The Unapproachable Norton Commando

Dr_Hiller · Joined: 09 Oct 2004 Posts: 159 Location: Seattle, WA USA

Panic:

I have your Amal Tuning book, and after some time with my 932's, I've come to a question I can't answer. The idle and low-end of the low speed circuit run rich. (Just off idle to 1/4 or 1/3 throttle)

Some background:
10.25:1, std stroke, 76.63mm bore, Johnson J360 cam. Keith also did my head: enlarged intake, stock exhaust valve, reduced intake port size (raised the port floor). Thermal barrier coatings everywhere appropriate. Open reverse-cone mega on 2:1, 1 1/2", 29"primary exhaust. Boyer is timed to 28deg (some pinking occurred at 31deg on a water-brake roller setup, none when I backed it off - larger main jet may cure this, see below).

Good shot of the megaphone below;

Carbs are resleeved 932's. 106 needle jet, needles in the middle position, as far as I can tell the float is properly set. # 3 slide cutaway. Possibly the source of my full throttle pinging, what seems like an undersized 230 main jet (plugs go white on high speed blasts and engine falls a little flat at full throttle). Idles clean with the air screw out 1 3/4 turns - falters and stumbles at 2 turns.

Whether I'm spinning it at 4k or lugging it at 1800rpm, the plugs get sooty and black at low throttle openings. I have some dyno time scheduled and am looking for your thoughts. I want to make the time as productive as possible while I'm paying.

I've never heard of someone using a 2 1/2 slide cutaway, so I've ruled that out. The carb's have brass slides, so it'd mean another set if that was the consensus answer. I'll go to VM34's if that's the case.

The needle position seems fine - and, if I understand this correctly, it doesn't come into play at low throttle openings. Your book suggests that one can enlarge the air correction port. Is that a reasonable project? Can I calculate the amount of enlargement needed from the A/F ratio from the dyno runs?

Thanks in advance.

Commando75 · Joined: 25 Aug 2008 Posts: 16

I am by no means an expert mechanic but here is my suggestion:

Try using the top notch (leanest) position on your needles. I messed with my new set of 932's for some time and it was never right until I lowered the needles. Now my bike idles and runs great. Give it a try. Good luck!

bill · Posted: Sun Oct 05, 2008 2:26 pm Post subject:

I would go up on the main jet and try a 3.5 slide cutaway. the larger # is leaner on the slide. if the cam is to far advanced it will cause low throttle opening problems like you are having from reversion in the intake tract.

windy

Jason Curtiss · Joined: 14 Jun 2003 Posts: 667 Location: HOUSTON, TEXAS

I agree with Bill; your throttle slides are too rich.

Install 3.5 slides and your problem should go away.

Dr_Hiller · Joined: 09 Oct 2004 Posts: 159 Location: Seattle, WA USA

Thanks for the replies.

First, whoops - got the lean-rich order backwards on the slide cutaways in my post. Embarassed

I'm betting you're right about the 3 1/2's being the answer though. It's the right part of the throttle progression.

I went with the #3 slides because of the similarity in my setup to the Combat build. The workshop manual calls for #3's, 106 needle jet and 230 main jets - so I used that as a starting point.

The Dunstall Tuning manual also calls for #3's, 107 needle jet and 270-310 mains.

This is a bit of a problem as I had the 932's sleeved and I'm pretty sure #3 1/2 cutaway slides aren't a drop-in replacement.

Anyone know if I can have a second set of slides sleeved without the trouble of sending the carbs off on a round-trip journey? Think I can send just the slides?

Can't seem to find the website for the nice guy in Canada who did the first set either. Is Rocky Point the other vendor people have used?

Thanks in advance.

Jason Curtiss · Joined: 14 Jun 2003 Posts: 667 Location: HOUSTON, TEXAS

You should be able to purchase a set of 3.5 slides without sending in the carbs.

