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RE: 1978 kz750 b3 engine bog at full throttle
Verfasst: Sa 8. Jul 2017, 12:56
von onkelheri
Maybe the fuel hose is sqeezed?
All that Filterstuff above is ok if you just open the bottom of the floatchamber and the fuel "runs"(!) out there.
The jetsize should growup apprx. 10 to 15% without an Airbox. The Airjet also had an influence of the Gasbuilding in the Brassflute, if they too less you'l drain the fire.
Heri
RE: 1978 kz750 b3 engine bog at full throttle
Verfasst: So 9. Jul 2017, 15:15
von Michael
Hi Jon,
sorry, haven't watched the linked videos yet.
With slip-ons you mean the exhaust pipes, correct ?
If they are fully open you need to use bigger main jets.
Heri suspected you have mounted funnels (Trichter) or something like K+N-filters.
These also need bigger main jets to run properly.
Both combined together you need even bigger main jets ;-)
As far as I've understood everything in the low and mid rpm-range seems to work, just the top end revving is missing.
Go for bigger main jets !
The Bs have standard main jet #125.
Often plus 10% (area, not diameter!) is working good for mildly tuned engines.
(either K+Ns or open exhaust)
Let me calculate:
standard main jet:
125 / 2 = r = 62,5
a = r² x Pi (3,1415926...) = 12272
10% bigger main jet:
a = 12272 + 10% = 13500
13500 / Pi => square root = r = 65,5
=> new main jet (+10%) is #131
To be on the safe side choose the next bigger one:
#132,5 available ?
Otherwise #135
Not the best fuel economy, maybe not best performance, but it should give the ability to run the engine even at highest rpms (red line at 7.800 rpm !)
PS: tank ventilation is tested automatically as long as the "fuel run-out test" was done with closed tank cap.
Or did you open it for that test ?
Good luck,
Michael
RE: 1978 kz750 b3 engine bog at full throttle
Verfasst: So 9. Jul 2017, 15:43
von onkelheri
Did you ever adjust the idlemixscrew? Or they US-typical sealed by brasscap? Open them by taping a 4mm threat...
Greetz heri
RE: 1978 kz750 b3 engine bog at full throttle
Verfasst: So 9. Jul 2017, 22:52
von jon707
Michael hat geschrieben:
Hi Jon,
sorry, haven't watched the linked videos yet.
With slip-ons you mean the exhaust pipes, correct ?
If they are fully open you need to use bigger main jets.
Heri suspected you have mounted funnels (Trichter) or something like K+N-filters.
These also need bigger main jets to run properly.
Both combined together you need even bigger main jets ;-)
As far as I've understood everything in the low and mid rpm-range seems to work, just the top end revving is missing.
Go for bigger main jets !
The Bs have standard main jet #125.
Often plus 10% (area, not diameter!) is working good for mildly tuned engines.
(either K+Ns or open exhaust)
Let me calculate:
standard main jet:
125 / 2 = r = 62,5
a = r² x Pi (3,1415926...) = 12272
10% bigger main jet:
a = 12272 + 10% = 13500
13500 / Pi => square root = r = 65,5
=> new main jet (+10%) is #131
To be on the safe side choose the next bigger one:
#132,5 available ?
Otherwise #135
Not the best fuel economy, maybe not best performance, but it should give the ability to run the engine even at highest rpms (red line at 7.800 rpm !)
PS: tank ventilation is tested automatically as long as the "fuel run-out test" was done with closed tank cap.
Or did you open it for that test ?
Good luck,
Michael
Hi Michael, Thank you very much for the detailed information. I much appreciate the time you took to do that!
Yes the mufflers are what I meant by slip ons....I did not fool with the stock airbox. So I will take your advice and go with the 132.5 if I can find one.
I will hunt for the jets and order them. When I am done with the job I will let you know the results.
Thank you again Michael : )
RE: 1978 kz750 b3 engine bog at full throttle
Verfasst: So 9. Jul 2017, 22:55
von jon707
onkelheri hat geschrieben:
Did you ever adjust the idlemixscrew? Or they US-typical sealed by brasscap? Open them by taping a 4mm threat...
Greetz heri
Hi onkelheri, Yes they are sealed with the brass cap. If the jet change does not work I may try your advice with the 4mm threads
Thank you
jon
RE: 1978 kz750 b3 engine bog at full throttle
Verfasst: Mo 10. Jul 2017, 01:14
von onkelheri
It would'nd work without this adjustment ...
You'll need a "flatend" Tappingdrill for Blindendholes...
BSsealsonicht.jpg
this shows what happen if you do it wrong...
Drill carefull with a 2mm then 3,2mm, be prpared that you reach the "cave" above the Idlescrew, ... but then take care that the Tapper hat a straigth, flat front(!) because if it reached the Idlescrew it will start to lift the brasscap. In other, topend, case the idlescrewslot will destroyed.
Screenshot_2017-07-10-01-19-57kl.jpg
Screenshot_2017-07-10-01-19-26kl.jpg
Screenshot_2017-07-10-01-19-50kl.jpg
Screenshot_2017-07-10-01-19-35kl.jpg
Greetz Heri