BritBike Forum logo
BritBike Sponsor BritBike Sponsor BritBike Sponsor
BritBike Sponsor

BritBike Sponsor

BritBike Sponsor
BritBike Sponsor BritBike Sponsor BritBike Sponsor
Jwood & co JRC Engineering dealers Jwood & co
Home | Sponsors, Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons, "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Member Spotlight
J Rowe
J Rowe
Orange, MA USA
Posts: 109
Joined: August 2006
Show All Member Profiles 
Shout Box
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
Who's Online Now
33 registered members (Al Eckstadt), 213 guests, and 452 spiders.
Key: Admin, Global Mod, Mod
Newest Members
hondapete1950, Gaspare, eberhard, Norman Woollons, LandoLando
10257 Registered Users
Top Posters(30 Days)
Stuart 76
Lannis 55
TBolt72 47
Popular Topics(Views)
610,743 mail-order LSR
Forum Statistics
Forums34
Topics67,150
Posts651,632
Members10,257
Most Online3,995
Feb 13th, 2017
Like BritBike.com on Facebook

Previous Thread
Next Thread
Print Thread
Rate Thread
High altitude jets, plugs and settings #383423
07/09/11 9:33 pm
07/09/11 9:33 pm
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
G
geryrace Offline OP
BritBike Forum member
geryrace  Offline OP
BritBike Forum member
G
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
1978 T140V with 11,400 original miles.

I live at 5,145 feet above sea level and occassionally go higher into the Rockies. The plugs soot up almost every ride.

Starts on first or second kick and runs fine. Points, tappets, timing checked and spot on as of yesterday. The bike was purchased new in Boulder, CO and came with 190 jets which I changed to 180's and still sooty black plugs. Throttle needle in top slot and checked the float bowl level some time ago and was fine.

Before I progressively keep going smaller with the jets is there anything I have missed checking or that you need to know?


gery race
Support Your #1 BritBike Forum!

Check out British motorcycles for sale:
British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Check out British motorcycles for sale:
British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Re: High altitude jets, plugs and settings [Re: geryrace] #383428
07/09/11 10:19 pm
07/09/11 10:19 pm
Joined: Nov 2008
Posts: 2,794
Bishop, Calif.
D
desco Online content

BritBike Forum member
desco  Online Content

BritBike Forum member
D
Joined: Nov 2008
Posts: 2,794
Bishop, Calif.
I live at 4,200' and spend most of my days at 7,000 and above, sometimes way above. Carbs on both bikes have been bored and sleeved and are running #3 1/2 slides with the needle in the middle and 106 needle jets. 180 or 190 mains don't seem to matter much. 180s will be too lean lower down.
NGK B7ES plugs.
Don't know what a 78 is supposed to be set at but carbs are carbs and unless you are running wide open all day the mains will not be much of a factor at high altitude.
Try a hotter plug and lean out the idle a tad first. Your needles and jets may be worn, try new ones. Then try a one size leaner needle jet. You will never get it perfect for all altitudes, the best will be a good compromise.


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
Re: High altitude jets, plugs and settings [Re: geryrace] #383429
07/09/11 10:20 pm
07/09/11 10:20 pm
Joined: Mar 2005
Posts: 10,131
Boston, Massachusetts
J
John Healy Offline

BritBike Forum member
John Healy  Offline

BritBike Forum member
J
Joined: Mar 2005
Posts: 10,131
Boston, Massachusetts
[quote]is there anything I have missed[quote]

The Amals are not "one trick ponies." There is more than one fuel circuit involved with change in elevation and change in temperature. Both effect air density. It isn't change the man jet and were done! There is some compensation for higher altitude as the temperature goes down as the air density get higher compensating for the altitude. But changes are usually required. Air density would be lower on a hot summer day than it would be at 50 fall day at 5,000 feet.

