MY Commando won't stay running...

Dave,
Do you need to run a tube up vertically from the drain plug hole to get a reading?

That's not the drain plug, they're old style bowls and don't have the drain. The line is connected to the banjo feed, and it just goes up to a small bottle, don't even need the bottle, just a funnel so you can pour fuel/whatever into the line. Make sure the bowl is tight against the plate with the gasket so the pivot bar is seated, I bolted them on with some 10-32. If everything works right, the bowl will fill until the needle stops the flow and you'll see the float level. If the needle doesn't seat, the bowl will overflow and you need to fix that. I had one that I had to fix. I've a solution to that too.

The petcocks should be checked that they don't leak either, easy to do, just fill the tank and close the taps and see what happens. I lost a whole tank of avgas that way before I knew. It evaporated from the carb overnight.



Dave
69S

Nice rig!...

Nice job on the float bowl test rig. It's good to see the safety shot of the well ventilated area you are working in with gasoline.

I agree that the fuel taps need to be checked for absolute sealing.

My best upgrade was to remove the stock taps and replace with the Italian made alloy taps. They were supposedly used on the last vertical twin Triumphs.
I discovered my old taps had leaked when I found fuel contaminated oil in the crankcase sump after a fairly long storage!

Now when I won't be riding for a while, I remove the float bowl drain plugs and remove all the fuel in the metal tank and store it in a proper gas can to use in lawn equipment as needed.

I want to try your float setting method when I put in some new stay-up floats (soon, before Vermont rally). Aren't the carbs tilted forward a bit on the bike? Do you take that into account?

I set the float level first to Amal's recommendations, it would not even tickle, so I went back to where they were with the old plastic floats and I get good idle with 1 1/2-2 turns. Don't know about accounting for the slope, what happens when you go around a curve or over a hill fast? I guess it all sorts itself out, anyhow carbs are running good now. I think JBA has them right.

Well ventilated, that's why I suggested alcohol or varsol otherwise.

Dave
69S

batrider said:

I want to try your float setting method when I put in some new stay-up floats (soon, before Vermont rally). Aren't the carbs tilted forward a bit on the bike? Do you take that into account?

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At some time Amal had a video on their site that showed them checking the fuel level on new carbs. IIRC, the carb was held level, the sight tube came out of the drain plug. I can't find it now. Maybe the stay-ups will come with directions.

If you have carbs that have a drain plug you can use the method described on this YouTube video. It shows the technique that applies to various carbs. It's at around 5:30
http://www.youtube.com/watch?v=_qAVXneKAkU

I'm just curious as to how others bikes run for the first 10min with a mikuni fitted. I still have one fitted on my 71 commando although I have ordered a pair of the new amal premier carbs. I live in an area of relatively mild temperatures 10-35 celsius. I can start my bike easily on the enricher which I then turn off after 30secs or so. Bike sits idling for 5 mins or so while I get myself organised plus another couple of minutes or so to get down to the gate and open/close. After this it would be about another 3 - 4 kms before I can wind the throttle on quickly. If I try any earlier than this it just misses ,farts and carries on. Is this pretty normal ?

ozzie041974 said:

I'm just curious as to how others bikes run for the first 10min with a mikuni fitted. I still have one fitted on my 71 commando although I have ordered a pair of the new amal premier carbs. I live in an area of relatively mild temperatures 10-35 celsius. I can start my bike easily on the enricher which I then turn off after 30secs or so. Bike sits idling for 5 mins or so while I get myself organised plus another couple of minutes or so to get down to the gate and open/close. After this it would be about another 3 - 4 kms before I can wind the throttle on quickly. If I try any earlier than this it just misses ,farts and carries on. Is this pretty normal ?

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yes. two stage enricheners are used on some Mik snowmobile carbs, more $$, really not needed, just warm it up, like you're doing

ozzie041974 said:

I'm just curious as to how others bikes run for the first 10min with a mikuni fitted. I still have one fitted on my 71 commando although I have ordered a pair of the new amal premier carbs. I live in an area of relatively mild temperatures 10-35 celsius. I can start my bike easily on the enricher which I then turn off after 30secs or so. Bike sits idling for 5 mins or so while I get myself organised plus another couple of minutes or so to get down to the gate and open/close. After this it would be about another 3 - 4 kms before I can wind the throttle on quickly. If I try any earlier than this it just misses ,farts and carries on. Is this pretty normal ?

