XBR - Lack of power at 4200 revs

[crackedhead]

The old XBR hadn't done more than a couple of thousand miles in the last 10 years (with it's previous owner) and doesn't run very well at about 4000 revs (in top gear) when going against the wind, or up against a steep hill.

I've done the usual things like change the air filter, check the valve settings, change the spark plug but to no avail. As it's also using a lot more fuel that it should I thought that a carb overhaul wouldn't do any harm. So £18 from NRP carbs got me a new kit. After several hours of fiddling with the carb and skinning knuckles in the process, the carb was dismantled and used a compressor to blow through all the holes before assembling. The bike now starts far better and took it out for a run and straight away there was a vast improvement. The engine now goes easily up to legal speeds ....and beyond! Well, it did for a while ....

The same problem has now returned. I wonder if it's dirt in the fuel tank, or 'gunge' in the carb that I've not cleaned out properly.

Looking about on ebay last week there was an XBR500 carb in very good condition, going for £20. It really doesn't look too used at all, so might be a bargain. Anyway, the 'new' carb arrived today so I'm going to try it tonight and see if it improves.

[Steve H]

Might be worth putting an inline filter in the fuel line. Cheap and much easier than constantly stripping the carbs

[crackedhead]

Thanks Steve. I tried to fit the fuel filter from my vfr750 but the connections are two large. Looks like I'll have to go and buy one.

Anyway, the newer carb is now in (I've got that down to a fine art) and is running pretty well. No problems at all at 4k, or at any other point in the rev range. Gave it a 40 mile shakedown run out to Edinburgh and back and the bike is running very well.

I think the problem with the other carb is probably due to fuel residue, as the bike  has done very few miles over the last 10 years. I can add the old carb to the list of ever growing XBR spares (swinging arm, centre stand, petrol tank, pegs, etc).

If I can now get the fork stanchions rechromed, I should be able to make the trip down to the thumperclub rally.

Cheers.

[guest27]

In line fuel filters - about 50p from a motor factors and well worth the money...

R

[bullet350]

my cbr600 had done 6000miles in 16 years when i bought it, and had been standing for the last couple of years.

it only ever ran right after rebuilding the carbs. each time i'd strip and reassemble them, finding nothing amiss.

then a day or two later i'd be down on power, stuttering and generally quite flat.

after the third rebuild (lots of fun with a full fairing and four carbs!) i gave up and got a used set of four from eBay from a tidy but regularly used bike.

£26 later it runs sweet as a nut and will pull 155mph on the clock (of course not on the public highway).

Before all this started a friend of mine who builds enduro bikes for the pro's said throw the carbs as they'll never be right once they've stood for ages.

bullet350

[crackedhead]

Steve, Rog & Bullet350, many thanks for your advice & comments, they are appreciated.

Tony

[Tuoppo]

Hi all.

I have the same problem. Fuel consumption is increased and feels like that the bike doesn`t have power. Worst thing is the hole between 4000-5000rpm. I tryed to clean carb but it was already pretty clean. I also noticed that carb needle have a scracts.

Today I ordered  a new Keyster carb repair kit from ebay. I also read from Od`s XBR faq that Honda changed the jet sizes to #152 -> #158 and #48 -> #52 at same time when honda gave a new instructions for valve clearance for XBR`s. I ordered repair kit with these bigger jets. Does anybody have experience how this jet upgrade affects on a stock bike?

[crackedhead]

Hi, could be quite a few things but from my recent experience, it could be either a worn main jet or the diaphram. First time i rebuilt the carb there was a complete lack of power around 4,000 revs and was caused by the diaphram not being seated correctly. It's a so and so to get in place, so ended up using a film of liquid gasket to hold in place.

See how you get on when you install the carb overhaul kit ... maybe put some redex in the fuel tank as well. By the way - the carb kit that I got had the 'old' 48 /152 jet sizes.

Good luck.

[guest7]

The revised jets don't make a massive difference to power, but in some cases they stop the bike stalling at every traffic light.

GC

[Tuoppo]

Hi all,

Today I installed the keystar repair kit in XBR carb. When I order repair kit I asked motorbay to change new size jets. The most dameged part was the needle. Also the mixture screw was warn from tip. Now the bike runs much better on highway and hole between 4000-5000rpm is gone. Almost perfect but ... 

now I have a new problem. Bikes idle is only 500rpm and when I turn idle screw and then drive couple of miles idle is between 2000-3000rpm. I also noticed that rubber in a vacuum chamber is stretch. Maybe it would be wise to replace it but new costs over 70€ ... Anyway tomorrow I try to adjust mixture screw. Maybe that will help. Does anybody have ideas what went wrong?   

[johnr]

the fine particles of rust from inside a fuel tank will pass straight through a fuel filter, the best solution is to empty and remove the tank, clean it out and seal it with petseal or one of the many other fuel tank sealants on the market. if youve an inset filler cap, check that its drain pipe is free too, if this gets blocked, any water that collects there will run into the tank every time you remove the filler cap.