DT-80 Starting Problems

Fred,
Be sure you have a good, steady flow of fuel from the tank to the carb,
also make sure that the float level is correct. When cleaning a carb,
the only was to be certain the the jets and passages are indeed open, is
to blow compressed air through them. If the fuel system is not an issue,
I would check the compression(this is actually step one in engine
troubleshooting), if the compression is ok, I would next look at the
crankshaft seals and bearings.
Chris
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"Chris Buckley" <cnbuckley RemoveThis @earthlink.net> wrote in message
news:401D22C9.E6AC2FE0@earthlink.net...
 >
 >
 > Fred,
 > Be sure you have a good, steady flow of fuel from the tank to the carb,
 > also make sure that the float level is correct. When cleaning a carb,
 > the only was to be certain the the jets and passages are indeed open, is
 > to blow compressed air through them. If the fuel system is not an issue,
 > I would check the compression(this is actually step one in engine
 > troubleshooting), if the compression is ok, I would next look at the
 > crankshaft seals and bearings.
 > Chris

One other 'small' thing. I always blow the air through the reverse way.
It's easy to get something lodged even worse with compressed air. If
something is stuck (sand, dirt, etc) that air won't get out, welding tip
cleaners work well. They are very small flexible wires.

John<!-- ~MESSAGE_AFTER~ -->
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In article <401d1b87.1693928660.TakeThisOut@news.ev1.net>,
Fred B. <van-designsREMOVE.TakeThisOut@ev1.net> wrote:

 > I then attempted to start the bike and it did indeed start on the
 >second or third kick. It ran for about 10 seconds before sounding as
 >if it were starving for fuel and died. It started a couple more times
 >but always died within a couple of seconds.

Sounds like a fuel delivery problem not a carb problem.

 > One question I have is; could bad piston rings cause a lack of
 >"suction" sufficient to draw the proper charge of fuel into the
 >cylinder?

No. Low compression makes two-strokes hard to start but it's
because of mixture leaking past the rings on the compression
stroke.

 >I mean, it *feels* like it has decent compression, but it's
 >hard to tell on these small bores (since they have so little
 >resistance to begin with). I suppose my next step would be a
 >compression test, huh? I'll have to see if I can find the factory
 >compression specs online somewhere. And then find someone who has a
 >compression tester and the correct fitting. I don't wanna pull the
 >cylinder just yet because I don't have a ring compressor (I really
 >need to get one though).

I've assembled hordes of two-stroke engines without a ring
compressor. I need one for large fourstrokes, but on two-strokes
_careful_ hand compression and fitting of the cylinder works
just fine. A trick I have read but never needed is to
use a cable tie to compress the rings.
Most Yamaha cylinders have a bevel at the bottom to make
fitting the piston easier. Just compress the rings with
your thumbs making sure that the ring ends are aligned with
the pins.

Before you fit new rings, measure the ring gap. I've gotten
mis-marked (too large) rings before.


 > I guess what baffles me is that the little TK carbs are pretty
 >basic... there's not a lot to mess up. You just have the one external
 >air screw (I set it at 1-1/2 turns out to start) and the external
 >slide adjustment (idle) screw. The slide needle is not adjustable and
 >the internal jets appear to be clean and open.

Are you _sure_ the idle jets' clear?

Have you cleaned the petcock out? Is the fuel filter
in the tank (the tower thing on top of the petcock) clean?
They often get gunked up on old bikes.


Eric<!-- ~MESSAGE_AFTER~ -->
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  >>"Chris Buckley" wrote:
  >>
  >> Fred,
  >> Be sure you have a good, steady flow of fuel from the tank to the carb,
  >> also make sure that the float level is correct. When cleaning a carb,
  >> the only was to be certain the the jets and passages are indeed open, is
  >> to blow compressed air through them. If the fuel system is not an issue,
  >> I would check the compression(this is actually step one in engine
  >> troubleshooting), if the compression is ok, I would next look at the
  >> crankshaft seals and bearings.
  >> Chris


 >On Sun, 01 Feb 2004 16:39:16 GMT, "spodely" wrote:
 >
 >One other 'small' thing. I always blow the air through the reverse way.
 >It's easy to get something lodged even worse with compressed air. If
 >something is stuck (sand, dirt, etc) that air won't get out, welding tip
 >cleaners work well. They are very small flexible wires.
 >
 >John
 >


Fred,
I would recommend staying away from torch tip cleaners for
unclogging/cleaning jets. The abrasiveness of the cleaners will
change the diameter of the jets.
Instead, cut a bristle off a new wire brush. (One that hasn't rusted
yet.) They are usually smal enough to fit in most jets.
Hold this with a pair of hemostats or wire pliers and use it to clean
the jets. The smooth sides of the bristle will help rub the jet clean
without changing the size or conformity of the jet.
After I dip a carb overnight, I first blow it out with either carb
or brake cleaner, and then again with compressed air.

