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bike runs perfectly from stop to 3900 rpm every gear neutral and all. dies at 3900 rpm and starts back up (while riding) no back fire nothing starts back up just fine. new coils new regulator new battery new fuel pump clean carbs full system electric tests have been performed and everything looks as it should. normal resistance and no voltage drop. not sure on the year but an early 2000s shadow 1100 not my bike helping a friend.
 

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'83 VT750C
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Are you sure it’s really 3900 rpm? Though it should hit a rev limiter rather than just shutting down like that. Check the plug wires and boots. Something could be grounding out when it hits a certain threshold. Also, do the resistance check on the pulse generator.
 

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1983 Honda vt750 Shadow
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Pretty strange on a bike that has a red line of maybe 8000 RPM the rev limiter comes on at 3900.
Unless you added a tach without the adapter and it reads 3900 when it should be reading 7800.
Dual fire, dual spark confusion.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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IIRC they make make power at 5500 rpm and max torque at 2500 rpm.
The engine is slightly undersquare they are closer to tractors than sport bikes, I've read somewhere the rev limiter kicks in at 6200 rpm.
If you are getting rev limiter symptoms below that I'd check for vacuum leaks, especially at the carb boots.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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Edit: I see I'm replying to a posting that has disappeared.

Nice first post. we are impressed!

A tachometer is nice to have for tuning, but with a slow revving engine that gives lots of feedback like the VT1100's not really essential. A speedometer is standard equipment and some versions marked with shift points.

Yep spark timing, likely nope.
It is a crank triggered system the base timing is fixed with one or two pulse generators depending on the model and year, this is not changing as long as they make required peak voltage and positioning cannot be adjusted without physical modification. On to the ICM which controls the timing curve, it is preprogrammed, bike specific and not adjustable. Typically it either works or fails completely on one cylinder or both. after that it's just coils, wires and plugs. The chance of timing change in my opinion is almost zero.

Fuel if stock it is not gravity fed there is a fuel pump.

"if it was a fuel/air issue it wouldnt have a definitive rpm that initiates the problem." This is wrong, do you know how a CV carb works?

As I previously posted, I'd check the carb boots, they should be rubbery like a new tire, but become hard and brittle and shrink so that the clamps no longer fit and cause a symptom like you are experiencing. They are also relatively cheap to replace.

Good luck with it.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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Low slow and poor oil circulation.
Not quite as bad as the Evo Harleys, but both have a minimum idle speed as specified by the manufacturer for the same reason.
 

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Edit: I see I'm replying to a posting that has disappeared.

Nice first post. we are impressed!

A tachometer is nice to have for tuning, but with a slow revving engine that gives lots of feedback like the VT1100's not really essential. A speedometer is standard equipment and some versions marked with shift points.

Yep spark timing, likely nope.
It is a crank triggered system the base timing is fixed with one or two pulse generators depending on the model and year, this is not changing as long as they make required peak voltage and positioning cannot be adjusted without physical modification. On to the ICM which controls the timing curve, it is preprogrammed, bike specific and not adjustable. Typically it either works or fails completely on one cylinder or both. after that it's just coils, wires and plugs. The chance of timing change in my opinion is almost zero.

Fuel if stock it is not gravity fed there is a fuel pump.

"if it was a fuel/air issue it wouldnt have a definitive rpm that initiates the problem." This is wrong, do you know how a CV carb works?

As I previously posted, I'd check the carb boots, they should be rubbery like a new tire, but become hard and brittle and shrink so that the clamps no longer fit and cause a symptom like you are experiencing. They are also relatively cheap to replace.

Good luck with it.
Hey thanks for the quality response to my not so quality comment. I had been to about half a dozen forums and read endless posts that didnt align with my limited experience based on a 1981 cx500 with a similar issue. I have been suspecting some voltage issues since its got 25k miles and the blinkers dim the headlight. however, i imagine the rpm range the problem happens at would provide plenty of juice. I really want to avoid yanking these carbs out. any 'easy', try this first eliminating tests to do first? poor plug gap on knew plugs possibly? a bad coil singnal from the after market tac? I really appreciate not being told to F off.
 

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1983 Honda vt750 Shadow
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If the blinker dims the headlight, that is a sign. Check voltage at the battery after double-checking that the terminals are clean and tight. And the 3 yellow wire connection from the stater is not burned.
It should hold up to 13.5 to 14.5 volts when revved up to 3000RPM or so.
A weak charging system and ignition can feel like running out of gas.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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Yep @swifty2014 has that right.
An important thing to remember is everything on these bikes electrical runs off the battery, from light bulbs to ignition.
It is critical for operation that the battery is in good condition and the bikes permanent magnet alternator and rectifier/regulator keeps up with the demands of replenishing it, that is their only job.
Check all the wires and the quality of the connections and don't forget the ground wires (usually green on these) connections to the frame, corrosion is your enemy here.
A battery can show enough voltage but can be week under load, unlikely if it starts the bike OK, but a load test at an auto parts store will tell you and most places is free.
 

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'83 VT750C
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Did you gap the plugs before installing them, or have any way to measure? You could always just give the bottoms a little crack on the ground to make the gap a little smaller to see if anything changes… But I would doubt it. The spark can be ‘blown out’, but that’s usually happens a bit more intermittently.
 

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99' Valkyrie/North Central Indiana
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Check the 3 yellow wire plug from the stator for signs of melting as Swifty mentioned. Recommend hard wiring regardless of condition. This can cause weird electrical issues including causing stator/rectifier issues. If a carb issue and sounds to be a high speed circuit issue, 1/2 can of Berryman B12 added to to a near empty tank and fill.
 
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