Well my troubles continue with my number 4 cylinder. I have now replaced the plugs and wires with no relief in symptoms. However, I have some new diagnostic information.
for those who may not have read my earlier post I recently diagnosed a problem with my #4 cyclinder. I get jerky acceleration, bag gas mileage, and variable idle speeds. The thing that narrows my troubles down is that the #4 exhaust manifold stays much cooler than the other 3. after a 30 minute ride you can still touch it. It is not COLD, you would not want to take firm hold of it but in comparison if you lick a finger and touch any of the other three it will sizzle.
here is the new info. in swapping my plugs and wires I took the opportunity to experiment a bit. I found that if I disconnected the #4 spark plug wire I could not get the engine to start. I have not had problems starting my bike. If I start the engine and then disconnect the #4 plug wire, there is a marked and dramatic change in engine idle speed and how it sounds. So, not having the cyclinder fire at all makes the symptoms much worse than they present on their own.
This leads me to conclude that either the #4 cylinder fires only sometimes, or it only fires mostly. let me explain. first option refers to the possibility that perhapse not every ignition takes place. if at 1000rpm that cylinder would normally fire 500 times per minute, maybe mine only succeeds 250 times out of 500. the second option refers to that cylinder generating far less power than the other three. for example, if the exhaust valve leaks it could lose a portion of its air/fuel mixture prior to ignition and subsequently have a much weaker power stroke than the other 3. Also, it could be supplied with less mixture by a faulty (i.e plugged main jet) or very badly sychronized carb.
The obvious test for option 2 is a compression test and synch the carbs. Other than an emmissions gas test probe I don't know how to test option one.
Give me your thoughts on how my logic here sounds to you, and suggestions on how to proceed. Also, I need to find a compression test fitting, the guage I have now is sized for a car.
Finally, a question of symantics to settle an argument. As I understand the #1 and #4 cylinders run on identicle strokes. My brother-in-law says they might spark together but that it sparks once per revolution and every other spark is a waste spark. the cylinders might travel together but are on opposing strokes. So, when cylinder 1 is on compression, is cylinder 4 on compression also or is it on exhaust? And of course the same goes for 2 and 3.
Thanks again all for your time and efforts helping me out.
strange goings on with my #4
#4 is firing at least some of the time and that is good. I had a similar problem on #3 after my first attempt at carb cleaning. I think possible problems could be partially or intermittently clogged jet on #4, perhaps an air leak somewhere in the carb area that alters air fuel mixture, or unsyched carbs. Have you syched them?
Another little test I did to see if all cyclinders were firing the same was to simply feel the exhaust with my hands about 1 or 2 inches from the back of the pipes. My 79 has the stock 4 into 2, so the exhaust should have the same temperature, force, and pulse rate. This technique seems to save myself from burning fingers.
Another little test I did to see if all cyclinders were firing the same was to simply feel the exhaust with my hands about 1 or 2 inches from the back of the pipes. My 79 has the stock 4 into 2, so the exhaust should have the same temperature, force, and pulse rate. This technique seems to save myself from burning fingers.
'99 1500 Drifter
Re: strange goings on with my #4
your brother in law is right with the ignition and strokes, 1+4 and 2+3 fire simultaneously. Moreover the plugs are connected in series which means if you completely disconnect #4 the circuit is open and #1 does not fire either any more. I guess this may explain your observation of hard starting. In case it should start on two anyway, the engine will not run smooth and have almost no power.
As the cylinder seems not to be completely dead and the carb of #4 is the one farest away from the carb fuel inlet, I would guess a fuel problem. Maybe the fuel cock or its filter screen inside the tank are blocked. You can use a hose and a glass to check how much comes out. Also check floater level of #4, or maybe the main jet is bloked or so.
A coarse compression check is possible by hand if you got some feeling in your wrist. Turn the engine two times to get all four compression strokes. They should feel identical. I remember my sensitivity to feel a difference was of about 1bar. To cause the cylinder run that badly due to lack of compression I would guess at least 3-4 bar must be missing. So I think in your case a "manual" compression check would be helpful to get at least already a hint.
As I already wrote in the "temp specs on exhaust manifold?" topic, I still believe it is a carb problem. They are hard to access, but did you check out anything for the carbs so far?
As the cylinder seems not to be completely dead and the carb of #4 is the one farest away from the carb fuel inlet, I would guess a fuel problem. Maybe the fuel cock or its filter screen inside the tank are blocked. You can use a hose and a glass to check how much comes out. Also check floater level of #4, or maybe the main jet is bloked or so.
