Bultaco ideas

weimedog

Damn Yankees
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Nov 21, 2000
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#1
I am building an old 1974 Bultaco Frontera. Its in good shape and tons of fun to ride. I put a twin plug ignition system from a 1978 Pursang in this bike and haven't fowled a plug since. Has anyone ever trimmed down a flywheel to increase throttle response? After running the new stuff that heavy flywheel effect is hard to get used to.

I have a couple of extra fly wheels...

Think it would work?
 

smb_racing

Master of None
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Jul 31, 2000
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#2
I'm not so sure about trimming down the flywheel, but no matter what you do it'll never rev as quickly as a newer bike, you could polish the ports on it and that would gain you some, perhaps repacking the silencer or try an updated exhaust system from vintage iron.

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Jeff-
'84 Can-Am ASE 250 (brutally fast rat bike)
'93 Kawasaki KDX200 (bored 40 over, FMF pipe, A-Loop suspension)
 

pursang262

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#3
What size primary drive weight do you have ?
The primary drive sprocket on the right side of the crank is available in a few different sizes. Usually the Pursangs have smaller ones and the weights on the trials bikes are huge.It's a cheaper part to throw in a lathe and experiment with than an ignition rotor.
Also since the crank tapers are all the same you can put the internal rotor ignition off a 125 Pursang on the bigger motors if you want really snappy response. I use my 370 Pursang for hillclimbing and I run the 125 ignition with dual plugs and the small primary weight and it responds instantly.
The downside is its much easier to stall.
 

weimedog

Damn Yankees
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Nov 21, 2000
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#4
You know I didn't even look on my pursang motor.....! (Red Faced) I have a bunch of weights for Alpina's and stuff. I didn't take that side cover off the 1978 Pursang motor I pulled the ignition from. Thanks for the tip!
 

markthomps

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#5
Weimedog, seems to me you should first talk to someone at Hugh's Bultaco or one of the other Thumbs-up specialty shops. They can tell you exactly what needs doing and have the parts to make it happen. If you need a phone # or web site link, let me know. Still, the ol' Frontera was never a snappy motor as I recall. It was a grunty motor and actually quite competent as an enduro bike, once you took care of the minor nits and Spanish pot-metal (sorry) build quality.

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'81 490 Maico (King Kong!), 2000 CR250, 74-1/2 GP400 Maico, buncha street stuff