All tuned and no fizzle

[Michaelo]

Check this out " cold set" below, plugs out, do the tappet clearance first, points, you can use a points file, then clean and set them don't leave any oil on the points, you can check advance mechanism when it starts (hopefully you have that sorted out now) with timing light...don't touch the carbs until you have timed the bike Aussie....

Bike wont start?, Running rough?

First: What have you just done? What have you changed? Has anything odd or different happened? Any new strange noises? Just bought it? Heard it running? Riden it? Been sitting?

- just bought it, well, don’t believe anything the PO has told you, ignore it​

- already your ride, you will already have a connection with this old girl, listen to your instinct, trust yourself? Ok…consider these anyway…​

- 3 things all motors require - power, fuel, air​

new purchase? been sitting? before you even kick it over…

- get a manual​

- check tank..rusty? empty, clean it properly, including petcocks tank cap-seal and air vent
- replace inline filter, if none put one in
- check and clean air filter, replace if necessary
- drain carbs, if the fuel stinks or smells odd, remove and clean, thoroughly…if it smells normal, you might be lucky, can be worth the chance in the short term but you wont get away with it forever
- if your inlet manifolds have vacuum barbs, check the rubber caps for cracks and fit
- if carbs are off, check the rubber intake mounts, they get hard and crack, replace with good ethanol resistant ones, don’t forget the boots connecting to the air filters, they get old and brittle too, replace if necessary carb guide
- check your throttle and clutch cables, if not teflon lined clean and lubricate, if teflon lined check they slide freely, if not replace
- while the lhs side case is off, check the clutch worm drive, don’t lose the ball bearing, clean the worm well, the worm-case can crack and expand when you pull the cable preventing proper operation, pack with grease-don’t forget the ball bearing, don’t reinstall the side-cover yet
- do a compression and or leakdown test, see below...
both cylinders should be within 10% of each other
under- 100 psi poor
100/125 psi good
125/150 psi excellent

- drain the oil, smells of petrol? the carbs have been leaking-floats are holed or not set properly or the float needle seat is compromised or the float needle o-ring is damaged, check and clean the filter screen as well
- check the oil, look for pieces of black plastic from the cam chain guide, it will need replacing, also alu pieces, normally cam chain hitting the case, sounds awful, hopefully it hasn’t reached the bearings, large bits may be 5th main gear or 3rd pinion gear dogs, crank bearing cage pieces have been found, also broken clutch primary springs
- check the suction-side sump filter, these break- oil filter thread
- check the pressure-side side filter, it can be washed, I prefer to change it
- fill with oil
- get help, bike on main stand, rotate rear wheel while going through the gears, 1 at a time, gives a feel for possible gearbox problems​

freaking yet?...dont worry, be happy…its all cheap insurance and helps you get to know your new friend, look after her and she’ll return the favour

- ready to go?..uh uh…not yet mate​

cold set

before running do a cold set..
.

- is your battery charged
- rotate engine counterclockwise to tension cam chain, adjust the tensioner so its flush, lock the backing nut...recheck when hot
- remove the lhs side-cover, bike out of gear, remove a plug, if you have a TDC finder….install it, if not, a plastic straw or knitting needle will do-put it in the hole so you can feel where the piston is, rotate the flywheel ccw, 17mm socket-for control-feeling for TDC, you will probably need to go round several times to get the feel, if you go over don’t rotate back, go around 1 more time so the tension is on the back of the chain
- now set the tappets, remove covers, rotate crank feeling for the top of the compression stroke, where both tappets are loose on the cam
- set tappets - model...inlet...exhaust

...XS1-B.....0.003"(0.076mm)...0.006"(0.15mm)
...XS2-650..0.006"(0.15mm)....0.012"(0.30mm)
...XSB........0.0024"(0.06mm)...0.004"(0.10mm)
...XSC-on...0.0024"(0.06mm)...0.006"(0.15mm)​

- rotate for the compression stroke on the other side and set those tappets too
- install new plugs, gapped, N7Y champion or BP7ES ngk ... 0.027-0.031" (0.7-0.8mm)
- if you have points, check the advance mechanism, pull the rod, clean and lubricate it, check the weights, make sure they move freely and arent loose, check the springs-the weights should snap back fully, if not shorten the springs-even better replace… video atu
- static set the points…key on, use a small 12v bulb, key off, use an ohm meter, first one set of points, then the other
- set them at the highest point of the points cam lobe 0.012-0.016" (0.30-0.40mm) against the points rubbing block
- rotate crank counterclockwise, the light or meter will show when the points open…keep in the same field of vision, next to the timing marks, easier observation, allows you to get the timing almost spot-on, recheck when running with a timing light…for greatest dwell angle set for smallest gap possible…advance with larger gaps, retard with smaller gaps
- time the rh cylinder-upper points set by rotating the complete backing plate
- time the lh cylinder-lower points set by moving the half plate only
- points opening before ‘F’ are advanced-opening early
- points opening after ‘F’ are retarded-opening late
- timed, motor running, BTDC 15° @ 1200rpm​

still wont start?