A coarse compression check is possible by hand if you got some feeling in your wrist. Turn the engine two times to get all four compression strokes. They should feel identical. I remember my sensitivity to feel a difference was of about 1bar. To cause the cylinder run that badly due to lack of compression I would guess at least 3-4 bar must be missing. So I think in your case a "manual" compression check would be helpful to get at least already a hint.
As I already wrote in the "temp specs on exhaust manifold?" topic, I still believe it is a carb problem. They are hard to access, but did you check out anything for the carbs so far?
update on progress
well Tuesday I got the thread in ports for the carb synch. Today I synched my carbs which turned out to be VERY easy because I didn't have to adjust anything. They were all within a 10mmHg variance. I think that is somewhat impressive given its been about 6 years and 15k miles since done last. I do not have the fitting yet for the compression test but it is on the way. Volker, I don't see how I can do your manual test with my plugs as recessed as they are.
I have recieved from an auction I won on ebay a spare set of 4 carbs. I also purchased a set of 4 rebuild kits (they consist of nothing more than a bunch of o-rings and a new float needle). If the compression test comes out as normal I plan on rebuilding/thoroughly cleaning the spare carbs I purchased and swapping them out as a set. I see this as the least dangerous way to work on my carbs. I have heard too many horror stories about working on carbs and the last thing I want to do is put my bike totally out of commission.
the only new diagnostic info I gained was this: The fuel flow from the tank is GREAT. It practically shoots out of the petcock when I supply vacuum. There is fuel in the float bowl of carb #4. I noticed when hooking up the vacuum hoses that when I disconnected the vacuum hoses from cylinders 1, 2, or 3 there was a very noticable difference in idle. Clearly because it let the mixture on those cylinders lean out significanlty. It even died if I left it open for more than a few seconds. On #4 it made no difference. I take this to mean, contrary to my last post, (and thank you volker for pointing out that disconnecting plug wire #4 also kills #1) that at idle #4 is completely dead. This is confirmed by the fact that the exhaust manifold on #4 never gets above about 100F (38C).
I assume at this point that I will be rebuilding this set of carbs that I bought. If you have any hints, tips, or relevant links for a first time carb rebuilder I am all ears. I have done as much reading as I could find on the general concepts and terminology of variable venturi carburetors. I have not found good info about the specifics of what I will find on my bike. examples of questions I still have are: Are my carburetors equipped with an accelerator pump? do they have only two jets or three? etc.
Well as always thanks for your help and wish me good luck.
I have recieved from an auction I won on ebay a spare set of 4 carbs. I also purchased a set of 4 rebuild kits (they consist of nothing more than a bunch of o-rings and a new float needle). If the compression test comes out as normal I plan on rebuilding/thoroughly cleaning the spare carbs I purchased and swapping them out as a set. I see this as the least dangerous way to work on my carbs. I have heard too many horror stories about working on carbs and the last thing I want to do is put my bike totally out of commission.
the only new diagnostic info I gained was this: The fuel flow from the tank is GREAT. It practically shoots out of the petcock when I supply vacuum. There is fuel in the float bowl of carb #4. I noticed when hooking up the vacuum hoses that when I disconnected the vacuum hoses from cylinders 1, 2, or 3 there was a very noticable difference in idle. Clearly because it let the mixture on those cylinders lean out significanlty. It even died if I left it open for more than a few seconds. On #4 it made no difference. I take this to mean, contrary to my last post, (and thank you volker for pointing out that disconnecting plug wire #4 also kills #1) that at idle #4 is completely dead. This is confirmed by the fact that the exhaust manifold on #4 never gets above about 100F (38C).
I assume at this point that I will be rebuilding this set of carbs that I bought. If you have any hints, tips, or relevant links for a first time carb rebuilder I am all ears. I have done as much reading as I could find on the general concepts and terminology of variable venturi carburetors. I have not found good info about the specifics of what I will find on my bike. examples of questions I still have are: Are my carburetors equipped with an accelerator pump? do they have only two jets or three? etc.
Well as always thanks for your help and wish me good luck.
I don't know anything about the specifics of an '84 cb650, since I have an '82 and the SOHC and DOHC bikes are totally different. However, I can add some info about cleaning/rebuilding your carbs.
