Engine Barely Runs

I have poured though many posts but didn’t find a clear answer, I need a more experienced opinion.

My engine was running great when I last rode it a month ago and sheared the already upgraded rear mounting bolts. I decided to use that as an excuse to upgrade to the SPB shift kit. And I used buying the shift kit as the excuse to buy a nicer gas tank. I installed the shift kit and the tank and found much to my dismay; I can’t get the booger to run. I am getting spark so that doesn’t look like the problem. Fuel is new and fresh from the pump that day.

My replacement gallon and a half tank didn’t come with a gas cap so I added some gasket material to the original tank cap to make it fit till the new one arrives from eBay. I considered that my homemade temporary cap might not allow it to vent but that doesn’t seem to be an issue because the cap wobbles and isn’t anything near airtight. I removed the cap while letting the fuel line flow into a catch tank and didn’t see any difference with the cap on or off.

It’s a 67 cc from Spooky Tooth with the CNS carb upgrade that worked flawlessly when I last rode it. With the shift kit I have to pedal the engine directly to start but I wasn’t able to get it to turn over. I did adjust the clutch to make sure that I was losing any effort due to clutch slip.

After a good 45 minutes of combined effort over several attempts I swapped the carb out back to the original carb that came with the kit. With the original I was able to get it to turn over a few times and run at low rpm’s. It looked like it was blowing smoke out at the head gasket so I tightened it. I can occasionally get it to run at say 1000-1500 rpm if I give it too much gas it stalls, too little and it also stalls.

So here is what I’m thinking, if both carbs were working fine when last used, both didn’t go bad at the same time. Fuel /oil mix and spark are not issues. The exhaust is a SBP expansion exhaust and it worked great when I last rode it. Other than the possibility that the intake manifold or exhaust pipe had something fall into them while they were on the work bench that is blocking the airflow, I am totally stumped.

I plan on taking the intake and exhaust off tonight to see if it could be that simple. But I kind of doubt it. Any suggestions?

sounds like an air leak or maybe the crankcase is flooded, frank

oops forgot check the plug to see if its wet, if so flooded

Hmmm. I did not check to see if the plug was wet. Thanks. I will check it tonight. But do you think both carbs would do that?

ya if you didnt fire right away your crankcase can get lots of oil in it. check the plug it may take a while to run the oil and fuel out and dry it up

Prof Fate,

It may be a combination of things:

Make sure that you have the deraileur, planetary hub, nuvinci...etc. in low gear. Pedal as fast as you can before releasing the clutch so that you are cranking the engine and not also propelling yourself at the same time.

This way you can spin the engine over quickly and, when it does fire, it will be in a gear that will allow the engine to rev.

As Frank said...it may be flooded at this point. Clear it out and try it again. To clear the engine: shut off the fuel, remove the spark plug, prop the frame up so that the rear wheel clears the ground, stand beside the bike and postion the pedal so that you can give a good kick downward to spin the engine. do this 1/2 dozen times with the throttle closed and the engine should be ready to fire again.

Clean or replace the plug. Hope this helps.

Jim

I tried starting it again last night and the plug isn’t wet so it doesn’t appear to be flooding. I checked and replaced the intake manifold gasket.
Jim your technique to start with the shift kit sounds like it’ll have a much better chance of starting than a power down stoke, sort of like a kick start on a motorcycle, which I had been doing. After the initial hard down stoke I had already found that by pedaling like manic it would sometimes start – again with the low rpm problem. Pedaling hard and then dumping the clutch will definitely be an improvement.

My next step is to try taking the kill switch out of the equation by wiring black to black and blue to blue.

I have read in other posts that sometimes you can get a spark to the plug when its outside the engine but when the plug is installed it doesn’t fire properly. Is there any way to identify a bad or weak spark other than replacing the CDI or magneto?

I think it's got to be the CDI or the magneto, so I'll have to order them.
Yet another weekend when I can't ride.

WOW-I would have thought that the same parts would be roughly equally priced at different vendors but the first place I checked wanted to charge over 2 1/2 times the cost of another.
For what has to be the same part? Again- WOW!:

The new CDI and Magneto arrived before lunch and were installed with much anticipation. Nooope. Not them. Off in search of a plug. With the amount of time I (several calls today without any luck) that will put in to find a usable plug locally I probably could have ordered it online and have it in my hand about the same time.
My bike looks great but will not run. Man that’s frustrating.

You may want to take the bowl off the carb and see if the float is stuck. It really sounds more like a fuel issue then a spark issue, either not getting enough gas or not getting enough air. Have you tried starting it with the choke open?