Author Topic: Static timing cb750 help please  (Read 2098 times)

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Offline Jaxbchcb

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Static timing cb750 help please
« on: April 07, 2015, 06:56:28 AM »
 Ok so I'm trying to adjust/check my timing on my cb750 sohc with one of those lights with a alligator clip because my bike is only running on cylinders 2 & 4. This is where I'm confused I guess I'm taking the alligator clip and attaching it to one of the fins on the motor and making contact to the points with the light then turning the crank and see the points open but the light never comes on!? I've tried with both set of points but still nothing so I'm stumped... Any help/advice would be awesome thank you! Here's a pic of my light

Offline evanphi

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Re: Static timing cb750 help please
« Reply #1 on: April 07, 2015, 07:08:46 AM »
When checking 1/4 points, for example, put the clip on the side that opens/closes, and the tip of the light/handle on the side that is stationary.

Make sure your bike is on (key in, and in run position).

Make sure your batter is good.
--Evan

1975 CB750K "Rhonda"
Delkevic Stainless 4-1 Header, Cone Engineering 18" Quiet Core Reverse Cone, K&N Filter in Drilled Airbox
K5 Crankcase/Frame, K4 Head and Cylinders, K1 Carbs (42;120;1 Turn)

She's a mix-matched (former) basket case, but she's mine.

CB750 Shop Manual (all years), searchable text PDF
Calculating the correct input circumference for digital speedometers connected to the original speedometer drive

Offline Jaxbchcb

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Re: Static timing cb750 help please
« Reply #2 on: April 07, 2015, 07:23:58 AM »
When checking 1/4 points, for example, put the clip on the side that opens/closes, and the tip of the light/handle on the side that is stationary.

Make sure your bike is on (key in, and in run position).

Make sure your batter is good.


Awesome thank you that worked and my timing is perfect! But I guess I have to figure out why cylinders 1 and 3 aren't firing?? They fire when I switch the coils around? Do you have any idea what that could be? I know the coils are good because I test them with a multimeter?

Offline evanphi

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Re: Static timing cb750 help please
« Reply #3 on: April 07, 2015, 07:53:53 AM »
When checking 1/4 points, for example, put the clip on the side that opens/closes, and the tip of the light/handle on the side that is stationary.

Make sure your bike is on (key in, and in run position).

Make sure your batter is good.


Awesome thank you that worked and my timing is perfect! But I guess I have to figure out why cylinders 1 and 3 aren't firing?? They fire when I switch the coils around? Do you have any idea what that could be? I know the coils are good because I test them with a multimeter?

What do you mean switch the coils? Swap plug caps to other cyls?

1/3 are not a pair. The leads from the cyls should be going to 1/4 and 2/3 (so make sure that is there first!). What about the wires to the coils, the blue/yellow ones. Could they have gotten swapped?

New plugs?
--Evan

1975 CB750K "Rhonda"
Delkevic Stainless 4-1 Header, Cone Engineering 18" Quiet Core Reverse Cone, K&N Filter in Drilled Airbox
K5 Crankcase/Frame, K4 Head and Cylinders, K1 Carbs (42;120;1 Turn)

She's a mix-matched (former) basket case, but she's mine.

CB750 Shop Manual (all years), searchable text PDF
Calculating the correct input circumference for digital speedometers connected to the original speedometer drive

Offline madmtnmotors

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Re: Static timing cb750 help please
« Reply #4 on: April 07, 2015, 08:21:00 AM »

1/3 are not a pair. The leads from one coil should be going to 1/4 and the leads from the other coil going to 2/3 (so make sure that is there first!).



+1
TAMTF...


Wilbur



Projects:
"Evolution": http://forums.sohc4.net/index.php?topic=100352.0
"P.O. Debacle": http://forums.sohc4.net/index.php/topic,126692.msg1441661.html#msg1441661
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                          
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
                                    http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Late model K7/K8/F2/F3 front sprocket cover removal: http://forums.sohc4.net/index.php/topic,178428.msg2072279.html#msg2072279
630 to 530 conversion: http://forums.sohc4.net/index.php/topic,180710.msg2094423.html#msg2094423

Sent from my Tandy TRS-80!

