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KZ650 MY78 WOT Problem - not possible full RPM 16 Aug 2020 06:45 #832994

  • Womtong
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Dear all
After rebulding the complete engine/complete bike i have now started to adjust the carbs.
I am not able to gain full power/full RPM...

Setup:
Delkevic 4 in 1 with Megaphone silener
Open Pods (cheap ones w/o Name
Dyna GreenCoils and Accent ignition
Piston, Valves - everything new
Motogadget minimum electronic with Lithium battery

Carbs:
VM24 with 17.5 Pilot and now 127.5 Main (!) Tested all sizes from 102.5 to 127.5 except 112 and 117.5 - no real difference
Needle at richest position (Y63 Keyster). Needle Jet Serial
Air reduction jets integrated (no big difference if using them or not)
All seals, jets new. Supersonic cleaned 1000 times now...
Synced (bench and with gauges) perfect. Idles like god :-)
Float Level adjusted with clear tube to exact 3mm each carb.

Problem:
Engine starts to sputter (like RPM limiter) at WOT (full throttle).
Strange: No real difference between Main Jet 110 to 127.5
Sputtering starts at approx. 5.5k RPM - minimum reduction of throttle to apr. 3/4 helps to rev. to approx. 7.5k.
Top Speed: 130km/ - no more possible because massive sputter.
Starts, Idles and runs below WOT very nice. No popping or something like that.
Clear to feel: Uphill WOT starts sputtering - minimum reduction of throttle helps to receive little more RPM.

Plugs shows me light tan - maybe a little to rich after cut off at full throttle (half mile WOT).

Guys, now i have no ideal how to proceed.
For me everything seems to be to rich. But Main Jet changes do not change anything (??)
Needle must be on riches position because all leaner positions makes 1/4 throttle positions impossible.
No Air leakage detectable (rubber brand new).

MAYBE Choke plunges are not sealing anymore perfect. Are they able to create such a mess?
Uphill at sputtering pushing choke make sputting worser.

Before i have used a inline filter. Now tested without that filter it is maybe minimum better. But more or less the same.
Petcock brand new serviced and working. Also on PRE tested.

Picture of bike attached.

Many thanks for your kind answer and your help in advance!
Nice greetings from Austria!

https://www.dropbox.com/s/3d9siufy9qsrijh/2020-07-12%2015.08.08.jpg?dl=0

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Last edit: by Womtong. Reason: Attachment link missing

KZ650 MY78 WOT Problem - not possible full RPM 16 Aug 2020 07:36 #833001

  • loudhvx
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It's difficult to do so make sure you are on a deserted road, but if you apply choke while trying WOT is the problem worse or better? If it's same or worse, then as you suspect, you are probably too rich. Plug color won't be affected by WOT if the bike doesn't fire at WOT.

Also, from the factory the carbs are usually set up to open farther than WOT, which makes everything richer when you go beyond. You need to check the full-throttle stop position and see if the slides move up farther than the roof of the carb bore.
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KZ650 MY78 WOT Problem - not possible full RPM 16 Aug 2020 10:29 #833014

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You are too rich that's for sure , the 127 main is way too big and closing the throttle to increase revs is proof of this as well as the choke test making the bogging worse
Get rid of the cheap pods and either get some K&N's or proceed with open carbs for now.
You should see an improvement with the cheap pods off.
Put all carb settings to stock for your model, pilots and needle position etc.
Try refitting all the original Mikuni needles etc as this may be your problem.
Fit air correctors and one size up from stock on the main and ALL other settings stock.
That's all you should need with the Delkevic.
Leaking choke plungers will cause over richness and non responsiveness from the mixture screws etc .
This is becoming an increasingly common issue with the old plunger seats.
New plungers are obsolete but i offer a worldwide Viton re-seating service for your original plungers if needed.
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KZ650 MY78 WOT Problem - not possible full RPM 16 Aug 2020 11:38 #833016

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I agree you are running rich and yes leaking choke plungers can cause this issue. But the main you are running 127.5 is way too rich. I would lean the needle one notch and start with a 110 main and 17 pilot. Keep in mind that dependent upon just witch set of vm24ss carbs that were stock in 78 there are differences between needles and needle jets used stock. Some actually had both an air screw and a pilot screw, other have one or the other which require different tuning. Some pods filter have been know to create issues with air travel to the pilot air jet and main/needle air jet. These pods have a lip on the inside of the connection to the carb that either blocks or creates turbulence with air getting to the air jets.
1977 KZ650 B1
Pods and Denco header


