no start issues after a 72 BBK installation

[Deleted]

Chris, If your engine is properly timed (crank to cam), and it does have spark, I think you are dealing with either not enough fuel or bad fuel. I am servicing a 150cc, that had not been started in a couple months. I pulled the carb, cleaned it like I do lawn equipment carbs, repaired an exhaust leak, and tried to fire it up. Wouldn't start. Small amount of ether, fired up, and ran until ether exhausted. Drained the fuel tank & carb. Replaced fuel, started up and ran nice.

Annealing:

As Niz76 said it is simply heating a single layer metal gasket until it gets not quite to the melting point. This can be done with a torch or it can be done in the hot coals in a fireplace or grill. The key is to warm it up evenly, then remove it quickly with a non thermal conductive rod and drop it on a flat cold (room temp) surface. Allow it to cool and it is ready for reuse.

It works only on single layer metal gaskets. Do NOT attempt with composite gaskets, like that one in the photo I posted.

I prepped the gasket by removing as much of the coating (black coloring) as possible by laying it on a piece of 2x6 and cautiously sanding with 240 grit paper. Then annealed in the fireplace and dropped it on a cold flat waterless cooking pan.

After that I evenly coated it with K&W's CopperCoat (spray form), allowed that dry, flipped it, coated the other side, allowed to dry and installed.

I torqued it in 3 stages with a mic style torque wrench after finger tightening the retainers.

5 ft lbs - all 6
10 ft lbs - all 6 - waited a couple minutes, and rechecked in order
15 ft lbs - 4 head nuts only - waited and rechecked again

Cylinder leak tested @ 15 psi & 175 psi and used soapy water spray around the head to cyl area watching for bubbles while at 175 psi.

NOTE: K&W's CopperCoat comes in two forms, spray and liquid. The spray form allows for a thinner more even sealant application, whereas the liquid can be applied to paper gaskets like the base gasket.

btw.. the base gasket leak was because the previous servicer had not trimmed the case half gasket and some was protruding.

[chris962]

Thanks niz76! I don't have a torch, but sounds simple enough to anneal the gasket. Thanks Bull! I think you're right, it's probably a fuel issue, so good tip, I'll drain that carburetor! I tried John's test of removing the carb and intake manifold and dribbled some fresh, premium fuel in the hole of the intake, while cranking the engine, and I got some smoke, but didn't start. On the other hand, I watched a whole bunch of videos of an ancient motorcycle, old cars, and a 1915 moped or motorcyle, some hadn't been started for years! One thing I noticed is that it took a very long time of cranking to get them to fire up! I also put 1/2 a gallon of fresh fuel in the tank a few nights ago, so too late there, but with some much fresh fuel in there and so little old fuel, there should be a good mixture, but the carburetor is another issue, so best to drain the old fuel there and prime it with fresh fuel. The other tip I found on engines that haven't been started for a while was from Matt at Rolling Wrench, who advised to pull the throttle six times before cranking the engine, so while I tried that on the 1st attempt, I didn't do that on the subsequent attempts to start it, was worried at the time that I'd flood the engine for some odd reason (fear I guess, metal shavings in the combustion chamber after 1st attempt, etc.). Anyway, I'll change the oil, drain the carb and prime it with new fuel, add some ether to the intake manifold to further prime it, the pump the throttle six times, and after a bunch of cranking, it just might fire up! 

Update:  It's a bit of a hike to where I did my BBK, but got there late and drained the carburetor, cleaned with carb cleaner the inside of the bowl, the main jet #90, and pilot jet, plus added some ether down the hole of the intake manifold. Of course I forgot I needed my 17mm socket for one of the bolts to do the oil change, so will try again tomorrow night. I also pumped the throttle 7 times before I hit the start button, but still all it did was crank. The last time I tried to start it I cranked it a lot, so think there wasn't much cranking power, maybe half a minute to a minute, before I noticed the battery dying down, but didn't have time to re-charge the battery, so took off. @ Bull, I might have said it above, but want to re-iterate that I tried for maybe 40 minutes last time I took the engine apart to get that cam timed right, but every time I put the rocker arms back on it moved slightly. I tried moving the cam a tooth and then the holes wouldn't line up perfectly, so only think there's one setting on there, so even though it moved slightly when I put the rocker arms on and a tiny bit more when I torqued all 4 bolts down, still I think the timing has to be right and checked for TDC on the piston when on the T-mark line, then locked it in place, so that's got to be right too. Btw, I took a look at that new head gasket I had and it had two opposing bigger holes, so that head gasket was probably fine, but it took me 8 hours on that 1st attempt and near the end my low back was killing me from bending over so much! Thus, I think what I may have done was put on that head gasket upside down, then was so tired that I didn't think to flip it upside down to see if the dowels fit on it. 

