G'day

Basically your starter does not have enough torque to turn the engine over hard enough. The engine is firing well before the piston gets to Top Dead Centre (TDC) and this is stopping it turning further. You may be using a bit too much Nitromethane as it tends to advance the timing of the engine or the plug may be too hot which again would advance the timing. Also, if the engine is primed slightly too little, the mixture may be slightly lean and this also will advance the timing and make it harder to start.

Back in the Dark Ages, many motor cycles had a provision to retard the ignition timing for starting but with our glow engines, the timing is set by the combination of compression ratio/nitro content/plug heat.

You need either a bigger starter or battery with higher capacity at the same voltage. You may just need to charge the battery. Or you need a cooler plug or SLIGHTLY wetter prime and/or less nitro or just some more time on the engine.

What sort of engine is it? Size?

I have found that when trying to start my larger engines - and especially when they are fairly new - that is is often easier to start them by priming them (but not flooding) then using the back flip techinque with a chicken stick. My Saito 100, 120 and 150 all needed this treatment when they were new.

Mike in Oz