miles two of the plugs fouled out. The question is; If you clean the fouled plugs and run the bike than, will it run well for a given amount of time? If so, than that might be your problem.

otakar wrote:

Something makes no sense????........For a motor of that size the stock 78 head will not flow enough to supply the cylinders......Why in the He** would someone leave a stock set of 26mm carburetors on an engine which had so much other effort and money put into it????????

You know, it's not only that he left on the stock carbs. HE LEFT THE STOCK JETTING IN THE STOCK CARBS. With all of these modifications. Sigh.:huh:

The prior owner did all these modifications.
He said he polished the head in some way, probably he polished on the intakes to reduce turbulence of the mixture as it enters the head.

WHY HE LEFT STOCK CARBS ON.

WHY, GIVEN THAT HE LEFT THE STOCK CARBS, WERE ALL THE JETS STILL STOCK WHEN I CLEANED THE CARBS.

I for the life of me don't get it.

*Surely* someone told this prior owner "Hey there, mac, whatcha doin' to the carbs now that you're boring it out and putting in them hotter cams?"

Just incredible, I don't know why he spent big buck$ on cams, an 1137cc kit, electronic ignition, and a 4-into-1 and DID NOTHING TO THE CARBS.

I do NOT know. He's too old now, he was already an older guy when he bought the bike new in 1978, he is OLD now. He doesn't even remember if the thing was sitting for 10 years or 12 years before I got it. Things get fuzzy with time, and age, and I won't bug him.

BUT IT IS *STRANGE*.

It's like having $100 million in the bank and choosing to live in the ghetto.

I'd love to get all the answers but he doesn't remember.