Tuning Issues

I have been having trouble with hot starts since the day I got my 1974 Commando. This is trouble that Debby was having with the bike even before it came into my possession. I have been determined to run it down.

Specs:
The bike is an 850 Commando. It is running two used Amal 932s mounted on the correct manifolds for the 30 mm intake ports. It uses the correct phenolic insulators. I running 260 mains, needle is on the lowest notch (highest needle setting) and pilot screw is 1 and 3/4 way out. Carb slides are sleeved and running stay-up floats set to .040 below the edge of the bowl. Valves are set to spec. Plugs are Autolite Platinum AP64 and color is tan to ash white. Uses WebCams #12 cam. It is very close to stock duration with slightly wider lobe centers and a little more than stock lift.

Bike Elevation 735 ft / 224 m above sea level.

Things I have done:
I pulled the carbs a few days ago, drilled the cap on the pilot jet side so I know the pilot jet is clean and cleaned out both carbs. I tapped the opening and used a cut down pilot screw as a plug. All jet have been dipped and cleaned with carb spray. Needle height has been checked and slide sync has been done. Checked timing with strobe and it looks fine at 31 degrees before TDC. (I hope) Valve clearance have been set. System is charging over 12.5 volts.

Operation:
The bike runs fine, takes gas fine but pops and farts with a closed throttle. Needs tickled when cold and pops back a little when cold. Pops back a little when trying to start hot.

Ideas:
I am wondering if it could be my Pazon electronic ignition. It's rare but I have seen ignition modules change timing when they get hot. I have strobed the bike but my wife has been helping me and it's tough to get an accurate reading with reluctant help.

Plugs indicate it may be running lean but the jetting seems pretty rich (260 main, highest needle position)

Blued pipes indicate hot running.

I am missing something but I just can't figure what? It could be that I am being incredibly picky and the blue pipes scare me enough to keep me from full enjoying the bike.

"All jet have been dipped and cleaned with carb spray."


That is not enough to ensure proper operation.


You must visually verify flow, through every passage, using aerosol liquid.

Out of interest what aerosol would you use ?

If the clips are in the top notch of the needles, you might need the smaller needle jets. They would cause you to put the clips closer to the centre notch and give you more control. If you have carbon deposits in the combustion chamber, they can glow and cause ignition to happen when it should not. - 'There is a fine line between pleausure and pain'. Heat build-up in air-cooled engines is a problem, even Honda discovered that, with their racing cars.

concours said:

"All jet have been dipped and cleaned with carb spray."


That is not enough to ensure proper operation.


You must visually verify flow, through every passage, using aerosol liquid.

Click to expand...

Did that with carb cleaner spray, I watched the spray come out of every hole.

Big_Jim59 said:

Did that with carb cleaner spray, I watched the spray come out of every hole.

Click to expand...

Air passage from the air horn?

Grandad said:

Out of interest what aerosol would you use ?

Click to expand...

Brakleen, (light viscosity, similar to gasoline) but WD-40 will work.

To clarify, this is NOT to remove blockages, but rather, simply to confirm flow.

What is your hot starting procedure? I find tickle when hot is not good on my 850 mk2....My bike seems to like a cracked open throttle for all starts...typically 8 or 9 out of ten are first kick fire ups last few months, hot or cold.


I'm running no chokes, needles in richest position and have good plug appearance, no pops after a few minutes warm up, and only a one or two when still cold. Plugs are Champion non-resistors N7Y's, gaped at .028". EI is Wassel-Vape unit (similar to Boyers). Cylinders are first overbore (.020 " over) if that makes any difference.

You mentioned setting the stay up floats by distance from top end of bowl. That is not current Amal guidance for Stay Ups....they rec using fuel level checks rather than float position. I made up a level checker from an old plastic bowl drain cap, drilled to accept a clear plastic hose tightly/leak proof. Held the hose against carb body and let fuel in to see where it came up to within the tube compared to bowl/carb flange. AN sells a little kit with such a level checker if needed.

What is condition of float needles/seats? New Viton tipped needles or older type? Are you getting a good shut off of fuel when bowls full, even when carbs are warm/hot? Seats can be polished with a q-tip in a hand drill and some Autosol or similar metal polish.

Does tickling when warm make things worse (more kicks to start) or better?

Pilot settings seem a little strange - they should be whatever gives the best tickover vs. pickup, not some pre-set value.
Symptoms sound a little like weak idle mixture, but from this distance it's hard to say.
I've typically had pilot screw settings from 3/4 to 1 1/2 turns out, once the rest of the carburettor has been confirmed good.

Tornado said:

What is your hot starting procedure? I find tickle when hot is not good on my 850 mk2....My bike seems to like a cracked open throttle for all starts...typically 8 or 9 out of ten are first kick fire ups last few months, hot or cold.


I'm running no chokes, needles in richest position and have good plug appearance, no pops after a few minutes warm up, and only a one or two when still cold. Plugs are Champion non-resistors N7Y's, gaped at .028". EI is Wassel-Vape unit (similar to Boyers). Cylinders are first overbore (.020 " over) if that makes any difference.