Step 1: Buy some yamaha carb cleaner. This stuff works wonders, eats everything except plastic and rubber. Here's an FAQ on how to use it during rebuilds (at the bottom of the page) http://www.sohc4.us/forums/index.php?topic=5410.0
Step 2: Obtain some used/new guitar strings (pref electric, but light acoustic strings are good too). The smaller the better. These are great for running through your emulsion tubes and getting any blockages out. Might have been something blocking your slow jet on #4 with the old carbs, since it seemed to be getting at least SOME amount of gas. Probably just running super super lean and therefore hardly ever igniting.
Step 3: Take a full day to work on them. Make sure to use tools that fit very well, because the jets and such are very easy to strip out.
I'm actually working on my carbs right now, and am getting ready to boil them in yammy cleaner. I'll let you know how it turns out.
Step 1: Buy some yamaha carb cleaner. This stuff works wonders, eats everything except plastic and rubber. Here's an FAQ on how to use it during rebuilds (at the bottom of the page) http://www.sohc4.us/forums/index.php?topic=5410.0
Step 2: Obtain some used/new guitar strings (pref electric, but light acoustic strings are good too). The smaller the better. These are great for running through your emulsion tubes and getting any blockages out. Might have been something blocking your slow jet on #4 with the old carbs, since it seemed to be getting at least SOME amount of gas. Probably just running super super lean and therefore hardly ever igniting.
Step 3: Take a full day to work on them. Make sure to use tools that fit very well, because the jets and such are very easy to strip out.
I'm actually working on my carbs right now, and am getting ready to boil them in yammy cleaner. I'll let you know how it turns out.
Does the boiling ready aid anything other than to speed up the process?
safety
I too would be concerned having a boiling pot of gasoline. sounds like something you would hear about on the news in a "this guy was so stupid" segment. 
make sure you have a fire extinguisher handy even if you don't use open flame to boil it.
thanks for the tip. the link you posted seems to be broken though. I read a few other reviews on the net. half of them say not to let it get on rubber or plastic parts, the other half say it is perfectly safe. and for anyone who thought boiling carbs sounded weird, there do seem to be alot of people who do it.
no other updates yet. I'm not sure when I will get time to get this all done.
thanks again for all hints and tips
make sure you have a fire extinguisher handy even if you don't use open flame to boil it.
thanks for the tip. the link you posted seems to be broken though. I read a few other reviews on the net. half of them say not to let it get on rubber or plastic parts, the other half say it is perfectly safe. and for anyone who thought boiling carbs sounded weird, there do seem to be alot of people who do it.
no other updates yet. I'm not sure when I will get time to get this all done.
thanks again for all hints and tips
I don't think I've ever heard of boiling carbs either. Sounds risky. I think having the lid handy for the pot would be safer than trying to use a fire extinguisher if things get out of hand. Smother the fire with the lid and remove the heat source 
Also, although I've never even heard of this process, I'd think an electrical heating element would be much safer than an open flame. I've used parts washers in the factory that are heated, but the detergent inside is non-flammable. Perhaps some sort of citrus cleaner would be safer and just as effective as carb cleaner? I'm really curious to hear how this whole process works out. Good luck.
Also, although I've never even heard of this process, I'd think an electrical heating element would be much safer than an open flame. I've used parts washers in the factory that are heated, but the detergent inside is non-flammable. Perhaps some sort of citrus cleaner would be safer and just as effective as carb cleaner? I'm really curious to hear how this whole process works out. Good luck.1980 CB650c
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DammitDan (as Guest)
Now that I reconsidered the situation, I realized that boiling the solution wouldn't have been smart. Toxic fumes and such... If you do it, only do it outside with lots of ventilation and a mask of some sorts. Course I live in an apartment complex, so I just put the stuff in a pot and let it sit/agitate it for several hours. So far, no leaky carbs after the rebuild. Guess it's OK on rubber gaskets after all cause the entire assembly sat in there for about 5 hours. Unfortunately the bike isn't running very healthy right now... Although I have yet to have adjusted the pilot jets. Hopefully that will help. Oh, and I found out why my bike was running so damn lean before I changed the carbs... Apparently the PO had put in 105 mains for some dumbass reason, and I just never noticed. Now it's running 118s and I think I'm still a bit rich with the new exhaust.
Of course you wouldn't boil it in gasoline either... it's a 50/50 water-solution mixture.
[Added Dan's username 28-6-2006. Volker_P]
Of course you wouldn't boil it in gasoline either... it's a 50/50 water-solution mixture.
[Added Dan's username 28-6-2006. Volker_P]
another small update.
Today I took another small step in confirming that it must be my carburetor that needs help. I did a compression test and found that no 2 cylinders vary by more than 10 psi. Thats good news, I don't need to have my valves and valve seats remachined.
