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#1: XR250R Fixed

Posted on 2006-07-18 20:49:54 by Swiver

Thanks everyone who offered advice on fixing my Honda. The B12 down the fuel
hose alone didn't work, I had to disassemble the carb. The main jet was
clogged, but witht he help of the B12 and a guitar string, I got it all
cleared up. The reason I hadn't taken the carb off earlier is because it's
such a pain to get off...unusually difficult. Well I found out this weekend
that my uncle had the bike bored out and put a carb from an XR600 on it, so
it's unusally big for the bike, making it awkward to get to. Knowing my
uncle, the bore-job probably increased the size of the 250cc engine
substantially. After riding the army surplus 250R (non bored), this baby
damn near shot right out from under me. Lots of fun :)

However, it's still running a little funky. It may have to do with the work
that's been done to the engine, but it seems like its running strange. It
acts just like there is a little water in the tank, but I ran a whole tank
through it and the problem persists. It's almost like it backfires
consistently in mid-range. Or like a governer cuts repeatedly on and off.
This usually happens in gears 2-4 or so. Like I said, it may be because of
it being bored out and played with. Anyone have any ideas? It's also
abnormally hard to start when its cold, if that helps.

One more question: The army surplus bike did not have a fuel filter on it,
so I installed one. With the length of the gas hose that the filter adds,
the hose dips below the carb. Will that affect the amount of gas that gets
into/needs to get into the carb? Or is the gravity enough to push the gas
through the hose below the carb and up into it?

Thanks :)

Swiver

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#2: Re: XR250R Fixed

Posted on 2006-07-19 00:30:35 by OH-

&quot;Swiver&quot; &lt;<a href="mailto:wires&#64;everywhere.net" target="_blank">wires&#64;everywhere.net</a>&gt; wrote in
news:m3avg.65783$<a href="mailto:e77.19570&#64;tornado.texas.rr.com..." target="_blank">e77.19570&#64;tornado.texas.rr.com...</a>

&lt;snip&gt;

&gt; such a pain to get off...unusually difficult. Well I found out this
&gt; weekend that my uncle had the bike bored out and put a carb from an XR600
&gt; on it, so it's unusally big for the bike, making it awkward to get to.
&gt; Knowing my uncle, the bore-job probably increased the size of the 250cc
&gt; engine substantially. After riding the army surplus 250R (non bored), this
&gt; baby damn near shot right out from under me. Lots of fun :)
&gt;
&gt; However, it's still running a little funky. It may have to do with the
&gt; work that's been done to the engine, but it seems like its running
&gt; strange. It acts just like there is a little water in the tank, but I ran
&gt; a whole tank through it and the problem persists. It's almost like it
&gt; backfires consistently in mid-range. Or like a governer cuts repeatedly
&gt; on and off. This usually happens in gears 2-4 or so. Like I said, it may
&gt; be because of it being bored out and played with. Anyone have any ideas?
&gt; It's also abnormally hard to start when its cold, if that helps.

That big carburettor will have lower air velocity than a more
correctly sized one. That gives potential for more top end
power but it will also make slow running and pick up from low
revs more problematic.

&gt; One more question: The army surplus bike did not have a fuel filter on it,
&gt; so I installed one. With the length of the gas hose that the filter adds,
&gt; the hose dips below the carb. Will that affect the amount of gas that gets
&gt; into/needs to get into the carb? Or is the gravity enough to push the gas
&gt; through the hose below the carb and up into it?

Just try how it works. I had a few that were like that and
they worked just fine.

--
Ole Holmblad - Göteborgs Prima MCK / MK Pionjär
TDM850 / TT600R FL#44 OTC#489 UKRMSBC#08
SGFPTH#00 Remove hat to answer by mail

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#3: Re: XR250R Fixed

Posted on 2006-07-19 03:06:25 by Wudsracer

You are either running lean (popping and backfiring) at the throttle
setting where the noise &amp; rough running is occurring, or you are
hitting the rev limiter.

Generally, to clean a carburetor jets, I use a fresh clean bristle
cut from a new wire brush (no rust or pitting in the wire) to agitate
the edges of the passage and then blow it out with aerosol carb
cleaner. The slick bristle won't &quot;file&quot; out the jets.
The guitar string is a good idea for passages.
This is normally after I soak the carb overnight in Berryman's carb
dip ($15 per gallon pail with a dipping tray inside. Looks like a
gallon paint can.) I finish with at least 100 psi air blown through
the passages.

