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Discussion Starter #1
My bike (2001 VN750) is having a hard time staying running without giving it gas for a minute or so on a cold start...

outside temperature is 45 degrees, cold motor, fully choked, twist the throttle a few times. Bike is stored outside.


In the summer time, it starts up fine.

I have not coastered my bike, only capped off the reed valves with giant vaccum caps.

The bike is jetted and the ears have been shaved and I have Vance and Hines pipes.

Carbs have been cleaned and and taken apart many times.

Petcock just taken apart and cleaned.

newer MF battery installed.

Factory Stator and R/R

I have not done the coil mod yet.


Any thoughts or ideas? It almost seems like it is fuel starved or something... Once it gets running and idling properly, it pops alot on decel now since it's really cold outside...
 

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Premium Member
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A stupid question but it must be asked. Are you using the choke? The on position is pulled toward you as you sit on the bike. It sounds stupid to ask this but you'd be surprised how many folks don't use the choke correctly.
 

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Yes, and the "choke" is in fact an "enrichment circuit" that is basicly tossing more fuel in. If you need to give it additional gas by twisting the throttle too, then something is not right. At full choke the bikes rpms should slowly rise without touching anything....usualy you need to back off the "choke" as the bike warms up.

How long are you letting the bike warm up?

45 is not that cold, but if you store the bike outside, I would first think you are getting some condensation in the gas tank... but your choke should work for cold starts without having to use the throttle.

KM
 

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Discussion Starter #4
Yes, it is choked.

I choke it and hit the start button and it will start up for a couple of seconds and dies... I have to help it out a little bit until it can idle on its own. I usually let it warm up to about 3k rpm's then I back the choke off completely (about 1-2 minutes, or enough time to gear up).

If there was any condensation in the tank with an empty tank, I would understand, but not a full take. Water is more dense than gas so it goes to the bottom of the tank which the petcock would not pick up when in the "On" position.
 

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Yes, it is choked.

I choke it and hit the start button and it will start up for a couple of seconds and dies... I have to help it out a little bit until it can idle on its own.


If that is all the issue is, you needing to "help it out" until the bike warms up and idles on it's own, then your choke, choke cable , or enrichment jet needs adjusting or cleaning.

If the bike runs fine once it is warmed up, it would not be gas. Although "winter gas" is crappier than "summer" gas due to additives.

I'd check to see if the choke is opening all the way, add some seafoam to the tank and not really worry about it if you do know HOW to start the bike when it is cold.

Because you did the earshave and it's always possible your jetting is not perfect. How many miles is on the engine, what brand/weight of oil do you have in it, and the condition of the gas all could make a difference too.

And water does sink in gas but not like a rock...it is as easy as pulling the bike up off the sidestand to make it "spread out" into the gas in the tank and enter the petcock tube.
We did this as an experiment once using blue dyed water and fuel in a small glass tank. The blue water would settle at the bottom, but if you tried to pick up the tank carefully and move it to another spot, the water would swirl up before settling down again.
You can not fill a tank all the way up easily, there will always be air pockets. I'm not sure you have any water in your tank, but if you did, the exact same thing you decribed could occur.

What size pilot jets did you install? Are you using iridium plugs?

KM
 

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Giggity!
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That's alot of water! I some times have to "help" the bike start up on cold morning. 40's. And once she warms up she's good to go. Being newish to bikes mostly carb'd engines the whole choke **** is still interesting to me. I've learned alot here about how this bike works. Just an "fyi" is your bike in the cold "tendered"? A strong battery is a world of differencr with this machine. As fall starts I just deal with the little extra "finnegalling". Once the repeated cold starts she's on a tender. Just my 2c worth.
 

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Calif Rider
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Another stupic question. Do you use the idle black knob on the left side of the bike, this is as you sit on it. Turning it clockwise will put the idle higher than usuall and then as the bike warms up, you have to turn the knob back to get the idle down to normal, after choking and engine warms up. Nothing was mentioned about if you used this knob or not.
 

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Linkmeister Supreme
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Another stupic question. Do you use the idle black knob on the left side of the bike, this is as you sit on it. Turning it clockwise will put the idle higher than usuall and then as the bike warms up, you have to turn the knob back to get the idle down to normal, after choking and engine warms up. Nothing was mentioned about if you used this knob or not.
I went back and reread his posts, and it sounds to me like he is just using the throttle and choke. He doesn`t say anything about the idle adjust screw.
 

