Running Rich

My '75 Mark 3 is newly operational after a 20 year sleep. It starts fine but runs very rich on the street. Blah is the word!

Carbs were thoroughly cleaned & adjusted & seem to be in good shape. The air filter, points, plugs & cables were replaced. Cable settings seems to be correct per the book.

I did not replace the existing 220 main jets, but stock calls for 230 jets.

I set the needles on notch 2, per stock instructions.

Suggestions are welcome.
Thanks,
Stephen

chasesa said:

Carbs were thoroughly cleaned & adjusted & seem to be in good shape. The air filter, points, plugs & cables were replaced. Cable settings seems to be correct per the book.

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What about float heights?

chasesa said:

I did not replace the existing 220 main jets, but stock calls for 230 jets.

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Depends which publication you are quoting from? The MkIII manual says 230, the parts book says 220.

chasesa said:

I set the needles on notch 2, per stock instructions.

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The MkIII manual says "Top" = weakest.

Also,

Presumably the slides are 3.5 cutaway?

Are the carbs the original 932/33 & 34 ("24" in parts book is typo I think) do they have the stepped spray tubes?

Do they have the "2-ring" or "4-ring" ID needles?

Exhaust system? - details?
Air filter? - details?

Sorry to ask such a simple question-but this does fool some people, are you operating the choke the right way? = Wire pulled tight is choke off.

Thanks. Here is my review of your checklist:

Before the latest road test the clip on the needle was set at the top notch which I understood to be weakest. The bike ran pretty much the same very rich way, which is what led me to install new cables and re-check all cable settings.

But, I did not re-check the float height. I also did not install 230 jet because I thought that would only increase the richness. (I was saving that in case I swung into the lean side).

The carbs the original 932s and the slides are the stock 3.5 cutaway.

I don't think they have the stepped spray tubes, and I don't know if they have the "2-ring" or "4-ring" ID needles, but I will check.

The exhaust system is the stock muffler with the cap on the end. The air filter is a new stock foam type (in the plastic air box. I did not impregnate it with oil (yet).

And yes, I was OK on the choke with wire pulled tight is choke off. True, it does operate opposite to my '68 Commando, but I figured that out!! (lol)

I just bought new needles and jets and had to drop them down to the top groove to get the bike to run right. I just came back from a very invigorating ride...it seems to have worked, the spark plugs finally look proper. I have 106 needle jets. I noted in a recent post the norbsa said he had started buying 105s and reaming them out to 105.5 because he was having trouble getting the 106s to run lean enough on the fuel available where he is.

Russ

Umm ,i have the same problem ,carbies cleaned checked float lvl,s standard jets {106 and 230} boyer ignition starts fine i dont know what else to check ,its that rich you can see a black smoke outta the exhast sometimes , was thinking of just putting a single carb on may be a mikuni 34 mm see how that runs ,would be a shame to take the duels off tho :cry:

Something not right in parts or assembly and settings if running rich with normal factory Amal set up as new age fuel is lean burning with the booze and other additives so generally must be richened up a tad to be in correct tune once warmed up, ie: needs tickle or choke or enricher for cold first starts. Needle Jets may be wallowed out is one thought that occurs to me.

chasesa said:

My '75 Mark 3 is newly operational after a 20 year sleep. It starts fine but runs very rich on the street. Blah is the word!

Carbs were thoroughly cleaned & adjusted & seem to be in good shape. The air filter, points, plugs & cables were replaced. Cable settings seems to be correct per the book.

I did not replace the existing 220 main jets, but stock calls for 230 jets.

I set the needles on notch 2, per stock instructions.

Suggestions are welcome.
Thanks,
Stephen

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Have you done a compression test?

What are the symptoms of pilot jet clogging? Organic Solvents don't touch zinc oxide crust, just acids, strong alkalies and physical attacks. Might try upping plug heat range if fouling before getting a full handle on carbs.

