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post #1 of 3 (permalink) Old 03-15-2011, 10:20 AM Thread Starter
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starting problem

Hi all, new here hoping somone can help me..just got a 85 700 runs great but after it warms up and sits for 5 mins it wont start backfires through exhaust
let it sit for 20 mins or so and runs like new again..i checked carbs to see if they where maybe pushing gas but they seem to be ok no back smoke when she long as i dont shut it off it will will fine..
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post #2 of 3 (permalink) Old 03-15-2011, 10:37 AM
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Your most likely problem is a weak battery. If it is a wet cell with the drain tube and covers you add water to, you will need to replace it with an AGM Maintenance Free battery. On the older bikes, it is not unusual for the wiring to be weak going to your coils so I'd at least check your voltage using the procedure below in my sig for the coil mod.

These bikes have some known weaknesses right from the factory with the wet cell battery and such. If you still have your goat's belly (pre muffler) and the regulator/rectifier is still mounted over the GB and under the battery box, the heat it needs to disperse gets combined with the heat from the GB and it stays really hot. Most of us have moved our R/R out from under there to a simple mount we make up from hardware store pieces, to get it out where it can get air flow and run cooler. (that mod is also in my sig) Then, most of us will purchase NGK Iridium plugs for our bike to replace the old ones. The iridium plugs seem to have a more consistent hot spark than the stock plugs and last many times longer.

The backfiring on trying to start the bike when it is hot is the main symptom of weak spark, which causes a rich fuel condition and this rich vapor tries to ignite with the weak spark and doesn't fully ignite, but when the exhaust valve opens to force out the exhaust, this vapor hits some fresh air and BAM! You get that "wake the dead" backfire. I did the R/R relocation, and the coil mod at the same time (coil mod was mainly to see how it worked on the 750, as I had done it previously on a couple of KZ's but no one had done it on the 750 so I decided to try it and it works great) so I don't know which one had more effect on the hot start issue I was having, but it was cured and I never had the problem again. I already had an MF battery at the time. In some cases, the MF battery cures the issue by its self, but others have had to do more, including rebuilding the starter motor.

So, start with the battery, then check your coil power wire voltage, get that r/r moved when you can, and plan on some iridium plugs asap. If you still have issues, you may have to mess with the starter, but I feel pretty confident you'll eliminate the problem before you get to the starter.

Kyle, TX member #707 VROC#19556
2002 VN1500 Classic
Spline Lube Procedure, with photos, R/R Relocation and Coil Mod
Rusty Tank Cleaning!
Electrical Fault Finding Flowchart

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post #3 of 3 (permalink) Old 03-16-2011, 03:01 PM Thread Starter
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700 not starting after warm

i moved rec/reg checked voltage at coil new 12.3 at battery 11.99 at coil
new battery but still the same..could it be cdi??? also checked wiring for corrsion didnt find anything checked for bare wire or cracked wire also..
i see what ya meen about r/r it does get pretty warm
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