150cc lifan, help!

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DrewLabenz

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I have a knock off Honda z50 which I put a lifan 150cc engine in. It starts up after a few kicks, but I am having an issue with any rpm over 2000. It spits and bogs whenever I try to give it gas. When I first put it on, it ran great for the first couple months of life. Slowly after that it started to run worse and worse at mid-range RPM. At first, it would bog about halfway through the throttle, but if I stayed on it, it would clear up and get into the higher RPM. The next few weeks it kept getting worse and worse, I was consistently changing the oil and checking the valve lash and everything was perfect, I tried to tune the carb with no effect on the mid-range bogs. I was tuning the carb too much and got fed up and bought a brand new makuni carb and installed it. I am still having the same issue I've played with jets and made sure I have no leaks in the intake manifold. what else can I try
 

T-rev86

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Things to check

Disconnect Kill switch incase faulty

Spark plug

Carb even new have problems blow out the jets go about 2 turns out on mixture screw, needle in mid clip

Double check all engine bolts are tight

Spark lead coil check it or replace

Check all wiring

Change out cdi

If you have done all this then could be stator, magneto problems

Also ive heard them slipping a tooth on timing chain and stuffing up timing
 

thedozzman

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Check the filter in the fuel tank tap and/or change the fuel line.

As previously stated, check the spark plug, even new Chinese plugs are known to dodgy so get a proper NGK copper core or even an Iridium tipped one.

Check the sealing surfaces on the inlet manifold, a small split in the gasket, dirt or debris, even a small gouge or scratch at either end could throw the vacuum signal off and make the engine spit back, especially on the head sealing surface.

Slack timing chain, the valve timing will be way off if the chain is stretched and those tiny 8mm chains stretch very quickly if the bike is used like it should be. Have to take the rotor and stator plate off to check the chain slack at the bottom, as you'll be able to see if the tensioner is at, or almost at its limit at rest. Unless the chain is absolutely stuffed, checking from the top of the chain through the cam cover won't show much as the tensioner should take up much of the slack you create.

Check the valve seats, Chinese motors are notorious for hammering the valves, especially the intakes, as the valve material is substandard and very soft from the factory. Wind the engine over until its on the exhaust stroke so the exhaust valve is fully open and shine a penlight up the exhaust port whilst looking down the inlet port. You shouldn't be able to see any light around the inlet seat if it's sealing properly, repeat the process on the exhaust by getting the engine to the inlet stroke and shining the light down the inlet port.
* Carboned up exhaust valves that aren't fully closing are another issue if the stem seals are leaking oil down the valve stem, chunky black carbon "fur" or wet oil on the exhaust port roof is a big indicator.
 

miniriders

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I have a knock off Honda z50 which I put a lifan 150cc engine in. It starts up after a few kicks, but I am having an issue with any rpm over 2000. It spits and bogs whenever I try to give it gas. When I first put it on, it ran great for the first couple months of life. Slowly after that it started to run worse and worse at mid-range RPM. At first, it would bog about halfway through the throttle, but if I stayed on it, it would clear up and get into the higher RPM. The next few weeks it kept getting worse and worse, I was consistently changing the oil and checking the valve lash and everything was perfect, I tried to tune the carb with no effect on the mid-range bogs. I was tuning the carb too much and got fed up and bought a brand new makuni carb and installed it. I am still having the same issue I've played with jets and made sure I have no leaks in the intake manifold. what else can I try
Hi @DrewLabenz , can you give us updates on your 150cc lifan?

 
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