Honda XL125V Varadero + Aftermarket Exhaust = Slower bike?

[chrisjpartrid...]

I have an '02 Varadero 125 which I use for commuting. The bike is overall is what I would describe as good condition though has started to suffer from a rusting mild steel exhaust - a common problem on these bikes.

It started to blow recently and after assessing the pipes the other week I found that the downpipes where rusted but repairable but the rear section (silencer/can and the pipe leading from it) were rusted through and not worth saving.
My plan became to replace the lot with stainless pipes, but looking at the cost of new parts I decided to spread this out a little.

I have since welded up the downpipes for now and discarded the rear in favour a second hand Devil can from eBay.
The can is it pretty good condition and now fitted I have no exhaust blows anywhere in the system.
I have left the "DB killer" in as it just sounds silly for such a small engine to make the amount of noise it does with it out.

https://i1129.photobucket.com/albums/m511/chrisjpartridge/Bikes/Varadero%20125/15052011308.jpg

Now here's the problem - The bike is noticably much slower!
I should point out I'm not expecting much here: The bike is a 125 and I'm in no way trying to tune it here, mearly trying to change to more robust parts.
When the standard exhaust was good the bike would happily sit at 60 MPH on levelish A roads, and with it blowing it started to struggle but would get there in the end.
Now though it struggles past 50!!

Though I have some theories I'm not too sure where to go from here so was wondering if anyone else has had similar issues.

[CaNsA]

is it Fuel injected or carbd?

[Shaft]

[chrisjpartrid...]

It runs on twin carbs - they changed to injection in 2007.

The exhaust is ment for this bike and the fit and quality seems pretty good (I've seen enough rubbish in the past to appreciate this!),

The bike ran fine right up until the change and the carbs have not been touched at all.

Back pressure was one of my theories though I'm not sure how it applies on an engine like this.
A good example of ruining back pressure to me is when you see all the dick heads who putting massive exhausts on small hatchbacks, removing the back pressure and in effect de-tuning their engines.

As the bike perfomed better than this with a blowing exhaust though I dismissed it.

Another thought that was carb related was that perhaps the carbs would need to be altered or up-jetted to suit this; however again I didn't thing so A) as it ran better with a blowing exhaust and B) I've not read about this being nessasary on a 125.

Having taken the bike out again this afternoon I would descibe the problem now as a distinct lack of torque and the bike refusing to want to rev into the top quarter of the range.

[JackDaniels]

Id say you should need to upjet a little, can you take your spark plugs out and post up a pic ?
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[Teflon-Mike]

Running with a blowing header.... not good.
First thing have you done the basic maintenence?
Tappets, cam chain(s), etc.
Hole in header usually means nil back pressure, & lean mixture.
May run very well for a while, but often at the cost of burned out exhaust valves or distorted pistons etc.
Could be, that the added oomph of fcuked header masked problem it causes inside engine.
Fixing header now shows up problem.
Next welded header.... how so done? have you choked the pipe pilling hole with weld, or did you plate over?
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[chrisjpartrid...]

The pipe has a plate welded over it.

Engine has done just over 9,000 miles - was on 8,100 when I bought it and the exhaust only failed about 200 miles ago and didn't seem severe at first, infact the holes it had were tiny as it'd just started to go, hence being able to repair it.
Tappets are fine and if it was a valve issue you'd know!
There is no rattle at all from the engine nor is there any smoke.

[Teflon-Mike]

[dangerousdave]

How is the performance with the db killer removed ?

Will it get to 60 then ?
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[HoggyF]

Why not check with Devil if they recomend re-jetting or if its supposed to be a direct swap?

[Rogerborg]

Another request to get your (plug) tips out for the lads.
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[Moxey]

Slip on cans normally don't require re-jetting unless specified. Sounds like the cause of the issue is a lack of back pressure if the bike was running fine before try removing the DB killer

[prawny1]

The fact that this pipe comes with a db killer would indicate it is a generic straight through pipe with a link pipe designed for it to fit the varadaro, most of the time it's only pipes with proper deflective baffles that you can get away without rejetting.

I would suggest trying to lift the slide needles in the carbs by lowering the circlip this will richen the wide open throttle fueling slightly if this help (which it will) then you neede to rejet,

sometimes if a bike is running lean you can try pulling the choke on when it starts to run out of puff if it picks up then again you know you need to rejet.

If you are keeping the standard air filter you usualy don't need to upjett too much, one size on the slow jet and 2 or 3 sizes on the main.
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[ClockworkJesu...]

Only problem with changing exhausts ect. is you ultimately change the design of the engine - and the variables the engine was tuned to run to!

I'd probably jump up a few jet sizes, as lean engines will burn themselves out; so its always better to run richer than leaner;

and besides; if it runs too rich you can always lean it out via the carburettor settings. So a rejet is a pretty safe change, unless you can't spare the £6 or so.

[chrisjpartrid...]

Update:

Had the pipes off today and checked them out only to find a large lump of carbon trapped inside the small pipe.
I've not put it back together yet but can assume that must have been blocking it.

It's always the simple things that cause the most head scratching!

Perhaps I should point out that the engine in the bike is not the origional as I bought the bike last winter with a seized engine and swapped it out so I'm blaming it on that!

I'm not going to bother putting it all back again though as I've just ordered some nice stainless downpipes for it - no more rot to worry about.

Thanks for all the suggestions though guys; I'll come up with a tougher puzzle next time!

[Rogerborg]

You've done a plug chop, right?
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[chrisjpartrid...]

UPDATE:

For anyone that's interested I have the bike all sorted now and can share some wisdom...

I have splashed out some more of my hard earned cash on some Motad stainless downpipes, stainless clamps, new seals, etc. and done the whole lot properly - No more repairs; just all new stuff that'll last and won't rust.
There's only so long you can patch things up for anyway.
Overall the Motad pipes are actually quite good for what they are though a little pricy. The quality is good but the little clamp the include doesn't fit!

The end result was a lot better performing and as it wasn't full of carbon and holes actually sounds a lot better and more even.
I was however still having performance issues which I have now traced to a sticking choke cable.
Basically it presses in but not fully unless you take a look at it and jiggle it back; not something you can notice or attend to while riding.
I plan to either just replace this or am considering making a remote cable to run up to the handlebars - something I'm supprised Honda didn't think to include on such a bike.

The whole thing runs smooth now and manages to get past 60 on the straights once more.

Next to get my 400 to run smoother as well!

[temeluchus]

The next person to say back pressure will be shot.
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[Fladdem]

I like the hand guards, did you fit them yourself? If, so was it difficult? Can you give me a make and model, please? I am thinking of playing about with my Varadero because my dad wants it afterwards, the 850's great, it's just you get better fuel economy in a spaceship. Just toying with ideas at the moment really. Sorry for not creating a new thread but that picture just looks so good.
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Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
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