1969 Honda CL350 Doesn't Go Above 40mph

My brother-in-law recently acquired said bike.

It wasn't running when we got it, so we cleaned up the carbs, changed
the plugs, redid the exhaust gaskets, and touched up other
miscellaneous ends.

Both carbs are running and the pressure out of the exhaust pipe is
even.
The bike is loud but that's probably normal on this kind of bike.

Unfortunately we can't get the bike to go above 40mph and I know this
bike should do about 100mph.

The bike doesn't run bad at all. When it gets to around 40mph it just
stays constant. It doesn't whine and doesn't push to go harder. There
is more room to pull on the throttle cable, but no power comes from it.
It feels like there is a governor on it.

I hope I provided all necessary information.

I saw another thread - Title: Ways to make motorcycle QUIETER? - where
a guy with a CB350 '71 had the same problem. Unfortunately the thread
went on for 40 more posts discussing ear plugs and not this problem.

Any ideas?

 

"nomorespameventhoughthejapanesespamgivesmeachuckle"

It sounds like there's either an air intake restriction, or more likely a
restricted exhaust. Are these the original pipes? If so they probably
are all rusted and partially plugged up.

The same thing happens to cars when their catcons burn up and
plug.

Ted

 

This was my feeling, having had exactly this problem on a Z400 twin a
couplew of years ago. Itwent happily up to 70mph, and then refused to go
any faster, no matter what I did to it.

No, you won't. Because all that's happening is the slides aren't opening
fully. It's not like an additional restriction is being put in place.

Actually, here in the UK we have NRP Carburettors (Google for them) who
replace diaphragms. They also do an export service. I've used them, as
have loads of posters on ukrm, and their service is *awesome*. Prices
are good, too - Kawasaki wanted £140 for a new pair of slides for the
Z400. NRP replaced both diaphragms for about £60.

You do have to send them your existing slides to allow them to do the
repair, though, which means a turnaround delay, but the quality of the
job and the price makes up for it.

 

I think I've found the problem. The air filters on the carbs (one for
each side) are very dirty and grimy. To the touch they leave a heavy
oil residue on the hands. We are going to try to get replacement
filters for them on Monday; if we can't get any what is the best way to
clean these out? I'm guessing that compressed air won't do the trick
because of the oily aspect of the contaminant, so what would clean the
oil out if need be? To envision the air filters, they look like black
cylindrical foam pieces that attach to the carb's air-intake with
clamps.

 

I would use kerosene to cleaner the dirt out of the filters, then
re-oil them with
foam filter oil or engine oil.

When foam gets old, it deteriorates and falls apart. That's why K&N
cloth filters are better.

 

nomorespameventhoughthejapanesespamgivesmeachuckle

AS FB says, paraffin (kerosene) or petrol, and lightly re-oil before
refitting,. But new ones would be better.

However, just take it for a very short run without the air filters
fitted. For a mile or two it won't harm it, and if there is an immediate
performance increase, you'll know the air filters are the cause.

Mind you, they sound like they need replacing anyway.

 

I think we'll try and clean the filters with some kerosene and petrol.
We live in Iowa and I'd hate to have a small piece of dirt or stone
from the gravel roads get taken up the air intake and make itself into
the engine and ruin a piston. We'll try this Monday night (if we can't
get new ones).

 

Methinks you worry too much.

If you are really really really worried about a bit of grit getting to
the piston, cover the carburetor inlet with some window screen.

Many years ago, before there was motocross, racers used to run their
engines with no air filters at all on dirt tracks, scrambles tracks and
even on beaches and dry lake beds.

The top piston ring is usally chrome plated on older machines before
about 1993, and they were able to survive season after season of racing
without damaging the pistons or evn showing appreciable wear to the
cylinder bore.

 

I thought the entire piston was extruded out of aluminum; that combined
with Iowa's dirt roads didn't sound like a good combination for me.
Didn't know the history concerning dirt bikes; how well did the bikes
hold up? Just because they did it doesn't mean that it didn't cause
dedgratation issues. I think we'd like to try to minimize any excess
wear on this bike seeing as it is over 30 years old already, extendind
the life as far as possible; though I might be talking out of
ignorance. We'll see what happens on Monday concerning acquiring new
filters. I do like your idea of the window screen =).

 

A Pasta-Matic extrudes soft pasta dough into clever noodle shapes.
Though I suppose it would be possible to extrude aluminum pistons
through a steel die, the pure aluminum would probably be so soft the
piston wouldn't hold its shape under the high temperatures and
accelerations (about 4000 X the force of gravity) stopping at the
bottom and tops of the strokes.

Pistons are cast of an aluminum alloy that contains copper and silicon
and other metallic elements to make the piston stiffer. If you really
want a stron piston, a softer aluminum is cast and then forged under
high pressure with a set of dies.

