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1984 Magna VF700C
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67 Posts
Discussion Starter #1
Looking for some technical advice here - I recently finished a restore on an 84 Magna and noticing now that it’s cold out and I actually need to use the choke...I can’t start it unless I adjust the throttle at the carbs. If I open the choke and turn the bike over it fires hard for about 2 seconds like it wants to start and then just normal crank and won’t start. I have to adjust the throttle to get it going and eventually it’ll run at about 500RPMs until it warms up and then I have to adjust the throttle back to where it was to get a normal idle. If I open the choke back up while it’s warming up the bike stalls quickly.
I suspect that when I cleaned the carbs I maybe didn’t do such a great job with the holes for the choke? The metal rods on the carbs move back and forth freely when I open and close it. Any thoughts?
 

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1983 Honda vt750 Shadow
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15,246 Posts
Sounds like you may have some vacuum leaks at the boots if all this changed after the carbs were off.
Is the factory air intake still all there?
 

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1995 VT1100C2
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3,880 Posts
Just to clarify: in order to start with full choke; no throttle you need to turn the throttle stop screw down ie reduce idle speed to 500 rpm from its original 1000 rpm? So either too much fuel at 1000 or not enough air. Does it start no choke; no throttle? Whats the A/F screw setting or is it still factory?
 

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1984 Magna VF700C
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67 Posts
Discussion Starter #4
Sounds like you may have some vacuum leaks at the boots if all this changed after the carbs were off.
Is the factory air intake still all there?
It’s all there - and I actually put new boots on when I reinstalled the carbs because the old ones were petrified. And just to clarify - the bike wasn’t running prior so not really a new problem so much as the most recent one, lol
 

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1984 Magna VF700C
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67 Posts
Discussion Starter #5
Just to clarify: in order to start with full choke; no throttle you need to turn the throttle stop screw down ie reduce idle speed to 500 rpm from its original 1000 rpm? So either too much fuel at 1000 or not enough air. Does it start no choke; no throttle? Whats the A/F screw setting or is it still factory?
Almost - I actually turn the idle up to get it to start with no choke, because using the choke kills it. It starts at 500RPM because it’s cold - and by the time it’s warmed up it’s closer to 2k and the. I adjust the idle back to where it should be and it runs great. Basically I’m adjusting the idle screw in lieu of using the choke since it won’t start with the choke open.
 

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1995 VT1100C2
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3,880 Posts
I would check to ensure the SE valve is working and adjusted properly. Whats your A/F screws set at? Turning the throttle stop to idle when warm at 2k means you are "manually" adding a lot of fuel into the system which is what the SE should do so I think SE is not adjusted or plugged. After warm does it idle and run well at a steady rpm or does rpms waver?
 

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1984 Magna VF700C
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67 Posts
Discussion Starter #8
I would check to ensure the SE valve is working and adjusted properly. Whats your A/F screws set at? Turning the throttle stop to idle when warm at 2k means you are "manually" adding a lot of fuel into the system which is what the SE should do so I think SE is not adjusted or plugged. After warm does it idle and run well at a steady rpm or does rpms waver?
I’ll see if I can adjust the valve. The potential for being plugged is what I was concerned about, since I would have to take the carbs off again to clear it. AF screws - are those the pilot screws? I set them to factory - I think it was 1 3/4 turns out. And yeah once it’s warm it runs like a top.
 

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1995 VT1100C2
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I’ll see if I can adjust the valve. The potential for being plugged is what I was concerned about, since I would have to take the carbs off again to clear it. AF screws - are those the pilot screws? I set them to factory - I think it was 1 3/4 turns out. And yeah once it’s warm it runs like a top.
Ok check the SE valve. Unfortunately I dont have the specs for Magna handy but what you do is remove choke cable boots at the SE valve at the carb, Loosen nuts and remove SE valves. Clean. Turn choke to fully off. Distance from threaded cable end and and closest part of SE valve is 10 mm. The adjustment is made at the choke lever by adjusting the elbow there.

A/F screws are also called pilot screws and once you have the SE correct (ie choke should change rpm), I would look at the A/F and enrichen the fuel mixture. I would go as far as 3 turns out but no further..
 

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1984 Magna VF700C
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67 Posts
Discussion Starter #11
Ok check the SE valve. Unfortunately I dont have the specs for Magna handy but what you do is remove choke cable boots at the SE valve at the carb, Loosen nuts and remove SE valves. Clean. Turn choke to fully off. Distance from threaded cable end and and closest part of SE valve is 10 mm. The adjustment is made at the choke lever by adjusting the elbow there.

A/F screws are also called pilot screws and once you have the SE correct (ie choke should change rpm), I would look at the A/F and enrichen the fuel mixture. I would go as far as 3 turns out but no further..
The magna is a bit different - the choke cable pulls a pair of metal rods - 1 across each pair of carbs, that cover an inlet on each carb when closed and open the inlets when the choke is open - I’ll have to look and see what adjusting looks like. Thanks for the help - I think this is the right path.
 
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