This is my Z

OLD KAW OWNERS SMILE ALOT
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KZ650 MY78 WOT Problem - not possible full RPM 16 Aug 2020 14:10 #833033

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zed1015 wrote: You are too rich that's for sure , the 127 main is way too big and closing the throttle to increase revs is proof of this as well as the choke test making the bogging worse
Get rid of the cheap pods and either get some K&N's or proceed with open carbs for now.
You should see an improvement with the cheap pods off.
Put all carb settings to stock for your model, pilots and needle position etc.
Try refitting all the original Mikuni needles etc as this may be your problem.
Fit air correctors and one size up from stock on the main and ALL other settings stock.
That's all you should need with the Delkevic.
Leaking choke plungers will cause over richness and non responsiveness from the mixture screws etc .
This is becoming an increasingly common issue with the old plunger seats.
New plungers are obsolete but i offer a worldwide Viton re-seating service for your original plungers if needed.


Thanks Zed!

- Really think that between cheap pods and K&N is a difference?

-Y63 Needle is crap? Question: How do I see which needle jet I have installed? They are old and I would like to change them. Recommendation which one and maybe which new needle from Mikuni?

- Plunges: Think they could be the problem. Will only the seal gets damaged over the years or also the plunge self? Do I have to send them to you? Thanks for instructions

- Needle Clip back to Stock: If I rise the needle from maximum rich one groove up the engine dies during starting driving around half throttle. Why that?? Leaking Choke plunges Problem?

Cheers

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Last edit: by Womtong.

KZ650 MY78 WOT Problem - not possible full RPM 16 Aug 2020 14:14 #833035

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loudhvx wrote: It's difficult to do so make sure you are on a deserted road, but if you apply choke while trying WOT is the problem worse or better? If it's same or worse, then as you suspect, you are probably too rich. Plug color won't be affected by WOT if the bike doesn't fire at WOT.

Also, from the factory the carbs are usually set up to open farther than WOT, which makes everything richer when you go beyond. You need to check the full-throttle stop position and see if the slides move up farther than the roof of the carb bore.


Thanks!
I have screwed throttle stop screw full in to avoid that problem. But slides are still moving up farther then the roof. Should I install longer stop screw?

Cheers

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KZ650 MY78 WOT Problem - not possible full RPM 16 Aug 2020 14:21 #833036

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gd4now wrote: I agree you are running rich and yes leaking choke plungers can cause this issue. But the main you are running 127.5 is way too rich. I would lean the needle one notch and start with a 110 main and 17 pilot. Keep in mind that dependent upon just witch set of vm24ss carbs that were stock in 78 there are differences between needles and needle jets used stock. Some actually had both an air screw and a pilot screw, other have one or the other which require different tuning. Some pods filter have been know to create issues with air travel to the pilot air jet and main/needle air jet. These pods have a lip on the inside of the connection to the carb that either blocks or creates turbulence with air getting to the air jets.


Thanks mate

This crap pods do not have this lip.

Because on original carbs the slides was totally stucked I have changed the carb bodies from other VM24 carbs. Mixed up good parts from each set to gain a good bank. Could that lead to a problem?
All seems that I have somewhere a leakage or something. I guess more and more the choke system....
Or worn/wrong needle jets. Please advise which one I should buy from Mikuni.

Thanks to all!

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Last edit: by Womtong.

KZ650 MY78 WOT Problem - not possible full RPM 17 Aug 2020 00:27 #833069

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Womtong wrote:
Thanks Zed!

- Really think that between cheap pods and K&N is a difference?

-Y63 Needle is crap? Question: How do I see which needle jet I have installed? They are old and I would like to change them. Recommendation which one and maybe which new needle from Mikuni?

- Plunges: Think they could be the problem. Will only the seal gets damaged over the years or also the plunge self? Do I have to send them to you? Thanks for instructions

- Needle Clip back to Stock: If I rise the needle from maximum rich one groove up the engine dies during starting driving around half throttle. Why that?? Leaking Choke plunges Problem?

Cheers


Some cheap pods are very restrictive and don't flow enough air regardless of them having a lip or not and can strangle the engine.
You get what you pay for. K&N, S&B, APE or Unifilter are proven quality.
Why spend good money on the engine rebuild then spoil it with cheap pods that don't let it perform or doesn't filter the intake correctly.

