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I would assume the copper would ok too since it is used to carry all sorts of fluids and chemicals, also its specific heat is lower (copper's specific heat is lower than aluminum's specific heat). I happen to have two 250cc bikes both in my garage for some time, and I have been away for most of the time lately, so no many chances to work on them or ride them lately; but I hope to change that soon. I haven't looked at the one that has a vacuum leak yet (maybe cracked manifold or cylinder head gasket damaged) but I hope to check it out this weekend. Nonetheless I have been working on the cooling system of the other ones (woody black 250cc, storm as well): I fabricated an underneath plumbing contraption out of aluminum pipes and fitting as shown below:



Partial setup shown below, red high-temp permatex gasket maker was used to the water pump housing, inside of the pump and impeller were checked and cleaned and seemed to be ok.


After assemblage, cleaning and adjusting of carburetor and then refilling of the coolant fluid (50% coolant, 50% distilled water) the bike started right up, but it was overheating very fast and with lots of intensity. On occasion of refilling the coolant I burped the system of any pockets of air by leaving it idling for a while with the coolant pressure valve open and rocket the bike help in the process. But the main radiator was completely cool (lower radiator), the upper radiator got hot after a 5 minutes of engine running), the copper pipes underneath were pretty hot, and then engine case and specially the rubber body of the enricher on the carburetor were very hot very hot indeed. So clearly not coolant was circulating up to the lower radiator (the larger and main one) and maybe not even circulating at all to some part of the engine. So I decided to take a closer look at the thermostat; removed, opened it up, and took a look inside, as shown below:



I was expecting to find some spring loaded mechanism inside the thermostat housing that would open or shut the flow of coolant to the engine depending on the engine temperature (shutting the flow in order to allow the engine to reach operating temperature for instance), but found nothing. Is that the way it should be?

Thanks,
tk3000

Hello Folks,
I know my way around the gy6 4-stroke engine and 2-stroke engines, but I am not very familiar with the CN250. Valves seems to be properly adjusted, installed new carburetor just in case since I suspected that maybe it was a carburetor related issue (enriching circuit or cut-off valve) and cleaned all the passageways and galleries, renews all vacuum lines/fuel lines and clamps, coolant and cooling system seems in good shape, etc. When I first turn the engine on and try to open the throttle it starts to sputter and wants to die even I try open the it slightly, after about 15 minutes of the bike running (idling) it starts to get more responsive and seems to respond to throttle input more or less ok. But still it seems to be restricted somewhat since it does not want to go fast enough (I did not try in a long stretch though). I tested engine compression with a cold engine and obtained around 100 PSI which at first seems low. Also to add up to the problem there is an oil leaking underneath the engine (few drops of oil that manifest themselves mostly when the engine is running and is still warm).

One possibility that I am considering is that the the engine case is not properly sealed (I verified the torque in some bolts, and they seemed ok; but I am not sure if I check all of them) and thus it is leaking vacuum and also some oil, and once it gets warmer the metal would expand thus acquiring better sealing which would then help minimize the sputtering and stuttering that tend to happen during the first 10 minutes of engine running whenever I would open the throttle. Also the oil leakage gets worse whenever the engine is running or still hot, the oil leakage does not seem to originate from underneath the engine. Is there any spot on this engine were the oil leaking and any vacuum leaking would be more likely to originate from; or maybe there are another root for such sudden death of the engine whenever I try to open the throttle for the fist 10 minutes of running the engine? Any input would be appreaciated.

tk3000

Mine is identical to yours (I have two identical models with different colors: one is chromed like yours, and the other one is wood black). It is an awesome bike, and in spite of some initial problems and issues the built qualit is decent and above the average in terms of a Chinese bike. (Too bad the winter in Michigan is long and severe which really shorten the riding season). It is the ultimate platinum experience.

tk3000

Thanks for the responses. Propane does not quite cut it for the aluminum rods; after a very long time of heating the best result would be a brittle, breakable, failing and faulty weld. I will try with the propane torch, and it does not work well enough I will try with a proper torch for mapp gas.

