Need help with idle problem

[mancave]

Okay, so this is my first at posting anything on cafe husky (so be nice) I am by no means a mechanic but learning as I go...

I recently purchased a 76 WR250. Bike was not running when purchased. No spark, so found that problem and after many many kicks got her started. Bike would run but when you let off the throttle it would die.

Had a replacement carb on it Mikuni looked new, thinking the low speed jet may be clogged took off, cleaned (though looked great) put back on, same problem. Adjusted the air screw (several settings) same problem... Had the original carb, so cleaned it and put it on the bike, same problem. Very hard to start and as soon as off the throttle she dies.

So now thinking the carb may not be my problem. Question, does this sound like a low compression problem? I can tell it does not have great compression from the kick (also have 77 CR250 and much harder to kick)... Any suggestions would be appreciated. have never tried to replace rings or a top end but with your help, sure I can do it.

Thanks!

 

[outdoorsman166]

Ask around for a compression test gauge. Local shop or a friend maybe? Since they didnt have power valves back then id say its a good guess unless the pilot jet size is way off

 

[justintendo]

low compression will make it harder to start...if it has low compression, then that needs fixed first

 

[mancave]

One other thing I have noticed is quite a bit of oil in the exhaust pipe when I take it off, even runs out into a nice small puddle. This is after only 4-5 minutes of riding. Is this normal or signs of needing new rings, or just a complete top end rebuild?

Thanks

 

[Ron]

What size is the low speed (pilot) jet, should be around #40 (in a Mikuni). Make sure the passage is clear. You can see through the pilot jet into the bore of the carb if everything is clear.
Also, check the rubber end of the choke plunger, it needs to make a good seal.
If your 77 250CR runs good, try that carb on the WR, it should run pretty close to the same.
I agree, low compression will make it had to start.

 

[justintendo]

and low compression will alter jetting as well...the less compression the richer it seems to run

 

[mancave]

Okay, showing my ignorance here but I really do not know the size of the low speed pilot jet, how can you tell the size? Did not see any markings on it or he other ones I have that were in box with carb.
Thanks for all the tips, will try them and see what works.

 

[Old Geezer]

One other thing I have noticed is quite a bit of oil in the exhaust pipe when I take it off, even runs out into a nice small puddle. This is after only 4-5 minutes of riding. Is this normal or signs of needing new rings, or just a complete top end rebuild?

Thanks

First off, I aint no expert but.....that much oil in the exhaust pipe might mean a bad wet side crank seal, sucking in oil and air...the air part causing hard starts and poor idle. Just a thought, I could be dead wrong....others will chime in.

 

[mancave]

The oil in the pike is BLACK! I just change the oil in the bike, so it is nice and clean. I spoke with a mechanic and he said the Black oil may be because the bike was in storage for some time and if the gas had been left on it could have caused this as the oil in the gas could have gone into the pipe and over time the gas evaporates leaving only black oil. At this time though you might be right as I am learning my problem may be caused by many problems. Oh well, this is how we learn to fix them... Good thing because even though I live in Houston no one wants to work on a vintage husky... glad we have this forum and glad all of you are so knowledgeable and willing to share your expertise. Thanks!

 

[Ron]

If your serious about getting it running right, you need to do a compression test and a leak down test. That's the only way your going to know what your dealing with.
The compression test will tell you the condition of the top end and the leak down test will confirm any air leaks.
2-strokes "must" be air-tight and jetted properly, if they're going to run right and not seize the first time you ride it hard.

 

[mancave]

If your serious about getting it running right, you need to do a compression test and a leak down test. That's the only way your going to know what your dealing with.
The compression test will tell you the condition of the top end and the leak down test will confirm any air leaks.
2-strokes "must" be air-tight and jetted properly, if they're going to run right and not seize the first time you ride it hard.

Thanks, do you have any suggestions as to where I can buy both compression gauge and leak down kit that will work with my bike?

