1994 VMax Intermittent Surging Issue

[cjb600]

I just purchased a 1994 VMax at the end of June. It had been in storage for 5 years. I got it running okay using the shotgun and pea shooter cleaning methods. I did notice it had a surging issue (very intermittent) about every 50 miles ridden. Dannymax recommended a thorough carb cleaning, so I did that and the issue has not resolved. Just wondering what else I could check? It almost feels like when the v boost kicks in. Could it be a malfunction with the v boost, or ignition? It pulls really hard for a 1/2 second then goes back to normal. Bike is all stock except a K&N air filter. Any info would be appreciated. Thanks!

 

[MaxMidnight]

Is this at constant throttle and at what revs?

Are you sure it is firing on all four cylinders? Can't think of anything else that would give the symptom you describe.

 

[Fire-medic]

I think another round of carb cleaning is in-order. Did you change the gas filter? The idle speed circuits are tiny, it doesn't take much to plug them.

 

[[email protected]]

Hard to pin down based on your description.

Fuel, air, or electrical. Is that vague enough?

Drain the float bowls and see if the fuel comes out perfectly clean or, if you see debris. Tank could be rusty, fuel filter dirty, fuel lines dirty and/or deteriorating. Carbs could still need cleaned.


Intake boots could be cracked.

Could be misfiring due to a bad plug, wire, coil, pick up, cdi.



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[cjb600]

The rpms are in the 3-4K range when I have noticed the surge. I'm positive it's running on all 4 cylinders, all 4 plugs are a light brown color, but I'm thinking it could still be a misfire. It looks like the plug wires, etc are original, bike has 28,000 miles. Is the OEM repair manual the best to follow for checking plug wires, coils, etc? I did install a new fuel filter before the carb cleaning. I'll do some more troubleshooting and let you know what I find out.

 

[Eugene Brad]

Could you try to go full/akways open on the vboost, to rule out your vboost theory. I think I recall you unplug the vboost relay as it cycles open when you turn on ignition. Take it for a ride like that and you could deduce from there.

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[cjb600]

Thanks, I am going to try that first. Seems fairly simple to rule that out first.

 

[Eugene Brad]

Actually just unplug the relay without it opening so you are running normal instead of vboost always. That may be easier to tell if it surges still

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[Fire-medic]

It's unplug the round plug to the VBoost when the ignition cycles-on and the VBoost opens. Under the left scoop.

You can trim a bit off the spark plug wire if you find one end looks green & corroded.

 

[[email protected]]

Does this surge seem to happen when you hold a steady throttle position? Or is it when you crack the throttle open after holding steady for a bit?

What exhaust is on the bike?
Whats your carb setup?

Lot of variables since its new to you.



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[Eugene Brad]

It's unplug the round plug to the VBoost when the ignition cycles-on and the VBoost opens. Under the left scoop.

You can trim a bit off the spark plug wire if you find one end looks green & corroded.

Thanks FM. My post lacked all of those key procedures.
If you unplug before the vboost cycle doesn't that disable vboost altogether? My thought is that would produce a more helpful diagnoses than running vboost always.

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[cjb600]

I think I have pinpointed the issue a little better. Today when I was riding, starting from a stop and accelerating in 1st gear then shifting into 2nd at about 4K rpms I felt the surging/hesitation. I was able to repeat that several times. It doesn't happen every time though. Otherwise, the bike runs and drives good otherwise. I was wondering if I have the dreaded 2nd gear issue that some have had?

 

[cjb600]

Does this surge seem to happen when you hold a steady throttle position? Or is it when you crack the throttle open after holding steady for a bit?

What exhaust is on the bike?
Whats your carb setup?

Lot of variables since its new to you.



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The surge/hesitation happens when I am accelerating, I haven't noticed it when I'm holding steady throttle. I think I narrowed it down a bit today when I shift from 1st to 2nd gear and hit 4-5k rpms, I get the surge/hesitation. I am starting to wonder if I have the 2nd gear issue that some have had. To answer your other questions, it has stock exhaust, stock carb setup with stock pilots and mains.

 

[D-Max2012]

I had this stubborn hesitation between 4-5K. Did everything you can think of.. Even went as far as pulling my tank to coat the inside. Ethanol laced fuels, draws in water from the air, which causes rust to build up in the tank. TMALSS, I used Seafoam in my fuel. 1/2 bottle to each 4 gallons at fill-up. At 2 1/2 times doing this, that stumble was gone and it's been pulling strong ever since. That was 4 years ago..

 

[Fire-medic]

Thanks FM. My post lacked all of those key procedures.
If you unplug before the vboost cycle doesn't that disable vboost altogether? My thought is that would produce a more helpful diagnoses than running vboost always.

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Yes, disabling the VBoost could aid in trouble-shooting. I was mentioning one way to have it open all the time.

 

[jdeitz1979]

You said that you did a carb cleaning, did you check the carb sync afterwards?


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[Eugene Brad]

You said that you did a carb cleaning, did you check the carb sync afterwards?


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Good call.

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[cjb600]

You said that you did a carb cleaning, did you check the carb sync afterwards?


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Yes, I did a carb sync afterwards.