Four stroking while cold

[mbearden]

I apologize in advance if this topic has been covered anywhere else, but I have gone over my bike multiple times and tried multiple things, and this is throwing me for a loop. Any ideas or suggestions would be greatly appreciated. So I have a heavily modded 66cc motor on a Genesis 29" cruiser with a SBP shift kit. I have a ported jug with a drilled on piston, RSE reed valve kit, R/T carb, expansion chamber exhaust on an X-port. My issue is that my bike is 4 stroking when the motor is cold. It's only before the motor warms up. This wouldn't bother me so much except my average ride when I'm going to work is only about three or four minutes (I live really close to work) and it doesn't really get a chance to warm up. When I go on longer rides, it's not an issue at all, and it runs like a champ. I have changed my jet size, I've put a different head on, (I have a high compression head on atm) I don't really know where to go from here. I'm sure there are other things I've done too, but can't think of off the top of my head.

 

[xseler]

Seems to be a normal thing for many of these engines. Mine acts the same way even with different carbs.

 

[mbearden]

Seems to be a normal thing for many of these engines. Mine acts the same way even with different carbs.

Does your engine have any of the same mods as mine? I have two other gas bikes, neither of which as heavily modified, and neither of them do it. I know this bike hasn't ALWAYS done it, but I've also re-built it probably 4 or 5 times, so fat chance of trying to eliminate the issue based on past builds. It's good to know I'm not the only one with the issue, and it is definitely something I can live with if there is no solution.

 

[crassius]

I doubt it is 4-stroking due to bad mixture coming from carb because it runs fine when warm - my guess would be that piston/rings haven't expanded enough yet at that temp to get good seal in cylinder (most likely other bad things are going on too at that temp, which may seriously shorten life of the motor) - why not let it warm up a bit idling before taking off?

 

[mbearden]

I doubt it is 4-stroking due to bad mixture coming from carb because it runs fine when warm - my guess would be that piston/rings haven't expanded enough yet at that temp to get good seal in cylinder (most likely other bad things are going on too at that temp, which may seriously shorten life of the motor) - why not let it warm up a bit idling before taking off?

Well, I honestly should, but most days I leave my apartment with about 5 minutes to get to work, so it's "start it up and roll!" However, once I'm done re-building my 26" 48v E-bike (on a dual suspension Avalon frame) then my short trips to work will be on the electric and the gas will be used for my weekend rides. I guess I need to start taking my time and letting her warm up if I want her to last longer.

 

[CRP]

The more you tweak up a motor the more time it needs to get working right. You just can't go from cold to full running with a modified engine.

 

[mbearden]

The more you tweak up a motor the more time it needs to get working right. You just can't go from cold to full running with a modified engine.

Good to know, I've been trying to take my time and let it warm up when I can. I've been taking the electric bike on the mornings I'm in a rush.

The high compression head makes the motor have a ring to it when it's running. The same noise can be heard if you run your finger over the fins of the head. I think it's kind of cool and gives my bike a more unique sound.