Topic: xl250 running but appearing rich?

[cb550fnewb]

I got my Xl250 running after a carb rebuild (back to stock).

Bike was running for awhile probably around 40 miles or so.  Then one day I started it up and when I hit around 4000 rpm's it sputters and backfires and barely runs.  The first time it stop after a few miles just like that.  Thought maybe something got lodged in the the main jet and fell out fixing it.  Then next time I started it I went to take off and it did the same thing again and after messing with the carb while idling I accidentally killed it.   It would not start until I walk home and put a new plug in. 

The plug was black obvious from fuel.  Also the gas mileage seems to be between 20-30 mpg (have not really check it but tank emptied fast.

What should I be doing now? I am lean towards leaning the carb but am afraid that I may have an ignition issue.  Points have be tuned.

[tbpmusic]

Lots of potential causes - first thing to do is get a compression reading.
If it has bad compression, no point in going any further till that's corrected. - anything else you do will be a waste of time and money..........

[scunny]

had the same thing happen on my 79 xl250 earlier this year. pulled carby, all iooked good, made sure the jets were clean, put it back together and no problem since. ?

[cb550fnewb]

Lots of potential causes - first thing to do is get a compression reading.
If it has bad compression, no point in going any further till that's corrected. - anything else you do will be a waste of time and money..........

Compression was 110 cold before I got it running.

Coil is a new (its a universal 6v/12v) not sure how it works but guessing maybe it is my problem.  timing is set.

Hard to visually tell how well it is sparking since it is a kick. 

I currently have it set to stock needle height and can move it up 2 positions to the leanest option but not sure if I should.

I tested resistance of my coil believe I did it correct.   The bl/w wire reads no resistance (when I do x10 OHM it puts the need past zero).  the old one reads the same.   Appears I have old and new coil at least.  The resistance from plug read 60 OHM which I believe is also low.  I do not have manual but believe the bl/wh wire is suppose to be 2 to 3 OHM and not sure on the plug wire side. 

I may have to order a new 6v specific coil. 

[tbpmusic]

Compression was 110 cold before I got it running.

Coil is a new (its a universal 6v/12v) not sure how it works but guessing maybe it is my problem.  timing is set.

Hard to visually tell how well it is sparking since it is a kick. 

I currently have it set to stock needle height and can move it up 2 positions to the leanest option but not sure if I should.

The manual shows a 9.1:0 compression ratio, which is in line with other models of the era.
In that case I would expect 180-190 psi to be the goal, with 150 psi (or so) to be the red flag area, your readings are well less than that.
Assuming your psi readings are correct, you need some top end work.

You can mess with carbs and timing all you want, I doubt the bike will ever run well till it has good compression.
If you were a customer I'd always check the compression first - then seeing 110 psi, I'd just stop regardless how much money you offered me to "just get it runnin'".
With low compression, I would fully expect it to run slobberin' rich.

[buffalogt750]

I would also check the valve adjustment. Valves that are too tight can cause all kinds of problems including low compression readings.

[cb550fnewb]

Compression was 110 cold before I got it running.

Coil is a new (its a universal 6v/12v) not sure how it works but guessing maybe it is my problem.  timing is set.

Hard to visually tell how well it is sparking since it is a kick. 

I currently have it set to stock needle height and can move it up 2 positions to the leanest option but not sure if I should.

The manual shows a 9.1:0 compression ratio, which is in line with other models of the era.
In that case I would expect 180-190 psi to be the goal, with 150 psi (or so) to be the red flag area, your readings are well less than that.
Assuming your psi readings are correct, you need some top end work.

You can mess with carbs and timing all you want, I doubt the bike will ever run well till it has good compression.
If you were a customer I'd always check the compression first - then seeing 110 psi, I'd just stop regardless how much money you offered me to "just get it runnin'".
With low compression, I would fully expect it to run slobberin' rich.

Should I test the compression cold or warm and wet or dry?  And how many kicks should I give it?  If warm I will have to wait for my new coil to get here Friday or Saturday.

Okay just ran out and did the test again.  After researching online a few places said kick until compression stops building. This was about 6 to 7 kicks.  I got a little better #'s this time.

