Proud owner of newly acquired 71 Bultaco Sherpa T 250 (seller said it was a '71 but I have not fully verified yet)

First question! It's about the petcock, which I think the seller gave me incorrect info about...After some testing I believe the pic below is the "off" position (lever at 3 oclock, aka, pointing at right hand side). Is that correct? And "on" would be straight down (6 oclock) and reserve pointing at left hand side (9 oclock) ? 

 

 

You are correct down is on The lever is usually marked with a C and R closed and reserve

Thank you @naichuff !

I am considering getting an original exhaust muffler but the fella who sold it to me complained that the original exhausts on these was "a lot" of back pressure. Wondering if anyone has thoughts on that. I love the look of the original exhaust with the chrome accent and am surprised they are on ebay

Back in the day nobody ran the triangular rear muffler as they did rob the bike of power, there was talk about a reproduction less restrictive one being available. You could always cut the original one open and make it less restrictive.

I run an aftermarket (modern) replica trapezoid end muffler on my model 49 and it does not take anything away except noise. I'm fairly sure mine is different inside to the genuine Bultaco trapezoid end muffler

Nice bike.Don't know if they add ethanol to petrol in Australia.If they do drain tank before leaving the bike for anytime as the ethanol attacks the fibreglass tank.

9 hours ago, feetupfun said:

I run an aftermarket (modern) replica trapezoid end muffler on my model 49 and it does not take anything away except noise. I'm fairly sure mine is different inside to the genuine Bultaco trapezoid end muffler

That sounds nice, where did you find that? Or did you have it fabricated.

15 hours ago, wilbur said:

That sounds nice, where did you find that? Or did you have it fabricated.

Mine came from Ivan Cirre in Spain. You will find their website using Google. It was the only place I could find one when I was looking about 10 years ago. They are probably more easily sourced nowadays.

In Motion has them on their webpage but it is saying out of stock just now.

A friend of mine made one that works well too. It wouldn't be hard

www.ivancirre.com

Thanks for the tips and the link. I had only looked at ebay and so it's great to see how many parts and stuff are available on ivancirre. Thank you!

Bike is running really well BUT if I try a sustained uphill (there is a steep dirt road behind our house) the engine will cut out regardless of gear/torque. My first guess is carb float height - this is my first Amal carb. Is float height easily adjusted? Anything else I should look at first? (I did add extra gas to the tank to make sure it wasn't the obvious!)

 

If it goes good before it dies during sustained high power then it's not float height.

From what you have said it sounds like the fuel level goes down with sustained high power. The usual causes for this (apart from low fuel level in the tank which you have already tested for) are:

Restrictive fuel tap. I can see in your photo that you have the original type fuel tap and they are notorious for having a poor flow rate.

Blocked strainer on the fuel tap inlet.

Blocked fuel strainer inside the banjo fitting on the carby.

Blocked in-line fuel strainer.

Blocked tank vent.

To answer your question about the float height yes you can adjust the fuel height by using different thickness bowl gaskets.

If I have misinterpreted what you said and you are actually saying that it dies when the front of the bike is above the back of the bike then that is a different kettle of fish and you can test for this by lifting the front of the bike up with the motor running and see if it makes a difference.

There is a weakness with concentric bowl AMAL carbys in that if the front of the bike goes a lot lower than the back of the bike as in dropping down something extremely steep, the idle speed can drop off sharply. That weakness is one reason I use a modern carby on my model 49.

Edited May 10, 20215 yr by feetupfun

@feetupfun thank you kindly for that great list of tasks to investigate - sounds like I need to do thorough checkup for fuel delivery to the carb, before I worry about float level.

"If I have misinterpreted what you said and you are actually saying that it dies when the front of the bike is above the back of the bike then that is a different kettle of fish and you can test for this by lifting the front of the bike up with the motor running and see if it makes a difference."

Bike dies when the front is above the back (going *up* a hill - ascending). I will do a lift test at idle and see what happens.

Replaced petcock, fuel line from tank to carb, and inline fuel filter. All those things helped. To be honest though... I think it needed *even more* gas in the tank. I realized the tank had been lined with something to protect the fiberglass from the ethanol. Which is great! But it gives the interior of the tank and bumpy and uneven inner topography. So I think it needs a pretty full tank in order to get full fuel delivery especially on a steep incline.

Regardless, it is very peppy going UP the dirt road now. Descending a steep hill I experienced the sudden drop in idle that you mentioned @feetupfun - if I was doing more serious rides on a frequent basis, I would probably look into replacing the carb, but for now I will just keep it original.

Thanks for the tips.