I assume you have Concentrics and not MKII Amals?????? (although this applies to both)
You need to address:
a. pilot air screw it might have to be turned out a turn.
b needle jet size - a lot of Colorado dealers fit .105 needle jets instead of the standard .106.
c. needle might have to be dropped one notch.
d main jet might have to be lowered about 15 to 20%.

scroll to the bottom of this link:
http://www.iwt.com.au/mikunicarb.htm

This link will give you information for main jet changes. They are showing the effect for the Mikuni/AMAL jet 4/042. You will get similar results with your Concentric.
http://www.jetsrus.com/FAQs/FAQ_rejet_elevation_and_temperature.htm


Re: High altitude jets, plugs and settings [Re: geryrace] #383446
07/10/11 12:16 am
07/10/11 12:16 am
Joined: Jan 2005
Posts: 1,662
East Bethany New York
Dick Harris Offline
BritBike Forum member
Dick Harris  Offline
BritBike Forum member
Joined: Jan 2005
Posts: 1,662
East Bethany New York
I think the .105 needle jet will help the most. Dick

Re: High altitude jets, plugs and settings [Re: geryrace] #383452
07/10/11 12:49 am
07/10/11 12:49 am
Joined: Dec 2006
Posts: 3,895
Massachusetts, U.S.A.
B
btour Offline
BritBike Forum member
btour  Offline
BritBike Forum member
B
Joined: Dec 2006
Posts: 3,895
Massachusetts, U.S.A.
Hi geryace,

You do not mention what you currently have for slide cutaway.


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
Re: High altitude jets, plugs and settings [Re: geryrace] #383545
07/10/11 4:12 pm
07/10/11 4:12 pm
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
G
geryrace Offline OP
BritBike Forum member
geryrace  Offline OP
BritBike Forum member
G
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
1. They are stock AMAL concentrics
2. I do not know what the slide cutaway size is. What ever came with it in 1978.
3. John's Mikuni link was helpful.
- it idles as fine as a two cylinder will. set at about 800 rpm's and seldom dies. Will pop if I quickly twist the throttle from idle implying to me rich mixture.
- I'll check out the carb in order of John's response starting with the easiest, pilot air screw.
- I assume the needle jet has a number on it and see what it is, but per the Mikuni link its at its leanest setting now in the top notch.
- My gut says its the main jet and 15-20% size reduction puts meat about a 140.

Thanks for the commentary and quick turn around.

PS: You guys were great a couple years back sorting out my rear brake issue that several repair shops couldn't sort out. Sometimes the simple stuff like screwing the master cylinder barrel out a turn or two can be overlooked by the professionals. I screwed with that for years with no success and avoided riding it for the lack of a rear brake.


gery race
Re: High altitude jets, plugs and settings [Re: geryrace] #383555
07/10/11 4:35 pm
07/10/11 4:35 pm
Joined: Dec 2006
Posts: 3,895
Massachusetts, U.S.A.
B
btour Offline
BritBike Forum member
btour  Offline
BritBike Forum member
B
Joined: Dec 2006
Posts: 3,895
Massachusetts, U.S.A.
Originally Posted By: geryrace
1. Will pop if I quickly twist the throttle from idle implying to me rich mixture.


Could be the cutaway on the slide. You undo top of carb. Pull out the slide, and look at the number on the underside of the slide.


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
Re: High altitude jets, plugs and settings [Re: geryrace] #383565
07/10/11 5:25 pm
07/10/11 5:25 pm
Joined: Jul 2009
Posts: 3,549
Vic. Australia
P
Pete R - R.I.P. Offline
In Remembrance
Pete R - R.I.P.  Offline
In Remembrance
P
Joined: Jul 2009
Posts: 3,549
Vic. Australia
The needle-jet is numbered.It would also be worn by bigger by now.
I would have thought about a 5% reduction in main jet.Read all that information carefully again.

Re: High altitude jets, plugs and settings [Re: geryrace] #383569
07/10/11 5:37 pm
07/10/11 5:37 pm
Joined: Mar 2005
Posts: 10,131
Boston, Massachusetts
J
John Healy Offline

BritBike Forum member
John Healy  Offline

BritBike Forum member
J
Joined: Mar 2005
Posts: 10,131
Boston, Massachusetts
When you mean "pop" do you mean it spits back out the carburetor?

If so this is an indication slide is lean, not rich. You can be rich overall and have a too lean slide.

The Concentric would have come stock with a .106 needle jet. If it hasn't been replaced in a while it will be worn, and the mixture at low throttle openings will be rich.

As far as the main jet is concerned the temperature is a factor and I am think you would start in the 170 range, not 140. The stock main was a 190 and you would have to do a lot of above 3/4 throttle work for this to be a bother at all at 5,000 feet.

