Triumph 1970 T100

[click]

Hi,

I got a Premier carb for my 1970 T100.

My air screw is 3 and 1/18th turns out this gives me a steady tickover but feels a bit 'woolly' coming off idle.
High speed runs give a light biscuit brown on the porcelain of the plug so, I think, the needles, NJ, slide & MJ seem to be OK?

The PJ has two rings, so #17

Since the air screw, being 3 and 1/8th turns out, is leaning out the mixture do I need to go to a #15 PJ, which I think is leaner?

This is my chart, is this correct?

Amal Premier PJ

LEAN END
1 ring #15
2 ring #17
3 ring #19
4 ring #21
5 ring #23
RICH END

 

[Bernhard]

Re; “Since the air screw, being 3 and 1/8th turns out,”

With Amal’s ,they are designed to run, at best , 1 1/2/ turns out. That is one complete turn-or 2 half turns plus another half.

Your “being 3 and 1/8th turns out,”- are you sure it’s not 3 half turns out?

 

[click]

Re; “Since the air screw, being 3 and 1/8th turns out,”

With Amal’s ,they are designed to run, at best , 1 1/2/ turns out. That is one complete turn-or 2 half turns plus another half.

Your “being 3 and 1/8th turns out,”- are you sure it’s not 3 half turns out?

Apologies for the delayed response!

Definitely 3 and 1/8th turns out, the air adjuster was nearly falling out of the hole!!

Since then I changed to a 15 PJ (one ring) & dropped the needle to it's leanest setting.

The air screw is now a little over 1 1/2 turns out.

It's still running a bit rich on the low end, less than half throttle, plugs are sooty and after an hour of running you can feel the engine is slightly loading and the tickover starts to falter a bit, I presume from the plugs loading up with soot.

Maybe I'm asking too much from the old design NEW premiere carbs?

 

[Fast Eddie]

Is it possible the sooty plug is caused by burning oil rather than richness ?

 

[click]

Is it possible the sooty plug is caused by burning oil rather than richness ?

Could be but I don't think so on a new engine, but anything is possible. Also both plugs are identical, difficult to believe I have exactly the same type and amount of oil ingress on both cylinders, but again when dealing with classic bikes anything is possible!!

I was looking at another thread on the Norton Commando section about reading a plug. This plug looks very similar to the plugs from the T100.

I think I'm just comparing how the bike was pre-rebuild with how it is now. It's different but running a lot better now.

I think I just need to use it more and stop posting about it on classic bike forums!! roll on the summer

 

[Bernhard]

Hi,

I got a Premier carb for my 1970 T100.

My air screw is 3 and 1/18th turns out this gives me a steady tickover but feels a bit 'woolly' coming off idle.
High speed runs give a light biscuit brown on the porcelain of the plug so, I think, the needles, NJ, slide & MJ seem to be OK?

The PJ has two rings, so #17

Since the air screw, being 3 and 1/8th turns out, is leaning out the mixture do I need to go to a #15 PJ, which I think is leaner?

This is my chart, is this correct?

Amal Premier PJ

LEAN END
1 ring #15
2 ring #17
3 ring #19
4 ring #21
5 ring #23
RICH END

You misunderstand, the pilot air screw , should roughly, give or take, if you have the correct pilot jet be, 1 1/2 turns out .
Over 2 turns, pilot jet is too small, less than 1 turn pilot jet is to big.

 

[Fast Eddie]

Could be but I don't think so on a new engine, but anything is possible. Also both plugs are identical, difficult to believe I have exactly the same type and amount of oil ingress on both cylinders, but again when dealing with classic bikes anything is possible!!

I was looking at another thread on the Norton Commando section about reading a plug. This plug looks very similar to the plugs from the T100.

I think I'm just comparing how the bike was pre-rebuild with how it is now. It's different but running a lot better now.

I think I just need to use it more and stop posting about it on classic bike forums!! roll on the summer

A rebuilt motor will use more oil until the cross hatching has been bedded in by the rings.

Also, sadly, these days is there’s dodgy parts around. Crap (new) rings were definitely a factor in my T140 being an oil burner. And the subsequent plug fouling palaver sent me down many ‘carb related’ rabbit holes !

 

[Bernhard]

In addition to my post above, it appears you are not running on the pilot system at all.
Are the pilot holes in the carb body blocked up forcing you to run on the needle part of the carb circuit?

 

[click]

In addition to my post above, it appears you are not running on the pilot system at all.
Are the pilot holes in the carb body blocked up forcing you to run on the needle part of the carb circuit?

I don't think I misunderstood you, I understand that Amal's, ideally, should be initially setup at 1 1/2 turns out on the air screw.

Since I initially had to screw my air screw out 3 turns to get the bike to run & tickover with the original 17 PJ, I felt I was leaning out the air with the air screw because the 17 PJ was too rich. Once I changed to a 15 PJ I had to re-adjust the airscrew to around 1 1/2 turns out which is a good starting point, which is the point you were making.

I take your point about checking the pilot holes in the carb, I did blow air through all the holes in the carb before I originally installed it due to reports of some Premiere's having swarf in the channels. I'll go in & have another look at the carb body, this time I'll pay full attention!!

As I said, at the moment it's actually running quite well, part of the problem is that I do very little miles on the bike each year but I had it out today for about an hour, probably only did 30miles, lots of slow 20-30mph stretches in traffic, probably only got up to a max of 50mph.

Really appreciate your comments, it helps me with my diagnosis.

 

[click]

A rebuilt motor will use more oil until the cross hatching has been bedded in by the rings.

Also, sadly, these days is there’s dodgy parts around. Crap (new) rings were definitely a factor in my T140 being an oil burner. And the subsequent plug fouling palaver sent me down many ‘carb related’ rabbit holes !

