Right cylinder giving fits

Will77

Will77

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Ok got a 79 xs650 runs good down highway but when taking off will miss and only run on left cylinder then comes out of it and will occasionally back fire out of right cylinder when decelerating from high rpm checked float hight 28 mm both carbs same checked for vacuum leaks none and I have to have the adjuster screw out 6 turns and it runs ok but not great on right cylinder I also bench synced the carbs and when I hook up vacuum gauge to ether cylinder it flutters between 0 and 20 good compression on both cylinders to I’m at a loss please help thanks
 
Some of the worst carburetor problems are electrical. Check all your ignition connections. Is it a stock points system?
 
No first hand experience, but I've read that Mikes points are chinese junk. Without gettin too far into the weeds.... when you're accelerating, the heavier fuel/air mix has a higher dielectric constant... yeah... off in the weeds.... :wink2:
Anyway, what this means is the coil has to work harder to make the spark. Early warning signs of an old weak coil nearing the end is when it starts breaking down under load... in this case, acceleration. Are they the original coils? Try swapping 'em and see if it's the other cylinder acting up.
 
Jim said:
No first hand experience, but I've read that Mikes points are chinese junk. Without gettin too far into the weeds.... when you're accelerating, the heavier fuel/air mix has a higher dielectric constant... yeah... off in the weeds.... :wink2:
Anyway, what this means is the coil has to work harder to make the spark. Early warning signs of an old weak coil nearing the end is when it starts breaking down under load... in this case, acceleration. Are they the original coils? Try swapping 'em and see if it's the other cylinder acting up.
Click to expand...
Ok will try that
 
If your floats really are set at 28mm, that's wrong. Spec for the '78-'79 carb set is 24mm. 28mm would give very low fuel levels in the bowls and lean running as a result. If by adjuster screw you mean the mixture screw, 6 turns out is really bad and should be throwing up huge red flags. Your very low fuel levels may have something to do with needing the mix screw open so much. Suggested set point for your carb set is 2.25 turns out and if the carbs are set up right, the mix screws usually dial in about there, sometimes needing a little more (like 2 1/2 to 2 3/4 turns).
 
Ok I think I ruled out spark issues I filed the points and swapped cylinders and runs the same and swapped cylinders with the coils. So next I’ll pull the carbs and reset the float hight to 24 mm. This thing is making my head spin it acting like it floods at idle and is running to lean running down the highway
 
It's running lean because the fuel levels in the bowls are so low. You can't do any carb tuning until you get them right. Once you get them set right, put the mix screws back at 2.25 turns out and fine tune them from there for smoothest running and fastest idle speed. As I mentioned, that will probably be somewhere between 2.25 to 2.75 turns out.

Is the bike modded (pod filters, freer flowing exhaust)? If so then some carb re-jetting may be needed. Usual routine for a '78-'79 carb set is one or two up on the pilots, same for the mains, and the needles leaned a step.
 
5twins said:
It's running lean because the fuel levels in the bowls are so low. You can't do any carb tuning until you get them right. Once you get them set right, put the mix screws back at 2.25 turns out and fine tune them from there for smoothest running and fastest idle speed. As I mentioned, that will probably be somewhere between 2.25 to 2.75 turns out.

Is the bike modded (pod filters, freer flowing exhaust)? If so then some carb re-jetting may be needed. Usual routine for a '78-'79 carb set is one or two up on the pilots, same for the mains, and the needles leaned a step.
Click to expand...
Yup that makes sense to me I’ll give her a try tomorrow it has stock air filters and full length straight pipes with home made baffles to calm her down a little and to give some back pressure I did go up one size pilot jet. I went up one size main jet that was to much she was flooding out
 
The thing about the '78-'79 carb set is that even one size up on the mains will make the upper midrange too rich unless you lean the needles a step.
 
So I reset my float hight to 24 mm and it runs 100 percent better both mix screws at 2 1/2 turn out thanks so much for the advise I have one more question is it normal to here ticking comming from then head on both sides or do I have to readjust my valves?
 
Well, these aren't the quietest motors around but you shouldn't have pronounced ticking coming from the topend. Yes, check your valve clearances. It could also be a loose cam chain. That will sound just like loose valves. I would check the cam chain first as it's very easy. You check and adjust it (if needed) while the engine sits there idling. Remove the acorn cover nut from the cam chain adjuster on the back of the cylinder. Now observe the movement of the rod in the center of the adjuster screw. It should have a slight in/out movement, maybe a MM or 2. If it's not moving at all, the adjustment is too tight and if moving much more than that 1 or 2mm, it's set too loose. Easiest way to set it is to tighten the adjuster until the in/out movement stops (too tight), then loosen it back up until you get the desired 1 to 2mm of "bounce". You can also demonstrate to yourself what a too loose chain sounds like by loosening the adjuster way up. The in/out movement of the rod will increase and eventually the chain will start "ticking" like loose valves. Tighten it back down and the noise will go away.
 
Jim said:
No first hand experience, but I've read that Mikes points are chinese junk. Without gettin too far into the weeds.... when you're accelerating, the heavier fuel/air mix has a higher dielectric constant... yeah... off in the weeds.... :wink2:
Anyway, what this means is the coil has to work harder to make the spark. Early warning signs of an old weak coil nearing the end is when it starts breaking down under load... in this case, acceleration. Are they the original coils? Try swapping 'em and see if it's the other cylinder acting up.
Click to expand...
Do you know where I can get some good points iv called Yamaha dealers and the said oem points are not available anymore or are china points my only option?
 
5twins said:
Well, these aren't the quietest motors around but you shouldn't have pronounced ticking coming from the topend. Yes, check your valve clearances. It could also be a loose cam chain. That will sound just like loose valves. I would check the cam chain first as it's very easy. You check and adjust it (if needed) while the engine sits there idling. Remove the acorn cover nut from the cam chain adjuster on the back of the cylinder. Now observe the movement of the rod in the center of the adjuster screw. It should have a slight in/out movement, maybe a MM or 2. If it's not moving at all, the adjustment is too tight and if moving much more than that 1 or 2mm, it's set too loose. Easiest way to set it is to tighten the adjuster until the in/out movement stops (too tight), then loosen it back up until you get the desired 1 to 2mm of "bounce". You can also demonstrate to yourself what a too loose chain sounds like by loosening the adjuster way up. The in/out movement of the rod will increase and eventually the chain will start "ticking" like loose valves. Tighten it back down and the noise will go away.
Click to expand...
I figured out the problem it was a exhaust leak the first thing I should have checked but at least my timing chain and valves are adjusted now
 
Will77 said:
Do you know where I can get some good points iv called Yamaha dealers and the said oem points are not available anymore or are china points my only option?
Click to expand...
OEM's will pop up on Ebay from time to time. Other than that.... :shrug:
 
What you'll be looking for is the Daiichi brand. They were Yamaha's supplier .....

DaiichiPoints.jpg
 

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