135 psi and if I add 5% for being cold puts me at 140ish.  I will try to adjust the values the next couple of days and see if I get any increase.

[scottly]

I got my Xl250 running after a carb rebuild (back to stock).

  It would not start until I walk home and put a new plug in. 

The plug was black obvious from fuel.  Also the gas mileage seems to be between 20-30 mpg (have not really check it but tank emptied fast.

What should I be doing now?

Not sure how you got side-tracked on compression and ignition when you were on the right track to begin with??
It might be a carb problem, or even a plugged up air filter? What year is your XR?

[cb550fnewb]

I got my Xl250 running after a carb rebuild (back to stock).

  It would not start until I walk home and put a new plug in. 

The plug was black obvious from fuel.  Also the gas mileage seems to be between 20-30 mpg (have not really check it but tank emptied fast.

What should I be doing now?

Not sure how you got side-tracked on compression and ignition when you were on the right track to begin with??
It might be a carb problem, or even a plugged up air filter? What year is your XR?

It is a 1974 XL 250. 

I have the carb set to stock and filter is clean and not over oiled.  I don't want to lean it out to find out my problem was weak spark leaving extra fuel.

The specs show that the in 1976 they changed stock needle position to one clip position leaner, so going up one shouldn't hurt?

[tbpmusic]

Running rich is just a symptom. Could be caused by many things.
Compression check is just basic diagnostic info, I do it first.
Can't rule it out if you don't know what it is.........

He didn't suggest that the bike ran great before he fooled with the carb.

The way it reads to me is - the bike was probably not running well, why else would he mess with the carb.
Messing with the carb didn't help..........
Start looking elsewhere........

[cb550fnewb]

Running rich is just a symptom. Could be caused by many things.
Compression check is just basic diagnostic info, I do it first.
Can't rule it out if you don't know what it is.........

He didn't suggest that the bike ran great before he fooled with the carb.

The way it reads to me is - the bike was probably not running well, why else would he mess with the carb.
Messing with the carb didn't help..........
Start looking elsewhere........

I bought bike and would barely start and foul plugs in 5 minutes.   I took the carb apart and someone changed the main jet (can't remember size but it was bigger and move needle to leanest setting.)

Since then I have rebuild the carb with the stock jets and replaced the coil (with universal 12v/6v), cleaned air filter, and checked points. 

[tbpmusic]

Did you check the timing, or just check the point gap?

[cb550fnewb]

Did you check the timing, or just check the point gap?

both

[scottly]

The manual shows a 9.1:0 compression ratio, which is in line with other models of the era.
In that case I would expect 180-190 psi to be the goal, with 150 psi (or so) to be the red flag area, your readings are well less than that.
Assuming your psi readings are correct, you need some top end work.

You can mess with carbs and timing all you want, I doubt the bike will ever run well till it has good compression.
If you were a customer I'd always check the compression first - then seeing 110 psi, I'd just stop regardless how much money you offered me to "just get it runnin'".
With low compression, I would fully expect it to run slobberin' rich.

Last I heard, atmospheric pressure was about 14.7 PSI. 14.7x9.1=133.77.
My first bike was a Honda C200. It developed a high RPM miss that gradually got worse over time, until it got to the point that it would hardly run over 1/2 throttle. The black plug pointed to a carb issue, but after tearing it apart 1000 times with no improvement, I threw in the towel and took it to the local dealer. They diagnosed the problem as low compression, and did a top end rebuild. I don't recall just what it cost, but it was a LOT of money for a 14 year old...
I was instructed to ride the bike at low revs for a while to break-in the new piston, so after dutifully babying the motor for what seemed like forever, I finally opened her up, only to find the bike ran no better than before the "repair" work.
After tearing the carb apart for the 1999th time, I got lazy and left the rubber coupling between the carb and the air filter off, and took it for a quick test ride. Whoo hoo! It ran like a scalded cat!!!! I fit the coupling back on, strapped on my helmet, and headed for the dirt.... and got 50 yards before it started crapping out. 
Turns out the stock pleated paper filter was plugged up, even after having been blown out with compressed air, and was choking the bike for air.       