I also took the opportunity and removed the boot connecting the airbox and the air intake of the #3 and #4 carburetors. I wanted to visualize the sliders in action to see if I could see any obvious differences or problems. two things seemed to suprise me. 1. with the right side air intake removed I could not get the engine to rev over 4k RPM. after 4k more throttle just bogged the engine down. 2. the #4 carburettor seemed to spit a small amount of gas back at me. I couldn't see it coming from #3 but of course the lighting for #3 is much worse than #4. neither of these really seems all that relevant or likely to be indicators of my problem. but for completeness I thought I would share them. Other than that the operation of both #3 and #4 appeared by gross visual observation to be identical. Also, supprisingly, when I removed the spark plugs (remember, these are only about 2 weeks old) they all looked identical. all 4 were beautifully grey-brown in color.
and yet another side question for consideration: Remember that I purchased a set of 4 carburetors on ebay to clean up and replace the ones currently on my bike. I have an '84 these were reportedly off of an '83. everything I have read indicates that the '83-'85 are mechanically identical. I think they were offered in a couple different paint colors but thats the only difference. Well the carbs I bought have an extra port on each carb that appears to be for connecting tubing. they are located directly above and behind the throttle plate. I don't know what they would be for. I think that I can just plug them and ignore the fact that they are there at all. I must admit that I am curious about their intended purpose though. also the #3 carb only has a small port on the bottom directly behind the throttle plate. this one is closer to the throttle plate than the ones on the top. it looks to be as close behind the throttle plate as the idle jet is in front of it, and thats very close. it is also made of brass unlike the rest of the carb body. I will try to borrow someone's digital camera and get some pictures to upload.
As much as I find out is NOT the problem I wonder what can cause this particular set of symptoms. what can make a spark plug look just like all the rest, cause the exhaust manifold to stay cool (not cold) at both idle and after a long ride, cause uneven power during acceleration especially at low RPM or when cold, greater than normal fuel consumption, and a lower than expected top speed? I suppose that its just all part of the process and the joy of working on your own bike.
thanks again guys for all input.
I also took the opportunity and removed the boot connecting the airbox and the air intake of the #3 and #4 carburetors. I wanted to visualize the sliders in action to see if I could see any obvious differences or problems. two things seemed to suprise me. 1. with the right side air intake removed I could not get the engine to rev over 4k RPM. after 4k more throttle just bogged the engine down. 2. the #4 carburettor seemed to spit a small amount of gas back at me. I couldn't see it coming from #3 but of course the lighting for #3 is much worse than #4. neither of these really seems all that relevant or likely to be indicators of my problem. but for completeness I thought I would share them. Other than that the operation of both #3 and #4 appeared by gross visual observation to be identical. Also, supprisingly, when I removed the spark plugs (remember, these are only about 2 weeks old) they all looked identical. all 4 were beautifully grey-brown in color.
and yet another side question for consideration: Remember that I purchased a set of 4 carburetors on ebay to clean up and replace the ones currently on my bike. I have an '84 these were reportedly off of an '83. everything I have read indicates that the '83-'85 are mechanically identical. I think they were offered in a couple different paint colors but thats the only difference. Well the carbs I bought have an extra port on each carb that appears to be for connecting tubing. they are located directly above and behind the throttle plate. I don't know what they would be for. I think that I can just plug them and ignore the fact that they are there at all. I must admit that I am curious about their intended purpose though. also the #3 carb only has a small port on the bottom directly behind the throttle plate. this one is closer to the throttle plate than the ones on the top. it looks to be as close behind the throttle plate as the idle jet is in front of it, and thats very close. it is also made of brass unlike the rest of the carb body. I will try to borrow someone's digital camera and get some pictures to upload.
As much as I find out is NOT the problem I wonder what can cause this particular set of symptoms. what can make a spark plug look just like all the rest, cause the exhaust manifold to stay cool (not cold) at both idle and after a long ride, cause uneven power during acceleration especially at low RPM or when cold, greater than normal fuel consumption, and a lower than expected top speed? I suppose that its just all part of the process and the joy of working on your own bike.
thanks again guys for all input.
Wow, I'm racking my brain on this one... 3 components of combustion are fuel, spark and air. You seem to have all 3. You're obviously not running on all four cylinders (else all 4 headers would be sizzling hot). The only thing I can think of is incorrect jetting on the acceleration/top speed problems. A bike that is running lean will start to act up at higher speeds.
