I recently bought a 75'. The numbers don't match. The motor has 2FO in the serial number. The carbs are BS 38. I rode it for a week and one day on a long trip, it started backfiring. It had sat for a few years and the gas tank had rust in it. I cleaned the tank, changed the fuel filters, and cleaned the carbs. It hasn't ran right since. Recently, I went 1 up on the pilot jet and 2 up on the main jets. It has straight pipes and pod filters. Compression is in the 128-135 range on both sides. Float height is at 24.5 on one side and 24.8 on the other. I am completely lost here! I have tried several different things from here and have read the carb guide. Someone enlighten me please!
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Starts with choke on, pull out choke when revs go high and then it dies
- Thread starter JRay77
- Start date
Hi JRay and welcome,
how exactly doesn't it run right?
The started backfiring thing is as likely to be sparks as it is carbs.
The poor running after the carb cleaning hints that the carbs didn't get cleaned as well as you hoped.
What I'd do is:-
Clean the carbs yet again
Go back to whatever jets that were there before.
Check the carb guide to make sure of the float height and of how to measure it.
Install in-line fuel filters.
And check the spark.
Note that open pipes are a swine to tune and think about adding backpressure.
Make sure the pods are UNIpods, most of the others are rubbish.
how exactly doesn't it run right?
The started backfiring thing is as likely to be sparks as it is carbs.
The poor running after the carb cleaning hints that the carbs didn't get cleaned as well as you hoped.
What I'd do is:-
Clean the carbs yet again
Go back to whatever jets that were there before.
Check the carb guide to make sure of the float height and of how to measure it.
Install in-line fuel filters.
And check the spark.
Note that open pipes are a swine to tune and think about adding backpressure.
Make sure the pods are UNIpods, most of the others are rubbish.
welcome Ray .
We could use a little more information on what the issues are . Is it mainly when cruising at part open throttle ? or wide open WOT ? or on deacceleration ? does it pop cough or splutter when starting, idling , or opening the throttle fom idle ?
Which jets did you fit ? if they are late BS38 then with open exhaust and pod filters you'll probably need to fit 30 pilots and 140 or even 145 main jets
If you can't post a video... you need to give us a lot more detailed information in order for anyone to diagnose your problem from thousands of miles away on the net
We could use a little more information on what the issues are . Is it mainly when cruising at part open throttle ? or wide open WOT ? or on deacceleration ? does it pop cough or splutter when starting, idling , or opening the throttle fom idle ?
Which jets did you fit ? if they are late BS38 then with open exhaust and pod filters you'll probably need to fit 30 pilots and 140 or even 145 main jets
If you can't post a video... you need to give us a lot more detailed information in order for anyone to diagnose your problem from thousands of miles away on the net
I have and in this order
1) checked and adjusted cam chain.
2) valves.
3) points.
4) timing is dead on. ( as close as it can get.)
5) checked rotor. 5ohms and did the slap test with a 9v battery and with ignition on.
6) new brushes.
What's the best way to test the stator windings? I'm seriously thinking my issues are electrical/charging system. When fresh off the charger it fires right up. It is running cooler with the larger jets. It was running 200 + F before. Now even with several short high rev runs it stays below 170 F
1) checked and adjusted cam chain.
2) valves.
3) points.
4) timing is dead on. ( as close as it can get.)
5) checked rotor. 5ohms and did the slap test with a 9v battery and with ignition on.
6) new brushes.
What's the best way to test the stator windings? I'm seriously thinking my issues are electrical/charging system. When fresh off the charger it fires right up. It is running cooler with the larger jets. It was running 200 + F before. Now even with several short high rev runs it stays below 170 F
funky
XS650 Junkie
Try turning the mixture screws out four turns, FIRST as is...
This is a complex issues so here is a simple answer that my help not confuse the issue,,,Your pilot jet and pilot air is the curcuit that the bike starts on.....You adjust the air fuel mixture with the mixture screws one on each carb.... your main jet is for full throttle and your needle jet is for midrange running.. these so called circuits overlap....