[cb550fnewb]

The manual shows a 9.1:0 compression ratio, which is in line with other models of the era.
In that case I would expect 180-190 psi to be the goal, with 150 psi (or so) to be the red flag area, your readings are well less than that.
Assuming your psi readings are correct, you need some top end work.

You can mess with carbs and timing all you want, I doubt the bike will ever run well till it has good compression.
If you were a customer I'd always check the compression first - then seeing 110 psi, I'd just stop regardless how much money you offered me to "just get it runnin'".
With low compression, I would fully expect it to run slobberin' rich.

Last I heard, atmospheric pressure was about 14.7 PSI. 14.7x9.1=133.77.
My first bike was a Honda C200. It developed a high RPM miss that gradually got worse over time, until it got to the point that it would hardly run over 1/2 throttle. The black plug pointed to a carb issue, but after tearing it apart 1000 times with no improvement, I threw in the towel and took it to the local dealer. They diagnosed the problem as low compression, and did a top end rebuild. I don't recall just what it cost, but it was a LOT of money for a 14 year old...
I was instructed to ride the bike at low revs for a while to break-in the new piston, so after dutifully babying the motor for what seemed like forever, I finally opened her up, only to find the bike ran no better than before the "repair" work.
After tearing the carb apart for the 1999th time, I got lazy and left the rubber coupling between the carb and the air filter off, and took it for a quick test ride. Whoo hoo! It ran like a scalded cat!!!! I fit the coupling back on, strapped on my helmet, and headed for the dirt.... and got 50 yards before it started crapping out. 
Turns out the stock pleated paper filter was plugged up, even after having been blown out with compressed air, and was choking the bike for air.     

Luckily mine is foam. 

[tbpmusic]

Clogged mufflers could also do it - critters build homes in them...

[tbpmusic]

Last I heard, atmospheric pressure was about 14.7 PSI. 14.7x9.1=133.77.

Maybe so, but Honda lists a similar ratio (~9:0 or so) for 450 DOHC, and expect to see 180 psi on a compression reading.
Real close for 350's (~172 psi) and most of the Hondas of that era.
My experience supports what the manual sez about the numbers.
How that all relates to the formula is injineer stuff - maybe they figured it out on Jupiter.......

[cb550fnewb]

Clogged mufflers could also do it - critters build homes in them...

Should I take it off to check it?  I am going to mess with it Saturday if it does not snow here in Utah. 

I got the new 6v specific coil today with condenser.  If the exhaust is not plugged, I plan to move the main jet needle to leaner.  How many clip positions should I move it if I do? 1 or 2?

[tbpmusic]

Fouled spark plugs are just a symptom of incomplete combustion.
A variety of issues can cause incomplete combustion.......

1) Weak spark or spark at the wrong time - or maybe bad plugs
2) Valves too tight (never totally close) or leaking
3) Poor compression - bad valves, bad rings, maybe cam timing out of whack
4) Too much fuel or too little air - carb float, jets, dirty carb, etc.
5) Restricted air filters or exhaust - I've seen both, usually due to critters looking for a home, or mud (on dirt bikes in particular.
   Remove them, shake like crazy, blow air into them, run coat hangers through them - whatever works to assure they're not plugged.

But there are other possibilities as well.
I'd be very careful about messing with your jets and slide needle. In good trim the bike should run well with stock jets/center needle clip, assuming you have stock mufflers and air cleaners.
Fooling with the tapered needle can cause the bike to run better at some rpm, worse at other rpms. You can end up really creating a mess for yourself.

This is one of the few bikes I don't have the manual for - but I'm fairly sure that 110 psi is not an acceptable reading - as I said before this assumes the readings are accurate. Again, the CB450 sports a similar compression ratio, but Honda expects 180 psi compression readings - in fact they recommend top end work at the "red flag" level of 162 psi......it's in the Manual....and they're not fooling based on my experience. They are Hondas, they will TRY to run no matter how bad they are - I've seen them try to start and run with only 110 psi. But the difference between a CB450 with 180 psi and one with 140 psi is startling.

