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Hey guys my name is AR. I am currently working on my 1981 Honda CB400t Hawk. I got the bike completely stock and then converted it to a bobber by added struts, peanut tank, and welded straight pipes. It is a screamer. This is my first Honda that I have worked with.

Problem: Cannot get it to idle. I have to have the choke all the way on while giving it some gas to keep it alive once I stop it dies instantly.

Cheers!!
 

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Retired twice: Navy and as a govt contractor
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12,778 Posts
Did you rejet the carbs when you put straight pipes on it? Also what did you do with the intake,
 

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ZAMM Fanatic
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Sounds TO ME like your carburetor's idle jet is clogged up.

MOST carbs have two jets, or "orfices" to flow fuel through, an idle jet and a primary or "main" jet. Sometimes a needle sits in the main jet orfice and moves up and down, varying the flow.

When the idle jet gets clogged, typical symptoms are that it won't idle, or that it "lopes" as the main jet opens, closes, opens, closes attempting to supply fuel. Another common sign of a clogged idle jet is poor acceleration from idle --- it's not getting enough fuel to get INTO the main jet.

Will it idle if you sit there and spritz starting fluid into the air filter? Of course it will...... that's all you're doing by pulling the choke on, sucking HARDER on a partially clogged jet. So pull the carb off and find someone who's "done it before" to rebuild it for you. Order the kit online ahead of time at a place like BikeBandit.com

And don't be a weenie like so many who come here and ask for help, once you get it running right, REPORT BACK to us on the cause, cure, and cost.

Cheers!
 

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ZAMM Fanatic
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Another common sign of a clogged idle jet is poor acceleration from idle --- it's not getting enough fuel to get INTO the main jet.
On lawnmowers, at least, this is why you DO NOT lean the idle mixture to maximum RPM, but instead, lean it to max RPM and then enrich 1/2 to 1 turn, so it's rich enough UNDER LOAD to get "into" the regime where the main jet is providing the fuel.

On emissions tested cars, you do what you HAVE to do to pass idle emissions, which is often lowering the RPM to rock bottom AND leaning, and then, after you pull out of the testing station...

I'm just not that familiar with motorcycle carburetors and which if any have idle MIXTURE (not rpm) adjustment screws, etc.

On lawnmowers at some point the EPA got too big for their britches and started forcing mfr's to seal over the idle screw with a plug so homeowners couldn't adjust idle mix. Of course this SCREWED the folks at high altitude whose mowers ran rich, fouled plugs, etc. We'd drill off the cap until they eventually began making carbs without the screw at all. Consumer got the screw(ed).

Bottom line is most internal combustion engines will run, even fairly decently, within a HUGE range of lean/rich and timing, and getting it really tuned well, well, it increases power slightly but will greatly improve miles per gallon, reduce plug fouling, etc. On virtually EVERY distributor car I ever owned ensuring PROPER spark advance, either by rebuilding or replacing any distributor with over 125,000 miles, made a humongous boost to performance relative to anything you could do with the carbs, headers, exhaust, air filters, etc. Sadly I know almost nothing about motorcycle magneto/point&coil/electronic ignition systems. Do modern bikes have a crank position sensor? Anyone?

Cheers!
 
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