Kawasaki VN750 Forum banner
1 - 20 of 25 Posts

·
Registered
Joined
·
27 Posts
Discussion Starter · #1 ·
So, finally got my 05 750 running good today. Had a issue with the front cylinder not firing but a new set of plugs seemed to fix it for now. Took it for a quick 5 mile ride down the back roads and she did pretty dang good but bottom end could have been a little better. So pulled the plugs when I got home and see that the rear cyl was running pretty rich and front cyl was pretty lean. Most of the ride I was very easy on the throttle but did open her up a couple times ( amazing ). So my question is, can I let the bike warm up in the garage and hold it around 2-3k rpm then hit the kill switch and still get a good reading on the plugs so I can adjust the air/fuel mixture?
 

·
Registered
Joined
·
10,315 Posts
So, finally got my 05 750 running good today. Had a issue with the front cylinder not firing but a new set of plugs seemed to fix it for now. Took it for a quick 5 mile ride down the back roads and she did pretty dang good but bottom end could have been a little better. So pulled the plugs when I got home and see that the rear cyl was running pretty rich and front cyl was pretty lean. Most of the ride I was very easy on the throttle but did open her up a couple times ( amazing ). So my question is, can I let the bike warm up in the garage and hold it around 2-3k rpm then hit the kill switch and still get a good reading on the plugs so I can adjust the air/fuel mixture?
You might get a general idea of how the pilot circuits are working. If the rear cylinder looks wet on that test, there's some problem.
 

·
Registered
Joined
·
27 Posts
Discussion Starter · #3 ·
They’re not coming out wet, the rear was pretty dark/black and front looked new with a little white on the tip. It runs pretty good as is just trying to get it in the ballpark till I can get gauges to sync the carbs
 

·
Registered
Joined
·
27 Posts
Discussion Starter · #4 ·
Watch Photograph Green Light Analog watch

Got my paws on a set of gauge last night. Gushes are reading about 7 inches of vacuum on each cylinder but the gauge also says late valve timing or Leak at intake manifold or heat riser. Seems to be running good so not too sure if the timing could be off or have a intake leak? And not sure what a heat riser would be. Checked the manual and see that the carbs need to be within 2cmhg of each other but don’t see what the actual vacuum pressure should be
 

·
Registered
Joined
·
10,315 Posts
View attachment 54957
Got my paws on a set of gauge last night. Gushes are reading about 7 inches of vacuum on each cylinder but the gauge also says late valve timing or Leak at intake manifold or heat riser. Seems to be running good so not too sure if the timing could be off or have a intake leak? And not sure what a heat riser would be. Checked the manual and see that the carbs need to be within 2cmhg of each other but don’t see what the actual vacuum pressure should be
You can't go by the text on the gauges, those are mostly just suggestions. I'll post a link with a chart that helps explain how to read a vacuum gauge.

As long as your readings are close to matching, you're good. Synch isn't quite as critical with CV type carbs, as long as the throttle plates open equally and at the same time, they're good.

When reading a vacuum gauge for diagnostics, the motion of the needle is more important than a specific number. Not to say the number means nothing, but how the needle moves will indicate specific problems in an engine.

These charts are in most repair manuals, and there's many on the interwebs, though I've seen a couple that aren't quite correct. No doubt there's some YouTube videos on this, and you can also get a magnetic chart to stick on your tool box. Link below.... Scroll down to the fourth image for the chart.

 

·
Registered
Joined
·
10,315 Posts
I use Mercury sticks. They are far more accurate. Don't know if you can buy them anymore.
You can make a liquid manometer with clear tubing and motor oil. Maybe even colored water. Can't match the density of mercury, but if the carbs are way off you'll know it.

Honestly, on CV carbs I just look at the throttle plates.
 

·
Registered
Joined
·
1,991 Posts
You can make a liquid manometer with clear tubing and motor oil. Maybe even colored water. Can't match the density of mercury, but if the carbs are way off you'll know it.

Honestly, on CV carbs I just look at the throttle plates.
AKA bench syncing😁.
Looking at the throttle plates doesn't address any differences with vacuum. Best to use some sort of gauge.
 

·
Registered
Joined
·
10,315 Posts
AKA bench syncing😁.
Looking at the throttle plates doesn't address any differences with vacuum. Best to use some sort of gauge.
Well you still have to adjust the air screws, but if the throttle plates are right what other adjustment is there?
 

·
Registered
Joined
·
1,991 Posts
Using the sticks, you're comparing the amount of vacuum that's being drawn through the intake manifolds after the carbs. Can't see that.
A friend of mine rides a valkyrie, 1500cc six. Never ran quite right. I told him many times to use my sticks and follow the book process to sync. Finally, he did and boom. Runs sweet now.
Another benefit is you can sync the carbs without removing them from the lovely engineered setup of our VN's 🙄😫
 

·
Registered
Joined
·
27 Posts
Discussion Starter · #12 ·
took it out for a ride yesterday, about 10 miles, and this is what they look like. Top pic is the rear cylinder bottom is the front. From what I understand, the rear cyl is just a bit lean and the front is pretty much where it should be? She ran great just had a little hesitation from 1k-2.5k rpm
Motor vehicle Light Automotive tire Automotive lighting Hood

Automotive tire Motor vehicle Fluid Liquid Gas
 

·
Registered
Joined
·
308 Posts
I usually have tried to set the throttle plates as close to the same as possible, but I suppose if one cylinder has less compression or it's valve chain is in worse condition than the other cylinder maybe having one open at a different time may lead to a more evenly running engine. I have always tried to start off my tune by making sure the pickup coils are gapped correctly, the throttle plates are set the same and the spark plugs are set right (even if right out of the box). Maybe I'll rig up a manometer and see how it compares.
 

·
Registered
Joined
·
308 Posts
It might make setting the air screws easier. Thoe plugs don't look too bad. What is the gap at?
 

·
Registered
Joined
·
10,315 Posts

·
Registered
Joined
·
27 Posts
Discussion Starter · #20 ·
Yea pretty much.. heard a lot about how all balls is pretty much just selling junk now so wasn’t sure. I did order a set a bit ago anyways. Just wanted to find some that actually hold up 👍🏼
 
1 - 20 of 25 Posts
Top