When you jet a carb (check the jetting), do so by the degree of turn
of the throttle. You do not jet by revs, but by how much air is coming
under the slide and how this interacts with the corresponding jets and
the taper of the jet needle at that slide position/height.

Good luck with the bike.

Jim Cook
2006 GasGas DE300
Team LAGNAF

***********************************************
&gt;On Tue, 18 Jul 2006 18:49:54 GMT, &quot;Swiver&quot; &lt;<a href="mailto:wires&#64;everywhere.net" target="_blank">wires&#64;everywhere.net</a>&gt; wrote:

&gt;Thanks everyone who offered advice on fixing my Honda. The B12 down the fuel
&gt;hose alone didn't work, I had to disassemble the carb. The main jet was
&gt;clogged, but witht he help of the B12 and a guitar string, I got it all
&gt;cleared up. The reason I hadn't taken the carb off earlier is because it's
&gt;such a pain to get off...unusually difficult. Well I found out this weekend
&gt;that my uncle had the bike bored out and put a carb from an XR600 on it, so
&gt;it's unusally big for the bike, making it awkward to get to. Knowing my
&gt;uncle, the bore-job probably increased the size of the 250cc engine
&gt;substantially. After riding the army surplus 250R (non bored), this baby
&gt;damn near shot right out from under me. Lots of fun :)
&gt;
&gt;However, it's still running a little funky. It may have to do with the work
&gt;that's been done to the engine, but it seems like its running strange. It
&gt;acts just like there is a little water in the tank, but I ran a whole tank
&gt;through it and the problem persists. It's almost like it backfires
&gt;consistently in mid-range. Or like a governer cuts repeatedly on and off.
&gt;This usually happens in gears 2-4 or so. Like I said, it may be because of
&gt;it being bored out and played with. Anyone have any ideas? It's also
&gt;abnormally hard to start when its cold, if that helps.
&gt;
&gt;One more question: The army surplus bike did not have a fuel filter on it,
&gt;so I installed one. With the length of the gas hose that the filter adds,
&gt;the hose dips below the carb. Will that affect the amount of gas that gets
&gt;into/needs to get into the carb? Or is the gravity enough to push the gas
&gt;through the hose below the carb and up into it?
&gt;
&gt;Thanks :)
&gt;
&gt;Swiver
&gt;

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#4: Re: XR250R Fixed

Posted on 2006-07-19 04:05:19 by Binder Dundat

Swiver wrote:

&gt; However, it's still running a little funky. It may have to do with the work
&gt; that's been done to the engine, but it seems like its running strange. It
&gt; acts just like there is a little water in the tank, but I ran a whole tank
&gt; through it and the problem persists. It's almost like it backfires
&gt; consistently in mid-range. Or like a governer cuts repeatedly on and off.
&gt; This usually happens in gears 2-4 or so.

There is probably still crud in the idle passages. You may have to
remove the idle mixture screw and squirt aerosol B-12 through the
passages as I have described many times here.

&gt; Like I said, it may be because of
&gt; it being bored out and played with. Anyone have any ideas? It's also
&gt; abnormally hard to start when its cold, if that helps.

A motorcycle that is hard to start from cold indicates that the idle
mixture passages are plugged up. An engine should start and idle with
the choke on without a lot of fussing with the throttle grip.

Putting a larger carburetor on a small engine reduces the vacuum
downstream of the throttle and that makes it hard for the engine to
pull idle mixture out of the float bowl.

If you have been paying attention to what I've been saying, you'll
realize that engines with constant vacuum carburetors run on the idle
mixture circuits most of the time and it's important to keep the idle
jets and idle passages clean if you want a good running engine.
&gt;
&gt; One more question: The army surplus bike did not have a fuel filter on it,
&gt; so I installed one. With the length of the gas hose that the filter adds,
&gt; the hose dips below the carb. Will that affect the amount of gas that gets
&gt; into/needs to get into the carb? Or is the gravity enough to push the gas
&gt; through the hose below the carb and up into it?

Believe it or not, you only have about 1/4 of a pound of fuel pressure
with your gravity feed system. If the float valves are sticking,
gasoline from the tank cannot fill the float bowls.

I prefer to have the straightest fuel hose from the gas tank to the
carburetor possible, but, if there is 1/4 of a pound of pressure in the
hose at the level of the carburetor inlet spigot, but the hose loops
down below the carburetor and gains another 1/10th of a pound of
pressure, and then the hose rises to the level of the inlet spigot and
loses that 1/10th of a pound, you wind up with 1/4th of a pound of fuel
pressure, just like you would if the hose didn't dip below the float
bowl...

