You are in the most complex and troublesome circuit. The fuel path is from the bowl supply up the primary main and over to the slow speed jet (the hole from pri main to slow is only a small distance up above the removable pri main jet. Look for the passageway, it's blocked off after drilling with a small brass "BB") The fuel flows forward to a junction and on to the holes. It is controlled by the idle mix screw. ALSO, air is mixed in at two places. The rubber buttons insure that fuel is channeled from the pri mains by blocking off any direct path. Sprying into the slow jets should come out the main discharge in the bore as it is the path of least resistance. Blocking that off with a finger should direct the cleaner along to the right place / path. Opening the mix screw will allow more cleaner through. SO, spray into the open screw hole and into the slow jet with the main discharge blocked off. It would seem that the tiny discharge holes are open but the path to them is gunked up. There are so many passageways in this circuit to clean out all I can say is be diligent. Trace out the flow paths by examining the casting and seeing all the cross-drillings that are plugged with small round brass BB's. The horizontal passageways are the most difficult to clean, but it can be done. If you block off the main discharge in the bore and spray into the slow jet, it SHOULD spray out the three small holes. Then, there's always the Sea Foam soak... I want to look for the photo you sent. I may be able to indicate the flow path.
--- On Thu, 5/14/09, Graham Rogers <[email protected]> wrote: From: Graham Rogers <[email protected]> Subject: [Nighthawk Lovers] Re: Graham's 1980 CB750F To: [email protected] Date: Thursday, May 14, 2009, 3:13 PM Okay Dennis, I have the carbs off the CB750F once more. Here's what I have observed after removing the black plug covering the slow speed idle jet. When I blast compressed air through the jets the air returns up through the primary main jet. A very small amount passes out the tiny hole(s) in the carb body. There are three holes in each carb body - two side by side covered by the throttle plate and one one the outside of the throttle plate. The amount is so slight I could only tell by holding a piece of tissue in the throat and watch for it to move when the air came through. I cannot tell whether it comes through one or more of them. It seemed the same amount came through on all four carbs. Spraying carb cleaner through the slow speed jet did not result in spray coming through those same holes. What now? Graham On Apr 24, 2009, at 11:10 PM, Dennis Hammerl wrote: My other E-mail rejects LARGE files. Total limit is one meg. With a long lay-up, I'm still going to stick with the carb malfunction. To do what you say, it has to have a blocked circuit. Large throttle openings dump fuel and the vacuum slides will control it. So much for acceleration. Steady speed requires the contribution of fuel by selected circuits. One of yours isn't doing it's job. --- On Fri, 4/24/09, kiwi <[email protected]> wrote: From: kiwi <[email protected]> Subject: [Nighthawk Lovers] Graham's 1980 CB750F To: "Nighthawk Motorcycle Lovers!" <[email protected]> Date: Friday, April 24, 2009, 6:38 PM Hi Dennis, yes, I repaired the broken idle mix screw and set them all at one and a half turns. It has four into one, air box is original with clean air filter. This is the way the bike was when I got it and probably how it ran before I got it. The bike sat for a long time. It started and ran when I got it but I didn't ride it so I'm assuming it had the same problem. Sent pics to your other address Dennis but everything came back. Don't know how to post them here --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Nighthawk Motorcycle Lovers!" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/nighthawk_lovers?hl=en -~----------~----~----~----~------~----~------~--~---
