One dry sooty plug

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Triton Thrasher said:
Needle jets wear out, causing richness at small throttle openings. You can’t fix that properly by lowering the needles.
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Is there a hole size gauge available to precisely measure the jet? Seems like such a tool would be a benefit to actually confirm wear, rather than blindly replace with new, not knowing if the replacement is within spec size.
 
I only brought up the new Amal Premiers because the older Amals aren't quite as tunable. Well, my old Amals aren't, but they might be much older. Also brought up the leave it alone as a excellent fall back solution. :)
 
Bob Z. said:
Is there a hole size gauge available to precisely measure the jet? Seems like such a tool would be a benefit to actually confirm wear, rather than blindly replace with new, not knowing if the replacement is within spec size.
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Yes. Called gage pins. Every machine shop has a set.
 
Bob Z. said:
Is there a hole size gauge available to precisely measure the jet? Seems like such a tool would be a benefit to actually confirm wear, rather than blindly replace with new, not knowing if the replacement is within spec size.
Click to expand...
A long time ago I had maybe 30 needles at a time when I thought they were worth saving. In order to match them I took a small piece of aluminum and drilled two holes side by side. Drop the needles in and see if the circlip grooves line up. Then swap the holes and see if the results are the same. It is interesting to see how much variation there was. Haven't done this in a long time hoping that modern mfg is more precise. I should not be so trusting.
Have you tried swapping the needles to see if you can move the problem to the other side?
Also, perhaps the pilot passageway has a partial blockage?
Since the carbs are original, 48 years old, and 12000 miles old, give them the heave-ho and install new premiers if the budget allows.
 
Interstate said:
No, did not check compression yet. I do have a new tester. I'll look up the correct compression value unless you know what the '73 850 engine should read when cold. Thanks for the advice.
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In this case the thing that really matters is, are they the same, if they are, compression is unlikely to relate to your problem. But do record what you get.

More likely is a worn needle jet and possibly needle if these are original parts. Inspect them for wear, but really, if they are 40 plus years old, just replace them.
 
Interstate said:
Needles & jets are original to the machine. My thought is the needle height adjustment may need to be lowered to decrease fuel intake, right?
Have not messed with the pilot air mixture screw yet. I wanted to gather some clues before I tear into the problem.

Thanks.
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And politely to those who are simply relating their own experiences, which may or may not be the basis of your problem.

You have a whole lot of other things to do and check out before you tear this down.

Like the other guy said, if it ain't broke, don't fix it.
 
Bob Z. said:
Is there a hole size gauge available to precisely measure the jet? Seems like such a tool would be a benefit to actually confirm wear, rather than blindly replace with new, not knowing if the replacement is within spec size.
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Buy from a reputable Amal source, and you should not have a problem.
 
I would replace the needle jets just on principle first. As stated above they wear out of round probably due to the severe shaking they get.
 
gortnipper said:
Assuming the ignition timing is correct and you get a nice fat spark on that side with a fresh plug, there are any number of carb related problems that can make it run too rich. Worn needle/jets, leaky float, float height, float hung up on gasket, etc.

Seeing as it is original carb, and you don't do many miles, it may benefit from a strip down and ultrasonic clean at this point. I would buy an Amal carb rebuild kit and jet removal tool and replace the parts on that carb that come with the kit. Also buy a new main jet and one smaller than you currently have.

Rebuild to current spec will eliminate worn parts. If problem recurring, then you can start changing heights, etc.

Rebuilding the Amal Mark 1 Concentric Carburetter | AMAL Carburetters

A detailed guide on dismantling, cleaning, inspecting, and reassembling the Amal Mark 1 Concentric carburetter.
amalcarb.co.uk amalcarb.co.uk


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Thanks a lot for the carb Rebuilding & Tuning tips....a great help! This is where I believe the sooting problem lies. Assuming all OTHER sooting possibilities are equal, left vs right, then a comparison between the right carb (sooted plug side) and the left carb (no soot side) should reveal the problem with the right carb. Confused....so am I. Thanks again.
 
Onder said:
Looking in through the spark plug hole with a good light, what does the top of the piston look like?
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OK, did that among some other observations today. Right side piston top has wet looking soot deposits that black out a q-tip end. Swabbed the left side piston top where q-tip shows a dry, light grey soot. Did a compression test....R.S. = almost 90 psi; L.S. = 100 psi. Also checked oil level in the tank after I had closed my wet sum ball valve at the end of last ride. I'm about 3/16" below the "L" line. Yup, it's bad enough I didn't check my oil but it appears the rings and valves should be done soon.

Thanks to all, specifically Onder for his check list items and follow ups. Anyone looking for a winter project?
 
Interstate said:
Thanks a lot for the carb Rebuilding & Tuning tips....a great help! This is where I believe the sooting problem lies. Assuming all OTHER sooting possibilities are equal, left vs right, then a comparison between the right carb (sooted plug side) and the left carb (no soot side) should reveal the problem with the right carb. Confused....so am I. Thanks again.
Click to expand...
Your L vs R carbs can utilize different settings to get each correct, so if it ain't broke don't fix it.
 
Interstate said:
OK, did that among some other observations today. Right side piston top has wet looking soot deposits that black out a q-tip end. Swabbed the left side piston top where q-tip shows a dry, light grey soot. Did a compression test....R.S. = almost 90 psi; L.S. = 100 psi. Also checked oil level in the tank after I had closed my wet sum ball valve at the end of last ride. I'm about 3/16" below the "L" line. Yup, it's bad enough I didn't check my oil but it appears the rings and valves should be done soon.

Thanks to all, specifically Onder for his check list items and follow ups. Anyone looking for a winter project?
Click to expand...
Your 90 psi is too low, suggests something wrong with top end hence it will not work efficiently.
 
Schwany said:
I only brought up the new Amal Premiers because the older Amals aren't quite as tunable. Well, my old Amals aren't, but they might be much older. Also brought up the leave it alone as a excellent fall back solution. :)
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Do Premiers have a better range of needle jets than Mikunis?
 
For those with kids of a certain age, your solution would be: Izzy wizzy, let's get busy!'
(apologies)
 
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