So my bike was running great the other day, but noticed some light repetitive knocking on the right side of the engine, which after inspection and talking with some friends of mine could be because I was using 87 octane and it may have been firing too early, so I'm now running 91. I'm noticing that it's firing on the left side but not very well at all on the right side, and what makes it weird is that when I open my choke both sides run fine like "normal" I suppose. No clogged jets, carburetor is spotless on the inside, valves are at .002" in, .006" out with the point space at .015" Spark plugs come out perfect, no carb build up or oil, etc. Outside Jets are turned 1.5 turns. Could it be the fuel change? maybe my points are wearing down? I need to figure this out before Friday this week lol Like I said before, it all ran normal on 87 octane, I believe that changing fuel could be this issue, but if not, why else would it be like this?
-
Enjoy XS650.com? Consider making a donation to help support the site.
XS650.com receives a small share of sales from some links on this page, but direct donations have a much greater impact on keeping this site going.
Odd ignition issue
- Thread starter Grimmith
- Start date
Have you put a timing light on it to see if both sides are firing at the proper time... and that the advance mechanism is not over advancing from wear?
No to both lol. Still learning as I go. Do I have to buy a timing light? and I'll have to wait till tomorrow to check the advance mechanism. If not too much to ask, and it's totally cool if don't feel like doing the work but could you point me to the correct pages for these issues? I can't do any engine running till tomorrow cuz literally all my neighbors around me wake up early...………….I have all morning and afternoon until 6pm central USA time tomorrow and same time on Friday this week.
Yea actually when I put it in 5th gear and go nearly half throttle it "runs fine" lol but its boggy and shitty running 1 through 4
Well, if you have a knock, the first thing you'd want to do is check timing at idle and at full advance. If timing on both cylinders is good, then you can explore carb issues. But chasing carb issues without first verifying good accurate ignition is kinda like puttin' your socks over your shoes.
So yeah... you need a timing light.... get ignition squared away and go from there.
Engine knock is caused by pre ignition. In older engines with low compression like 7.5 and below it wasn't much of a problem.
To get better performance they upped the compression ratios. This gave more power but caused more knock. To prevent knock they upped the octane rating. This higher octane allowed more advance on the ignition which gave more power. To much advance increased knock.
Bit of a vicious circle type thing.
When they built our mid compression engines they worked well with the fuel available at the time.
Todays fuel blended with ethanol has the less energy per pound of fuel. Thus lowering the effective octane rating. Upping to 91 will help reduce the knock. I try to run 93 in my bikes.
The way your engine is running may have been due to the fuel change, not because of the octane rating but most higher octane fuel has more additives. These additives may have loosened something in your fuel system that is now blocking your idle circuits in right side carb.
When an engine runs poorly at idle but runs ok with the choke partly on or runs well at higher rpms indicates an idle circuit issue.
Since you have noticed this issue, have you torn down the right carb to check the idle circuits?
If not you might try flushing the idle circuit by removing the air filter on that side and the float bowl. removing the idle mix screw. hold throttle open. Use a spray can cleaner insert the tube into the mix screw hole. plug off the pilot jet with a fingertip, Spray the cleaner, This will push the cleaner out the tiny holes by the throttle plate. It should spray out all those holes. If not you have a blocked idle circuit. Keep spraying till the cleaner does come out all those holes.
Once it does, reassemble the carb and air cleaner and see how it runs.
Leo
To get better performance they upped the compression ratios. This gave more power but caused more knock. To prevent knock they upped the octane rating. This higher octane allowed more advance on the ignition which gave more power. To much advance increased knock.
Bit of a vicious circle type thing.
When they built our mid compression engines they worked well with the fuel available at the time.
Todays fuel blended with ethanol has the less energy per pound of fuel. Thus lowering the effective octane rating. Upping to 91 will help reduce the knock. I try to run 93 in my bikes.
The way your engine is running may have been due to the fuel change, not because of the octane rating but most higher octane fuel has more additives. These additives may have loosened something in your fuel system that is now blocking your idle circuits in right side carb.
When an engine runs poorly at idle but runs ok with the choke partly on or runs well at higher rpms indicates an idle circuit issue.
Since you have noticed this issue, have you torn down the right carb to check the idle circuits?
If not you might try flushing the idle circuit by removing the air filter on that side and the float bowl. removing the idle mix screw. hold throttle open. Use a spray can cleaner insert the tube into the mix screw hole. plug off the pilot jet with a fingertip, Spray the cleaner, This will push the cleaner out the tiny holes by the throttle plate. It should spray out all those holes. If not you have a blocked idle circuit. Keep spraying till the cleaner does come out all those holes.
Once it does, reassemble the carb and air cleaner and see how it runs.
Leo
Well if that happens we can do more trouble shooting.
But for much more trouble shooting we would need a bit more info.
A lot of us put the bike info on our signature line. Year, model, any mods, that type of stuff.
Leo
But for much more trouble shooting we would need a bit more info.
A lot of us put the bike info on our signature line. Year, model, any mods, that type of stuff.
Leo
check timing BOTH sides also. Piston tops are thin it's doesn't take long to burn a hole through one, and the RH side is most likely to get holed.
So I cleaned the carb like you said, re checked the timing and it's still acting like it doesn't want to fire correctly on the right side. After setting the timing and points I took off the right spark plug and saw it sparking on the timing rhythm. Could it maybe be a weak spark? 91 is harder to combust. I'll have to check the clearance gaps on the plugs. unless I'm just doing it all wrong in the first place lol feel like a new author for "failing for dummy's" 
Your tappet gap seems a but small at .002"......general consensus .003", so the feeler gauge is just a bit loose to a tight .004" where the feeler cant quite get under............and .006"
