Not firing

[pa23driver]

So i recently cleaned the carbs and put the correct jets in my 1977 BS 38's. The sizes i chose were 27.5 on the pilots and 132 on the mains. so i tried starting it, it would run for a couple seconds then quit and would not accept throttle. after a nasty back fire (blew the carb out of the boots) i decided i better check the timing (points). so i reset the point gaps after putting in new adjustment screws, and re-timed the ignition. so i try restarting it and got nothing. so i proceeded to pull the plugs and found that they were completely fuel fouled, so i bought new spark plugs and installed them, and for the hell of it tried running the bike again - nothing. so i figured it was a low battery caused by tinkering with ignition switch on too long (had no spark on new plugs), set the charger and went to bed.

messed with the bike again today, checked to see if there was spark (there was) and tried restarting the bike - nothing. rechecked the timing (dead on) and decided maybe i'm just too rich, pulled the float bowls and put in size 25 pilot jets (stock size). tried restarting and nothing, not even a rumble. pulled the plugs and they looked brand new, not a spot of carbon on them, but i could smell fuel. sprayed some starting fluid into the carbs, kicked about 20 times, got her rumbling for a few seconds until she died. pulled the plugs and they looked brand new with no carbon at all on them. decided maybe i should check valve clearences - they're within spec. and throughout this i was playing with the idle mixture going between 1/2 turn to 2 1/2 turns with no luck.

so my question is any ideas as to what is going on with this thing?

is it possible i'm really that bad at timing the ignition (static timing with a test light)?

or is it possible that the bad backfire could've done something to my carbs or engine?

any input is much appreciated

 

[retiredgentleman]

Check that there is no oil on the points. Sometimes feeler gauges can transfer oil to the points.

Correct jets for your 77 carbs are MJ #122.5............PJ #25

If you are using stock original ignition coils, I recommend you replace them with a new single coil with dual high voltage outputs. Those old coils were only putting out 10K to
13K volts when they were new. The new coils put out 30K volts or more.

You could use points to fire a single coil..................connect the 2 sets of points together in parallel and disconnect one of the condensers. A Pamco to fire the coil is another option. Mikexs coil # 17-6822 (37K output) is a good coil at a good price.

 

[5twins]

Your timing is still probably a little off. I assume you set it statically since the bike won't run and allow the use of a timing light. It can look right on by the static method but still be off when you check with a timing light. Also, if your points are used, set them towards the minimum gap as opposed to the max. Used points pit and the spark jumps between those pits. You can't measure that with a feeler gauge and the gap is actually larger than what you're measuring. Too large a point gap will make the bike hard or next to impossible to start. Used points are best set using a dwell meter.

Your jetting may be a tad rich but maybe not. Still the bike should start and run, just blacken plugs if the jetting is too fat. With those jet sizes, you should have the needles leaned a step as well. Get the timing and points gaps closer and I think she'll start.

RG's comment about oil fouled points is a good one, too. It doesn't take much to contaminate them. Clean the mating surfaces with contact cleaner or alcohol. I wipe my feeler gauge blade with cleaner too before I use it on points, then oil it back up afterward.

 

[pa23driver]

points are almost brand new, probably dont even have an hour of running time on them. I'll yank them off, check for oil contamination or pitting and give em a good cleaning.

i knocked the pilot jet back down to the #25 stock size and the main down to #125 (i do have some mods), i'll play with it more once i get the thing running as the plug was quite black before my timing apparently went to shit.

dwell angle... from the little i've read about it doesn't the engine have to be running in order to check it?

 

[5twins]

Yes, you need a running engine to use the dwell meter, just like a timing light. The dwell meter eliminates the need for a feeler gauge and hence, the possibility of contaminating the points faces.

You can clean your points in place. Cut 1/4" strips of plain white business card, dip them in solvent, and pull them through the closed points. You may need to use several strips until they pull out clean. That will clean up the contact faces for you. If it still won't fire up, try closing your gaps a little.

When I had points and used a dwell meter, correct dwell on new points would put the gap around .014". Used, pitted points usually needed a gap in the .010"-.012" range.

 

[pa23driver]

i'll give it all a shot, half tempted to ditch the points and go pamco... guess i can give it one more go

 

[retiredgentleman]

Your first post said that the engine would not accept throttle. To me, that means there is a blockage in the pilot circuit.

