Honda-SOHC

SOHC.co.uk Forums => CB750 => Topic started by: Arch stanton on August 30, 2019, 02:16:35 PM

Title: Too rich pilot?
Post by: Arch stanton on August 30, 2019, 02:16:35 PM

Hello.
Looking for some thoughts here.
My K1 starts without choke. But drives really smooth once on the move.
But the idle hangs, then settles to a too slow tick over. Also when it warms up it pops & crackles on deceleration.
And stutters from closed throttle.
I can eliminate most of these niggles. By turning the pilot screws out. But it take 3.5 turns to do it.
Am I right in thinking. I need smaller pilot jets?
Maybe #38 or #35?
I am aware that it would be best to used standard pipes & filter. But I am very happy with things in general. But I find this little problem annoying.
So any help would be appreciated.
Sean.

Title: Re: Too rich pilot?
Post by: K2-K6 on August 30, 2019, 05:53:20 PM

I read that the same as you have.  It's really "asking" for less fuel right at the bottom end of idle jet response,  which is what the 3.5 turns is effectively giving it.

Unsure of your overall setup but it looks reasonable to edge it slightly leaner by just one step of idle jets to bring it closer in range to cleaner running.

Without standard setup it's really suck it and see so I wouldn't worry too much about standard screws settings to get what you want.

It looks from your description that you are trying to lean it out right at the very lowest response of idle circuit without spoiling the transition from idle to main jet section if that is responding ok now.

Title: Re: Too rich pilot?
Post by: Arch stanton on August 30, 2019, 11:46:29 PM

Thank you for your response.
I will try to obtain some #38 jets.
At 3.5 turns out. The screws are wobbling side to side. So I think they are as far out as they can be. Without falling out altogether.

Title: Re: Too rich pilot?
Post by: Skoti on September 03, 2019, 08:16:27 AM

Hello Arch,
I had the same problem and renewed the pilot jets which did not cure it.

However after renewing the needle jets the problem was solved.

Good luck with your carbs. 

Title: Re: Too rich pilot?
Post by: gp_st3 on September 05, 2019, 02:32:29 AM

I also had this problem about a year ago (657A carbs with 110 mains / 40 pilot and needle 4th from top) ...sooty plugs, poor idle and stalling when puling away from standstill once the engine was hot (fine when cold).

Wasted a lot of time and effort adjusting pilot screw and needle positions; finally went for #38 jets and what a difference!! - all running great with good response from closed throttle and clean/tan plugs.

Incidentally, now need full choke for starting regardless of ambient temp, but switch off completely soon after the engine has fired up and maintain the revs using the throttle until it warms up to steady tickover.

I buy genuine Keihin Jets at reasonable prices from allensperformance.co.uk

Title: Re: Too rich pilot?
Post by: gp_st3 on September 05, 2019, 02:45:01 AM

p.s. just remembered also fitted new needle jets when I originally cleaned/refurbed the carbs as they were badly worn and causing plugs to foul.

Title: Re: Too rich pilot?
Post by: Arch stanton on September 21, 2019, 09:59:27 PM

Yes. It was worn needles.
Just had a very enjoyable blast through the Trough of Bowland. I was looking for problems. But could find none.
Other than. The suspension to soften. & a bloody awful brake squeal. To sort now.