11 replies to this topic

[FSB]

Hi I'm new and I come from germany, so my english maybe isn't so good sometimes.

I have a sherpa from 1971 or 1972 (don't know it exactly) with 250ccm.

If I ride for about 30 minutes everything is ok, but then it begins to smoke and doesn't want to go to high rpm. If I then ride a few seconds at full throttle for about 10 seconds it's ok but after another 20 seconds normal ride it begins to smok again.

Seams to run too rich but closing the fuel tap doesn't bring any improvement. Also I've allready thought about dirt in the float-valve (is that the correct word??) but adding a fuel filter also didn't bring any success.

Yesterday I put the condenser under the tank because I thought that it is too hot and so the spark isn't good enough but today I had the same problem.

But today I noticed that the smoke doesn't smell like my 2-stroke oil but rather like gear oil. At the moment I think about the crankshaft seal at the transmission-side but I don't know why it should only leak when it's hot.

Do you have any suggestions for me? Is it possible the seal only leaks when it's hot?

Thanks, Felix.

Edited by FSB, 23 July 2008 - 03:30 PM.

[swooshdave]

I had a very similar problem. It was actually the gasket between the engine cases that was leaking gearbox oil into the crankcase. The exhaust definitely has a different smell when that happens.

The good news is that the engines are relatively easy to work on. With a minimal number of tools you can split the cases yourself, if so inclined.

Get the gearbox oil leak addressed and then you can see about get it running correctly.

Can you post the model number of your bike? That will let you know the approximate year.

You're English is just fine, much better than most.

Edited by swooshdave, 23 July 2008 - 04:14 PM.

[feetupfun]

Hello Felix
If you are getting gearbox oil into the crankcase once the motor gets hot, you may have a problem with the vent for either the gearbox or primary drive case. If one of the vents is blocked, there will be pressurisation when the oil gets hot. Bultacos like yours usually have two vents - one for each compartment. The primary drive vent is usually a hole in the filler cap (at the front end of the primary drive casing) and the gearbox vent is usually a hole through the filler plug (located under the carby).
The path of the oil leak may well be as Swooshdave found with his bike (through the centre gasket), or it may be through the crank seal or crank seal holder gasket.
You may find the leak is not a problem once the pressurisation problem is fixed.
David

[FSB]

Hi.

Thanks so much for your reply.

The idea with the vents seams to be logicaly, I didn't think about this. But is it possible that there are no holes in my filler caps? Both are made of grey plastic and they seam to be stock...

Maybe I should drill a small hole in each of them and put a little tube in it.

Yesterday in the evening I removed the primary drive casing and modified the crank seal holder because my Bulto dealer has send me a bigger and wider seal as this one which was in it. The new seal has two lips (with two springs) whereas the old one only had one lip and one spring. Maybe this could be an improvement.

@swooshdave: A friend of our family who comes from Nederland gaves me the Bultaco. I don't know who the previous owner was before our friend owned the Bulto, but obviously he did grind the frame and engine serial number away.

But here is a picture. Like I sad I think it must be 1971-1972 because the frame should be build in this years and also the front hub with its brake should be '71-'72.

Only the silencer is from a later model I think.

If the year of construction would be 1971-72 would it then be a T73 or T80? I don't really understand the way like Bultaco have named their models, it's a little bit confusing for me.

edit: I forgot the picture.



Bye, Felix.

Edited by FSB, 24 July 2008 - 11:20 AM.

[PeterB]

Hallo FSB,
Hab gut English geshcrieben!
The frame looks like a 1972, silencer from a 73/4 model - didn't work as well as the larger type of silencer but was lighter.
I am fairly sure that on the clutch side, there should be an O ring seal on the oil seal carrier, inbetween the crankshaft and the carrier. Also the oil seal carrier will either have a paper flange gasket or an O ring seal.
The gearbox is vented via a small hole in the LHS casing just to the right of the kickstart shaft exit, primary casing should be vented from the cap.
If the smoking does not turn out to be from the primary drive or gearbox and if it does still have the original carb or an old Amal concentric Mk II, it could well be the carb is worn out. A DellOrto PHBL26 from a Gas Gas works very well and goes straight on, more or less, with just a change to a 95 main jet.
Bye, PeterB.

