It won't start!

[matthewmosse]

Ok, an old chesnut, got good compression and valve timing now as per manual ( last owner had it out by a lot but valves survived somehow.) I've set the points as per factory manual and carbs came off a running engine on the bench. New air filter fitted, fresh fuel, good spark. tried re setting points several times. However when engine turns over it won't fire and there's air/fuel blowing back into the airbox... the compression tester shows normal compression on all 4 cylinders. Is there normally air movement in the 'wrong' direction?
this bike has it in for me at the moment...... I've run my 500/4 for years as a commuter but recent gearbox problems meant switching to a spare 550 lump from a breakers until time allows a rebuild of the original motor.

[Dave M]

Plug leads on the right plugs?

[matthewmosse]

yes they are, gessing that I'm no good at setting points............... but It should have fired at least.

[SteveD CB500K0]

Even with the points/timing out, I'd expect it to pop and fart!

You have to be systematic:

1. Is there a spark on the plug?
2. Is there fuel (are plugs wet)?

Answer those first.

[matthewmosse]

Ok the mystery deepens;- cylinders 2&3 suck air in the normal way (though weakly) and have damp plugs.
1&4 appear dryer and blow air quite stongly back thru the carbs putting lots of fuel in the airbox, like great clouds of it. The engine is something of a curiosity in itself by the way. It has no stamped number in the usual place, and a number has not been erased either, what it has instead is a silver sticker nearby which says 'honda assighned engine no.'
I'd be expecting all 4 cylinders to suck air from the carbs with equal enthusiasm, not blow air out of the inlet. Could it be possible that  I've ended up with an odd shaped crank or camshaft? the valves are all opening and closing fully. 
I've rebuilt 550 engine's in the past and never seen anything like it, Not that Ive checked if cylinders are blowing air bach thru the inlet...
Seems the engine is a bit of an odity to me. It simply isn't possible to put in any parts the wrong way appart from valve timing which I've checked. The camshaft cut out faces foreward and is flush with head top face when 1&4 tdc timing (T) mark is is lined up. However there is no knowing what a past owner may have done. Could be a case of full engine strip down........... Damn
Anyway Thanks All for the advice. Ps anyone know of the origins of an engine with no stamped number? could it be a warrantee replacement set of cases or something?

[SteveD CB500K0]

I've heard of a few 750s with blank crankcases.

If they were replaced due to damage (usually when the drive chain let go on the 750), the dealer/mechanic should have hand stamped the engine number onto the replacement cases.

It obviously didn't happen.

[florence]

If you take a length of brass wire (long enough so you can't drop it completely down the plug hole) you should be able to put it down the plug hole and as you turn the engine over gently on a spanner you can feel which direction the piston is moving.  Take off the rocker caps and watch that the inlet valve is opening as the piston goes down rather than when it is coming up.  The valve timing may look right but in fact could be 180 degrees out.  If someone has assembled it incorrectly a top end strip will sort it out.

As for the blank cases, a friend of mine bought cb350 crankcases new from david silver spares as his original ones were damaged.  The new part came without a number on it.

[matthewmosse]

Good idea, I'll give it a shot as this could explain things, Also it occors that camshaft or rockers will be a much easyer prospect to replace, I've just got a set off ebay recently, just a bit of a pain as I only got this engine to avoid spending the time cleaning up enough and then rebuildig an engine as the workshop is currently a building site as well. Such is life, I'm lucky to have a workshop at all really. Oh well, geuss I'd better set to and do, sometime or other..........
Cheers for now.
Matt

[Bryanj]

If you or somebody previous didnt use the trained spider to hold up the rockers when fitting the top cover some valves may be bent
Also cam 180 out dont matter a stuff as 1&4 rise together and spark together (as do 2&3)
What is the actual compression reading as less than 140 will make for hard starting on an engine thats been stood
how long have the carbs been stood
apart from oil peeing out there is no reason you cant do a compression check with the rocker cover off--as long as the cam is in with chain connected

[matthewmosse]

Hi, I checked compression with rocker cover on and off. I always check the oilways this way on an unknown/ rebuilt engine as the first one I rebuilt had a dodgy o ring that was too big and defrormed when cranked up and closed up the oilway, result a dropped valve, knackerd jornal bearing and camshaft, holed piston and bust con rod and a hole in the cases. all from a cheapo pattern gaskett set with dodgy sized o rings. Moral of the story:- always have a genuine set to compare against and always check oil circulation before touring Scotland and back! I agree on the cam timing comment, I'm thinking maybe someone installed a funny proflied cam. I actually tried spraying easy start up the exhaust and for the first time It tried to run! then I decided to install a new bathroom and tidy the shed! I found an engine that only needs the kickstart sorting! by the way Haynes tell us we need to split the cases to sort the kickstart mechanism. Not true! The kickstarter can be replaced with sump off and cluch cover removed. I tried and succceded! I've found a few bloomers like this in the manuals the actual reading is a bit duff on compression tester, if I believed the numbers my tester read none of my engines would ever have run but they compare well with known good motor, as in started if I breathed on the button, shame the gearbox and primary chain were worn out. When the bathroom is done I geuss the bike will get a look in

[Bryanj]

Never tried doing the kickstart through the sump, but then never had one go bad either, always took it that as the little circlip was a swine to fit with lots of space it would be even worse keyhole style.
Found out years ago that less than 140 wasnt good, on a C70 of all things---it made 115 with a shot exhaust valve but was a swine to start and had no reliable tickover, new valve 165 compression ran perfect.
Do know the pilots block for a pastime with modern petrol and standing
If you put easystart up the exhaust and it coughed are you running it backwards???

[SteveD CB500K0]

If you put easystart up the exhaust and it coughed are you running it backwards???

Is it possible to run a 4 stroke backwards?

[matthewmosse]

If a camshaft was wrong then it would be possibe but it means the exhaust and inlet cams are back to front? can this be done with a dodgy rocker box reassembly? or odd camshaft? any probability of a racing camshaft having radically altered timing? or of one twisting? I'll pull it appart when the bathroom is done(ish) and compare the various components with ones out of a runner just out of interest. I'll post my findings just out of interest. Blocked jets could be to blame for hard to start if it wern't for the clouds of fuel blowing into the airbox which created a mini fireball. One of the reasons I'm not willing to play for a while......... I'll just have to carry on using my good lady's bike until the parts arrive to indulge in my guilty secret, a kh125 2 stroke that kick started my biking career in my 'L' plate days and has been sat in the shed with a holed piston for years til I forked out the

[Bryanj]

Yes Steve it is---as any old trucker WITH A T about Gadiner diesels----Greta fun when the cab fills with exhaust smoke and the governor dont work cos its running backwards!!

[matthewmosse]

Hi, thought I'd doo an update before heading back to my cold, damp shed
Thanks to florence for the suggestion of a brass rod down the plug hole it solved at least one (bloody obvious when you think about it) problem. Doh! The advance retard mechanism looked perfectly normal, functioned fine etc. BUT when removed and closely compared to a spare it turned out to be a rouge one from godknowswhere. looked identical appart from the peg in the back is about 120 degrees out. No idea what it should be on as I've no other 4 cylinder bikes so I binned it. Just got to heliciol 3 rocker cover screws and put it back together, fingers crossed it will work!
Geuss the cam timing wasn't wrong in the first place after all! Doh!!!!!!!
Thanks All for the advice!!