Carb Adjustment - Honda Shadow Forums : Shadow Motorcycle Forum

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Old 10-01-2012, 01:48 AM   #1 (permalink)
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Default Carb Adjustment

A week or so ago I posted the question and had a few answers. I tried and failed.

The bike - 85 VT500C - runs well on highway and plugs read nice and tan. Around town plugs get black and sooty, so tried adjusting the....uh....pilot screws ?? The little ones deep in the hole low on the carb ??

The rear cylinder responds fine to adjustment and was at 2 turns, so moved it in to 1 turns. Idle sounded better. Went to front cylinder and screwing it in all the way didn't make any difference until it was "almost" seated, then idle speed would increase.

I had asked about the WD-40 test for vacuum leaks and someone suggested carb cleaner as a better choice, so I went and bought a can and carefully sprayed each hose, tube, connector, gasket on both sides and no change in idle. Finally just soaked the whole thing with the cleaner and it made no change at all, so I doubt if I have a vacuum leak......but front cylinder is still the same.

The bike runs fine but idle is iffy. Sometimes at a light it'll idle just fine, others it'll stall on me. Sometimes idle is higher.

In rolling foothill country at 6,000 ft elevation on the highway I can hold 65 mph in 6th just fine, even on moderate hills.

Meantime, it's giving me 50 mpg overall and power is great, which pleases me and as I say it runs fine.......it just isn't "right." Any ideas ??

Thanks............Lar.
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Old 10-01-2012, 02:46 AM   #2 (permalink)
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Check in the stickies for your bikes manuel and check the carb adjustments there. If its not a stable idle when adjusted properly then try running seafoam in your gas. Idle is affected by two things electrics and gas. Pull one plug wire at a time with the bike running and see If you get an rpm drop, If yes that plug and wire is ok, if not you have an electric problem too maybe. If its truely the carb and it won't adjust properly then try a rebuild. Check the air filter too.
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Old 10-01-2012, 10:49 AM   #3 (permalink)
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Both of the pilots should be at the same setting. Any difference in operation should be dealt with by syncing the carbs.
Are the plugs "fouling" around town or just getting a little black? You may well be over thinking it. If you run on the open road and the plugs are fine but you are a little rich in town and they are a little black then really there is no issue.
The pilot circuit provides more or less fuel at idle but is still delivering fuel at mid throttle settings. I wouldnt worry about being a little rich in town as it will have the added benefit of running a bit cooler.
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Old 10-01-2012, 11:49 AM   #4 (permalink)
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Quote:
Originally Posted by cl65ame View Post
Both of the pilots should be at the same setting. Any difference in operation should be dealt with by syncing the carbs.
Pilot screws should end up close to each other but do NOT have to be the same. The jets don't have to match, why should the settings of the screws. AF mix is adusted for each carb INDEPENDANTLY. Sincing DOES not even address the AF mix, it is an adjustment of the throttle, so the the carbs FLOW at the same rate.

Quote:
Originally Posted by cl65ame View Post
Are the plugs "fouling" around town or just getting a little black? You may well be over thinking it. If you run on the open road and the plugs are fine but you are a little rich in town and they are a little black then really there is no issue.
The pilot circuit provides more or less fuel at idle but is still delivering fuel at mid throttle settings. I wouldnt worry about being a little rich in town as it will have the added benefit of running a bit cooler.
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Old 10-01-2012, 12:22 PM   #5 (permalink)
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Actually if you would like to get technical the sync adjustment sets the Manifold air pressure to the same value for each cylinder. In doing so you are in fact adjusting the air fuel ratio to meet the requirement by altering the throttle position of ONE carb to match the other.
The manual is quite specific as to the setting of the pilot screws and the procedure is outlined in the manual.
The jets in the cylinders do not match for a reason. The flow characteristics of the intake system as well as the operating temperature of the rear cylinder are considerations taken into account. The main jets are the only ones that differ from front to rear but it is not always the case.
At any rate having the screw almost seated is not the correct position for the screw since the reference starting point is two turns out from seated.
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