this post was submitted on 26 Jun 2026
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My motorcycle smells strongly of gasoline at higher rpms (and still a bit for lower RPMs). Where do I start troubleshooting first? (lemmy.world)
submitted 1 month ago by dingus@lemmy.world to c/motorcycles@lemmy.world
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Hi all. Noob here back again. I got the screws out of the front master cylinder, but I have been having a different problem.

When under higher RPMs, the bike gives off a VERY strong fuel smell. It's still noticeable at lower RPMs, but not as bad. It didn't do this initially when I got it a few months ago, but I didn't ride it much initially.

Bike is a 2017 Honda Rebel 300. Fuel injected. No carb.

I noticed that the gasket to the gas cap was a bit cracked and distorted so I got a new gas cap. Didn't resolve the issue.

There are no visible leaks anywhere that I can tell.

The smell is very strong around the gas cap and engine, not so much the tailpipe. The bike seems to run great otherwise.

Unfortunately, googling seems to show this as a very nonspecific issue, so I'm a bit lost as to where to begin. I'm a huge noob when it comes to mechanical things.

Thanks!

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[–] gabmus@retrolemmy.com 5 points 1 month ago (1 children)

I am no expert but I'd try tracing the path that the fuel makes from the tank to the injectors and see if there's any leaks. The cracked gas cap gasket could suggest that other rubber parts in your bike might also be degraded.

Might be worth investigating the ICU sensors, I believe there should be some attached to the exhaust pipe. Could also be a problem with the ICU itself.

[–] dingus@lemmy.world 0 points 1 month ago (1 children)

The latter paragraph requires more specialized diagnostic equipment, correct?

[–] gabmus@retrolemmy.com 1 points 1 month ago

Most likely

[–] OwOarchist@pawb.social 4 points 1 month ago (1 children)

Use UV tracer dye (specifically the gasoline-compatible type) and then you'll be able to detect any fuel leaks relatively easily by looking for them with a blacklight at night.

That's a relatively affordable way you may be able to diagnose this.

[–] Nomad@infosec.pub 2 points 1 month ago (1 children)

Might already be in gaseous form, use soapy water and look for bubbles forming

[–] dingus@lemmy.world 2 points 1 month ago (1 children)

I have done this with tires before, but could there be some danger in doing this with engine fittings by potentially getting water in the engine?

[–] Nomad@infosec.pub 2 points 1 month ago (1 children)

Should be positive pressure, so nothing should get in while running. Also rain water doesn't get in either? :)

[–] dingus@lemmy.world 2 points 1 month ago

Lol fair point. I tried spraying around and really didn't see anything. Altho part of the thing is that I wasn't aggressively revving the bike while doing it because I live in a condo complex and don't want the neighbors getting pissed at me lol. I was just idling it and revving it lightly, but that might not have been enough to spot a leak. I lifted the tank up to see the underside while doing this and the fittings underneath all seemed fine.

I don't have easy access to the evap canister tho because of an aftermarket thing on the side of my bike that is zip tied to it (need to get some zip ties so I can put it back on if I take it off). But that is next on my to do list.

Idk I feel pretty lost and dumb here!

Also the new gas cap is real shit quality lol the key immediately bent already lolol

[–] officermike@lemmy.world 3 points 1 month ago (1 children)

I'm not a mechanic and don't really have motorcycle experience. I don't know what would be the best approach, but I do have thoughts on where I'd start. If you don't readily see any obvious leaks, and you're convinced it's not coming from the tailpipe (which would indicate it's running rich and there's a sensor, ECU, injector, or tuning issue), I'd probably look into getting a fluorescent dye that can be used in fuel systems. With a bright UV flashlight, this will make any liquid leaks glow, so any leaks in fuel lines, tanks, inline filters, petcocks, or maybe even the engine block or cylinder head would show up. If the leak is on the vapor side of the fuel system, I don't expect the UV dye would help find it.

Alternatively you might be able to find it with a sniffer tool. I'm not endorsing the linked item below. I don't own it and I've never used one, but I'm including it as a reference. https://a.co/d/00jpwJua

[–] dingus@lemmy.world 1 points 1 month ago

The UV dye is a very interesting idea! I really think that it's likely just vapor itself leaking which is why I haven't seen any drips anywhere, but it's something to keep in mind. I don't really feel that it is running rich because the smell seems to come from the engine or tank, but it is also worth investigating. The sniffer tool looks interesting. Never heard of that either. Lots of ideas to ponder!

[–] CADmonkey@lemmy.world 3 points 1 month ago (1 children)

I would look for blocked vents and bad fuel lines if its not making a fuel smell from the exhaust.

[–] dingus@lemmy.world 2 points 1 month ago

How would I be able to tell if something is blocked? The rubber hoses look ok to my untrained eyes.

[–] Mac@mander.xyz 2 points 1 month ago* (last edited 1 month ago)

Stock airbox?

I wouldn't expect injector orings to be bad with that new of a bike but it's possible.

Check intake boot, gaskets, etc