Intermittent No Start

Hello, I think this is my first time posting. My friend and I like building and riding motorbikes. Right now I am on my 4th one. The first 3 went fine. We have been using the Raw 66cc slanted engines. This bike I am working on now was working just fine until a few days ago. There is probably only 20 or so miles on it. I am using ~80:1 Chevron 87:Opti-2, NGK B6L spark plug, larger fuel filter, black fuel vapor hose instead of the clear stuff, and I made sure everything was nice and tight. Head bolts were gradually tightened in an X pattern to 12 ft. lbs. Lock Tite was used on all the usual fasteners, except the magneto - haven't done those yet.

I don't know what is going on with it. I don't see any leaks. The bike rolls free with the clutch disengaged and the back wheel skids once the clutch is engaged. The exhaust muffler is unrestricted, same as the intake. All wires are secure and taped off where metal is showing.

At first I thought it could be a fuel delivery problem like a stuck closed jet or something. But I opened the line and pumped the primer and sure enough it flowed into the bowl. So I know it gets air and fuel. When it does run, it runs strong and fast. Sometimes. Other times it ranges from weak to strong. I just can't explain it.

I measured the resistance of the wires and it was only very slightly higher than what the manual says. I don't see how it would matter since it runs strong as **** when it wants to.

One piece of advice I can stand by is never use any tools to screw on the cap of the throttle to the carb. You might warp the slide's cylinder and the slide will get stuck. Very cheap material we are dealing with here.

Something I would like to have is a washer type wire connector for the green ground wire that could actually fit on an exhaust stud or a splash guard screw. Right now I am just using a bent U-type connector on the exhaust stud. But I think it only matters while using the kill switch anyway. Haven't had this problem with my other 3 builds. I wouldn't have been able to get as far as I have without this site. I have learned a lot already.

It just seems like I am striking out right and left lately. ****, I just got turned down for food stamps because I am in college full time. I guess they figure I can get financial aid for that. Well I already spent that on engine kits and supplies. School is almost out, can't they cut a guy some slack?

Thanks for your input,
Pat

Sorry I didn't say the circumstances regarding the skid, yes, that is when i am rolling it, not riding it. The piston moves fine, the plug is fine. The old plug was fine, but I am using a new one now anyway. OK more on the fuel delivery now. Well I tried 3 different carburetors because I didn't see the filter filling up with fuel like it should. At least part way, in my experience. I would remove the line from the carb and fuel would flow. I tried the stock and my larger fuel filters. No difference. If the jet was clogged/stuck, would pushing the primer let fuel in or would it not? It still has to go though the jet right? Anyway I find it hard to believe the jet on 3 different carbs would be clogged/stuck. I took each of them apart and made sure they could move.

Other than that, I have no idea if the carb is capable of providing the proper air/fuel ratio. The throttle slide moves freely up and down.

As for spark, how might one determine if it is there? Should I just wait til dark and then pull the boot and look for a spark while trying to start it?

Would needle position (throttle position) have anything to do with the bowl's ability to fill? I mean, in the past all I had to do to get that to happen was open the fuel petcock. I didn't have to open the throttle. Hmmm...

Thank you. I feel like a jackass for not searching for that. I actually tried it by just removing the wire not the plug last night and saw nothing but that's probably just cause there is lower voltage present than there would be in a car. So I'll give this a shot...

OK I read those pages, they didn't seem to help in this situation or maybe I am missing something. Well I've got a long journey to class since I'll be using public transportation. I probably won't be able to tinker with my baby til later tomorrow. I will keep trying and I will let you guys know what works.

ok i tested it, i've got spark. i even loc tited the magneto screws. i even redid the wire connectors just in case. that did nothing. then i inspected my head gasket, looked fine, short of a small amount of oil. so i cleaned it and the mating surfaces and put it back together. then magically it started. but i noticed exhaust coming out of the head gasket. so i tightened the nuts some more and fixed that problem. it would seem my $20 6 year old beam type torque wrench is a tad inaccurate. then i rode it around for a good mile or two and it just died. well no big deal i thought, i was out of gas. after putting in more gas/oil, the damn thing wouldn't start.

i opened the line and checked for flow at the end of the hose that meets the carb - nothing. i blew through the fuel filter and fuel would come out just fine. i guess the next step is - even though i just put in a new petcock a few days ago - is to check it for restrictions. well i blew from the end of the line to the tank and i could hear the air coming out in the tank. frustration is an understatement. somebody on here has got to know what is going on. am i right?

Thanks Nougat! I'll give her a go.

Took the petcock apart and cleaned it. It was leaking past the inner metal crush ring. Found out the female threads of one of the screw holes were stripped. Replaced screw with a coarser threaded copper screw. Fixed that problem for the most part. Still didn't fix my motor not running sometimes problem.

Found out my right side crank seal is busted. I don't know for sure but I am guessing the red grease I put where the gears mesh led to its demise. Funny though, the other 3 builds haven't had this problem. I understand these are really crappy materials though. Should I have them swap me for another motor or should I find a seal and replace it myself? No cash right now. Not sure if Raw charges for shipping on returns yet. About to give them a call.

Thanks dude, I called Raw and told them about it. They are sending me a new seal (crappy seal). After thinking about it, I think this seal actually busted from inside, from the blowby. See, the first 3 bikes I did used normal 2 stroke oil. 32:1. This bike of course, uses the Opti-2, ~80:1. What do I notice about this bike that is different? Much better power. Higher top speed. Since the seals ARE crappy, and I loaded the geartrains in my previous bikes with grease just the same as this one, I am thinking my seal blew due to the extra crankcase pressure that must be present in this bike.

So, now I just have to figure out how to remove the crank gear to get to the seal. Do they make a screwdriver that fits that sucker? I'm thinking about using/possibly modifying a chisel to tackle that one. Time to search again.

Thanks a lot, that steers me in the right direction. Been busy lately so I haven't had a chance to get around to it yet but I plan on it today or tomorrow.

Worked like a charm. Well I just used the world's biggest flathead screwdriver to get the gear screw out but other than that. And of course I shoved a fat pencil in between the two gears to stop them from turning. Had to sharpen and bend what's left of my ice pick. Seems like it did the trick, starts right up now. The fuel still didn't want to come through the line at first, but i sucked on the end for a fraction of a second and then it started flowing. I added some regular 2 stroke oil to the mix so I don't have quite as much seal busting power available.

Interesting. Now that I think about it that makes sense. If the piston rings are loose enough to allow lower lubrication, then they should allow matter to flow the other way, should pressure build. Yeah these kits come with the cheapest materials available, is my best guess.