Good luck!


Jim
(On Deb's Computer)

"99 Gas Gas EC274 (Sweet Baby)

Team LAGNAF
<a style='text-decoration: underline;' href="http://www.smackovermotorsports.com" target="_blank">www.smackovermotorsports.com</a><!-- ~MESSAGE_AFTER~ -->
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On Sun, 01 Feb 2004 18:02:25 GMT, "Eric M" <root DeleteThis @127.0.0.1> wrote:

 >Sounds like a fuel delivery problem not a carb problem.
 >
 >Are you _sure_ the idle jets' clear?
 >
 >Have you cleaned the petcock out? Is the fuel filter
 >in the tank (the tower thing on top of the petcock) clean?
 >They often get gunked up on old bikes.
 >
 >
 >Eric


The petcock was a brand spankin' new unit. I used new, clear
yellow fuel line. So the only other possibility as far as fuel
delivery is concerned would be if rust or gunk has already clogged up
the new petcock. I'll pull it out and check it. Buuut, when I first
turned the gas on after the latest reassembly gas began pouring out of
the float bowl overflow hose. I turned off the gas and shook the bike
firmly from side to side to free up the float. When I turned that gas
back on the overflow problem stopped.

As for the carb jets, I could see daylight through both of them.
So they aren't plugged completely, but may be restricted a little by
debris.

From the Yamaha service data sheet, I see that my float level
should be 22.0 mm. How is this measure taken?

Fred
'85 RM 250
'79 YZ 80
'81 DT 80<!-- ~MESSAGE_AFTER~ -->
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On Sun, 1 Feb 2004 10:44:28 -0700, Eric <ericbish.RemoveThis@yahoo.com> wrote:

 >Screw the compression tester, just pull the top end and spec it out.

Okay, it's good to know a ring compressor isn't necessary. And
since I now have the Yamaha service data sheet, I know the
manufacturer bore, skirt clearance and ring gaps.


Thanks guys!

Fred
'85 RM 250
'79 YZ 80
'81 DT 80<!-- ~MESSAGE_AFTER~ -->
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In article <401d62c6.1712167737.RemoveThis@news.ev1.net>,
Fred B. <van-designsREMOVE.RemoveThis@ev1.net> wrote:
 >On Sun, 01 Feb 2004 18:02:25 GMT, "Eric M" <root.RemoveThis@127.0.0.1> wrote:
 >
 >
 > The petcock was a brand spankin' new unit. I used new, clear
 >yellow fuel line. So the only other possibility as far as fuel
 >delivery is concerned would be if rust or gunk has already clogged up
 >the new petcock. I'll pull it out and check it. Buuut, when I first
 >turned the gas on after the latest reassembly gas began pouring out of
 >the float bowl overflow hose. I turned off the gas and shook the bike
 >firmly from side to side to free up the float. When I turned that gas
 >back on the overflow problem stopped.

That happens a lot. Floats get hung up when putting the carb
on the bike. I whack 'em with the butt of a screwdriver.

Try taking the fuel line off the carb and putting it into a
clean jar. Then open the tap to see how well it's flowing.

The real way to check flow though is to install the carb on the
bike with the float bowl off, and make a drain trough to go under
the bowl-less carb. Then measure flow. That way you measure
the flow through everything.

 > As for the carb jets, I could see daylight through both of them.
 >So they aren't plugged completely, but may be restricted a little by
 >debris.

I have had idle jets that were partially clogged but it was
hard to tell by looking through them. It's an awfull small hole.

 > From the Yamaha service data sheet, I see that my float level
 >should be 22.0 mm. How is this measure taken?

Usually the top of the float should be parallel to the carb bowl
mating face. If you check you'll see that the float needle has a
spring thing on the back that can be compressed by the float tang.
You want to measure where the float closes, not the float height
with the spring compressed.

But, unless someone's really (and obviously) fscked up the carb, the
float won't be so far off that it doesn't run.

Is the enrichener ("choke") working and its passages open?

Float chamber vents ok?

Gas tank venting ok?

Maybe someone put in a blue powerband instead of
the yellow one?


Eric<!-- ~MESSAGE_AFTER~ -->
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On Sun, 01 Feb 2004 22:29:22 GMT, "Eric M" <root.TakeThisOut@127.0.0.1> wrote:


 >Usually the top of the float should be parallel to the carb bowl
 >mating face. If you check you'll see that the float needle has a
 >spring thing on the back that can be compressed by the float tang.
 >You want to measure where the float closes, not the float height
 >with the spring compressed.

