Hey everyone, I’m Matt from Howtomotorcyclerepair.com. In today’s video, I want to share with you the most common problems I see when servicing
older motorcycles. This video is going to cover how to diagnose these problems and also
what it’s going to take to fix them. Now, before we begin if you’re unsure or uncomfortable
with any of these procedures, please seek professional help and get your motorcycle
repaired properly. If you’re going to DIY these projects, make
sure you have the factory service manual for your year make and model. A service manual
is an invaluable tool to own and also makes for some great bedtime reading. Also, make
sure you wear safety glasses, the proper gloves and have a fire extinguisher in your work
area. The first most common problem in older motorcycles
is rust forming inside the metal fuel tank. What will happen is the rust will break down
over time into small little pieces and work their way into the fuel system, into the fuel
lines, clogging fuel filters and eventually clogging jets in the carburetor.
To look for rust, open up your fuel tank cap and take a peek inside and search for signs
of rust. Try and look all the way to the bottom of the tank, if possible. If you do find rust,
the proper way to fix this problem is to have the rust removed or neutralized and then seal
the tank with a high quality tank sealer. There are various products on the market that
will help you remove the rust and seal the tank.
Here’s a quick tip to prevent rust from forming in the first place. Keep your fuel tank full
and the fuel fresh. This will keep moisture out and minimize rust from forming in the
first place. The next most common problem are vacuum leaks.
A vacuum leak is where air is introduced into the system after the carburetors and it causes
the motorcycle to run lean. Now, normally, air enters into the air box
through the air filter and then finally through the carburetors. Air that passes through the
carburetor gets mixed with the proper amount of fuel that the engine needs. A vacuum leak,
on the other hand, is air that is not passing through the carburetor it doesn’t get mixed
with any fuel and, therefore, it causes the engine to run lean.
Some symptoms of vacuum leaks are: decreased engine performance and throttle response;
the engine will run better with the choke partially on; it will be difficult to set
the idle speed — it might idle a little higher or little lower; and lastly, the engine
may run better at higher RPMs. The most common area for vacuum leaks are
the boots that hold the carburetors in place, also known as intake boots or carb holders.
They are made from rubber which degrades over time and cracks can develop. If you find any
cracked rubber boots, replace them as well as any gaskets there may be. To check for
vacuum leaks, have the bike fully warmed up and idling. Take a spray bottle with water
in it and spray the intake boots. What you’re looking for is any change in idle RPMs indicating
a vacuum leak. Another common problem on older motorcycles
is that the carburetors will have to be cleaned or rebuilt at some point in their life. The
reason is because fuel can get stale and turn into varnish over time, and what that does
is it clogs small fuel passages in the carburetors. Older motorcycles that have not been ridden
in a while or started in a while will definitely need to have their carburetors cleaned.
Here are some symptoms of dirty or warn carburetor parts if the engine will only run with the
choke partially on or fully on that’s a classic symptom that it has clogged or partially clogged
jets and they will need to be disassembled and cleaned out if fuel leaks onto the ground
or into the air box that is a sign that your float needle valve is either dirty or worn.
The float valve is a moving part, so it should be inspected for wear and replaced as necessary.
The best way to clean carburetors is to remove them from the motorcycle, fully disassemble
all components, thoroughly clean them, reassemble and reinstall. Once the carburetors have been
cleaned, follow up with a carburetor vacuum synchronization procedure. Vacuum syncing
the carburetors adjusts the carburetor butterfly plates or slides to achieve uniform vacuum
signals across all carburetors. And finally, the fuel mixture screws can be adjusted to
achieve highest idle RPM. All this will make for a nice smooth and responsive running engine.
The next common problem I typically see is leaky fork oil seals. If the leaks are severe
enough, the fork oil will leak down the fork tubes and onto the brake pads. Oil on braking
components is not good. Also as oil continues to leak out, the front suspension loses its
damping capabilities and really makes it unsafe to ride. Forks in this condition should be
rebuilt with new bushings, oil seals and fresh fork oil. If oil was found on any brake components
they should be degreased and brand new brake pads installed.
Another problem I see is old tires. Older bikes probably have sat around for some time
and while there’s some usable tread left on the tire, the tire simply degrades over time
and cracks can develop or it can become dry rot. Inspect your tires for cracks and replace
them if necessary. Now, you can easily determine the age of your tire by looking for the Department
of Transportation — also known as the DOT — number located on the sidewall of the
tire. Prior to the year 2000, there was a three-digit
code which represents when the tire was manufactured: the first two digits would indicate the week,
while the third digit would indicate the year. If your tire has a three digit code you need
to replace it — it’s just too old. After two thousand the number consists of four digits.
The first two represent the week, while the last to represent the year of when the tire
was manufactured. For example, 4014 means the tire was made in the first week of October
2014. So, at what age should you replace your tires?
Well, there seems to be much debate about this topic and that is simply because there
are so many factors that can affect tire life such as UV light exposure or temperature.
So as a result most experts say replace your tires anywhere in the 5 to 10 year timeframe.
Once your tire hit five years old, I would have it professionally inspected on an annual
basis The next problem I often see is oil leaks.
The last thing you want is oil leaking on the road and having your rear tire roll over
it — that is not good. Leaks on older motorcycles can be pretty easy to visually locate since
most of them will not have any fairings and the engine may be exposed. For really hard
to locate leaks, I add UV dye to the oil and then use a light to find the leak. Oil leaks
can be repaired by disassembling parts, scraping old gaskets off and installing new gaskets.
Make sure to refer to your service manual for torque specific nations during reassembly.
Something else that can give you grief with older motorcycles is the electrical charging
system. Here is a quick test you can perform to see if you’re charging system is operating
properly. Hook up a multi-meter to your battery and record the voltage with the engine off.
Next, start the engine and record the voltage an idle. Finally, rev the engine up above
idle and record the voltage. Now, the service manual will usually specify what the voltage
should be at a given RPM. So, we are definitely going to need that information for this test,
Now, I do want to mention that many older motorcycle charging systems struggle to maintain
nominal battery voltage at idle, by design. The alternator or generator has a higher output
and higher engine RPMs, so that is why it’s important to check the charging system at
those conditions as well. The last problem I want to talk about is the
braking system. Most motorcycle manufacturers recommend changing the brake fluid every two
to three years and this is often overlooked. Brand new brake fluid should be amber or clear
in color which darkens over time. If you don’t remember the last time your brake fluid was
changed or appears dark brown in color, have your brake fluid flushed and your brakes bled.
You also want to check the condition of your rubber brake lines. Inspect them for any cracks
or damage and replace them immediately. Check with the service manual on the service interval
for the brake master cylinder and caliper seals. These seals do not last forever and
should be replaced from a safety standpoint if too old. When a master cylinder seal fails,
it will be unable to build pressure in the system.
Without pressure, the brakes will not work. You can diagnose a bad master cylinder seal
by squeezing the lever and holding it if the lever creeps towards the handlebar grip it
is faulty and should be replaced. The lever should have a nice firm feel to it. Now, if
the caliper seal fails, they typically leak brake fluid. So in this case, the caliper
needs to be completely disassembled, the piston needs to be inspected for corrosion and then
it can be reassembled with the new piston seal.
All right, well I hope you enjoyed that video. If you want to see more of my videos, head
over to Howtomotorcyclerepair.com or check out my Youtube channel, MatthewMCRepair. I’m
also on Facebook and Twitter. Just remember, if you’re unsure of anything
mentioned this video, please seek professional help. Alright, thanks for watching and I’ll
see you in the next video.