Offline Jaxbchcb

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Re: Static timing cb750 help please
« Reply #5 on: April 07, 2015, 08:44:59 AM »
When checking 1/4 points, for example, put the clip on the side that opens/closes, and the tip of the light/handle on the side that is stationary.

Make sure your bike is on (key in, and in run position).

Make sure your batter is good.


Awesome thank you that worked and my timing is perfect! But I guess I have to figure out why cylinders 1 and 3 aren't firing?? They fire when I switch the coils around? Do you have any idea what that could be? I know the coils are good because I test them with a multimeter?

What do you mean switch the coils? Swap plug caps to other cyls?

1/3 are not a pair. The leads from the cyls should be going to 1/4 and 2/3 (so make sure that is there first!). What about the wires to the coils, the blue/yellow ones. Could they have gotten swapped?

New plugs?

That is what's weird I know they are not a pair. But if I take coil cap #2 and put it on 3 it fires
« Last Edit: April 07, 2015, 09:08:59 AM by Jaxbchcb »

Offline madmtnmotors

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Re: Static timing cb750 help please
« Reply #6 on: April 07, 2015, 09:25:15 AM »
First of all, what method are you using to determine whether a plug is firing or not? Are the plugs still in the engine and running on two cylinders checking for hot exhaust pipe? Are plugs still in the engine but using an inductive timing light? Are you removing the plugs, grounding the body of the plug, and checking for spark at the tip? Something else?

I would recommend removing each plug, and checking for spark at the tip while grounding the body of the plug and post those results here.
TAMTF...


Wilbur



Projects:
"Evolution": http://forums.sohc4.net/index.php?topic=100352.0
"P.O. Debacle": http://forums.sohc4.net/index.php/topic,126692.msg1441661.html#msg1441661
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                          
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
                                    http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Late model K7/K8/F2/F3 front sprocket cover removal: http://forums.sohc4.net/index.php/topic,178428.msg2072279.html#msg2072279
630 to 530 conversion: http://forums.sohc4.net/index.php/topic,180710.msg2094423.html#msg2094423

Sent from my Tandy TRS-80!

Offline Jaxbchcb

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Re: Static timing cb750 help please
« Reply #7 on: April 07, 2015, 11:08:11 AM »
Thanks for the replys! I found a wiring diagram and found out what yall were talking about that 1 and 4 are on one coil and 2 and 3 are on another. I guess the guy who had the bike before me put the coil wires on 1234 haha so no wonder it was acting all crazy!! But I corrected it and everything is good now

Offline madmtnmotors

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Re: Static timing cb750 help please
« Reply #8 on: April 07, 2015, 11:42:15 AM »
Thanks for the replys! I found a wiring diagram and found out what yall were talking about that 1 and 4 are on one coil and 2 and 3 are on another. I guess the guy who had the bike before me put the coil wires on 1234 haha so no wonder it was acting all crazy!! But I corrected it and everything is good now

From what you described many of us believed that to be the case. Hence my suggestion to check each plug one by one to get you to look at every plug and every wire. The "dual fire" coils had me scratching my head way back in the beginning, one just gets a wasted spark.
TAMTF...


Wilbur



Projects:
"Evolution": http://forums.sohc4.net/index.php?topic=100352.0
"P.O. Debacle": http://forums.sohc4.net/index.php/topic,126692.msg1441661.html#msg1441661
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                          
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
                                    http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Late model K7/K8/F2/F3 front sprocket cover removal: http://forums.sohc4.net/index.php/topic,178428.msg2072279.html#msg2072279
630 to 530 conversion: http://forums.sohc4.net/index.php/topic,180710.msg2094423.html#msg2094423

Sent from my Tandy TRS-80!