Lack of power bogging down

[mavar1ck]

Hi Peeps,

I have a problem which seems common on the forum. When I go to open her up she bogs down around 4.5k rpm sometimes lower. She was working fine full the full rpm range. Will start ok and tick over even rev to red line but does miss now and then. I think it is petrol starvation but not 100% sure.

Things I have checked so far.

Checked fuel tank breather, clear and free
Checked breathers to carbs and routed them straight down as advised in another thread.
Plugs light colour not black so not over fueling but definately feels like petrol starvation.

I have not altered anything since it was running ok so this is a fault developed overnight so to say. No CCT failure or anything like that.

Should I check fuel tap diaphragm?
Should I check carb top diaphragms?

Got the day off work tomorrow so any help would be appreciated.

Cheers
Mav

[tony.mon]

Should I check fuel tap diaphragm?
Should I check carb top diaphragms?

Got the day off work tomorrow so any help would be appreciated.

Cheers
Mav

You could check both of these, but also try swapping plugs for known good or new ones, and put a meter on the battery to check that it's not overcharging.

Try riding for a very short distance with the filler cap on the tank open a crack, if the problem only happens after a short while of riding. It could be a blocked vent.

[mavar1ck]

Thanks for the tip, I have tried running with the fuel tank cap open makes no difference also checked the charging recently before I left for a long trip around 13-14v. I got caught out with my old Blade when the rectifier went on me at a Portugese toll booth. Excellent timing!

I know how to check the fuel tap diaphragm I think just give a suck through the pipe and see if there is resistance but how do you check the carb tops? Is it purely remove and examine?

[tony.mon]

Yes, to be sure, but you can also remove the airbox top and manually lift each slide and note whether they fall back down at the same rate as each other.

[mavar1ck]

Ah, did this yesterday and they did seem to fall back at the same rate but weren't sure wether this was a check or not. Tomorrow I might just start again from the tank and follow through the route checking as I go.

Do you think it is a fuel starvation problem or could I be barking up the wrong tree?

[VTRDark]

I don't think it's a starvation problem. What air filter have you got in and how clean is it? Also what's the bike like at idle? Does it fluctuate at all? and when you say open her up, is that full throttle or a gentle twist?

(:-})

[mavar1ck]

K&N and it is clean not really any bugs in the mesh either. Best I can describe is when you go to over take and you twist a little more to get you by. Tried again today and pulls away right up to about 4k rpm then dies until change gear and then once back up to about 4k rpm dies again like hitting a limiter is the best way to describe it.

[VTRDark]

Sounds like a lean surge to me. But first check the vacuum hose on the left hand side of bike that runs from the rear carb up to the fuel tap. Make sure this is connected to the fixing directly behind (feel with your hand) the fuel hose on that side of the tank at the 3 o clock position. It's a common mistake to put this on what looks like a connector on the bottom at the 6 o clock position.

It's an easy check and best to rule it out. How does the bike idle, does it fluctuate much?

(:-})

[mavar1ck]

Flutuates a bit +/- 1000 rpm but was running fine stopped for an hour got back on then the problem started this is where it gets weird as I haven't done any work on the bike between running ok and then sick.

[tony.mon]

Where are you in the country?
This is where having your location in your personal details helps, as it shows on the right beside your posts.

It could be an ECU/igniter module issue, which is easily checked by swapping them for a known good one. I keep a spare set for exactly this sort of test.

But it also sounds like it could be a blocked main jet/ jets.

[mavar1ck]

I'm in Nottinghamshire. Added my details now thanks for the pointers. When the rain stops what other characteristics does a failing ECU/igniter show?

The guy who had it before me has tuned it, I know he has changed the needles and had it on a Dyno somewhere in Peterborough but like I said ran fine so I don't think that has anything to do with it. Was an odd moment when frustration got the better of me and I opened the throttle to its max, nothing happened other than a deep noise from the bike then jumped into life like nothing was wrong but this didn't last til' it was back to bogging down.

The revs it happens at varies from 2k to 4.5k up to 6k and at the moment 3k which makes me think it's a fuel issue. Also I have checked the old plugs before this happened they are slightly black but ok around the ceramic area, the new plugs are white and clean (done 2000 mile on them) possibly a little too lean?

Just guessing really.

[tony.mon]

a deep noise from the bike then jumped into life like nothing was wrong

This sounds more like a sparks problem, when one cylinder is cutting in and out.

When you say it's bogging down, does this happen suddenly, or over a few hundred yards?

[mavar1ck]

If you keep the revs and speed down you wouldn't notice anything wrong but if you accelerate then it just bogs down with no increase in revs or speed.

[VTRDark]

the new plugs are white

This indicates either lean mixture or over advanced ignition timing so it could be either. Though to get a true spark plug reading you need to get to the speed and revs where the problem lies, dip the clutch, switch off engine, coast to a stop and pull plugs. Or the plugs may be the wrong heat rating.

A new ECU could be expensive, it's really something you need to verify first. Are there any storm owners local to you. You could swap the ECU temporally, go for a run and see if it improves things.

Or you could try richening the pilot mixture screws a bit by turning them .25 to .5 turns anti clockwise to richen slightly. It's not easy to access them though and may be easier to remove carbs. Idle fluctuation also indicates the mixture is not set right. The other possibility is that there is an air intake leak somewhere. Check the carb rubbers at the base of carbs make sure they are done up nice and tight and have no splits.

Stick your location in your profile via the user control panel.

(:-})

[mavar1ck]

Thanks for all your replies, hopefully on the right track. Just removed the carbs to check the diaphragms found something nasty. Carb slides are rubbing and there is a black dust in the carb tops from this also in the float bowls can only be described as sand???

How could this even get in there? Are there no filters in the fuel system?

How do I attached photo?