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No, it is not normal...but a common defect when undersize Pilot jet is fitted. Commando needs a 35 or 40 Pilot to cure that warm up misbehaviour.

Mick

No, it is not normal...but a common defect when undersize Pilot jet is fitted. Commando needs a 35 or 40 Pilot to cure that warm up misbehaviour.

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If the pilot jet was undersized wouldn't that make it leaner at idle and low revs making it run hotter and hence warm up quicker ? it does run fine up to the first 1/4 of throttle movement too which is when the pilot jet is in effect right ? , which is why I thought pilot jet was ok. It's only when I roll on the throttle too fast when it's not up to temp; it just seems to take ages to get up to temp. If I roll on the throttle very slowly up to speed no problems. Do you still think it's the pilot jet ?
In comparison I have a 66 Bonnie with the twin amal monoblocs on it which you just flood the float bowl for start and then your off straight away. Warms up real fast and no missing,farting or hesitating even if you roll the throttle on quickly while still not up to temp. I must say it's not a real problem as I like to have bikes up to temp anyway before opening them up quickly but I just thought it odd that the Mikuni takes so long.

Understand what you are saying - but seriously the Mikuni is different to the Amal and the symptoms are identical to what I and several of my mates have experienced. 5km warm ups, throttle on - fart, fart. The transition from the Mikuni pilot to slide & needle jet is very sensitive. Stick a 40 into it and be amazed. Well, thats all I can offer at thius point.

Mick

Commando needs a 35 or 40 Pilot to cure that warm up misbehaviour.

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Ok thanks for the tip. I will give it a go as it sounds like you are speaking from experience with the same problem.

Ozzie, theoretically if your Pilot is too small (lean) you won't have had your Mixture screw
turned out (anticlockwise) very much at all... say 1/2 to 1 complete turn, ish. You should look to getting your
best mixture at about 1 1/2 turns out.
If you'r currently running less than 1 complete turn out then....
Yep +1 on a bigger pilot,
However If it is Idleing nicely after 30 seconds with the Choke off, but wont run properly at 1/4 throttle
(which is where the Primary taper of the Needle is working), then you may want to have a play with the Needle.
If raiseing the Needle makes things too rich, you can try shiming the needle to get a 1/2 notch equivalent.
OR, you may need a slightly richer Primary taper, on the Needle, which will only affect 1/8-1/4 openings.
Slide Cuttaway will also effect initial throttle openings up to 1/4 but won't harm mixture much at all after that,
so you can also try a Slide with less Cuttaway.
If you like to play...
If it's an Alloy Slide, you can remove some material from the bottom of the Slide to lessen the cuttaway height,
which is measured in millimeters, to lessen Air flow and richen the mixture.
If the new Pilot fixes the problem, all's good.
AC.

Thanks for your suggestions AC. Will take them into account as well.

Just installed my new Stay-Up floats and it looks like the rightside concentric is running lean. Idle screw in too much now to compensate and tickling takes too long now . So will pull the bowls and attempt bending the needle tab arm a tad upwards ,re-install with the idlescrew reset at 1 1/2 (where it should be and take a test drive.Could take awhile.

So.... It turned out to be a multitude of issues. When I rebuilt my carbs the first time, I didn't want to get the parts mixed up so I took them apart at two different times. When I had them apart this time, I noticed there where two different size needles. Got the right needles and had them put back together and tuned. Also there was not a proper ground on the stator and the rectifier was no good. No charge = no spark :evil: So rectifier is on its way, Put some new plugs in just in case, new ground from the battery to the engine and from the battery to the frame. When I rode her home she had more power then I have ever felt off the line. Now with the carbs adjusted, the strait pipes are not to loud, so I will leave them the way they are with no baffle.... Oh soooooooo happy to be back on her.