Problem, is it intake reversion?

Yes, sorry if I was not clear, I was speaking of needle position, not the clip. I moved the needle up and it was richer and ran worse, the blubbering rpm band got bigger. Could it be the transition from midrange to main jet? If so what might I try? Fuel levels were set with the clear tube method. The carbs were rebuilt by WG and rechecked by me.

Here is a followup. The bike has just never had nearly the power I felt it should for the modifications done and the blubber in the middle of the rpm band was a real PITA. I have seen a number of threads complaining about this with never any resolution. So, I pulled the head and epoxied up the ports following the instructions at www.mototuneusa.com/ using the 65% rule. I put the engine back together and it ran MUCH stronger. The 5K blubber was reduced to just an instant "miss". I have been a gearhead for 40 years working on sports cars, bikes-2 and 4 stroke, boats, and small airplanes and am ashamed to admit I have been reading plugs wrong! After reading this link www.empirenet.com/pkelley2/sparkplugreading.html I leaned out my carbs (everyone kept telling me to go richer). I had already machined adjustment grooves in the needles and dropping the needles down a notch really put me spot on. The 5K spot was gone! The bike runs very crisp through the entire rpm range. Plug chops from WOT look good as do chops after cruising at 60 mph. The bike had been very weak above 100 mph, now it is still pulling hard at 130 when I backed off. I now have to fix a front wheel imbalance that shows up above 100 mph:)

That's interesting, the Mototune epoxy deal on a 2 valve motor.

I know a racer in Australia that tried it, killed ET and MPH. He didn't go to 65% but only epoxied up the SSR a bit to see if he could pick up CFM.

It did pick up a few CFM on the flow bench however.

After a weekend of going slower, he yanked the head back off, removed the epoxy, ET & MPH picked right back up again.

Combinations are everything. If it works for you, then Great!

Glad you got your bike sorted out. Enjoy it!

I'm going to put some putty in a stock port this week and duplicate the 65% Motoman setup. That's taking a stock 30mm runner down to 23mm right at the SSR. It's got to absolutely kill airflow.....I'll let you know shortly.

Another odd thing.... 100 MPH should be about 6300RPM [give or take depending on your tire]. At that RPM with those cams on 108 lobe centers, it should have been pulling strong, even with a stock head.

Larry C





Exitpupil wrote:

Here is a followup. The bike has just never had nearly the power I felt it should for the modifications done and the blubber in the middle of the rpm band was a real PITA. I have seen a number of threads complaining about this with never any resolution. So, I pulled the head and epoxied up the ports following the instructions at www.mototuneusa.com/ using the 65% rule. I put the engine back together and it ran MUCH stronger. The 5K blubber was reduced to just an instant "miss". I have been a gearhead for 40 years working on sports cars, bikes-2 and 4 stroke, boats, and small airplanes and am ashamed to admit I have been reading plugs wrong! After reading this link www.empirenet.com/pkelley2/sparkplugreading.html I leaned out my carbs (everyone kept telling me to go richer). I had already machined adjustment grooves in the needles and dropping the needles down a notch really put me spot on. The 5K spot was gone! The bike runs very crisp through the entire rpm range. Plug chops from WOT look good as do chops after cruising at 60 mph. The bike had been very weak above 100 mph, now it is still pulling hard at 130 when I backed off. I now have to fix a front wheel imbalance that shows up above 100 mph:)

There is a strong possibility I did something wrong when I ported it originally. I have delt with textile dryers (read 2'-4' ports)and have used pitot tubes etc but race head porting is not my expertise. Although I spent many hours getting each runner tapered right and the same as the other three. Larry, I would eventually like to get a head done by you and some bigger cams too. Interestingly the mototune guy says the epoxy ports will not show the best on the flowbench, but is as you said-part of a system. He says that the flowbench does not properly duplicate the many variables of engine induction. Anyway, the bike puts a big grin on my face when I ride it now. And I discovered I have a front tire out of balance which is the reason I had to back out of the throttle at 130.

ExitPupil - First of all I want to thank you for the EXCELLENT article on plug reading. I've also been a gearhead for a while and I learned a lot from that article. I also came across the mototune site a while ago so...

