Topic: CB750F3 carb Qs

[Davidov]

I'm currently getting my 78 CB750F tuned just right before I get it on the road. I have some questions is anyone can provide some knowledge that would be excellent.
They're stock Keihin PD carbs.

1. After the initial 1 3/4(1.75) turns of the pilot screw. I ended up with them all screwed out about another full 1 turn. Is this OK? Or should they be left at 1.75 out?

2. The lowest idle I can get is about 1500 RPM. I know the recommendation is 1000 RPM, but it just doesn't want to run solid at that speed. I tuned everything, cleaned the carbs, etc.. Is 1500 OK?

3.This sort of relates to #2. I was spraying around the carbs with cleaner looking for any intake leaks. I noticed a gap at each choke plate shaft?

Once again, sorry for all the dumb questions. I figure somebody out there has been in my shoes!

[Gearheadgreg]

Yep even my new rider lawn tractor would not idle when stored over the winter, you guessed it clogged slow speed jet!!! 
Got to Love E-10 gas    If you did not pull your slow jets and clean them your adjusting screw will not respond much,, If you have stock exhaust and a stock airbox it should run good at 1-3/4 to 2-1/2 turns out,,mine is 1-3/4 and idles @ 1000 rpm solid. don't forget to check the 0 rings on the mixture screws it will run like chit if broke or missing.

[Davidov]

These carbs have pressed in slow jets, but I did thoroughly spray through each one with carb cleaner. I made sure the accelerator tube(proper term?) was clear.

It's a stock airbox, and an aftermarket muffler on the stock 4-1 750F exhaust. I need to try a few more tricks on the idle.

I'm still confused about being able to see light around the choke plate shafts? I did some intensive research, but pictures aren't as good as real life. Should there be a perfect seal around each one?

Thanks again.

[Spanner 1]

Seeing light at the choke shafts is not critical IMO..... but not pulling the slow jets is !
Those pressed-in slow jets do come out by pulling/twisting with a parallel jawed pliers... wrap some cloth around under the plier's jaws will help to not mar the sides. I bet the cross drilled holes are all blocked as well as the jet itself..... you can see light thru' it when held up at just the right angle... good luck 

[Gearheadgreg]

If you have a slip muffler and the stock headpipe it will lean out a already Factory lean motor, These PD carbs have a accelerator pump to over come fuel starvation for EPA reasons, My 78F 3 was all over the place at idle and popping on decel a couple of weeks ago, just installed  # 38 slow jets and smooth as silk No popping through my slip on pipe with stock header and enjoying the ride 

[fatkid]

hey gearhead nice f man thats a sharp one

[Gearheadgreg]

Thanks Fatkid. I like to look at everybody's bikes so pictures are a must 

[Davidov]

Seeing light at the choke shafts is not critical IMO..... but not pulling the slow jets is !
Those pressed-in slow jets do come out by pulling/twisting with a parallel jawed pliers... wrap some cloth around under the plier's jaws will help to not mar the sides. I bet the cross drilled holes are all blocked as well as the jet itself..... you can see light thru' it when held up at just the right angle... good luck 

Ok, thanks. This is the type of response I needed. I did overlook the slow jets, I assumed "pressed" meant a permanent fit!

If you have a slip muffler and the stock headpipe it will lean out a already Factory lean motor, These PD carbs have a accelerator pump to over come fuel starvation for EPA reasons, My 78F 3 was all over the place at idle and popping on decel a couple of weeks ago, just installed  # 38 slow jets and smooth as silk No popping through my slip on pipe with stock header and enjoying the ride 

Good to know as well, off come the carbs....again! 
(BTW, that's a slick 750F!)

[Davidov]

I couldn't find the original post that I read, but.....is the Honda Manual for CB750 K8 and F3 misprinted about carb types?
I have Keihin carbs stamped PD 42A 105 main jet, 35 slow jets.

This particular manual has those specs listed for a 750K. 

Now these two sites list the carb type and jet size properly. Right?
http://www.hondachopper.com/garage/carb_specs/carb_specs.html
http://www.motorcycleproject.com/motorcycle/text/specs.html