We are really only recommending that you try running the engine without
the air filters for a short time to eliminate the old foam filters as a
possible induction tract restriction. We aren't saying to go out and
run in a scrambles race with no air filters.

The need for air filtration depended upon exactly what the race was all
about. Like, there were up to 1000 motorcycles starting in desert races
in the 1960's, but they were usually 2-stroke machines. Dirt in the air
would get down into the crankcase and destroy the needle bearings in
the rods.

But a 4-stroke engine just blows the air through the top end of the
engine. I could even make the argument that a small amount of dust
blowing through the top end would help seat the piston rings. After
all, old time mechanics knew about the Bon Ami cleanser trick. They
would dribble a handful of kitchen cleanser through the carburetor of
an engine with piston rings that failed to seat.

Well, it's your machine and it's up to you what you want to do with it.
We don't think that running without air filters for a few miles to
prove whether or not the pods are a problem, unless the miles you are
riding
are behind somebody throwing a cloud of dust into the air.

 

I was wondering if the pistons were put though a cast process or
extruded, and working primarily with housings for AC motors at a local
company I picked extruded (that's what the company does for the
housings). I understand that extruding would require a softer metal
and that makes sense that you wouldn't want to extrude a piston.

So here's my concensus:

It's probably not a blockage in the exhaust because the pressure feels
(with my hand) the same out of the ends of both pipes. It would be a
mighty coincidence that both jets are bad in both carbs. It seems
probably that it is the air filters because both are in poor quality.
Am I right to come to these conclusions?

Thanks for all your help. Let's wait until Monday to see if we can get
some new filters before we start exploring our two-minute filterless
option =)... though maybe we should check before we go for parts since
it's an hour trip and it would be nice to consolidate the trips if we
find out we need a different part.

 

If the pods are not plugged up, that leaves torn diaphragms in the
carbs or stuck piston slides or
plugged up idle mixture passages or a plugged up idle jet.

Motorcycles that had ignition points suffered from dirty pitted points,
and occasionally somebody would manage to install the points cover so
it grounded out the ignition on one cylinder.

 

I'm almost positive that this bike has ignition points, which I know
nothing about, so I'll have to do some research on this. What is the
housing for the ignition points called? There is a line that goes into
this housing on his bike that leaks oil because of a missing o-ring
(another part we are picking up on Monday). This housing I am refering
to looks like an oval on it's side. The diaphrams in the carbs looked
good. How would idle mixture passages and idle jets affect this
problem? Wouldn't this concern the high speed jets? If the jets were
plugged wouldn't it be highly coincidental that both are plugged up?
Not to be critical, just trying to understand =)!

 

nomorespameventhoughthejapanesespamgivesmeachuckle

It does.

Points housing, spookily enough.

 

I am positive that your bike has ignition points, I have had occasion
to replace them before. I just don't happen to remember if it has one
set of points or two sets. There were two types of crankshafts that
Honda used on twin cylinder machines.

The 360 degree crankshaft was arranged so the pistons rose and fell
together, so the cylinders were always on opposite strokes. That type
only needed one set of ignition points because the cylinder that was on
the exhaust stroke had no problem with a "waste spark" being fired with
the exhaust valve open.

There are two marks on the alternator rotor, T and F. The ignition
points gap is set when the T on the rotor lines up with the arrow on
the stator. The ignition spark will occur when the F mark lines up with
the arrow.

To avoid a lot of hassle with ignition timing lights, you can static
time your points by turning on the ignition key and slowly rotating the
alternator rotor with a wrench. Hold a transistor radio next to the
points, and, as you turn the crankshaft slowly, you'll hear a static
POP! as the points open. They will open as the T or LT marks on the
rotor line up with the arrow on the stator.

The other type of crankshaft was a 180 degree crankshaft, the pistons
would come up and fire, one, two, followed by the other non firing
strokes over the other 540 degrees of crankshaft revolution.

Honda found that the 360 degree crankshaft arrangement had a lot of
vibration at road speed of only 60 or 70 mph, and went to the 180
degree crankshaft on some road going models, but they seem to have gone
back to the 360 degree crankshaft on so-called "Scrambler" models with
the "CL" prefix in their model number for better traction in the dirt.

There are parts diagrams for the CJ-360T at www.partsfish.com. But
those were made in 1976 and 1977. They were third generation Honda
twins that were evolutionary from the early 1960's Honda twins. Your
CL-350 is a second generation twin.

I haven't found a parts diagram or online manual for the CL-350, but I
do have a manual for the older CB-250 and CB-305 twins. Their ignition
points were on the opposite side of the engine, from what the CL-350
has.