 

[husqyhamm]

Any and all oil that has passed through crank-case of a running engine, into combustion area and out through exhaust port will be black.
Blown crank seal partially filling crank-case will result in low compression. Same as when you drown engine.
Take plug out, petcock closed, carb drained, and kick engine through quite a few times. Then drain gearbox(fuel tank too), turn bike upside down and crank kickstarter. If oil spews out plughole you know crank seal gone.

 

[husqyman]

You mentioned the oil in the exhaust. Could it be that you have a severely crudded up exhaust (causing to much back pressure for tickover) have you given the expansion chamber a caustic soda clean? a silencer re-pack could be on the table as well, have read on here that husky's like a clean exhaust, you have fuel/spark & it runs after a fashion, a clear exhaust route is often overlooked (this comes from experience of owning small british two strokes running 20/25:1 mix)

 

[mancave]

Guys, THANKS for all the advise. Bottom line I have lots of things to try. Some within my talents others maybe not. maybe I should change thread to read Just Need Help!
Thanks again and will see what works. Everyone very helpful

 

[Ron]

Thanks, do you have any suggestions as to where I can buy both compression gauge and leak down kit that will work with my bike?

You can buy a compression gauge at an auto parts store. It will go into the spark plug hole. Kick the motor over hard 4 -5 times with the throttle wide open. Anything below 125psi is going to be hard to start.

Here's what I made for doing leak down tests. I use a pipe plug in the exhaust flange and the other part I made to go into the intake boot. It has a gauge and a schrader air valve.
In a leak down test I pump air in to the motor, 6-7 psi and watch the pressure drop.
Should not drop more than 1 psi per minute.

http://i226.photobucket.com/albums/dd246/ronsracers/LeakDownTest001_zps5fc7e990.jpg[/IMG

 

[Ron]

You can buy a compression gauge at an auto parts store. It will go into the spark plug hole. Kick the motor over hard 4 -5 times with the throttle wide open. Anything below 125psi is going to be hard to start.

Here's what I made for doing leak down tests. I use a pipe plug in the exhaust flange and the other part I made to go into the intake boot. It has a gauge and a schrader air valve.
In a leak down test I pump air in to the motor, 6-7 psi and watch the pressure drop.
Should not drop more than 1 psi per minute.

 

[mancave]

So, went to Auto Zone and they actually have a compression tester you can borrow. (well almost borrow) pay $40 dollars and when you bring it back they give you your money back... (they give you 3 months) Worked like a charm! Had correct plug size and very simple to use. Followed Ron's "how to" and we do have low compression consistent reading was 120 had one spike of around 145 but only once.

Here are my follow up questions:

1)would this low compression (once started) cause the bike not to idle or run when off the gas? Remember carb is clean and had same problem with two different carbs (both clean)
2) could this be the cause of oil in the pipe and oil seeping from around the exhaust port?

Just an FYI, Auto Zone has many such tools you can borrow

 

[Ron]

Forgot to ask, does it smoke a lot when it runs? Does either of the carbs work correctly on your other bike?

Basic's first:
Verify the idle screw actually lifts the slide when screwed in.
Check the float level.
Check the ignition timing.
Carb may need more cleaning. Some passages are very small and not accessible.
You can only soak the carb and use high pressure air. Just because the jet is clean
doesn't necessarily mean the passage is clean.

 

[justintendo]

the good news is that you probably dont have excessive damage to your topend, the bad is that you need a top end...a fresh one will be 150-160 psi..im not sure if thats low enough to not idle but it will defintely run richer and spooge as it loses compression...

 

[mancave]

Okay, took off head and removed piston. First time ever taking the head off and attempting a Top End Rebuild... from what I have read and seen looks like maybe this was my problem. Obviously burned below the ring and black underneath the piston... Anyone care to diagnose from looking a the pictures????

Now my question: Does my cylinder head need to be re-bored for a new piston or can I just replace the piston and rings?