Cam sprocket index marks on 1979 model?

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ScottBowl
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Joined: Tue Apr 15, 2014 3:16 pm

Cam sprocket index marks on 1979 model?

Postby ScottBowl » Sun Aug 26, 2018 10:29 am

I have done head gasket replacement on 2 seperate 1981 models in the past and I distinctly remember two punch marks at the 3 and 9 o'clock position of the sprocket - I'm doing the same service on a 1979 model now and I don't see the marks.

The motorcycle is not running properly and will not idle (running on 2 or 3 cylinders) so for all I know the cam timing is improperly set. Any thoughts on this?

I am replacing the head gasket because there is a huge hole in the gasket on the left hand side and it is leaking oil badly.

I believe the timing is correct (cam notch facing forward at TDC 1.4)

Here are some photos: https://imgur.com/a/TCnWjJd

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Volker_P
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Re: Cam sprocket index marks on 1979 model?

Postby Volker_P » Tue Aug 28, 2018 1:08 am

The camshaft notch is relevant for timing, marks on the sprocket may be nice but they are not crucial for timing.
Camshaft timing look all right from your pictures.
Note that ignition timing uses the "F" and not the "T" mark.
Compared to CV/VA carbs, the piston/PD carbs are quite sensitive to the air side.
A 1979 could have carbs with still the cutoff diaphragms.
People here reported that the bike may run somehow but bad if they are gone (see e.g. viewtopic.php?f=4&t=722)
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

ScottBowl
Posts: 50
Joined: Tue Apr 15, 2014 3:16 pm

Re: Cam sprocket index marks on 1979 model?

Postby ScottBowl » Tue Aug 28, 2018 11:15 am

Volker_P wrote:Compared to CV/VA carbs, the piston/PD carbs are quite sensitive to the air side.
A 1979 could have carbs with still the cutoff diaphragms.
People here reported that the bike may run somehow but bad if they are gone (see e.g. viewtopic.php?f=4&t=722)
The air cutoff diaphragm is there but there was a small tear along the outside edge, I thought I'd repair it with a bit of epoxy. I'll show a photo of the repair when I return from the head gasket replacement today.

The slow jets were badly clogged, so those have been soaked and I can see the pinhole clearly against a light source. They are a bit scuffed with vice grip teeth marks but I tried not to compress them...

We soaked the ports under each slow jet then blew them out with compressed air to ensure good flow. I am just waiting on new float valves for re-assembly (carb #1 overflow was leaking constantly)

Here is some data on what I did earlier this year to ensure the timing was correct and the misfire was not an electrical problem:

Ignition coil readings (same readings for both coils tested individually):
between small blades going to wiring harness 2.5 ohm
between plug cables 12.28k ohm

Plug Caps (not sure which reading belongs to what plug): 5.1k, 5.1k, 4.7k, 4.5k

"Pulser Generator" readings:
Measured at connector located next to the battery box
Between yellow wires: 515 ohm
Between Blue wires: 492 ohm
Gap set to 0.406mm between pins and crankshaft on both positions.

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Volker_P
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Location: southern Germany

Re: Cam sprocket index marks on 1979 model?

Postby Volker_P » Wed Aug 29, 2018 12:53 am

ScottBowl wrote:The air cutoff diaphragm is there but there was a small tear along the outside edge, I thought I'd repair it with a bit of epoxy. I'll show a photo of the repair when I return from the head gasket replacement today.

Well, there are four of them, only one is accessible without separating the carbs.
The single diaphragm at the rear bottom of the carbs is for the accelerator pump. A crack here will result in poor throttle response when opened from completely closed.

If you did pull and clean the idle jets and also were able to blow through the channels it should idle on all four at least somehow.

Your electric values seem all right. If your plugs should look different, swap them between cylinders and watch for possible changes.

Make a visual check of the carb synchronization as long as they are out: Turn out the black manual idle knob completely so all four sliders are completely closed. Then turn in slowly until all four open simultaneously to the same tiny gap. This visual carb sync should be sufficient for good idle and throttle response. Vacuum sync is fine tuning and only makes sense if everything else is close to perfect for sure.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues


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