nighthawk750.freeforums.org

hello all,brother and i jus picked a 92 nighthawk 750 as a spare bike.very clean,and when running,goes thru each gear very smooth.problem is starting and idling-it constantly needs the choke.previous owner put 4 into 1 vance&hines exhaust,told us mechanic did rejet.we pulled carbs,bowls are spotless and center jet looks brand new compared to lowest one.no dirt at all.also noticed the packing in muffler smells stongly of gas,were guessing from always being on choke.besides needing choke to idle,its very hard to start hot,have to give it the right amount of throttle.thanks for any advise

Sorry to hear of your NH idle problems. A couple of things to consider. Some argue the stock NH's carbs are set from the factory on the lean side causing the bike to run hot. Personally I think the engineers at Honda got it right which is why we all love the bike.

With the addition of the V&H 4 into 1 exhaust the flow of air/fuel through the sytem changed. The new exhaust prompted the mechanic to rejet the carbs to allow a richer air/fuel mixture. Perhaps a little too rich and while dumping fuel into the combustion chamber and allowing it to exit more easily will give you a mild increase other issues that should have been addressed don't appear have been addressed. Opening up the exhuast without increasing the ability to intake more air (not just fuel) sets the system out of balance especially if the new jets weren't just right.

You stated "packing in muffler smells stongly of gas." I am not suprised if the fuel/air isn't able to fully combust then stuff starts getting coated with unburned gas which is a mess. My guess is that the richer mixture may have fouled your plugs. Check the plugs or put in some new ones and also check the ignition system and timing. You want to ensure you have a good spark for all that rich air/fuel mixture.


Once you get it fixed, I have found letting the bike sit an idle to warm up when first started is a BAD idea, it fouls plugs. Instead let it idle long enough to circulated the oil then ride it gently till it is fully warmed up. You can use the choke when first riding but monitor the engine and lose the choke as soon as the bike is running normal. Take the bike out on the highway keep your rpms up for a while and burn the excess carbon out of the system.

Hope this helps.

as i stated,carbs were spotless,reinstalling them we found idle screw was too low! i know shouldve checked 1st, but bike sat around so we figured they would be dirty. So bike starts cold and hot.idles good when warm_got it around 1100 right now, bike still has problem when initially throttling,spit and cough then race.am i in the ballpark sending it for sync?