sherpa325

Love the Tank. where did you get that from. Greg

Looking at your top triple clamp , it appears to be modified to move the bars back and up similar to a bultaco, a modification Rathmell had on his bike if I am not mistaken

I agree with Max and Pete always turn the fuel off, particularly when travelling, also you need to check the float valve in the carbie and clean the valve itself and the insert it seals against, a small amount of grit can cause this valve to dribble slightly causing your problem. You need to take off the brass tang that operates the floats to get to the valve. Also make sure all the vent hoses on the carbie are clear and not kinked or blocked. I also find when starting my 300 not to use any throttle when hot or cold. Hope this helps Cheers Greg

198 and 199a frames are different so figures taken from a 198 may not be correct,The swinging arm pivot was moved and the ground clearance increased, wheelbase should be the same, not sure about head angle though. It would be helpful if you posted some photos of your frame because at the moment it is difficult to work out where and what mods have been carried out. Its difficult to see how you can shorten a frame by 3 inches without some serious cutting. Cheers Greg

Dellorto instead of a keihin

Your next problem is to find a good machinist who can work to close tolerances. I had one of my 325 sherpas bored back in the 70's and after puting it back together was delighted to hear almost as much piston slap as before the rebuild, not happy, and that was the local importer. You dont need much wear in the larger bores for them to become noisy, which is why bultaco added the rubber bungs to the cylinders in the mid seventies. The smaller 250's can tolerate more clearance before they become noisy. I dont think the extra clearance detracts too much from the performance, I just find it annoying particularly after you have just spent your time and money on the rebuild.

Hi , I have to agree with Jon , I have two 199A's that have been bored to 340 and both were done with 1.5 thou clearance. I took great care running them in, ie heat up and cool down several times using an oil rich mixture. Both bikes are very quiet and run perfectly. My experience is that the larger bore motors can develop noisy piston slap with clearances that wouldn't cause noticable noise in a 250. My advice is to keep clearances on the small side and be careful running in and you will enjoy a quiet motor and long lasting rebuild.

Any mono is at least 20 to 30lbs lighter, has a one finger clutch standard, has primary kickstarting, electronic ignition, reed valve, brakes that work,my guess is they are significant advantages. The fun of twinshocks is restoring your bike and trying to improve the performance within the rules and believe me when you get involved with a bunch of friends playing with these bikes it is great fun. Converting a mono is plain and simple CHEATING

Does anyone know why the 250 and 350 sherpas from 75 through to 77 had different frames,I have always been curious as to why this was done. The 250's 158 182 and 190 had this shorter frame with more ground clearance with a shorter set of forks as well as a different bottom triple clamp and airbox, any ideas why? From 1978 both bikes used the same frame which was based on the earlier 350

Sutty take a deep breath, sit down and maybe pour yourself a stiff drink, because as far as I know we live in a free country and you dont actually have to buy a Racing Gasser - problem solved

Hi, the easiest way to tighten or loosen the bolt at the bottom of the fork leg is quite simple, put your bike on your trailer and using tie downs, compress the forks as much as you can, this will apply enough internal pressure to the dampner rod via the fork spring to stop it spinning, you will now be able to either undo or tighten the allen bolt. This method has never failed me, so fingers crossed it should work for you as well, Cheers Greg

The early Sherpas have non vented caps and cause no problems, the later vented caps can actually leak oil after a hard days riding resulting in many riders I know actually sealing up the vent, with no adverse effect. The action of the forks is the same. All my sherpas have a circlip holding the seal in place, I have never heard of anyone blowing a seal with either setup and Ive had sherpas since 1970

Most people are using the dellorto 26mm [off gasgas or sherco ] or alternatively the 28mm keihin flatslide which will be illegal to use in competition. Both will work well with the supplied jetting- jets are easy to come by. Which ever way you go you will have to change your manifold as well!

I think you have to ask yourself why would someone build one of these bikes, and the answer is to gain an advantage or more to put it more bluntly cheat. I dont buy the engineering side of the arguement at all as anyone who competes in twinshock trials will tell you there is ample room to use you skills in setting up one of these older bikes. The brakes, suspension, carburation etc can all be tweeked within the rules and restoring and keeping one of these bikes competitive is more difficult and satisfying than maintaining a modern mono. If you want to test your engineering skills and build a 'special' well why dont they convert a bully or an ossa into a mono, put disc brakes on it and go and compete in the mono classes and I am sure no one will complain as clearly there will be no advantage. Any organisers who allow these bikes to compete are not doing anyone any favours, they are just fueling the problem. For those of you who can remember when the monos came out in 84 it took about one year for all the twinshocks to disappear from trials and almost the entire entry to be yamaha mounted such was the advantage of this style of bike. They were at least 20lbs lighter, the clutch worked as did the brakes and suspension not to mention the electronic ignition, all in all a huge improvement over the twinshocks.

