Perform the obvious checks first. Check the air filter and pull the spark plugs and inspect and replace if needed. Take note of their condition. (smell like fuel? / Showing signs of a rich/lean condition? / broken? / etc)
Now, lets have a look at the
fuel pressure regulator.
The fuel pressure regulator is operated by the vacuum line that's attached to it. Since vacuum readings are directly related to throttle position the more throttle, the more fuel (quick/short explanation).
When there is no vacuum it supplies maximum pressure. Also may cause extra undesired fuel to leak into one of the throttle.
There are a few different ways these regulator fail.
- The vacuum line going to breaks is disconnected.
- The diaphragm that is inside of it fails.
When this happens it can cause a ton of different symptoms. One of them being your exact issue.
To check it you'll have to lift the tank up. Then locate the fuel pressure regulator (
FPR) (use the photo above for reference) and disconnect the vacuum line attached to it.
Inspect the vacuum line. Are there any signs of fuel?
Keeping the vacuum line disconnected turn the key to the
ON postion ###(DO NOT START THE BIKE)###. Does this causes fuel to drip?
If so, then we've found our culprit. The vacuum line should be completely dry and, the spark plugs should not have excess fuel on them what so ever.
Make sure that while you have everything opened up to take a look at any other vacuum lines you can see and replace them as needed. Since you're not reporting that the
RPMs are fluctuating at idle and it's simply the hesitation & vacuum readings you're getting. Then I'm almost certain it's going to be the
FPR and you most likely wont find any other vacuum leaks.
NOTE: If you're using any fuel additives. Now is the time to stop. It seems to show up much more in bikes that use them.