Motorcycle Repair: DT175 follow up, spark arrestor, stock value

Question
Wayne,
Thanks for the reply. So as a follow up.
Clarification on the needle. I meant that I moved the clip up to the 4th position, which by the books states it as leaning. And for the main jet I replaced it with a stock value for a 1979 DT175 which is 140.
so, I took the spark arrestor off the end of the pipe. (its a forest approved type...) It was covered in sliming oily goop! So then I took the rest of the exhaust arrestor off and it too was very wet and oily. I sprayed carb cleaning down inside and wiped it out really good. Then started the bike up (without the end insert in), and low and behold, it actually help some! I got up to 7000RPM. I road it around the block once and was actually able to get up to 40mph before it began to load up. So I think you are right the exhaust is gunked up. I will see if I can split it up. unfortunately if I do this I will have to have it welded. I may just see if I can find a new replacement.
So would this also be the cause of it being so hard to start when it is cold? When cold, I pull the choke on, then kick it over a couple times and it will fire up for about 2 seconds then dies. I go through this process about 12 times until it finally stays running for about 5 sec and then I quickly push the choke off and if lucky it will continue running. But once I get it running it idles just fine.
If after I replace the pipe, and IF it is still a bit rich, then should I move the throttle needle clip back to the 4th position again? or leave at factory? Or should I change the main jet down to a 130?
...i think I am getting close!

Answer
Hi David,

Try to either clean out the pipe well
or get another pipe that is cleaner.

Once you have that working better
as you have already then
just put the slide needle
clip in the middle position
or one up from the middle.

Run the bike hard and stop the
engine quickly. Check if the spark
plug is a brown color. If it still
sputters or the plug is black then
go one size down on the main jet.

Once the pipe is reasonably clean
you want to have the largest
main jet you can that doesn't
sputter and allows you to get
full RPM's.

Starting is not affected much
by the main jet only
a plugged up idle pilot jet
would restrict your fuel
during starting.

Also the choke is on when either pushed down
or pulled out depending on the style.
Any plugged carb passageways might affect
the choke enrichment.

If the bikes dies when cold
it might be an air leak around
the carb mounting rubber or
choke passagways plugged in the carb.

Try a quick spray of starting fluid
or carb cleaner and see if it
starts, if so you may have to
check the fuel supply, float level,
choke plunger, carb passageways.

It might help to get the pipe
and main jet tuned and then see
how it runs after a good warm up.

Spark plug color should be tan or light brown
ideally after a fast run when all is right.


Luck!
Wayne S.
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