Hi guys I hope some on can help

I just put a 125cc chinese engine in my sons 90cc quad. I have 2 sons 2 quads. both quads ds 90 2005 bomb/can am.

both got new 125cc engine.

Both run once started but one will not start with out me push starting it.
It starts right up with a hard push.

It runs faster than the other one to.

It cranks fast with the starter. And sometime with it on a charger it will start but its real if'y


I have
regrounded the bat
I have wd-40 and checked all 5 wire out of the stratory
checked for spark. it spark fine when i push the starter.

Other one start easy?

 

When you check for spark with the plug outside the engine, the engine will crank much faster. And you said the engine starts up when cranking faster (by push starting, or raising the battery voltage a bit with the charger).

When you are having trouble starting the quad with the starter, try using the plug from the other quad (or a spare plug), but leave the existing plug in place so that the engine compression slows down the cranking. Do you have spark then?

I'm wondering if the trigger voltage from the trigger pickup coil in the stator is marginally low. The output voltage is directly proportional to engine speed, and spark triggers either happen or they don't (through the CDI) based on whether it meets the trigger threshold level in the CDI. Cranking speeds are around 600 RPM, while engine idle is 1500 RPM. So you could have a trigger voltage that is too low while cranking, but just fine when running.

 

Great thanks.

I original checked the spark with another plug. So the original was still in. I had a good spark.
I will double check this tonight and let you know for sure.

Thanks for helping. I am truely lost on figuring this one out.

Do you think it could be a bad battery or just low voltage. It will start if I jump it off another running quad. If the other quad is not running it takes a little more time to start.

The thing I dont get is with the old 90cc engine it would start even with a low battery. If it would turn over it would start.

now it is turning over fine. At a decent speed but it just will not start.

 

Valve adjustment perhaps? Once it starts up and runs for 30 seconds does it start up and run fine thereafter until it cools all the way back down?

I you have good spark at low cranking speeds then look to compression issues (including tight valves) or carburetor issues.

 

its a brand new engine. It does not start via starter button even after it has warmed up.

 

Ok now I am worried. I put a brand new battery in the quad and still will not start with button.
I double checked and I have a good spark on a spark plug with original plug still in.
Starts up easy with a push. I have good voltage 12.8 before I hit started 11+ while starting.
Turn over really good just will not start.
after push start idle volts are 13 even.

I have switched over the cdi from the running quad.

Same engine from same manf in same quad. One starts other will not I dont get it.

 

It doesn't look like an ignition/spark problem to me. You have spark while cranking with the starter motor. The ignition system seems to be working. If you really want to eliminate the ignition system as a problem you could try swapping the coil between quads as well - but this is not likely the problem. But it is easy to do, so it is maybe worthwhile.

That leaves fuel and compression. Marginal engines start better when spun up faster while starting. It also seems your problem is getting worse, no?

 

does the quad have a headlight? if so, try to disable the lights and then start it. Sounds weird, but the little stators dont have enough juice to crank the engine when the light is on sometimes ( it will all work fine once the engine is running)...

 

I will switch the coils. I dont think that is the problem. I switched the rectifier and it made no difference. It starts so easy pushing it I had rules out carb and compresion. I think it is electrical. But what. I took a similiar 90cc engine out and it started fine.
I have to believe it is something regarding the timing and the starter button effecting that. I just cant wrap my head around how.
I am considering removing the strator parts from the running 90cc engine and swapping them into the 125cc.

What do you think am I just creating 2 engine that will not start?


I have installed a headlight but I did not have it on for the starting.

I am starting to get worried I will not resolve this.

I just dont get this and I leave for little sahara next friday.

Any help is appreciated!

 

I am not an expert here in any way, but I think you are right about it being electrical.
a. It runs great when push started - rules out mechanical or even carb issue i would think.
b. It turns over good - rules out bad battery
c. since it does run and function - should rule out timing or actual WIRING problem ( stator,coil, cdi...)

It really sounds like you have a power drain when you turn it to an "ON" position..and this drain is too much for the stator...you know, if the battery is weak it can be strain on the system. Have you tried jumper cables?