Re: Motobecane builds, post your mods!
care to weigh in on Jesse’s "ultimate AV7" on this thread? Parmakit with Doppler Endurance w/19 PHBG/G3? I’m basically building the same thing.
Mick,
I've been speaking with Jesse on his plans for that build and it's absolutely solid in concept. I think the idea is to make the port timing even more aggressive for a higher rpm range. I'm not certain on what the timing comes stock nor what Jesse's plans were for the final port timing numbers, but the goal is to match the exhaust duration to the pipe used, since the G3 is a midrange pipe, it would like an exhaust timing between 170-180 degrees or so. You then want the transfer timing to be 60 degrees less then that.
The endurance crank is _overkill_ for any av7. Yes it is beefy as fuck and is rated to ~17k rpms, but it is also heavier then the other cranks. A conti or regular doppler or any other cheaper stuffed crank will do on a av7 build.
If you can fabricate your own 21mm intake, then go for a 21phbg over a 19. The larger carb will help with increasing top speed. Use a 19mm carb with the 19mm Malossi intake.
The variator is up to you and what you plan to do with the transmission. If you are going for balls out top speed performance, you need the Malossi Variotop and a clutch pulley. A lot of people in the States like the Doppler ER3 but word on the streets in Frenchmen land is that they wear out quickly and or break much sooner then either the Variotop or the Bidalot variators. The Bidalot is about the same size as the stock variator and is a great choice as well, just it will not give you the same topend as the Variotop which has a diameter 15mm bigger over stock/bidalot.
You are probably going to have to modify your tensioner spring to use either the Variotop or the ER3 to it's fullest without it colliding with the driven pulley.
Only one option on clutch pulley: Doppler.
For the pipe, the G3 will probably be the best choice overall for the av7 motor. The Doppler ER1 pipe would also match up to the Parmakit well but it's powerband hits about 1k rpm's later then the G3 (@ 6.5k rpms) which is significant for a piston ported motor. The rest of the 'real' expansion chamber pipes are designed for super high rpm motors and would perform poorly on the 70cc parmakit.
Find any 70cc head that you can that does not have a decompression valve and it MUST have a proper squish band on it. You probably want to deck the head to get a squish clearance of between .5mm to .7mm, lean on the greater side to avoid unwanted detonation and use of racing fuel. I'm not sure if anyone still makes a proper 70cc head, so snag a doppler head and have a new squish cut in it to match your kit.
Ignition? CDI of your choice, or keep points if you like. Play around heavily with ignition timing. Start at 2mm BTDC and go from there. I have no idea what heat range of plug you'd need, b7hs maybe?
~finny
Mick,
I've been speaking with Jesse on his plans for that build and it's absolutely solid in concept. I think the idea is to make the port timing even more aggressive for a higher rpm range. I'm not certain on what the timing comes stock nor what Jesse's plans were for the final port timing numbers, but the goal is to match the exhaust duration to the pipe used, since the G3 is a midrange pipe, it would like an exhaust timing between 170-180 degrees or so. You then want the transfer timing to be 60 degrees less then that.
The endurance crank is _overkill_ for any av7. Yes it is beefy as fuck and is rated to ~17k rpms, but it is also heavier then the other cranks. A conti or regular doppler or any other cheaper stuffed crank will do on a av7 build.
If you can fabricate your own 21mm intake, then go for a 21phbg over a 19. The larger carb will help with increasing top speed. Use a 19mm carb with the 19mm Malossi intake.
The variator is up to you and what you plan to do with the transmission. If you are going for balls out top speed performance, you need the Malossi Variotop and a clutch pulley. A lot of people in the States like the Doppler ER3 but word on the streets in Frenchmen land is that they wear out quickly and or break much sooner then either the Variotop or the Bidalot variators. The Bidalot is about the same size as the stock variator and is a great choice as well, just it will not give you the same topend as the Variotop which has a diameter 15mm bigger over stock/bidalot.
You are probably going to have to modify your tensioner spring to use either the Variotop or the ER3 to it's fullest without it colliding with the driven pulley.
Only one option on clutch pulley: Doppler.
For the pipe, the G3 will probably be the best choice overall for the av7 motor. The Doppler ER1 pipe would also match up to the Parmakit well but it's powerband hits about 1k rpm's later then the G3 (@ 6.5k rpms) which is significant for a piston ported motor. The rest of the 'real' expansion chamber pipes are designed for super high rpm motors and would perform poorly on the 70cc parmakit.
Find any 70cc head that you can that does not have a decompression valve and it MUST have a proper squish band on it. You probably want to deck the head to get a squish clearance of between .5mm to .7mm, lean on the greater side to avoid unwanted detonation and use of racing fuel. I'm not sure if anyone still makes a proper 70cc head, so snag a doppler head and have a new squish cut in it to match your kit.
Ignition? CDI of your choice, or keep points if you like. Play around heavily with ignition timing. Start at 2mm BTDC and go from there. I have no idea what heat range of plug you'd need, b7hs maybe?
~finny
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