XS400 carb swap from later model

I think the pre 80 xs400 had points, 80-81 had this particular CDI,
and the 82 -> Maxim had another type of electronic ignition.
Thanks for the help though. I love the GS850, 83 GL with 30K, paid
$600, in perfect shape. More fun than a barrel of monkeys, save the
cornering. I think I will check out some shocks, and maybe a softer
tire. The Dunlops on it are a bit rigid and are about half gone
anyway. I put some superbike bars on it, and that really made it a lot
more fun. Next are some new springs, and I will look into shocks. Then
I will get some tires. So many bikes, so little time.

Suzuki GS850
Kawasaki 454LTD
Yamaha XS400
Kawasaki KDX200
Honda CD175
Honda CB750

 

The 850 was a huge heavy lardy thing. We never got the custom version
in the UK, only the pure roadster. I rather liked it, because the
engine was so good. Comfy seat as well. As you say, it didn't corner
too well, but it was a lovely tourer. Good ones are quite sought-after
here.

 

The relatively narrow 16XMT2.75 rear wheel limits you to a bias-ply
tire.

Dunlop recommends their 130/90-16 67H GT-501, but the rear rim is
marginally narrow, probably making the tire "crown" a little in the
center, IOW, you might not be able to lean the motorcycle far enough
without going off the edge.

"L"-model motorcycles have an inherent problem with front-rear tire
mismatches, anyway, the front tire has to struggle to cope with
stabilizing the motorcycle while the 16-inch rear tire is continuously
veering off to the right or left.

A friend of mine tried to race a GS450L that he got cheaply. It scared
him so badly, he quit road racing.

http://www.dunlopmotorcycle.com/tirecatalog_tire.asp?id=8

http://www.mawonline.com/mfglinks.htm

 

I don't doubt it. The silly 454LTD I have could easily outperform it,
and it is a cruiser. Scary fast at times, however. Not sure how you
can make a bike that is so comfortable yet so fast and agile. I just
wish I liked the way it looked. I feel like a poser biker riding it.
The XS400 I am building should handle fairly well I hope, although it
also has the mismatched tires. It is lowered about 2.5 inches, and
stripped of everything non-essential. Just got the carbs back
together, so tomorrow hopefully I will have good news.

I really love the 850 though. Even with it's problems, I can't help
it. Sounds like a sewing machine (literally), is a bit of a buffalo.
Valve adjustments are a pain, and I used to lose the shifter sometimes
(bent retaining bolt, took me by surprise. Try getting from a dead
stop back into traffic stuck in 5th gear). Really should have come
with a 6 speed. I really wanted a GT750, but this was what I could get
down in south Georgia. On the highway, like you say, at about 70, it
is a smooth riding machine. The only thing I hate about it is
emergency stops. Very unpredictable. If the rear wheel locks, watch
out. You never know where it is going.

I am thinking about an RD400 or a GT550, any suggestions? I can't
afford an H1 or H2. I really want a 2 stroke race bike. I grew up
riding dirt smokers and would love to have a street bike. My KDX200
would be great, except I can't get it tagged. No title or MSO.

 

That's a fair assessment. I was actually on the launch of that
horrible-looking thing. It was launched, believe it or not, at Jarama
circuit, Madrid, Spain, alongside the GPZ600R. Present was Kork
Ballington, world 250cc and 350cc champion for Kawasaki.

Korky led the assembled world's press, all mounted on the new 600
sportster, on a couple of sighting laps of the circuit, him mounted on
the 454. Believe it or not, nobody could keep the sod in sight. I have
never ridden with *anyone* like that. It ain't what you've got, it's how
you use it. But's that what being a World Champ is all about, I s'pose.

They don't handle. They're horrible things, really. And they vibrate
badly. The engine was never fitted with a balancer, and to be honest it
needs it. The engine's quite torquey, but from new they were dogged with
carb problems. I've owned a couple, and the 250. Economical, mind.

RD400 every time. As fast as the 550, lighter, better handling, more
fun, less thirsty. I owned an H1 once. I loved it, but I'd never own
another, except maybe for sunny Sundays.

 

If I want to get seriously nervous, it's cheaper to chew guarana
berries...

But the ultimate Japanese two strokes are the Yamaha and Suzuki square
fours,
as I recall they were the RV500 and the RG500. I rode both of them and
realized that ownership would require a serious commitment that I was
unwilling to make.

The RD400 Daytona Special was a very nice final version of the air
cooled Yamaha twins that evolved from the earliest copy of a German
design. I had a 1961 YDS1 and a bastard YDS3 that I assembled in 1967
from various parts obtained from $tealer$hips and $alvage yards.

All of those old Yamahas and the R5 and the RD series that evolved
from them were too small for a person of average size. Even the
Daytona Special felt small to me.

And the water-cooled versions like the LC and the RZ350 were still
small and don't seem to be capable of extended high speed operation at
high RPM on open roads, if Bob Nixon's experience proves anything.

I only remember about two riders that had GT550's with the ram air
cooled heads. The GT750 was a much better long distance road machine,
it liked to run at 90 mph all day, and surged and bucked if I tried to
go slower.