You might also try contacting some of the guys at www.vjmc.com to see
what they have to say about setting ignition points on your machine, if
you cannot find a Clymer or Chilton or Haynes manual for it.

But the procedure is much the same for all old Honda twins. You clean
and gap the ignition points. You can remove the pits with a points
stone, which is a long narrow plastic strip with abrasive material on
it. You want to get the contacts on the points all nice and shiny
looking and clean all grease and grit off the points.

Then gap the points with a feeler gauge to 0.014 to 0.015 inches with
the rubbing blocks set on the high point of the oval-shaped breaker cam
that pushes them open. You set the right hand points gap when the T
lines up with the arrow and the left hand points gap when the LT mark
on the alternator rotor lines up with the arrow. The alternator rotor
will be under the large round plate on the left side of the engine.

The two points models will have the ignition points on a round plate
and you adjust the points gap by loosening the two screws holding the
points to the points plate and then turning an eccentric screw that
moves the contact points apart.

Then the right side timing is adjusted by loosening the screws holding
the base plate to the cylinder head. The right cylinder firing should
occur as the F mark on the alternator rotor and the arrow on the stator
line up. The left cylinder timing occurs when the LF mark lines up with
the arrow. If the timing is a little off, the points gap is adjusted
slightly to correct the timing.

And, just to make things more interesting, there may be a centrifugal
ignition advance unit behind the points plate on your machine. As the
camshaft spins the lobe that opens the points, some weights move
outwards and turn the breaker lobe a little further to open the points
earlier.

If those weights are stuck in the retarded position, that will limit
acceleration, the engine will only run so fast. If the weights are
stuck in the advanced position, you won't have much low end power.

And, if the centrifugal advancer was stuck in the full advanced
position, that would really mess up your attempt to statically time the
igniton points. They could be off as much as 40 degrees advanced...

It's the points cover. There should be a fabric covered wire harness
going into it to get power to the points. If there is a lot of oil
dripping out from under the cover, your points may be wet with oil. I
don't have a parts diagram for that model so I can't tell yuo if
there's supposed to be an oil seal.

The idle jets on a CV carburetor are very large and the engine runs
mainly off the idle jet until it develops enough vacuum to raise the
vacuum slide high enough to get the tapered part of the needle out of
the needle jet. This occurs between 75% throttle and 100% throttle, but
only IF there is enough vacuum to raise the slide that high.

If your idle mixture passages and idle mixture outlet ports are plugged
up with gum and varnish, the
engine will never develop enough vacuum to raise the slide.

CV carburetors are hard to understand, it took me 30 years to figure
out what was going on with the idle mixture passages and all the
different ports.

 

<snip>

It does. Two sets, on the left-hand end of the camshaft.

It also has a 180 degree crank. Honda never fitted a 360 degree crank to
the CB250/350/360 series. They fitted one to some smaller twins - the
175/200 series.

If you have a manual for a Honda 305, it's for a totally different bike.

 

If you have the details of what the timing marks are on the alternator
rotor, then post them. They are probably the same. T, F, LT, LF, and
some punch marks for the full advanced timing.

And, can he adjust the left hand cylinder timing without messing with
the left hand points gap?

Ignition timing works the same way, though. The points plate and the
alternator rotor with the timing marks are just on the OTHER side of
the engine from the original series of Honda twins.

 

I had a CJ250 - as you say, the next development of the engine. That had
those marks, and AFAIK they're common to most Hondas of the era.

Yes, on that bike, you can, IIRC.

Ther one you *definitely* can't is the 450/500.

 

The air filters cost $45 a pop IF they can get them in... so we ran
around a little with the air filters off and it made no difference. I
tightened the nut for the throttle cable a bit and we were able to get
about 10 more mph out of the bike... When we reach the pinnacle of our
speed, it now sounds like it wants to go faster but can't. The exhaust
pops a lot and it tries to push. I noticed that the bike does not want
to go above 5000rpm.

We have another more pressing problem though. Some how my
brother-in-law managed to strip the threads that hold in a spark plug.
I know, it sucks... We tried running around with the spark plug - kind
of in - but no where near tight. The plug ended up popping out on me
when I was doing about 50 (kapop!). Any good ideas on how to get the
plug to stay? Do we need to tap it? Can we use something like
plumbers grease to get it to stick?

Oh the misery... one more thing, I can't adjust the cam tensioner or
gap the points because one of the screws on the alternator cover is
completely stripped so I can't turn the engine over with a wrench... so
it looks like we may be drilling it out.

 

Besides the obviously obvious answer concerning looking for a different
bike =) what options do we have here?

Is there any other way to secure the spark plug besides taping? If we
were to tap, how would we go about guaranteeing we get no metal bits
into the engine?