JS Motorsport Pistons/Rods First Impressions

My first ride on the Commando, I broke down after 3 miles, because I forgot to turn the choke off. After cleaning the plugs, it didn't run right until I put fresh plugs in.

I find it interesting that each bike has its own starting needs.

On the Commando, with a single mk2 Amal (no tickler), my bike will not start first thing without the choke. Now, choke on, start, immediately choke off using the throttle to keep it running, start riding, 2,500 revs for 500 yds and it ticks over without throttle at my first road junction. True for all weather temperatures. Don't need the choke for the rest of the day, just a little throttle to start.

Can't do that on my 4 x Keihin Honda, which needs full choke to start and half choke for 500yds to keep running on all cylinders. It soots the plugs if i let it idle on the choke. My 4 x Mikuni Bandit is similar, but less fussy on when I turn the choke off. It will warm up happily on the drive on a reducing choke.

Mart UK said:

My first ride on the Commando, I broke down after 3 miles, because I forgot to turn the choke off. After cleaning the plugs, it didn't run right until I put fresh plugs in.

I find it interesting that each bike has its own starting needs.

On the Commando, with a single mk2 Amal (no tickler), my bike will not start first thing without the choke. Now, choke on, start, immediately choke off using the throttle to keep it running, start riding, 2,500 revs for 500 yds and it ticks over without throttle at my first road junction. True for all weather temperatures. Don't need the choke for the rest of the day, just a little throttle to start.

Can't do that on my 4 x Keihin Honda, which needs full choke to start and half choke for 500yds to keep running on all cylinders. It soots the plugs if i let it idle on the choke. My 4 x Mikuni Bandit is similar, but less fussy on when I turn the choke off. It will warm up happily on the drive on a reducing choke.

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Japanese use metric remember… try riding it 500 metres instead of 500 yards…

johnm said:

I guess you idle so low because you don't have chokes.

With chokes my Commando will idle happily at 1800 or so settling to 1100 to 1200 when warm and no choke.

The only reason to idle at 700 is if your aim is to destoy your cam and followers.

A very very bad idea in my opinion.

I know I'm probably going to get flamed with this comment but Amal did include a choke for a reason.

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You didn't read what I wrote! 700 immediately after starting cold which increases to 1000-1100 when warmed up.

Cam and followers are getting plenty of oil. The oil to the head is about the same and therefore the oil down the exhaust pushrod tunnel is about the same but the cam and followers are doing less work.

If chokes make your cold engine idle at 1800, you need to adjust your carbs correctly.

marshg246 said:

You didn't read what I wrote! 700 immediately after starting cold which increases to 1000-1100 when warmed up.

Cam and followers are getting plenty of oil. The oil to the head is about the same and therefore the oil down the exhaust pushrod tunnel is about the same but the cam and followers are doing less work.

If chokes make your cold engine idle at 1800, you need to adjust your carbs correctly.

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I'm pretty sure I read it right. 700 rpm immediately after start up when cold. That's how I read it.

How long will you run the bike at 700 rpm when cold before it comes up to 1100 rpm?

johnm said:

I'm pretty sure I read it right. 700 rpm immediately after start up when cold. That's how I read it.

How long will you run the bike at 700 rpm when cold before it comes up to 1100 rpm?

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Since I hate idling Norton engines, I start and ride so I've never timed that. At my first stop, it's at about 1100. I suspect that it would be less than 3 minutes if just sitting idling but I never do that with a Norton and rarely with any bike.

BTW, I DO NOT set it to 700. When setting up the pilot circuit, I get the engine up to temp by riding and then set it up between 1000-1100. With Premier carbs and Tri-Spark ignition they will idle at 700 when started cold and they will not die. If they do die, I fix whatever is wrong. This works for all standard Nortons (750, 750 Combat, 850).

I discarded the choke on my first Triumph in 1968 and every tickler equipped bike I've had since then. I had no transportation other than my Triumph 500 while in college and often rode in sub-freezing weather. I never engage the choke on Amal-equipped customer bikes and it's fun to show the owner that it is simply not needed when properly setup. So many people put the choke on and then crack the throttle - think about it!

marshg246 said:

Since I hate idling Norton engines, I start and ride so I've never timed that. At my first stop, it's at about 1100. I suspect that it would be less than 3 minutes if just sitting idling but I never do that with a Norton and rarely with any bike.

