Why Your Motorcycle Is Losing Power When Accelerating & How to Fix It!


Oops! No power. So it happens, you are pushing dirt uphill and you are on full throttle. All of a sudden your engine feels like it is losing steam, and the sound slowly fades and you can feel that you are slowing down. You try to gun and regun your throttle but nothing happens, the engine slows down to a hum and almost dies down.

Then you realize you no longer have power and some may call it “Bike is bogging.”It is a metaphor for slowly getting stuck and not being able to get anywhere. So, what you are actually experiencing is a loss of power when trying to accelerate.

Let’s get straight to the possible causes: (the common ones)

Injector type:

• Fuel pump not working
• Fuel filter dirty or clogged
• Low-quality fuel

Carburetor type:

• Fuel intake adjustment (flooding or too little fuel)
• Spark plug (either needs replacement or cleaning)
• Blocked jets
• Float height (needs adjustment)

Other possible issues: (carburetor and or injector)

• Too high or too low oil level
• Air Filter
• Vacuum leak on the carb
• Carburetor spring issue
• Carb tuning due to change in altitude
• Slack in the throttle cable
• Poor Valve timing

Injector Type

Fuel Pump not Working (Injector or carb)

This works for both injector type and carb engines.

Symptoms:

Whining sound from the fuel tank: A normal functioning fuel pump just makes a low hum. However. if it’s broken it emits this loud whining sound, and this can happen when you are on the road or when you are on idle.

Sudden Acceleration: Suddenly your bike accelerates like you are gunning it, and this is without you actually squeezing the throttle.

Engine won’t start/or suddenly dies: Assuming that you know all the other parts are okay, suddenly your engine won’t start or it dies in the middle of the ride.

Fix:
Replace Fuel Pump. (link to Amazon)

Fuel Filter Clogged (injector or carb)

Symptoms:

• Engine power is noticeably reduced
• Random misfires and hesitations
• Decreased response under heavy loads

Fix:
Replace fuel filter.

Low-Quality Fuel (Injector or carb)

Symptoms

• Hard starting
• Unusually high fuel consumption
• Rough idle
• Higher smoke emission
• Engine Stalling

Fix:
Change fuel brands and use unleaded or premium gasoline with high octane.

Carburetor Type (Possible Causes)

Cause #1: Fuel Intake Adjustment (Carb)

A motorcycle carburetor (just like any) runs on a ratio of fuel vs air intake. Mostly, a loss of power or a stalling engine could mean too much fuel and too little air. Too much fuel floods the carb that prevents proper combustion, which results in no power.

Fix:
Refer to your OEM manual, or you can check online and locate the fuel screw on your carburetor where you can adjust it to the required valve opening. This involves how many turns you have to make off the fuel screw to either limit or increase fuel intake.

The standard number of turns for the fuel screw is 2 and turns. Note: This depends on the specs of your motorcycle. Again, please refer to your manual and by the way, this process can be done assuming that you have the proper air intake adjustment. So check your air intake as well. The goal is to have the correct ratio of fuel to air intake.

Cause #2: Spark Plug Issue (Carb)

Depending on the age of your motorcycle, spark plugs may become dirty by way of too much carbon accumulation on its contact point. This usually looks like burnt oil and grime. The contact point may also turn overly white which is also another form of residue that is preventing spark.

Fix:
Remove the spark plug and clean it using a wire brush. If you haven’t replaced it in quite a while, or maybe you remember that you actually never replaced it yet, do reload a new spark plug and start your engine. Don’t forget to look up what type of spark plug is recommended for your engine model.

Cause #3: Blocked Fuel Jets (Carb)

Normally a carburetor has two jets, the main jet, and the pilot jet. You can do this fix only if you have some experience with carburetor assembly, or you have the time to study it. For posterity sake, if you suspect a jet problem, you can always take your bike to your expert mechanic for inspection.

Or, if you are a certified bike head and tinkering is your thing, go ahead and disassemble. Just make sure you follow every step in the book on carburetor assembly. Although it isn’t as simple as it looks, where would be the fun in discovering the fix right?

Fix:

Remove the carburetor from the bike. Uninstall jets and peep through both of them against the light. If there are blockages, you can use pressurized air to remove them and wash them with gasoline to clean out any remaining residue. Reinstall jets and reinstall carb. Start the engine for testing.

Cause #4: Incorrect Float Height (Carb)

This is a common problem in older carburetors, and sometimes with newer ones. Float height inside the carb for some reason is set incorrectly, causing the carb to flood or lack fuel entirely. If all the other possible causes check out and you still have the problem, we recommend that you bring your bike to your expert mechanic for float adjustment. If you prefer to do DIY, then check your manual for float height measurement that is required.

Note: this requires some professional expertise, otherwise be precise when doing it yourself.

Fix:
Remove carb. Disassemble to open the float chamber and check the rubber float for any damage. Check the float distance then make the necessary adjustments. Reinstall carb.

Other possible issues: (Carb)

It is important to note that the order in which this guide is made regarding which issue came first, is not ironclad. Meaning, any one issue can come before the other. So it is up to you as the owner of the bike to note the history and age of your motorcycle. You are the one who knows when and what has been done to your bike in the past.

