The Grom was released by Honda back in 2014 and was regarded as an instant classic.
It’s hard not to love the compact, mini 125cc fuel-efficient motor.
The Grom is an excellent choice for entry-level riders looking for an easy learner bike they can commute on.
That said, it’s also a popular choice for stunt riders looking for a bike they can easily customize and ride the tires off, literally. This makes used Groms a somewhat risky purchase if you don’t know what to look for.
In this article, we”ll cover the solutions to the most common Grom problems.
Unfortunately, one of the most talked about problems with the Honda Grom is that the scooter won’t stay running. As we said up front, the Grom is a popular choice for heavy upgrades that often interfere with its engine performance, especially if other adjustments aren’t made to accommodate.
That said, the issue doesn’t always happen on used models that have undergone heavy upgrades.
At one point, Grom owners were claiming that fully stock models wouldn’t stay running either.
In some cases, these were brand new Groms with no previous owners.
The main reason a Honda Grom won’t stay running is due to a failing fuel pump. In fact, by 2015 the growing number of 2013-2015 year model groms experiencing running problems due to fuel pump failure forced Honda to recall close to 18,000 units.
To be fair, this was the first two years the Grom was on the market – first-year models often receive interim updates in the form of recalls.
Still, this is important info for any readers who might be shopping for used Groms – here’s what you need to know:
- Honda recalled 17,643 units due to symptoms commonly associated with a failing fuel pump
- This affected Groms made between 2013 – 2015
- You can run a VIN check on your bike to see if you’ve been affected.
- The particular culprit within the pump was the resin bracket.
If the resin bracket in the Grom’s fuel pump swells, it will seize the pump’s impeller and riders will experience problems with their Groms not running.
In addition to not staying running, a Grom with a bad fuel pump will exhibit the following symptoms:
- Erratic idling
- Whining noise from the fuel pump
- Your Grom’s engine will surge or sputter
- Your Grom’s Engine might crank but not ignite.
- Dip in engine performance while accelerating.
- Overall loss of engine power
- Frequent stall out (Honda Grom Won’t Stay Running)
Although this is often related to the 2015 Honda Grom fuel pump recall, it is a common issue for Groms, especially in the earlier model years and is also due to fuel pump problems.
Simply put, if your fuel pump fails your engine won’t get enough fuel to sufficiently accommodate its ignition cycle.
This affects your throttle sensitivity and your Grom’s idling.
If you’re on a 2013-2015 Grom and its idle is off, or if your Grom won’t idle and just dies, this could be a symptom of the swelling fuel pump resin interfering with the pump’s impeller. Your best bet is to replace the whole fuel pump.
The faulty pump wears out continuously until it fails completely, and therefore your Groms idle will get more and more erratic until eventually, it might not idle at all.
With a fuel pump that can’t meet the Grom engine’s fuel demand, your idle might splutter, surge or cough before eventually just dying.
To confirm that this is caused by a faulty fuel pump, keep an ear out for the dreaded whine that sometimes accompanies failure.
As the resin swelling strains the pumps Impeller, eventually wearing it out, the accompanying vibrations can cause a whining sound, but not in every case.
That said, the fuel pump failure isn’t the only reason a Grom won’t idle.
One experienced Grom home mechanic gave the following info:
- “My friend bought a grom with the same [idling] problem.
- Perform a 3-step ECU reset on order.
- Clear DSC codes. Reset throttle position sensor. Then the ECU reset that you hold the throttle open.
- To set your idle correctly, find the black plastic screw on the throttle body.
- Turn it to the right gently until it bottoms out.
- Now back up 2 complete rotations.
- Next, you check your butterfly stopper.
- It’s underneath where your throttle cables connect to your throttle body, an 8mm nut, and a little Allen stopper, [around] 1.5mm.
- Make sure your butterfly is not being held open by the stopper.
- Start the bike and WARM IT UP.
- Let it idle for 15 minutes before adjusting the butterfly.
- If it won’t idle when you start it, screw the butterfly stopper in to bring the revs up enough so that it stays alive, then adjust to 17-1800 rpm.
- Let it cool off for an hour and start it again to double-check.”
Another common complaint about the Honda Grom is how sometimes it clicks but won’t turn over.
To further explain what we mean, let’s turn to a consumer report regarding the issue:
“I was cruising on a back road doing about 45 mph in 4th gear when the bike suddenly lost power and died. The AFR gauge was reading steady at about 12.9 to 13.3, when I lost power it did start to drop into the 11’s before it died. I attempted to push start/jump it with no luck. I loaded the bike in a truck and brought it home and have been banging my head trying to figure it out ever since.
“Bike cranks, sparks, and I can smell fuel, but will not start. Occasionally it does make a pop sound (like a backfire) when cranking.”
“I have the three basics covered: air, fuel, and spark, but the bike doesn’t want to run. Mods are in my signature, the most recent being the PCV and the WB2, both of which have been removed and readded with no change in the status. I’ve checked the VIN for the fuel pump recall and it’s not supposed to be impacted (doesn’t mean the pump isn’t bad, but it does prime).”
This could be several things, but to us, it sounds fuel related. In fact, it could once again be related to a bad fuel pump, although any fuel system complication could be responsible.
In addition to the fuel pump, the culprit could be a bad fuel injector, a fuel hose, a bad spark plug, or a faulty wire or fuse in the fuel systems wiring.
Finally, in some cases, a Grom won’t turn over because of poor cam timing, a bad cam sprocket, or inadequate piston compression in the Grom’s engine.
One of the more frustrating issues Grom owners vent about in the forums is when their Honda Grom Won’t shift.
