Motor chokes when +20mph, tried multiple things, need more ideas

[dmopedMA]

Hello everyone! I hope someone with more experience than me can help my out.

While doing the breaking in period I noticed that when I was going "too fast", more than 20 mph, the engine most of the times choke and almost die, if you slowdown a little bit, it comes back and keep running fine. Since I was breaking in, I though that could be normal and I just kept under 20mph.

After breaking in, and after using the regular gas/oil ratio (30:1), I noticed it again, that most of the times (and yes, that's funny, not always...) I can't go more than 20-22mph, because it chokes. This problem is there eve downhill, so it's not related to the load, I believe is more related to the RPM, since it does the same even stopped with the clutch lever pressed.

Reading I though that maybe too much gas in the mix, so I changed the needle of the carby (NT stock one) one point up, with same issues. Then I changed it to the top setting, but still same problem. I even tried moving it one point under the center (to check) and it was the worst configuration, no even low rpms worked.

Then I started thinking about the fuel line, maybe too thin (I took it from a car), I change it for a wider one that fits well, but nothing changed... I tried opening the tank cap too, nothing.

I tried to run without air filter and nothing, same issues, I even made some holes in the filter cover to promote better air flow, but nothing changed.

Then I though about the muffler, I removed the muffler cap and I went for a spin, oh boy, that was loud! but still had same issue when I got 20-22mph.

I replaced the spark plug (just in case) and the CDI Ignition Coil since I had an spare one, but still same issue.

NOW THE FUNNY PART! If I run with the fuel valve CLOSED it chokes less and I can get 32mph... If I go over 20mph with the valve closed and then I open it after +22mph I can run on +25mph... getting to 32mph as max speed I ever got.

**In case that useful, I have an 66/80cc Chinese engine kit.**


Summary:
Motor chokes, even die when trying to go over 20mph things I tried:
- 4 different configurations of the carby needle, top 4 ones.
- Running with no filter
- Running with no muffler cap
- New spark plug and CDI
- Runs better when I close the fuel valve while getting to 20mph and opening it up over 25mph


I hope someone can give me a hand on it.

 

[crassius]

sounds too rich, check float level and main jet

 

[dmopedMA]

sounds too rich, check float level and main jet

Thanks for the answer.

What you mean with check? I opened it up and float was there and main jet was in place... something I'm missing?

 

[gary55]

If you are going 20, it starts choking and then you go up hill does it stop choking? It sounds like it just needs a smaller jet, but it could also be loose motor mounts causing enough vibration to interfere with proper carb. function.

 

[Frankenstein]

Well, there's likely 1 of 2 problems, and either one can by partially solved by closing the fuel valve (and leaning things out as a result) it's either slightly too high a float level but since you aren't choking out all the time it's probably not it, or you have too rich a jet, and you just need to put a smaller one in. Even a loose jet can make things odd I would say if you don't have a jet to replace the other with maybe try the float level just for the hell of it and if no improvement then put it back and work on getting a jet

 

[dmopedMA]

Thank you all, this is really helpful!

@gary55 it did choke this morning going uphill, it's true that it does vibrate a lot, but my understanding is that this is kind of normal. Anyway, could be related.
@Frankenstein I'm gonna try lowering the float, maybe is something to do with being a little bit to high that increase the problem when it vibrates a lot (20mph is when it vibrates the most) and it does fix the issue.

I would like to take the chance to ask you guys about these bottles http://www.ebay.com/itm/49-66-80cc-MOTORISED-BICYCLE-BIKE-BOOST-BOTTLE-KIT-Grubee-skyhawk-GT5-Angle-fire/162565256355?ssPageName=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649 and if you think that could help me reducing vibrations.

 

[Frankenstein]

Thank you all, this is really helpful!

@gary55 it did choke this morning going uphill, it's true that it does vibrate a lot, but my understanding is that this is kind of normal. Anyway, could be related.
@Frankenstein I'm gonna try lowering the float, maybe is something to do with being a little bit to high that increase the problem when it vibrates a lot (20mph is when it vibrates the most) and it does fix the issue.

I would like to take the chance to ask you guys about these bottles http://www.ebay.com/itm/49-66-80cc-MOTORISED-BICYCLE-BIKE-BOOST-BOTTLE-KIT-Grubee-skyhawk-GT5-Angle-fire/162565256355?ssPageName=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649 and if you think that could help me reducing vibrations.

They won't help the vibration but they can leak and lean out the mix for you. Stay away from it since they aren't right for these motors apparently but @Steve Best has gone through the motions of making ones that actually do work. If anything follow his design if you feel amped enough.

 

[dmopedMA]

They won't help the vibration but they can leak and lean out the mix for you. Stay away from it since they aren't right for these motors apparently but @Steve Best has gone through the motions of making ones that actually do work. If anything follow his design if you feel amped enough.

Thank you for the tip.

Talking about vibrations, I know that there is a lot of controversy about how to reduce them, people saying that is better to have rubber between the frame and the holder, people saying that this make it worst... a part of having the motor 100% align with the frame and having the nuts tight, any other tip that can help out with vibrations that doesn't require opening up the cylinder?

 

[Frankenstein]

Don't use rubber mounts, it's not even a controversy it's just people who really want to sell them (or plain don't understand that a vibrating motor still vibrates even if that vibration isn't being fed into the frame) and people who know you shouldn't buy them.

Without opening the motor there's virtually nothing you can do to change how much is vibrates, that's fact. By making sure the motor is snug to the frame you can help it in the long run by keeping the engine from destroying itself as easily, since some energy is dispersed into the frame.

How much did you pay for the engine kit? If you cheaped out then it makes sense that you got a motor that vibrates a lot, though that can simply happen to any motor honestly. If your hands are numb after riding then it's vibrating too much, only balancing the internals fixes that, or buying another motor with better quality control..

 

[gary55]

As for the vibration issue, I didn't describe it correctly. The loose mounts don't cause it they just allow it to become violent enough to effect the carb. function. The signs of this are the engine speeds up to the point where it starts vibrating then it slows down till it stops vibrating and just continues this cycle of speed up slow down speed up slow down with out any change of throttle position. The fuel in the bowl of the carb under such vibration becomes foamed up and the needle is vibrating inside of the jet tube. This is a common prob. and easily remedied by tightening the mounts. If these are not the symptoms you are experiencing then it is most likely just to rich and needs a smaller jet. Boost bottles, some people like em some don't. From what I have picked up unless you know how to tune it to your engine it is a waste of money, but that's the opinion of someone who has never tried one. Also I agree with Frankenstein. No rubber. Some will tell you that a CDI with a correct advance curve will help reduce vibration. This has not been my experience.