Ignition timing question

[dave Esch]

When I rebuilt the bike I stated I had issues setting the timing. Not issues, but I didn't have that warm fuzzy feeling about it. After riding the bike the past few weeks I feel pretty confident my chain and cam are in time. The bike pulls way to hard for the timing to be incorrect. I do, however, have doubts about my ignition timing. I pulled the cover off today and found all adjustment screws holding the assembly in have been slightly stripped. So I know the timing has been adjusted previously. My question is how do you know if the ignition timing is correct? I not only get a ton of backfiring on decel, but also pops while sitting at idle. 76 cb750k I was considering making a small adjustment and going for a ride. Then adjust the previous way. I know it's close, but I'm thinking this is my issue. Wanted to get some input.

[TOOLS1]

I use a timing light. You do the points on the left first, then the ones on the right.
TOOLS

[Lucky 1]

You have popping on decell and backfiring etc.,.
It could have air leaks or the jetting is all wrong.
Do you have stock exhausts and the stock air box?


I need all of the facts.
Also you need to order replacement screws to replace
those timing screws, BEFORE you make any adjustments.

1976 CB750
Exhaust type?
Intake type.
idle jet size?
Main jet size?
Slide needle clip position? Counting down from the top.
Mixture screw adjustment.


Also have your replaced the float needles and set the float levels?

[rrgunslinger]

I use a static light.  Not perfect but works. Set your gap first on both points, then like Tools said do the left first then the right. Rotate the motor to the timing point for the left side, then hook up the light and turn on the ignition. Rotate the plate until the light comes on then back it off until it goes out. Turn off the ignition then tighten the plate screws and then rotate the motor (clock wise) to the second timmin mark and set the second set.  If the gap is correct it should be real close.  I have also used cigarette paper putting it between the points and setting the timing to where you can pull the paper out from between the points with a little drag but not tearing the paper.

http://i373.photobucket.com/albums/oo172/grandpaslinger/100_0706.jpg

 

On Wed, Sep 12, 2012 at 11:28 PM, Lucky 1 [via Honda CB750'S] <[hidden email]> wrote:

You have popping on decell and backfiring etc.,.
It could have air leaks or the jetting is all wrong.
Do you have stock exhausts and the stock air box?


I need all of the facts.
Also you need to order replacement screws to replace
those timing screws, BEFORE you make any adjustments.

1976 CB750
Exhaust type?
Intake type.
idle jet size?
Main jet size?
Slide needle clip position? Counting down from the top.
Mixture screw adjustment.


Also have your replaced the float needles and set the float levels?

Working on a CB750 Digger named Rover

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[Lucky 1]

I would like to add that on the static timing if you use the volt/ohm meter on the Ohms X 1000 scale IGNITION key off, instead of a 12 v light you can get the static timing even closer.

To test this for yourself: use your 12v timing light.
Then use the Ohms X 1000 Resistance method.
Also your brand new points contacts will not just sit on the timing
mark and sizzle until you shut the key off.

You will see a different and better result.
The light bulb itself has resistance and that will make the timing a little late.

[rrgunslinger]

Good point,

On Thu, Sep 13, 2012 at 10:01 AM, Lucky 1 [via Honda CB750'S] <[hidden email]> wrote:

I would like to add that on the static timing if you use the volt/ohm meter on the Ohms X 1000 scale IGNITION key off, instead of a 12 v light you can get the static timing even closer.

To test this for yourself: use your 12v timing light.
Then use the Ohms X 1000 Resistance method.
Also your brand new points contacts will not just sit on the timing
mark and sizzle until you shut the key off.

You will see a different and better result.
The light bulb itself has resistance and that will make the timing a little late.

Working on a CB750 Digger named Rover

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[dave Esch]

I'll be honest, I have no idea what's inside those carbs. I'm a car guy lol. As far as the airbox, I have the dreaded pod filters. I also have a 4 into 1 drag pipe which I know contributes to the decel popping. But regardless it seems a little extreme. I'll have to do some research n learnin on the timing. The advice is great but beyond setting timing marks I wouldn't know where to begin with a timing light. That's before my time as a mechanic. I'd probably use it as a strobe light and end up giving my neighbor a seizure.

[TOOLS1]

rrgunslinger wrote

I use a static light.  Not perfect but works. Set your gap first on both
points, then like Tools said do the left first then the right. Rotate the
motor to the timing point for the left side, then hook up the light and
turn on the ignition. Rotate the plate until the light comes on then back
it off until it goes out. Turn off the ignition then tighten the plate
screws and then rotate the motor (clock wise) to the second timmin mark and
set the second set.  If the gap is correct it should be real close.  I have
also used cigarette paper putting it between the points and setting
the timing to where you can pull the paper out from between the points with
a little drag but not tearing the paper.
http://i373.photobucket.com/albums/oo172/grandpaslinger/100_0706.jpg


On Wed, Sep 12, 2012 at 11:28 PM, Lucky 1 [via Honda CB750'S] <
[hidden email]> wrote:

> You have popping on decell and backfiring etc.,.
> It could have air leaks or the jetting is all wrong.
> Do you have stock exhausts and the stock air box?
>
>
> I need all of the facts.
> Also you need to order replacement screws to replace
> those timing screws, BEFORE you make any adjustments.
>
> 1976 CB750
> Exhaust type?
> Intake type.
> idle jet size?
> Main jet size?
> Slide needle clip position? Counting down from the top.
> Mixture screw adjustment.
>
>
> Also have your replaced the float needles and set the float levels?
> Working on a CB750 Digger named Rover
>
>
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>  If you reply to this email, your message will be added to the discussion
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WHAT????? You hook up the timing light, and start the engine. Then set the timing marks. Just how young are, you guys?
TOOLS

[Lucky 1]

You do not need to use the timing light.

But if you did put a timing light on it what you would see is,as you rev it
up slowly to 2500 rpm is two marks lining up with 1 mark inbetween  the two marks.
Like this ll l  Two marks i on mark inside of  two marks. Simple.

It just means the timing is advancing.

[Lucky 1]

A cigarette paper is only .006  not enough at all.

[rrgunslinger]

It works is all I'm gonna say.

On Thu, Sep 13, 2012 at 9:16 PM, Lucky 1 [via Honda CB750'S] <[hidden email]> wrote:

A cigarette paper is only .006  not enough at all.

Working on a CB750 Digger named Rover

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[Lucky 1]

We used to talk about that method out in the desert if we had no tools.
Except the myth back then was to use the cellophane wrapper.
Also useless.
But I never actually saw anyone ever use that method.
People just like the say they knew about it.

Points gap should be .012 - .016 thousandths.

[dave Esch]

You crack me up. I understand the concept of the timing light. I just have no experience with them. I own one that I used on my trans am and that was ten years ago. I have feeler gauges so I won't need to wedge a cigarette butt or any lighter flints into my points.
I'll get the book out and see if there is a picture of the marks in the correct position.

[rrgunslinger]

The paper is for setting the timing! not the gap!

On Fri, Sep 14, 2012 at 11:32 AM, dave Esch [via Honda CB750'S] <[hidden email]> wrote:

You crack me up. I understand the concept of the timing light. I just have no experience with them. I own one that I used on my trans am and that was ten years ago. I have feeler gauges so I won't need to wedge a cigarette butt or any lighter flints into my points.
I'll get the book out and see if there is a picture of the marks in the correct position.

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