If you've ever had a dirt bike that the throttle sticks, or that the throttle return action is just a little slow and stays on long after you're done using it, or if you've ever had to (or still do now) turn the throttle back to closed manually when you are ready to shut-off, you're braver than I if you're still riding it and the tips below should be a must see for mine and yours safety.
Your throttle return rate should be crisp when you release it, but if it doesn't slam shut by itself when you simply relax your grip on the right side of the handlebars then this article has just the thing for you, whether you ride a two stroke smoker or a four stroke thumper either carbureted or fuel injected, here's just the info you need to know to have a factory feeling throttle.
If your throttle is sticking and you're still riding the dirt bike because you think the throttle's operation is a mystery, or it's going to be hard to fix. I'm here to tell you, It's not a mystery, nor is it hard to fix and this article should help to demystify this part of your dirt bike and allow you to fix it yourself so you can have a throttle return to CLOSED On It's Own when you're ready to let off.
You may not be aware but there are a lot of dirt bikes running around that when you're ready to let off the gas, they just keep on pulling for another fraction of a second and there's One Word for This: Scary. If you know something about that, this article will get you dialed with a throttle that actually snaps shut when you let off the gas and doesn't keep on pulling another 25 ft or so, or until you manually shut the throttle by twisting the grip forward, so let's get into it.
Below, we'll cover pretty much anything that could cause your throttle to stay on for longer than you want it to, (or it should) and we'll even start with what's it's supposed to work like, then we'll go into some diagnosis and repair of the most common causes for a less than ideal performing throttle.
Even without the engine running, when you let off the gas by just relaxing your hand on the handlebars, the throttle return rate should be that of slamming shut in a way that you can hear the throttle tube on the handlebars hitting it's stop solidly and crisply.
In addition to hearing the throttle tube slam closed on the handlebars, you should hear something near the engine hitting metal. (This would be the slide hitting the bottom of the carburetor on a two stroke, or the throttle linkage hitting the stops on a four stroke whether fuel injected or carbureted).
If you don't hear anything such as these noises, or you just have a feeling that the throttle return is not as quick as it should be, keep reading!!
A throttle cable that is externally damaged, frayed or dry can easily and certainly cause a throttle to not return / close properly resulting in some wild, carnival style rides so it's important to determine if this is what the problem is before getting into other possibilities.
If all looks well so far but you're still wondering if the problem is cable related, the following steps should help you determine if the problem is a cable that is frayed or just dry and causing problems.
When you twist the throttle, does anything feel rough and as if it is coming from inside the cable(s) anywhere? Can you disassemble the throttle housing and look at where the cable(s) connect(s) to the throttle tube?
How about pulling the top off of the carburetor or the cover from the side of the carburetor or throttle body that is covering the linkage and looking at the cable where it leaves the sheathing and comes into the carburetor or connects to the linkage on a four stroke carburetor or fuel injection throttle body. Have you seen any damage anywhere? Seen any places that look like the strands are coming unwound?
If all looks well so far but the throttle still doesn't slam shut like it should when you let off the gas, and you're still wondering if it is cable related problems, you should lubricate the throttle cable(s) before continuing but don't just force any lube down the cables without proper preparation which includes removing the top of the carburetor and disconnecting the cable from the slide on a 2 stroke so as to prevent making a mess which will ultimately run down into the carburetor, potentially causing jetting or other problems.
If you have a four stroke, whether carbureted or fuel injected, there will likely be a cover over the linkage that you'll need to remove so as to be able to remove the cables and / or just be able to control the ensuing mess that occurs when lubricating the cable(s).
Once the throttle cable is well lubricated, if you STILL don't have a throttle that snaps shut check out the following tips.
Before getting into the info regarding the throttle tube, a couple things to keep in mind and check first is that if you've been white knuckling the right grip when you ride, you could have the grip shoved up against the throttle housing and this will cause a throttle return problem since the rubber flange on your grip will rub the housing and not allow the throttle tube to have free movement, as will having the throttle tube dragging against the end of the handlebars.
If the throttle side grip is torn at the end it will easily allow dirt and other strange things to find their way between the throttle tube and handlebar resulting in a throttle return rate less than what you are desiring. If you have a grip that is torn at the end, worn through at the palm area or is just in need of replacement, be sure to see the article on grip replacement where there are some tips for installing the grips that will greatly lessen the amount of movement that your grips move.
A throttle tube that has dirt and things of that nature trapped between the throttle tube and handlebar will cause a throttle to not return to closed properly when it's time to let off, so it is a good idea to frequently remove the throttle tube from the handlebars, and clean this area.
If you still have the stock throttle tube on the dirt bike in question and you're well rehearsed in crashing on the right side, then the stock plastic / nylon throttle tube has likely been damaged and is in need of replacement, at which time It's recommended that the throttle tube is replaced with an aftermarket throttle tube, as these will even provide a better feel at the grip than that of the stock plastic / nylon throttle tube.