NJ”S
Every bike is just a little different and every bike needs a close look at the plugs. It is true that many bikes can benefit from new NJ’s.
106’s that have been checked with pin gages are really needed. Only about 2/3 of the NJ out there are made right you should be running a matched pair at least. To check them I have a set of pin gages starting at .1048 than .105 than .1055 than .1052 than .1058 and .106 on up through .107+ .
Unless you have reamed small holes in brass you might want to skip making your own set of .1055 NJ but they have done well in about 10 bikes for me. The finish that the reamer leaves is as important as the size. Our bikes run almost all the time on the donut of fuel that is made by a .098 rod in a .106 hole and even if you step this up to +.001 run a .107 you would find your bike pig rich on the street. This fit is lost on bikes with as little as 10,000 miles depends on the bike. When you’re on unleaded gas your plugs should have very little color seen by the un-aided eye. The gray or pink is way up inside were the ceramic cover meets metal. On a nice long 55 MPH say over one hundred miles run you need to be getting almost 60 miles per U.S. gallon. If you are anything below fifty MPG you could use some tuning. Do not discount the freshness of the fuel anything over a month might run in the bike but don’t set your carbs by it.

This may sound silly, but is the choke off?

It seems conterintuitive if one is not familiar with Amals, but the choke lever pulls the choke OFF, while slackening the lever lowers the slides, richening the mixture by restricting air flow. Bike will run - and probably run quite fine - with the choke on, but I doubt you'd get more than 3500-4000 RPM out of it.

Blocked pilot circuit can be cleared by either running a wire into the pilot jet - like a single strand from an old cable - or gently running a #77 drill bit into the jet, available from Grainger, an electrical and industrial supply store. I glued a #77 bit into the tip of a hypodermic needle (its that small) and use it on a fairly regular basis to make sure the pilot jet is clear. I just push the drill into the jet and gently twist the base of the needle, like a jeweler's screwdriver.

Before I got rid of the about useless chokes I've rode off on them still down but not for far as so misfiring so fast I couldn't hardly keep the fire going till my error was found, then some mile or more to un foul plugs to even firing again. So even though thought occured to me I doubt its the choke mistake here unless super lean base line tuned with chokes up so won't start or run unless chokes down.

BillT said:

This may sound silly, but is the choke off?

It seems conterintuitive if one is not familiar with Amals, but the choke lever pulls the choke OFF, while slackening the lever lowers the slides, richening the mixture by restricting air flow. Bike will run - and probably run quite fine - with the choke on, but I doubt you'd get more than 3500-4000 RPM out of it.

Blocked pilot circuit can be cleared by either running a wire into the pilot jet - like a single strand from an old cable - or gently running a #77 drill bit into the jet, available from Grainger, an electrical and industrial supply store. I glued a #77 bit into the tip of a hypodermic needle (its that small) and use it on a fairly regular basis to make sure the pilot jet is clear. I just push the drill into the jet and gently twist the base of the needle, like a jeweler's screwdriver.

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LOL I had the same response written this morning, but after re-reading his pasts, I deleted it. He's a veteran Amal user... B U T . . . . he said that his two (Brit)bikes work opposite??? From the OP's second post: "And yes, I was OK on the choke with wire pulled tight is choke off. True, it does operate opposite to my '68 Commando, but I figured that out!! (lol)"

norbsa48503 said:

NJ”S
Every bike is just a little different and every bike needs a close look at the plugs. It is true that many bikes can benefit from new NJ’s.
106’s that have been checked with pin gages are really needed. Only about 2/3 of the NJ out there are made right you should be running a matched pair at least. To check them I have a set of pin gages starting at .1048 than .105 than .1055 than .1052 than .1058 and .106 on up through .107+ .
Unless you have reamed small holes in brass you might want to skip making your own set of .1055 NJ but they have done well in about 10 bikes for me. The finish that the reamer leaves is as important as the size. Our bikes run almost all the time on the donut of fuel that is made by a .098 rod in a .106 hole and even if you step this up to +.001 run a .107 you would find your bike pig rich on the street. This fit is lost on bikes with as little as 10,000 miles depends on the bike. When you’re on unleaded gas your plugs should have very little color seen by the un-aided eye. The gray or pink is way up inside were the ceramic cover meets metal. On a nice long 55 MPH say over one hundred miles run you need to be getting almost 60 miles per U.S. gallon. If you are anything below fifty MPG you could use some tuning. Do not discount the freshness of the fuel anything over a month might run in the bike but don’t set your carbs by it.