Hi Eddie glad to hear you undone the bolts and replaced the seals without any problems, the forks take 180cc of oil, as the forks were made 30 odd years ago you will find that todays lightweight oils dont work that well in them, so you need at least 10w I would think, I have used ATF in mine with no problems, you may have to add some longer alloy spacers to the top of the fork spring [25mm on my bike] as the springs are soft and tend to sag over time Cheers Greg

Thanks heaps Jim

Hi , I have always found the easiest way to undo and tighten the allen screw on the bottom of the forks is to compress the forks. Use your tie downs to pull the forks down as far as possible- the screw should be able to be undone without any problems. Cheers greg

Hi , do you guys have any more photos you could post of the bikes that were at the event, I can hardly believe the attention to detail and care that has gone into the restoration and modification of these twinshocks, in particular the Puma Racing Bultacos. Living on the other side of the world we don't get to see bikes of that calibre. Cheers Greg

Hi I currently own an 09 300 and without a doubt the best bike I have ever owned. The bike is a big improvement over the previous models, lighter, more stable and an incredibly powerful motor. I have ridden a beta evo 300 and the motor was very smooth but did not make the outright power of the gasser, the suspension was plush the bike felt light and was a big improvement over the rev3, but i still prefer the gasgas. This is the 3rd pro I have owned 05 300, 07 280, and the 09 300. All of the bikes have been ultra reliable with no real problems with any of them. I ride at least one full day each week all year round. If the motor is too powerful they are easy to detune- slow throttle[black tube] head spacer[lowers compression] and flywheel weight as well as lowering the gearing[one tooth less on the front sprocket] All these are available through your gasgas dealer. Cheers greg

Hi, before I went too much further pulling apart the engine I would check to see if the crankshaft is bent. I know this sounds silly but if you have split the cases it is not too difficult to bend the crank either getting it apart or putting it back together. Take the plug out and the magneto cover off and rotate the motor - checking to see if the flywheel is running true, not wobbling up and down { should really use a dial indicator}. If the crank is bent the motor will run fine for a period of time - after awhile the main bearings start getting hot! and the crank seals will stop sealing as they lose their elasticity creating problems similar to those you have mentioned. This is an easy check to perform, and by the way I hope this is not the problem as you will have to split the cases to fix the crank. Cheers and good luck Greg

Hi , I just thought I would throw my thoughts in on this topic. I have been riding competitions for 37 years and at last count have had 30 trials bikes, I still have four in the shed. That said I am very fussy about the tuning of my bikes and without a doubt the mono yamaha is the most difficult bike to get to run correctly, even back in the days when they wre new. The easiest way to stop the problems with the detonation is to run two headgaskets[reduces compression ratio and runs cooler]. The 350 is more prone to it than the 250 [i have owned both] The correct way to do it is to make a .5 mm headgasket [std is 1mm]and machine or sand the combustion chamber to achieve the same volume- this will give you the correct squish and correct combustion ratio. The bikes are prone to overheating so the compression ratio and fuel quality are critical ,the 350 is worse due to less fins to dissapate the heat, less compression means less heat! I became so frustrated with mine I really started to look deeper into these motors and found some strange facts,- first of all the motors run a 68mm stroke, much longer than any other trials engine 60mm is the norm, this is going to make the motor rough at lower revs, secondly the port timing is like no other trials engine. I did mine back in 85 and compared the timing against a 348 cota , a 325 sherpa and a 325 italjet [all the european bike were nearly identical whereas the yam was completely different] If I remember correctly John Shirt made some radical engines for these bikes where he changed the bore and stroke presumably to mirror the europen style bore/stroke and porting .I cant recall anyone ever doing this to any other trials motor.You would have to ask yourself why bother going to this much trouble if there wasn't an inherent problem. I dont know if this will help but these are my thoughts from the 80's.

Hi I'm just after some travel advice as we are going to Europe for 5-6 weeks in 07. We have been before to the major Cities [Paris, Rome, Vienna etc ] This time we would like to go to some smaller Cities/Villages in France, Switzerland and Germany. So is it easier to hire a car and drive or should we catch trains, buses or maybe internal airflights. Any advice will be appreciated Cheers

In 05 I swapped from a sherco 290 to a 300 pro and experienced the same starting problems, my friend however [a long time pro owner] could start it first kick hot or cold. It took me a while to work it out but I finally figured NO THROTTLE as you kick[and you need a decent kick] as the kick start stops and the motor starts to spin open the throttle a small amount and it should fire every time. Head spacer does make it easier to kick over if thats your problem Hope this helps

It just goes to prove money can indeed buy happiness if you are a large Multi - National like Honda

Has anyone tried aftermarket reeds in their bike, I had a sherco before my gasgas and fitted a set of aktive reeds, which sharpened up the power. There are quite a few brands out there so I was just wondering if anyone has tried them and what is the feedback. I am also having trouble finding anyone who actually advertises them on a website, any ideas. Cheers [ps do the sherco ones fit a gasgas, just a thought]