Can you guys help me with 250 probs? Too much fuel I think

4lex · Post by **4lex** » Tue May 30, 2006 12:47 am

Evening all,

I'm an expat Brit living in Sydney. There's quite a market for 250s down under due to the learner rider restrictions allowing up to 250s (but not strokers), or up to 650 with low power to weight ratio. Anyway, long story short, the local driving authority didn't recognise my CBT and insisted I go through their learner programme, so I'm on a ZXR250a.

I was recently having fuel starvation problems, caused by a crappy, rusty old tank, and no fuel filter. Fitted a filter, stripped and cleaned the carbs and had them balanced by a bloke with a vacuum gauge.

Thing is, it seems the partial fuel blockage was masking an over-fuelling issue, she runs frine from 8-10k all the way to 19k, but stumbles a bit below 8k as if running on 3. Smells really fuelly and is using a bunch more fuel, so I'm thinking in terms of float levels being too high?

Just wondering if anyone has any tips on adjusting them correctly? The 250 uses Keihin CVK d30 carbs, which I'm guessing probably work the same way as the d32 on the 400?

Last thought, how about banging an aftermarket can on it? Does it follow if the exhaust flows more freely the engine will be able to burn the extra fuel, or is this (and I suspect this is the case) only likely to affect high rpm WOT?

Cheers all - hoping for some decent technical insight from you guys - the best I get from the Aussie forums seems to be 'get a tune up and hope it fixes it'.....

Alex

Post by **Xphyral** » Tue May 30, 2006 1:14 pm

It sounds like a flatspot, which would mean the need to setup your carbs properly. If it is a flatspot then balencing wont tune it out. I dont think an aftermarket can is going to help atm.. but:

How long ago did you buy the bike?
Do you know if it had an aftermarket exhaust prior to sale?
Was it jetted for the exhaust?
If jetted was it setup for standard?
How do your spark plugs look?
When was the last time you changed plugs?

If it had an aftermarket exhaust previously and has been setup for that then a standard can put on for it's sale then you'll get fuelling problems. Hell the previous owner might have installed a jet kit because of the fuel blockage. I dont know your history with the bike so if you havent had it for long check into that.

4lex · Post by **4lex** » Wed May 31, 2006 12:23 am

Thanks for the response.

Xphyral wrote:How long ago did you buy the bike?

Just over a year, then it was about half market price of a good one..

Xphyral wrote:Do you know if it had an aftermarket exhaust prior to sale?

It doesn't now, and I can see no evidence that it's ever been removed (no scratches on fasteners etc)

Xphyral wrote:Was it jetted for the exhaust?

I suspect not. It doesn't strike me that the bike has been looked after by an enthusiast in the last ten years, if ever

Xphyral wrote:If jetted was it setup for standard?

Don't know how to tell?

Xphyral wrote:How do your spark plugs look?

Plugs look great, dry, biscuity brown and uniform across pots. I'm not all that surprised there, as I tend to avoid running it in the rev range where the fuelling problem is evident - means I go everywhere as fast as possible

Xphyral wrote:When was the last time you changed plugs?

I haven't changed the plugs, based on my evaluation of them they look fine, and in my estimation may well have been changed shortly before I got it.

My (basic) understanding of these carbs is that if it runs well at high rpm then it would indicate that the jetting is right, and that the cause of overfuelling in the mid range is a result of fuel level too high and rough idle down to over rich idle mixture screw?

Has anyone seen a how-to on the web anywhere (ideally with pictures for the uninitiated) which details how to set up fuel levels in the carbs? It would appear that setting the floats involves bending the the tangs which shut the fuel off much like a ballcock system - seems a bit hit n miss to me?

Thanks,
Alex

RedexRobB · Post by **RedexRobB** » Wed May 31, 2006 9:23 am

Id get it on a dyno, and find out that way. And if your going to go for a race pipe you'll wanna set it up anyway. They can tell you if it is a flat spot and why its there usually.

Post by **masterofinsanity** » Wed May 31, 2006 9:39 am

have you got a service manual? if you look at the fuel section in the manual it will tell you how to check and adjust the float levels, it also tells you the height that it should be, if you don't have a manual i have one in pdf.

RedexRobB · Post by **RedexRobB** » Wed May 31, 2006 9:57 am

for the 250 Baz?

Post by **masterofinsanity** » Wed May 31, 2006 10:05 am

yes mate for the zxr250

and the zx7r

and all the gsxr1100's

4lex · Post by **4lex** » Fri Jun 02, 2006 2:19 am

[quote="masterofinsanity"]the fuel section in the manual it will tell you how to check and adjust the float levels, it also tells you the height that it should be, if you don't have a manual i have one in pdf.[/quote]

That link would be great mate, thanks for the offer.

Anyone know of any other bikes which use the CVK.d30 carb/s? Parts suppliers keep laughing when I ask for ZXR250a parts.....

Cheers,
Alex

-edit- can't make the quote tags work? Identical to my previous above which worked fine...