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 -~----------~----~----~----~------~----~------~--~---
