I have a resto-mod Rupp Roadster 2 with non hemi Predator 212cc

GustoGuy

Active Member
#1
Top speed mid 50mph. GPS clocked it at 53mph still a bit of top end left . ARC Billet rod and flywheel with 22lb valve springs. Stock camshaft holding me back? Pulls really hard to 40mph after that acceleration flattens out a bit. Bottom end torque really good will pull a wheelie if you cracked the throttle too quickly. Members here on the forum recommended a 308 cam. It is a very fast bike especially off the bottom but seems to loose momentum after 45mph or so. Would an aftermarket camshaft make a difference over the stock cam? -1447397221_20210525_194056_12715936_resized.jpg
 
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GustoGuy

Active Member
#3
Thanks Ole4. Over all it is a very fast bike. I took a nice 4 mile ride on Tuesday and I noticed that at about 40 mph is were the acceleration starts to flatten out most likely due to the stock camshaft. It will still make it into the low 50mph range and I guess that's not bad but out of curiosity I was wondering how much better a new camshaft would make it. I was driving on paved roads and I certainly would not want to go 50+ mph on a gravel road for fear of wiping out our having someone in my family wipe out. Still it is by far my fastest bike compared to my other two bikes. Does someone make a slightly bigger cam than stock that I could still use my 22lb valve springs with? I know a camshaft will be another $100 or so dollar expense. Fortunately I have a non-Hemi Predator 212cc so I will not have to remove the crankshaft and grind the area where the connecting rod attaches.
 
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#4
Yours is almost identical to mine. I have a BM Jr in mine and it is very quick. I never had it to top speed so I have no idea how fast it would go. It did almost throw me off one time I goosed it in my driveway and it almost went over.
 

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GustoGuy

Active Member
#5
Yours is almost identical to mine. I have a BM Jr in mine and it is very quick. I never had it to top speed so I have no idea how fast it would go. It did almost throw me off one time I goosed it in my driveway and it almost went over.
It is amazing how much power can be tweaked out of Predator 212cc. On my long ride on Tuesday I really noticed that the acceleration was definitely going flat after 40+ mph. I was wondering if that is due to the limitations of the stock cam. I don't have a tachometer so I am not certain about how fast the engine is spinning when it starts to go a bit flat but I heard the stock cam which is made more for low speed torque tends to go flat over 4000 rpms. Overall still a very fast bike that will more than keep up with city traffic but on the highway I would be definitely be riding on the bicycle shoulder. I still noticed on flat sections of road the speed will creep up and the top speed is just over 50mph (actual GPS'd 53mph) but from 40 to 50mph the acceleration is fairly lackluster. From zero to 30 mph it is a beast and is almost motorcycle like quick and a novice could definitely hurt themselves if they crack the throttle too fast on it because it will wheelie even with the heavy Suzuki K10 Motorcycle fork. 20210525_193133.jpg
 
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#6
Is it a tav 30? Could it be that it is just going into overdrive and the motor cant pull it? You need a tach to see what is going on. Stock cam should make plenty of torque up to about 4K rpm. I would hate to see you add a cam and windup going slower. You need a tach to make sure you are not over geared. I can't tell you how many times people complain about the Tav 30 slowing their bike down when it is because it is geared wrong. Folks always seem to think less gear will go faster, that is only true if you have the torque to do it otherwise it just loads down the motor.
 

GustoGuy

Active Member
#7
Is it a tav 30? Could it be that it is just going into overdrive and the motor cant pull it? You need a tach to see what is going on. Stock cam should make plenty of torque up to about 4K rpm. I would hate to see you add a cam and windup going slower. You need a tach to make sure you are not over geared. I can't tell you how many times people complain about the Tav 30 slowing their bike down when it is because it is geared wrong. Folks always seem to think less gear will go faster, that is only true if you have the torque to do it otherwise it just loads down the motor.
I have a 20 series steel Chinese made TAV. Not a 30 series. I heard that the 20 series were easier to install on the Rupp and less likely to affect performance due to over shifting. The stock TAV on the Rupp was similar in design to the comet 20 series yet made out aluminum and ran a 5/8th inch belt instead of 3/4th inch wide belt that the 20 series runs. I seen that you have a 30 series TAV on your bike. I put a 20 series on mine. Decent off the start performance yet my bike does not seem to want to to go much faster than 45 or 50mph. Off the start it accelerates very quickly to 30+mph and then goes a bit flat over 40+mph. Still way faster than my other two bikes and it should be a decent trail riding machine since it seems to have gobs of torque off the start. It may be possible to change the tension of the secondary spring I heard such as moving it to the 3rd hole can slow the upshift and increase the downshift and that can improve performance. I redid my secondary clutch on my Polaris snowmobile with a black ice SLP Helix and added a stiffer blue-green Polaris secondary spring and that really made a difference on the acceleration of my snowmobile especially when coming out of a corner it will down shift quickly and is very responsive. Is it possible to redo the secondary spring on Chinese made 20 series secondary driven clutch? I certainly would not allow any little kids or novices to try and ride this bike since it most likely would most likely be overwhelming and more than they could handle when compared to a bone stock Rupp Roadster 2 HS40 it would totally smoke the stock bike in a race.
 
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