Here’s how one Grom enthusiast explained the problem:
“ Sometimes it doesn’t allow me to downshift, it feels as though something is stopping the shift level from moving down. If I keep hitting the shifter eventually I’m able to change gears. I’m riding along in 4th and slowing down to a stop, I pull the clutch and change down to 3rd, then pull the clutch and attempt to get 2nd but I’m not able to push the gear lever down, feels like it’s blocked..? Sometimes I can just keep kicking down and it’ll click, other times I have to clutch back out and try again. Happens to pretty much all the gears, although not so much 1st.”
The usual culprit is a poorly adjusted clutch cable, especially on some of the pre-owned Groms out there.
A poorly adjusted clutch cable might go unnoticed while you’re upshifting through the gears, but once you switch to downshifting a maladjusted clutch cable becomes obvious as it feels like you can’t shift down through the years.
Related: How Long Do Honda Grom Last?
More than a few Grom riders say their bike won’t go into neutral from time to time. This can be frustrating, especially while parking or trying to start your Grom.
Here’s how one real-life Grom owner explains the unfortunately common problem:
“Have just over 3500 miles on it and have been using Honda synthetic oil since about 1000 miles. At a complete stop engine running in first gear, clutch pulled in, it’s super hard to kick it up into neutral, so hard in fact that I even have a very hard time pulling it up with my hand. 2nd to neutral is pretty hard too and it seems that it wants to just skip past neutral and go right into 1st. At first, I thought it was the clutch adjustment and I tried adjusting it but it was the same thing. With the engine off it goes into neutral easily. Shifting through the gears while moving feels normal but I noticed while downshifting it kind of skips neutral and just goes into first. “
The issue is a hard nut to crack. Some riders say the throttle adjustment is to blame while others blame the chain tension.
That said, one Grom home mechanic we encountered claims to have discovered the reason why their Honda Grom won’t shift into Neutral:
“I adjusted the throw on the gear lever… 5mm adjustment and it was back to normal… vibration had rattled the lock nuts loose on the toe lever adjustment and lengthened the arm that connects the box to the toe lever…Once I adjusted it back it was immediately fine again”
The clutch can come unadjusted on any motorcycle.
Maybe the Grom receives so many complaints about it because it attracts lots of first-time riders, maybe it’s because it attracts so many custom stunt bike builders.
Either way, the first thing to check when your Grom’s clutch won’t disengage is the clutch cable tension, as being overtightened is the most common reason why the clutch gets stuck engaged even when you pull your Grom’s clutch lever in.
Other culprits have been discovered to be the clutch disc, pressure plate, or spring plate that needs to be adjusted, seated, or tightened.
Another frustrating issue Grom owners experience is problems with their motorcycle when it won’t start at all.
The experience goes something like this:
“I was riding around about 2 months ago, stopped at the store and when I was leaving I started my grom up and went into 1st gear then it immediately died. It will turn over no problem but it just won’t fire up. I changed the fuses and spark plug and did all the basic checks but still got nothing.”
This rider did the right thing, checking for spark, fuses, battery, engine timing, and air and fuel, but for various riders just like him, it has nothing to do with bike maintenance or the lack of rider upkeep.
In some cases, Honda Grom can develop problems starting due to a corrupted ECU. Sometimes getting your ECU reflashed by a Honda dealership technician is enough to get her firing up like new, while in other cases riders are forced to replace the whole Electronic Computer Unit with a new or used but reflashed one.
Honda’s are unfortunately notorious for charging issues, and the Honda Grom is no exception.
Take a quick crawl through the forums and there’s no shortage of complaints from riders who sound just like this:
“First noticed that on a long ride, [my Honda Grom] would occasionally lose power, bog/sputter, or even after fire dropping from 80% throttle down towards 60% or so. It slowly got worse to the point that it was sputtering, jerking, and bogging to almost being unrideable.”
The Honda Grom is a simple machine; charging issues on most bikes start with either the battery, Stator, or Regulator/Rectifier. That said, the Grom has a particular problem with its stator failing due to crank vibration.
According to a few Grom owners we heard from, the vibration is subtle enough to evade the rider’s detection, but as the micro-vibration rattles the stator slowly, in due time, the stator eventually shorts out and fails.
Apparently, multiple aftermarket Honda part manufacturers make a crank support bearing that supports the crank in the stator, but be advised, as installing a third-party part could void your Grom’s warranty.
The early year model Honda Groms was notorious for fuel delivery problems, including the notorious Fuel Pump Recall on the 2013-2015 YM Groms.
The main reason for a Honda Grom to stop fueling is because of a faulty fuel pump. In fact, by 2015 the growing number of 2013-2015 year model groms experiencing fuel delivery issues on account of faulty fuel pumps forced Honda to recall almost 18,000 Honda Groms.
Here’s an issue that comes up often on used Groms that have been heavily modified, as the modifications run through the bike’s Electronic Control Unit to tweak its performance settings.
Your Grom’s spark is regulated by your bike’s ECU. If you install aftermarket enhancement accessories that override your ECU, it may cause problems with the core functioning responsible for your Grom’s spark.
That said, in some cases, the ECU fails on a Grom that’s almost primarily stock.
This frequent and confusing issue surfaced mostly on the 2018 year model Groms, and to my knowledge has never been officially addressed by Honda.
Still, we’ve heard enough complaints to warrant answering the question once and for all.
The main reason a Honda Grom’s Speedometer stops working is because of the speed sensor.
The Grom’s speed sensor is located on the left of the crankcase, held in place by a bolt.
If the bolt or the sensor wire loosens, the speedometer will receive inaccurate readings, which can put the order in danger. If nothing else, a faulty speed reading could get you a traffic citation.