Tag Archives: Starter-valves

Balancing the Starter Valves on a VTec VFR

Last time around, I built a manometer, with which I could balance the starter valves on the VFR. The current model VFR has a chequered history with respect to fuelling issues. My pet peeve, is with the abrupt nature that the throttle travel starts. From closed, rolling on the throttle results in a “nothing… still nothing… BANG WE’RE ON” feeling from the engine. I’ll save some of you a lot of reading: After performing the starter-valve balancing procedure, the bike still has this light-switch style throttle. Subjectively, maybe the bike is a little better, but I wouldn’t dismiss “wishful thinking” may be biasing my opinion.

EDIT: After much consideration, I have revised my opinion. Rolling on the throttle from “closed” is still tricky to do smoothly, but it has become possible since performing this operation. I leave my original statement in the blog entry, but my revised statement is that this operation has definitely helped my bike and made for a more pleasurable riding experience.

Before I begin my walkthrough, there are several things I need to point out.

  • I am not a mechanic: Read my disclaimer.

  • When referring to the bike’s left or right, front or back, the directions will be orientated as they would be if you were sitting on the bike riding it.

  • I described fitting after market exhausts as “easy”. I would describe this job as moderately tricky. This walk-through is more about putting pictures to the procedure outlined in the workshop manual. There are risks associated with performing this task and if you never got past the disassembly / reassembly of some old equipment without having left-over pieces then I recommend you don’t try this one.

  • Balancing the starter valves should be done with the engine running at normal operating temperature. (presumably this is so the bike isn’t fast idling.) From experience I can tell you that it is possible to remove the parts of the bike required without burning fingers, or alternatively run the bike to warm it up when it is partially disassembled.

To get to the starter-valves, you need to lift the tank and remove the airbox.

The tank is hinged at the rear and can be lifted once the two 8mm bolts are removed from the front of the tank.

Tank bolts

The bike toolkit comes with a C-spanner and handle precisely the right length to get “maximum lift” from the fuel tank and despite its appearances is quite steady when in place. The tank has a “restraining wire” that prevents it being lifted too far. Pay heed and don’t attempt to lift it higher!

Once properly positioned, carefully remove the Number 15 vacuum hose from the variable air-intake diaphragm on top of the airbox. (i.e. make sure you don’t tear the rubber hose!)

removing vacuum hose

The airbox is in two halves (upper and lower). There are seven Philips head screws to be undone to remove the top half of the airbox.

Airbox screwAirbox screw

Screw locations

Once the top half of the airbox has been removed, the air-filter will lift straight out.

Remove the four air funnels in the airbox by undoing the two Philips head screws on each funnel.

Air funnels

On the left side, remove the PAIR air hose from (near) the rear of the airbox.

PAIR hose

Slightly lift the airbox and disconnect the white IAT sensor.

IAT sensor connector

The PAIR solenoid valve is attached to the rear of the airbox via a rubber strap. Slide this off the prong on the airbox.

The other end of the PAIR hoses connect to the cylinder head covers. These should be blocked off for performing the starter valve synchronisation. Rubber stoppers or even a bunched-up clean rag should be sufficient to do this.

PAIR reed valve cover

On the right side, remove the PAIR air hose from the rear of the airbox, the electrical connector from the MAP sensor and the vacuum line on the bottom of the MAP sensor.

MAP sensor and PAIR hose

About half way along the right side of the airbox is the bypass control solenoid valve. Disconnect the grey connector from the bypass control solenoid valve and the number 12 vacuum line from the one-way valve.

Grey connector

You should then be able to lift the bottom of the airbox off the bike.

Undo the MAP sensor from the airbox (held in place by a Philips head screw) and reconnect the vacuum hose and electrical connector. It wasn’t possible to access the screw that holds the MAP sensor in place until the airbox had been removed.

Now you’re ready to connect your manometer.

