So your HT bicycle engine won't start, well let's take a look

[push'n'shove]

hi all, i have come here to find a solution to why my (new) engine wont start, and first of all....wow! so much valuable info here guys!....thanks!!

For the last week i have been trying to find a solution on you tube to no avail, and all the questions i have had over the week have all been answered in this thread!...... just need to clarify one thing though,.... i checked the cdi blue=black with a multimeter and got no activity ( as i saw in an earlier thread) is that normal? forgive me for being dumb but i have not a clue when it comes to electrics, .... thanks in advance

 

[crassius]

few folks have had good results trying to test CDI with a multimeter

blue to black & ground on the mag should read around 350ohms - if you have that and wiring is right, then if you hold plug in hand and hand against ground and feel nothing when you roll the bike, then CDI is bad

CDI may still make a spark that is at wrong time, but one needs a CDI tester to spot that

 

[Mossy]

You want a blue to purple spark with the plug out of the motor... Do it at night so you can see it.. a yellow spark is weak and indicator something is on its way out not connected properly or just junk to begin with...
Great thread to 'bump'...

 

[Cawater]

Chinese HT engine won’t start? Well let's see what might be the cause of your problen.

Electrical
1. Improper wiring. Black magneto wire to black CDI wire, blue magneto wire to blue CDI wire. White…either remove or isolate.
2. Kill switch defective. Do not hook it up until you get the engine running. When hooking up the wires, don’t pay attention to colors. One wire connects to the blue magneto/CDI wires; the other wire connects to the black magneto/CDI wires.
3. Defective magneto..testing All readings are approximate.
Use Low Ohm-Meter Scale 200 Ohms
Check Ohms between BLACK wire and WHITE wire. 2 Ohms
Check ohms between BLUE wire and WHITE wire. 300-400 ohms.
4. Defective CDI..testing All readings are approximate.
Use Ohm Meter High Scale About 200-K
Positive lead on BLUE wire and Negative lead on BLACK wire
infinite (no activity)
Positive lead on BLACK wire and Negative lead on BLUE wire.
130-150 K ohms
Positive lead on Spark Plug wire and negative lead on BLUE wire.
135-155K ohms
Switch to Low Scale 20K
Measure between Spark Plug wire and Black lead. 2.5 - 2.7 K ohms
Magneto and CDI testing .. credit goes to 2Door
5. Replace Spark plug (I like NGK’s plugs, number depending on your engines condition) also replace the high voltage lead from the CDI. Use a wire core lead.
6. Check for proper timing. At TDC the cut outs in the magnet will be
in the 12:00, and 6:00 position. The key will be at the 1:00 position
7. Do away with the cheap connectors on the magneto.CDI. Replace with good ones, solder them and wrap with tape or better yet heat shrink as I do.
8. Re solder the blue magneto wire. Have seen cold solder joints from the factory. I change the wire to a better grade and to a 16 gauge.

Fuel
1. Clean fuel tank, and screen filter (in the tank) out. Tanks have been known to have trash in them.
2. Install an inline fuel filter. One might not be included in the kit.
3. Carburetor piston, check for proper instillation.
4. Carburetor to intake manifold leak. An “O” ring installed can help solve this problem. Check manifold gasket.
5. Ensure that the internal components in the carburetor are installed correctly and not loose. Later you might need to adjust the needle (attached to the carburetor piston…5 different positions)
6. Ensure the float operates correctly and the needle seals off the fuel flow through the seat.
7. Tighten bowl screws.
8. Screw on the NT carburetor only adjusts the idle.

Compression
1. Blown head gasket. Mill head replace gasket
2. Broken rings. Replace rings/piston
3. Leaking seals on the crankshaft. Replace
4. Spark plug not tight or threads stripped.

Vacuum Leaks
Shouldn’t cause a no start problem, but can cause a RPM issues.

If you don't have a Volt/ohms meter, I suggest you get one. Harbor gives them away quite often. I have gotten 4 of them. One in the house/garage/5th wheel and in my truck. ALL FREE


Looking for any other causes that will lead to a NO START problem. Please don't make this a sticky till its finished...

I am trying to install an engine for a friend. He bought the engine still in the box on Facebook Marketplace.
I’ve got the engine installed and I removed the magneto cover so I can spin the engine with my electric drill. The engine will not start. I pulled the plug and grounded it to the block while I spun the engine with the drill. I’ve got spark. Also have proper gap.
I’ve dropped some gas into the plug hole, reinstalled the plug, spun the engine and still it will not start or even hit once or twice..
the plug is dry even after spinning the engine with full choke. I’ve made certain the engine is mounted with the carburetor nearby level. It seems like the engine is not pulling in anything from the carburetor. I opened up the carburetor and everything seems to be in order. The intake manifold is clear and all connections are secure. I’ve checked compression and it’s about 55psi which is low but according to a post on this site is adequate for the engine to run.

Does anyone have any suggestions?

 

[wrench]

IMO your compression is way to low it should be at least 90 - 120psi

 

[Venice Motor Bikes]

One thing to know about spinning the engine with a drill... (I'm assuming you have a 2-stroke HT engine)?
The engine spins in the OPPOSITE direction as the rear wheel!!
So, if you're spinning it off the magneto nut?, it will be turning clockwise!