[Woody]

Yes, I'd agree that the frame looks like a model 80, 1970-72.

Crankshaft oil seal carriers on the early models only had a paper gasket, on later models the seal carriers were shaped differently to take a large O ring instead of the paper gasket. All models use the smaller O ring inbetween the crankshaft sleeve and the main bearing on the clutch side.

[FSB]

Hi.

@Peter: Thank you .

There is mounted an Amal carb, but it works pretty well. I only had to do some adjustments at the idle screw and now it has a good throttle response which wasn't so good before adjusting it.

At the crankshaft is an O-Ring between sleeve and bearing but I didn't change it because I don't have one at the moment. The seal holder has a paper gasket which I degreased and mounted with Hylomar.

If the primary vent is allways in the cap, this could be the source of the problem because there was no hole in the cap. I drilled a hole in it and put a little tube in it which ends behind the engine near the swingarm.

Hopefully the wether is good tomorrow, then I could do a test ride. I'll report.

Bye, Felix.

[FSB]

Hello all.

The problem is solved. Probably it was the vent which wasn't in the primary cap or it was the seal which was worn out (no sharp edge on the lip).

After 30 minutes I was excited and watched to the exhaust pipe every 100 meters, but the smoke didn't come, not even after 1 hour and 15 minutes. Due to the fact that the problem allways started after 30 minutes and now it wasn't there, I think it's solved.

By the way, I think the Bultaco has an Amal MK1. Is that correct?



Felix

Edited by FSB, 28 July 2008 - 05:22 PM.

[swooshdave]

That would be the Mk1.

Extremely simple to work on and despite a reputation of having to fiddle with it, not that bad.

Couple things to look out for:

1. Loose or stuck slide. Permanent fix is to get the carb rebored and a sleeved slide. There are a couple (or were) places in the US to get this done. A new carb will not be as good as a sleeved one. Also over-tightening the carb to the manifold will distort the carb and cause the slide to stick (this would be undesirable).

2. Clogged pilot jet. If I leave gas in the carb for too long and the bike is difficult to start I pull the carb off and clear the pilot jet. Usually solves the problem.

[FSB]

The slide looks very good and doesn't have any wear. There is just a tight clearance between slide and case, so it will work for a time I think.

Setting also seams to be good, there is only a little bit smoke sometimes but not much and only when I ride upwarts a hill wide open. At the moment I run 1:40 with fully synthetic oil. I think it should be ok .

Felix

[FSB]

Hi.

I have found out that my O-ring from the idle screw is damaged. Now I wonder if this gasket/seal set http://cgi.ebay.co.uk/AMAL-genuine-gasket-...1QQcmdZViewItem would be right for my Amal MK1. Can anyone help me?

edit: Just have seen that this auction ends in 20 minutes, but would a seal set for an Amal Mk1 600/900 be right for me? Is the 627 of my Bulto just a special type of the 600 series due to its size (27mm)?

Thanks, Felix.

Edited by FSB, 18 August 2008 - 06:11 PM.

[swooshdave]

FSB, on Aug 18 2008, 11:06 AM, said:

Hi.

I have found out that my O-ring from the idle screw is damaged. Now I wonder if this gasket/seal set http://cgi.ebay.co.uk/AMAL-genuine-gasket-...1QQcmdZViewItem would be right for my Amal MK1. Can anyone help me?

edit: Just have seen that this auction ends in 20 minutes, but would a seal set for an Amal Mk1 600/900 be right for me? Is the 627 of my Bulto just a special type of the 600 series due to its size (27mm)?

Thanks, Felix.

From what I understand the 627 is just a part of the 600 series. Amal parts are extremely common from a wide variety of vendors. If you are uncertain about details most any vendor should be able to assist you.