Most of your riding should be in the 1/8 to 2/3 throttle range and you would never see the main jet at those throttle openings. Most of your riding will be on the needle jet and the needle's taper.

Go slow. Make small changes. Do one thing at a time.

If you have air cleaners you can just remove them. For most filters it is is the same as going down one main, maybe two jet sizes. This might make it pop more on the slide, but run better above that circuit. This action leans out the mixture in all the fuel circuits.
a. pilot circuit (idle to 1/4 with some effect to near full throttle)
b. needle jet diameter (0 to the point where the straight part of the needle leaves the jet approx. 1/3 throttle).
c. needle taper - which groove needle clip is in (approx 1/3rd to 3/4 throttle).
d. Main jet (3/4 to Full throttle).
From there you can tape your throttle and see how each circuit performs.


Re: High altitude jets, plugs and settings [Re: geryrace] #383570
07/10/11 5:42 pm
07/10/11 5:42 pm
Joined: Mar 2005
Posts: 10,131
Boston, Massachusetts
J
John Healy Offline

BritBike Forum member
John Healy  Offline

BritBike Forum member
J
Joined: Mar 2005
Posts: 10,131
Boston, Massachusetts
Dick Harris has done quite a bit of touring on a 1970 Bonneville in the West above 5,000 feet. I think he carried a spare pair of .105 needle jets with him. When he got off the plains he would change them for the ride across the mountains to California. How about it Dick?


Re: High altitude jets, plugs and settings [Re: John Healy] #383623
07/10/11 9:50 pm
07/10/11 9:50 pm
Joined: Jul 2009
Posts: 29
Phoenix, AZ
D
Dale Hoover Offline
BritBike Forum member
Dale Hoover  Offline
BritBike Forum member
D
Joined: Jul 2009
Posts: 29
Phoenix, AZ
FWIW, I can chip in my personal experience riding at high altitude. I had both a '67 and '68 Bonneville with concentrics running pretty well (thanks to this forum) in my primary operating range of 6,000 to 8,000 feet in SW Colorado.

My set up was .105 needle jet, standard (two groove) needle set in the middle clip position, 3.0 slide cutaway, 170 main jet, stock exhaust and filters. The carbs were new on the '67 bike, and rebuilt carbs w/new brass and sleeved slides on the '68. Floats set at .080 below the mounting surface.

Very good idle and good throttle response throughout. The plugs always looked a little more rich than what I thought was ideal but the bikes both ran well. I always wanted to try a 3.5 cutaway but never got around to it.

Now we live in Phoenix so I'm going back to factory settings, but that's another story...

Re: High altitude jets, plugs and settings [Re: geryrace] #383758
07/11/11 10:48 am
07/11/11 10:48 am
Joined: Jan 2005
Posts: 1,662
East Bethany New York
Dick Harris Offline
BritBike Forum member
Dick Harris  Offline
BritBike Forum member
Joined: Jan 2005
Posts: 1,662
East Bethany New York
As John said,I carried two jet holders with .105 needle jets and two step smaller mains (dont recall the number) I just had to pop the float bowls make the change and I was good to go. Dick

Re: High altitude jets, plugs and settings [Re: geryrace] #383813
07/11/11 3:57 pm
07/11/11 3:57 pm
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
G
geryrace Offline OP
BritBike Forum member
geryrace  Offline OP
BritBike Forum member
G
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
Pull the carb apart and was surprised at what I found.

1. Throttle slide is marked MB 5 and 928
2. Needle jet is as expected, a 106
3. Main jet is a 170, which surprised me. I do still have the original 190's.
4. The plugs are Champion N4C's so it looks like I tried going hotter at some time in the past as the Handbook says N3's. I have some NGK B7ES plugs as suggested above.
5. Float is set at 24/64ths below the bowl rim.

John: I have only 11,400 original miles on the bike. Would needle and its jet wear out in that time frame? (Didn't I read that when replacing needle or jet it is done only as a set? So if I went to the 105 I would be well served to replace needle at the same time?)

I thought the "pop" was from the tailpipe, not back through he carb.