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You said that you've had the carbs apart, but have you synchronized them? Mine acted similar to yours before I synced them. They were never that far off, but it made a world of difference in cold starts, idling, hot starts, and low circuit. I still have not gotten an MF battery, and have had no problems since I synced. If you haven't, there are $1.55 carb sync kits you can assemble from your local Ace Hardware.
http://www.powerchutes.com/manometer.asp
 

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Discussion Starter #11
I have 40 and 41 pilot jets if I remember correctly... it seems like the rear cylinder is having a difficult time cranking over... the bike was laid over a few years ago and I cleaned it up and re-did the carbs and it hasn't run the same ever since. I guess it is possible the carbs got out of sync according to what tincanman said, especially if it was laid down pretty hard...

I am using iridium plugs.

The idle adjust screw is set fine because it idles fine once it warms up.

I didn't think about this before... but when the air gets colder it gets a lot more dense... more dense air means it will need more gas (bigger jets). This would explain the popping on deceleration.

I will check the sync on my carbs first though since the rear carb has always been kind of weird.

things to test:
Carb synchronization
Air/Fuel mixture screws
Battery Tender every night
 

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Discussion Starter #12
I synchronized the carbs with a home made manometer... the rear was pulling a lot more vacuum than the front carb. They are now set at the idle position to be pretty equal.

I put the the battery on the charger as well.

I also adjusted the idle air mixture to make it a little bit richer than before on both carbs.

Synchronozing the carbs helped a little bit with the over all running condition of the bike, but none of this helped with the cold start. The rear cylinder still seems to not be firing when fully choked... any other ideas? stuck float? air getting sucked in through carb boot? not enough spark?
 

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That's a tough one. It could be an old/hard carb boot like you mentioned (*). One way to test for vacuum leaks is to use propane. Take a propane torch, start the bike, open the valve on the torch and run it around the carbs/boots (without lighting it!) and listen for a change in idle speed. That may not be as effective as you have shaved the ears and so your intake is right there, but worth a try. When she first turns over what do the rpms do during warm weather starts vs. cold weather starts? Do they run up to 1.5 to 2k at first start, drop immediately to idle, then slowly climb, or just fire off and run at idle/slowly climb? Pull your air filters and check your vacuum pistons for ease of movement/sticking. Have you checked your compression? With all the mods you have done, you're most likely running a hotter engine which can burn valves easier, and puts you valve springs at a higher risk of failure. Which side did she go down on, and do you know if she was left running on her side after the spill? Good luck, and remember that failure is not an option.

* I always coat my boots/o-rings/ext in vasalene, wrap them in a lite rag, and set them in the warmth atop my old CRT computer monitor to soak while I'm working on the rest. Vasalene is to petroleum based plastics as linseed oil is for wood, or neats foot oil is for leather. It's the good old hard liquor derived from the same base stuff. Gives em new life. I also use a hair drier to warm the crap out of them directly before install, to make them supple, and to conform. Cause we all like conformity sometime, right?
 

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The Professor
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I synchronized the carbs with a home made manometer... the rear was pulling a lot more vacuum than the front carb. They are now set at the idle position to be pretty equal.

I put the the battery on the charger as well.

I also adjusted the idle air mixture to make it a little bit richer than before on both carbs.

Synchronozing the carbs helped a little bit with the over all running condition of the bike, but none of this helped with the cold start. The rear cylinder still seems to not be firing when fully choked... any other ideas? stuck float? air getting sucked in through carb boot? not enough spark?
With the engine running you can spray wd-40 around the boots to check for leaks. Check the voltage going to your coils, you could also swap coils and see if there are any changes. If coils check out and boots are not leaking then your problem will be in the fuel enrichment circut, could be stuck or clogged. Good Luck!

P.S. Did you shim the needles when you did the re-jet?
 

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aka Smokymtnvulcan
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I have a similar problem only my engine backfires really loud then usually starts! What's up with that?
 

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I have a similar problem only my engine backfires really loud then usually starts! What's up with that?
Weak battery... You have an AGM battery?

Wet cell batteries are kinda useless on this bike. They seem to work fine when brand spanking new ....but given the bikes poor electrics, it should never had one put in it. (many bikes now come with AGM batteries stock)

Installing a set of NGK iridium plugs can help alot too...
 

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First thing you should do is check your negative connection. Mine, in the cold, can get a touch loose when things contract from the temp. Usually, for me, the signs can be any one (or all) of: back firing, slow crank when you press the button, spark from negative terminal, slight smoke from negative terminal (you are drawing more current through a smaller area if the connection is bad which can sizzle some insulation).

Take the negative lead off, use some sand paper on it and screw it back down then give it a whirl.
 
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