Topic: CB750F Jet size

[HonderCB]

Hello,
Can anybody tell me what size jets i need to run in my 77' 750F.  It has pod filters and an HM410 Honda exhaust.  I suspect the previous owner didnt properly jet it when putting on the pods.  I live in Southern IL so elevation is probably around 600ft.

Thanks for any help,
-Scott from IL

[HonderCB]

The problem i am having is at idle.  It wont do it without choke being on.  Anything below 5k RPM runs good with choke on, but once i get out on an open road and really open it up it sputters until i rememeber to close off the choke, then it puts me back in the seat.  With the choke off i can keep it running, but i have to keep revving it from idle, and it kind of sounds like its sucking air.  I figured the jets might be clogged from sitting, but while i had them out i need to check to see if they are even the right size.

It also has an inline fuel filter between the petcock and carbs, is it possible that this is restricting the fuel flow and thats my problem?

Thanks again

[Gearheadgreg]

First thing you may want to do is locate the stock Airbox, the PD carbs are factory set very Lean, My 78f would hardly run with the airbox off when i tried to start it,,Your SLOW jet will need to enriched from a 35 to a 38 to improve your idle quality and give you some mid-range. you will be pleasantly surprised whit this mod. Greg.

[dtmmil]

First thing you need to do is take them off and clean them so you can blow air through every passage, sounds like your idle ports are plugged, most likely your pilot jets themselves. then try tuning. Try 120 main jets, should get you close for a start. But, you won't get anywhere if your carbs arent clean, which they arent.

[HonderCB]

Well, pulled the carbs and they were clean as a whistle.  The mains were 110's which is one size bigger than stock i believe.  The pilots were only turned out between 1 and 1 1/2 turns.  The book says start at 1 3/4, so we set them there for starters.  Me and the father in law fiddled with the pilots for a while, half-turn one way check.  oh, got worse, go the other way, etc...  For the better part of two evenings we tried and tried to no avail.  He owns about 5 750's in various states of completion, and one happens to be a 77 F model parts bike, so we pulled the stock air box off, cleaned it up, stuck it on, and turned the pilots out until it was running good (which ended up being around 3 turns).  So now it runs like a top and my father in inherited a new set of pod filters to use on his 69 K that he is building.

[Gearheadgreg]

Awesome! It sure is great when we hear back from a member that it was something simple, them PD carbs are touchy,my F3 has a slip on muffler and it required re jet. 

[HonderCB]

yea, luckily my father-in-law (read: mechanic) had what was left of a 77F scrap parts bike down in his back shed.  I was able to rob his air box and trade him my pods for another filter he had.  The filter that was in it when we pulled it off was non existent, the mice had taken all the paper leaving nothing but the mesh, and it was a rotten rusty mess.  I was able to pilage a few other parts off it too, a turn signal and the little strap that holds the glove box closed.  I'll probably snag a few more parts off it before all is said and done.