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Can you upgrade the exhaust without a re-jet?

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THERE IS NO "ANSWER". The point of an aftermarket exhaust is to IMPROVE performance. An aftermarket exhaust improves performance by allowing air to be evacuated from the cylinder faster, thus flowing more air. An internal combustion engine has an optimum mixture...meaning it runs best at a certain fuel/air mixture. When you flow more air through the engine without increasing fuel, you screw up the ratio (the bike runs worse.)

It is theoretically possible to add a lighter (aftermarket) pipe which would not increase air flow (not improve performance)...but no aftermarket company would make that because THEY WOULDN'T SELL. If you can't work on a carb, drop the bike off at the dealership with the new pipe and tell them to jet it for you.

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Which is exactly what I've done with other bikes, and intend to do with this one, but it brings up an interesting point about which I've wondered. How on God's green earth do they *find* this magic fuel/air proportion you mention? Is an exhaust sniffer *required* to determine exactly the CO2 levels that are "right"? I know that most bike-specific jet kits come with recommended settings, but I also know that every copy of a model is slightly different, and so some fine-tuning is often beneficial.

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Which is exactly what I've done with other bikes, and intend to do with this one, but it brings up an interesting point about which I've wondered. How on God's green earth do they *find* this magic fuel/air proportion you mention? Is an exhaust sniffer *required* to determine exactly the CO2 levels that are "right"? I know that most bike-specific jet kits come with recommended settings, but I also know that every copy of a model is slightly different, and so some fine-tuning is often beneficial.

There is usually a base to start with which is set by others running the same/similar mods at similar elevation. I can usually tell by riding the bike for a while if the jetting is right...but if you're in a hurry, a "plug chop" will allow you to look at the plugs and get a good idea of the mixture.

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Wow, maan this ones a searin' hot debate.

I dont wish to jump in and sort this out but what i'm gonna say goes against most of wot iv'e read in this thread.

I made my own pipe for my 94 dr 650. I put it on and expected it to run like shit. On it went and to my astonishment not only was it sounding like a moto gp bike but it completely smoothed out two other problems I had ( stalling when moving off in 1st and alternating tickover ). I did ask around to try & find out if even its running great , perhaps I might be doing some damage. I have other bikes and dont use the DR much but I will check the plug condition and quite fancy doing the jet kit & airbox mod.

Hope Iv'e not thrown petrol on the fire here.

Photos of the pipe in my garage.

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I had a problem of too rich last summer. The bike ran great. The plugs always looked good (I did not do the throttle chop and check, I just checked when it was in the garage). The rich problem was enough to require a valve job (while it was apart for a base gasket). The pipe had some soot in it, but I figured the plugs looked good so it had to be jetted OK. When I got it back, from the shop, I put the 11th disc in the supertrapp and it was getting cold so I figured that would help lean it also. It still seemed rich and I think I am going to go to the 160 DJ and retune from there. 11 discs is also very LOUD.

Moto Mombo - very nice pipe and chain guard. Obviously you are a much better machinist than photographer!!

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<<How on God's green earth do they *find* this magic fuel/air proportion you mention? >>

Ever wonder why a measly jet kit costs $100? You are paying for the research done to find this magic fuel mixture.

:thumbsup:

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Wybs.

Yeh,the photos could be better. Someone was curious to see the pipe so I took the only opportunity I had....at night with flash. You shoulda seen them before photoshop !

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