Big Bore kit smoking

[krat]

I just installed an 80cc big bore kit on my Tao-Tao 50cc gy6.

Did it by the numbers following a reputable source on the internet, not some crazy kid. I have also rebuilt several auto engines way back when, same principles.

The Big bore kit smokes.

It fired up on the third or fourth spin of the engine and runs like a top. no strange noises and it has plenty of power, phenomenal torque increase!

I ran it to warm up and the smoke decreased.

As soon as I rode it down the road the smoke poured out, then reduced some. I rode for a mile and when I got back home it had nearly stopped.

Are the new rings just seating in?

Now this was a cheap kit from E-bay. No new head, just a 50cc jug and piston. The rings were over sized and I had to trim them in order to compress them into the jug.

Did I do something wrong or is this just the result of installing a $30 kit rather than going for the big buck option?

[JerryHawk250]

Does the head have a lot of hours on it? Did you replace valve seals? A leaking valve seal will smoke like crazy.

If you put the proper gap on the rings you shouldn't have any issues.

[krat]

The motor only had 100 miles on it and did not burn any oil.

I have already decided that the increase in power I see right now is worth the effort of buying and installing a better quality kit, if that becomes necessary.

[JerryHawk250]

Like you said it was a cheap kit and It may not be perfect so may take a little break in time. Being that you've done mechanic work before I'm sure you clocked the rings as required. I guess just run it and see if it gets better. Hopefully it works it's way out.

[tortoise]

Originally Posted by krat

installed an 80cc big bore kit on my Tao-Tao 50cc gy6 . . Did I do something wrong

Don't know what we don't know? Carb pilot and main jet sizes? If NOT changed, lean air-fuel ratio high running temps could have cracked the piston?

Always perplexing WHY the BBK aggravation is acceptable . . as compared to selecting a 150cc scooter and leaving it stock? Unless this is "liquor cycle" situation, or lack of initiative to get a motorcycle license, very little scooter cost difference.

Example . . Icebear Vision 50cc $620 . . 150cc $640.

[krat]

Thanks for the concern and speculation.

This just happens to be my fun scooter and I had the 50cc version running so well I decided to try the big bore variant. It's something to play with.

If I wanted to shy away from equipment that I had to mess about with I would not have the scooter and a 250 china bike, nor would anyone else here and there would not be uncountable pages of shop talk.

I have a full license and own several larger motorcycles. Have not had a traffic ticket in 20 years and never a DUI,
so my query is completely for the challenge of making this experiment work and not due to desperation over a suspended license.

That done away with The new kit smoked from the first crank of the motor so it was not a condition due to running, it is an inherent difficulty. I first thought it was the oil I had used to pre-lube the new piston and rings burning off, then it did not stop.

Don't worry, I have already ordered a new kit w/head and will start over when it arrives. If all else fails I will return to the 50cc condition and ride it as it was.

The extra torque sure is nice though.

I did remember that since I used the stock head I did not disconnect the emissions system. Would having the old emissions tubing still connected cause smoking?

[krat]

I did a tear-down and evaluation and discovered the problem and it was my fault as expected.

It appears that I looked at the wrong set of numbers scribbled on the workbench and gaped the rings to the specs of my 650.

Ring gap is supposed to be .008 and .010 and I am sitting on .015 and .020 inches.

So I am blowing smoke out the ring gap.

I could cure this simply with a new set of properly installed rings but I am going to wait and install the new kit that has larger valves in a new head. I will also tune the carb at that point and see how it performs.

[krat]

I just realized that I did no follow up on the results of this effort.

I obtained a new jug and head and gaped the rings properly this time. Put it back together and it ran like a charm. I put 10 miles on it with the stock carb and reworked the intake system.

I opened the air box, eliminated the restrictions and pulled the carb.

I absolutely could not get the top plate off the carb. It will have to be drilled and retapped but I don't think it is going to be necessary. It is doing fine with the needle in the stock setting so I may leave it alone.

I drilled the main jet to .90 and went to a .36 idle jet. It had a .26 stock.

I had already opened the exhaust when it was still a 50cc stock unit.

I am still breaking it in but I easily have double the torque. Not only will it take off from a dead stop without a duck walk, it will accelerate going uphill on a gentle rise and I lose no speed on most uphill climbs. I am no lightweight either at 215#.

Top speed is not really an issue with me. I had it doing 45 on level ground as a 50cc and I really don't care if it will go any faster. If I want to go fast I have bigger bikes to ride.

Fact is, as a 50cc scooter with open exhaust it was faster than my TBR7 was out of the box!

[Merlin]

That's great. Thanks for letting us know.