The four cylinder vacuum hoses are connected to a 5-way adapter. (The fifth line is the other end of the map sensor vacuum line)

5 way connector

Disconnect the four lines from the adapter and plug in your manometer. It’s not really important which hose connects to which tube, as long as it’s logical to you! You will need to know which vacuum line is attached to which manometer tube.

All hooked up!

The moment of truth starts here! With the bike in neutral and on the centre stand start the engine and cross your fingers! Well, actually, don’t cross your fingers – because you may need to turn the bike off in a hurry if something has gone wrong and oil starts travelling up the manometer tubing at an alarming rate. Note that the “FI” light on the dashboard will be showing. At a guess, this is because the ECU has detected that some of the sensors are “missing” / disconnected or are giving funny readings. This is hardly surprising given the amount of stuff we’ve disconnected.

There are three brass 7mm adjusters, allowing you to adjust the vacuum generated by each cylinder relative to the fourth cylinder. The aim is to have the same amount of suction on each cylinder, which means you will have even amounts of oil in each tube of the manometer.


The adjusters are on a spring-loaded ratchet style arrangement. That is, they turn in “clicks”. It’s a confined space and difficult to get tools in there neatly. Assuming you don’t have a tool that neatly fits in the area provided, the way I see it, you have three choices:

  1. You can “unload” the ratchet making the adjusters free to turn by hand, by pulling the brass adjuster “out”. (That is: pulling the adjuster away from the throttle body assembly) The problem with this method is that whilst the adjuster is “out” you have altered the amount of vacuum generated on that cylinder hose.

  2. You can use an open ended spanner. This works okay, but you are limited as to how far you can adjust each cylinder to around two clicks before you need to take the spanner off and reposition. If the starter-valves are a long way off being balanced, this can be a frustrating experience.

  3. You can use a socket on a T-bar that doesn’t sit squarely on the adjuster. Normally I wouldn’t condone such a practice as it is a great way of rounding off the edges of a nut. This is especially true seeing as though the adjuster is made from brass (and therefore very soft). However, in this case you don’t need to exert much force to overcome the “click”. As long as you are careful this technique works well.

Adjusting the adjuster!

Turning the adjusters changes the amount of air that can be drawn through two holes on the throttle body. The more the air is drawn through these holes, the less the suction will be on the cylinder vacuum hose.

Air hole

Turning the adjuster clockwise opens the air hole and thereby reduces the suction in the vacuum hose. (the oil in the manometer will drop). Turning the adjuster in the opposite direction causes the oil in the manometer tube to rise.

Now it’s just a matter of patience until you get the oil-levels in the manometer as even as possible.

There are a few tips I picked up along the way:

  • The procedure should be done with the engine running at 1200rpm. Use the throttle stop screw knob (on the right side) as necessary to keep the revs consistent. (The starter-valve adjustment can affect the idle speed).

  • When you first connect the lines, if one of the adjusters is a long way off correct, oil may drain quickly out of one of the manometer tubes. If the tube empties completely, air will be drawn into the manometer and this is a “bad thing”. To quickly force oil to be drawn back up the manometer tube, you can cover the air holes with your finger.

  • The workshop manual has the usual line of running the engine in a well ventilated area. They weren’t kidding! Leaning over the engine with it running exposes you to far more exhaust gasses than you normally get. Don’t take the suggestion of “well ventilated” lightly!

  • Running the bike at idle is not sufficient to recharge the battery. The Australian model VFR does not have a headlight switch. (they are “hard-wired” on whenever the engine is running). If you can’t turn off your headlights, it is a wise idea to disconnect them so that they are not drawing current from the battery. Depending on how long you run the bike for, or if you need to stop and restart the bike a few times, the process can be quite taxing on your battery.

The workshop manual also indicates you should reset the ECU after balancing the starter-valves. The (correct) reassembly of the bike will be sufficient to prevent the FI light from remaining on, but I can only guess that it keeps some “memory” of the sensors having been disconnected.

And that’s about it! As the manual states: “Reassemble in the reverse order”.