Carb Sync

[surfish95747]

Okay guys so I got all set up to do a carb sync on my 19809 CB750k, warmed up the engine and made sure the choke was closed. This is what I got.



The red says "Late valve timing or leak at intake manifold or heat riser".

Does this mean I need a valve job? I don't know how there could be a leak at the intake manifold as I have new rubber from the engine to the carbs.

When I did a compression test I get 100 -110 at all 4 cylinders.
Any ideas?

[Re-run]

100+ shouldn't be a big problem. I don't know what it should read for sure, but the sync is more about getting all 4 cylinders about the same for optimal operation. If things drop under 100, then you can look into the cause.

[surfish95747]

Re-run, what I'm concerned about is the carb sync seems to show I hardly have any pressure. I guess I'll look around for leaks, but I don't know.

[TOOLS1]

Ignoir the writing on the gauges. You just want to sync the carbs together. They should be around 5-7 Inches vacuum. Engine compression has nothing to do with vacuum.
TOOLS

[Re-run]

Yeah, as TOOLS said, ignore the writing. The gauges are used for multiple things. I should have clarified that better before. You want even vacuum between the 4. Other measurements are for engine compression, among other things.

[surfish95747]

Ah, thanks guys. So cylinder 2 is right on the money?

[TOOLS1]

Its close, but that should be the cylinder that is permanently set, you adjust all the others to it. However as you adjust the others that cylinder might change. Just start adjusting, and be sure to blip the throttle after each adjustment. Then when they all read the same, adjust the idle again.
TOOLS

[Re-run]

Yep, #2 doesn't adjust. It is the base cylinder to adjust the others to. So, get the engine warmed up and then put a fan in front of it to prevent over heating.
Start on #1 and get it the same. Blip and let things settle. Then I go to #3 and get that the same as #2, blip and repeat for #4 and blip again. Adjusting idle each time to maintain about 1200 rpm or so.

You will notice that the readings dont stay where you set them completely, but the engine will gradually settle into smoother idles.

Repeat the steps with #1 - 4 again. Buy then, things should be staying very close. You can do it a third time, but might not need to. Keep in mind the readings do not have to be 100% perfect, within 10% is usually pretty good.

This is my method and it has worked well for me.

[surfish95747]

You guys are the best. Thanks for the help. I'll be doing the sync tonight when the sun goes down and its not 110 degrees!! Thanks all.