Hi folks! I am new to this forum. My son has a 5 year old Tao Tao T125 quad that we have issues with for the last few years. At about two years, with conservative use, a Tao Tao dealer had to install a new head because the valve retaining clip had broken and bent the valve & scored the head. For the past couple of years, it seems like it is now having a fuel or carb issue. I have tried no less than (6) aftermarket carbs on this thing, different brands & intake sizes (20mm & 22mm), with no success. I have also tried rebuilding original carburetor and cleaning out all the jets & ports, with no success. Whenever I think I have a carburetor dialed in, it will inevitably reveal a “fuel” issue once again. it will either not idle properly or not accelerate properly under load. It can’t be that all these carburetors. I am trying are bad. I did a compression test this past week and the engine was at 60 psi. Is this enough to keep the engine running smoothly or do I need to deal with a problem with the head again? this unit is so frustrating! It ran well for my son the first couple years he had it, and then we’ve had nothing but problems. He has since gotten into dirt biking, but I would still like to get this machine running, if possible. I would hate to junk it. I appreciate any and all input! Thanks!

 

I have an issue too that is similar which I’ll post about. . I’ll keep an eye on your thread too.

 

60psi is pathetic. Check valve clearances at TDC on the compression stroke, reset at 0.002" gap for both. If that doesn't restore compression, remove head and cylinder and check piston and cylinder for scoring. Measure the bore with a micrometer if you can, (0.002" wear is about the limit). Remove the top ring, mark which way up it was, and put it in the bore, measure the end gap with feeler gauges 0.020" is the limit on that. Grind the valves in, making sure the seats and valve faces are contacting all the way round. If anything on the cylinder/piston is over the limits get a new cylinder kit, or a rebore and oversize piston. If just the ring gap is excessive, new rings. If you have another bent valve, get either a new valve and grind it in, or a new cylinder head kit.

 

Thank you for your reply. I can’t find the specs on what factory compression is. I thought 60 psi might be a bit too low. That stinks that there may be another issue with the head. I will start with the valves and work my way to the head. Thanks again!

 

The Honda 90 is supposed to be 178psi. In my experience you never get anything like that. With a decompressor, and the speed you can spin an engine on the starter, you will be getting 130psi on a good engine and 90psi is regarded as time to go for a rebuild.

 

Thank you. I am going to tear down the top end or replace it altogether, as the entire assembly can be had for $50-60. The valve covers are so tight that I have to remove the head anyways to muscle them off.

 

Steady on, replacing the whole thing when it may just be a valve clearance setting, is a bit over the top. Usually it is easier to get valve caps off with the head in place as it gives you something solid to turn the spanner against. Hexagonal sockets are best as they give more purchase on the hex head cap, if there is room for one.