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#5: Re: XR250R Fixed

Posted on 2006-07-19 20:47:57 by Swiver

&gt;
&gt; There is probably still crud in the idle passages. You may have to
&gt; remove the idle mixture screw and squirt aerosol B-12 through the
&gt; passages as I have described many times here.
&gt;

This is the first thing I tried, actually. The idle passages should be free
and clear.
As long as I can remember, the bike has always been hard to start from cold.
There isn't a lot of throttle fuss, it just takes a lot of kicks before it
wants to fire. A new plug probably wouldn't hurt. That's my next step. (This
weekend)

Someone also mentioned that it may be running too lean. This could very well
be the case. I'll play with the idle screw some more this weekend and see if
I can get it any better.

Would it be better to run the gas out of the carb for storage, or use some
fuel stabilizer and leave the carb full?

Swiver



&quot;FB&quot; &lt;<a href="mailto:flying_booger&#64;yahoo.com" target="_blank">flying_booger&#64;yahoo.com</a>&gt; wrote in message
news:<a href="mailto:1153274719.448569.187000&#64;m79g2000cwm.googlegroups.com..." target="_blank">1153274719.448569.187000&#64;m79g2000cwm.googlegroups.com...</a>
&gt;
&gt; Swiver wrote:
&gt;
&gt;&gt; However, it's still running a little funky. It may have to do with the
&gt;&gt; work
&gt;&gt; that's been done to the engine, but it seems like its running strange. It
&gt;&gt; acts just like there is a little water in the tank, but I ran a whole
&gt;&gt; tank
&gt;&gt; through it and the problem persists. It's almost like it backfires
&gt;&gt; consistently in mid-range. Or like a governer cuts repeatedly on and
&gt;&gt; off.
&gt;&gt; This usually happens in gears 2-4 or so.
&gt;
&gt; There is probably still crud in the idle passages. You may have to
&gt; remove the idle mixture screw and squirt aerosol B-12 through the
&gt; passages as I have described many times here.
&gt;
&gt;&gt; Like I said, it may be because of
&gt;&gt; it being bored out and played with. Anyone have any ideas? It's also
&gt;&gt; abnormally hard to start when its cold, if that helps.
&gt;
&gt; A motorcycle that is hard to start from cold indicates that the idle
&gt; mixture passages are plugged up. An engine should start and idle with
&gt; the choke on without a lot of fussing with the throttle grip.
&gt;
&gt; Putting a larger carburetor on a small engine reduces the vacuum
&gt; downstream of the throttle and that makes it hard for the engine to
&gt; pull idle mixture out of the float bowl.
&gt;
&gt; If you have been paying attention to what I've been saying, you'll
&gt; realize that engines with constant vacuum carburetors run on the idle
&gt; mixture circuits most of the time and it's important to keep the idle
&gt; jets and idle passages clean if you want a good running engine.
&gt;&gt;
&gt;&gt; One more question: The army surplus bike did not have a fuel filter on
&gt;&gt; it,
&gt;&gt; so I installed one. With the length of the gas hose that the filter adds,
&gt;&gt; the hose dips below the carb. Will that affect the amount of gas that
&gt;&gt; gets
&gt;&gt; into/needs to get into the carb? Or is the gravity enough to push the gas
&gt;&gt; through the hose below the carb and up into it?
&gt;
&gt; Believe it or not, you only have about 1/4 of a pound of fuel pressure
&gt; with your gravity feed system. If the float valves are sticking,
&gt; gasoline from the tank cannot fill the float bowls.
&gt;
&gt; I prefer to have the straightest fuel hose from the gas tank to the
&gt; carburetor possible, but, if there is 1/4 of a pound of pressure in the
&gt; hose at the level of the carburetor inlet spigot, but the hose loops
&gt; down below the carburetor and gains another 1/10th of a pound of
&gt; pressure, and then the hose rises to the level of the inlet spigot and
&gt; loses that 1/10th of a pound, you wind up with 1/4th of a pound of fuel
&gt; pressure, just like you would if the hose didn't dip below the float
&gt; bowl...
&gt;

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#6: Re: XR250R Fixed

Posted on 2006-07-20 05:06:21 by Binder Dundat

Swiver wrote:

&gt; Would it be better to run the gas out of the carb for storage, or use some
&gt; fuel stabilizer and leave the carb full?