Plan:

Reassemble carb
Leave the 170 mains in
Needle clip at top most slot (leanest)
NGK B7ES plugs installed
Adjust pilot air screw outwards
Go ride.


gery race
Re: High altitude jets, plugs and settings [Re: geryrace] #383818
07/11/11 4:13 pm
07/11/11 4:13 pm
Joined: Dec 2006
Posts: 3,895
Massachusetts, U.S.A.
B
btour Offline
BritBike Forum member
btour  Offline
BritBike Forum member
B
Joined: Dec 2006
Posts: 3,895
Massachusetts, U.S.A.

quote=geryrace] 1. Throttle slide is marked MB 5 and 928[/quote]

That is not the number you want. There is another number on it. If not, then put the slide on a flat surface and measure the distance to the top of the cutaway. The number that should be there, would reflect how many 1/16 ths.

quote=geryrace] I have only 11,400 original miles on the bike. Would needle and its jet wear out in that time frame? [/quote] Yes.

quote=geryrace] Plan:

Reassemble carb
Leave the 170 mains in
Needle clip at top most slot (leanest)
NGK B7ES plugs installed
Adjust pilot air screw outwards
Go ride.
[/quote]

The 170 mains may be too small for what you want. If the main is too small it will effect the lower carb circuits as well. One finds the proper main by putting in bigger mains until the engine 8-strokes ( You can experience 8 stroking by running the bike without a main jet), then go down one size main.

You amend your plan accordingly, and after determining slide cutaway, try a larger one.

Or amend your plan for high altitude riding, by doing exactly as Dick Harris said.


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
Re: High altitude jets, plugs and settings [Re: geryrace] #383853
07/11/11 6:42 pm
07/11/11 6:42 pm
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
G
geryrace Offline OP
BritBike Forum member
geryrace  Offline OP
BritBike Forum member
G
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
Plan completed as described above. Took her for a 7 mile spin up a foothill with top speed about 50 mph then pulled clutch in and killed it coasting to a stop and pulled plugs. They looked good. Not white nor sooty. Did I do it right?

Question: I have minimal (less than a 360 degrees) of air screw adjustment on left carb before it revved or died off whereas I had nearly twice that on the right. Is that common or indicative of another issue?

Question: It doesn't feel as peppy as it should and as I remember my '73 being. Best plan is to get the 105 needle jet assembly and play with the 170 and 190 mains that I have to see what I get?

Question: Saw no other numbers on the slide. Location?
If I measure the cutout in sixteenths, then what do I do with the number?


My parts book says:
Needle 99-1036
Needle jet for 106: 99-1035 (105?)
Jet holder 99-1034

Got better numbers?


gery race
Re: High altitude jets, plugs and settings [Re: geryrace] #383858
07/11/11 6:51 pm
07/11/11 6:51 pm
Joined: Nov 2008
Posts: 2,794
Bishop, Calif.
D
desco Online content

BritBike Forum member
desco  Online Content

BritBike Forum member
D
Joined: Nov 2008
Posts: 2,794
Bishop, Calif.
Difference in air screw adjustment could indicate a partially blocked idle jet.
Did you look for slide numbers on the bottom of the slide, the part that sits in the seat?
105s and new needles will be in when?


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
Re: High altitude jets, plugs and settings [Re: geryrace] #383877
07/11/11 7:48 pm
07/11/11 7:48 pm
Joined: Nov 2005
Posts: 7,384
Back on the mainland!
JubeePrince Offline

Life member
JubeePrince  Offline

Life member
Joined: Nov 2005
Posts: 7,384
Back on the mainland!
Originally Posted By: geryrace
Question: Saw no other numbers on the slide. Location?


gery...you gotta look closely. There should be a small-font number nearby as shown in the photo:



HTH,

Steve


'77 T140J
"Vintage Bike". What's in your garage?

"The paying customer is always right."

Fitting round pegs into square holes since 1961...
Re: High altitude jets, plugs and settings [Re: geryrace] #383924
07/11/11 10:28 pm
07/11/11 10:28 pm
Joined: Mar 2005
Posts: 10,131
Boston, Massachusetts
J
John Healy Offline

BritBike Forum member
John Healy  Offline

BritBike Forum member
J
Joined: Mar 2005
Posts: 10,131
Boston, Massachusetts
The needle, being stainless steel, doesn't wear at any where near the rate the soft brass jet does. I have routinely replaced worn needle jets with out replacing the needle

I wouldn't go any smaller than the 170 at this time.

A #3 slide would measure 3/16". Each slide number is a 1/16 of an inch.

