Help or advice with this 1977 xs400 project's engine?

[dan warr]

Hi guy's,

Haven't posted in a while, been off doing house upgrades so haven't had much time to play with the bike until today.

New standard size piston rings came from the USA, and got them installed and bores slightly honed. Ring gaps and Clearance's are loads better now!
Top end then put back together exact to the book.

Turning the engine over now can feel way better compression, although haven't tested it with a comp tester as cant seem to think where i've left it
guess it'll turn up in the end, but its definitely a step forward anyway

Bike farts a bit now with some easy start but keeps backfiring it out of the carbs?

Further investigation obviously needed.

Full set up with points adjustment to make sure they're still good.
Still couldn't get it to fire on the correct stroke for each side, and their wasn't enough adjustment on the points plate to rotate it enough.
It was sparking on the first compression stroke, when the inlet valve opens, when really it should be sparking on the second compression stroke just before the exhaust valve opens.

Definitely know the cam way the right way up as i checked, double checked, and triple checked it all before i put it back.

After wracking my brains about if i'd somehow gotten the cam in 180 degrees off even with all my checking, decided to take the points off and double check the little cam pin from the outside without taking the engine top off, to match up with the LT mark and what the valves are doing.

Found out the reason why it was firing on the wrong comp stroke. the little end sleeve which goes on the end of the cam at the points, which determines when the points open or close, was 180 degree out, making it fire on the intake stroke.
When i'd been setting the cam up i hadn't fully stripped it before and just left that end bit on to save time and as thought it wasn't necessary. Just shows you, always do a thorough job of it.

So went about setting the points up again, much better this time, both sides firing when they should on the LF & RF marks on 2nd comp stroke before exhaust valve opens.

Time to try and kick her over. Which resulted in the bike wanting to start and getting a constant backfiring and coughing (now coming out of the exhaust end, as should be).

So big improvement but still not a runner.

LH side is coughing continuously but RH side is lacking behind a bit. Checking the RH plug shows its a bit dry and maybe not getting much fuel.

Carb bowls are full with petrol, so fuel line in is ok. Had the carbs apart loads and their looking in the best shape they've been (especially after the lemon juice boil down)with best bits out of both these and the donor carbs. So carbs should be good?
Unless i've got adjustments wrong somewhere.

Think float height was set to 31mm ish on both sides (as book says 32 +/-1), and not sure about the mixture screws how many times they were wound out? Any tips on what they should be maybe.

Only other thing I can think of doing for now is maybe swapping the coil wires over, the orange and grey ones to see if that makes a difference?

Other than that it must be just fine tuning with the timing, or carb adjustment issue????

Any ideas guy's?????

 

[Arclight88]

Hi there, and I wish you all the best on the build. It is good to hear that compression seems better with the new rings. It sounds like the carb settings or carb cleanliness may be the issue. There are some great threads on this site that are very detailed on how to clean and adjust the carbs.

I went through a total first time rebuild last year and appreciate your situation. Just take your time and work through the manual posted on this site.

 

[dan warr]

Hi, thanks Arclight88.
Rebuilds been fun, just a pain when you get stuck with something's.

Yea thinking carbs could be the issue as with the RH side not getting enough petrol.
Guess its just another strip down and clean again. Thought I had it pretty well sorted when I boiled them as got a load of muck floating about in the water afterwards. Repeat, repeat and repeat again, lol.

Other than stripping down and cleaning the carbs again, which ill probably get round to today or tomorrow, has anyone else get any experience or advice on other thinks I could check or alter?

Cheers

 

[dan warr]

Rite update guy's.

Checked compression, got 50 on both sides dry, and 75 both sides wet. Seem to have done worse to it by changing the rings even though the gaps measured better and fitted better in the barrels? Unless my comp tester has packed up on me? Tested with & without choke & with throttle full open and closed, still no good?

Now here's a twist for you tho. Have a few other bits spare such as tanks and seat, etc, but also have a set of xs250 carbs, dirty looking as owt, but out of curiosity decides to try them, as was getting it firing with the 400 carbs on but wouldn't start.
So 250 carbs on, wasn't liking it much with the electric start but was firing a bit, switched to kick starting, 3 rd kick it jumps into life, and is revving high on idle, after a bit of adjustment I've got it ticking over nicely and will rev up smooth as anything no back firing or anything?

Should this work? Or could it be a combination of low compression (if comp tester is correct) and smaller carbs/ fuel/air intake? :\

Gonna try the 400 carbs again today since confirmed it will run, now gonna set the float heights to 26mm as many have suggested on other threads, what should I be aiming for on the air pilot mixture screws?

Cheers

 

[Philodoxo]

Ignition

I'm most certainly not the right one to give any advice. But with help from among others Drewpy and bcware, I actually got my sons ignition adjusted just perfect - and I started out with exactly the same problem as You.

Not only must the chain on the camsprocket be right. Also the contact breakers / points most be adjusted - and it is to be done in both of the two screws in every point. And then the opening-place must be set.

I started by setting the low of the to adjustment-holes on the point. I set it so close to the camshaft, that It was open long time.

Then I adjusted the top one to the right distance.

Then I turned the entire ignition-plate to open at the right time.... and then had to adjust the opening distance again.

And then to the other point - same procedure....

It was properly pure luck - but it worked !!!

My frustration and learning can be seen here: http://www.xs400.com/forum/showthread.php?t=9504

 

[dan warr]

Cheers philodoxo,

Got ignition timing set up there abouts spot on as far as I can tell. My main problem at the moment was that it was running on 250 carbs and not the 400's.
had a play today, with the 400 carbs float height set to 26mm now (rather than 31/32 as stated in Haynes) the bike will now start on the 400 carbs!!!!
Hallajeuha ! Lol

Bike runs and idles spot on, bit of tappet noise but re altered the valve gaping and cleared that up. My problem now is that when I rev up, which it does fine, it doesn't want to return and rev back down to idle. I can get it to return by either physically moving the throttle back at the carbs or by switching lights on (by switching lights on asks more of engine so revs down).???
Could this be that the main needle jet isn't seating correctly or for some reason the butterfly valves aren't shutting correctly and has a bit of resistance? As I didn't strip the butterfly assembly as with carbs off the bike, returned smoothly before?

Any ideas anyone?????

Cheers