Diamond Back
Active Member
- Local time
- 9:48 AM
- Joined
- Jun 11, 2016
- Messages
- 137
I have a GT5 66cc 38mm stroke engine with 160 miles on it, Run Bel Ray Synthetic oil 32:1 and a little bit of octane boost on Sunoco 93..
The problem is my motor wont rev past 7,560 rpm at 32.7 mph, have tach and speedo,when I first got the engine I took it apart and cleaned up the cylinder of any casting slag and port matched exhaust to Banana Pipe and intake to intake pipe, I also removed casting lip on transfer ports and widened exhaust and intake ports a hair on both sides,, I did not raise or lower anything,, I believe I got a pretty good motor cause it was pretty clean to begin with not to much to clean up ,, I also case matched the lower end where the cylinder meets lower gasket and case, trimmed gasket then beveled the case edges to gasket and lower part of cylinder jug so its an even flow,,
using only Banana pipe and stock slant head it 4-stroke like crazy,, under load or hill climb it would run better but still 4-stroking,, running really rich moved needle clip to top and did nothing, so I took a pointed center punch to the left side of main jet hole and tapped it to indent the soft brass fitting and close up hole a little and it worked,, engine ran better... any way to make a long story short I was able to rev out to 35.7 mph and still had more to go but let off due to breaking motor in still....
I went and bought a RSE compression 6cc head and hour/tachometer,,, I also was given a micro drill bit set sizes #60-#80...which i dont get cause they show 80 as the smallest and 60 as the biggest..I installed head with copper gasket and hooked up hour/tach, and the main jet was a #71 and soldered and drilled using a smaller #67 drill bit...
Right off the bat I noticed more compression and low end midrange power and it 4-stroked a lot less but still there,, but also felt different in the top end..i had some pinging and detonation at low rpms so i was worried and added a nother head gasket and used a smaller #62 main jet,,, bad Idea ....very hard to start and keep running and noticed big lose in power..
so I took head gasket out and just use one aluminum one with copper gasket seal liquid,, and drained gas and added new 93 octane gas and lucas octane boost,,, that got me my power back and no more pinging/detonation, but this is where the trouble with throttle and high revs started,, if i gave it gas like 3/4 throttle at 4,500 rpm the bike took of and planted you in seat,,(NICE).. but if I gave it full throttle it bogged like a dead spot, if I backed off 20% off full throttle it ran better and reved up a little more. So I increased the main jet back to 67 and it helped with the full throttle but not 100%.. I can only twist throttle to 90% percent and then hit bogging dead spot from 90% to 100% and the bike 4-strokes again now a little more but not to terrible but did a plug chop and it is running rich,, moved clip to top slot on needle using 5 position needle which is longer,, have to use choke for about 15 seconds then take off and let warm up for 3 minutes then good to go but still 4-strokes with no load half throttle cruising 5,000 rpms but still have that dead spot at 90-100% throttle,,, so what should I do ????????????????????????????????
I am hooking up a 15mm WALBRO in a few days which should be awesome,, also going to add a 3-4 inch header section on Banana pipe and make a side mount stinger which is longer and seal up end of pipe,, or should i just extend stinger at the end into a dual mini mufflers.. will get a dirt bike pipe soon like a KX 65,,, should i increase main jet some more or what,, and I also have a slotted magnetto key so I can advance or retard timming,,,have not messed with that,, still stock 12:30 position,,, should I retard it,,,
so the bike has plenty of low mid grunt and torque , still runs rich black plug NGK B6,, cant really feel a kick in the butt on the pipe POWERBAND cause pipe design is to high needs a long header section to lower when powerband kicks in... BUT on a flat wide open road cant get it to rev past 7,560 at 32.7 mph,,,,,just wont budge any more,,,,
what should i do to stop 4-stroking and rev up to 10,000 rpms,,, but I still want all my power and torque low-midrange so I can put a 36 sprocket on...... thank you for your help,,, will try anything,,
The problem is my motor wont rev past 7,560 rpm at 32.7 mph, have tach and speedo,when I first got the engine I took it apart and cleaned up the cylinder of any casting slag and port matched exhaust to Banana Pipe and intake to intake pipe, I also removed casting lip on transfer ports and widened exhaust and intake ports a hair on both sides,, I did not raise or lower anything,, I believe I got a pretty good motor cause it was pretty clean to begin with not to much to clean up ,, I also case matched the lower end where the cylinder meets lower gasket and case, trimmed gasket then beveled the case edges to gasket and lower part of cylinder jug so its an even flow,,
using only Banana pipe and stock slant head it 4-stroke like crazy,, under load or hill climb it would run better but still 4-stroking,, running really rich moved needle clip to top and did nothing, so I took a pointed center punch to the left side of main jet hole and tapped it to indent the soft brass fitting and close up hole a little and it worked,, engine ran better... any way to make a long story short I was able to rev out to 35.7 mph and still had more to go but let off due to breaking motor in still....
I went and bought a RSE compression 6cc head and hour/tachometer,,, I also was given a micro drill bit set sizes #60-#80...which i dont get cause they show 80 as the smallest and 60 as the biggest..I installed head with copper gasket and hooked up hour/tach, and the main jet was a #71 and soldered and drilled using a smaller #67 drill bit...
Right off the bat I noticed more compression and low end midrange power and it 4-stroked a lot less but still there,, but also felt different in the top end..i had some pinging and detonation at low rpms so i was worried and added a nother head gasket and used a smaller #62 main jet,,, bad Idea ....very hard to start and keep running and noticed big lose in power..
so I took head gasket out and just use one aluminum one with copper gasket seal liquid,, and drained gas and added new 93 octane gas and lucas octane boost,,, that got me my power back and no more pinging/detonation, but this is where the trouble with throttle and high revs started,, if i gave it gas like 3/4 throttle at 4,500 rpm the bike took of and planted you in seat,,(NICE).. but if I gave it full throttle it bogged like a dead spot, if I backed off 20% off full throttle it ran better and reved up a little more. So I increased the main jet back to 67 and it helped with the full throttle but not 100%.. I can only twist throttle to 90% percent and then hit bogging dead spot from 90% to 100% and the bike 4-strokes again now a little more but not to terrible but did a plug chop and it is running rich,, moved clip to top slot on needle using 5 position needle which is longer,, have to use choke for about 15 seconds then take off and let warm up for 3 minutes then good to go but still 4-strokes with no load half throttle cruising 5,000 rpms but still have that dead spot at 90-100% throttle,,, so what should I do ????????????????????????????????
I am hooking up a 15mm WALBRO in a few days which should be awesome,, also going to add a 3-4 inch header section on Banana pipe and make a side mount stinger which is longer and seal up end of pipe,, or should i just extend stinger at the end into a dual mini mufflers.. will get a dirt bike pipe soon like a KX 65,,, should i increase main jet some more or what,, and I also have a slotted magnetto key so I can advance or retard timming,,,have not messed with that,, still stock 12:30 position,,, should I retard it,,,
so the bike has plenty of low mid grunt and torque , still runs rich black plug NGK B6,, cant really feel a kick in the butt on the pipe POWERBAND cause pipe design is to high needs a long header section to lower when powerband kicks in... BUT on a flat wide open road cant get it to rev past 7,560 at 32.7 mph,,,,,just wont budge any more,,,,
what should i do to stop 4-stroking and rev up to 10,000 rpms,,, but I still want all my power and torque low-midrange so I can put a 36 sprocket on...... thank you for your help,,, will try anything,,