Starting issue after build

[agent laraby]

Hi so i have done full rebuild on one of my xs360 motors and it just isn't firing with the choke on and actually tries to start with the choke OFF.
so here the is list of the pot build tune up and and things I have checked to cut down on specualtion

full rebuild new valves cut in, new rings pistons, big end, etdc rebore at .75 155 psi cold compression test both pots so the re is no compression issues
valve clearances set to spec and re checked on LT and RT
timing chain cog and cam spigot set to 12:00 o'clock (lobes down )
condenser tested and in spec
Coils tested and in spec primary and secondary.
reasonably new contacts cleaned and gapped to spec
Static timing bang on on LF and RF
fresh fuel direct from container with vacuum line capped as well as carb boot cap on So not running petcock (which was recently replaced any way)
Stock position stock jets with stock boxes.
Float height set set to manual specs
Tried two sets of carbs with no change so doubt its carbs, carbs ultrasonically cleaned as well.
coil to points leads checked for correct firing order.
bike bike ran prior to rebuild but had clutch bearing that went after rebuild that screwed a fresh rebuild so this is rebuild #2
Battery is new

So thought I would ask here as it seems to have got me scratching my head more than normal
I'm definitely missing something it seems like timing as I think fuel can be ruled put after running 2 sets of cleaned carbs with stock jets.

Any thought form the XS400 hive mind would be greatly appreciated

 

[agent laraby]

OK, after writing all that down, I had a thought, if the bike is trying to start with no choke but the carb circuit isn't over rich (i know the xs360 carbs run rich but not so they wont run...) as it's just set up stock it must be firing in the wrong part of the stroke, it it smelt rich and plugs were wet, plugs had good spark, so I moved the points plate to see if that got it to fire. With the points plate rotated all the way to the right fired up on full choke idled at 900-1000 rpm.
So my thoughts are clearly the timing is out I'm thinking that I am 1/2 a tooth/link out on the cam sprocket, but that seems weird as at L TDC the valves are spot on. will have another look tomorrow with a fresh head. Has any one had one of the SOHC models a tooth out?

 

[xschris]

Check it running with a strobe on it. Maybe the ATU is sticking or the springs are bad. Just some ideas.

 

[amc49]

Assumptions that 'they all run rich' are the kind that get people in trouble all day long. No engine is set up 'rich'; it kills gas mileage and early damages engines and the OEMs spend millions to get the mixture right. Most engines that appear to be rich are actually having carb troubles or engine wetting out from leaking oil like valve seals. Or somebody has been messing them up. I have worked hundreds of new engines both car and bike and if you can't get to light tan or grey on the plugs pretty quick you have messed things up.

Beyond that, plugs wet scream it flooded and maybe the carbs overflowed, I hear that design does it to leak internally. That and not wanting choke both say carb issue. Thinking that just because the carbs were sonically cleaned therefore they MUST be clean is even more misplaced. It may well mean nothing. People grasp at that while not knowing that every single carb passage is 100% clean and open and how so many mishaps come into being. If you are not good enough to know what every single passage and hole in a carb does then you are not good enough to say it isn't the carbs.

More trouble at the cam, if the chain(s) are not new you often have to make a decision one way or the other to intentionally seem to mistime the cam or cams as they may well be off a 1/2 tooth and you need to install them to have cam slightly retarded instead of advanced as that is what they do when worn. That commonly leads to cam being off one tooth when the wrong direction is chosen.

Turning the point plate 'all the way' is incompetent. The timing was claimed to be 'on' so why are we making things worse by changing it? Go the wrong way and you instantly wet the plugs out and what causes all the rest of the misery, trying to start a wetted plug engine is the height of how you mess things up to be intolerable.

On a points ignition you simply DON'T set point gap using feeler gauges, most can't and then both sides vary wildly in dwell and then the plug or plugs foul very quick. I use a car dwell meter to set them and no other way is acceptable, to me anyway.

If it doesn't crank up and run almost perfectly right off the bat you have done something wrong. The physics always repeat and I haven't had an engine not start up and run right in so long I don't know what I would do if it did happen.

WET PLUGS mimic both slow timing ignition and cams, when they are wet the burn slows way down to act like other issues, they will drive you nuts if you do not recognize the problem pretty quick as you then mess everything else up second guessing chasing a problem that may not even exist. .

 

[amc49]

'.....it must be firing in the wrong part of the stroke, it it smelt rich and plugs were wet, plugs had good spark, so I moved the points plate to see if that got it to fire. With the points plate rotated all the way to the right fired up on full choke idled at 900-1000 rpm.'

I rest my case.

Now lost, the timing is wildly off but we think it must be right because it's running. Best way to hole brand new pistons there is.

Not trying to be mean at all but it is what it is.

 

[agent laraby]

Thanks Chris
ATU is on the locator and the points cam is set in the right location
Re strobe, yep usually the gun on it after I set the static firing and get it running bit dubious about it running while the timing is so off

AMC49 thanks for you input
I know something is not right that's why I asked ..... when ever I rebuild a motor it is usually fine tuning with fuel curcuits and minor ignition timing if any and have done heads and rebuild on these before with instant starting once the the carrbies were primed.

