drill exhaust question

Hello I found some instruction on how to modify the exhaust on my bike
fj1200. I removed the inner tube and left the tube around it. I believe
the bike is running lea and i am having problems starting the bike. I
was able to dirve for a couple of miles with the choke on. I will leave
the bike off for today, i am thinking may be the carbs overflow or
something. But my best beat is that i have to open up the mixture
screws just a little bet. Any suggestions?
thanks.

 

I think it was who stated:

Find another stock system and install that.

-Don

 

Or if you decide to drill out the carb jets to match the exhaust,
be sure to start at least a couple drill sizes smaller.

 

Lets pretend you're serious:
Those tubes were there for a reason.
You will probably start to see 'burn` on the headers.
If you did it to decrease back-pressure and the bike is now
running lean, congratulations, you've succeeded. So now
you do need to richen the mixture.
Do try the mixture screws before rejetting, - it might even work.
MadDog

 

Thanks I was worried about air flow but i guess it is all in the mix.
yes i got dynos, i might have to go to the next size in the kit but i
will try the mix today.

 

A manufacturer spends a sizeable sum of money in matching the exhaust
to the engine, and then some dork comes along with an electric drill
and reckons a quick whizz or two will turn the bike into a
rocketship.....

 

I don't think that modifying your exhaust would have much effect on
starting the engine. You might notice a big flat spot in the midrange,
from 5000 RPM to 7000 RPM, but your starter doesn't turn the engine
that fast to start it, so how would less back pressure affect starting?

A well-tuned and properly adjusted engine starts up in only half a
dozen turns of the crankshaft, so there's just NO TIME for any back
pressure to build up in the exhaust system.

Actually, I suspect that your carburetors are dirty, the idle jets and
passages are all plugged up with gum and varnish.

I recommend that you mix some Berryman B-12 Choke and Carburetor
Cleaner with an equal amount of gasoline.

You need about a pint of the mixture in some kind of plastic squeeze
bottle that doesn't melt when you put the B-12 in it. B-12 is composed
of xylene, acetone, and methyl alcohol which will attack plastics after
an hour or.

Then, find the float bowl drain screws on your carburetors and drain
them into an old rag if there are no carburetor drain hoses. Then close
the drain screws and squirt the B-12/gasoline mix into the fuel hose
going to the carbs to fill up the float bowls.

Let the mixture sit in the float bowls half an hour or so and then
start the engine, using the choke. The exhaust will stink and burn your
eyes, so do this in a well-ventilated area.

The engine may start up and idle much too fast, so you need to know
where the master idle knob is at. It may be between the #3 and #4
carbs, or it may be a cable operated master idle knob on the left hand
side of the motorcycle, near your thigh when you're riding.

You want to be able to turn the idle RPM down as you reduce the amount
of choke applied, and, when the idle jets and passages are cleaned out
you can adjust the master idle knob so the engine idles at the
specified RPM.

For a more thorough carb cleaning, mix about 4 or 5 ounces of B-12 with
a full tank of fresh gasoline and go for a slow ride to get the
B-12/gasoline mix to go through the idle jets and passages.

It's not a good idea to use high RPM while the B-12 is in your
gasoline, washing lubricant off the cylinder walls.

Opening the idle mixture screws about 1/2 to 1 full turn may help the
throttle response.

You will know you've opened the idle mixture screws too far when the
idle RPM hangs up after you close the throttle.

 

Did you perhaps also read any disclaimer that this may not work to your
satisfaction? On what engineering basis did you determine that modifying
the exhaust in such a way would improve performance rather than just make
noise? How is it that a modern 1200cc bike is not powerful enough for you?

It's one thing to install a properly engineered after market "performance"
exhaust system that possibly includes tuning advice, but to simply start
chopping things willy-nilly is foolish at best and could cause damage to
your engine at worst. If you live in one of those locales that enforces
sound and emissions levels, you may be elligible for buying a replacement
exhaust system.

The best advice I can give is to restore the exhaust system to stock form.

- Nate >>

 

well seems to be up and running now. I was not able to start it so I
wasted no time and got a new set of spark plugs. then I rich the
mixture and drove the bike for a mile but i seem like it overheated a
little bet. So i drove back and let it cool, then i cover the holes
left from removing the front cover off the exhaust with exaust repair
epoxy. Sand it to make it look nice and painted with high temp paint. I
drove around again after adjusting the mix and it seems to be ok for
now, starts right up. I guess i will have to drive around for a little
bet longer to make sure it is running ok. Thanks for the help!

 

<Holds head in hands>

You drilled holes in an exhaust that cost tens, if not hundreds, of
thousands of dollars to develop, then bunged them up with glue, and then
disguised the blodge.

You're going to sell this abortion now, right?

 

<Scuffs point of boot in dust>

Yeah, all right, OK.

 

I guess you are right, the best thing to do is to get a louder exhaust
design for my bike.

 

Mark, give it up. He's never going to admit in a public forum now that his
bike is running slower, even though I would bet $10 that it is. If he
actually
did something like dynoing before bashing holes in the exhaust, then dynoing
it afterwards, he would see that he has less power now.

Ted

 

Ted Mittelstaedt schreef:

But why did nobody tell him how to overcome slower running?

I always drilled my exhausts for every bike I had.
And then I clipped off 7 (seven) links from the finai drive chain.
I even have had bikes that ran faster than they did before.

Rob.

 

What?

 

The Older Gentleman schreef:

A newbie may want to drill holes in his exhaust.
A newbie would say: 'Thank you' when people
advise not to tamper with the pipes, because the
bike will loose power.

But when that newbie complains that the answers
are not nice, and still drills holes, then that newbie
is a moron.

A moron might be stupid enough to shorten his chain
an odd(!) number of links.

Rob.

 

And this old geezer moron says why as sprockets are not square or have
an even number of teeth.

Ian Singer



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