#2 1/8"
#3 3/16"
#4 1/4"
Each 1/2 slide number is an additional 1/32" in cutaway height.


Re: High altitude jets, plugs and settings [Re: geryrace] #384065
07/12/11 2:38 pm
07/12/11 2:38 pm
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
G
geryrace Offline OP
BritBike Forum member
geryrace  Offline OP
BritBike Forum member
G
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
Thanks for the pix Steve, but you call that a number! I couldn't discern the one on my slide much less the one in the pix. I'll measure and look again when I get the the 105's. Moving methodically as John suggested

I'm going to get the parts first before disassembling again as I want to see if the 105's are an improvement. I'll also get another 106 to address John's comment of wear. I read something about a Viton needle. Can anyone comment about it?

I wondered in my earlier email if anyone had the parts number for the 105's as my parts book only had the 106. Klemf doesn't have any of the parts and I'm waiting for BritCycle.com to respond back to my email. I kind of like them better than BritishOnly. Other sources?

Partially blocked idle jet! My AMAL exploded view has a pilot jet, needle jet and a main jet, but no idle jet. Explain please and how do I clear the potential blockage?


gery race
Re: High altitude jets, plugs and settings [Re: geryrace] #384084
07/12/11 3:53 pm
07/12/11 3:53 pm
Joined: Nov 2008
Posts: 2,794
Bishop, Calif.
D
desco Online content

BritBike Forum member
desco  Online Content

BritBike Forum member
D
Joined: Nov 2008
Posts: 2,794
Bishop, Calif.
Pilot jet=idle jet. #78 drill bit and lots of spray carb cleaner.
Moore's Cycle Anaheim, Calif. 714-447-4402. Nice guy, loads of parts and knowledge and no attitude.

Last edited by desco; 07/12/11 3:56 pm. Reason: addition

1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
Re: High altitude jets, plugs and settings [Re: geryrace] #384217
07/13/11 10:50 am
07/13/11 10:50 am
Joined: Jan 2005
Posts: 1,662
East Bethany New York
Dick Harris Offline
BritBike Forum member
Dick Harris  Offline
BritBike Forum member
Joined: Jan 2005
Posts: 1,662
East Bethany New York
Morn'n Geryrace,tip your head 90 degress to the right and the number starts to make sense. The viton needle that was mentioned is for the float.It takes the place of the plastic needle. Dick

Re: High altitude jets, plugs and settings [Re: geryrace] #392515
08/31/11 9:16 pm
08/31/11 9:16 pm
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
G
geryrace Offline OP
BritBike Forum member
geryrace  Offline OP
BritBike Forum member
G
Joined: Jul 2006
Posts: 53
Berthoud, Colorado
I thought it good to follow up with what I found, did and got from the efforts. Hate to leave a post unfinished as its no help to anyone who comes along later. Yes I'm anal.

First off, thanks a bunch Desco for putting me onto Moore's cycle. Keith was great to work with and a lot of help walking me through some of the testing.

Bottom line: I'm successfully running the same set up as Dale Hoover in his earlier post and the plugs are not carboned.

I had previously made certain none of my issues were mechanical (valves and timing) or electrical (points and plugs).

Took the Amals off and a part, cleaned them well in a can of parts cleaner and got two rebuild kits from Moore's. Blew carb cleaner through the carburetor to make certain the orifices were not clogged. (Keith walked me through this over the phone.) I also leveled the intake ends with a sheet of glass and emery cloth so no light showed when a straight edge held to them.

What I found is that the Moore AMAL kits had a thick gasket between carburetor and intake that I never had from day one.

Installed the .105 needle jet and 170 main jet and set the needle on the lowest of three grooves. I have the #3 cutaway slide by the way. Did a little needle jet air screw adjustments as well as, throttle stop and I'm good to go.


Thanks again to you all.


gery race
Re: High altitude jets, plugs and settings [Re: geryrace] #392526
09/01/11 12:21 am
09/01/11 12:21 am
Joined: Nov 2008
Posts: 2,794
Bishop, Calif.
D
desco Online content

BritBike Forum member
desco  Online Content

BritBike Forum member
D
Joined: Nov 2008
Posts: 2,794
Bishop, Calif.
Moore's Cycle. Try getting that kind of help on E-Bay.


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.

Moderated by  John Healy 


Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.6.1.1