- flat battery
- this is not necessarily the carbs, its easy to waste time on them when youre really chasing an electrical problem, check for spark by rotating for closed points, open them manually-you should see the spark, a good one should be blue and about 6mm
- no spark…condenser, replace…dirty electrical connections...kill switch, coils, plug-cap-lead, TCI
- burnt points...condensor
- kicking back...atu
- weak spark…coil, leads, plug caps
- intermittent spark…broken power feed to points, check behind the points plate…coil, test when hot...broken solder connections in the TCI, resolder…dirty electrical connections, check them, clean, use dielectric grease to seal them-1 at a time​

ignition problems

- fuses, kill switch, batt terminals, ignition switch, dirty connections
- worn, burnt or pitted points
- worn points rubbing block
- points plate off centre or not seating correctly
- worn points cam
- broken points wires
- points or atu cover seals leaking
- condenser kaputt
- coil kaputt
- TCI kaputt, TCI pickup kaputt
- side stand relay-if fitted
- atu return springs too long or weak
- atu shaft not lubed or worn bearing surfaces
- atu shaft pin broken-shouldn’t rotate more than 40°​

- a very interesting site for TCI ignitions , covers this way better than i ever could

only now should you contemplate looking at your carbs, this is the second to last step, the last being synchronisation

- as far as the carb is concerned there are 4 main operating functions that affect fuel delivery at various stages... ...0-100% throttle...pilot air screw/jet , 6-50%...slide cutaway, 20-85%...needle jet/jet needle, 33-100%...main jet​

- most problems stem from blocked primary circuits, thus affect your idling, your bike wont idle when these are blocked
- fuel must come out the 3 tiny holes in the throat...use a small guitar string bent in an L to gently probe the 3 holes as you spray - cover the other holes with your fingers to increase spray pressure...when spray comes out the 3 holes they are clear​

- set the mixture screws...see the table at the end of the carb guide p 27 ...hat-tip weekendrider
- set each side at operating temps for light-black/grey 1/3 the way up the electrode
- set each side mix screw independently for plug color...rhs runs 25 degrees hotter, requires more fuel​

...these carb readings are worth the effort, esp this for the CV carbs and this for VM34-36 ... read and reread until youre dreaming the stuff

...go here for dell'orto carbs

...this isnt finished...carb syncing to follow...feel free to rip this to pieces, neither complete nor perfect...so, at it - fix it for me...i will be interested to see what you think ive done wrong

 

[AussiXS]

Awesome little cheat sheet there, cheers!

The bike now runs great, its weird but I am happy to accept it. The only issue is that it surges in First gear but nothing else, even if I change to second real early. Does anyone know how to sort that?

 

[retiredgentleman]

That surge could be due to the ATU springs not tensioned correctly. They may be too strong, so that when you first rev the engine, the fly weights don't move out in a linear fashion. When the fly weights do come out, they come out really quickly, which gives a sudden burst of power as the spark advances quickly. Over the years, owners have played with the springs, such that they are way out of the correct tension, that they had when they left the factory. I would not trust springs from Mikesxs to be any better.
New OEM springs would work, if they are available. I gave up on the ATU many years ago, and bought a Pamco E-advancer. It gives a very repeatable 100% linear advance curve, which gives a constant rate of acceleration.

 

[Bob Kelly III]

have you looked for a vaccuum leak ? I just discovered one on my '83 that has slipped by me several times from the petcock to the intake manifold on the left side.... it causes the cylender to die at idle or die completely you could be running around on 1 cylinder not 2 hense the big surge every once in a while when that other cylinder finally kicks in..... it's not a moped if it don't yank you down the street something's definately wrong
I can't say for the timing Mine has electronic stuff in it , not points.... but it do definately sound like the points are not working correctly
if you can get that beast to idle put it on it's centerstand and feel the exhaust even with a crossover pipe you should be able to tell if both cylinders are fireing real quick..... they will push air normially if its not fireing but if it's not Hot it's not working !
I knoticed on my bike that with it running on 1 cylinder it puts a strain on the engine and oil leaks appear.... get it working on both cylinders and I bet they go away ! an engine needs 4 things to run Gas, compression and ignition and ALL in the right order.
with a vaccuum leak on one side the bike will preform like you have discribed ..... it will also do the same thing with Ignition problems
which makes it hard for others to help... you need to eleminate one from the list of problems so we can help better !
other wise we have to assume that the carbs are ok for the moment and they are working ok and that there is no vaccuum leaks.
..... I like using an emery board on points to clean them up Most mechanics would gladly shoot me for saying that but I do <GRIN> a file don't get it!
you can static time your machine with a trouble light clipped to the points and slowly turn the enine over when the trouble light gets brighter they just opened and the mark should line up on the flywheel that is when the spark Happens in the spark plug..... if it's off one way or another it ain't going to run very good !
.... another way to tell if both cylinders are working is from a cold start , fire it up and quickly feel the exhaust pipes by the headder if their getting hot on both of them their working if one is hot and the other one not, only one is working ! .... get it to work !
..... my 2 coppers FW.I.W. LOL
Bob...............