Unless the plungers are physically damaged it's only the rubber plunger seat that wears and yes! you would need to send them to me in the UK.
Cost is £61 returned.

Worn needles and jets will richen up the fueling overall but not to the extent you are experiencing and usually don't need changing unless damaged.

It sounds like you have changed too many things and need to go back to as close to stock as you can .

I would put all the stock Mikuni needles etc back in on all stock settings and start from there as i mentioned in my last post.

Just because parts are old does not mean they are worn.

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Last edit: by zed1015.

KZ650 MY78 WOT Problem - not possible full RPM 17 Aug 2020 02:41 #833070

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zed1015 wrote:

Womtong wrote:
Thanks Zed!

- Really think that between cheap pods and K&N is a difference?

-Y63 Needle is crap? Question: How do I see which needle jet I have installed? They are old and I would like to change them. Recommendation which one and maybe which new needle from Mikuni?

- Plunges: Think they could be the problem. Will only the seal gets damaged over the years or also the plunge self? Do I have to send them to you? Thanks for instructions

- Needle Clip back to Stock: If I rise the needle from maximum rich one groove up the engine dies during starting driving around half throttle. Why that?? Leaking Choke plunges Problem?

Cheers


Some cheap pods are very restrictive and don't flow enough air regardless of them having a lip or not and can strangle the engine.
You get what you pay for. K&N, S&B, APE or Unifilter are proven quality.
Why spend good money on the engine rebuild then spoil it with cheap pods that don't let it perform or doesn't filter the intake correctly.

Unless the plungers are physically damaged it's only the rubber plunger seat that wears and yes! you would need to send them to me in the UK.
Cost is £61 returned.

Worn needles and jets will richen up the fueling overall but not to the extent you are experiencing and usually don't need changing unless damaged.

It sounds like you have changed too many things and need to go back to as close to stock as you can .

I would put all the stock Mikuni needles etc back in on all stock settings and start from there as i mentioned in my last post.

Just because parts are old does not mean they are worn.


K&N RC-2314 right now ordered.
I will go now to complete stock setting. But i would like to have a new Needle Jet.
Which one is the right one from Mikuni?

Thanks for recommendations!

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KZ650 MY78 WOT Problem - not possible full RPM 17 Aug 2020 07:03 #833084

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The factory service manual should identify the correct needle for your bike.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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KZ650 MY78 WOT Problem - not possible full RPM 17 Aug 2020 07:41 #833085

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Since you put different body's together did you keep the parts seperate to that carb........... the nettles should be marked and there are 4 diff ones (on Partzilla) a 5cl10, 5cl16, 5cn15 or the 5dl3 which I'm 99% sure is in mine. Fourth clip. Diff years and models.

If your used nettles match I'd listen to Zed about going back. Where is your pilot..... a 17.5 I think would be about right. Jets are us might have more info on the nettles too. Ed has a nice list of parts vs models that if we could find might help too.
1978 KZ650 b-2
700cc Wiseco kit 10 to 1.
1980 KZ750 cam, ape springs, stock clutch/ Barnett springs.
Vance and Hines Header w/ comp baffle and Ape pods, Dyna S and green coils, copper wires.
29MM smooth bores W/ 17.5 pilots, 0-6s and 117.5 main
16/42 gearing X ring chain and alum rear JT sprocket....
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KZ650 MY78 WOT Problem - not possible full RPM 17 Aug 2020 08:02 #833089

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KZB2 650 wrote: Since you put different body's together did you keep the parts seperate to that carb........... the nettles should be marked and there are 4 diff ones (on Partzilla) a 5cl10, 5cl16, 5cn15 or the 5dl3 which I'm 99% sure is in mine. Fourth clip. Diff years and models.

If your used nettles match I'd listen to Zed about going back. Where is your pilot..... a 17.5 I think would be about right. Jets are us might have more info on the nettles too. Ed has a nice list of parts vs models that if we could find might help too.


In that case i think i have (maybe) mixed that parts. But Needles i have used the new Keyster ones (Y63) which should be same like 5dl31.
Pilot is 17.5 now.
Question is only:
German Mikuni guy is asking, which needle jet i have (but they are not marked).
Jet 258 4 VM24/488-O-8 OR O-4 14,3 This is what he have in the Kawa documents.
Question is if O8 or O4 is used in my carbs.

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