The carb set is ready for installation on Project 17, but in anticipation of syncing the carbs I'll want to attach the tool's adaptors and hoses. This is much easier with the carbs off the engine.

I use a Morgan Carbtune. After struggling with mercury and mercury-substitute devices I discovered the Carbtune and it's found a permanent home in my toolbox.

(Below) The adaptors are screwed into the intake manifold vacuum ports. Remove the screw in each manifold. On California-spec models and 1990+ models, two or more of the ports will have hose adaptors in place for the emissions hardware. Remove and replace with screw plugs if you're removing the emissions hardware, as I am on this California-spec 1986 VFR750.

The adaptors are lightly screwed in place; no need to compress the rubber seal beyond what's needed to make a seal. I then connect the hoses to the adaptors, which I've labeled #1 through #4, and plug the ends with golf tees.
Ready for carb installation.

Progress continues on Project 17. With valve clearances checked and cylinder compression verified, it's time to clean, inspect, assemble and install the carburetors.

I first completely disassemble the components, scrub the carb set in the sink with degreaser and hot water rinse, then give the small parts a dunk in the ultrasonic cleaner. All the passageways are given a blast with compressed air and verified clear. As a matter of course I replace the fuel tube o-rings and fuel lines (see the Maintenance page for a detailed tutorial). 

​(Right) ​This carb set was pretty grungy on the outside, but surprisingly clean inside. Someone had replaced the float bowl screws with generic allen screws which have since acquired a lovely rust patina.

(Right) In order to remove the pilot screw adjusters, the factory caps need to be removed. This is made easier by applying gentle heat from a small torch while gently pulling on the cap till it comes off. The caps are an emissions thing (to prevent owner adjustments) and don't need to be reinstalled unless desired. The screwdriver groove will have some grunge in it so clear that out with a small blade.​

​(Below) Turn out the screw, being very careful to avoid losing the spring, washer and o-ring inside — these little parts are NLA from Honda, though I have sourced replacements for the o-ring and metal washer. I use a small nail with a bent tip to dig for the washer and o-ring if they're left stuck inside the hole.

​(Right) This needle is stock OEM, which tells me that no jet kit was installed in this carb set.

(Below) After reassembly, the five California-spec vent tubes will need to be capped. I source rubber (not cheap plastic) caps from NAPA; four 3/16" and one 7/32". Install them using the original OEM spring clamps.
(click on an image to enlarge)

(Below) An additional aspect of California-spec bikes is the method of fuel tank venting. Instead of venting through the filler cap the CA bikes vent through a tube in the underside of the fuel tank. DON'T PLUG THIS VENT. Run an open hose downward in the front area of the frame and terminate somewhere that fuel vapors won't ignite on a hot engine part.
Ready for installation!

Spark plugs are simple-looking little devices, but in reality they're highly-engineered components lying at the heart of an engine's combustion process while living in an unimaginably harsh environment.

Fortunately for us home mechanics, they're simple to deal with. I'm re-installing the plugs in Project 17 in preparation for test running the engine, and my basic tools are a plug gapper and an old tube of anti-seize lubricant. I've had this tube for at least 20 years, so a little goes a long way.

The idea behind the plug gap is to afford the largest gap that your ignition can fire, thus giving the largest flame to ignite the combustion mixture. But with use, the spark plug gap will increase so it's best not to go with the widest gap at initial setting — give the plug a little extra to work with. The range on our plugs is .03-.04" so I set mine at .035".

A word about heat range. The specified NGK plug for the '86-87 VFR 700/750 is DPR9EA-9. The letters and numbers are fitment and resistance values, but the middle number, 9, is the heat range value. NGK numbers their plugs higher for "colder," lower for "hotter" (some manufacturers are the opposite). Hotter vs colder is simply the ability of the plug to dissipate heat. A hot running engine needs a cooler plug, and vice versa. Honda specifies either a number 8 or 9 for this model. Why would you choose one over the other? If you run consistently in an unusually cold environment you may want to choose the number 8 if your engine exhibits some carbon fouling or sooty deposits. This was much more of a concern in the old days of air-cooled motors, not so much anymore. What you don't want to do is run a hotter plug 'cause someone on the internet said it's "higher performance" or some such nonsense. Not true in any sense and too hot a plug can cause engine damage. To consider a plug heat range change for performance modifications is unlikely — it would require an increase of about 75 HP to warrant a cooler plug. So, a K&N air filter, slip-on mufflers and a jet kit DO NOT require a plug change. This is a case where the engineers at Honda are smarter than us.

After checking the gap, I smear a bit of anti-seize on the threads, being careful not to allow any near the tip which could cause a hot spot and pre-ignition. To make certain that I don't cross-thread the plug I use a short piece of rubber hose to thread the plug in place. Dealing with a cross-threaded plug hole in your cylinder head will have you rethinking your life decisions.

Final tighten with a socket wrench. If you don't have a feel for proper spark plug torque, use a torque wrench till you do. See the life decisions discussion above. A stripped plug hole from over-tightening or a popped plug from too loose a plug will also ruin your day.

I like to put a big dab of di-electric grease on the end of the plug wire. This lubricates the fitting making it a little easier to remove in the future and also forms a water and humidity seal.

Next up; carburetors.

Next on the list for Project 17 is checking the cylinder compression before attempting an engine start. Cylinder pressure readings can tell us much about our engine's health — if the piston rings are weak or broken, if the cylinder bore is damaged, if the valve seating is compromised, if the head gasket is leaking. In other words, if everything is okay or not.

There's an even more comprehensive check called a leak-down test, where constant air pressure is applied to the cylinder via the spark plug hole while a separate gauge tells us if that pressure is being held within the cylinder. The advantage of a leak-down test is that if a leak is detected it can be pinpointed by listening to the exhaust pipe or intake tract for the telltale hissing sound of escaping air. The leak-down test is common in aircraft maintenance and requires specialized equipment...which I don't have.

But the simpler compression check is still a viable check for me, as I don't know the history of these projects. One of the three critical ingredients to combustion is compression, so if I find a cylinder with low or no compression, well....Houston, we have a problem. To Honda's credit, in my years of checking these engines I have never found one with compromised compression readings.

The process is quick and simple and only requires an inexpensive compression tester, shown at right. The tool will provide adaptors to fit different spark plug hole sizes and threads. Rubber o-rings provide sealing with only hand pressure used to seat the adaptor into the plug hole.

A proper compression test is done on a recently run (warm) engine — that's not possible for me as my projects haven't been run yet, but the test will still tell me if we have adequate compression.

With all the spark plugs removed and the kill switch "off" (or the plug wires grounded to prevent damage to the ignition system) screw the tester into the plug hole and connect the gauge. Crank the engine over with the starter till the pressure reading stops advancing — that's your reading. Repeat for the remaining cylinders while recording your readings.

While specific values are sometimes provided in service manuals, the bottom line is that all the cylinders should have similar readings, with the lowest vs. highest within about 10% of one another. My typical readings for the VFR are around 150 psi (cold engine). In this case, my readings were 160-197 psi. I don't apply the 10% rule here, again, because this engine hasn't been run in many years. Once the engine has some run time, the readings will be different and probably very close to one another.

The reason my readings were high is due to the fact that I'd added oil to the cylinders before testing (to protect the cylinders and rings). Adding oil is a technique used to isolate the reason for low pressure readings — if adding oil increases your reading, then the cause most likely lies with the piston rings (the oil is helping the rings achieve a seal), as opposed to valve seating being the cause. In this case, I'm happy with these readings — they tell me that it's OK to move forward with this project.