High Idle, Smoke Coming from Exhaust - Honda Shadow Forums : Shadow Motorcycle Forum
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post #1 of 32 (permalink) Old 05-16-2019, 07:06 PM Thread Starter
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High Idle, Smoke Coming from Exhaust

Howdy Howdy.

Did a valve adjustment recently and jetting change on the carbs (including removing the jet shims), I had to remove the cam holder to heli-coil a bolt my friend broke inside the cam holder as well but it shouldn't have effected much.. and have come forward with an issue of a greyish color exhaust coming out of ONLY the rear cylinder and smells burnt but not sweet indicating it's not coolant.
Could this be an issue of A/F? Could the valves be set incorrectly?
I've been racking my brain and google for a few days about this now.
I checked the intake boots, and they seem fine, no major cracking or breaks (I also used silicone on the outside just to be sure). the idle jet is the same as stock with 2.5 turns out roughly. Which is the same as previous so the rough idle and smoke wouldn't make any sense.
Figured a collective opinion might be more helpful than one person trying to attack it alone.

https://photos.app.goo.gl/cP5t6WGV1M5SkvBCA

It's usually like this, sometimes worse for a second or two.

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post #2 of 32 (permalink) Old 05-16-2019, 07:14 PM Thread Starter
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Also, being so the rear idle is kinda lumpy, not as smooth as the front

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post #3 of 32 (permalink) Old 05-16-2019, 10:13 PM
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Did you have to move the valve adjusters very much? Usually they are only out a thousanth or so and don't need much of a turn to adjust.


Pull the spark plugs to see what their color and appearance is.

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post #4 of 32 (permalink) Old 05-16-2019, 10:54 PM Thread Starter
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Quote:
Originally Posted by swifty2014 View Post
Did you have to move the valve adjusters very much? Usually they are only out a thousanth or so and don't need much of a turn to adjust.


Pull the spark plugs to see what their color and appearance is.
They weren't terribly off, but we brought them within spec and put everything back together after a double check.
I had to helicoil the thread that was broke off, but removing the entire camshaft holder couldn't have done much for the adjustment no?

And in regards to the sparkplug, it's still quite fouled up from the previous jetting (which was realllllly rich. Part of the reason I messed with the needle and main jet to bring it down)
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post #5 of 32 (permalink) Old 05-16-2019, 11:07 PM
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Maybe start with new plugs and go from there.

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1983 750 Shadow
From the past=
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1962 Honda 305 Dream
1965 Honda 305 Dream
1971 Honda 175 scrambler
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post #6 of 32 (permalink) Old 05-17-2019, 06:16 AM
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The rear cylinder which is burning the oil is the same one that was running in your words "realllly rich" previously. If this condition lasted long wnough, there's always the possibility that the excess fuel was washing the oil off the cylinder and scored the walls themselves.


I'm just trying to brain-storm here and not trying to diagnose it at this point.
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post #7 of 32 (permalink) Old 05-17-2019, 11:10 AM
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New plugs are always a good start giving a "clean slate" spark plug diagnosis.

I'm joining Chuck in the brain-storm.

I know from past experience with my 750 ACE that the mis-routing of choke/enrichment cables can create problems with the plunger thing in a carb not going fully into the hole despite the choke control being fully pushed in.

This causes a high idle on the effected cylinder and blackish smoke from the one cylinder, when the engine is throttled up.
This is usually accompanied by "the neighbor's lighting the charcoal grill" smell.
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post #8 of 32 (permalink) Old 05-17-2019, 08:19 PM Thread Starter
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Quote:
Originally Posted by Chuck_Michigan View Post
The rear cylinder which is burning the oil is the same one that was running in your words "realllly rich" previously. If this condition lasted long wnough, there's always the possibility that the excess fuel was washing the oil off the cylinder and scored the walls themselves.


I'm just trying to brain-storm here and not trying to diagnose it at this point.
Well, the smoking wasn't prominent before, this happened with the recent (I guess you'd call it) full tuneup of the valves and misc.
I did put new plugs in, and it didn't change anything. Gonna take it apart tonight and see if the timing is off (as the honda dealership suggested) incase we did accidentally change the valve lashings off-timed.
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post #9 of 32 (permalink) Old 05-17-2019, 11:15 PM
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If you didn't unbolt the cam gear and slip off the chain the cam timing should still be where it was.

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1983 750 Shadow
From the past=
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1962 Honda 305 Dream
1965 Honda 305 Dream
1971 Honda 175 scrambler
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post #10 of 32 (permalink) Old 05-17-2019, 11:50 PM
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Quote:
Originally Posted by swifty2014 View Post
If you didn't unbolt the cam gear and slip off the chain the cam timing should still be where it was.
That is true.

I think what the dealer's advice might be considering is the valves may have been set at the wrong cam position, it is a bit if a stretch, but the crank timing positions do line up twice per cam revolution, so two potential choices and only one of them is the right place to adjust the valve clearances.

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