A common problem we see out there on the forums is grossly limited rpm and speed in the higher range.
This can be devastating news for any rider, but especially for anyone who rides a motorcycle that has more power in the higher ranges, such as performance sportbikes.
So what happens if a motorcycle won’t go over 7,000 rpm? A quick note-we’re using this rpm as the metric, but generally, all of this information will apply to any known limitation on rpm.
An Explanation of RPM and How It Affects Performance
Rpm, or ‘rotation per minute,’ is the measurement of the working speed of any given engine.
The rpm is measured on your tachometer (the dial on your dash that isn’t the speedometer).
If we are speaking in basic terms, the higher the rpm, the higher speed you will likely be going. So, simply put, your bike’s rpm directly correlates to your speed.
If your bike won’t go above 7,000 rpm, then you won’t be able to go as fast as you want and it will also affect your performance metrics such as power and torque.
A lot of sportbikes and crotch rockets rely on much higher rpm to deliver the top performance horsepower and torque in a specific range, known as the power band.
A lot of times, when a bike’s rpm is limited before they hit the max you know they can make, a bike will seem bogged down, or perform rather sluggishly. This can have long-term effects, so we need to make sure our bikes are always performing to the best of their abilities.
We’ve rounded up a few of the common reasons why your bike won’t go above 7,000 rpm as well as some solutions for this problem. Take a look below and you might just find a solution that will get your bike performing as it should!
1. Bad Fuel Filter
A whole slew of issues with limited rams can come from the fuel delivery system on your motorcycle. Sometimes this starts within the tank’s primary fuel filter or any inline fuel filter somewhere between the petcock and carburetor or fuel injectors if your bike has them instead of a carburetor.
Now, more than ever, it is important to use high-quality fuel because the ethanol present in lower-quality gas can gunk up and clog your fuel filter.
If your fuel filter clogs up from lower-quality gas, it doesn’t allow enough fuel to pass through the fuel delivery system into your engine. Without enough fuel, your bike won’t be able to surpass 7,000 rpm.
It is simple enough to diagnose and fix, and fortunately, replacing a fuel filter is an inexpensive solution.
If you have a gravity-fed fuel system, your primary fuel filter is inside the bottom of the tank, often attached to the head insert of your petcock. To diagnose if this is the case, you will have to drain your fuel tank.
One way to do this is to remove a section of your fuel line from one connection and drain the fuel into a gas can. Make sure you have one large enough to hold the amount of fuel your tank can hold.
Once the fuel has been sufficiently drained, remove the petcock from your gas tank and visually inspect the fuel filter. If it is clogged with ethanol leavings, go ahead and replace it. If you have an inline fuel filter, chances are you’ll be able to see any clogging. Simply turn your petcock to the off position, remove the filter and replace it with a new one.
This could be the reason you aren’t spiking up to the high rpm you need for top performance and fuel filter replacement will get you running properly.
2. Bike Needs New Fuel Pump
Unlike bikes with gravity-fed fuel systems, some bikes have an electric fuel pump. Fuel pumps, just like any other part on the bike, will start to malfunction over their life and will eventually need to be replaced.
This is especially easy to diagnose because a fuel pump will prime itself when you switch the bike on.
Every time you turn the bike on, you should be able to hear 5-10 whirring clicks as the fuel filter fills itself for optimal fuel delivery during engine performance.
If you hear only one paltry little whirring sound, or nothing at all, you can be sure your fuel pump needs to be replaced.
Remove the old fuel pump and replace it with a new one. This is a good time to check your fuel filter for any blockage because a fuel pump will work overtime to bring fuel into your system and wear itself out long before its normal life has played out.
3. Damaged Or Kinked Fuel Line
Any damage or kinking in your fuel line will also be responsible for limited rpm over 7,000. If your bike isn’t getting the fuel it craves for combustion, higher rpm are unattainable.
Visually inspect your fuel line for any kinking. If you find a section of fuel line that is stopping up the fuel delivery, replace it and see if you don’t rocket above 7,000 rpm in no time!
Chances are, if you have a damaged fuel line, you’ll be able to smell leaking gasoline. This is a problem because your bike has a specific amount of gas to mix with air and power your bike.
Any damaged, leaking fuel lines will need to be replaced and secured with the proper style of clamp. These metrics will be available in your service manual, so be sure to order the correct size of fuel line, which often comes with a set of correctly sized clamps.
4. Common Issues With Carburetors
If you find that your bike won’t climb above 7,000 rpm, there is a whole slew of issues within the carburetor that can limit your engine’s working performance.
It is a good idea to periodically remove your carburetor and check for issues like clogged jets, improperly working floats and minor adjustments that need to be made to ensure the proper air/fuel mixture for your bike.
Clogged fuel jets are common culprits for limited air/fuel mixture. This can easily affect your bike’s performance, especially in the higher range of rpm.
Sometimes you don’t need to remove your entire carburetor to rectify this issue.
Simply open up the accessible areas of your carburetor like the air intake behind the air filter or the float bowl and spray a good amount of carburetor cleaner up in there. It may be enough to clear any clogged jets and get you revving as high as you like!
If that doesn’t work, it is worth it to remove, disassemble, and clean out your fuel jets individually with a small piece of wire.
5. Fuel Injectors Are Clogging
While fuel injectors are the modern, more efficient way to deliver fuel into your engine, they are quite a bit more complex than a carburetor and require computerized readings to diagnose any issue with them.
Visit a local professional to have your fuel injection system diagnosed. Be prepared to replace them if they are malfunctioning, and get ready to shell out some serious clams to rectify the situation.
6. Vacuum Leak Causes Bogging
Your bike’s air delivery system needs to be tight with a capital ‘T.’ That’s why it is referred to as a vacuum system. No extra air should be coming into your system because, when it does, your bike will bog down and you’ll be left around 7,000 rpm or even lower.
Air can enter the vacuum system from loose connections or cracked rubber tubing. Visually inspect your bike’s vacuum system for any signs of loose clamps or cracks in the rubber air hose.
If you can’t see anything amiss but have a suspicion that a vacuum leak is responsible for your limited rpm range, then you’ll need to do a simple test with carb cleaner.
Start your bike and leave it at idle. Slowly target areas where you suspect any leaking might be allowing air into your system that shouldn’t be there. If you spray around a connection or a cracked rubber hose and the bike suddenly revs up, you definitely have a vacuum leak.
Replace any part of the airbox, air cleaner tube, or connectors/clamps that are bad and you should be running just fine in no time and won’t feel the bogging that is limiting you to only 7,000 rpm.
7. Old Throttle Cable Has Too Much Slack
Throttle cables are made of braided metal wire, which can expand over time. Even if you adjusted the throttle cable appropriately when they were new, they have a tendency to stretch.
If this is the case, your throttle won’t be able to open up enough to deliver the fuel you need for higher rpm and speeds.
Check your throttle cables to see if there is any extra slack. If you have been feeling more and more play at the hand throttle itself, it’s probably good to adjust it to your service manual specifications.
Once you properly adjust (or replace) your throttle cable, the bike should be able to dump enough fuel in the system to allow you higher rpm, speeds, and quality performance!