A classic symtom of over-rich slides is that the bike will stall at a stop sign/light after a period of trailing throttle. This occurs when the bike is warmed up and is less noticeable when cold.

panic · Joined: 20 Sep 2005 Posts: 54 Location: Hempstead, New York

Since the slides are $$, I'd try a .1055 needle jet 1st.

Benton · Joined: 17 Dec 2005 Posts: 12 Location: Sweden

Hello!

I have a -73 750 Interstate running new 32mm. Amals.The old Amals on my bike was running rich like yours.I made a temporary fix by adding an extra groove above the top notch on the needles.This compensated for my worn needlejets and needles until they were replaced. When I finally replaced both carbs I found 3 1/2 slides in the new ones.I run 230 main , .106 needlejet and peashooters The difference I could see was some sneezing during warmup at 1/4-1/3 throttle, esp. when chokeslides were rised early.I belive the 3 1/2 slides came with the 850 Commando.
I have learned to live with them now,and and when the motor is warm there is no difference that I can notice.

Benton

batrider · Posted: Mon Oct 06, 2008 10:07 am Post subject:

Bruce Chessell (Triton Machining) in Ontario is the nice guy in Canada. He no longer maintains the website but he is still doing the resleeving as far as I know. I don't think you can just drop in new slides because he opens up the body somewhat. Try this e-mail: bchessell@odyssey.on.ca

Russ

kommando · Joined: 07 May 2005 Posts: 322 Location: Scotland

Get hold of 2 old 3 1/2 slides and send them to your original carb resleever, they should be resleeving to a std size expect for badly worn carbs. Need to do the same to a Victor, it has a resleeved 932 850 MK2A carb with a 3 slide and is rich just off idle, needle is on top groove.

norbsa48503 · Joined: 07 Apr 2004 Posts: 1034 Location: Flint, Michigan

If you are very sure of yourself there is no reason to not use the book Panic sold you and file the cutaway to a leaner one. I believe that about a 1/32 does it for one step So a 1/64 for a half and so on. I have decent used ones around of each size and they can be used to scribe a fine line for this work.
I bought the .1055 reamer that Panic recommended from MSC and make my own jets the bought ones are all over the place. This in fact could be your problem. Check those needle jets with a gage pin do not trust the #'s on the side. Out of 6 new ones you are lucky to find a pair within speck.Buy 105 and ream em.

panic · Joined: 20 Sep 2005 Posts: 54 Location: Hempstead, New York

Although creating a super-lean position with a new top clip groove will cause leaner mixture, it also disturbs the circuit function progression overlap and sequence. Can't hurt to try it, but moving the entire taper out of the original range is likely to cause other strange maladies; typically it will require another 1/2 to 1 size larger needle jet to compensate for the fact that the larger diameter is obscuring the jet until at least 3/4 throttle, where you do not want to be lean.

Dr_Hiller · Joined: 09 Oct 2004 Posts: 159 Location: Seattle, WA USA

Thanks for the info.

I ordered 105 needle jets and 270 through 310 mains. I also e-mailed Bruce about sleeved 3 1/2's. It'd be nice to get the off-idle fuel curve sorted once and for all.

I'll post dyno results when available. My appointment is for the end of next week, but I may have to push it back if I can't get the right slides.

Dr_Hiller · Joined: 09 Oct 2004 Posts: 159 Location: Seattle, WA USA

Well, it's pretty clear to me that Bruce Chessell is an outstanding human being. He's going to recut my slides to #3 1/2 specs (23 degrees from 20 degrees) at no charge.

Thanks again to all for your help and suggestions.

cash · Joined: 10 Nov 2006 Posts: 445 Location: west cumbria

[I bought the .1055 reamer that Panic recommended from MSC and make my own jets the bought ones are all over the place.

I can remember Amal claiming that the jet numbers did not relate to a measured hole but a specific flow rate. Is that why you are finding differing bores for the same jet number? Probably not QC went off Amal's radar years ago

Cash

The Unapproachable Norton Commando

At the end of 1967 the Norton Commando was announced.