I'm not assuming it's right to ride on the current timing with the plate at the first point on it's range it just used as diagnostic to confirms to me that timing could be out. I won't be running it till I sort it. Again that's why I am asking..so I can correct it.

Regarding fuel
My first assumption was to rule out fuel....
Two sets of carbs tested yesterday and now a third set that were all professionally cleaned with the exact same result ( they also ran fine on my other motor ) I know that it's totally important to rule out carbs being over rich for lots of reasons other than getting the tunning right, Fouling plugs wash down on rings,build up under valve seats, consumption, etc etc.
I don't see my self as an expert but all of my bikes run BS34 variants and I understand the fuel curcuits and have no problem tuning them. Yes these models can leak but they are fully rebuilt and floats set to manual.
For the record the xs360 bs34 runs slightly rich and my statement is just acknowledging that it seems too rich even out side the "standard" range. (Which I usually address through colour tune. I just start every rebuild with stock everyting.

Like I said I appreciate your input on being fuel but I don't think two sets of carbs both professionally cleaned that run perfectly on my other motor means fuel is the problem. Plus I just tried a 3rd set I got from XS Chris that have sat cleaned since purchase in dry storage this morning and no difference. Ps all carbs were rebuilt, and I check diaphragm and inspect jets before installing.jets are removed for cleaning sesperately. Float heights on all sets are set to manual and float tested. I really don't think it's an issue with the carbs.

Cam chain is new so it seems odd that its of 1/ 2 a tooth off
Investigating the cam and other timing is a reasonable approach for me ask about others who have had the same issue given the likelihood that two (now 3 ) sets of cleaned, inspected and tested carbs produce the same results. I think I would waste more time pissing around with carbs.
So I will continue to investigate the timing.
I usually gap points to set them and TBH have never had a problem most if the cars Ian's bikes I restore run points but I will look into a dwell meter. Both cylinders fire evenly when the plate is moved to Point where it fires so I don tg think they are too wacky but a dwell meter will be good to get it being on.

I don't think you are mean, I'm sure many people would find your communication patronising.
Personally I don't really care TBH how people communicate on forums. I will just evaluate your technical input in relation to the evidence I have at hand. And I appreciate you taking the time to share your thoughts.

 

[amc49]

'...that run perfectly on my other motor...'

Tell us that to begin with, or maybe I missed it. I'm gruff but you can live with me. (No not that way)

You guys need to put it into your tuning books that ALL CV carbs open slides fastest slightly lean. Look up what the term 'lean best horsepower' means. It is the point at which the engine makes the most power to also draw hardest on a CV slide to open it with no delay, delay on CVs is bad, it automatically goes rich as the slide opening slower has lost timing to be open a bit less to increase vacuum on the metering point. Why they seem to go rich. So, usually them being 'rich' means your engine is off slightly. Been through it a thousand times on CVs on DOHC Honda fours which are MUCH harder to get right as they do not have positive seal rubber diaphragms on them like these. Lean best horsepower is dangerous, you are very close to melting the engine there and why most carbs run a little bit richer but if CV then the slide slows down opening rate. A tradeoff but if you are racing you melt the motor to beat the other guy.

Use a dwell meter to set point gaps and you will find out real quick how much variance you can get setting and resetting the same point set over and over as carefully as you can. Sometimes you will be close but lots of time not.

Bear in mind on cam timing even the slop in sprocket bolt holes can throw you off 5 degrees.

 

[agent laraby]

All good, I Learn from gruff people and less gruff people alike.
Yeah did mention I several functioning sets of carbs, you just assumed I assumed they were good, like I say all good.
I will be back at it in couple in days and will take the rocker box off and have a look. I have obviously missed something.

I also checked the rotor assembly to make sure the woodruff hadn't come out of the locator on the shaft which I have known to happen with these giving false readings LT/ TDC readings.

You might be right something secondary contributing to the cam timing like the cam sprocket locator holes.

 

[amc49]

I've done enough DIY aid to pick up on the fact that most people do not know what good means as far as battery, alternator, carbs, etc. Also loads of it when I did garage work. You simply have to assume they do not know and them claiming to (don't take that personal) usually means they know even less. You just got caught in the percentages, It's always about them. Why long ago I threw all caution to the winds and simply assumed they know nothing. It saves time but frays other people's nerves a lot. Not my problem, if they want a fix they have to put up with it. So many forget the help is FREE and try to act like they are paying for it in the way they treat you. I don't have a high tolerance for that.

Why my favorite saying is that you have to fix the driver first, then fixing the vehicle becomes so much easier. It's not a real good get along with people viewpoint but it jumped me up and over others so many times in my work history you won't believe it. Bosses love those that go right to the core of problems to fix them quick rather than play footsies with people's feelings. Of course I got the lectures on how I have no tact, but they usually came with raises.