I had lots of confidence in the GT750 chassis, after I installed
bronze swing arm bushings and after market shocks and lighter springs
on the back. I used to go squirreling around on mountain roads with
the RD350 guys.

The short wheelbase made the RD350's prone to wheelstanding when they
came on the power and they would also drag their solid footpeg bar
that ran under the engine, so those guys would cobble up their own
footpegs or install aftermarket rearsets.

But the GT750 was always wearing out tires, brake shoes and chains,
and always needed to have the ignition points cleaned and re-set. I
got tired of all the nit-picking maintenance after a few years

Those things are very expensive nowadays.

Well, if you don't have to ride very far, and you do most of your
riding on back roads,
an RD400 will probably work just fine.

There are also grey market 2-strokes like Aprilias with Suzuki 250
motors and Honda triples. I think the triples were NS250's.

If you can find somebody who have gotten an Aprilia registered for the
street in any state, it might be worth considering, even if it does
cost $5K.

Some local riders bought the grey market two strokes to ride on the
Angeles Crest Hwy above Pasadena. The 2-strokes are so thirsty, they
can barely make it 25 miles up to the roadhouse at Newcombs Ranch,
then they have to go back down the hill to buy gasoline.

But the short wheelbase 2-strokes don't need to lean so far over to go
through a turn, so they can go around the curves very easily.

 

I finally got the guy running, wow. I was running WAY too rich, ended
up with 1/2 turn out on the idle screw. I assumed I would be running
rich with the pods and straight pipes, but the different carbs must
have changed things. Turns out these idle jets don't have the plugs,
they pull fuel directly from the bowl. So I ended up with the 82 pilot
and idle, and the 135 main from the 80 carbs. The bike has WAY more go
that stop I am afraid, the single disc in front and wimpy drum in back
don't want to slow the guy down. It accelerates like a monster, and
sounds fantastic. My neighbors probably hate me now. I am removing the
starter tomorrow, anything special need to do to take it out? Adjust
the valves next, still need to balance the wheels. It doesn't exactly
handle great, but it is fun to drive. I was hoping for a better
tracker, but it probably won't do the job. Oh well, fun build anyway.
Maybe the CB750 SOHC?

 

Wrong. One even competed in the Bol 'Or 24-hour race (and finished!).

 

A guy from Britain told me that the RD350's caused a change in the UK
graduated licensing laws because because newly-licensed teenagers could
immediately outdrag most cars if they had one of those bikes.
Apparently before they came out, the authorities equated displacement
with speed. Is this true?

I got a kick out of taking apart an old Suzuki (IIRC) 500cc engine that
had two crankshafts. You could see how it was actually two of their
250cc two-stoke engines put together. Maybe somebody here can remember
the model (I think the nickname for the smaller one was Gamma) but
apparently both are quite prized now.

 

No. It's complete nonsense.

They did a 250cc version of the RD, and at the time there was a 250cc
learner limit. A year or two later they dropped the learner limit to
125cc, but that was because when the 250cc limit came in, years before,
a decent Brit 250 was pushed to exceed 70mph, whereas the Japanese were
building 90-100mph 250s from the early 1970s.

It's debatable whether the RD250LC contributed to the 250 learner ban.
It certainly didn't help.

RG500. They did a 400cc model too. The Yamaha RD500 also had two cranks.
Yes, they're hugely collectable.

 

Have been having fun riding it, still have a bit of a backfire in the
right side cylinder (farthest from inlet).
The left side has no backfire. Both are a nice blue in the colortune,
save the backfires bright white. Any ideas?

 

It might be lean idle mixture on the right hand side, so open the idle
mixture screw another 1/4 of a turn to see if that helps. If the idle
mixture port is dirty, it may clean out, and then the idle mixture
will be too rich again.

I add about 4 or 5 ounces of Berryman B12 to a full (5 gallon) tank of
gas a few times a year to keep the idle mixture ports clean.

Another possibility is that your intake valves have a build up of
carburized oil on the valve heads which keeps them from seating.

If your engine smokes on one cylinder when you start it, it may be oil
leaking past the valve guide oil seals, down the valve stems. Chevron
makes Techron Concentrate to clean off the intake valves.

 

If there is carbon on the valve seats, would that require a valve job
to fix, or could I just knock it off? I am going to readjust them
tomorrow when they are cold, i will inspect them. I call myself
cleaning the carbs thoroughly, but I will re-examine. Thanks everyone!
This bike handles surpisingly well for a home build. I am still a bit
nervous about taking too hard of a lean on it, not knowing how it will
react to the harder shocks and the lower stance, but I am getting
there.

 

You can decarbonize an engine by CAUTIOUSLY spraying a fine mist of
water into the carburetor intakes while revving the engine up.

The carbon will come flying out the exhaust pipes.

But, don't go crazy with the water spray. You could bend a rod if you
hydraulically lock a cylinder at high RPM...

There are also chemical fuel additives that you put into the gasoline
to decarbonize a cylinder. If the chemical contains a lot of alcohol,
you need to be careful with high RPM, as alcohol tends to wash the oil
film off the cylinder walls...

