Honda Mtx125 running badly

[Lynxx]

Hi all i baught a 1984 Mtx125 about 3 months ago, it ran for about a week then blown the headgasket and bored a hole in the piston, not hurting the bore in any way. i did some research to find the spark plug was not the right one and was a Bpr5es. after rebuilding the bike and replacing the gasket and piston. i rode it about 15 miles and it started to spit and sputter when the rpm got anything over 6000. the compression is still good and i have checked the air filter, cleaned the carb and reset to stock 1 3/4 turns on air pilot screw. checked the flywheel for timing and to see if the woodruff key has stripped. and the flywheel was perfect along with the key, the bearings on the crank are tight with no movement, also the bottom end bearing and small end were tight. the exhaust on the other hand is very very heavy unlike anything i have had before, the expansion chamber feels like its full of water but it isnt. if the bike is in neutral it will redline. but as soon as its in gear it wont do over 7000, even after its warm. i have also checked the petrol tank filters and cleaned them. Please help me,

Thankyou for any help on the matter Tom.

[sumpgard]

the front pipes are always heavy they are full of sound deading in cased in a mesh. find a good welder cut the pipe in to sections and remove all the insides there is also a restrictor pipe inside about 14 inches long that is welded in to the back of the pipe . the hole in your piston is probably caused by a weak mixture try raising the needle in the carb one notch at a time until the plug goes a golden brown colour this could be the cause of the spluttering hope this helps.

[Lynxx]

The plug is brown now. and the needle was 1 notch above half (richer)

[sumpgard]

what size jets are you running

[Lynxx]

i dont know at the moment but i have been thinking and what you said about the mesh, i decoked the exhaust and i recon it shifted the crap loose into the mesh.. so im gana cut it open and pull all the baffles and crap out of it and give it a good wire brush.. if that doesnt help ill pull the carb and post jet settings... i had a similar problem on the exhaust with my Ts50x.. it would run perfect in Neutral and when geared in, it wouldnt pull. replacing the exhaust for a brand new one fixed the problem. and i havnt really got the cash for a new pipe at the moment, and i can weld and cut very good now, so ill take it to my old work place and pay them somthing to use there welder.

[dougon2wheels]

i had exactly the same problem on a mates mtx a few years ago,wouldn't pull more than 4k in gear(had got slowly worse with use),stripped the motor,new piston and rings.....still the same,turned out to be the standard end can,full of carbon !!!,was fine after i cleaned it out..

[Lynxx]

alright i paid somone 10 pounds to oxy sedeline the pipe, it weighed alot less, then cut it open and pulled everything out of it. then finished it off with a coat of Hamerite high heat black paint. looks alot better and weighs less. lets hope it runs right, i will know tomorow when i pick up my stator from post office. Thanks for all the help guys, i hope it fixs the damn thing

[Lynxx]

[Lynxx]

just to add the exhaust didnt help shit, i repacked the muffler and oxy sedelined the front pipe + cut the baffles out. I got a Br9es spark plug today and it fixed all my problems, will now redline over 10,000 rpm not that i want to try it untill i break it in.