vintagemotoworx Posted January 9, 2013 Report Share Posted January 9, 2013 Hi All, I'm building a 350 Jumbo for competition and was wondering if anyone has matched the cases on the motor? Did it make a difference? If so what difference? Thanks Quote Link to comment Share on other sites More sharing options...
woody Posted January 9, 2013 Report Share Posted January 9, 2013 What do you mean by matched the cases? What sort of difference are you looking for? The Jumbo is the most powerful air-cooled trials bike I've ridden. Mine had the reed cage fitted, most didn't. With a flywheel weight and the ignition fully retarded it still pulled like a train and I could easily shut right off and bring the power back on in 4th gear up steep banks. With the timing at normal setting and no flywheel weight, it was very agressive Biggest frustration was the clutch action. Quote Link to comment Share on other sites More sharing options...
baldilocks Posted January 10, 2013 Report Share Posted January 10, 2013 when the bike was launched in 83 one of my dads sponsored riders got one for the ssdt. This guy normally rode a 340 bulto, he looped the jumbo in the shop car park pulling wheelies in 5th ! doubt you need any more power unless the engine is in a bad way. reed block was removed later in an attempt to slow it down... Quote Link to comment Share on other sites More sharing options...
b40rt Posted January 10, 2013 Report Share Posted January 10, 2013 when the bike was launched in 83 one of my dads sponsored riders got one for the ssdt. This guy normally rode a 340 bulto, he looped the jumbo in the shop car park pulling wheelies in 5th ! doubt you need any more power unless the engine is in a bad way. reed block was removed later in an attempt to slow it down... I remember the crew used to invade a few events like the Rogart trial, all turned up in an ancient Merc' Good times. Quote Link to comment Share on other sites More sharing options...
lineaway Posted January 10, 2013 Report Share Posted January 10, 2013 (edited) I`m more interested if we have a rider to match the power? Should be a good year starting in New Mexico and ending in New Mexico! Edited January 10, 2013 by lineaway Quote Link to comment Share on other sites More sharing options...
sadrob Posted January 10, 2013 Report Share Posted January 10, 2013 Like Woody says it has to be one of the most powerful air cooled trials bikes ever built The clutch can be a problem getting used to especially after using a modern clutch Mine is now standard timing, reed cage fitted, flywheel weight fitted and a brand new carb jetted for the reed cage Its amazing and makes me smile every time I ride it ! Quote Link to comment Share on other sites More sharing options...
vintagemotoworx Posted January 11, 2013 Author Report Share Posted January 11, 2013 (edited) Thanks for all the replies.....I'm not saying that i'm looking for more power....looking for better power! @ sadrob: how much did you take off the flywheel? I rode one yesterday with the reed block plate in and found that it had linear power but not too much/enough power. I found it not very sharp and very rideable. I'm glad I got the chance as mine came to me in a box My motor is completely apart right now and i replaced EVERY bearing, crank, piston and rings ETC. So once it's done it'll be a brand new motor for all intents. @ lineaway....not sure who you are but did you ride last years ITSA? If you look at the overall standings on Modern twin A loop, you will find the rider matched the power on a 200 4stroke, so I'll just need adjustment time to the Jumbo and I'm sure the rider will "match the new power"....lol. More power is better right? LMAO J/K Edited January 11, 2013 by vintagemotoworx Quote Link to comment Share on other sites More sharing options...
lineaway Posted January 11, 2013 Report Share Posted January 11, 2013 Yeah I rode. I was hoping the build was for a new rider! The green Bul get sidelined? Did you notice the schedule is out? Quote Link to comment Share on other sites More sharing options...
woody Posted January 11, 2013 Report Share Posted January 11, 2013 ...looking for better power! @ sadrob: how much did you take off the flywheel? I rode one yesterday with the reed block plate in and found that it had linear power but not too much/enough power. I found it not very sharp and very rideable. Rob's bike is my old bike, it has a flywheel weight fitted, not weight taken off the flywheel, there is absolutely no point or need to take weight off the flywheel Are you sure it was a Jumbo you rode? As said before, in standard form the Jumbo motor is sharp and will lift the front wheel in 4th from tickover without even trying, they are very powerful. If it was a Jumbo, there was something wrong with it or it had been de-tuned somehow. Even with the flywheel weight and the timing on full retard mine would still pull from tickover in 4th up a steep bank - more than a 340 Sherpa is capable of. Quote Link to comment Share on other sites More sharing options...
