.105 vs .106 Needle Jets

elefantrider · Aug 8, 2019

My bike has good 106 jets but it likes the needles in the lowest position (clip on top groove).
Idle screws are three quarter turn out. Any more out and it will backfire on decel.

Plugs are still a little rich.
A little hunting in lower throttle openings.
Idles OK above 1000RPM.

I am going to try dropping down a size to 105 so I can run the needle in the middle position. I think I will pick up some low RPM torque and better low RPM throttle response.

Anyone else finding they need to run 105 needle jets with our 10% ethanol gasoline?

acadian · Aug 8, 2019

I run 105s with needle clip in top slot, bike runs well and plugs look good

acotrel · Aug 9, 2019

If you cannot force your motor to cough by lowering the needles, the needle jets are too big. With petrol, the slightest bit too rich is too much, if you want good performance.

elefantrider · Aug 9, 2019

Stock was 106 (107 in S) and for some time, I was reluctant to go smaller.

I picked up some some 105 jets today at my favorite local shop and will try them, raising needle to the middle position.

elefantrider · Aug 10, 2019

I noticed the PO installed chrome slides with different cutaways, left side was a 3 and the right side a 5!

Chrome slides had no wear marks and glide with little friction.

Removed them and installed new Anodized Amal slides I got from Andover, #3 for both sides.

Are these slides measured after the Anodized coating is applied?

One Anodized slide does not glide at all , got stuck and required being pushed back up from the bottom. Not good.

Switched sides, a little better but still have a little stiction in one spot.

Dry lapping by hand helps a little, with all the screws backed off on the carb, but these are tight fitting, and not exactly the same straightness/diameter between the 2.

Less slippery than chrome also.

Onder · Aug 10, 2019

Perhaps the bores of the carbs are out of round. Not unusual.

marshg246 · Aug 10, 2019

elefantrider said:
I noticed the PO installed chrome slides with different cutaways, left side was a 3 and the right side a 5!

Chrome slides had no wear marks and glide with little friction.

Removed them and installed new Anodized Amal slides I got from Andover, #3 for both sides.

Are these slides measured after the Anodized coating is applied?

One Anodized slide does not glide at all , got stuck and required being pushed back up from the bottom. Not good.

Switched sides, a little better but still have a little stiction in one spot.

Dry lapping by hand helps a little, with all the screws backed off on the carb, but these are tight fitting, and not exactly the same straightness/diameter between the 2.

Less slippery than chrome also.

I've never had problems with new slides but damaged bodies, many times.

Top screws overtightened? Bowl screws overtightened? Mounting bolts overtightened? In all cases, just tighten until the lock washers are flat - no more. If that's what happened and you can tell which way they are oblong, you can sometimes squeeze them the long way and get them back to round.

I recently was working on a bike that all screws and nuts were so overtightened that I could not get the slides out until I pinched them in a vice, but the bodies were too far gone to use. http://www.gregmarsh.com/MC/Triumph/T100R_1970.aspx

elefantrider · Aug 10, 2019

Yes, likely one carb bore is out or round but switching slides in the bores made a world of difference.

acotrel · Aug 10, 2019

If there was enough ethanol in the fuel to make a difference to the tuning, you would expect it to run leaner. Alcohol has a high latent heat of vaporisation, so it causes the carbs to be colder. That increases the air density in the incoming charge requiring more fuel to get the combustion conditions right. So you would be more likely to need the bigger needle jet.

elefantrider · Aug 10, 2019

Yes, that would be my assumption also. But new plugs don't lie.

With 105 jets and needles in the highest position, plugs are still too dark within 5 miles.
BUT I am not sure if they are dark from idle or from the needle jet. I did tune for idle a bit on the ride.

Fuel level is 5-6mm below the top of the bowls which is on the low side per Amal's recommendations.

Previously, I had 106 jets and needle in the lowest position.

Throttle response off idle is better and it makes more power.

marshg246 · Aug 10, 2019

Sorry if I missed it, but what engine, what year, and what carbs?

