Have you ever wondered what causes a poor throttle response on your motorcycle? Maybe your bike was running fine and then suddenly it started bogging down on acceleration, or maybe there is a delay between twisting the throttle and the bike launching. These are all signs of a possible throttle issue, but what causes these issues?
Poor throttle response or lag can be caused by a variety of issues. Some of these reasons include worn spark plugs, a dirty air filter, carburetor issues, bad gasoline, or even the incorrect type of spark plugs.
1. Worn Spark Plugs
Dirty or worn spark plugs could be the cause of your issue. Your engine relies on the spark plugs to ignite the air fuel mixture in the combustion chamber. With a dirty or worn out spark plug, the plug won’t be able to ignite the mixture properly.
As an engine runs it will build up carbon and oil residue on the spark plugs. This residue will lessen the strength of the spark plugs spark causing reduced power and poor acceleration. A rich engine can foul up plugs pretty quickly. For more information on how to tell if you have dirty or worn spark plugs, check out our post about it here.
2. Dirty Air Filter
Air filters are a common maintenance item that can be often overlooked. How long air filters last depends partly on the environment that you ride your bike in. Dusty areas won’t last as long as forest areas, but what happens if your motorcycle’s air filter gets clogged?
A clogged air filter can cause all sorts of performance issues for your bike. Your engine needs a precise mixture of air and fuel to run properly. A dirty filter can throw this ratio off. In fact a clogged filter could reduce the amount of air getting to the engine. This causes the engine to have an excess amount of fuel in the combustion chamber. Generally speaking rich engines don’t run well and tend to bog down when trying to accelerate quickly. This could also be the cause of poor throttle response for your motorcycle. To learn more about the types of motorcycle filters and how long they last, check out our blog post here.
3. Carburetor Issues
A carburetor is a device that mechanically mixes air and fuel together and delivers it to the engine. A carb relies on the venturi effect to function. Many motorcycles these days are fuel injected, but if your bike is from the early 2000s or earlier, it likely is carbureted.
Over operating time and sometimes due to neglect, a carburetor can get clogged. Sometimes its due to bad fuel other times its just caused by long operating hours. As the carb ages, gum and varnish deposits will from on it. These deposits can form in critical areas with tight tolerances like a jet. This can restrict the flow and mixture of air and fuel into the combustion chamber. If your motorcycle has sluggish acceleration the carburetor is a likely suspect for the root cause of the problem.
If you’ve cleaned your carburetor and you’re still having acceleration problems, then you might have a vacuum leak. A vacuum leak is when there is a leak in the carb and it is sucking in (vacuuming) more air. This excess air can cause your engine to run lean and throw off the air fuel mixture. An improper mixture will cause problems for your bike like poor throttle response.
A good way to check for vacuum leaks is to turn on your motorcycle, and spray the carburetor with carb cleaner. If the motorcycle’s idle rpm increases, then you have found your leak.
4. Bad Gasoline
Gasoline doesn’t last forever, and since motorcycles aren’t usually ridden year round its not uncommon for a bike to have old gas in it. Gas can go stale in as little as thirty days, so its a good idea to add stabilizer if you are an infrequent rider.
These days gasoline is mixed with ethanol. The ethanol will absorb moisture over time weakening the potent gasoline. This diluted fuel can cause your motorcycle to run poorly and even experience poor acceleration and throttle lag.
If the gas in your bike is very old, its probably a good idea to drain the gas rather than run it through the bike. Adding stabilizer in the first place is a great way to avoid these problems.
5. Incorrect Spark Plugs
Sometimes the reason a bike isn’t accelerating well is as simple as it as the incorrect spark plugs in it. Are your spark plugs pre-gapped or did you have to gap them yourself? Spark plugs have different gap sizes and heat ratings. These settings are all designed to work with specific engine conditions. If you have spark plugs that aren’t designed for your engine, they won’t work very efficiently. This could easily be the cause of poor throttle response and acceleration in your motorcycle. For more info on spark plugs, check out the drive’s article here.
There could be many reasons why your motorcycle is not accelerating like it used to, but this is something that you can look into at home. To start we suggest that you do the following:
- Check your spark plugs to make sure they are not worn or dirty
- Measure the spark plug gap and compare to the manufacturers specifications
- Check your engine air filter and replace it if it is dirty
- Clean your carburetor if you can’t remember the last time it was cleaned
- Check your carburetor for leaks by spraying it with carb cleaner while the bike is running
- Drain the gas tank if the gasoline has been sitting in the bike for a long period of time.
- Verify that the spark plugs on your motorcycle are correct for the application
These are all steps that you can take to solve your problem at home.