Guy's XR400 Cylinder sizes please?

Syris D Indomitable · Nitrous Nuisance Joined: 12 Feb 2011 Karma :

Sorry I mean't piston sizes

I have it running sweetish now, My last prob turned out to be the mixture screw on the carb not being set right. (Way out)
It ran rough as hell when cold. (My de-restricted exhaust doesn't help either)
I do have low compression though, my bike has been thrashed.
It's nothing serious but when I kick it over I get a metalic crack sound.
Anyway I'm going to go for a new piston kit as the compression is low.
I will be fitting a new piston kit soon and need some advice please.

Do they go up in size by .25mm or by .5mm.
I'm going to go for a barrel rehone if they go up by .25.
If they go up by .5, I guess I will need a re-bore.
Thanks!

..... · Quote Me Happy Joined: 15 Jan 2005 Karma :

How do you know the compression is low? Have you done a compression test yet?

0l0dom0l0 · World Chat Champion Joined: 21 Oct 2009 Karma :

One again, you totally jumping the gun.

Just because you have a metalic 'click' when you use the kick-start doesn't automatically mean you have low compression. Its probably the locking mechanism or something working. I suspect its the kickstart cogs and such like. You could take it off and oil all the parts maybe? But then you will probably need a new kick-start, and gearbox.

Your bike has done 3500 miles, you won't need a new piston.

As I last thread you made, do a compression test. If its low, put a teaspoon of oil down the barrel. If the compression increases then the rings are worn, if it doesn't change it means its the valves.

No point in guessing.
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Bikes: 2007 Derbi GPR 50, 1998 Yamaha Fazer 600 (written off), 2002 Yamaha Fazer 600, 1994 CBR 600F, 2003 Triumph Daytona 600, Kawasaki ZX6R J1.....Current: 2006 Yamaha FZ6, 1998 Suzuki TL1000R and a Honda VFR 400 NC30.

Syris D Indomitable · Nitrous Nuisance Joined: 12 Feb 2011 Karma :

Ok above will do. My trusted mechanics a bit busy at the mo.

Martay · World Chat Champion Joined: 20 May 2009 Karma :

Just because it kicks over easily doesnt necessarily mean compressoin is low. Get a compression test done, one how it stands now, and one with a little oil in the cylinder.
A friends honda CG would kick over as though the spark plug was out, but never failed to fire up first time.
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serlant · Brolly Dolly Joined: 06 Jul 2009 Karma :

And just to add, next door has a ktm 640, and kicking it over with the plug out once it made quick a clicking noise each time he kicked it over, i'd say its normal? just the ratchet going as the pistons moving?
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tatters · Exxon Valdez Joined: 04 Jan 2004 Karma :

0l0dom0l0 · World Chat Champion Joined: 21 Oct 2009 Karma :

Syris D Indomitable · Nitrous Nuisance Joined: 12 Feb 2011 Karma :

Syris D Indomitable · Nitrous Nuisance Joined: 12 Feb 2011 Karma :

chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

Put all the tools down and walk away from the bike, you will lose money waste time and probably lower the value of if.
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MarJay · But it's British! Joined: 15 Sep 2003 Karma :

Syris D Indomitable · Nitrous Nuisance Joined: 12 Feb 2011 Karma :

Ok cheers!, I spoke to Honda And they go up in size by .25
Just wondering if your aware of how much hammer xr400's get?

I Read thread on here a while back, I guy's Cylinder on his XR400 was oval after being thrashes.

It is an off bike.

As for schooling, I would think it would be better to ask the person who asked the original question more questions in order to investigate based on your expertise. This is what all skilled trades men do, and even doctors alike.

A lot of the responses I have had on here have been miss-informed judgemental assumptions, a bit like your above.

I have had some good info too.

So I now know even if I go up by .25mm oversized I will need a rebore.
I got this from XRV too.

..... · Quote Me Happy Joined: 15 Jan 2005 Karma :

Have you registered on this site before? Esoteric1? The Thinker?

weasley · World Chat Champion Joined: 16 Oct 2010 Karma :

0ddball · World Chat Champion Joined: 15 Jul 2005 Karma :

Has it even been established the bike has a genuine problem? Not by you (op) as tbh you don't have the slightest clue and only seem to be happy if it does have a problem.

Usually i'd encourage someone to have a go for themselves but in this case i echo what many others have said. Put the spanners down and take it to someone who knows what they are doing. Don't go in telling them there is this and that wrong with it, you are just guessing and most likely wrong. Let them tell you exactly what, if anything, is wrong with it.

Peoples patience is wearing thin.
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Syris D Indomitable · Nitrous Nuisance Joined: 12 Feb 2011 Karma :

Anyway guy's, it still runs like a bag of shit when cold.
I am not going to mess with my new carb to suit the De-baffled exhaust. I am going to see if I can pick up a second hand standard end can.

Anyway what exacerbated the problems I had in the first place was Badly set valve clearances, Molested carb which included damaged pilot jet, damaged screws, choke flap not closing properly and the De-Baffles exhaust which Honda apparently took a long time to engineer. It was also in need of a good service.

Thanks for the help guy's.

All I need now is a replacement end can then I am sorted.
You lot helped eliminate issues i thought i had.
Cheers!
Chow!

..... · Quote Me Happy Joined: 15 Jan 2005 Karma :

I'd be surprised if the end can makes that much difference. If it runs well when warm then just leave it. Warm it up and ride it instead of going round in circles in your garage chasing a different problem a day.

How long does it run badly for when cold? My XR was hesitant when cold and my XT is but warm up quicky and run fine.

Syris D Indomitable · Nitrous Nuisance Joined: 12 Feb 2011 Karma :

It's run really bad for around 5 mins, it keeps coughing (Like an overweight granny's incontinent fart), and cutting out. I have to start it like 5 times and hold on the revs.

My carb is new with standard settings. I have read if you de-baffle or fit an after market exhaust you need to upjet and re-tune the carb on these.??

Syris D Indomitable · Nitrous Nuisance Joined: 12 Feb 2011 Karma :

He is the troublesome one in question.
https://www.youtube.com/watch?v=7_7_pZ2aVFA

..... · Quote Me Happy Joined: 15 Jan 2005 Karma :

That exhaust looks like it has the baffle in.

DrDonnyBrago · World Chat Champion Joined: 03 Jan 2010 Karma :

LOL.

FFS mate, get it to a fecking mechanic, any mechanic will do if your one is busy. All you want is a compression test. One test as it is, then one with some oil down the bore. Post the results on here.

Seriously just listen to the advice you are being given, you get good advice, ignore it then somehow figure you need new valves and a new piston!?!?!

Rebuilt multiple engines my ass, I wouldn't trust you to rebuild a rollerskate.

Syris D Indomitable · Nitrous Nuisance Joined: 12 Feb 2011 Karma :

Ok will do, cheers.
Going to book it in and ask him if he can fabricate something for me too, that's if I can't pick up the genuine one in the mean time.

It has been De-Baffled Joe, there are spot welds on some tiny tube they fitted coming out from the rear.

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

Saying stuff like "It still runs like a bag of shit, so I need a rebore." Is not unlike saying

"I have a pain in my chest so I must need a coronary artery bypass graft!"
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devojunior · Brolly Dolly Joined: 12 Sep 2010 Karma :

ffs people the guy is trying to fix his bike and all you mr know it alls are acting like right cocks.

If nobody has anything helful to say to him which may help him fix his bike, instead of trying to act the cool guys who spend every god dam minute on here why dont you suggest a mechanic who has good rates or someone who could look at his bike for some beer tokens local to him.

oh well good look with your bike pal.