I never adjust the valves for such a bike, but it should be simpler than with a gy6 since you don't need to remove the cylinder head to do so (I have done it in my 150cc gy6, and had to remove the head). But you probably will need to remove the CVT case in order to put the piston in the TDC (Top Dead Center Position). Below are couple of links related to such subject:
www.ch250.net/techtips/5.htm
www.ch250.net/techtips/5.htm

And if you do a search in this forum you probably will find how-tos related to valve adjustment for the CN250)

I am not sure how approach using a free flow filter air flow for such a bike since emission lines, breather tubes, and vacuum lines are hooked up to the airbox and other components. I installed a free flow air-filter in my 2-strokes, but that is a completely different beast. And since you are at the carburetor you may want to also remove the air-fuel mix screw (locate at the bottom of the carb on the intake side) clean it and adjust it (I found out that 1200 degrees adjustment should be good for such bike: remove and clean it, then turn it 1200 degrees clockwise in)

Our scooter use a CN250 clone engine and parts (Honda Helix) so there are plenty of information and documentation available. And lots of other Chinese scooter use the same engine and ancillary parts (carburetor, starter, air-box, etc).

tk

Recently I identified a previously very small hidden leak (given its tiny small proportion) that got much worse. The spot that is leaking is the aluminum plumbing underneath the bike: when I opened the radiator cap the pressure builds up inside and the tiny small hole/segment on the pipe that was leaking showed all its leakage potential. Welding light aluminum does not seem work most of the time, so the first thing that came to mind was JB-Welder, but I am not sure about how well it will hold (and for how long). The plumbing is designed and arranged to maximize the surface area of contact with the air as shown below:



Any insights on other ways to approach such issue would be appreciated.

tk3000

I don't have a specific questions because I am not sure about what the root or roots of the problem are, and apparently there are a multitude of issues going at the same time, and all such issues are electrical related. It stems from the fact that quality of the harness and the very soft copper connections (made of pure copper) and other components of the system are rather low and very often the wires are simply hold and hanged on poor soldered connections without any type of basic mechanical relief mechanism whatsoever. To make things worse I bought a voltage regulator that simply fried all the bulbs in my AC lighting system because it failed to simply regulate the voltage for the lighting circuit.





The secondary path to the ground that I created solved the starting issue for good, and never had any sign of overheating wire in the perimeter of the stator again.

And as I mentioned before the problem not only is of electrical nature but it is also is not circumvented to any single part, region, or system, but is spread throughout different parts.
Sometimes I have to ask myself if something whose quality is so poor is worth the time and effort...

Anyhow today I found some time to work on the bike again, and found out another problem the light switch simply wasn't bridging the yellow (live wire) with the other wires (for low and high beams), so I fixed that small thing and now there is voltage going to the main headlights (but it is too low).

I am testing from different points (or with different circuits connected or disconnected to the system) of the in the system, as follows: The main problem more or less isolated now: 1) very low voltage coming from the stator from the yellow wire when the stator is connected to the main harness and voltage regulator => about 8 to 9 Volts AC (normal idle) seems very low specially considering that there is no load from the lighting system; 2) But when the stator is not connected to harness at all, the voltage coming out of the stator (yellow wire) is around 20 Volts AC; 3) When the Yellow wire from the stator is connected to the Main Harness but the main Harness (and by extension the stator) is not connected to the voltage regulator the voltage measured is 0 Volts AC. Maybe a wire connected directly from the yellow wire coming from the stator to the voltage regulator could be a possible approach, since the the yellow wire inside the main harness may be crushed, crunched and/or frayed. With every connected and the bike running: DC voltage for the charging system is ok (13 to 14 volts dc), and AC Voltage going to the CDI and Ignition system is ok.

Sorry, but I went above my one paragraph (or few lines) quota since I had more or less explain all the issues that cropped up together out of Roketa/jmstar standard of quality concerning the electrical system of the fiji150cc. But you should only take into account the paragraph above, it nails down the problem as it presents itself now.