High speed problems

[CB ARGH]

Hey guys,

I went for the first real ride on the bike today after I got her re-registered/warranted etc.

All was going excellent, perfect I must say. I hit the motorway, all was fine, engine was at about 9000 RPM's at 100km/h which I don't really like the sound of, but still the temperature was normal so I kept going at around 85km/h.

I hit the country roads and was getting my speed up there quite a bit, speeds where I had never been on a motorbike, well, 100km/h again, this time, for a longer period of time. I get to a hill and it starts to cut out, I think "F**k I'm out of gas!", so I flick it onto reserve and let the engine catch up a bit, then take off again. Same thing happens again after about 2 mins at 100km/h. I rock into the fuel station and open the tank, it's full still... "what the?".

I set off again thinking nothing of it. The problem happens again, this ain't good. I decide to let it cool down for half an hour and take off again. Still happens.

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My idea is that there isn't enough fuel getting into the carbeurettors at 100km/h (around 9000RPM). This could be because I installed an externel fuel filter (one that goes between the tank and the engine), however it also has a filter IN the tank. That means the fuel passes through two filters before it reaches the engine.

Should I remove the external filter? Or would it be another problem?

HELP!

Thanks,

STEVEN.

PS: Sorry for the long post.

[sinfull]

Be a good start !

[MSTRS:Me]

Elimination...
If nothing is untoward with your engine temp, then fuel feed is most likely. If it didn't do this before the addition of the filter, then that's your problem. If you don't know, then remove it and see what happens.
Otherwise, it is probably electrics - ie the coil(s)

[AllanB]

Also ensure the fuel cap vent hole is clear.

[iamkirk]

9000 rpm at 100km/h is normal with that engine. i have the same motor and it seemed a bit high at first too, i personally think it must be because of it having bugger all power below that anyway.

[xwhatsit]

Well they do 19,000rpm quite happily so I wouldn't worry about doing less than half of that.

It does sound like fuel starvation, don't it? Pull the fuel hose off the carbs and turn it to `Prime' if you have a vacuum feed tap (or `On' if you have a proper On/Off/Reserve tap). Does it piss like a racehorse? If not, then that's your problem.

If you do have a vacuum feed tap, does it work any better if you run around on `Prime' rather than `On'? You do see the occasional complaint about the diaphragm in the fuel tap not quite doing its job on bikes with those sorts of fuel taps.

[motorbyclist]

wtf would you add a 3rd (or is it 4th?) fuel filter?

there's one in the tank, one at the float valve, and i'm pretty sure these have fuel pumps too(very surprised when i first saw one), so there's be one there also.

ditch the filter. those revs are fine btw; built to do more than 19k etc as xerxes said

[JMemonic]

When you added the filter did you take a corresponding amount of hose out??, it could be that the hose route now has a kink in it that you can not see, try lifting the tank an observing the path of the fuel line, if it appears to enter a bend that closes it ie a kink or fast 90 degrees try removing that.

As to the effect a filter will have on the flow it would be minor, the in tank filter is rather coarse and will only get the larger partials, if you have any at the float valve they would take care of the smaller partials, as to a fuel pump having filters it would be a bit odd that the manufacturer would include a filter at this point and on in the float. I will wait till I see the manual to be sure that this is the case, it would also be odd that a non injected bike would have a fuel pump unless the tank is lower than the carbs and gravity would not feed them.

In theory you don't need a filter at all but small particles can get past the filter in the tank and build up in the carbs so a 2 dollar filter will potentially save you either a lot of effort and time or money.

[motorbyclist]

As to the effect a filter will have on the flow it would be minor, the in tank filter is rather coarse and will only get the larger partials, if you have any at the float valve they would take care of the smaller partials, as to a fuel pump having filters it would be a bit odd that the manufacturer would include a filter at this point and on in the float. I will wait till I see the manual to be sure that this is the case, it would also be odd that a non injected bike would have a fuel pump unless the tank is lower than the carbs and gravity would not feed them.

yeah i was pretty surprised to find these have pumps too, assumedly to maintain an adequate fuel supply at 19krpm, at which point that marginal impedance from the extra filter may be a major (although without actually seeing it we can't say anthing for sure)

a filter post pump is very common - injectors you'll find include filters despite the pump. they are to stop any contaminates from the fuel line or the last time you disconnected the pump, and to not have them at float valves with or without a pump would be very bad practice (something i'd expect from china, not honda)

[motorbyclist]

double checked on wikipedia and from 1990 onwards they had "a completely new set of VP carburettors that feature smaller throats reduced from Ø32 mm to Ø30.5 mm. These carburettors are now fed by a vacuum operated pump for fuel delivery."

also see here ontrademe/econohonda (ie, it is infact electrically powered and the part does exist)


i would just give pics from the microfiche, but being in japanese makes it pretty difficult to find the one part

[JMemonic]

Just finished downloading the service manual, no mention of a pump, hmm this is odd after looking at the info you have, and no mention of filters at the floats.

Anyhow I stand by my initial suggestion of looking for kinks or sharp bend in the fuel line after the addition of a filter, its a common mistake and easy to find and fix.

If it has a pump there should be some measurement for the flow rate and pressure that could be tested to eliminate that as an issue causing the fault described, most of the manual suggestions around the fault deal with fuel as its primary cause.

[motorbyclist]

yeah a bent fuel line is a pretty likely fault

where'd you find the service manual? i wouldn't mind an english one myself
the pump seems to be on mc22 and later - got the right one? the closest looking microfiche part i can find looks like the starter motor though...

the only reason i know they're there is from helping a mate with his cbr, and going "wtf is a mitsubishi (electric) fuel pump doing in here?!" when i found the fuel line went from tank to pump rather than tank to carbies

EDIT:might clarify the pump was located above the geabox, but NOT attached to tank by anything other than fuel line. only saying this as all other fuel pumps i've seen in my limited FI experience have been bolted to the underside of the tank

[MSTRS:Me]

where'd you find the service manual? i wouldn't mind an english one myself

This help? http://www.manualz.info/

[CB ARGH]

Cheers guys!

I've been riding it around low speed zones (less than 80km/h)... I'll have a look if there are any kinks in the fuel line tomorrow morning, as I didn't cut out the equivalent fuel line when I installed the other filter.

I'll give it a go removing the filter and see how she goes at 100.

Churr!

PS: I rode Huia Road today (just past titirangi, Auckland), god it's amazing. Quite a few wet patches that I slowed right down for though!

[The Pastor]

Ok lets clear a few things up.

MC22's DO NOT HAVE A FUEL PUMP.

MC22's ONLY HAVE ONE FILTER INSIDE THE TANK.

Now onto the important things. YOU DONT LIKE THE SOUND OF 9000+ RPM? wtf are you nuts? Thats the best thing about the bike (and of cource its killer in the corners)

Possiable problems

Kink in the fuel line

Flat spot with the carbs.

New filter slows the flow of gas down so that when its using the most (100k+) it can't fill the float bowl fast enough.

Might want to check the filter inside the tank - it could also be clogged adding to the problem.

Air filter might be blocked as well.