Honda Grom banner

1 - 13 of 13 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #1
So Ive owned my Honda GROM for about 4 months now, the bike had 500 miles on it when I purchased it and it was 3 years old.
The bike was previously owned by a multi-millionaire bike collector at first apparently or so the dealer said who had the bike modified to his spec with lots of aftermarket parts.
Anyway Ive recently just completed 1100 miles on the bike but I have noticed an issue. When I first had the bike I would be able to hit up to 68mph on a flat in 4th and even had it go as fast as 73mph downhill, redlining obviously.
However i recently had an issue where the bike will noy exceed 58-60mph if I'm lucky even going downhill.
Basically I was riding home from work, and when I came out of a corner I didnt realise that I hadnt shifted out of third properly, and tried to accelerate.
I was already at about 6000rpm and tried to accelerate out of the bend aggressively, and almost immidiately the bike redlined and you could hear the bike hitting the rev limiter in 3rd.
This startled me and I panicked as I was already taking this bend faster than I should have as there was ststionary traffic in the othet lane and I was to focused on not running the corner wide and hitting someone.
Anyway I hesitated changing gear and made a right mess of it changing up into 4th, and as I changed gear i swear I heard and felt like something grinded and then effectively sheared off or almost fell off the inside of the bike and hit the inside part of my left boot. I can remember what sounded like the distinct sound of something metallic making contact with the ground.
Almost immediately after changing up into 4th I realised that there was no urgency or power coming from the bike in 4th. It struggled to accelerate from 40mph to 45mph, and at that moment i knew that I had really fucked something.
I braked a bit and quickly shifted down into 3rd to try and regain some speed and power and noticed the bikes rpm reaching nearly 7500rpm just to hit 35mph when before it would reach that at just over 500-5500rpm.
I changed back up into 4th and there just seemed to be no desire from the bike to then accelerate past 45mph. I opened up the throttle as there was a long stretch immediately before me but even then the bike refused to climb past 51mph or go above 8000rpm, when literally minuted before it wouldve redlined at 9000rpm no problem.
Since then ive been riding the bike and the problem persists, awful acceleration and top speed in 4th, topping out at about 58mph now. I used to be able to confidently overtake other vehicles when need be and hit 68mph in 4th no problem but now im struggling to even match the car infront most days.
Ive just paid to have the bike serviced, oil change, compression test, sprockets checked, chain adjusted, spark plugs checked and changed and they even took the bike out themselves but called me and said that they couldnt get the bike passed 58-60mph downhill.
Now im basically faced with an unknown issue that now even my local mechanic can fix.
My concern is that Ive damaged the gearbox maybe, specifically 4th gear, but honestly i have no idea and clearly the mechanic doesnt either. Its frustratung because I was planning on buying a big bore kit for the bike and some other performance mods but with the issue im having with 4th I dont even know if its worth the hassle if I cant get it back to the level it was running at not even a month ago? Losing the ability to overtake at higher speeds and effectively <15mph off the topseed on a bike like this is a big deal to me as legally I cant ride anything larger than a 125cc and I was quite proud of having a small bike that looked the way it does and could pull as well as it did.
 

Attachments

·
Registered
Joined
·
865 Posts
I am just going to throw this in here.......I do not know what the issue with your bike is — or — more to the point — IF your bike even actually HAS an issue. Based on your detailed post, I can see that this is a significant concern for you. Here is one data point which I can offer: the top speeds reported for this bike — evenly basically as stock — have been widely variable. If you do some searching about on this forum, you’ll eventually find a number of discussions related to this point. (A confounding factor is when people change from the stock gearing, but that does not appear to be relevant in your case).

We would next need to know what modifications have been done to this machine.
 

·
Registered
Joined
·
1,082 Posts
From the pics it appears you have a stock motor. At least from the outside.

Felt like something grinded and then effectively sheared off or almost fell off the inside of the bike and hit the inside part of my left boot. I can remember what sounded like the distinct sound of something metallic making contact with the ground.

This would concern me.
You said that you mechanic changed your oil, I assume this is after the above happened. Dump the oil into a CLEAN pan & check for flake or shiny pieces of metal. If you have am issue, even if the oil has been changed, you still might be able to see particles in your oil.

I would pop off the clutch side case & see if there is any debris on the screen. Immediatly!

You could be experiencing clutch slippage. 10 buck part from REN Motorwerks (60% stiffer).

Keep us informed of the issues. We will try to help.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #4
The mechanic informed me that when they took the bike for a test ride, they did not feel any clutch slippage or at least they were not aware of any, however they said it did feel like there was something restricting the bike in 4th gear that was limiting its accelleration and top speed.
I know the bike has a Tyga exhaust System and uprated sprocket however im uncertain of the spec, could it be that aggressively red lining in 3rd gear maybe tripped some safety measure in the bikes electronic mapping maybe that could have messed with a performance profile of some kind. Im aware that when people install an aftermarket exhaust system they also have to install an electronic component to recalibrate something to do with the bikes emmissions. Is it possible that this could have an impact or is it even a possibility.
Would it be worth taking the bike for a dyno run and maybe getting it electronics remapped with a new profile installed?
 