Click to expand...

I built a Mk3 a few years ago and had serious rich problems as well (new carbs). I mentioned this to my Amal importer and he sold me a set of pin gauges, told me that Amal had major QC problems during one of their transitions. Bottom line, the 106s I thought I had were north of 107. I dug through my Amal junk yard and found two that guaged properly at 106, makes a big difference.

Bill.

Hi Billt
On my carbs there is no choke cables and where they would have been they have been blocked off by a rubber gromet thingie ,so like u say it sounds like the choke is permantly on , i guess they all came out with chokes & cables ? and if u say the choke cable has to be pulled tight to take choke of this would be the problem im having ive only just got the bike so im not to cluey about it , so looking at the workshop manual it seems theres a few parts missing like airvalve assemble because when i took the top off the carbs all that was underneath the lid was the throttle valve spring needle and clip and throttle valve, next question were can i get the missing parts from plz

Slippary said:

Hi Billt
On my carbs there is no choke cables and where they would have been they have been blocked off by a rubber gromet thingie ,so like u say it sounds like the choke is permantly on , i guess they all came out with chokes & cables ? and if u say the choke cable has to be pulled tight to take choke of this would be the problem im having ive only just got the bike so im not to cluey about it , so looking at the workshop manual it seems theres a few parts missing like airvalve assemble because when i took the top off the carbs all that was underneath the lid was the throttle valve spring needle and clip and throttle valve, next question were can i get the missing parts from plz

Click to expand...

If the choke slides are not in there, then you shouldn't have an issue, as you have no choke at all. Quite a few here run without a choke. Slide assemblies would available from anybody who sells Amals. The slide would come out of the carb with the top when undoing the two cap screws. The only way they would be in the carb without a choke cable would be if someone dropped the choke slide into the throttle slide after starting it into the body.

The choke assembly in the carb consists of the slide (sort of T-shaped when looked at on end) spring and brass insert in the spring. On the top cap oif the carb, you would need the cable adjuster (identical to the one for the throttle), and then the cables, which are just like the throttle cables - two lower cables going into the junction, then one upper cable going to the choke lever.

Without a choke, the rich running sounds like the pilot circuit is blocked, the floats are not set to the right height, or the bike is jetted wrong.

The pilot circuit (the horizontal screw at the front of the carb) adds air into the carb fuel idle circuit, leaning the mixture a bit. Normal starting point is about 1-1/2 turns out from snug in. behind that screw is a little brass plug with a precisely drilled hole - the pilot jet. if that hole is plugged, the bike will run a bit rich. If moving this screw in or out has little or no change in the way the bike runs, its plugged.

The floats open the inlet valve, letting fuel into the fuel bowl. There is a precise setting for these floats. Too low, and the bike is starved for fuel as the bowl doesn't have enough to feed the engine. Too high, and you may be feeding more fuel into the engine than it needs. If the inlet valve (little brass thingy hanging on the tab on the float) is dirty or the seat is gummed up, the fuel may not shut off completely, but if that were the case, you should see a little dribble of fuel out of the tickler. Float level is the first thing to check when tuning these carbs.

Quick recap:
Check the float level
Check that the pilot circuit is clear
Check that there are no air leaks
Check that the cut-out, needle jet and main jet are the same for both carbs, and that they fall in the general range for your engine

Tuning procedures can be found at either the Burlen Amal site or places like Old Britts