D
DannyMotor
Guest
Nope. Have not fiddled with chain tensioner or cams. The timing advance is working, but I dont think its advancing enough... could explain why so many different jetting combos are leading to the same result.
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platinum2
Guest
sounds like a kinked fuel line to though
its letting in just enough to keep her going until you "step on it"
maybe check the fuel for kinks, and dirty lines, also!- under the needle and seat in carbs- there is a screen they ALWAYS collect dirt and rust from the tanks! mine did do this! and fuel wouldnt keep up, hope this helps
its letting in just enough to keep her going until you "step on it"maybe check the fuel for kinks, and dirty lines, also!- under the needle and seat in carbs- there is a screen they ALWAYS collect dirt and rust from the tanks! mine did do this! and fuel wouldnt keep up, hope this helps
D
DannyMotor
Guest
Tank and screens have been gone through. fule line is new and unkinked with an inline filter and needles and seats are new.
Steve
GS Whisperer
One other thing that I noted.
That higher number actually lowers the fuel level, making everything run leaner than it should.
You will be chasing your jetting all over the place until you get the float level set correctly.
.
Stock float height for the '78 750 is 23.0 mm +/- 1.0 mm.
That higher number actually lowers the fuel level, making everything run leaner than it should.
You will be chasing your jetting all over the place until you get the float level set correctly.
.
B
BassCliff
Guest
Hi,
Somehow I missed the float height spec and inline filter. Good call, guys.
Remove the inline fuel filter and set the proper float height. Then let's see what happens.
Thank you for your indulgence,
BassCliff
Somehow I missed the float height spec and inline filter. Good call, guys.
Remove the inline fuel filter and set the proper float height. Then let's see what happens.
Thank you for your indulgence,
BassCliff
Just got home and yup I agree with the ditching the inline fliter..if the tank screen is clean and good then that really is all you should need. And they are spot on about the float hghts too. And be sure that you measure WITHOUT the bowl gasket installed. Bare metal from the little raise edge to the top of the FLOATS..as in BOTH of them in each carb. Such as this...
Last edited:
D
DannyMotor
Guest
Crap crap crap crap crap.....
Specs:
Float Heights = 23mm perfectly
Main Jet = 102.5
Needle = (the fat original one) 2nd grove (from bottom)
Fuel line = new clear tube, no filter
Fuel screw = 3/4 turns out from soft stop
Air screw = 1.25 turns out
530 chain, 110 links, 42 rear, 17 front, 2.47 final gearing
Double checked tank and petcock... all's well in operation. Fuel flows freely on all settings (with vacuum on RES and ON of course).
Timing is set dead-nuts .012" points gap... timing is set to F on 1&4 and 2&3 perfectly. (This was off from before... it's slightly more advanced than previously, and the gap is down from .016".)
Bench synced the carbs 100%.
---------------
The motor was cold (well, cool) and I re-installed everything... airbox, yadda-yadda.. turned it to prime, gas over-flowed from the carb tubes (which hadn't happened at all before) I put it on choke and it fired right up... so we're at a good place there.
---------------
Took it for a ride.
MUCH smoother than before... however, 4000rpm, it bogs still...
Through the gears: It'll hover at 4000rpm, try to crack the throttle more and it just bogs, not decelerating, just not accelerating (but it's acting like it wants to). Once you get into 5th, it'll hit 70mph at about 4200rpm, just cruising at about 1/4 throttle... try to go more and you can feel it want to, but it still stumbles and won't accelerate.
-----
SO, I tried this.... Because I wanted to see what would happen.
When it started to bog, I pulled in the clutch... VROOOM... it revved right up to redline no issue, just like in neutral in the garage.
Let the clutch back out... and it was back to bog-ville. Prior to all the above changes it WOULD NOT rev up like that at all... not even in the garage.... not that smoothly anyway.
-----
Another test: I took it down a hill.... 5th gear, 65-70mph and just cracked the throttle to WOT. It maintained, but didn't enjoy it.... once the ground leveled out the bike bogged ALL THE WAY to 3000rpm, throttle input did NOTHING, once it hit about 2900rpm it picked back up to 4000rpm and continued on it's bogging ways.
-----
So in closing, it's still too rich. I'm going to drop the needle to the middle position and see if it improves. It feels like it's RIGHT THERE...
---
Current concerns still bugging me:
1- Could the super high gearing be causing this? (the 530 42 rear is about 2.5 inches SMALLER in diameter from the 630 41 tooth stock)
2- I'm using the same spark plugs through all of this. Would a new set help?
3- I got a mild zing from touching one of the plug boots while running, could this cause a loss in power like this?
4- What was the stock position of the needle? Middle? or 1 up from middle?
If I say anything that gives any of you an "ah-ha!" moment... please let me know. At this point, I'm going to continue fiddling with the needle height... and THAT'S IT. If that doesn't fix this, I don't know what will.
The fact that it even revs to redline that easily has me thinking I'm on the right track...
Specs:
Float Heights = 23mm perfectly
Main Jet = 102.5
Needle = (the fat original one) 2nd grove (from bottom)
Fuel line = new clear tube, no filter
Fuel screw = 3/4 turns out from soft stop
Air screw = 1.25 turns out
530 chain, 110 links, 42 rear, 17 front, 2.47 final gearing
Double checked tank and petcock... all's well in operation. Fuel flows freely on all settings (with vacuum on RES and ON of course).