Madnorton · Aug 11, 2019

Sounds like shot carbs, with the 105,s fitted the plugs are black after 5 miles says it all. You get to a point with worn carbs that no what you do or change they are hard to adjust or don't adjust.
With 105 or 106 jets, you should be able to set up tickover to a sensible level, again another indication of worn carbs.
A lot of the Amal concentric bodies were most probably out of tolerance when they came from the factory, made on worn out machines, surprising some work as long as they do.

acadian · Aug 11, 2019

elefantrider said:
Yes, that would be my assumption also. But new plugs don't lie.

With 105 jets and needles in the highest position, plugs are still too dark within 5 miles.
BUT I am not sure if they are dark from idle or from the needle jet. I did tune for idle a bit on the ride.

Fuel level is 5-6mm below the top of the bowls which is on the low side per Amal's recommendations.

Previously, I had 106 jets and needle in the lowest position.

Throttle response off idle is better and it makes more power.

You mean needle clips in the BOTTOM groove, right?

Needle jet controls mixture just off idle to approx 1/2 throttle, clip position across entire range. Look down into the plug to see where the transition is.

You should drop your needles.

Danno · Aug 11, 2019

There are different spec needles, I think. Much easier to swap than needle jets.

dynodave · Aug 11, 2019

acadian said:
Needle jet controls mixture just off idle to approx 1/2 throttle,
clip position across entire range.

HUH?
from amal list 117/3 issue #5
"from 1/8 to 1/4 open throttle cutaway"
" 1/4 to 3/4 open needle position"

I have been successful tuning my carbs by using the published information. Reinterpreting the physics only complicates things and slows tuning progress...

marshg246 · Aug 11, 2019

elefantrider said:
Idle screws are three quarter turn out. Any more out and it will backfire on decel.

I'm stuck on 3/4 out - that's why I wondered which engine/carbs. To me it's pretty clear that you have air leaking,or wrong pilot jets (if any), or clogged idle passages.

Generally speaking, new carbs will have the air screws out 1-1/4 to 1-1/2 turn. I start 1-1/2 out and once warmed up, turn them in until there's no stumble when blipping the throttle - almost always comes out to be 1-1/4 turns. At 3/4 turn, I would figure out why before going further.

Also, the spray bar and needle are different from standard on 850's according to Amal.

elefantrider · Aug 11, 2019

Bike is a 4000-original-mile '71 SS.
It sat for a long time before I got it a few years ago, and now I'm fixing a previous mechanic's mistakes.

Carbs are not shot. Slides are slightly a different dimension but they work.

I went on a longer, 20 mile ride last night, and it's burning too much oil, intermittently on acceleration.
So plug reading is actually OIL contamination, not mixture richness.

Probably the rings are not seating. Cylinder head is tight.

Madnorton · Aug 11, 2019

It is not burning oil intermittently, it is burning it all the time, you just notice it when accelerating. The physical reason will still be present accelerating or not.

With the carbs removed you should be able to determine the reason for the oil burn to three areas, then just a case of lifting the head and barrel if two of the three are not visible with the carbs removed.

If you notice oil being burned from both sides, as you say, rings / bores.

The fact it is original and only done 4,000 miles is irrelevant. I would not waste anymore time, just lift the head and barrel and fix it. There is nothing probable about burning oil, it is, fact, so best to fix it.

marshg246 · Aug 11, 2019

I would check to make sure the rocker area is not over-filling with oil. Bad or no intake seals and flooded rockers could cause your problem. If the drain is plugged/partly plugged you could be flooding the rockers and you could end up with other problems.

Also, I can't imagine how oil burning would cause you to need to turn the air screws in more than normal.

acadian · Aug 11, 2019

dynodave said:
HUH?
from amal list 117/3 issue #5
"from 1/8 to 1/4 open throttle cutaway"
" 1/4 to 3/4 open needle position"

I have been successful tuning my carbs by using the published information. Reinterpreting the physics only complicates things and slows tuning progress...

Yes, you're correct, clip position only 1/4 - 3/4... which happens to be 90% of where most people ride 99% of the time

needle jet, aside from some overlap areas, pretty much off idle to 1/2 throttle

.105 vs .106 Needle Jets

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