Author Topic: CB750 k3 with pods  (Read 829 times)

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Offline adamalk3

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CB750 k3 with pods
« on: May 07, 2018, 09:48:18 AM »
Hey, all.
I've come here because I've spent countless hours doing research and have finally given up and I'm now asking for your advice. Sorry for being that guy.

Bike:
- CB750 k3 SOHC
- 657a carbs, completely rebuilt and cleaned
- #42 pilot jets
- Pod filters
- New coils
- Electronic ignition, timed
- Valve clearance set
- Carbs synced
- Brand new carb holders, boots, manifolds, whatever you prefer to call them.
- 4 into 1, no name headers, no baffle

Not sure if it matters that much, but I'm in Detroit, MI, so whatever elevation that is.

I've attached an image of the brand/type of pod filters I'm running.


Symptoms:
- Comepletely dies when blipping throttle quickly, at idle or under load.
- Sputters a lot when giving it a bit of throttle, 1/4 all the way to WOT, while riding.
- Bike won't even go over 70mph, just sputters hard while trying to push further at WOT.

I've tried jets 115 thru 140. But haven't done ALL needle clip positions. I realize this will take a LOT of time going through all combinations of needle positions and jets.


Which brings me to my questions:

- What is a typical set up for my carbs with the pods I'm using?*
- Could there be other factors other than jet size and needle clip position playing into the issues I'm having?*


Before anyone suggests putting the stock airbox back on, I know. I've considered it, but I do not have a stock airbox and I would prefer to really TRY pods first. I've owned the bike for 4 years and I haven't been able to get it running properly.



Offline PeWe

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Re: CB750 k3 with pods
« Reply #1 on: May 08, 2018, 02:44:36 AM »
My CB750 with pods and rather open 4-1 that had a baffle inside.
- Pilot (stock 40)
- Needles 1 step richer wich is 4:th from top instead of 3:rd notch.
- Mains: Huge 147.5
This was in the 80's with real fuel and bike ran great. No issues at all with pods.
It had 836, ported head, cam.

Your description verify too use stock pilots. (sputter on low lift, too rich)
Needles too lean due to twisting throttle problems.

Completely wide open system will probably give less torque on lower rpms and problems to get it to work at all on low lifts.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline adamalk3

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Re: CB750 k3 with pods
« Reply #2 on: May 08, 2018, 10:07:21 AM »
Thanks for the response!

My bike is a 1973, stock engine other than pods and exhaust. Stock jets are #40  pilot and #110 main, needle clip stock at 4th from top (2nd from bottom).

I do understand what adjusting is to be done, but when I'm having troubles with is finding the right settings/jets. So I'm asking for what is typically done with my setup.

Thanks again!

Offline flybox1

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Re: CB750 k3 with pods
« Reply #3 on: May 08, 2018, 10:40:06 AM »
Run the engine to operating temps.  toss in a new set of D8EA plugs and fire it up.  let it idle under a box fan for 4-5 min.
Take out the plugs.....what do they look like?

check this...
http://forums.sohc4.net/index.php?topic=146178.0

« Last Edit: May 08, 2018, 10:42:03 AM by flybox1 »
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline PeWe

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Re: CB750 k3 with pods
« Reply #4 on: May 08, 2018, 11:01:47 AM »
Change pilot to 40, mains to at least 125, minimum. 130 is better
My K6 had 115-120 with 4-1 and stock air box. Pods need more fuel since air will flow much more.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Bankerdanny

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Re: CB750 k3 with pods
« Reply #5 on: May 08, 2018, 01:32:59 PM »
Thanks for the response!

My bike is a 1973, stock engine other than pods and exhaust. Stock jets are #40  pilot and #110 main, needle clip stock at 4th from top (2nd from bottom).

I do understand what adjusting is to be done, but when I'm having troubles with is finding the right settings/jets. So I'm asking for what is typically done with my setup.

Thanks again!

I think stock mains are 105 (I know that is stock for my '76 750F), so 110 isn't a very big jump considering the open exhaust and pods.
"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline flybox1

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Re: CB750 k3 with pods
« Reply #6 on: May 08, 2018, 01:46:51 PM »
Gotta get idle/IMS/Pilot jet dialed in first.   A plug chop gives you the starting point...otherwise its a shot in the dark.
Correct bowl fuel level.    Clean, known-good pilot jets.  Chop it.
Dial in the IMS for tan plugs.  If you reach the end of the usable adjustment range, change pilot jet.
Retest until its right.  Only then move to dialing in the needle clip position...

'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"