Topic: Honda CB400F Problem

[lizard]

Hello. My name is Larry and I'm brand new to the forum so if this is in the wrong place, I apologize. I have a newly acquired CB400F that is driving me up the wall! Just got it recently and found that the plugs are almost immediately fouling with a dark black soot. Running very rich Right? Pulled the carbs and the jets were correct for this bike but the floats were set extremely high with the carbs upside down as the book suggests. (Very low with the carbs up-right). Set the floats correctly, found one secondary jet clogged on #4 and one secondary jet evidently enlarged on #3. Put new jets in and tried again. Same story, fouling plugs. Runs like crap at idle and just above idle but runs decent at WFO. Timing is correct and carbs are in sync. The only thing I can find wrong is that the timing chain adjuster lock bolt has been broken off but the timing chain is not rattling like it was loose. Any suggestions would REALLY be appreciated.

Thanks, Larry

[Gordon]

I don't know what book you're looking at, but the float levels should not be set with the carbs upside down.  They should be on their side with the float tang just touching the valve. 

[keiths]

How is the air filter? Does it run any better if you remove it?

[lizard]

Yes you are absolutely right. I set the floats with the carbs tilted up and the tangs just touching without compressing the needle. The bike does not run any better without the air cleaner (Tried with air box off and carbs completely open.)

[MoMo]

Did you remove part #3 the mid range tube?  http://www.mrcycles.com/fiche_section_detail.asp?section=121666&category=MOTORCYCLES&make=HONDA&year=1975&fveh=2911

Welcome...another Larry

[camelman]

It sounds like your emulsifier tubes are dirty. Check out the FAQ on carbs for an explanation. Easy fix, and you'll live it afterwards!

[lizard]

Sorry about the late reply to suggestions on the 400F but been gone from home a few days. I pulled the carbs again and have taken one of them completely apart like I should have don in the first place! Only had time to check #4 and the jet tube was indeed partially stopped up. I'll have the other 3 carbs clean by the time I return home this weekend (yes I did bring them with me on this trip) and hopefully that will cure the problem. Will post results as soon as I find out. I appreciate all the help from you guys!

Larry

[faux fiddy]

It sounds like your emulsifier tubes are dirty. Check out the FAQ on carbs for an explanation. Easy fix, and you'll live it afterwards!

 From the top, attack towards  where the needles are  housed after you remove the piston.

Use the plastic bic pen with the cap on top to remove the  emulsion tube pushing from the top.
It wil push the main jet out if you are not that far.


Clean the [w] HOLES.

[Cundalini]

I don't know what book you're looking at, but the float levels should not be set with the carbs upside down.  They should be on their side with the float tang just touching the valve.

I have always set mine upside down! According to the haynes manual? I think! I turn upside down then lift the float bowl until it is just touching the needle ,then measure the distance to carburetter float bowl surface!It sounds like previous owner was a right bodger!

[Bankerdanny]

When you hold the carb upside down the full weight of the float will push the valve in. The float height is set to determine the max fuel level in the bowl before the valve starts to close.

Your way you will set the float too low and start to close the valve too soon.