·
Registered
Joined
·
1,082 Posts
The mechanic informed me that when they took the bike for a test ride, they did not feel any clutch slippage or at least they were not aware of any, however they said it did feel like there was something restricting the bike in 4th gear that was limiting its accelleration and top speed.
I know the bike has a Tyga exhaust System and uprated sprocket however im uncertain of the spec, could it be that aggressively red lining in 3rd gear maybe tripped some safety measure in the bikes electronic mapping maybe that could have messed with a performance profile of some kind. Im aware that when people install an aftermarket exhaust system they also have to install an electronic component to recalibrate something to do with the bikes emmissions. Is it possible that this could have an impact or is it even a possibility.
Would it be worth taking the bike for a dyno run and maybe getting it electronics remapped with a new profile installed?
I do not think a dyno run will help at this point. yet. Your machine was running fine for a thousand miles & something happened. We are trying to nail down what happened.

I think it would be worth a shot at taking the bodywork off & see if you do or do not have a controller first. Some parts, depending on the controller, might be under the seat. You need to know what you have to start out with. Especially with diagnostics.

The restricting part in 4 th gear, sounds like a possible mechanical issue.

Do this...

Take off the front sprocket cover.
Take off the chain.
Put bike in neutral
Rotate front sprocket. Anything feel weird? Tight spots, clicking, rough bearings, etc.

Pull spark plug.
Put bike in gear & using the starter any odd noises?
Try 4th gear. Any odd noises? prolly cant hear because of the starter, scratch that...

Put chain on, leave plug out.
Put bike in 4th.
Raise rear wheel.
Try to rotate rear wheel & see if you feel anything odd.

I would still take that clutch cover off & have a look see. Especially the screen. Will tell you A LOT. Can even check clutch plates for signs of heat (slippage).

Also with the clutch basket off you can rotate the bikes transmission at will & see if you have issues.

Let us know what you find.
 
  • Like
Reactions: Paultergeist

·
Registered
Joined
·
276 Posts
Follow what WV says, especially the oil and oil screen part. Post pics if you're unsure what you're looking for. We can look and see if anything is out of the ordinary and it'll also give us an idea of what's been done to the bike.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #7
So Ive got the bike back and ridden it, and this is what Ive found.
Almost immediately the throttle felt "lighter" if that makes any sense. I would open up the throttle to accelerate and normally it would feel more taught and offer a tangible resistance (not stiff like it was fighting back) as you opened up the throttle, with you feeling the revs through the throttle as it accelerates.
Now the throttle simply seems to almost slide as i open it fully, with no resistance, and no tangible feedback from the thtottle as far as revs and accelerating are concerned.
The bike also doesnt accelerate as aggressively or quick as it used to, as sitting in third i could accelerate from 30-40 in maybe 3 seconds but now its more like 5. Also I find I have to ride the bike a lot higher in the gears before changing if i want to maintain acceleration and not have the momentum effectively drop off.
I ALWAYS used to shift gears at around 4000-5000rpm, maybe 6000rpm at most but now Im having to ride the bike to 7000rpm in 3rd just to have the bike maintain momentum so that when i shift into 4th it doesnt take forever to accelerate to 50mph.
If i change into 4th at around 4000-5000rpm now, the bike will take around 6+seconds to accelerate past 50mph, and I have to ride the bike at the limiter which now seems to be 8000rpm for it to even want to accelerate into the 60's. I managed to do 71mph downhill riding it on the limiter at 8000rpm but it took like 15 whole seconds from changing it 4th at 41mph to do so.
Something is definetely off with the bike but as far as the mechanic is concerned the bike "is only a toy" and ive no business riding it that fast anyway.
 

·
Registered
Joined
·
1,082 Posts
I think it would be worth a shot at taking the bodywork off & see if you do or do not have a controller first. Some parts, depending on the controller, might be under the seat. You need to know what you have to start out with. Especially with diagnostics.

The restricting part in 4 th gear, sounds like a possible mechanical issue.

Do this...

Take off the front sprocket cover.
Take off the chain.
Put bike in neutral
Rotate front sprocket. Anything feel weird? Tight spots, clicking, rough bearings, etc.

Pull spark plug.
Put bike in gear & using the starter any odd noises?
Try 4th gear. Any odd noises? prolly cant hear because of the starter, scratch that...

Put chain on, leave plug out.
Put bike in 4th.
Raise rear wheel.
Try to rotate rear wheel & see if you feel anything odd.

I would still take that clutch cover off & have a look see. Especially the screen. Will tell you A LOT. Can even check clutch plates for signs of heat (slippage).

Also with the clutch basket off you can rotate the bikes transmission at will & see if you have issues.


Let us know what you find.

Did you do any of the above checks yourself or by a competent mechanic?
 