You mentioned setting the stay up floats by distance from top end of bowl. That is not current Amal guidance for Stay Ups....they rec using fuel level checks rather than float position. I made up a level checker from an old plastic bowl drain cap, drilled to accept a clear plastic hose tightly/leak proof. Held the hose against carb body and let fuel in to see where it came up to within the tube compared to bowl/carb flange. AN sells a little kit with such a level checker if needed.

What is condition of float needles/seats? New Viton tipped needles or older type? Are you getting a good shut off of fuel when bowls full, even when carbs are warm/hot? Seats can be polished with a q-tip in a hand drill and some Autosol or similar metal polish.

Does tickling when warm make things worse (more kicks to start) or better?

Click to expand...

Float needles are the Viton tipped items. Tickling makes it worse. I have been wondering about the plugs. I have zero experience with Autolite AP64 plugs. I have always used NGK B7ES which is now BP7ES I guess. I might order a set of Champion N7Ys.

B+Bogus said:

Pilot settings seem a little strange - they should be whatever gives the best tickover vs. pickup, not some pre-set value.
Symptoms sound a little like weak idle mixture, but from this distance it's hard to say.
I've typically had pilot screw settings from 3/4 to 1 1/2 turns out, once the rest of the carburettor has been confirmed good.

Click to expand...

Turning the screw out make's it richer? (Asking for a friend)

concours said:

Brakleen, (light viscosity, similar to gasoline) but WD-40 will work.

To clarify, this is NOT to remove blockages, but rather, simply to confirm flow.

Click to expand...

Yes, I blew carb cleaner through, one side to the other to verify flow. Also could see a tiny point of light through the built in pilot jet. Blew carb cleaner (auto parts store brand) to verity that all jets were open including the two tiny jets in the throat of the venturi.

i think your on the right track looking at the ignition…check the timing scale —they’re known to be off…Pazon? Maybe? Hot pipes, popping…check that timing again…
Rod

Britbike850 said:

i think your on the right track looking at the ignition…check the timing scale —they’re known to be off…Pazon? Maybe? Hot pipes, popping…check that timing again…
Rod

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I am almost inclined to replace the EI. I am using a Wassel unit on my T100 and it has been pretty good. (It was fiddly to set up but then again my "66 has no provision for a strobe.)

I am suspect of the Autolite Platinum AP64s it is running. I am going to try a pare of Autolite 63s which show a Champion N7Y equivalents. It probably won't help but it's worth a try.

Big_Jim59 said:

Yes, I blew carb cleaner through, one side to the other to verify flow. Also could see a tiny point of light through the built in pilot jet. Blew carb cleaner (auto parts store brand) to verity that all jets were open including the two tiny jets in the throat of the venturi.

Click to expand...

The pilot circuit starts in the bottom of the bowl - blowing straight through doesn't prove much.

Big_Jim59 said:

Turning the screw out make's it richer? (Asking for a friend)

Click to expand...

No, it's an air screw. When you turn it out you are allowing more air in, not less.

OK, It's better. I screwed the air screws out only 3/4 as at starting point and I set the idle up a bit. I changed plugs from Autolite AP64 to Autolite 63 (I couldn't locate and Autolite AP63s) It took it for a ride and got it hot. Noticed that the farting and popping on a close throttle is gone. I dialed the idle down and it runs nice and takes gas well when bliping the throttle. The true test came later. I let it sit in the garage for three minutes and it fired off. I let it sit for another 15 minutes and again it fired off.

I've generally found I needed to tickle after letting any of the bikes sit for more than 5 minutes or so.

Big_Jim59 said:

Float needles are the Viton tipped items. Tickling makes it worse. I have been wondering about the plugs. I have zero experience with Autolite AP64 plugs. I have always used NGK B7ES which is now BP7ES I guess. I might order a set of Champion N7Ys.

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NGK B7ES and BP7ES are not or ever were the same plug. The “P” means protruding electrode which Commandos have always required.

Ignition timing with "reluctant help". Thanks that made me laugh.

Looks like you got it under control, but an alternative in the future if something points at the ignition.... Get a TriSpark ignition from Greg and static time it by yourself without the "reluctant help" using one of the things shown below and old piston height measuring methods to find 29 degrees BTDC. I wrote up the procedure and verified it all with a degree wheel. It might be considered taboo by the more enlightened, but it works if there is no other easy way to get it done.

Big_Jim59 said:

OK, It's better. I screwed the air screws out only 3/4 as at starting point and I set the idle up a bit. I changed plugs from Autolite AP64 to Autolite 63 (I couldn't locate and Autolite AP63s) It took it for a ride and got it hot. Noticed that the farting and popping on a close throttle is gone. I dialed the idle down and it runs nice and takes gas well when bliping the throttle. The true test came later. I let it sit in the garage for three minutes and it fired off. I let it sit for another 15 minutes and again it fired off.

Click to expand...

I use Autolite APP3924 plugs in my Norton engine. Easy to find smaller 5/8" wrench resistor plug. Never have trouble starting the motor hot or cold.