GRAB THAT 650 ! The pipes alone will return much more than $200. If your "valve" couldn't supply enough fuel, no amount of choke would make up for it. duh The choke gets it's supply from the same bowl... Now, a further lesson. A motorcycle carb has many stages and they are ADDED as RPM increases. Without the fuel from the blocked slow speed circuit, all stages are too lean. If it "went to bed" above 5k, the problem would be at the high speed circuit. Bear in mind that bikes of that period (late 70's~early 80's) were just flat too lean to start with (blame the EPA compliance / CARB standard) any congestion becomes critical. An increase to #37 of the slow jet makes them run a good bit better. Now, contrary to popular belief, "if some's good, more's better" does not apply. A #40 slow jet makes for poor running. Jet numbering is a percentage of 100. A #35 supplies 35% as much as a #100.
--- On Sat, 3/7/09, Graham Rogers <[email protected]> wrote: From: Graham Rogers <[email protected]> Subject: [Nighthawk Lovers] Re: Nighthawk S starting problem To: [email protected] Date: Saturday, March 7, 2009, 2:08 AM Thanks Dennis, I ran my own 'petcock' system (a plumbing shut off valve) from the tank when I couldn't find a good stock petcock for a CB750F so I'll start there. The breaking up happens at any speed when the choke is not on. I'll get back to my CB700 when I've got this one ready to sell. By the way I came across a 1983 CB650SC last week real cheap ($200) to use as parts for another one I have. This parts bike has pipes in mint condition and I'm hoping anything else I'll need for my CB700 (the N/gear indicator problem) I can get from the CB650. On Mar 7, 2009, at 12:34 AM, Dennis Hammerl wrote: So, we switch bikes ? OK, this one sounds like clogged slow speed circuits. "Breaking up" (is hard to do ?) is a lean condition. Rich mixtures are just sluggish, lean ones crackle and pop. Again, check jet sizes. 1980 CB750F should be; primary 68, secondary 102, slow 35. Now for all the tuners; you can over jet so much that the result is just like being too lean. The air velocity is too slow at low engine speeds that it doesn't carry that much fuel in. snap-crackle-pop. and then.... WHOOSH as it hits an engine speed that can make it all work. When it all works like it should, things are sooo boring. They start and run, pull from low engine speeds and go pretty good. If rejetting is ever indicated following an exhaust change, start with a base-line of stock jetting and correct as necessary. Inspite of "enclosed instructions" most after market exhaust systems require only slight changes to jetting if any at all. --- On Fri, 3/6/09, Graham Rogers <[email protected]> wrote: From: Graham Rogers <[email protected]> Subject: [Nighthawk Lovers] Re: Nighthawk S starting problem To: [email protected] Date: Friday, March 6, 2009, 7:59 AM This bike CB700) is on hold for a little bit. I'm having to make the difficult decision to sell one of my Hondas. So I'm going to sell my 1980 CB750F. But first I have a problem. I restored this bike as much as I can (paint job, new decals, new seat cover and detailed clean, including carbs). The bike runs good as long as I keep the choke on some. The bike breaks up and dies if I do not use the choke. Here's what I suspect may be the problem and this is where I need help. I could not find a vacuum leak by spraying around the carbs while it was running. The bike has a 4 into 1 exhaust system. That's how I got it. Should the carbs have been modified/adjusted for the change from the original exhaust system and had they not, would that cause it to run lean and so need the choke activated? If that's the case what do I need to do? Installing stock exhausts/mufflers is too expensive. Thanks guys, Graham On Feb 26, 2009, at 12:38 AM, Dennis Hammerl wrote: They are your carbs. Investigate what passages are blocked. It would seem that you have sufficient intake vacuum, Hand choking increases that. If all was well, after hand choking, the plugs would be saturated. Because they aren't, the path from bowl to intake via choke valves must be blocked or the choke valves don't work properly. They can be removed without too much trouble. Very simple devices. --- On Wed, 2/25/09, Graham Rogers <[email protected]> wrote: From: Graham Rogers <[email protected]> Subject: [Nighthawk Lovers] Re: Nighthawk S starting problem To: [email protected] Date: Wednesday, February 25, 2009, 5:46 PM I cranked the motor over - it tried to start, at least on one or two cyl. Then I checked the plugs. They were dry on the tips and porcelain but a little wet on the rim of the plug. It didn't smell like gas however. I then tried to start the bike with my hand restricting the air flow at the air filter. It did start but died when I moved my 'hand choke' I probably could have gotten it started that way. So, it looks like the choke isn't working eh? Now what?Graham On Feb 25, 