Dr. Jekyll and Mr. Hyde ( a pair of KZ400s)

z just the balance 'factor' is changed.
The weight I removed was on the throw side,not the counterwieght side.

2) 400 = 64* 62 ,use a KZ650 Wiseco piston @ 65mm,3 over stock 62mm
440 = 67.5 * 62,use the KZ750 Wiseco piston @ 69mm,3 over stock 66mm

((Edit/When using either Wiseco pistons you can milled the head other .035 in.
because those pistons have a shorter dome
This will be a total of .070 in. off the head.
Bringing the compression ratio up to roughly 10.3 with each combination.
Milling just the original .035 will result in a 9.3 ratio.
The valve pockets are 5 degrees off which might cause a problem with a milled
head and high lift cam.))

The drop in pistons I have are from a discontinued Wiseco kit from eBay.
It is a drop in for the 440.

If I were you I'd do a compression check etc. first, to see what condition the engine is in.
Then if it's good leave it alone and find another to hop up.
Because there is nothing worse than walking by a motorcycle you could be riding. 8)
 
Nebr_Rex said:
Because there is nothing worse than walking by a motorcycle you could be riding. 8)

Too true. Walk by it every morning out to the truck :-\ I just keep telling myself it'll be ready for next riding season :)
 
Not much to report here lately.
Been to busy trucking and bought another old pickup ('78 F250 w/460).
I'm taking vacation starting the 23 for about 10 days before I lose them.
During that time I'm planing on getting the fuel injection sorted out.
Last winter when it I had it running the injector pulse was all messed up.
This lead to fouling the plugs and switching back to carbs.
I think I have it figured out, just need to compute the values of the resistors,transistors,etc....
Oh,by the way did I mention that it is transistorised electro/mechanical fuel injection, NO COMPUTER.
That means electrical switches controlling others,along with mechanical means.
No computer chips anywhere,that's the plan anyway.
I had a leaking clutch cover gasket, so I decided to do a little painting.
Here are some pics.
 

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Well I forgot my vacation started on the 17th.
Planning on boring a couple of blocks sometime over the holiday.
All depends on when the owner/lead mechanic will be there after hours.
During that time I have access to their boring bar.
Will post about that later.
Today's post is about using 2 stroke carbs on a 4 stroke engine.
On Dr. Jekyll I'm temporarily running a pair of vm28s from a Yamaha.
The air bleed going to the needle jet is to large.
If you look at a 4 stroke carb there is a brass insert with a small hole like this one.
 

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I used a pilot jet from a bs34 Mikuni for a restrictor.
Drilling a .8 mm or .032/32nd in. hole to start with.
 

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Next I tapped the air bleed with a no. 12nc (24 threads/in.) machine screw tap.
Threads are not a prefect match but real close.
 

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For now jetting is 15 pilot and 100 mains.
So if you are fowling plugs,maybe to much air is getting thru that little hole and forcing extra fuel out.
 

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Next time just tap the mouth for standard Mikuni air jets which come in different sizes :)
 
teazer said:
Next time just tap the mouth for standard Mikuni air jets which come in different sizes :)

Just using what I have on hand.
Maybe you could post your own thread on the subject.
 
From left to right;

1) Old Wiseco big bore KZ400 piston,listed at 10/1,12 cc dome,11.5/1 for my application, 67.5 mm (440 bore ) 223 grams

2) Wiseco KZ750/4,5.2 CC dome,8.3/1 with the stock 440 combustion chamber,9.3 for me,69 mm,239 grams

3) Old JE(?) piston for a KZ750/4, modified/lightened skirt, 68 mm, taller dome than piston no. 1, but deeper valve reliefs, maybe 1 CC more dome volume than no. 1, my calculations come up with 11.7/1, 238 grams

4). Unmodified version of no.3, 252 grams

I'll be using a head that is milled .035 in. and no base gasket.
 

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I decided to go with the old high domes with the modified skirt.
Freshly bored and honed cylinders.
 

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A mock up of what it will look like when assembled. 8)
 

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Almost have the wiring done on Dr. Jekyll.
Wiring a KZ440 engine and charging system in a KZ400 frame.
Making sure everything works with extras for the future addition of fuel injection kind of sucks.
 
Nebr_Rex said:
Just using what I have on hand.
Maybe you could post your own thread on the subject.

I'm not being critical. Hope my brief response didn't come across that way. :)

We have to do that mod on almost all GT750s with stock BS40 carbs because they surge. Suzuki used to sell special air jets which of course were available from Mikuni for a whole lot less. I have a reference to that carb at http://pinkpossum.com/GT750/carb/BS40carbs.htm

BTW, nice collection of pistons.
 
I knew the Holley tuners used removable air jets.
Didn't know about Mikuni's.
I think I need to take a harder look at the Sudco catalog.
Do you know what size thread is required?
 
Hmm. I forgot to include that in the blog. I'll go and measure one.

edit: I just checked and it's a 4mm x0.7mm tap which is available from any decent hardware store - mine was from our local ACE. Air jets are used extensively in larger VM carbs. Typically two strokes are 2.0mm or no jet and 4 strokes are much smaller. On the Suzuki GT750 we add a replaceable air jet to the pilot air system to trim slow riding stumbles.
 
teazer said:
Hmm. I forgot to include that in the blog. I'll go and measure one.

edit: I just checked and it's a 4mm x0.7mm tap which is available from any decent hardware store - mine was from our local ACE. Air jets are used extensively in larger VM carbs. Typically two strokes are 2.0mm or no jet and 4 strokes are much smaller. On the Suzuki GT750 we add a replaceable air jet to the pilot air system to trim slow riding stumbles.

Thanks for the reply,the info will be put to good use.
 
Finally got Dr. Jekyll rewired and all the stock circuits are working.
It will need to be 'refined' for a better fit at a later date,I might even get it color coded.
I'm have choosen to use the turn signal lights from a small Honda CB bike.
Was going to use them on Mr. Hyde, but they look better than the huge stock lights.
Probably end up just running a head and tail light on the evil one.
Also been messing around with getting my fuel injectors to fire.
I have visited the local Radio Shack more than the auto parts store lately.
Earlier I had it running off the pickup coils and two ignitor boxes.
Had the dwell/pulse width running from about 24° at idle to 41° at high rpm.
With some transistors and resistors soldered to a circuit board I'm getting .001° to .01°
of pulse width according to the Chinese meter from harbor freight I'm using.
So the next time I'm home I'll be 'refining' my harness for a better fit.
Then the fuel pump,throttle bodies, etc. can be reinstalled and see how it runs as is.
 
Been doing a little experimenting with some circuits.
It's slow going since I have to self teach myself.
Seem I have forgotten everything I learned in high school electronics class.

First pic is of what hasn't worked so far.
Second pic shows a more complex circuit I just finished.
Testing will have to wait until next time I'm home.
 

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