77 xs400 starting problems

Alright fellas I am in need of some advice as I have reached something that has stumped me.
All this started with h pipe and pods, fresh battery and synced carbs after each change. Checked valve timing, good. Checked ignition timing, good.

Last post was about loss of power, turned out the bowl gasket was blocking a passage causing that. Modified gasket and it runs but still maxes at 3k.

Started, 145 main and 42 pilot, raised needle one clip position boggy and too rich ro run well. This also put the needle in the last clip position.

Returned needle to previous position, 147.5 main and 45 pilot, same thing too rich to run.

Swapped pilot out for 42 and left the larger main, runs but won't make it past 3k.

Ended up getting the stuff to rebuild the stock air system. Emgo filters and airboxes fitted, same thing. Pegs at 3k.

Did some plug chops and noticed that the lean condition was coming back to more stoic.
Some things I noticed while I had the carbs off, left side carb needle is bent. Must have been from whatever got sucked into the carbs from the PO. Cant find one to save my life, not sure how much performance will be affected but I know it will wear eventually and that will cause issues. Thought maybe the auto advancer for the ignition timing was sticking so I looked into that and it moves freely and returns fine. Even advanced the timing to see if that would help but it didn't. Also of note, riding it when you start to crack the throttle in 1st its not firing evenly and smoothly and it's a little sluggish till it hits 2k and then it pulls pretty hard. Also when you are pushing at 3k, you can feel it pull a little and then stop, pull a little and then stop.

I've got the jets and needle to go bone stock if I have to but I dont think that needle is gonna work.
Truly scratching my head on this one and im at the point to where if you point at a rock and say look under that I will. Thanks in advance for any help you can send my way
Once you crack the throttle open, the carb mixture starts transitioning to the needle jet. That needle and slide control everything until you start getting to WOT where it is all main jet. So, you can change pilot and main jets all day and not fix the issue you have right now. The problem you describe is a mid-range fueling issue. Regardless of the needle you have in the carbs right now, the fact you can't get past 3000rpm is most likely because your slides are not lifting properly.

If you are running those cone pods directly off of the carb bodies, try removing them and just do a test run to see if your mid-range performance improves. The cheap pods block the critical air passage to the underside of the slide diaphragms if they are mounted directly on the carb and will cause this issue. If taking the pods off of the carbs doesn't do anything, then check your diaphragms again for pin holes and tears and make sure the slides operate smoothly in the bores.

Aftermarket needles are probably going to be an issue at some point (The shape of the ones that come in rebuild kits I have seen are really not what this bike will need), but take care of the slide lifting problem first.
Here's the setup I'm running now, stock air system. Wanted to get a baseline so I eliminated all potential problems. I did the light test with the diaphragms to look for tears and holes and they checked out fine. Slides move up and down fairly easily and smoothly. Mix screws are out 3 turns on the right 2.5 on the left. Maybe I need to fiddle with the mix a little. Truly a head scratcher
Dumb question, but how is compression on each cylinder? Also a quick and dirty operational check on the diaphragms you can do is to blow a little compressed air into the ports circled below:
Carb Intake.JPG

If everything is okay, you will see the slides lift.
I havent checked the compression with a gauge as I would have to buy but I've kick started it from cold conditions and hot conditions and you really have to bow up on it to kick it over.
I havent blown air into it but I just did a drop test with some Teflon tape and my thumb. Pushed them up and covered the hole, both gradually return home. One a little faster than the other. I guess I need to look a little closer at the diaphragms.
Oh I did just blow some air into it and they rise up and stay wherever they are if you blow consistently
Oh and does anyone know if the 4ohm single output coils off of mikes xs are a good replacement? I'm thinking this carb problem might actually be an ignition problem
Gotcha. So as I understand it regulator has three wires, green to ground, black from power source and red black is sensing wire. How does that translate down to 2 wires?
The ground from the bike goes to the metal body of the regulator (it would have been bolted to a metal inner fender on the old Dodge cars/trucks that used these). I'll have to double check mine for you but it was pretty easy to wire up.
Oh I see thats pretty straight forward. I got a question a little off topic but when you measure the resistance of the ignition coils, you do that by isolating coil from the harness and test resistance on orange wire and the red wire with the white stripe?


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Dumb question, but how is compression on each cylinder? Also a quick and dirty operational check on the diaphragms you can do is to blow a little compressed air into the ports circled below:
View attachment 38466
If everything is okay, you will see the slides lift.
Got the tool to check compression, ~145 on both sides. Number was taken on cold bike choke all the way out and throttle wide open. Manual says to take reading when warm so when I put everything together and give it a spin I will take it again just figured it would be good to have a cold number to compare to
Hey tsitdham, have you installed a gauge that measures voltage in real time when you ride? If so where did you find that?
Yes, I found one off Amazon pretty cheap along with a universal handle bar clamp mount. Wired it to the battery with a small 5 amp inline fuse and grounded to the screw mounting on the clamp.


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Alright so I wrenched on it all week and and have some things to share.
After swapping some jets and needles and doing lots of plug chops I found a combo that got me stoic and pretty dialed in. Still breaks up at 3-3.5k rpm though. Went through the valve timing and it was good. Ignition timing was a little retarded at static so advanced and found that I couldn't advance enough. Plate maxed out so am I wrong in thinking that maybe the cam shaft is a tooth or 2 off? When i got the strobe on it, it showed retarded timing at idle and at 3k. How many degrees of advance at that range? 10?

Anyways replaced coils, plug wires and caps to eliminate weak spark as a condition. Capt chrome you think its the diaphragms not raising correctly, would a bent needle do that? The drop test looked alright, not stellar but not terrible. Also checked compression on warm motor and ended with 150 on the left and 145 on the right. Kinda at a loss outside if thinking the cam chain might need to move a tooth or 2. If the diaphragms are a thing I know there's a supplier for them but I cant remember off the top if my head.

Any ideas on this one guys?
Oh a friend of mine also mentioned that maybe the points were too worn and were causing the issue, is that a possibility?
I'm still chasing this thing like a dog. Got a carb rebuild kit from nichecycle that had the y264 needle that I've read is a decent replacement so no more bent needle. Also their rebuild kit actually came with correct components for yesr model. I think with this i can take carbs, compression and air off the table as potential problems.

I think this problem is coming from the regulator, the old one charges but not very well so I purchased the transpo c8313 which arrived today. I did a little research and it seems that green wire goes to field coil, so the sensing wire in this case. The other blue wire goes to ign according to manufacturer so I am guessing this is the wire that feeds current to battery. Ground from bike goes to body of regulator, does this sound correct Tstidham?
That does sound correct and for mounting it, I unbolted the fuse box and slid it into the void below, drilled two holes through plastic splash guard and through bolted it using one of the bolts to attach the ground wire.
Alright cool I'll get that installed this afternoon. As far as mounting it is concerned I'll probably have to get a little creative because it appears previous owner has lowered the rear end or put a larger rear tire on. Tstidham, did you turn the pot in the regulator all the way down before firing up/is there a risk to frying electronics if it overloads or is the charging system pretty robust?