poor Idle on 84 vf700f shoting flames and backfiring from the exhaust

Hi everyone, Recently I have upped my jet sizes one step up with the mains and the idles. Per advise to keep the motor running cooler. After that it did not want to idle properly. Had to babysit the throttle until it warmed up to operating temp. I had some misfiring so I replaced all plugs. I now have major misfiring even when warm to the extent of flames shooting out from the exhaust. Any input would be appreciated.

 

check plug gaps and be sure you have the correct OEM plug size

 

What size pilot and main were in there, and what size did you put in--one step up doesn't tell us anything.

Did it require choke to start when cold? If so did rpm drop when choke was off?

Please explain what you mean by babysit the throttle...

Is the temp gauge working? Has the thermostat been tested to verify it's working properly?

i would first suspect the thermostat to be the cause an engine over-heating issue, not the carburetors, unless the carbs were dirty and clogged. But the fix for that is to clean the carbs, not dump a bunch of fuel and create a flame-thrower.

Everyone else's bike runs fine without overheating using the stock jetting--why does the brainiac think you need fat jets...?

 

First off you don't cool a stock engine by changing jets and not knowing what you are doing. If you need to increase your jet size for some reason you almost always change needles with them in motorcycle carbs of this type. For the most part in stock motors. Who ever told you that doesn't understand much about engines.

Is your bike over heating? Have you gone thru the cooling system if it is? Have you checked to make sure your timing is correct for the bike? Either of those will make a bike run hotter than normal. That's if you have an over heating problem.

Go back to your stock jetting and see if the bike runs correctly. If it does then you over jetted the bike which didn't need it. To rich = lower power and running problems. If you have over heating problems then start in the other areas first.

Cooling cylinders by adding more fuel is a fine line adjustment on modified engines basically. Sometimes it is a band-aid for other misadjusted/built motors.

 

I apologize for not looking into the problem before posting as it was an easy fix. I pulled the plugs and there was almost no gap on one of the plugs. I checked the gap before I installed them and thought they were fine. I had a friend start the plugs on one side and he must have dropped one without telling me. Hence the old saying," if you want it done right, do it yourself" I also cleaned the connection tabs on the coils as they were crudded up with oxidation. I now have the smooth start up
On the subject of the jetting, I increased them one size mostly do to a UNI air filter and a set of Cobra F1 R slip-ons. With the stock idle jets I had a whole lot of cracking from the exhaust when I would decelerate. I also shimmed the needles a few mm to rid it of the mid range lean stumble.