Dunc
XS650 Addict
I checked mine before fitting them, first one was spot on, but the second was 3mm lower.
Tuning help needed
- Thread starter devildrums
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devildrums
XS650 Enthusiast
Ok, started from scratch today, just an idle test. After warming up and a few spits, changed plugs and ran 2 new tests with the air filters totally off, each one five minutes at 13-1500 rpms. Ran at a nice idle, but Air screw at 1 1/2 turns and 1 turn no change, still backfiring about every 45 secs. Plugs did look perfectly normal after each test.
Two things I could use a little clarity on. What is the ideal idle rpms for these tanks and if the backfire is supposed to come from the fuel not totally burning to begin with, what is the most likely thing I should be trying to adjust first, if there is such a thing. Apparently I am a really big fan of this bike.
Two things I could use a little clarity on. What is the ideal idle rpms for these tanks and if the backfire is supposed to come from the fuel not totally burning to begin with, what is the most likely thing I should be trying to adjust first, if there is such a thing. Apparently I am a really big fan of this bike.
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Specified idle speed is 1100-1200 rpm, and that's where you want to run it. Any lower and the bike can (and will) randomly just stall. Any higher and the ignition can start into it's advance curve. That can cause the idle speed to increase even more which will cause more advance, more speed increase, more advance, etc. It's a self-feeding problem. The bike could end up sitting there running at 2000 or 2500 rpm, without you even touching the throttle.
devildrums
XS650 Enthusiast
I had that a few times last year before i got my new ignition and timing straightened out. Any help on what to look at first with the backfiring through the carb problem? Right now that is my biggest problem and I just don't want to keep going around in circles because i am doing something out of order. And if the answer is "nothing that specific", that is okay, I know by now these old bikes are tough.
valve clearances checked, compression tested (recently) timing checked again recently. timing chain tension checked.
those carbs CAN be swapped side to side.
those carbs CAN be swapped side to side.
devildrums
XS650 Enthusiast
We had done those things back in December, but not in the last few weeks. guess the reason I sound so puzzled is i rode it fine with the 185 mains, and only problem was the engine sputtering after 3500. When i changed to 180 is when the current carb problem started, but the function of the bike overall seems okay when i ride it. I would assume that any or all of those things being off would make it not run good as a whole. Right?
T'wer it me, I'd be checking cam chain and valves (again). 'Specially if this is a "just woke up from a long nap" motor.
Here's my take and angle on this: It DID run the same on both sides, jetting, carb changes, have been applied to both sides, theoretically the motor should run the same on both sides, it's not. I'd want to be looking for/ eliminating issues that are on "just one side" or related to differences in left right carbs, hitting on synching carbs (usually limited to slide setting by mechanical means (drop, raise on a drill bit is popular) not easy on VM's.
We want you to suceed!
Here's my take and angle on this: It DID run the same on both sides, jetting, carb changes, have been applied to both sides, theoretically the motor should run the same on both sides, it's not. I'd want to be looking for/ eliminating issues that are on "just one side" or related to differences in left right carbs, hitting on synching carbs (usually limited to slide setting by mechanical means (drop, raise on a drill bit is popular) not easy on VM's.
We want you to suceed!
Remind me what ignition do you have?
devildrums
XS650 Enthusiast
The mike's xscharge e-edvancer model. when i checked both sides with timing light it was consistent, so i assume it was working properly.
I note that WideAwake (he's ~ sea level too) suggested 35 pilots (2.5 slide) and 5twins also suggested going richer (~27.5). What pilots are you at currently?
If too lean, you can get a misfire and incomplete combustion and the plugs will read dark and cause popping in carbs (and also exhaust on decel)- just a theory ATM.
I'm trying not to let the presence of an XSCharge Ign. prejudice me - but, they will play games and don't like low voltage (really don't like capacitors). So, have you checked voltage at the ignition coil (+)?
devildrums
XS650 Enthusiast
I know, have seen many different posts against that ignition. My current pilots are 20, down from 22.5. I missed that from 5twins and most of my research and un-education about backfiring through the carb led me to believe if all of the fuel is not combusting early, maybe smaller pilots will help. A few recent test rides has it running through all of the gears and rpms properly, just maintains that carb spit about every 45 seconds at idle. After the rides, plugs were still coming out dark, which typically means rich.
Also, seeing what you wrote, I wasn't aware that the plugs would darken if running lean. Every plug chart i see says rich. This idea of lean in / rich out is what has had me so confused.
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If you're referring to the mix screws, there's a rule of thumb for bike carbs.... Mikuni's
If the mix screw is downstream of the slide... 'tween the engine and slide... the screw regulates the fuel. Turning the screw out increases the fuel in the mix and richens the mixture. The stock BS carbs use this setup.
If the mix screw is upstream of the slide.... 'tween the slide and air filter... it's an air mix screw. Turning the screw out increases the air in the mix and leans the mixture. VM carbs use this setup.
might be the "spit", that's one cylinder fire that didn't ignite. So the next firing has extra unburned gas from the previous miss hanging around,
Perhaps air leaking onto the exhaust pipes is causing backfire??? Check all joints.
Note: I am into my 2nd Week working on Virago carbs. I now have one sorted and hope the other will soon follow???
Note: I am into my 2nd Week working on Virago carbs. I now have one sorted and hope the other will soon follow???
