Sherpa T In Trials Mods?

[alan_nc]

Group,

Planning on riding a Model 92 Sherpa T in AHRMA Modern Classic this

coming year and have several questions.

1. Carb mods(jetting suggestions)

2. Flywheel mod

3. Clutch/Cable mod

4. Brakes

5. Timing

6. General suggestions

Bike already has the electronic ignition. Someone put a lighter 250

flywheel on the bike - do I want to go back?(what flywheels will fit).

Do you use stuffer plates? Has a dual plug head with a compression

release in one hole - do I want to change this? Anyone going with a

second head gasket to lower compression? Do I stay with the AMAL or

put a MIK on? Any suggestion on gearing or sprocket size? Do they

make a longer lever for the clutch (isn't exactly a 2 finger pull).

Do they make a 'slow' acting throttle - just touch the throttle and

the front wheel if off the ground. Any modifications that are

standard for the brakes - they do seem to work fine.

Any and all suggestions appreciated.

Thanks in advance.

Alan_nc

[copemech]

Do I stay with the AMAL or?

Although I am from that genre, or whatever you call it, and know nothing about making them things actually work, AMAL was a dirty word some 30+ years ago, go figure!

[swooshdave]

Group,

Planning on riding a Model 92 Sherpa T in AHRMA Modern Classic this

coming year and have several questions.

1. Carb mods(jetting suggestions)

2. Flywheel mod

3. Clutch/Cable mod

4. Brakes

5. Timing

6. General suggestions

Bike already has the electronic ignition. Someone put a lighter 250

flywheel on the bike - do I want to go back?(what flywheels will fit).

Do you use stuffer plates? Has a dual plug head with a compression

release in one hole - do I want to change this? Anyone going with a

second head gasket to lower compression? Do I stay with the AMAL or

put a MIK on? Any suggestion on gearing or sprocket size? Do they

make a longer lever for the clutch (isn't exactly a 2 finger pull).

Do they make a 'slow' acting throttle - just touch the throttle and

the front wheel if off the ground. Any modifications that are

standard for the brakes - they do seem to work fine.

Any and all suggestions appreciated.

Thanks in advance.

Alan_nc

I use my compression release. Not often but occasionally. It does a wonderful job in the right situation.

Compression should be low enough already. I guess you will soon find out that there is no head gasket.

I believe there is a trials-specific throttle.

What is your rear sprocket now?

I have a re-sleeved Amal on my M49 and think it works just fine.

Edited October 8, 2007 by swooshdave

[alan_nc]

Dave,

Thanks for the reply. Compression on my 92 is so high that I can stand on the kick start lever. Did someone make a high compression head or piston for this engine? I'll check sprocket teeth - my problem at the moment is that I can't get the bike to go slow enough.

Alan

[swooshdave]

Dave,

Thanks for the reply. Compression on my 92 is so high that I can stand on the kick start lever. Did someone make a high compression head or piston for this engine? I'll check sprocket teeth - my problem at the moment is that I can't get the bike to go slow enough.

Alan

Compression on my M92 is pretty stout too. And I don't think it's that fresh. But it is a 350-ish, so there is a bit of piston there. My 250 is not so bad to kick and the 125 is a breeze. With that kind of logic, I'm not surprised at the 350 being a bit of effort.

If it's too much then a compression release may be handy. Either that or eat more of that NC BBQ.

[woody]

Strange that your 92 is snappy off the throttle as they are generally a softer power delivery. Mine was quite soft even when it was fully rebuilt, a mate owns it now and it still has soft delivery despite a new piston/rebore. I also remember another 92 that I used to ride when they were new and that was pretty soft too, especially compared to the 159 that someone bought when they came out.

Returning to the original heavier flywheel may help damp things down a bit and retard the ignition as much as you can. Check also that the big flywheel on the clutch side hasn't been lightened as well as this was sometimes done in conjunction with the lighter ignition flywheel to quicken throttle response. Never tried head spacers to lower the compression so can't comment on the effect of that on the Bult.

Fit a domino slow action throttle.

Amal carb probably isn't the best out there but should work fine as long as it isn't worn out, my old 92 still has the original Amal and it works fine. A Mikuni may possibly liven it up a bit more if it carburates cleaner off idle than the Amal.

You can swap over the front brake and clutch arms as the front brake arm is longer. Alternatively, just lengthen the clutch arm by cutting in two and adding a piece in. In the UK, Venhill make featherlite cables which are teflon lined (or something) and these give a smoother lighter clutch action due to the lesser resistance of the cable. They work. Maybe there is something similar in the US if you can't get Venhill there.

In the UK, a mod for the brakes is to replace the chrome liner in the hub with a steel insert if the chrome has worn out or is pitted/flaking. Yes it adds some weight but (my opinion only) people get far to obsessive about the weight of a bike. In reality it isn't going to make a scrap of difference in a negative sense to the way it rides.

I used standard gearing on mine.

Slightly longer shocks will make it steer a bit quicker if the steering bothers you - never bothered me but they can feel a bit long, depends what you're used to.

Hope you get it sorted to your liking - they're a nice bike

[alan_nc]

Woody,

Thanks so much for taking the time to respond so fully. I have a 15 tooth front sprocket and 51 tooth rear, which the book I have says should be should be 11/46. I will try and find a smaller front sprocket. The comment on backing off the timing is probably spot on. I have seen the domino throttle and will try to find one of those.

Brakes are fine to me so probably won't do anything there. Will look into a longer arm for the clutch cable. Bike usually starts 1st kick when hot and runs well.

Alan

[feetupfun]

Woody's suggestions about the clutch cable and arm length will make a big difference compared with standard equipment. Also make sure you have a handlebar clutch lever with high mechanical advantage. The AMAL levers that would have been on the bike when new are good in this regard while some aftermarket and Japanese levers have less mechanical advantage.

A further reduction in clutch pull is available by fitting Barnett clutch plates. Using these allows the clutch pressure plate spring preload to be run a lot lower than with the standard all-steel Bultaco clutch plates. Have a look at your clutch before you order them though as they may have been fitted to the bike already. They should be available through any decent motorcycle shop.

Be careful not to gear your 325 too low. They do feel a bit fast in first until you get the motor running sweetly. Standard gearing with the motor purring nicely will not limit you in the tight stuff. A M92 that is not running sweetly however can be a bit of a handful in the tight stuff.

Even when you get the clutch pull nice and light, the action has a wide engagement point that can take some getting used to after Jap twinshocks or modern bikes.

[swooshdave]

Interestingly I don't really worry about my clutch pull. The only time I touch the clutch is at the beginning of a section. Never during the section.

This is because the trials that I attended, always vintage, mostly AHRMA, are "no stop" and the sections are specifically set so that you can keep rolling. Even at the slowest sections the bike can run slow enough to get through.

I'm using Yamaha pattern levers. They allow two fingers on the front brake, which is plenty and are a bit longer on the clutch side, but still enough. And they are plenty cheap, something like $10 for each side. I did have to hog out where the barrel goes, but that was easy.

Blog entry on levers

If you drop to the 11 front you will definitely go slow. Just call up Hugh's and get one. No need to search too hard.