Make sure the pod filters are not blocking the air intake holes at the carb front entrance.

If you have good points, then changing to a Pamco trigger will not make any difference. What will make a difference is going to an ignition coil with more output voltage. Those old stock coils have weak spark.

 

[pa23driver]

ok, so i cleaned the points as 5twins recommended and set the points to around .012 instead of the .014. regapped with a clean, oil free feeler guage and double checked timing

still wouldnt kick over

checked the spark plug gaps and go figure they're at .032 instead of the .024 they're supposed to be. so i regapped and got some life out of the old girl.

left cylinder was running eratic at best, right cylinder seemed to be pumping along steadily. still wouldn't accept too much throttle and did not like the choke. couldn't get the bike above 3000 rpms. pulled the plugs and they were black and moist.

checked the restistance on the coils (both primary and secondary) and it was well within tolerances stated in the manual - they were a touch high but thats probably cuz its back to being cold outside

i stuck a screw driver in the spark plug caps, grabbed a hold of the engine and screw driver, kicked the bike over and got a pretty good jolt - so i'm pretty sure the coils are in good enough shape to have this thing atleast run.

I also do not have the pod filters on the carbs right now, so they should be running as lean as they're ever going to

any other suggestions?

 

[pa23driver]

complete shot in the dark...

would the spark plug cap make a difference? Mikes offers two different kind for the 650, would it have mattered if installed the 5k resistance one, instead of the non-resistor type? i can't remember which one i ordered

 

[5twins]

You can use either type with points. Originals were a resistor style but you may get a bit more juice through the system if you switch to non-resistor type. If you go electronic ignition, you need the resistor style. Do you still have the original caps or have you changed them? They can go bad and choke off the spark. And how about plug wires? Have you replaced those or at least trimmed some off the wire ends to get to some fresh wire?

It does sound like your ignition is getting weak. The fact that closing your plug gaps allowed it to fire up indicates that. Smaller gaps fire easier.

 

[pa23driver]

yep, new plugs and wires...

well, looks like i'm buying new coils. wanted to try everything else prior to spending more money. I'll likely go with the stock dual coil setup, just with the non-resistor type plug caps (checked the receipt and i have the 5k type). i'd like to keep everything as near to stock as possible until i decide to switch over to an electronic ignition.

Thanks everyone for the help, all input was greatly appreciated. i'll update once i get the coils installed.

 

[retiredgentleman]

If you are using stock original ignition coils, I recommend you replace them with a new single coil with dual high voltage outputs. Those old coils were only putting out 10K to
13K volts when they were new. The new coils put out 30K volts or more.

You could use points to fire a single coil..................connect the 2 sets of points together in parallel and disconnect one of the condensers. A Pamco to fire the coil is another option. Mikexs coil # 17-6822 (37K output) is a good coil at a good price.

I just cut and pasted my post (#2) from above. Replacing with new stock type coils will still only give you 10K to 13K volts...................thats weak voltage. Pamcopete has tested and recommended the #17-6822 in the past. It gives you flexibility...............can use your points (2 sets) now, and later change over to the pamco trigger if you wish.

Hope I'm not ranting on here.................good luck on whatever way you go.

 

[pa23driver]

not ranting, just getting your point across and its cool. keep in mind i don't have more than a basic understanding of how points and coils work so... i guess i'm just not understanding how it would work... with a single coil and the points connected in parallel wouldn't a point always be open not allowing the coil to do its thing?

i'm considering your single coil idea as it would make the transition to pamco cheaper later on, i just want to make sure i understand it enough so i can make it work

 

[retiredgentleman]

When using 2 sets of points connected in parallel, 1 set closes for 93 degrees and then there is a gap of 87 degrees in which both sets are open; then the other set closes for 93 degrees, followed by 87 degrees again having both sets open. The pair of points take turns firing the single coil everytime the pistons rise together. One cylinder on compression and one on exhaust stroke (lost spark method).

The TCI and the Pamco use the same method, but they may use different dwell time (time used to charge up the magnetic field around the coil)

 

[pa23driver]

thanks for the explanation, i wasn't sure that both points stayed closed long enough for the coil to generate a field. i don't mind giving it a shot especially if it saves me 40 bux down the road.