Second, I came to a similar conclusion about intake ports and D Shaping but I made my D Shapes removable for side by side comparisons on the street, track and dyno. Here's a quick rundown of what I did:



The combination: 1075, drop-in-cam 0.365 lift, RS34s, pods, V&H megaphone with homemade 2.5" comp baffle and ported head.

The fist row of images shows the removable D Shape. It is made form a piece of perforated metal sandwiched inside two layers of epoxy putty. It's held in place with a machine screw that passes through the intake port runner and threads into a SS nut (not shown) that is also sandwiched into the epoxy and perfed metal. Notice the hole on the bottom of the D Shape (last image of the first row)

The second row of images shows a before and after of the bowl from the combustion chamber.

The third row of images shows a before and after of the port opening.

The port is 32mm at the opening. Choke point is 30mm open and effectively 25mm with the D Shapes installed. The D Shape reduces total port volume by about 18%.

The result: MUCH better throttle response and mid range torque with the D Shapes installed and peak HP numbers were comparable on the dyno (through a drive shaft) 97RWHP with open ports and 94RWHP with the D Shapes installed...but those numbers don't tell the real story. The open ports only made more power above 8500RPM. Below that, the D Shape ports made more power with a broader torque curve and higher peak torque (65lbft D shape ports - 61 open ports).

Also, The D Shape ports experience less reversion in the mid range and provide a better signal at the carburetor jet. Therefore they require a leaner needle jet setting.

I haven't done a side-by-side at the track yet but it doesn’t matter too much to me because this is really a street bike. It might post marginally better number at the track where the engine needs to be constantly spinning between 7000 and 10000RPM. But on the street, where 95% of my time is spent below 6000RPM there's no comparison. With the smaller ports, this engine will pull STRONG in top gear with no hesitation or flat spots from 40MPH to 130+ What it really needs now is another gear.

Big open ports might work well on a big block, big cam, 1/4 mile bike but in my experience, port velocity and choke point are crucial for a mild performance street engine.

An easier way to accomplish all this with a stock KZ head is to carefully blend the ports to match the carbs and perform a professional 3 angle valve job. Then leave it alone and concentrate on cam, carb, ignition and exhaust tuning.

Great info Dave and very clever experiment. I agree with your advice too. I don't have the valve job yet, that comes this winter. My epoxy starts at the beginning of the runner where I had port matched it to 34 mm carbs so it has a slight ramp up then D shaped the rest of the way. My pinch point at the SS radius is a tiny 24mm and it pulls strong to 10K which is my shift point. Unexpected was a perceived slight loss of power under 3k?? But it is great everywhere above that. You can tell by the grin in this picture!


Steell- In rereading the post sorry I missed your post. I had an Edlebrock A/F mixture monitor with the sensor just behind the collector. It does not seem to respond fast enough to catch a quick blip, but it was 12:1 pretty much all the time, any rpm and throttle setting except deceleration. The pipe I have now does not have a sensor hole so I just read the plugs.

Dave,

You do really nice craftmanship. Really, I mean that.

I think what you guys are running into is simply a case of over carburetion for the size of your engines. That's why port reduction helped your bottom and middle but took HP away from the top.

A 1075 motor with stock head IMO doesn't need anything larger than a 31mm carb to feed it. I don't like 34's on KZ engines on the street until you hit 1200cc at least. Other's can agree / disagree....everyone has their own preferences, experiences and opinions.

Looking at the port photos, I can pretty much tell you within probably a few CFM what the head flowed without epoxy in the port.

I've read the Motoman website before...had discussions with other professionals regarding the process.....left the door open for conclusions on a case by case basis. Opinions are best formed after applying testing and science.

Epoxying up the port floor is nothing new. Motoman certainly didn't invent it. He simply advocates it's use. In some situations, there are benefits, in other situations it just plain doesn't work out.

Had you dynoed your bike, then shipped the head out and then dyno tested again to find a few peak HP losss.....well, most would not be very happy;) This of course says nothing of the lower RPM gains you achieved.