 

Thanks for the info. It seems to clear up when warmed up, so I am
thinking it is carbon.
Now I have another problem. Once the bike warms up good, and starts
running well, if I bring it to a sudden stop, it shuts off almost like
the switch was flipped. I can then not get it to crank back up for a
while. It almost seems like it is running out of gas, but priming the
engine doesn't help. Overheaded CDI? Coil? ANy ideas? I am removing
the starter tonight (can't use it anyway, it pulls so much juice from
the ignition it won't fire!) and some other stuff, so any ideas would
be appreciated while I have it apart. Thank you guys for all of your
help, if you are ever in south Georgia holler and we'll go for a ride.

 

You might have tight valve clearances that prevent the engine from
making enough compression to start. Carbon on the valve heads will
cause the valves to tighten up.

It might be vapor lock. Cautiously open the float bowl drain and see
if gasoline runs out. Don't get gasoline on your hot exhaust pipe
though.

Don't ask how I know that.

Overheaded CDI? Coil? ANy ideas?

When an ignition coil overheats the engine starts shooting ducks out
the exhaust pipe. Boom. Boom.

Your motorcycle doesn't have a true CDI, it has a transistorized
ignition module. They usually either work or don't work,
and the only times I ever had a module that acted weak was the ones
inside the distributor of my car.

Those modules were exposed to engine heat and steam from overheated
engines.

I went down to Pep Boys and asked for the ignition gizmo that went
inside my distributor, and the guy came back with an ignition lock.

I said, "No, I need the little circuit board that goes *inside* the
distributor."

He sez, "We don't have nothin' like that."

His more experienced co-worker said, "He needs the ignition modjoe."

I said, "Yeah, that's it. I need the modjoe."

So I installed the new modjoe and it worked for another 100,000 miles.

 

Wow, sounds like some of the parts places around here...

I had a modjoe ;-) on my 86 Pontiac Fiero (or Fierjoe) that died every
1000 miles or so... It had a lifetime warranty so I swapped it like
100 times. The guy said "we can't keep doing this if you are
overheating the module" I said "your part claims it is an OEM
replacement, and this is the (albeit badly designed) OEM engine, and
it makes a lot of OEM heat. If it can't take it that ain't my
problem". He saw it my way until I lost my reciept... Funny thing was,
the original one worked fine forever until I changed distributors and
forgot to take it off of the core. I then bought a true ACDelco module
and it burned up too. Never did figure that one out.

I will try opening the bowls, I thought of trying that too. I hope you
weren't too badly burned learning that lesson ;-)
If it is vapor lock, could it be that my tank is not breathing?

 

No, fortunately there wasn't much gasoline left in the fuel hose. I
just got a flash of flame and it was done.

What happened was I'd bought a brand new Yamaha engine from a $tealer
$hip for a good price, as somebody had ordered the engine and then
decided they didn't want it after all. The $tealer$hip probably made
money off of me and guy who'd paid for it.

The first time I rode the motorcycle it started overheating and I
noticed that the idle was too fast. I momentarily thumbed the kill
button and the engine didn't slow down, because it was actually being
ignited by the overheated spark plugs.

It was really idling too high, so I turned off the gas. Then I
disconnected both spark plugs. I pulled the fuel hose off and got the
little fire I described.

I was removing the spark plugs when the engine finally stopped
running...

It's easy enough to remove the gas cap and see if that helps get the
engine started sooner.

Riders used to install clear plastic fuel hoses so they could see if
there was any gas in the lines. They would *always* see
air spaces in any bend in the line.

No matter how they re-routed the lines, they could never get rid of
the bubbles. Air spaces in the gas lines can get so hot that the
evaporating gasoline creates a pressure in excess of the static
pressure head due to the weight of the gasoline in the tank.

There is only about 0.25 psi of static head on the gasoline in the
line. At least you cannot see air bubbles in the black rubber fuel
hose that is standard equipment of motorcycles.

I ran into a problem using *automotive* fuel hose which is thicker and
has a fabric cord between layers of rubber.

I bought a set of carburetors from a friend, and he'd been using the
automotive hose.

I didn't realize that the hose was so thick it was kinking up under
the gas tank and was shutting off the flow of gasoline.

I was stuck on the highway and couldn't get home without climbing a
hill. The motorcycle would quit everytime I went uphill.

I theorized that the fuel line must be kinking, so I removed the rear
bolts from the gas tank and stuck a crushed beer can under the tank to
prop it up, and then I could ride up the hill and get home...

All the crap I went through learning how to keep a motorcycle running
makes me realize how many silly things can keep a bike from running.

 

Any thoughts on converting this to kick only? I have removed the
starter, and will make a nice bracket to replace it so I can bolt the
cover back over the hole.
Only thing I seem to have trouble with is the battery. I have tried
removing it and going with a huge capacitor, but i can't seem to get
it to crank without a battery charger. Once it gets going it is fine,
but getting it going is not easy. Any ideas? Headlight also won't come
on, I have replaced the diode to the relay, I guess it was a 12V
zener??? No info on that guy anywhere...

 

It's a pretty crap bike with carbs that were notorious for problems, and
an electric starter that didn't spin the engine fast enough.

You can't polish a turd.