Bike 'bogging down' when throttling on

[rustyrobot]

When I was riding to work the other day, the bike started spluttering and losing power as I was riding. Was about due to switch on to reserve tank so I thought it was that, but switching over made no difference. Spent the day at work and then on the ride home it was no different. The bike starts up okay, idles fine and runs okay to a certain point but if I give it too much throttle or when it gets to around 6000rpm, it starts to 'bog down', losing power and with the engine making a different (deeper) noise.

Bike is a 1988 Honda VT250L Spada. Probably waaaay overdue for a general service. I have no technical mechanical experience, and about the same amount of spare money at the moment, so was hoping I could at least isolate the problem myself, even if I am incapable of remedying it.

Logical first guess for me that the problem would be in the fuel system somewhere (carburettor, fuel filter), or something like the air filter. Problem is that to check most of these the tank has to come off, so thought I'd ask what the other possibilities might be so I could check through them first.

So, any ideas? Is it something obvious that I am likely to be missing?

[onearmedbandit]

I had one of these years ago, and it suffered from very similar symptoms that you describe. Turned out that there was gunk in the petcock assembly. A simple clean out of this by removing solved the problem, and yes the tank needs to come off. Another member here had a similar issue and I think this resolved that for him too.

[rustyrobot]

I had one of these years ago, and it suffered from very similar symptoms that you describe. Turned out that there was gunk in the petcock assembly. A simple clean out of this by removing solved the problem, and yes the tank needs to come off. Another member here had a similar issue and I think this resolved that for him too.

Awesome, exactly the sort of thing I was after, will see if I can find the original post, but this site isn't the easiest for searching. Was the petrol cock easy to clean out? What did you use? Guess I might as well get the tank off and can check the air filter while I'm at it.

Stupid question of the day... do I need to drain the tank first?

[onearmedbandit]

Awesome, exactly the sort of thing I was after, will see if I can find the original post, but this site isn't the easiest for searching. Was the petrol cock easy to clean out? What did you use? Guess I might as well get the tank off and can check the air filter while I'm at it.

Stupid question of the day... do I need to drain the tank first?

Didn't clean it with anything, just took it apart and blew it all out. I didn't need to drain my tank, you just need to position the tank as such that the fuel level is below the petcock and the lid.

[Mom]

Yeah, I am ging to go with the dirt in the fuel supply line. With my bike it was in the carbs, I ended up having to treat the tank for rust to finally fix the problem. Clean fuel tap, any filter that is fitted, and then the carbs. Work in that order too. You never know it may be fixed in the tap.

[rustyrobot]

I didn't need to drain my tank, you just need to position the tank as such that the fuel level is below the petcock and the lid.

Hmmm, so an almost full tank is going to be too full then?
Oh well, it wouldn't be called trial and error if there wasn't any room for error.

I did a search and the majority of posts I found regarding problems with Spadas seemed to be about the fuel tap in one way or another, so thinking you probably hit it right on the button.

[mikemike104]

Good luck Rusty !

[SMOKEU]

My lawnmower is suffering from the same problem. It's running way too rich.

[rustyrobot]

Took the fuel tap off and had a look. Seemed clean as a whistle inside and no obvious deterioration of any sort. Where to from here? I don't know if I am game to take the crabs apart, but would that be the logical next place to look? Are there tricks for testing parts? I mean, without having seen one brand-spankin' new, I can't tell if the parts are looking as they should.

Air filter also seemed in fine fettle, just a little blackened along the tops of some of the ridges. Didn't get round to the plugs, but after that... I just don't know what to try next. Ideas?

[onearmedbandit]

Took the fuel tap off and had a look. Seemed clean as a whistle inside and no obvious deterioration of any sort. Where to from here? I don't know if I am game to take the crabs apart, but would that be the logical next place to look? Are there tricks for testing parts? I mean, without having seen one brand-spankin' new, I can't tell if the parts are looking as they should.

Air filter also seemed in fine fettle, just a little blackened along the tops of some of the ridges. Didn't get round to the plugs, but after that... I just don't know what to try next. Ideas?

Have you reassembled it and test ridden it? Because when I checked mine I didn't sight any obvious gunk but test rode it immediately afterwards and all was well.

[rustyrobot]

Have you reassembled it and test ridden it? Because when I checked mine I didn't sight any obvious gunk but test rode it immediately afterwards and all as well.

Ummm...well... errrr.... actually I haven't. That would be a most fantastic and embarrasingly obvious next thing to do. Fingers crossed then.

[Shadows]

Sounds like it's running too lean. Make sure your airbox is properly sealed, there are no splits in the box or in the air feed to the carb, and that the connection to carb is secure.

[ducatilover]

Hey mate,
If your spada is stuttering or acting lean here's a few ideas [Spada owner for three and a half years]
Check the Vacuum line to the Fuel tap [Right hand side, on the rear cylinder intake manifold] these tend to get loose with age and heat, make sure it fits tight and has no cracks/leaks.
There is a screw on the front cylider intake/head on the right hand side, make sure this is tight.
The fuel tap could have an internal leak, this is worth checking [If this is the case certain CBR250 and VFR400 have the same tap set up, do not buy a Spada one, overpriced as hell. econohonda are a great shop if you can't find the bits though]
The air box may suffer from leaks [Common] they are a hard plastic and can crack around the mounting screws in the bottom half of the air box.
Check for breaks or cracks.
Double/triple check the rubber intake tubes [between airbox and head] for external AND internal damage, these can cause many problems.

The standard tune on a Spada is forgiving, you can replace the rear muffler, even the whole exhaust, without a miss, so this is not the problem.

With the symptoms you describe it sounds like a leak on the intake side, or, your vacuum slides are not working or may be leaking in the carbs. A leak is more common and as mentioned the fuel tap/vacuum line and airbox are culprits. I have also seen thins get stuck in the intake snorkel up in the apex of the frame/headstock.

Good luck.

[imdying]

Have you reassembled it and test ridden it? Because when I checked mine I didn't sight any obvious gunk but test rode it immediately afterwards and all was well.

Sounds like you might have originally had a kinked fuel line which you fixed when you refitted the tank.

[Jonno.]

Could very possibly be a rip in one or both of the slide diaphragms.

A rip will give very similar problems almost instantly.

Check your SLIDE diaphragms for pinholes or tears (should only take 10minutes).