 

[AussiXS]

Its funny that you mention that Bob Kelly, I did find that my air hose connected to the carb boots did come off on yesterdays ride. I'm not sure that is the problem but you never know. It was only off for the one journey but i didnt feel anything wrong. I am also hearing a tappet ratteling at hard acceceration, so I will fiddle with that and report back.

I did get new springs for the Advance units but they were not OEM, I think they aren't correct. I will do what RetiredGentlemen has said and get a Pamco, get into the 21st century, I do not want to deal with points. Which one is the best?"

 

[Bob Kelly III]

AussiXS : Can you conferm that the bike is running on both cylinders ?
or like mine running on both intermittantly ( it's dropping the left cylinder ,usually below about 2000RPM)....
I think my problem is simply Sparkplug.... when I was in the business and had my own shop In Reddng Cal. I could buy 4 NGK sparkplugs and get 1 good one !!!!..... Champ's were worse AC Were as bad as Champ's the best were NGK's but 4 to 1 ratio was horrable at best !
I am sure the quality has gotten better over the years and it's not that bad any more, but I expect a 2to1 ratio on sparkplugs ! sparkplugs just plane suk they are the weak link in the chain and can cause anything from a simple miss to not running at low or high RPM or not work at all
a good spark plug is a treasure ! ...and alwayse carry spares with you....
being a twin is better than a single when it comes to sparkplugs ! the other cylinder helps run the other side to a certain extent.
having been away from bikes for 4 years sense the big fire I do not have a large supply of sparkplugs like I used to have...
.... you can Isolate if a sparkplug is good or bad by simply swapping the sparkplug to the other cylinder..... if the miss now appears on the other side of the machine when running you found the culpret ! you can clean old spark plugs but chances are it won't help... it's best to toss them and buy 4 or 5 new ones..... one of them should be good ! ....
SPARK PLUG Gap is critical.... on the old 2 strokers you could widen the gap and get away with it... on 4 strok machines not so much... if the plug is giving you trouble you can decrease the gap and get it going again just to get home.... in my case I have tried everything I know to get that stupid plug to fire correctly.... to no avail.... it needs to be replaced !
You wouldn't think that the price of a silly sparkplug would be a show stopper but in my case it is ! it sux !
.... running rich , or burning oil is a sparkplugs DOOM..... even good plugs go bad fast ...
....another thing you might try is dump the gas out of the gastank and put in FRESH Gasoline ! this gas now days only lasts about 3 months
the gas in my tank is about 8 months old but I added a tad of 2 stroke oil to help keep it alive durring the winter.... its obviously needing to be replaced..... but my syphoning hose is now 6" shorter than it was and I dunno if I can get any out of my truck or not ! LOL
...... when you get your bike set up right as mine was at one time, you can turn on the key turn on the choke and hit the starter and it will rarely take a full revolution to be running...and it will stay running...not die.... don't touch that throttle ! its not a dirt bike ! it starts completely different !
after it has had a chance to warm up ...about a minute and a half, slowly take the choke off and let it idle a bit longer,... then touch the throttle
it should revup with no problems if it's still cold it may cough and die or cough and then grab the R's.... each bike is a bit diferent but this is what I found on mine...... its very cold blooded !
( that gas in my gastank could be 50% of my problems so tomorrow if it's not raining I will remidy that ! )
hope this helps !
Bob............

 

[Bob Kelly III]

Also with electronic ignition you widen the gap of your spark plug you run the risk of burning out something in the ignition system !
possably the ignition coil as they are weak from the factory. if anything gap your plugs accuratly a bit smaller than recomended
this will do 2 things, cool down the plug which you may or may not want..... but make it easier to start in most cases.
it will also make for smother high RPMS believe it or not....
Bob........

 

[AussiXS]

Well Bob, your advice ha she been great. I started my bike from cold and left my hands on both cylinders and the left heated up so much quicker, the problem is I swapped spark plugs and it's the same story. Any ideas on that? I also found that my vacuum hose was fitted by a moron and it was a cheap hose, it melted and sealed shut so no air could move around. I re fitted a similar hose and will get some heat proof stuff soon . With the pamco e advanced, did you get the new coils too or just get the plate and e advancer?