Old timers used to idle their engines until they ran out of gasoline,
but since fuel stabilizers have been around I throw some of that stuff
into the gas tank.

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#7: Re: XR250R Fixed

Posted on 2006-07-20 08:38:07 by chateau.murraySPAMKILL

FB &lt;<a href="mailto:flying_booger&#64;yahoo.com" target="_blank">flying_booger&#64;yahoo.com</a>&gt; wrote:

&gt; Old timers used to idle their engines until they ran out of gasoline,

Heh. I still do.


--
Trophy 1200 750SS CB400F CD250 Z650
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

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#8: Re: XR250R Fixed

Posted on 2006-07-20 15:33:40 by Binder Dundat

Swiver wrote:

&gt; As long as I can remember, the bike has always been hard to start from cold.
&gt; There isn't a lot of throttle fuss, it just takes a lot of kicks before it
&gt; wants to fire. A new plug probably wouldn't hurt. That's my next step. (This
&gt; weekend)

Turn the idle speed knob all the way down when starting from cold or
when your machine has sat unridden for months on end.

Single cylinder 4-stroke engines have always been hard to start,
especially if they are of the larger displacement sizes. Old time
British riders got into a starting drill once they realized what the
problem was.

Since it takes two full turns of the crankshaft to get the engine to
suck mixture into the cylinder just once, engine vacuum is critical.
You need to have enough of it at the right time.

So, the old time British single riders figured out that they needed to
turn the idle speed screw all the way out to let the throttle slide
close so the engine would suck
fuel air mixture into the intake tract.

Of course they were working with old Amal carburetors that were less
sophisticated than the modern Mikuni and Keihin mixers we enjoy today.
The Amal wouldn't even have a choke, it would have a float bowl
&quot;tickler&quot;, which was a rod that pushed the float down and admitted
extra fuel to the float bowl, raising the level and making it easier
for the limited amount of vacuum to lift fuel out of the bowl.

The British rider might put his finger over the float bowl &quot;pee hole&quot;
that squirted raw fuel out the back of the bowl (or pre-mixed fuel/oil
in the case of a 2-stroke, what a mess that was when the
gasolineevaporated, leaving a coating of oil all over everything!)

When he felt his finger get cold and wet, he would stop tickling and
start kicking, carefully feeling through the kick start lever when the
engine was coming up on the compression stroke with the ignition switch
off to avoid preignition, then turning it on and then taking a furious
kick with all his might at the kick starter lever.

If the ignition was manually retarded and the idle screw was set just
right, the engine would fire up and the British rider would warm it up
manually and then reset the idle speed screw.

Some early model Japanese machines had actual choke plates to assist
starting by raising engine vacuum downstream, but the modern
Mikuni/Keihin method is to use the bypass starting enrichener system.

It's just an air passage that bypasses the throttle slide or butterfly.
A little valve in the passage is opened or closed by the &quot;choke&quot; knob
on the carb, or by a &quot;choke lever&quot;.

When the valve is opened, the engine vacuum sucks fuel directly out of
the float bowl through a starter jet and this very rich mixture goes
into the engine downstream of the throttle.

But, just as in the days of the old time British single owner, vacuum
downstream of the throttle slide or butterfly is critical, so, if an
engine is hard to start, the drill is to turn the idle speed screw all
the way down, and use the old British system of finding when the engine
is coming up on the compression stroke by gauging the kick starter
lever's resistance to being pushed.

If the throttle slide or butterfly is too far open while using the
bypass starting enrichener, vacuum is too low to suck fuel through the
bypass. If the throttle is really too far open, you get excess fuel
through the acceleration transition ports downstream of the
butterflies. So, turn the idle speed all the way down when starting
from cold.

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#9: Re: XR250R Fixed

Posted on 2006-07-20 19:12:46 by Swiver

Me too :) And I'm only 21!

I guess the old man taught me a thing or two after all.


Swiver


&quot;The Older Gentleman&quot; &lt;<a href="mailto:chateau.murraySPAMKILL&#64;dsl.pipex.com" target="_blank">chateau.murraySPAMKILL&#64;dsl.pipex.com</a>&gt; wrote in
message news:1hirjs5.4je63715bqv7aN%<a href="mailto:chateau.murraySPAMKILL&#64;dsl.pipex.com..." target="_blank">chateau.murraySPAMKILL&#64;dsl.pipex.com...</a>
&gt; FB &lt;<a href="mailto:flying_booger&#64;yahoo.com" target="_blank">flying_booger&#64;yahoo.com</a>&gt; wrote:
&gt;
&gt;&gt; Old timers used to idle their engines until they ran out of gasoline,
&gt;
&gt; Heh. I still do.
&gt;
&gt;
&gt; --
&gt; Trophy 1200 750SS CB400F CD250 Z650
&gt; GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
&gt; BOF#30 WUSS#5 The bells, the bells.....

