Engine Trouble Quick question CNC “Racing Heads”.

[Carl Walichnowski]

I suppose you could take the bowl off the carb and test the fuel inlet (into a cup) by gently pushing the tangs upwards to open the valve. I wouldn't be able to tell you what the ideal rate of flow is, but obviously more is better than a drip. Check it shuts off properly too, of course.
And you have presumably already made sure there's no vacuum being created in the tank by a cap that seals too well?

I did wonder about the gas cap but since I switched it from another frame I didn't think that would play an issue. I switched the gas/oil since the MB sat for a whole year. Maybe the new filter is also playing a part with the fuel not flowing freely. Even though the fuel fills the 1st part of the hose I still need to check the petcock. I figured since I was able to blow fuel to the carb that temporaily elimitated that as a possible issue.

 

[Carl Walichnowski]

Take the gas cap off, hit the tickle button under the idle screw about 10 times real quick, and see if it fires up and keeps running without the cap on. If so the cap is defective. Rarely does this happen, but it does happen. I really need to look back through all your symptoms. If you get the chance to write down what has happened and has been checked or changed since it was last running well in order and how you checked then it will help. Things like "I figure the electrical is ok" doesn't work. It has to be "I checked for spark and it was good". Sometimes you can even have spark when testing but after a short ride the CDI stops working right and starts running like crap and dies. Things can be tricky.

Ok here's a run down of what's been going on with the MB.
I originally had the Grubee Skyhawk 66cc motor on a Schwinn Cruiser that had spring forks and horrible brakes. The engine was running good though. After deciding to switch to a Mongoose Mac for disc braking and better shocks I also dedcided to upgrade the pipe and got an expansion chamber (from MZ parts on eBay I think) . I also purchased the aftermarket CNC Head.
When torquing down my new head two of the threads in the jug were stripped so I held off on the new head and the stock head had the bike cruising along at 28 mph. While the jug threads were stripped I was riding and I was involved in an auto accident putting me and the MB out of commission for a year.
So the Mac was destroyed. Mongoose has the best warranty dept and they sent me out a whole new frame. So I paid someone else to rethread the jug and switch the kit over once again to the new Mac. So the guy I paid is a brother in law and he says he has the bike running and gets my kid to pick it up.
He tells the kid that it's running but stalls while stopping so the idle screw is pretty far in. I get the MB and take it for a test ride and within 1\4 mile or so it dies while stopping...... and the troubleshooting has begun. When I drove the MB for that 1/4 mile that was with the CNC head. I have since changed the carb to a new one, got new gas line and filter, new spark plug, changed the gas\oil., rewired and replaced the connectors on the electrical, did a visual spark test and I seen a nice spark when cranking the wheel. I also put the stock head back on and I'm using copper gaskets, a medium out of the 3 or 4 I bought. My next move is to clean the petcock out and if possible do a compression test, besides that I'm lost.

 

[gary55]

What a s**t storm of bad luck. If the compression comes in good which I believe it will, then with having good spark the alternatives are, 1. Starved for fuel, 2. a possible though unlikely blown crank seal, 3. a s**t CDI throwing off the timing. 4. a magneto that has a intermittent short. I'm at a bit of a loss too. I wish I had it in front of me. Nothing is making since to me cause it ran well for 1/4 mile then went south. I'm leaning toward a s**t CDI.

 

[Carl Walichnowski]

Regarding the starved for fuel possibility, how do I troubleshoot that and fix the potential problem? I do have a new cdi and magneto so I can switch that out asap too.

 

[gary55]

Open the petcock for a minute, turn it off, take the bowl off the carb and see if it has fuel in it. You could also turn the fuel on with no bowl and operate the tangs to see if the float needle is working properly.

 

[Frankenstein]

How old is the exhaust? Did you check it for carbon build up? Remember having all worlds of trouble getting the bike started for maybe almost a week, think when it came to the point I was going to remove the engine pulling the exhaust revealed that dirty little secret... Of course it would be good to wait until you have a gasket, but you can even try starting without a muffler and see if that changes anything.

Another oddball is the air filter, the kind the delorto clone uses can get saturated with oil when some gets spit back up the intake, if it is soaked the bike wont want to go, carb cleaner (or swishing it around in fresh gas before adding oil to it, which is cheaper and doesnt make your hands burn) takes care of it.

 

[Frankenstein]

And come to think of it you might be able to stick your pinky in the exhaust port with the head off, you may be able to gauge a problem if it's there.

 

[Carl Walichnowski]

Open the petcock for a minute, turn it off, take the bowl off the carb and see if it has fuel in it. You could also turn the fuel on with no bowl and operate the tangs to see if the float needle is working properly.

Great Suggestion, working on the MB this weekend.

 

[Carl Walichnowski]

And come to think of it you might be able to stick your pinky in the exhaust port with the head off, you may be able to gauge a problem if it's there.

Well the expansion chamber is basically brand new, about 25 total miles of useage., it's super clean as is the Airfilter, that and the carb are new.