But, this head gasket didn't seem like it was in any better shape than the stock head gasket. Btw, a friend told me to take off the carb, then put my hand over the intake manifold, and simultaneously crank the engine and the suction was really strong there, so the air part of the equation should be fine. I just got that premium gas a few days ago, so adding 1/2 a gallon of it to very little old fuel in the tank should dilute the mixture to very good gas after draining out the old gas in the carb and cleaning it, so gas isn't the problem. Timing shouldn't be the problem either, so other than a low battery tonight and a sluggish hard to fire up engine, I can only think of one thing, I checked for spark on the 'old' NGK plug and it was fine after the 2nd attempt I think, so I had spark, then got a new NGK plug and installed that one, so spark is good outside the engine for certain, but read somewhere something about a weird situation whereby the spark is good on the spark plug test, but no spark when inside the combustion chamber. Is this a possibility for this current no-start? This scooter has me thoroughly pissed off and I just don't get it! The thing ran great before I did the BBK, so while I didn't check the piston rings after cross-threading that spark plug on the old head, I did check the crown of the piston and cleaned that and checked inside the cylinder and that was very clean and didn't need to be cleaned, so think I did a good job on installing those piston rings as I remember it was hard to compress them and simultaneously get them into the cylinder/jug, but once I did I think they formed a tight seal, plus I lubricated the sides and head of the piston. and the cylinder wall, with motorcycle oil, so really I don't think any metal shavings got into the engine case below....so this no-start is puzzling me. Of course, it can once again be something really simple, like I simply didn't have much cranking power left in the battery once I hit the start button tonight, so a couple hours on the Battery Tender Junior tomorrow night and it will have plenty of cranking power. That's the only thing left I can think of that is wrong, not enough cranking power in the battery. Why the heck is this thing harder to fire up than an ancient motorcycle from 1915? Oh yes and 'why' would the plug spark outside the engine and not in the chamber? 

[Deleted]

Spark outside but not inside is nonsense, unless the plug has a cracked insulator, thus a bad plug.

I was not familiar enough with CDI type ignition to truly comment intelligently on it, so I did some research. Here is a great video of how the Vac CDI system functions.


Pay real close attention to how the ignition power is generated by the stator and then stored in the CDI capacitor. The video producer did miss one very important point about the energy storage in the capacitor, but he is still mostly accurate. When you consider this it becomes very obvious that IF the engine is spinning too slow, either from a weak battery, excessive friction in the engine, or low ambient temps (even temps in the 50 degree F) the system can not generate enough power for a good spark inside the cylinder.

You have checked things over enough to satisfy proper testing, so why no start?

My thinking is that the ignition coil 'saturation time' is so limited that it can not produce a good enough spark like that found in a Vdc ignition system on a car with higher coil saturation times.

I have not checked the CDI output or the ignition coil saturation time @ different temps with a lab scope but that is the next step for me.

What about a conversion to a Vdc CDI system?

You still have the same coil saturation time, so most likely you will gain nothing.

So how do you get your scooter to start?

You simply need to get the engine spinning faster. You can't do anything about low ambient temps, because IF you store the scooter in a garage and drive it to work, then park outside it may not start.

Low viscosity index oil will help, but most likely not by itself. If you have a fully charged battery and a small 10amp charger hooked up to the battery you might get it to fire up. But that still doesn't guarantee that it will start when away from the charger.

I have tested this ambient temp, battery charger suggestion as I now have enough 50cc scooters to leave a couple outside- and it does happen.

If my assumptions about 'coil saturation' time is correct then some retrofit could alleviate this problem, not only for you but everyone else that experiences it.

btw.. when changing the plug, to keep it from being cross threaded, use a small piece (about 2" long) of 3/8 ID rubber hose shoved on the top of the plug as an install helper. that will provide the reach needed