Timing is set dead-nuts .012" points gap... timing is set to F on 1&4 and 2&3 perfectly. (This was off from before... it's slightly more advanced than previously, and the gap is down from .016".)
Bench synced the carbs 100%.
---------------
The motor was cold (well, cool) and I re-installed everything... airbox, yadda-yadda.. turned it to prime, gas over-flowed from the carb tubes (which hadn't happened at all before) I put it on choke and it fired right up... so we're at a good place there.
---------------
Took it for a ride.
MUCH smoother than before... however, 4000rpm, it bogs still...
Through the gears: It'll hover at 4000rpm, try to crack the throttle more and it just bogs, not decelerating, just not accelerating (but it's acting like it wants to). Once you get into 5th, it'll hit 70mph at about 4200rpm, just cruising at about 1/4 throttle... try to go more and you can feel it want to, but it still stumbles and won't accelerate.
-----
SO, I tried this.... Because I wanted to see what would happen.
When it started to bog, I pulled in the clutch... VROOOM... it revved right up to redline no issue, just like in neutral in the garage.
Let the clutch back out... and it was back to bog-ville. Prior to all the above changes it WOULD NOT rev up like that at all... not even in the garage.... not that smoothly anyway.
-----
Another test: I took it down a hill.... 5th gear, 65-70mph and just cracked the throttle to WOT. It maintained, but didn't enjoy it.... once the ground leveled out the bike bogged ALL THE WAY to 3000rpm, throttle input did NOTHING, once it hit about 2900rpm it picked back up to 4000rpm and continued on it's bogging ways.
-----
So in closing, it's still too rich. I'm going to drop the needle to the middle position and see if it improves. It feels like it's RIGHT THERE...
---
Current concerns still bugging me:
1- Could the super high gearing be causing this? (the 530 42 rear is about 2.5 inches SMALLER in diameter from the 630 41 tooth stock)
2- I'm using the same spark plugs through all of this. Would a new set help?
3- I got a mild zing from touching one of the plug boots while running, could this cause a loss in power like this?
4- What was the stock position of the needle? Middle? or 1 up from middle?
If I say anything that gives any of you an "ah-ha!" moment... please let me know. At this point, I'm going to continue fiddling with the needle height... and THAT'S IT. If that doesn't fix this, I don't know what will.
The fact that it even revs to redline that easily has me thinking I'm on the right track...
Last edited:
K
kjsamm
Guest
That sounds like a Nettle Jet problem. Not Jet Needle.
D
DannyMotor
Guest
Wait... what? You think I should up-jet, or down-jet?
Or are you correcting my terminology?
Or are you correcting my terminology?
D
DannyMotor
Guest
Im going to try de-oiling the KnN filter... then just 'lightly' oiling it. It may be too restrictive.
P
platinum2
Guest
is the valve cover vent clear? how about the intake manifolds, " carb boots on motor side" could they be leaking and sucking to much air at higher revs?
M
Mop Bucket
Guest
I had a very similar issue and went through checking everything on the bike. The problem ended up being crap in the tank. That crap went in to my carbs and I had a 4500 Rpm limit.
I cleaned everything again, tank, filter and most importantly the carbs. Once it was all cleaned I was burying the needle on the speedo and didn't have a rpm limiter.
You said you had sediment in the tank so you need to clean again. My filter looked clean too, but, there was still junk in the carbs.
I cleaned everything again, tank, filter and most importantly the carbs. Once it was all cleaned I was burying the needle on the speedo and didn't have a rpm limiter.
You said you had sediment in the tank so you need to clean again. My filter looked clean too, but, there was still junk in the carbs.
D
DannyMotor
Guest
Jesus tap-dancing christ!
Well... Apparently... IT WAS THE AIR-FILTER!!!!
I just washed the KnN... let it dry, went over it with a heat gun (lightly, just to quicken the process) re-installed dry...
THE THING IS A FRIGGEN BEAST!!!!!
1100rpm to 9000rpm without a hickup! Smooth as silk.
Live and learn, and let this be a lesson... do not over-oil your air filter.
Wish I knew that a week ago. Thanks for all the suggestions guys! I knew I wasn't crazy!
Well... Apparently... IT WAS THE AIR-FILTER!!!!
I just washed the KnN... let it dry, went over it with a heat gun (lightly, just to quicken the process) re-installed dry...
THE THING IS A FRIGGEN BEAST!!!!!
1100rpm to 9000rpm without a hickup! Smooth as silk.
Live and learn, and let this be a lesson... do not over-oil your air filter.
Wish I knew that a week ago. Thanks for all the suggestions guys! I knew I wasn't crazy!
S
steveu812
Guest
I never would have suspected this issue, but it was the problem with my bike too. Wouldn't rev past 5500 under load. Removed the K&N and she runs to redline no issues!
Thanks to this forum - this is awesome!!
Thanks to this forum - this is awesome!!
S
Seana23
Guest
Good on ya Danny.
...and Steve too!
Well done.
So, what jetting and needle settings did you end up with?
Xxx
...and Steve too!
Well done.
So, what jetting and needle settings did you end up with?
Xxx