2009, at 12:21 AM, Dennis Hammerl wrote: Spraying it optimizes the conditions needed for starting. Which... means the chokes aren't working. If it has a strong vacuum when cranking if you hold your hand over any carb throat, the chokes aren't passing any fuel. WHY ? The "gas chokes" are very simple valve devices. If they have access to fuel from the float chamber and they are open to the bores when activated, all should work. With the throttle plates closed, the high vacuum (or , more properly, low pressure) should draw fuel up through the choke circuits and into the motor. It's as simple as a faucet. I don't want to get into any abstract at this point. Are the plugs getting wet when you crank the motor with the chioke operated ? Knowing that is a must before proceding. If they are, we look elsewhere. If not, we stay in the carbs. --- On Tue, 2/24/09, Graham Rogers <[email protected]> wrote: From: Graham Rogers <[email protected]> Subject: [Nighthawk Lovers] Re: Nighthawk S starting problem To: [email protected] Date: Tuesday, February 24, 2009, 8:05 AM Tried starting the bike this morning and there doesn't seem to be any improvement. It would 'bubble' along like it was trying to catch (it acted like a weak spark) but again it took starting fluid and the choke seemed not to play apart. Once it had 'caught', restricting the air flow through the air filter with my hand significantly increased the rpms. Maybe I should also check the state of the battery huh?Incidently I noticed the fuel gauge didn't work until I revved the engine significantly and held the revs. That was a new one to me, Graham On Feb 23, 2009, at 11:02 PM, Dennis Hammerl wrote: Let us know how that works out. The neutral wiring is grounded and that's why it always shows N / green light. Let's get into that later. You have multiple issues. One at a time. --- On Mon, 2/23/09, kiwi <[email protected]> wrote: From: kiwi <[email protected]> Subject: [Nighthawk Lovers] Re: Nighthawk S starting problem To: "Nighthawk Motorcycle Lovers!" <[email protected]> Date: Monday, February 23, 2009, 1:16 PM Blasted those tiny holes that allow the gas through when using the choke with compressed air and spent 2 hours reinstalling the carbs. It still took starting fluid to get the bike started BUT, not very much and the choke worked a little. I'll see how it starts tomorrow when it is back to winter temperature. Second problem with this NH is the neutral/gear indicator. It reads N all the time and won't show what gear the bike is in. I found a little black box under the tail section that I think is part of the N/gear indicator system. Is there a way to check it? Third problem should be simple. The left front turn signal is 'bright' when ignition is on but will not blink when it should. The others work as they should. That left one shines a lot brighter than the right front when ignition is on. On Feb 22, 11:11 pm, Dennis Hammerl <[email protected]> wrote: > I will assume your carb clean was a complete operation. Let's examine how the choke works. The cable opens valves that will permit raw fuel to be sucked into the motor during cranking. Now, lets say that works fine.Your plugs should be wet after cranking for a short while. Y-N ? The most common cause of the plugs being dry after cranking is the throttle plates being open too far and causing insufficient vacuum. Same as opening the throttle while trying to start. When the intake air flow is too low, no fuel will be drawn in from the choke circuit. If the plugs are wet, you're flooding the motor. > We start here. Additional checks of compression and a leak-down may be in order. > This may take time to resolve. Get at it. > > --- On Sun, 2/22/09, Graham Rogers <[email protected]> wrote: > From: Graham Rogers <[email protected]> > Subject: [Nighthawk Lovers] Nighthawk S starting problem > To: [email protected] > Date: Sunday, February 22, 2009, 6:18 PM > > I have a 1986 Nighthawk S. It ran before I got it but always took > starter fluid in the air filter to get it going. I pulled the carbs > and thoroughly cleaned them and used to compressed air in all the > holes. However the bike still will not start without stater fluid > and even then it takes along time with the fluid. I noticed that > using the choke seemed to make no difference at all so, thinking that > perhaps the choke isn't working at all I removed the carbs again > (they are terrible to remove) and did what I could toi ensure the > choke was working right. The mechanism moves as it should and I used > compressed air in the holes to the where I presume the choke opens. > Now, before I reinstall the carbs, any suggestions? Could the > problem have been the choke or is there something else that would > cause the same problem. By the way, once the bike was warmed up, it > ran fine - just when it's cold I have to use starting fluid, Graham --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