 

[Bob Kelly III]

Definately replace both plugs.... ( new plugs can be bad from the factory so watch it)
it sounds exactly like the problem I had and that was the pilot air screws Hidden under the cap.....
I first turned the screws out 2 1/2 turns on both carbs( they were at 3/4 from the factory !!!!)
that still was not enough I still had the one cylinder dropping.... i pulled the tank again and wound up replaceing the vaccuum line like you did as well as the gas line to the carbs ( added a small in-line fuel filter too)
and i turned them out to 3 1/2 turns..... the dropped cylinder went away..... and it started running at idle like it is supposed to
its now time to do the "dead cylinder " carb adjustment I won't repete it here its long and involved but do it or you'll probably start foweling plugs and you don't want that..... I havn't done mine yet but I will net sunny day I get !
Keep after it ..... you'll get'er going !
Bob............

 

[AussiXS]

Thanks for the help Bob! There was a sale at repco so I'll stock up on plugs. I have had those screws all the way in, when you say 2 1/2 screws that's from all the way in? I'll research the dead cylinder method and see what I can do. I got new fuel filters too, haha

 

[Bob Kelly III]

YES all the way in..... to the seats don't over tighten them or you'll hurt them,
turn them out 3 turns and try it from there... I bet both cylinders will fire at idle then !
then do the dead cylinder adjustment ... its easy but requires a small gastank hung from the handle bars.... and the vaccuum line plugged
take the plug lead off one side and put a plug in it leave the other one in the engine. clamp the spark plug to the head so it can't wiggle loose
start the engine.... adjust the pilot screw on that side for highest idle and back off the idle screw and do it again till you get the highest speed at the lowest idle..... then do the same thing to the other side....
this will get the mixture just right..... no more guessing..... then start thinking about carb syncronizing ....that needs to be done too ! there is a good section here on this site about that.
.... once you get that thing going good try not to hit any Kangroos ! eh ? lol
..... I hit a bird on my Honda 50cc once . I was rapped out doing 55 to 60mph and a dumb bird swooped down and I cought him on my forhead between the helmit and sunglasses..... i did a 360 degree spin on the seat and didn't fall off ! I had a lump on my forhead for weeks after that ! ...the bird didn't make it.... but I duck for birds now !!!!! LOL and don't ever hit a deer, the parametics don't know what pieces to pick up !!!!! its nasty !
.....
later !
Bob........

 

[Bob Kelly III]

oh, you'll probably have to go a long way in with the idle screw on the left carb just to get it to idle on the one cylinder.... hard to say sense one's not fireing now anyway..... between 3 and 4 turns out is the area you want but what ever the "dead cylinder" adjustment gives you leave it at that.
...Bob......

 

[Bob Kelly III]

My bike is really close right now , once warm its crisp on the throttle and their's no smoke at all that I can see....
the "Dead cylinder adjustment" will fine tune even that ! the idea is to get it to it's highest running RPM while keeping the idle low
and the butterflys in the carb closed, so your using the pilot curcuit only too high an RPM will start pulling fuel from the main jet and you don't want that
just keep the Idle low and fiddle with the pilot air screw till you get it at it's highest Idle RPM..... lower the idle speed and do it again to fine tune it even more..... then do the other side the same way..... it's not hard it just takes some fiddling ! LOL
Bob......

 

[650Skull]

just a cautionary note on swapping plugs from side to side as an electric diagnostic tool........................Swapping the leads will diagnose a problem up stream if the problem follows the leads............... if the problem stays the same then a plug is more likely to be the problem....Or carbs................Swapping both the plugs attached to the same leads will not necessarily help at all.

Do some research on the pilot mixture screw settings............Your carbs are BS38's and they have different recommendations for the pilot mixture screw setting to the later TCI 80-83 BS34's

 

[azman857]

Do you have a maintenance manual? Haynes, Clymer or Factory?

 

[Bob Kelly III]

Thank you Skull,.... all that time and I missed that his bike was a 78'.... Sigh ! makes a world of diference....
don't you just set the fuel/air screws to 1 1/2 on the 38's ? do you fiddle with them to get them to operate good like on the 34's ?
all the bikes I had in the past you just set them the perscribed turns out and forgot them....even on twins....
never had one ya had to adjust the airscrews to get them right ! LOL
......
Bob..........

 

[650Skull]

Bob, sometimes it is better ask questions to give the right answers.........giving answers willy nilly clutters up threads and can cause the OP to make mistakes..........If your not sure a quick search on some of the op's posts or threads will set you right...........Or in this case a read of the whole thread or precisely post #1 gives the relevant info on what the bike is in question.................

 

[Bob Kelly III]

yes sir ! duly noted..... i already knew that... sorry for the mistake !
.....
Bob.......