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83 vt500 Won't Start When Warm

10K views 13 replies 11 participants last post by  rrounds 
#1 ·
I have a problem. My bike starts fine when it's cold but once it gets warm, if I shut it off and try to start it again it will crank but won't fire. Also, if I can get it started when it's warm it's a very weak for a couple cycles until it gets going.

It did the same thing just after I bought it last summer and it turned out the battery was bad. I replaced it but I'm afraid I may have killed it between the harsh winter we had and my trying to jump start it and charge it many times.

The only other thing I can think of is yesterday I pulled out the spark plugs and cleaned them up with some fine sandpaper. I didn't regap them because I could find my guages and figured they were fine already.

I also changed the oil/filter and coolant but I don't think that's the problem.

Any thoughts?
 
#2 ·
Most bikes, including mine, seem to be the exact opposite - trouble cold starting, great warm starting.

I haven't the foggiest so couldn't hazard a guess, but I can't think that many of the reasons for cold start issues would apply for you, surely.

How long does it take to restart?

Make any pops or odd noises?
 
#3 ·
Never clean your plugs with sand paper, there is no need, use a wire brush. Gap them correctly so you know you didn't shave off enough to increase the gap passed the point of it wanting to spark. Second possibility could be a coil going out, when the bike warms up the gaps all expand including any possible cold solder points in the coils. When it doesn't want to start pull your plugs and check for spark.
 
#4 ·
You could also be experiencing vapor lock. Next time its warm and won't start try removing the gas cap and starting it. Could be your tank vent is plugged.
 
#5 ·
All the shadows I have owned have needed a different choke setting to start and then, after 30 seconds, none to run..maybe you just aren't used to the bike yet, or maybe it just needs a long fast run to clean the cobwebs out, or maybe the carbs or air filter are dirty, watch out for poisonous spider nests..

John.
 
#6 ·
I'm pretty sure the problem is battery related. I gave it a good charge and the problem went away. I think maybe I didn't get a full charge after winter. I still want to get the battery and charging system checked and I'm going to carry my emergency jumper until I'm sure it's good. I'll also be investing in a battery tender.

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#7 · (Edited)
Agreed, probably the battery. While you're warming the engine up for a few minutes, it's draining the battery at idle rpm. Don't know if you have a faulty charging system, different topic, different topic. Sounds like the battery is on it's last leg though. I would kill the engine and try start the bike up a second time, you don't necessarily want the "second" start-up miles away from home. [edit] forgot you had an emergency jumper unit.
 
#8 · (Edited)
Common problem with the VT500c. you can say it is several things acting on the engine keeping it from starting. First: the starter is located behind the rear cyl. this is a place that gets hot. heat increases resistance in the windings so the 30 year old starter is slightly slower. A rebuild or good cleaning of the starter will help this. Second : the coils are located above the front cyl and tend to get hot also. if you have the repair book you can test them somewhat. If you test them cold and then again when hot you may have an issue there. Third: the charging system was never strong. The battery may not be getting fully charged while riding. After an hour or 2 to cool down the battery has regained a small amount of juice, the starter is a bit cooler and the coils are cooler all contributing to the bike starting after cool down. I have managed to get mine to start hot by rebuilding the starter and using a battery tender at all times. I also learned to bump start it when I was not sure it would crank up. Good luck
 
#9 ·
I'm wondering. Could I be running too rich? It fires right up even when cold although I have to let it warm up or it bogs down when I give it gas. When it's hot it cranks just fine but I have a hard time getting it to fire.

The reason I ask us because when I'm at a light I can smell in burnt gas.


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#13 ·
It might be electrical. I have a 1985 VT500c that I used for about a year as a daily driver. It is soon to be my son's bike. About 3,500 miles back, I started having the same problem. Then, without warning, my solenoid melted down on me. I changed out the solenoid-got one off ebay for dirt cheap-and presto, the problem has gone away. Might not be the problem, but could be.
 
#14 ·
As parts age, some times they don't put out as much volts. So you can replace a lot of parts($$$) or you can do this, just close the gap on the plugs a little. Every older bike I have I run the plugs about 3 or 4 thousandths less than what the book calls for(so if your bike calls for a gap of .031 to .035 I'd gap the plugs at .027 to .028 ). That has worked for my older bikes.

ROD
 
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