If replacement of the throttle tube is something you have in mind, it's important to not try to lubricate anything with conventional lubricants upon reassembly and there's more on this below.
A throttle assembly that is nasty inside is a condition that has to be addressed as this will easily cause a throttle return rate much slower than that of what you're after.
If you have ever thought you were doing yourself a favor by lubricating the workings of your throttle with grease (even if it was light grease) or any other type of petroleum product such as wd-40 or similar lubricants you may have found out it was a big mistake. Use of any type of petroleum product such as wd-40 or light grease in the throttle assembly will only attract dirt, which mixed with oily products results in a soup that will greatly diminish the throttle's return abilities.
If the inside of your throttle housing does have any lubricants inside, or lubricants between the throttle tube and handlebars, be sure to completely disassemble everything and clean all the parts well with brake clean, or other similar contact cleaner type solvents and allow everything to fully dry before reassembly.
The best way to lubricate your throttle assembly is with a dry graphite powder or nothing at all. Yep, Nothing. Clean and dry in here is the best policy, and as far as between the throttle tube and handlebar goes... You can take some silicone spray and apply it to a clean rag then wipe it onto the handlebar while the throttle tube is off, allowing it to dry completely before reassembly of everything, as this will enable the throttle tube to have a little quicker return action, but doing so will require more frequent disassembly and cleaning to keep the action fast and crisp, as even silicone can attract dirt and other fine particles resulting in a dragging and slow throttle return rate.
In the world of carbureted style dirt bikes, a carburetor that is improperly assembled could result in a slow throttle return rate or no throttle control at all (Read: Stuck Wide Open). Being that anything is possible when talking about whether someone assembled a carburetor properly or not, It's practically impossible to cover all possible scenarios but following are a few things you can check that should get you started in the right direction.
If the throttle return rate on a fuel injected bike is the issue there are only a few things that could cause this as discussed below.
On a 2 stroke carburetor, there is not much that can be assembled improperly which could cause a throttle return problem short of the slide being improperly installed in the body of the carburetor, in this case the throttle is usually stuck wide open with no control at the twist grip. If you are pretty sure the slide is installed properly and you have checked all the other recommendations listed above, yet the throttle is still not returning properly, there is a chance that the carburetor was improperly assembled last time someone had it apart. If this is the case, it is recommended that you obtain a service manual specific to the dirt bike you are working on and follow the steps outlined in the manual to properly disassemble, clean and reassemble the carburetor as this will likely remedy the situation if your problem is truly carburetor related.
If you're working with a 4 stroke carburetor that the throttle is not closing or returning on properly there are a multitude of things that could be out of adjustment, bent or improperly assembled such as the way the throttle cables connect to the linkage, the alignment of the throttle plate to the shaft, the accelerator pump and linkage being bent or improperly assembled, among a multitude of other possibilities. If you are suspecting problems with a 4 stroke's carburetor, you should be able to find solace by disassembling, cleaning, and reassembling the carburetor
If the dirt bike you are having a throttle return issue with is fuel injected then there is not much that could be askew as there is generally not much need to disassemble, or parts to dissasemble on a fuel injected dirt bikes throttle body. If you are suspecting problems with a dirt bikes throttle body operation, It's recommended that you check to be sure the throttle cables are not binding or crossed anywhere and causing a slow return of the throttle when released, as short of this there is not much else that could cause a binding or sticking throttle as far as the throttle body or fuel injection system is concerned.
If you reviewed all the other tips listed above and have concluded the throttle return issue is related to a carburetor or throttle body that is dirty, a thing to remember is, a carburetor or throttle body that is dirty likely got that way from neglected air filter service or an air leak between the air box and intake boot drawing in unfiltered air and at which point the carburetor should be completely disassembled and cleaned per the procedures outlined in the factory service manual specific to your dirt bike, followed with better air filter maintenance and / or sealing of the air box to intake boot seal before the next outing.
Lastly, (Although not very common). A throttle return spring that is sacked out can also cause a throttle return action to seem a little slow as well.
Sacked out throttle return springs are not very common as just mentioned but can happen, after all, anything is possible.
If your throttle return spring were worn out, your throttle would likely have varying rates of closing with being most responsive after letting off from wide open. If you are suspecting a worn out throttle return spring It's recommended that you replace the throttle return spring with an OEM spring as would be available through the OEM parts finder on our dirt bike parts page
Now, on the idea of an improper spring... This would be "No telling" how your throttle would react. An improper spring could cause all types of problems so if you have something that doesn't look right inside your carburetor or wound up on the side of your carburetor or fuel injection throttle body on a 4 stroke, it's probably not right and It's suggested that you replace it with the correct spring, then check or follow the other steps listed in this article to ensure a continually reliable and responsive feeling throttle.