Synchronization Reading

I am trying to sync the carbs on my '78 kz1000. My service manual says the reading on my gauges should be between 7.9" and 10" (20cm to 28cm). My local shop says due to old age, 49,000 miles, that the compression will be too low to get that good of a reading, so find the lowest one and set to that. Then there is the idle screws, local shop says 2 1/2 turns out should be good.

some advice? I have never done 4 carbs before.

my bike is bone stock. only thing different is the part of the air box under the seat with the two tubes is gone. Just the part with the air cleaner in it remains. all the rest is stock.

SuperTrey wrote:

I am trying to sync the carbs on my '78 kz1000. My service manual says the reading on my gauges should be between 7.9" and 10" (20cm to 28cm). My local shop says due to old age, 49,000 miles, that the compression will be too low to get that good of a reading, so find the lowest one and set to that. Then there is the idle screws, local shop says 2 1/2 turns out should be good.

some advice? I have never done 4 carbs before.

my bike is bone stock. only thing different is the part of the air box under the seat with the two tubes is gone. Just the part with the air cleaner in it remains. all the rest is stock.

The point of synchornizing is to get all four pulling the same amount of vacuum. To do that, they have to be machanically synced first so that at a given idle position, all the butterflies are open about the same physical distance. Then dialing the fuel-air mix screws is what equalizes them when they are running so each is pulling the same.

If the copmpression is low, it would make the readings lower so I assume you would want them to all be the same even if they were below the book spec. I am not so sure 49k miles would hose the rings that much, but depends on maintenance.

I think that perhaps you should find another source of information as it is obvious that your "local shop" doesn't work with many vintage bikes. Lower compression will lower vacuum readings but if you can start the bike fairly easily, then your vacuum readings will be in the range suggested by your manual. If you have significantly lower readings, the normal reason is that bench synchronization was not done properly and your slides openings are open too far and take you below the suggested vacuum levels. As fas as how many turns out for the pilot mixture screws (on float bowl towards front) on most of the 78 VM26s, about 1 3/4 turns out is right. The 2 1/2 turns suggested will soot up your plugs as it is definitely rich.