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· Registered
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Discussion Starter · #1 ·
Hello All,

I have a 1986 Nighthawk 450. It's the California legal one, if that makes a difference.. but, it is definitely not California legal anymore (i pulled all that emissions crap off). However. I have been working on it very slowly over the past couple years while I've been finishing engineering school. Thus, time has been scarce, and so has money. Therefore, I have been doing everything as cheaply as possible.
That said, I have removed the air box, and that is where the battery now lives. I have also removed the "common collector" and now have each of the exhaust pipes running essentially open. There are some small "shorty mufflers" on the pipes, but they don't do much in terms of restricting air flow.

The Problem
I now seem to be running super hot/lean, even after running through a bunch of jet changes. The stock main jets were 125s. I ran 162s today, and my plugs still look similar to "hot/lean" in any chart i reference. Plus, I can tell the bike is just running hot as ****. However, it does start fine, and it idles fine. I bumped the idle jets up by 5 from 40s to 45s. (i think, it's been a while since I pulled them, but they haven't seemed to be the problem)

Has anyone ever done anything similar as far as bike modifications, and if so.. how much did you have to bump your jets up? Is it possible that I am also idling too lean/ have too big of a gap between idle/ main? My power slump seems to be in the mid throttle range. Thus, I'm thinking maybe i could bump the idle jet up a bit more? so there's less of a gap between the two? I have never done any of this before, so everything i know is from reading stuff from the internet.

Any help would be appreciated. Even if you just want to call me an idiot and point me to a thread where this problem has been solved before.


· Premium Member
23,965 Posts
These carbs are a sequential cumulative type, each circuit is active full time and added to by the following circuit.
These engine are a lean burn design. Most of the plug charts were printed in the 60's, maybe 70's, and are only good for a very generalized reference. They are not good for diagnosis. The plugs should be an off white, slightly more towards tan than pure white.
You've eliminated the air box so you have the inherent problem of keeping air velocity into the carbs, there's a sticky about pod filters in this section that may help.
The power chamber has been eliminated so there's a decrease in back pressure as well as primary pipe length plus the open/short mufflers have lost almost any possible back pressure.
These are the single main jet carbs which applied to 1985/86 only and to date no one has really messed with them other than rebuilds.
So here's a couple of questions. Compression readings? Is the ignition system 100%? all resistances in spec and timing advances properly
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