If you want to run the bike on idle you need to put your filters on and play with the pilot circuit and mixture screws if the bike back fires its not enough air, turn the miture screws out.
MULITIPLE JET CHANGES WILL NOT HELP... ONE CIRCUIT AT A TIME >>>>MAIN JET AND NEEDLE ADJUSTMENTS WILL NOT IMPROVE STARTING ISSUES...CONCENTRATE ON PILOT JET >>>PILOT AIR JET AND MIXTURE SCREWS for fuel starting issues...
Jetting is a long process and should be done a circuit at a time... then you can see if what you have changed had a good effect or poor effect.
Questions Are
are the carbs clean and balanced, valve lash correct, timing correct ,tensioner correct ,spark plugs good with correct gap...
breather from tank connected.
breather holes on tank cap clear
pet cock not on prime this will flood the carbs and is an easy error. reserve or "ON" is what you need
Recap
First Circuit ...Pilot air Pilot jet and mixture screws are your Idle circuit (for starting the bike and upto quater throttle)
Second Circuit .....Needle jet then comes onto play overlapping with the first circuit and last circuit... Known as mid rage to 1/4 to 3/4 throttle..
Third Circuit .....Main jet when you have the throttle fully open giving it the BEANS....BOOOOOM...
This is the best and easyest way to think about it...Carb theory is more complex than this ,,,but remebering the above will help get you in good area, in terms of getting the bike running.
once the bikes running,, then beleive it or not,, you start with the main jet ,then you work your way back through the other jets.. your eyes inside the engine are the spark plugs they will tell you if you are running rich (too Much fuel) or lean (too little fuel )...
Dont forget set the carbs up on the bike with the air filters on and the mufflers you are going to use fitted . adding thes components later will change everything...
best of luck FUNKY
This is a complex issues so here is a simple answer that my help not confuse the issue,,,Your pilot jet and pilot air is the curcuit that the bike starts on.....You adjust the air fuel mixture with the mixture screws one on each carb.... your main jet is for full throttle and your needle jet is for midrange running.. these so called circuits overlap....
If you want to run the bike on idle you need to put your filters on and play with the pilot circuit and mixture screws if the bike back fires its not enough air, turn the miture screws out.
MULITIPLE JET CHANGES WILL NOT HELP... ONE CIRCUIT AT A TIME >>>>MAIN JET AND NEEDLE ADJUSTMENTS WILL NOT IMPROVE STARTING ISSUES...CONCENTRATE ON PILOT JET >>>PILOT AIR JET AND MIXTURE SCREWS for fuel starting issues...
Jetting is a long process and should be done a circuit at a time... then you can see if what you have changed had a good effect or poor effect.
Questions Are
are the carbs clean and balanced, valve lash correct, timing correct ,tensioner correct ,spark plugs good with correct gap...
breather from tank connected.
breather holes on tank cap clear
pet cock not on prime this will flood the carbs and is an easy error. reserve or "ON" is what you need
Recap
First Circuit ...Pilot air Pilot jet and mixture screws are your Idle circuit (for starting the bike and upto quater throttle)
Second Circuit .....Needle jet then comes onto play overlapping with the first circuit and last circuit... Known as mid rage to 1/4 to 3/4 throttle..
Third Circuit .....Main jet when you have the throttle fully open giving it the BEANS....BOOOOOM...
This is the best and easyest way to think about it...Carb theory is more complex than this ,,,but remebering the above will help get you in good area, in terms of getting the bike running.
once the bikes running,, then beleive it or not,, you start with the main jet ,then you work your way back through the other jets.. your eyes inside the engine are the spark plugs they will tell you if you are running rich (too Much fuel) or lean (too little fuel )...
Dont forget set the carbs up on the bike with the air filters on and the mufflers you are going to use fitted . adding thes components later will change everything...
best of luck FUNKY
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