Too much air at higher speeds

[andym]

On the CBR everything is fine up to around 75mph, but anything over that and it feels like it's being starved of fuel for up to 2 seconds at a time no matter how far the throttle is twisted, the faster I go the worse it gets with the speed topping out at 110 (unless I'm going down hill with a tail wind).

Anyway, one of the things I was told to try was using the choke and see if it sorted it.... today I got to around 80 and it started to get a little lumpy again so I started pulling the choke lever and at around 1/4 open (or would that be closed?), the bike started running better up to around 90 before slowing down again.

I was thinking of partially blocking off one of the air pipes to see if that made any difference. Although I'm open to suggestions

[RhynoCZ]

Isn't it revs related, rather than speed of the motorcycle?

If it's revs related, than I'd suggest there's water in the system.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[andym]

[temeluchus]

Possibly

Water in the carbs (causing fuel starvation on prolonged acceleration)

Something fuel tap/filter/filler cap vent related

Air leak in the inlet tract somewheres
____________________
Some shite cruiser. Now with guns and FREEDOM!

[mysterious_rider]

Does it have ram air?
____________________
KAWASAKIIIII

[RhynoCZ]

I understand. Clogged fuel tank breather, faulty pump, dirty fuel filter and some other bits could cause fuel starvation when going at high constant speed/revs.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[andym]

Lets see:

Carbs were cleaned a few weeks ago (third time since I've owned the bike.)

Balanced last week.

New fuel tap around 10 months ago.

No ram air that I know of (think that was on slightly later bikes.)

No leaks in inlet tract that I've found.

Vacuum fed, so no fuel pump.

Not sure where the thickest breather pipe leads, but I've tried sucking air through it and it didn't seem blocked (got a nice lung full of petrol fumes.)

Don't know if it has a fuel filter in the tank, but it doesn't have 1 outside it.

Tank has never been run low enough to hit the reserve.

But again, with the exception of blocked breathers, I'd have thought all the above would have affected the bike at all rev ranges, in all gears.... not just anything over 80mph. I haven't taken it for a really long run, but it will sit quite happily at 70 in the lower gears without so much as a cough for about 20 miles.

[MarJay]

I thought you did a compression test and found one cylinder was at 80psi and the others at 130?
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[WD Forte]

Clogged tank strainer?
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bikers smell of wee

[weasley]

[Robby]

You say you've cleaned the carbs 3 times while you've owned the bike. This rings alarm bells for me, carbs should only need cleaning if the bike has been standing for so long that the fuel has turned to varnish - in which case they need to be cleaned once, and really well.

Common problems on bike that have had the carbs cleaned:

1. Knackered throttle shaft seals. Would have been ok, but if the carbs were separate off the rail then these seals get disturbed and often need replacing. Often shows up as a weak idle and weak low speed running, getting worse as the engine warms up.

2. Split/torn/folded/poorly fitting carb rubbers, often caused by cack-handedness. More common on straight-4s because the carbs can be such a swine to refit.

3. Float heights all wrong. I recommend measuring the fuel level by using a bit of clear tube attached to the carb drain rather than by setting float heights, it's more accurate and easier to check. Still just as hard to adjust.

4. Clogged mixture circuits - because people decide to clean their carbs by cleaning the big holes that always have solvent running through them, not the small holes that like to clog.

5. Air leaks from the vacuum balancing ports - because they were only covered by a rubber cover that has hardened with age and didn't like being moved, or because they lost the tiny copper washer that sits under the plug for screw-blanked ports.


Of course, it's a CBR600 so it could just be your reg/rec shitting itself.

[RhynoCZ]

[andym]

[temeluchus]

You are an ungrateful drunken scot. Thats why we love you.

https://www.cmsnl.com/honda-cbr600f-1992-englandkph_model2266/partslist/F__1400.html#results

Diagram shows a pump but does not list a part number. Weird.
____________________
Some shite cruiser. Now with guns and FREEDOM!

[andym]

[Snod Blatter]

A possibly silly question but does the airbox still have the snorkel fitted? Some strange people remove these thinking they are restrictive..
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[davebike]

Sounds to me like the missing fuel pump is the problem exactly the symptoms of a poorly pump

Pump is held to the frame below and slightly to the rear of the back of the tank by a large rummer fitting

Fuel line from tank though in line filter to pump them to carb
____________________
Dave
NC750Xdct + others at work !
davebike1@gmail.com

[Copycat73]

[RhynoCZ]

Rhyno 1:0 BCF
____________________
'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Suntan Sid]

Probably no help but, I had a 1992 CBR600F, in Cyprus, it had normal carbs, not flat slides and there was no fuel pump.
What it did have was restrictors in the inlet rubbers, before I removed them!
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"Everybody needs money, that's why they call it money!"

[andym]

[weasley]

[andym]

OK this is bugging me now.... I've phoned a couple of places and have been told that no it doesn't have a fuel pump as the vacuum line is doing that job..... another place has said that if the bottom of the tank is above the level of the carbs then it doesn't need a fuel pump.

I've been told where the pump would be located, so there should be a multiplug around the area where it should have been. I've also been told (by a lecturer) that if it should have a pump but doesn't it will affect the top speed and cause poor running at speed.

I've also been told that because it doesn't have the standard can on there it isn't getting enough back pressure and that is affecting the top speed (but allegedly 35mph.... seriously?).

Looking for information on this has thrown up a site that said it was only '95 and afterwards that had fuel pumps......

And Weasley.... do you honestly think I would pay anywhere near that for a fuel pump? I'll just find one second hand if I do need 1.

Ma heed's gonnae explode

[davebike]

Honda part list shoes fuel pump for 1992 CBR600F
Symptoms match lack of pump
Pump hard to mend and expensive to replace
If previous owner only used it at low speed / fairly full tank he not be bothered
____________________
Dave
NC750Xdct + others at work !
davebike1@gmail.com

[mysterious_rider]

Definitely fit a pump. I removed mine for a test and had same problems top end.maybe try a second hand one.
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KAWASAKIIIII