I am rather new to working on Nortons and am looking for some help. I bought a 73 750 last year. It was in OK condition but had a terrible wet sumping issue. I fitted a shut off valve and that has prevented the sumping issue from being an issue. The bike was running OK. I periodically had to replace the plugs to keep it running. In an attempt to solve this issue I tuned the amal 932s per amal instructions. I noticed during this process that the primary side exhaust was cold. I cleaned out the pilot jet with guitar string. No change. I also ran the left side spark plug wires to the right spark plug and vice versa. No change. I verified spark in the dark. Took the carbs off and they look great. Both recently rebuilt. I am planning to fit a single mikuni from my other Norton to see if this makes a difference. Bike has a boyer ignition. Any other suggestions?
Misfire on primary side.
- Thread starter djsktr
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Start with the easiest, simplest, least expensive items first. Fully charged and load tested battery, 2 new plugs. Clean Petcocks and fuel filters. Bad wire on Boyer? Bad coil? Good compression.
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Can you swap the carbs over, left for right?
tomspro said:
The plug does look fowled but I am not sure if it is from oil. I have not seen wet oil on the plug but I do see black buildup. I have seen some white smoke on that side but not much. Any tips on how to determine if oil fowling is the cause. I assume it would be from piston rings or valves. Not sure how to diagnose either.
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Smoke on acceleration points to rings, smoke on deceleration points to valve guides or seals. Someone spotted my MK2a smoking from the driveside exhaust taking away from lights, fitted new rings and sorted. The driveside seems to wear more than the timing side possibly due to oil supply being lower as its the far side of the crank.
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djsktr said:
Unlikely, but it might be wise to replace the stepped spray tube so the carbs match, also the carbs with stepped spray tubes (850 models) normally have a different (928/104) needle.
http://amalcarb.co.uk/rebuilding-mark-1 ... arburetter
maylar
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tomspro said:
Sometimes when dealing with Amals you get frustrated enough to just throw money at the problem and replace them. BTDT. New 932's come with the cutaway spray tube. If the PO replaced one carb with a new one, that's what would have been fitted. Most folks wouldn't notice the difference.
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djsktr said:
I wouldn't do that.
o0norton0o
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remove the air cleaner. Either visually or poke a finger gentley inside the carb opening to verify that the choke lever bodies are up, and the inner carb bodies with their attached needles go up and down when you twist the throttle.
do the bleeders work...?
start the bike:
A warm pipe's cylinder isn't firing. If you spit on an exhaust pipe and the spit doesn't instantly give a puff of smoke and boil off, then that cylinder isn't firing because of either: no fuel, no spark, no timing, or no compression...
twist the throttle to raise the RPM, does the cold cylinder "kick in" at some point?? (easy to test, just spit on that pipe to see if it puffs smoke) If non-firing cylinder "kicks in" at higher RPM's, then your idle circuit being the culprit is most likely. I've poked my idle circuit and thought I had it clear. I ended up drilling out the opposite side of that carb body and sure enough, that idle jet was clogged. poking it with a long sewing needle from the back side cleared it. I also removed the carb on the non-firing side, bent a guitar string and poked out the 2 tiny ports that come off the idle circuit mixing chamber, then blew them out with air... *(pic of them below)
Try pumping the bleeder on the non-running cylinder while the bike's running, Did that help? or do anything?
Try spraying some carb cleaner on the OUTSIDE of the carb intake manifold as it runs to look for a manifold air leak or a cracked manifold. (I had a cracked manifold from over tightening)
Sometimes a carb needle can slip out of it's retaining clip, and drop into the jet, or the retaining clip can pop out of it's recess and be tangled in the spring. In both cases the needle and jet relationship is fautly.
Electrical.... Yeah, it's not electrical... unless it's a spark plug, plug wire, or coil, which can all be switched to the other side to test. Everything else would effect both cylinders at the same time.
do the bleeders work...?
start the bike:
A warm pipe's cylinder isn't firing. If you spit on an exhaust pipe and the spit doesn't instantly give a puff of smoke and boil off, then that cylinder isn't firing because of either: no fuel, no spark, no timing, or no compression...
twist the throttle to raise the RPM, does the cold cylinder "kick in" at some point?? (easy to test, just spit on that pipe to see if it puffs smoke) If non-firing cylinder "kicks in" at higher RPM's, then your idle circuit being the culprit is most likely. I've poked my idle circuit and thought I had it clear. I ended up drilling out the opposite side of that carb body and sure enough, that idle jet was clogged. poking it with a long sewing needle from the back side cleared it. I also removed the carb on the non-firing side, bent a guitar string and poked out the 2 tiny ports that come off the idle circuit mixing chamber, then blew them out with air... *(pic of them below)
Try pumping the bleeder on the non-running cylinder while the bike's running, Did that help? or do anything?
Try spraying some carb cleaner on the OUTSIDE of the carb intake manifold as it runs to look for a manifold air leak or a cracked manifold. (I had a cracked manifold from over tightening)
Sometimes a carb needle can slip out of it's retaining clip, and drop into the jet, or the retaining clip can pop out of it's recess and be tangled in the spring. In both cases the needle and jet relationship is fautly.
Electrical.... Yeah, it's not electrical... unless it's a spark plug, plug wire, or coil, which can all be switched to the other side to test. Everything else would effect both cylinders at the same time.
I have to deal with this exact same problem every year. Sometimes more then one a season. Like the previous post it will be your pilot jet. I have a original glass interstate tank that I believe is the problem. I have got a new steal tank to go on next year and I ordered new Amal premier carbs that as I type this just showed up at my door. If you have a glass tank I suggest you replace it with a steel one or line it to prevent deteriating from the modern fuel.
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