·
Registered
Joined
·
8 Posts
Discussion Starter #10
Okay so I just took the bike out on a late night run and have filmed the bike accellerating as fast as possible from stationary out of a laybye or a road. I will upload the footage to here so you guys can see how the bike performs and its slower accelleration in 4th gear.
 

·
Registered
Joined
·
1,082 Posts
Dood,

For us to help we need specific questions answered. We are trying to play doctor over hundreds (or thousands) of miles.

Put in the work, find answers to the above questions, and we will proceed.

A video at this point is pointless. Unless it blows up on video, then maybe we can deduct from the color of the exhaust what got eaten first.
 
  • Like
Reactions: Paultergeist

·
Registered
Joined
·
6 Posts
So Ive owned my Honda GROM for about 4 months now, the bike had 500 miles on it when I purchased it and it was 3 years old.
The bike was previously owned by a multi-millionaire bike collector at first apparently or so the dealer said who had the bike modified to his spec with lots of aftermarket parts.
Anyway Ive recently just completed 1100 miles on the bike but I have noticed an issue. When I first had the bike I would be able to hit up to 68mph on a flat in 4th and even had it go as fast as 73mph downhill, redlining obviously.
However i recently had an issue where the bike will noy exceed 58-60mph if I'm lucky even going downhill.
Basically I was riding home from work, and when I came out of a corner I didnt realise that I hadnt shifted out of third properly, and tried to accelerate.
I was already at about 6000rpm and tried to accelerate out of the bend aggressively, and almost immidiately the bike redlined and you could hear the bike hitting the rev limiter in 3rd.
This startled me and I panicked as I was already taking this bend faster than I should have as there was ststionary traffic in the othet lane and I was to focused on not running the corner wide and hitting someone.
Anyway I hesitated changing gear and made a right mess of it changing up into 4th, and as I changed gear i swear I heard and felt like something grinded and then effectively sheared off or almost fell off the inside of the bike and hit the inside part of my left boot. I can remember what sounded like the distinct sound of something metallic making contact with the ground.
Almost immediately after changing up into 4th I realised that there was no urgency or power coming from the bike in 4th. It struggled to accelerate from 40mph to 45mph, and at that moment i knew that I had really fucked something.
I braked a bit and quickly shifted down into 3rd to try and regain some speed and power and noticed the bikes rpm reaching nearly 7500rpm just to hit 35mph when before it would reach that at just over 500-5500rpm.
I changed back up into 4th and there just seemed to be no desire from the bike to then accelerate past 45mph. I opened up the throttle as there was a long stretch immediately before me but even then the bike refused to climb past 51mph or go above 8000rpm, when literally minuted before it wouldve redlined at 9000rpm no problem.
Since then ive been riding the bike and the problem persists, awful acceleration and top speed in 4th, topping out at about 58mph now. I used to be able to confidently overtake other vehicles when need be and hit 68mph in 4th no problem but now im struggling to even match the car infront most days.
Ive just paid to have the bike serviced, oil change, compression test, sprockets checked, chain adjusted, spark plugs checked and changed and they even took the bike out themselves but called me and said that they couldnt get the bike passed 58-60mph downhill.
Now im basically faced with an unknown issue that now even my local mechanic can fix.
My concern is that Ive damaged the gearbox maybe, specifically 4th gear, but honestly i have no idea and clearly the mechanic doesnt either. Its frustratung because I was planning on buying a big bore kit for the bike and some other performance mods but with the issue im having with 4th I dont even know if its worth the hassle if I cant get it back to the level it was running at not even a month ago? Losing the ability to overtake at higher speeds and effectively <15mph off the topseed on a bike like this is a big deal to me as legally I cant ride anything larger than a 125cc and I was quite proud of having a small bike that looked the way it does and could pull as well as it did.
Have you resolved this? If so , what was it? I am having this issue with my girlfriends Grom and I cannot figure it out. I am losing top speed, but the revs are not INCREASING, they are also feeling restricted. I don't think it is the clutch. The engine should be spinning higher as the clutch slips. This just lags. I can't get past 6500 RPM /45 mph.
Nothing in the airbox ( I half expected a mouse nest of something in the airbox) , Changed the plug, electronics are fine.
In my opinion, it almost feels like a bike that is jetted wrong.
 

·
Registered
Joined
·
33 Posts
Have you resolved this? If so , what was it? I am having this issue with my girlfriends Grom and I cannot figure it out. I am losing top speed, but the revs are not INCREASING, they are also feeling restricted. I don't think it is the clutch. The engine should be spinning higher as the clutch slips. This just lags. I can't get past 6500 RPM /45 mph.
Nothing in the airbox ( I half expected a mouse nest of something in the airbox) , Changed the plug, electronics are fine.
In my opinion, it almost feels like a bike that is jetted wrong.
No jets in the Grom. Only jets on carbed Grom Clones. It's fuel injected. Could be a clogged fuel injector. Any mods on the bike?
 
1 - 13 of 13 Posts
Top