I think I'm running a bit rich...

Bonzo

Bonzo

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I changed over to a single Amal carb just over 400 miles ago.

I noticed yesterday that it was a little reluctant to start. I checked the plugs and they were pretty black, so I checked the gap on a new set and popped them in.

This is what they look like after 80 miles...

I think I'm running a bit rich...

I think I'm running a bit rich...

Bike is running great with a good even tick over, pulls nicely throughout the rev range thought I'm sure I heard a bit of popping on the overrun on last nights ride.

Should I raise the clip a notch?

'74 850 Mk2 (has the mute insert in the peashooters). Single Premier 32mm, 260 main, 19 pilot, 106 needle. Without looking, I think the clip is on the middle slot.
EDIT* Champion N7YC plugs.
 
Because you just have one carb twice as much air goes through it and at lower throttle openings this makes a much higher vacuum so more fuel is pulled through the jet. At higher throttle openings the engine will deal with it and at large throttle openings the size of the carb will be a restriction. But at lower throttle openings you will be rich compared to two carbs due to the fact two carbs have much lower vacuum to pull fuel.
Pilot jet and air screw adjustments should help.
 
Like a broken record....


Unleaded fuel does not color the plugs, until WAAAYYY off the map too rich.


It's been 50 years....


There are so many other indicators.

Smell
Dull, thudding sound
Throttle response
Measured fuel economy
 
Last edited:
Bonzo said:
1,000 miles.
Click to expand...
How much oil are you using ? I have a similar condition that i am working on .. I just replaced valve stem seals and that took much of the wet , shiny condition away . Plugs now are a dusty black . Still using about 450 ml over 250 miles . Rings were replaced about 1500 miles ago . Compression 175 both sides , leak down compression test is good . Head fully rebuilt 2 years ago . I added 2 ounces of oil to each cylinder and did another leak down test .. Absolutely no drop in pressure which indicated to me that i have leakage past the rings .

Like your bike , it starts great and runs great . Single mikuni for last 18 years .
 
The porcelain in the centre of the plug should he light brown or white with a black ring on the porcelain right down inside where it meets the metal. The plug heat range determines the rate at which the carbon burns off the porcelain. So use hotter plugs for tuning. Plug colour is usually only used as a guide for setting the main jets after using full throttle at high speed for a considerable distance. If you have a miss when riding the bike - stop and raise the needle.
 
Look for smoke out the pipes...if on return to closed from throttle blips, a sign of leaking valve seals. How is the inlet rocker box drain hole (tiny and half covered by valve seat...I think its around the 5 O'clock position viewed down, facing forward on bike. See how long a few tablespoons of oil take to drain down. Poke a good length of wire down all the way to the timing chest 90 degree bend. Blow air/WD40 etc through and re-check oil drain times.
 
Bonzo said:
I changed over to a single Amal carb just over 400 miles ago.

I noticed yesterday that it was a little reluctant to start. I checked the plugs and they were pretty black, so I checked the gap on a new set and popped them in.

This is what they look like after 80 miles...

I think I'm running a bit rich...

I think I'm running a bit rich...

Bike is running great with a good even tick over, pulls nicely throughout the rev range thought I'm sure I heard a bit of popping on the overrun on last nights ride.

Should I raise the clip a notch?

'74 850 Mk2 (has the mute insert in the peashooters). Single Premier 32mm, 260 main, 19 pilot, 106 needle. Without looking, I think the clip is on the middle slot.
EDIT* Champion N7YC plugs.
Click to expand...
I've seen a lot worse tbh
 
I'll just keep an eye on it and hopefully enjoy a full spring & summer of riding the thing 👍
 
Popping on the overrun could just be air leaks in the exhaust system.
At other times could be a sign of a weak mixture, which doesn't look to be the case here...
 
Ron Hulton said:
How much oil are you using ? I have a similar condition that i am working on .. I just replaced valve stem seals and that took much of the wet , shiny condition away . Plugs now are a dusty black . Still using about 450 ml over 250 miles . Rings were replaced about 1500 miles ago . Compression 175 both sides , leak down compression test is good . Head fully rebuilt 2 years ago . I added 2 ounces of oil to each cylinder and did another leak down test .. Absolutely no drop in pressure which indicated to me that i have leakage past the rings .

Like your bike , it starts great and runs great . Single mikuni for last 18 years .
Click to expand...
I may be wrong but I would question the rings if compression INCREASED when tested wet after dry.... - ? No change wet to dry to me means the rings are okay. Am I wrong (wouldn't be the first time)?
 
While your plugs are black, you are in no danger of burning valves or pistons. But if you seek performance, you are running miles too rich. I suggest it is impossible to get the best performance out of a Commando engine using Amal carbs on petrol, unless you fluke it. Amals cannot be jetted fine enough with petrol. The steps in the jetting are usually too big. Japanese bikes of the same capacity have better engine management systems - so are more powerful.
The reason my bike is quicker than many others, is - with methanol the jets flow twice as much, so increments in jet sizes have half the effect. The difference in jet sizes between quick and slower are extremely small.
 
Al we aren't using methanol on road going bikes and really I have never had any problems with getting my bike running great with Amal carbs, I have gone one size up in the main jets for my motor and all is great, can run from low revs to full revs without any misfire, ignition and fuel are the two major factors to tuning, but the fuels we have these days are just not the same when we had leaded fuels and modern fuels can go off real quick if let sit too long and we are still lucky here in Aus in what fuel we choose to run E10 and 91 unleaded is a no no for my bikes, 95 or 98 premium is what I use for best performance.
Sometimes I think Al has been sniffing too much methanol over the years and not enough riding, sorry Al but you keep telling us all the time.

Ashley
 
BrianK said:
I may be wrong but I would question the rings if compression INCREASED when tested wet after dry.... - ? No change wet to dry to me means the rings are okay. Am I wrong (wouldn't be the first time)?
Click to expand...
Opinions are always welcome 👍 ... Can the rings be that bad if i have 175 psi compression on both sides ? By adding the oil to each cylinder , i eliminated ring gap . For what i know , if you have a gap in your rings ...air will get by. Although the rings should have bedded in by now , and then again . ??

Cheers
 
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