Yeah, I knew the float needle was spring loaded and that the float
tang sat on it. So you're saying if the carb is removed and inverted,
then I'd measure the distance between the bowl mating surface and the
top of the float, with the float just resting on the needle seat and
*not* compressed?

 >But, unless someone's really (and obviously) fscked up the carb, the
 >float won't be so far off that it doesn't run.

Okay. I'd still like to get it straight for future reference
though. Thanks.

 >Is the enrichener ("choke") working and its passages open?

Funny you should ask! Today (without making any changes) I again
attempted to start the bike. I had previously assumed that the choke
was "off" with the lever up. But I began to wonder. So I set it to the
"down" position before trying today. The bike fired right up and
stayed running longer than before. It was idling real high though and
there didn't seem to be any throttle response. When it started bogging
down, I switched the choke lever back to the "up" position and it ran
just a bit longer (with a *little* throttle response) before dying. So
I still suspect that the "up" position is "off." But now I'm wondering
about my custom Terrycable one-piece throttle cable and whirlpool
throttle assembly. I haven't been real comfortable with this set up
since installing it. First, the cable appears to be about an 1/8" too
short (after maximum adjustment). I say this because the carb slide
won't sit all the way down into the slide bottom. With the throttle
all the way closed there's still an 1/8" gap at the bottom of the
slide... adjusting the idle (slide) screw makes no difference.

Secondly, the whirpool throttle appears to be waaay too quick.
From idle to full throttle is a quarter turn or less! I'd revert to
the oem stuff, but I never had those pieces to begin with. I'm
wondering though, if I can acquire the original throttle assembly and
still use the one-piece Terrycable. I'll have to get 'em and see I
guess. The one-piece cable was 26 bucks (+ shipping) and I hate to do
away with it completely.

Still though, you wouldn't think that this alone would cause the
problems we're experiencing, would ya?

 >Float chamber vents ok?

As far as I know. The bowl itself only has one vent -- the
overflow tube -- and I admit that I haven't tried to blow out the carb
passageways with compressed air. Mostly because I'd have to take the
thing over to my brother's to use his air compressor.

 >Gas tank venting ok?

I assume so. I mean, it's got an original metal tank with the
original chrome steel (non-vented) gas cap. I *did* check the flow
through the gas line itself last time I tried starting the bike. It
was flowing like the river Nile! Haven't tried the "through the carb
flow" yet though.

 >Maybe someone put in a blue powerband instead of
 >the yellow one?

I bet it was one of those damn black ones! Those things NEVER
work! I dunno why all the kids today want 'em...

Fred
'85 RM 250
'79 YZ 80
'81 DT 80<!-- ~MESSAGE_AFTER~ -->
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In article <401dbf1b.1735804524.DeleteThis@news.ev1.net>,
Fred B. <van-designsREMOVE.DeleteThis@ev1.net> wrote:
 >On Sun, 01 Feb 2004 22:29:22 GMT, "Eric M" <root.DeleteThis@127.0.0.1> wrote:
 >
 >
  >>Usually the top of the float should be parallel to the carb bowl
  >>mating face. If you check you'll see that the float needle has a
  >>spring thing on the back that can be compressed by the float tang.
  >>You want to measure where the float closes, not the float height
  >>with the spring compressed.
 >
 > Yeah, I knew the float needle was spring loaded and that the float
 >tang sat on it. So you're saying if the carb is removed and inverted,
 >then I'd measure the distance between the bowl mating surface and the
 >top of the float, with the float just resting on the needle seat and
 >*not* compressed?


Where to measure the distance will be in the book.
But generally the float should look level
compared to the gasket surface.

  >>Is the enrichener ("choke") working and its passages open?
 >
 > Funny you should ask! Today (without making any changes) I again
 >attempted to start the bike. I had previously assumed that the choke
 >was "off" with the lever up. But I began to wonder. So I set it to the
 >"down" position before trying today. The bike fired right up and
 >stayed running longer than before. It was idling real high though and
 >there didn't seem to be any throttle response. When it started bogging
 >down, I switched the choke lever back to the "up" position and it ran
 >just a bit longer (with a *little* throttle response) before dying. So
 >I still suspect that the "up" position is "off."

On all the enricheners I've seen (TK, mikuni, kehein), up is
on and down is off.

The bahaviour you're describing is normal. Most twostrokes need
the enrichener to start, then need it on and off while
warming up. BTW, use NO throttle for starting... opening the throttle
makes the enrichener less effective.


