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. :blink:

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. :wacko: 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. :wacko: 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. :pinch: 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. :yes:

[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).

[onearmedbandit]

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

No, all fuel lines were fine as I had checked them previously.

[imdying]

Well taking nothing out of the tap can't have fixed it! :laugh:

[onearmedbandit]

Well taking nothing out of the tap can't have fixed it! :laugh:

Who said I took nothing out of it? All I said was I didn't sight anything. That does not mean there wasn't something, just maybe it was that small that it was easy to miss. All I know is that after weeks of checking everything, reassembling, test riding and with no result, it was finally resolved when I removed the petcock assembly, 'cleaned' it out and reassembled it. It never suffered from that problem again.

[imdying]

I bloody hate it when that happens. Well more so now, back when I was a teenager I would've just been stoked it went at all :D

[onearmedbandit]

I bloody hate it when that happens. Well more so now, back when I was a teenager I would've just been stoked it went at all :D

I'm quite confident that was where the problem was, as others have experienced issues with the tap on this particular model being blocked easily. I replaced no parts, and checked everything else with no success.

[ducatilover]

I've see problems with the diaphragm returning to the closed position before and I've heard of one or two "sticking" and blocking fuel flow. Mine was returning, it would start and run for a few minutes then die, would drain the carbs/fuel line and take years to start :wacko:

[rustyrobot]

Have you reassembled it and test ridden it?

Well, tried that and no luck. Will take it all apart again tomorrow (was working this weekend) and have another look at everything as suggested by ducatilover, shadows and Jonno.

It's actually pretty inspiring to see that people get/got so much more out of their Spadas. If my bike was running like that it would be like having a new bike. Let's just hope it doesn't cost me as much as a new bike to get to that point.

Problem is that the Spada Service manual I have has hand-drawn black and white pictures so it's hard to tell from the pics what I am looking at sometimes. Also have to convert all of your jargon into total idiot-speak so I can understand what to work on

Had good motivation to get working on it this weekend, cycling to work and back 3 times in the windiest storm the Waikato has seen for a fair while certainly got me ready to get into it.

[ducatilover]

Send me a PM if you need any further help mate, more than happy to try talk bikes =D

[ducatilover]

Another quick thought, the airbox is made of three parts, top, middle and a steel base that screws to the carbs. The middle cracks where it screws to the steel as I mentioned before, but, there is two "trumpets" in the airbox, these can leak every now and then at the base. :crazy:

[rustyrobot]

Well, I tried everything suggested by all of you, plus two suggestions from Warr... 1) disconnecting the fuel line from the carbs and the vacuum line from the (whatever its called) and sucking on the vacuum line to test the vacuum action (on both 'res' and 'on') and 2) unscrewing the screw on the base of the carb float bowl and draining the gunk out of the carbs.

I found nothing at all conspicuously wrong, put all back together and... voila! It runs! Thanks everyone for your suggestions, one of them helped, and I know a whole lot more about the fuel system of my bike.

Now to tweak it so I get the same performance as other people's Spadas. Suggestions?

[barno]

I'm having a similar problem with my 87 impulse. 95% of the time it's fine. Then sometimes when it's warm, at the lights, it just wants to die. If you accelerate off at low revs, it splutters like hell until you get up to about 4000 rpm then it roars off like a rocket. Bloody annoying as it doesn't do it all the time. So far the suggestions I've accumulated (Not sure if I can discount any at this stage because it happens sporadically as opposed to always):

Vacuum leak somewhere
Bike running a bit lean
Crap in carbs, fuel line
Fouled plugs?
Cooked coils?
A dodgy plug lead?

It's probably going to cost a bit to get the carbs and fuel line cleaned, with a new filter, as well as new plugs and lead / coil checking, wondering if folks have any suggestions which to get done first?

Apparently the coils were done a few thousand km ago, and it apparently has iridium plugs. No guarantee of course they're set to the right gap, but you might think if one was seriously off, the bike would always be spluttering....

[ducatilover]

Set your fuel screws to the factory settings.
If it's below 4000rpm needle height and main jet shouldn't have to much effect.
Check for air leaks/blockages.

If it's spluttering it's too rich.
Lean is flat hollow sounding power.

Good luck mate. :yes:

[The Pastor]

also check out the air filter, it could be clogged, How many cylinders does an impluse have?

[ducatilover]

4cyl 60hp ish. Like a Gixxer 400 motor.

[The Pastor]

4cyl 60hp ish. Like a Gixxer 400 motor.

if it were me, (and i dont know shit) after checking things like, leads, plugs, airfilter etc I would clean and balance the carbs.

[ducatilover]

if it were me, (and i dont know shit) after checking things like, leads, plugs, airfilter etc I would clean and balance the carbs.

Good idea. My first suspect is the idle circuit fueling is on the piss.

When you rev it when it's hot, do the revs drop back below idle when it settles?

[bogan]

I like the 'high idle' circuit method of setting the fuel screws. Also checking plugs is always a good plan. Could be float valve sticking/leaking as well; Factory Pro tell me if the bike doesn't accept full throttle from around 2k, a good thing to check is fuel level.

[barno]

4cyl 60hp ish. Like a Gixxer 400 motor.

yep that's it. A beautiful 59hp 4cyl 400. Just had the air filter cleaned on it; so I"m down to "fuel-related" or "intermittent-electrics related"

[barno]

Good idea. My first suspect is the idle circuit fueling is on the piss.

When you rev it when it's hot, do the revs drop back below idle when it settles?

Nope, it pretty much settles straight to idle speed quite quickly. Really bizarre. The bike is a bitch to warm up -starts fine, idles fine for about 2 mins, then starts to die off and you have to hold the throttle gently open for another 2 mins. Then it's fine to ride.

THe annoying spluttering only ever happens when the bike's nicely warmed up.

[ducatilover]

Have you cleaned the carbs and set the fuel screws? A bad idle when warm is a rich running issue, or, unlikely, your fuel line is heating up something chronic but, I highly doubt that :yes:

[barno]

The guy that had it before me (about a month ago) said he had the carbs cleaned out, and I have the bike booked in for a fuel line clean, filter install, and general sniff around on Sat morning, which will eliminate that out of the equation. I'm not that mech-minded but I'll consult the manual to see if I can find the location of the fuel screws (different to idle screw?). Worth a look!

cheers

[ducatilover]

The guy that had it before me (about a month ago) said he had the carbs cleaned out, and I have the bike booked in for a fuel line clean, filter install, and general sniff around on Sat morning, which will eliminate that out of the equation. I'm not that mech-minded but I'll consult the manual to see if I can find the location of the fuel screws (different to idle screw?). Worth a look!

cheers
The fuel screws are on the bottom of the carbs, different to the idle screw.
Good luck mate

[barno]

cheers I will have a nosey, noting carefully before the position of the screws before I do anything :)