Warm engine if possible, wide open throttle, NO CHOKE.
Take several readings, then squirt a bit of motor oil into the cylinder.
Then take more compression readings - if it increases dramatically, that's usually a sign of bad rings.
I keep harping on it because it's the most basic kind of diagnostic info.
When you go to the doctor, first thing they do is take your pulse and blood pressure, doesn't matter you're there because your knee hurts.
If your blood pressure is 180/140, the doctor won't care about your sore knee, you have other more pressing concerns.

[cb550fnewb]

Fouled spark plugs are just a symptom of incomplete combustion.
A variety of issues can cause incomplete combustion.......

1) Weak spark or spark at the wrong time - or maybe bad plugs
2) Valves too tight (never totally close) or leaking
3) Poor compression - bad valves, bad rings, maybe cam timing out of whack
4) Too much fuel or too little air - carb float, jets, dirty carb, etc.
5) Restricted air filters or exhaust - I've seen both, usually due to critters looking for a home, or mud (on dirt bikes in particular.
   Remove them, shake like crazy, blow air into them, run coat hangers through them - whatever works to assure they're not plugged.

But there are other possibilities as well.
I'd be very careful about messing with your jets and slide needle. In good trim the bike should run well with stock jets/center needle clip, assuming you have stock mufflers and air cleaners.
Fooling with the tapered needle can cause the bike to run better at some rpm, worse at other rpms. You can end up really creating a mess for yourself.

This is one of the few bikes I don't have the manual for - but I'm fairly sure that 110 psi is not an acceptable reading - as I said before this assumes the readings are accurate. Again, the CB450 sports a similar compression ratio, but Honda expects 180 psi compression readings - in fact they recommend top end work at the "red flag" level of 162 psi......it's in the Manual....and they're not fooling based on my experience. They are Hondas, they will TRY to run no matter how bad they are - I've seen them try to start and run with only 110 psi. But the difference between a CB450 with 180 psi and one with 140 psi is startling.

Warm engine if possible, wide open throttle, NO CHOKE.
Take several readings, then squirt a bit of motor oil into the cylinder.
Then take more compression readings - if it increases dramatically, that's usually a sign of bad rings.
I keep harping on it because it's the most basic kind of diagnostic info.
When you go to the doctor, first thing they do is take your pulse and blood pressure, doesn't matter you're there because your knee hurts.
If your blood pressure is 180/140, the doctor won't care about your sore knee, you have other more pressing concerns.

Tomorrow I plan to check values again, check timing with timing light, and just checked carb float again.  I believe the exhaust and air filter are fine and are stalk.  I will check pressure again but if it is low (140's still) I am not willing to put any top end work into it.  I paid 300 for this and planned to beat the crap out of it on USFS roads and have two coils and a few plugs in it (so 60ish).  I do not think it is worth having the top end done.   

[scottly]

Let's get back to the carb. Did you remove/clean the emulsion tube, check the actual fuel level in the float bowl with the "clear tube" method, check the needle jet for wear, etc?

[cb550fnewb]

Let's get back to the carb. Did you remove/clean the emulsion tube, check the actual fuel level in the float bowl with the "clear tube" method, check the needle jet for wear, etc?

Carb is completely rebuilt 40 miles ago so new jets/needle/etc. and it is apart on my table right now everything looks good.  Not sure what the "clear tube" method is I will Google it. Just checked height with card stock cut to proper float height.

[cb550fnewb]

Cannot do the clear tube method the drain bolt head has been broken off.

[cb550fnewb]

Think I may have found a/the issue.  The choke spring is very weak and barely returns to no choke, so it may be on just a little.  I popped it off and bent it about 1/4" and it now returns properly. Crossing my fingers will she how it goes tomorrow.

If that is it I feel stupid.

[tbpmusic]

Think I may have found a/the issue.  The choke spring is very weak and barely returns to no choke, so it may be on just a little.  I popped it off and bent it about 1/4" and it now returns properly. Crossing my fingers will she how it goes tomorrow.

If that is it I feel stupid.

There you go - that would make it run rich, and affect compression readings as well.

Don't feel too stoopid - it usually is something simple........