77 xs400 starting problems

It was already preset to 14.2v so I left it alone. I should add that at idle, I'll have high 12v to low 13v. Also, you need a little rpm blip to get it charging. Cruising around I see 13.6 to 14.2.
 
Alright installed and now its charging, flat spot persists but now that I can rule out poor spark I should be able to do a proper tune and timing check
 
Still ironing out some tuning issues but here it is in all its dirty glory
 

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After doing some thinking and riding this bike to and from work for a few days I still think im getting a weak spark. Seeing as how it isn't a throttle dependent problem, it happens at all throttle positions from cruising at 40mph with the throttle barely open at 3k rpm to raw dogging the throttle all the way up to 3-3.5k rpm. Cant possibly be a carb issue. I can feel it advance too especially in first gear and ive seen it advance with a strobe light and my dynamic timing is good enough to turn the bike over with a split second touch of the starter. I took the points off and hit them with some Emory to clean them up, reinstalled and got the gap set. The only thought I have is maybe the points are too worn. I mean its the only part of the ignition system I havent replaced.
Having said all that, has anyone tried the points off of mikesxs? They look like they are the made in China. I sourced some oem from a guy in PA but thats gonna cost about 100 bucks. Would I be better off just going for a the pseudo TCI?
 
Hey captchrome you suggested that I should advance my timing. Im guessing this is to make up for lost compression due to wear and age. How much advance are we talking here. There are no marks to note degrees of advance just a TDC, LF and the full advance marks. I played around with it and got it to fire right as the F passed the mark. Not sure if you can make that out but thats about where I had it.

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I dunno how much would make a change but I dont wanna put a hole in a cylinder so any advice would be greatly appreciated
 
you suggested that I should advance my timing
I wanted you to check that the timing advances with rpm. Your timing is set at idle so that the timing light shows the 10 degree line to the right of the LF mark in the window (I think you have your idle timing in the wrong place if you are firing on "F"). Now have a friend roll on the throttle slowly to bring the revs to 4000 rpm while you hold the strobe and watch the timing window. If all is well, you should see the timing advance from 10 degrees BTDC up the various marks on the flywheel and max out with at least 36 degrees of advance if your advance mechanism is working properly. Here is a picture of what the flywheel marks represent:

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I wanted you to check that the timing advances with rpm. Your timing is set at idle so that the timing light shows the 10 degree line to the right of the LF mark in the window (I think you have your idle timing in the wrong place if you are firing on "F"). Now have a friend roll on the throttle slowly to bring the revs to 4000 rpm while you hold the strobe and watch the timing window. If all is well, you should see the timing advance from 10 degrees BTDC up the various marks on the flywheel and max out with at least 36 degrees of advance if your advance mechanism is working properly. Here is a picture of what the flywheel marks represent:

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Okay I see now. Yeah initially I timed it to the LF tick after you mentioned advancing it i thought you meant idle timing. Ill bring it back to the factory mark. Would it hurt to ride it 6 miles back to the garage with idle timing at the 20 degree mark?

It does advance i suspected that might have been a problem early on which is why I got the strobe. Ive never used one before so I have a question. There is a dial on the back, when I go to set dynamic timing do you set the dial to zero and strobe it making sure the idle timing is bang on? Then run the throttle up and see if it advances? If thats the procedure then yes it does advance and rather abruptly and more like at 2k rpm. Bike won't even make it to 4k... could it possibly be some worn out springs on those weights?
 
Would it hurt to ride it 6 miles back to the garage with idle timing at the 20 degree mark?
You will, and the bike will be just fine doing that.

do you set the dial to zero and strobe it making sure the idle timing is bang on? Then run the throttle up and see if it advances? If thats the procedure then yes it does advance and rather abruptly and more like at 2k rpm. Bike won't even make it to 4k... could it possibly be some worn out springs on those weights?
That is the procedure I use. The dial on the strobe is handy if you don't have as many advance marks as this bike does. In that case, you can roll on the throttle and then turn the dial to bring the LF mark back into the window and then read the degrees of advance on the dial.

There is a rev range for reaching full advance. The specs for the points bikes doesn't address it, but the specs for the electronic ignition bikes has an advance curve that indicates that you reach full advance between 2700 and 3400 rpm. It sounds like yours is working fine, and I wouldn't worry about it since you have made sure you are getting proper advance as you open the throttle off of idle.
 
