Topic: CB750K1 Running Rich

[Chase Rhodes]

I am restoring a 1971 CB750K1 model.  Carbs have been rebuilt and engine is running excessively rich.  I will attempt to document current state of engine.  Completely Honda stock except exhaust replace with 4 into 1.  Plugs are NGK D8EA, timing is set, point are set at 0.14, values are set per spec, float level is 26MM, main jets are 120, slow speed jets are 40, jet needle is set at center position, air adjustment is approx one turn out on all four carbs and standard air filter (not K&N) & the carbs are in sync.

However, engine is running excessively rich at top end (> 3,500 RPM), black smoke.  My thoughts are to step up one heat range in the plug NGK D10E and set jet needle up one position (second from the top).

I know going from stock 4 into 4 exhaust to 4 into 1 the carbs should have been re-jetted, but the were not.  This is how a received the bike.  I don't know if the jets should be larger in number or smaller.  Also, I don't know where to get just the jets.

Any help would be appreciated.

[Chase Rhodes]

This is my first post.  Did I not get this posted correctly.  It appears the post has been read multiple time but I am not getting any feedback .

[graeme7]

You posted right, i guess all the viewers just dont have any good advice for you.

Unfortunately, nor do i.

But someone will eventualy.

You might find some similar situations discussed before if you search?

[bollingball]

Here is a good place to get the jets I go for the ones that have 4 or 5 different sizes. With your set up I would start at 110. Leave the plugs at D8. remember do your plug chop at 3/4 throttle position under load maybe up hill. There are several post on plug chops and how to do it. Did you do the work you spoke of or did someone tell you it had been done?
Have you read this?
http://forums.sohc4.net/index.php?topic=5410.0;all

[Chase Rhodes]

Thanks for the good input.  I didn't see a link to go and find new jets.  Maybe down sizing from main jet of 120 to 110 may be the answer.  The CB750K1 appears to have never been jetted after previou owner replaced the original exhaust with the 4 into 1 exhaust.  I did all the work myself.  This CB750K1 was set up since 2005 with the gas left in the tank and carbs.  I had a real mess to correct.