 >But now I'm wondering
 >about my custom Terrycable one-piece throttle cable and whirlpool
 >throttle assembly. I haven't been real comfortable with this set up
 >since installing it. First, the cable appears to be about an 1/8" too
 >short (after maximum adjustment). I say this because the carb slide
 >won't sit all the way down into the slide bottom.

OK that's why it's not starting or running well.
The enrichener needs the full vaccuum of the closed slide to work
properly.

 > With the throttle
 >all the way closed there's still an 1/8" gap at the bottom of the
 >slide... adjusting the idle (slide) screw makes no difference.
 >
 > Secondly, the whirpool throttle appears to be waaay too quick.
 >From idle to full throttle is a quarter turn or less! I'd revert to
 >the oem stuff, but I never had those pieces to begin with. I'm
 >wondering though, if I can acquire the original throttle assembly and
 >still use the one-piece Terrycable. I'll have to get 'em and see I
 >guess. The one-piece cable was 26 bucks (+ shipping) and I hate to do
 >away with it completely.
 >
 > Still though, you wouldn't think that this alone would cause the
 >problems we're experiencing, would ya?

Yes it would. Along with getting the sign wrong on the
enrichener. (you must be a Honda four-stroke rider, I could never
deal with the 'up is off' backwardsness of my wife's XR200 choke).

  >>Float chamber vents ok?
 >
 > As far as I know. The bowl itself only has one vent -- the
 >overflow tube

The small brass tube thingies on the side are vents. Put
hoses on em.

 > -- and I admit that I haven't tried to blow out the carb
 >passageways with compressed air. Mostly because I'd have to take the
 >thing over to my brother's to use his air compressor.
 >
  >>Gas tank venting ok?
 >
 > I assume so. I mean, it's got an original metal tank with the
 >original chrome steel (non-vented) gas cap.

It is vented even though it has no hose.
The hoses are used to route the spillage away from
the rider.



Eric<!-- ~MESSAGE_AFTER~ -->
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On Mon, 02 Feb 2004 22:25:32 GMT, "Eric M" <root.TakeThisOut@127.0.0.1> wrote:


 >Where to measure the distance will be in the book.
 >But generally the float should look level
 >compared to the gasket surface.

I get it now, thanks Eric.

 >On all the enricheners I've seen (TK, mikuni, kehein), up is
 >on and down is off.

Okay, that helps clear things up a bit.

  >> I say this because the carb slide
  >>won't sit all the way down into the slide bottom.
 >
 >OK that's why it's not starting or running well.
 >The enrichener needs the full vaccuum of the closed slide to work
 >properly.

I see. Funny, my brother said the same thing but I didn't believe
him (plus, he didn't sound as convinced as you). He also said that the
rings being worn and causing low compression was an unlikely culprit.
That he's seen bikes start with almost no compression. Maybe I should
start listening to him more.

 >Yes it would. Along with getting the sign wrong on the
 >enrichener. (you must be a Honda four-stroke rider, I could never
 >deal with the 'up is off' backwardsness of my wife's XR200 choke).

Actually I had a '75 or '76 GT-80 myself, but that's been about 25
years ago and I couldn't remember exactly how it went. My other bikes
had chokes too, of course, but it's been 10 or 11 years since then
and, well, I suck.

  >> As far as I know. The bowl itself only has one vent -- the
  >>overflow tube
 >
 >The small brass tube thingies on the side are vents. Put
 >hoses on em.

Oh yeah, sorry, I forgot about those. I did indeed put [new]
rubber hose on each of them. The overflow vent I know is clear because
it was flowing generously with the float stuck. The other vent I'm not
positive about though... I'll re-check it.

  >> I assume so. I mean, it's got an original metal tank with the
  >>original chrome steel (non-vented) gas cap.
 >
 >It is vented even though it has no hose.
 >The hoses are used to route the spillage away from
 >the rider.

I should have known this. Duh. Even with a good gasket the tank
will still leak (vent) if the bike is laid on it's side. So to answer
the original question; yes, the tank is venting properly.

I really appreciate your help with this, Eric. You've served to
both rekindle lost knowledge, as well as re-introduce some new. I know
it's often frustrating when dealing with those less knowledgable (or
those who've been out of the loop for a while), which makes your help
all the more appreciated. I'll consider all the advice and attempt
some revisions to the system and see if I can't get 'er goin'. If not,
hopefully you'll be kind enough to render advice again. Thanks Eric!

Fred
'85 RM 250
'79 YZ 80
'81 DT 80<!-- ~MESSAGE_AFTER~ -->
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