Point taken & understood.

 

[Fast Eddie]

As I said, at the moment it's actually running quite well, part of the problem is that I do very little miles on the bike each year but I had it out today for about an hour, probably only did 30miles, lots of slow 20-30mph stretches in traffic, probably only got up to a max of 50mph.

Click for that kind of riding I’d seriously consider a grade hotter plug (lower number if using NGK).

 

[click]

Click for that kind of riding I’d seriously consider a grade hotter plug (lower number if using NGK).

Good suggestion, I know I’m asking a lot from old, air cooled, non-fuel injected engine tech!!!

I’m mainly going to use the T100 for short‘ish trips, no motorway spins, so a hotter plug might be the ticket I’ll proceed with caution and see what results I get.

Thanks for the suggestion

 

[Fast Eddie]

Don’t forget, back in its day it was a youngsters scratcher, the RDLC of its day. They’d rev to 10,000 rpm (!) so would have had a plug choice according to such use.

 

[Onder]

There are two very small holes in the body forward. You spray in carb cleaner from the air filter side of the carb (small holes
in the back of intake horn) and watch the streams that issue forth. One is smaller than the other. Check that your streams are good.
I had a new premier where the stream from one of the little holes was not a good tight stream but looked like a crooked fan. The holes are so
small it likely isnt that hard to bugger them on manufacture.
Black plugs can be richness, rings not up to snuff or the guides. Most brit bikes of our era have no guide seal and likely fairly generous
guide to stem clearance or will have in short time. Commando has intake seals which I think is a great help.

 

[click]

Don’t forget, back in its day it was a youngsters scratcher, the RDLC of its day. They’d rev to 10,000 rpm (!) so would have had a plug choice according to such use.

This was my first ever motorbike, which I got around the mid-eighties. I trashed it all over Ireland & Europe camping, two up! I tried to race lads on RDLC’s and bigger Kawasaki Z’s. At the time nobody understood why I was on an ‘old’ bike, truth be known I probably didn’t fully understand myself

It was my only means of transport for nearly 10 years, so I learned a lot about maintaining an old bike and made plenty of mistakes!!!

 

[click]

There are two very small holes in the body forward. You spray in carb cleaner from the air filter side of the carb (small holes
in the back of intake horn) and watch the streams that issue forth. One is smaller than the other. Check that your streams are good.
I had a new premier where the stream from one of the little holes was not a good tight stream but looked like a crooked fan. The holes are so
small it likely isnt that hard to bugger them on manufacture.
Black plugs can be richness, rings not up to snuff or the guides. Most brit bikes of our era have no guide seal and likely fairly generous
guide to stem clearance or will have in short time. Commando has intake seals which I think is a great help.

Thanks for the info. I’ll pay particular attention to these small holes.

 

[Triton Thrasher]

...Over 2 turns, pilot jet is too small, less than 1 turn pilot jet is to big.

If the pilot jet is too small, the pilot mixture is weak. You screw the air screw in to compensate for that and enrich the mixture, by restricting the pilot air supply.

If the pilot jet is too big, the pilot mixture is rich. You screw the air screw out to compensate for that and weaken the mixture, by opening the pilot air supply.

 

[Onder]

Did anyone post this link? If not here it is: http://jba.bc.ca/JBCycle/Resources/Bushmans Carb Tuning Secrets.pdf

 

[click]

If the pilot jet is too small, the pilot mixture is weak. You screw the air screw in to compensate for that and enrich the mixture, by restricting the pilot air supply.

If the pilot jet is too big, the pilot mixture is rich. You screw the air screw out to compensate for that and weaken the mixture, by opening the pilot air supply.

Appreciate all your patience with my ramblings!!!

Triton Thrasher & Bernhard; OK, so the opposite of what I was doing is true!!

So, I had, originally, a rich result on the plugs with the air screw 1 1/2 turns out, I could only get the bike to tickover well with the air screw 3 turns out which should have been leaning the heck out of the carburetion!!

I changed to a bigger PJ (from a 17 to a 15, correct me if I'm wrong but these new PJ's are measured in thousands of an inch so 15 is bigger than 17) which should richen the mixture but I had to re-adjust the air screw to 1 /1/2 turns to get a steady tickover, which should be creating a more rich running condition, my head hurts!!!

I wonder if originally the carb had an obstruction in one of the passageways, which would, I think, give a lean mixture and I compensated by turning the air screw out 3 turns?

When I changed the PJ from a 17 to a 15 I gave the carb another clean & maybe cleared the obstruction, hence the reason why the 15 seemed better! not because of the PJ change but because I cleared the obstruction.

Do I have the logic right hear regarding lean/rich, big/small, air screw in/out.

I always get this muddled in my mind, less air = rich, more air = lean, for some reason my brain always defaults to the other way around!!!

Once again I appreciate your patience and knowledge, I do/did know this stuff but I so rarely use the brain cells relating to carburetion they tend to, over time, go back to my incorrect default state!!!

OK, the plan is:

1. Remove PJ & airscrew to ensure passageway across carb is clear. Spray cleaner into the two small holes near the air intake, I'll use some guitar string to carefully poke around in the holes.

2. For my curiosity I'll put the 17 PJ back in & see how far I need to turn the airscrew out to get a steady tickover.

3. Consider using a hotter plug for the short, slow speed pottering around I'm doing & don't forget to change back if I plan on doing any high speed runs! (unlikely)

 

[click]

Did anyone post this link? If not here it is: http://jba.bc.ca/JBCycle/Resources/Bushmans Carb Tuning Secrets.pdf

Thanks, believe it or not I have this document, I need to read it more carefully!!