1. Remove the camshaft cover
2. Pull the plugs and rotate the engine until the timing inspection window pointer is on the LT mark indicating the left piston is at TDC.
3. Pull the points and the advancer mechanism so that the drive pin on the left end of the camshaft is visible.
4. Looking at the camshaft from the left side of the engine the valves are timed correctly if: the drive pin on the camshaft is at the 12 o'clock position, the "pip" on the edge of the cam gear bolt hole is also at the 12 o'clock position and the two stamped lines in the face of the cam gear are parallel with the top of the head.

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Had some time to work on it today after work. Ive gone through all electrical components related to ignition, new points gapped and timed with a light. We know the auto advance works and I measure voltage at coils as well as resistance of coils and all checks out. I dont wanna fool with the cam shaft and timing chain unless I absolutely have to so we shall continue down the road of troubleshooting to see if we can get closer.

Took carbs off today and cleaned them again, checked float height and put it all back together to get some gas. I knew it was running a little rich just for the hell of it took the stock air boxes off and ran it with just the h pipe. Getting somewhere now, smoother throttle response and climbs up to 3.5k now. Did a plug chop and no surprise looks to run a little lean. So I've come back to carb tuning lol. I'm gonna go play with some needle clip positions and maybe some smaller jets to see what I can get to work. Some might say that little electrical/ignition/timing detour was a waste of time but i think i learned some valuable things about this electrical system. Thanks for all the help so far, I really appreciate it and because of all your help I will not stop till this thing runs like it should.
 
check the battery status to see if it's charged and if all connections are stable. Then, make sure you have the right tools and technical documentation, like the Clymer manual that you already have. Another step could be checking the engine oil and fuel level. If you have experience with industrial machinery repair, you should be able to handle basic tasks such as cleaning and checking the air filters and fuel system. Also, remember to check the ignition system and the condition of the spark plugs.

Best regands Christopher 😊
 
So I've come back to carb tuning
You know, sometimes you just need to go back to basics, especially when you run out of rope on the path you are on. I agree that you have not wasted time so far. I am running along a similar path getting my bike fine tuned. I too am back at the carb mixture (specifically the pilot mixture screws) and it is producing surprising results. If you are a home mechanic without access to a gas analyzer or a dyno, learning as much as you can from what you have done and then going back to the start is the only way to really get these things running right.
 
I think I might be right there with you now captchrome. Every time I wrenched on this bike I get it higher into the rpm band and it starts running a little smoother. Ran out of time today but I think I got the jetting good so I was working in the mix needle. 3 turns out and its getting me up to 4k rpm. When it gets up there closer to 4k it really sounds like its screaming, I've got the stock exhaust on it too. Is this normal? I mean this is my first bike and I see that the red line for this thing is up there but still. Can anyone clue me in on that?
 
3 turns out and its getting me up to 4k rpm
3 turns out on the pilot mix screws is a pretty common starting point, but if the engine is at 4000 rpm at idle with that mix screw setting, you need to lower the idle back down to 1250 or at least below 2000 rpm with the idle speed screw under and between the carbs. Having idle rpm go up when opening the pilot mixture screws is normal as increasing rpm is the sign that you are moving from a lean condition towards a proper idle mixture. If you open the pilot mix screw and nothing happens with idle rpm, it means you are past the optimum idle mixture for that carb and are going too rich. If you go past say 4 turns out on the pilot mix screw and idle rpm is still increasing, that is a sign that your pilot jet is too small.
 
Thats me being a poor communicator. The idle is fine, sits at around 1.2k rpm. Im dealing with a flatspot that starts at 3k rpm. With the jetting and mix screw at 3 turns out I am able to get it up to 4k rpm. It doesn't idle there that is just a note about the progress I've made and that I think I am getting close
 
Thats me being a poor communicator
No, that's me reading too much into what I look at!

Good you are making progress. Keep it up as slow progress is when you learn the most.

Im dealing with a flatspot that starts at 3k rpm
That is sounds like a needle jet/jet needle mixture issue as you will have definitely transitioned off of the pilot circuit and onto the mid-range circuit. Lowering the clip position on the needle would be a step to take to reduce the flat spot. It could also be related to the shape of the needle you have installed.
 
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