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#10: Re: XR250R Fixed

Posted on 2006-07-21 00:24:01 by OH-

&quot;FB&quot; &lt;<a href="mailto:flying_booger&#64;yahoo.com" target="_blank">flying_booger&#64;yahoo.com</a>&gt; wrote in
news:<a href="mailto:1153402420.778660.179890&#64;75g2000cwc.googlegroups.com..." target="_blank">1153402420.778660.179890&#64;75g2000cwc.googlegroups.com...</a>
&gt;

&lt;snip&gt;

&gt; Single cylinder 4-stroke engines have always been hard to start,
&gt; especially if they are of the larger displacement sizes. Old time
&gt; British riders got into a starting drill once they realized what the
&gt; problem was.

Having owned a SR500 and now riding a TT600R, I'd say the
main problem the old time British riders had was their old time
British machines.
With good spark plugs and reasonably correct idle adjustment
my &quot;jap crap&quot; never require any exotic starting drill.

The only time things can get a bit tricky is with a hot engine.
Cold starts have never been a problem.

--
Ole Holmblad - Göteborgs Prima MCK / MK Pionjär
TDM850 / TT600R FL#44 OTC#489 UKRMSBC#08
SGFPTH#00 Remove hat to answer by mail

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#11: Re: XR250R Fixed

Posted on 2006-07-21 04:01:39 by Binder Dundat

OH- wrote:

&gt; Having owned a SR500 and now riding a TT600R, I'd say the
&gt; main problem the old time British riders had was their old time
&gt; British machines.
&gt; With good spark plugs and reasonably correct idle adjustment
&gt; my &quot;jap crap&quot; never require any exotic starting drill.

Old Amal carbs didn't have the tiny air emulsion holes that Mikuni and
Keihin carbs have in the pilot jets and the needle jet. So the fuel
didn't mix very well with the air and the low vacuum available to pull
fuel/air mix into the cylinder allowed the intake charge to re-separate
into its gaseous and liquid components, making starting very
problematic.

My friend who owned a 1965 Greeves MX-5 insisted that there was nothing
wrong with the square barrel Greeves version of an old Villiers design
and that the Amal concentric worked just fine.

So I loaned him a spare 26mm Mikuni carb that came stock on my 250cc
Yamaha DT-1 and asked him to just try it for a few rides. He went ahead
and bought a 34 mm Mikuni carb within a week.

The increased fuel air mixing ability of Mikunis and Keihins made it
possible to use venturi sizes that were much larger than the Amals that
came as original equipment.

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#12: Re: XR250R Fixed

Posted on 2006-07-21 05:33:09 by unknown

Post removed (X-No-Archive: yes)

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#13: Technical Time Travelling

Posted on 2006-07-21 15:45:42 by Binder Dundat

Gene Cash wrote:
&gt; &quot;FB&quot; &lt;<a href="mailto:flying_booger&#64;yahoo.com" target="_blank">flying_booger&#64;yahoo.com</a>&gt; writes:

&gt; &gt; The increased fuel air mixing ability of Mikunis and Keihins made it
&gt; &gt; possible to use venturi sizes that were much larger than the Amals that
&gt; &gt; came as original equipment.
&gt;
&gt; And now, of course, that we have carb design down to a science, we start
&gt; all over again with fuel injection.

I nominate the radial flat slide carburetor cum accelerator pump as the
epitome of motorcycle carburetor design.
&gt;
&gt; It was interesting to give everything a good hard look at &quot;Art of the
&gt; motorcycle&quot; from the point of view of mechanical design. I listened to
&gt; two old guys standing next to the Ariel Square 4 arguing &quot;well, a V-4 is
&gt; just a square-4 split down the middle&quot; - &quot;WOT! nowgh eet's nowt!&quot;

As English socialism engulfed the British motorcycle industry, the
designers still dreamed of a world beating GP machine flying the Union
Jack and circulating the racetracks using novel techologies. But the
Triumph and BSA factory was unable to
even produce designs that had been upgraded to the level of Japanese
mediocrities.

The guy who resurrected Triumph from the dustbin of history had to send
engineers to the Kawasaki factory to find out how they had designed
Ninjas a decade before...

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