With the history of your bike in mind, you will be able to make an estimate of what the issue might be. This is regardless of the order that is listed here. So feel free to diagnose in any way you think you’ll be able to get to the solution faster.

Other cause #5: Too High or Too Low Oil Level (Injector or Carb)

Choosing the right type of oil to use for your motorcycle is critical to your engine’s longevity, and the amount of oil you put is as important too. Too much oil over the required level on your dipstick can impair your engine’s capacity to drive its pistons at the right speed and the right timing. It becomes sluggish and components are overburdened by the sludge.

It is similar to little or no oil in the engine, where friction and dry metal to metal action will literally break your block.

Fix:
Check the oil level, then top up if necessary. Find the right type of oil depending on your engine’s type and age.

Other cause #7: Dirty Air Filter (Injector or Carb)

Whenever an air filter may have outlived its service life, it begins to accumulate dirt and dust in which it becomes unpassable. Nevertheless, if your filter is clogged, replace it with a new one. It is not recommended to reuse an air filter by cleaning it with air pressure, it damages the filter and impairs filter performance putting your engine at risk with more dirt and dust.

Fix:
Replace filter. Do not reuse damaged or expired filters.

Other Cause #8: Vacuum Leak on the Carb

A leak happens on the carburetor when due to the age of the carb, it might already have faulty gaskets or cracked intake boots. This results in unwanted air getting mixed into the carb chamber. Too much air and too little fuel impair combustion which leads either to a very lean burn or stalls your engine entirely.

Fix:
Locate your carburetor intake boots and clamps. Tighten clamps and check boots for cracks. If boots are cracked, replace them. Ensure that the gaskets in between the float bowl and the rest of the carb chamber are not brittle or cracked. If you find that they are, replace gaskets where and when necessary.
Ensure airtight seal upon reinstall of carb, then test engine.

Other Cause #9: Carburetor Spring Issue

Sometimes, when you have a motorcycle that had a previous owner who tried to rebuild the bike, he may have tinkered with the carb assembly and failed to make it work. So the problem is, it could be a spring in the carb that was mistakenly put in backwards. The reason that this issue is significant to the acceleration problem is that when you put in the spring the wrong way and you squeeze the accelerator what it does exactly is the opposite, which is to decelerate.

Fix:
Again, depending on your skill level as a rider/hobbyist/part-time mechanic, you can open the carb without having to remove it. Check to see if the spring is put on backwards, then you can test it by squeezing the throttle and see how the butterfly valve reacts. If it opens when you squeeze it and closes when you let it go, the spring is in the proper position. If it does the opposite, remove the spring and reattach right side up. Close the carb, then test engine.

Other Cause #10: Carb Tuning Needs Adjustment Due to a Change of Altitude.

You might be wondering why your motorcycle has been working well in the lowlands, or maybe in a valley near your home, but then when you climbed a few thousand feet above sea level high up in the mountains, suddenly your bike seemed a little too slow to respond or maybe doesn’t respond anymore when you gun the throttle.

The likely culprit to this would be the lack of oxygen in the air. Since high altitude means thinner air and even thinner air pressure, you could be running rich in fuel only because there is not enough air that gets into the carb or the crankcase on an injector.

Fix:
Adjust your fuel and air intake settings using the screwdriver to adjust the screw adjuster on the underside of the carb. Refer to your manual for the required turns. If power is still unsatisfactory, adjust accordingly to your estimates with the resulting desired acceleration output. You can literally play it by ear for the exact fix.

Other Cause #11: Slack on the Throttle Cable

Sometimes an extra slack on the throttle cable is preventing full control of the butterfly valve in the carb. You can diagnose this by looking at the butterfly valve while squeezing the throttle all the way, and see if the valve opens fully. If the valve doesn’t open fully chance are there is an extra slack on your throttle cable. This could also explain why you are not getting full power.

Fix:
On some other older bikes, the throttle may already have stretched due to age, so what we recommended is a cable replacement. Otherwise, you can simply tighten the knob connecting the throttle cable to the carb. Either way, it should fix the problem.

Other Cause #12: Bad Timing Advance (Injector)

This applies to injector type engines. A good timing advance electronically regulates when the spark plugs fire exactly when it is needed to. In an injector type engine, the faster your bike goes, the faster the firing of the spark plugs. The way these components operate together has much to do with engine timing. If engine timing advance is in the correct settings, you won’t have problems accelerating and decelerating at any rate. If the timing advance is not correct, the spark plugs will not fire at the right moment.

The motorcycle will not accelerate properly and will likely misfire and eventually stall.

Fix:
This is a problem that we recommend you take to your expert mechanic for diagnosis and repair. More often than not, even veteran riders might not have enough experience in this kind of repair. To the be on the safe side though, it would be wise to do so. An improperly timed engine could literally break pistons inside the block if not addressed.

Final Word

Once again, these possible causes are in no particular order. If you’ve had your motorcycle for a long time, you are the best person to make estimates on which might be causing the problem. Anyhow, finding the fix won’t be as difficult with your homegrown expertise. Good luck and ride well!

Luka Barron

Motorcycle mechanic, writer and Heineken lover. A bit like Hank Moody on a Suzuki.

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