I've been wanting to try it out myself but I felt from the beginning it was not going to be worth the effort on the types of engines I do for most guys. I'm really glad you gave it a whirl and posted your pics and dyno results. Posts like this are very productive. If the Internet overall was comprised of such intelligent, informative posts, I'd find it hard to drag myself away from my computer. This thread is one of the best threads I've read on any forum this entire year related to motorcycles.

Excellent work from both of you. Congratulations on your objectivity and your approach to engine building.

Best Regards & many thanks for your posts,

Larry C

Larry, in addition to the over carb size, wouldnt the cams come into play, Ididnt notice anything about how the cams were degreed, and the valve lash
I was wondering if moving the cams forward or backward a few degrees would have changed the condition.
Granted the ports and the shape play a large part in the power band, and the over all performance.

Several years back the big bang theroy was to add dimples in the ports, the thought was that it kept the air/fuel in a better state of mix, have you ever tried this?

Sure the cams come into play. Nobody tried advancing both cams to put bottom end in the motor from what I gather.

I'd like to build 2 similar KZ motors. Both the same size and with the same cams. Difference being one epoxied up port job and one of my normal port jobs that flows significantly more air. Put any carb you want on the epoxied up head and I'll put 31mm Keihins on the traditional ported head. Then dyno them and ride them for a comparison test.

That would be a very fun project IMO.

I forgot to comment on the dimples. I don't use them in these heads. However, textures, even ribs, have been used for many years to get the air to grab the surface and help it turn. There are valves out there with dimples applied that can be purchased for some of the car engines. I'll try to find you the link and post it.

Look inside some old V8 cast iron manifolds and you'll see ribs on the floor.

Very shiny ports can cause the fuel to puddle and believe it or not, even flow losses.

larrycavan wrote:

Epoxying up the port floor is nothing new. Motoman certainly didn't invent it. He simply advocates it's use. In some situations, there are benefits, in other situations it just plain doesn't work out.

Thanks for the compliment about the craftmanship and definitely agree about D shaping and mototune. But he isn't the only one that got me thinking about it. Check out www.bertaut.com/gsengine.html He's an old timer that specializes in GS1100/1150s hot street and drag bikes. He was doing epoxy D shaping in the early 80s. I also a have an old motocycle article where Rob Muzzy is extensively interviewed about the mods he made to Eddie Lawson's AMA KZ1000 superbike. He reviels A LOT about what he did to the bike and in the process mentions D shaping the intake ports, maintaining a tight choke point, and spends most of his time discussing combustion chamber and exhaust design! He actually goes out of his way to downplay the importance of camshaft specs...It was also believed that his KZ dominated in the early 80s because of its mid range power and broad, flat torque curve. I will post this article when I have a chance.

Here is an excellent site for calculators to help with engine design and 1/4 mile stats. www.wallaceracing.com/Calculators.html The engine calculators are set up for units in cubic inches but they will work fine for any engine as long as you do the inch-mm conversions. Many of these calculators are derived from a program called Pipe Max written by Larry Meaux - The same guy who wrote the excellent article on reading plugs!

Check out the choke point calculator www.wallaceracing.com/chokepoint-rpm.php This will calculate the optimum choke point area for maximum torque/VE. You must provide bore, stroke and desired RPM for peak torque (Notice how cam shaft specs and carburetor size are not factored in...) 6000RPM is a good place for peak torque on a street bike. According to this calculator optimum choke point area for a 1075cc engine (2.6 inch stroke and 2.8 inch bore) is 0.70 inches squared. That converts to a 24mm diameter. My original choke point was 30mm. According to this calculator, that puts peak torque at 10,000rpm for my bore and stroke. Definitely no good on the street.

I also agree that there are many theorys (and many different calculators). It's all food for thought and experimentation...and none of it is any good without countless hours of testing, tuning and most important riding!

I met a mechanic for a successful Datsun road race team in the late 70's that used D port mods back then. He claimed he got the idea from a famous NASCAR head developer at the time. I probably missed out on some flow from lack of a multi angle valve job. My head only had 4000 original miles on it so I just lapped the valves good. Maybe this winter I'll get the valves done professionally.

cut the cv slide springs a inch shorter.
drill the cv slide equalision hole just a tiny bit larger.