vintagemotoworx Posted January 11, 2013 Author Report Share Posted January 11, 2013 (edited) lineaway....yes i saw the schedule. NM is too far I might have to miss the first and last event again. The Italjet is just too nice to ride for me right now.....This one should be just about perfect for intended purpose. As far as new riders I have 2 new ones coming to a few events... @woody: yes it was a jumbo I rode, 350 jumbo it had the reed block off on it so the reed was not active. Not sure where the timing was set nor the flywheel. I'm assuming stock. I felt the flywheel weight is right on that one but as I said before it was too smooth for my taste. Did you ever end up fixing the clutch? I'm assuming too on/off? What I mean by "matching the cases" is making sure the intake tract is free of casting bumps from factory, transfer ports line up....etc. It's all apart now so this is the time to do it. Edited January 11, 2013 by vintagemotoworx Quote Link to comment Share on other sites More sharing options...
woody Posted January 11, 2013 Report Share Posted January 11, 2013 Sorry, mis-read your previous post as the Jumbo you rode had the reed block assembly fitted, not blocked off with the plate. With the reed blocking plate fitted (therefore no reeds, it's either / or) it does flatten the power off a bit at the bottom end, but not much, but it will still pull like hell when opened up. With your engine completely rebuilt and with a reed fitted, I don't think you'll find it too linear. If you do you should have been world champion... As I said, mine had the extra weight and fully retarded timing and a carb that wasn't spot on tune - it still pulled any gear you wanted and I'm 17.5 stones (250lbs over there) Understand what you mean now with matching the cases - no, nothing like that was done, it was just stripped and everything rebuilt - honestly, it doesn't need anything, but if you can do that sort of thing, I guess it won't do any harm. I repacked the exhaust on mine too, middle and tail pipe as this makes a big difference to how smooth they run. And when they are packed properly they have a superb exhaust note. The clutch is heavy, even with the extra arm under the tank. If you try to lighten it by elongating the actuator in the casing I think you have the situation where the clutch doesn't fully disengage as the lengthened arm doesn't throw the plates out far enough. If you adjust it on the centre adjuster to eliminate the drag it will then slip. The clutch action and actual bite of the plates can be juddery as well although this seems to fluctuate from bike to bike (clutch is the same as 240/280 SWM) The actuator runs on 3 ball bearings and there are 3 different sizes, so it may be worth trying other cases with the larger (12mm) diameter balls. I also found that the actuator was rubbing on the casing which didn't help things, so I ground back some of the ribbing so that it didn't catch. It is possible to get them working to your liking, just takes a bit of time and trial and error. I also tried running 2 less springs but the motor has too much power and the clutch will slip if you're trying to fire it off the clutch in 4th gear up big climbs. Best get it working with all springs in. Best twinshock there is in my opinion (but there's another one I have never tried yet, so you never know...) Quote Link to comment Share on other sites More sharing options...
vintagemotoworx Posted January 11, 2013 Author Report Share Posted January 11, 2013 Woody....thanks! The clutch info is helpful and will give me a direction when setting up the motor. I will try a different style of plates maybe from Barnett and also check the actuator. The exhaust is sooo damn heavy! While I have my complete stock one, I do have a machine shop here within my place and going to attempt to make an aluminum mid box and back box to try and relieve some weight. I'll be keeping the dimensions close to stock to be careful and not screw up the spread of power. I'm planning on making the mid box re packable as well as the muffler. I'll start posting pics as It starts to come together (which should be soon as my season will start in a couple months) Quote Link to comment Share on other sites More sharing options...
woody Posted January 11, 2013 Report Share Posted January 11, 2013 Have fun getting the motor back in the frame..... I did... You may want to try fitting the frame around the motor before fitting any other parts to it. It's awkward because there is only one rear engine mount and the swingarm spindle goes through it. It was a bit of a wrestle as I remember. I use Barnett plates in my Ossa and Bultaco and they work very well. I tried them in the Jumbo but they made no noticeable difference (why I didn't mention them) which is what led me to believe that the main problem was the actuator mechanism rather than the clutch itself Quote Link to comment Share on other sites More sharing options...
vintagemotoworx Posted January 12, 2013 Author Report Share Posted January 12, 2013 Yeah I was wondering about the motor install....looks a little tight and since I got it in a box i'm sure it'll be fun. I've built 1- 370 Can Am and 2- 400's and they have the same clutch set up and they worked ok....obviously not in a trials setting. Speaking of clutch....my side case has a hole in it. Do you know anyone willing to part with a rotax clutch cover? Quote Link to comment Share on other sites More sharing options...
woody Posted January 12, 2013 Report Share Posted January 12, 2013 . Do you know anyone willing to part with a rotax clutch cover? I don't, no. Most are holed because of the kickstart stop missing. It's the kickstart that does the damage if it goes all the way round and uses the fragile magnesium casing as a stop. The casing for that engine is hard to come by. It will repair ok with metal bond etc. but make sure you have the stop fitted. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.