BTW, I DO NOT set it to 700. When setting up the pilot circuit, I get the engine up to temp by riding and then set it up between 1000-1100. With Premier carbs and Tri-Spark ignition they will idle at 700 when started cold and they will not die. If they do die, I fix whatever is wrong. This works for all standard Nortons (750, 750 Combat, 850).

I discarded the choke on my first Triumph in 1968 and every tickler equipped bike I've had since then. I had no transportation other than my Triumph 500 while in college and often rode in sub-freezing weather. I never engage the choke on Amal-equipped customer bikes and it's fun to show the owner that it is simply not needed when properly setup. So many people put the choke on and then crack the throttle - think about it!

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OK. So I think we are going to the same place.

Indeed I hate idling cold engines and only idle at traffic lights etc when warm.

I tickle both carbs, start my 1974 850 Commando on the choke and idle it on the choke at the end of the drive while I shut the gate. Ride maybe 500 metres take choke off and it idles perfectly at 1100 or so thereafter . Also on Premiers that had the jets changed from 17 to 19. Apart from that standard Mk11 settings with the needle on the left hand carb raised one notch to get the plugs looking the same. Carbs balanced with guages. Pazon ignition set at 28 on calibrated primary case scale. Strobed at around 31 above 3000 rpm. Bike runs fine.

It's my old bike. Bought it in 1978. My days of riding in snow are long gone The bike I rode back then in 1968, 15 years old and snow was a Matchless G3LS. Pretty sure it had a choke but that carb was pretty worn anyway. Would have been a Monobloc.

I am a fair weather rider in California no need for a choke, I run Keihin CR carbs on the Norton, Amal concentrics on my 70 Triumph, when the concentrics wear out I have a pair of Mikunis waiting. The carb is not the issue when it comes to my idle issues, my ignition is.

In general I think that the advance curves on these electronic ignitions are set for the Triumph which is timed around 39 to 41 degrees with vintage specs and lot of guys running 37 with modern fuels, even then 4000 rpm is way too late to hit full advance, and mid range power is lost. From the seat of my pants testing I like full advance around 2500 rpm on the Norton, the Tri Spark comes closest to this in the available EI options.

I have FCRs and had all the JS parts, rods, pistons, cam, lifters, blah blah in my 750 Norton engine. I still have the JS2 cam and lifter setup, but different rods and pistons currently. No problems with idle warm with either set of rods and pistons. Won't idle at all right off dead cold start. Throttle has to be blipped for about 2 minutes then held open for 2 more minutes before it will start slow idling pre-warmup. I use the TriSpark ignition at static 29 degrees. No strobing a P11. It runs better mid summer.

I warm up my engine, but not idling. I do make sure it will idle before I head up my driveway to the surface street. To me it all seems completely typical of my Norton. If it had fuel injection and a computer controlling the fuel delivery, it would probably idle dead cold.

I did not ditch the JS long rods and pistons. I wanted to try another long rod set when I plopped on a new set of barrels. If I am repeating myself I'd be the last one to know it.

When I tune my 850 motor, I get carburation as lean as possible in the midrange, but rich on the main jets. I set the idle so that it idles perfectly when the motor is hot. My carbs are MK2 Amals so they have the enricher similar to a Mikuni. To start the motor, I usually have rollers which are powered by an angle grinder. When the motor is cold, I open both enrichers, then start the motor on idle without opening the throttle, and allow the motor to idle until it starts to slow. Then I close the enrichers and open the throttle.
I do not rev a cold motor. Even when the motor is hot, I start it with the throttle closed and let it idle. I use methanol fuel, however I would do the same with petrol.
Two-strokes are not much different to four-strokes, but if you crack the throttle while starting one, they usually refuse to start completely.
My 850 motor is tuned very similarly to a two stroke. Many guys probably do not realise the significance of that. The difference in jetting, between extremely fast and slow is bugger-all.
With a two-stroke, it is stop or go. If you get the midrange wrong, they will not even start.

Riding a race bike is different from riding a road bike. When you race you use lean jetting around all the slow parts, and full throttle when you are fairly well down the straights. With a road bike, you might use lean jetting for much longer, if you set it up like a race bike. With a race bike the main time when valves and pistons get burned are when full throttle is being used. A road bike might be different.