What you're seeing on your plugs may just be the overall situation on the fuel/air mixture. It may turn out that you're actually running severely lean at 1/2 to wide open throttle (which limits top speed and acceleration) and rich at idle to 1/2 throttle, making the plugs "even out" when look at em. Did you do a plug chop at each individual throttle setting (with a fresh set of plugs each time?) Idle to 1/8 throttle is controlled by the pilot jet (adjustable), 1/8-1/3 throttle is slow jet, 1/3-2/3 is the main jet needle, and 2/3 to wide open is the main jet. Or something like that. You need to test at each of these to see what your jetting is really doing.
Now, as to why you're getting good readings on dead cylinders... I have no clue.
Might want to hit up the http://www.sohc4.us/forums/index.php forums. Even though you're a DOHC, I'm sure they'd still help you. A CB is a CB, after all!
What you're seeing on your plugs may just be the overall situation on the fuel/air mixture. It may turn out that you're actually running severely lean at 1/2 to wide open throttle (which limits top speed and acceleration) and rich at idle to 1/2 throttle, making the plugs "even out" when look at em. Did you do a plug chop at each individual throttle setting (with a fresh set of plugs each time?) Idle to 1/8 throttle is controlled by the pilot jet (adjustable), 1/8-1/3 throttle is slow jet, 1/3-2/3 is the main jet needle, and 2/3 to wide open is the main jet. Or something like that. You need to test at each of these to see what your jetting is really doing.
Now, as to why you're getting good readings on dead cylinders... I have no clue.
Might want to hit up the http://www.sohc4.us/forums/index.php forums. Even though you're a DOHC, I'm sure they'd still help you. A CB is a CB, after all!
next update
today I finished the task of cleaning and reassembling the carbs i bought. I have never seen of dirtier carbs than these. everything in the float bowls was coated in green sticky goo, I was picking out plant matter of some kind from the air passages, I found a bee in one of the float bowls, etc. etc.
I got some of the yamaha carb cleaner dammitdan recommended. It is (according to the bottle) to be diluted 3:1 gasoline to concentrate (not a water solution). I did not boil the carbs. I did however soak for a long time. I disassembled each individual carb and put all the small parts and float bowl into their own small container full of mixture. This probably soaked for 3-5 days, I don't remember exactly. I only had one container about the right size to soak the carb body, I gave each one of those 24 hours soak time before I took them out. Each part got a good wipe down. I don't have them installed yet but if appearances are an indication I don't see why these won't work perfectly. Those nasty gross parts came out of the soak looking new. The solution turned from colorless/slightly cloudy to a clear but very brown solution. The bottoms of each of my soak containers has a layer of sediment in it. I got a rebuild kit for the set of 4 so all the o-rings are new, the float needle and the float bowl gasket are all new.
I am excited to get these installed and try to get them properly adjusted. I did remove the pilot screws on each so I will have to adjust the mixture on each one. This is what I need the precision tachometer for, the procedure refers to adjusting the mixture until an rpm change of > 50 is shown. I don't think the stock tach is precise enough.
I did get to confirm that these carbs have stock 115 mains. I couldn't find where they were stamped before the soak, the numbers were full of goo.
I'm going on a bit of vacation this coming weekend so I won't have a day off where I can try and get these swapped and adjusted for a couple weeks.
I do have other good news though. I bought another bike. I got an '04 Honda 750 Shadow Aero. A sweet ride if I do say so myself. My Nighthawk will be on the market soon. Either whole (if this carbs thing works out well) or as parts (if it doesn't). With the new bike payments I can't afford to put anymore money into the Nighthawk.
wish me luck.
I got some of the yamaha carb cleaner dammitdan recommended. It is (according to the bottle) to be diluted 3:1 gasoline to concentrate (not a water solution). I did not boil the carbs. I did however soak for a long time. I disassembled each individual carb and put all the small parts and float bowl into their own small container full of mixture. This probably soaked for 3-5 days, I don't remember exactly. I only had one container about the right size to soak the carb body, I gave each one of those 24 hours soak time before I took them out. Each part got a good wipe down. I don't have them installed yet but if appearances are an indication I don't see why these won't work perfectly. Those nasty gross parts came out of the soak looking new. The solution turned from colorless/slightly cloudy to a clear but very brown solution. The bottoms of each of my soak containers has a layer of sediment in it. I got a rebuild kit for the set of 4 so all the o-rings are new, the float needle and the float bowl gasket are all new.
I am excited to get these installed and try to get them properly adjusted. I did remove the pilot screws on each so I will have to adjust the mixture on each one. This is what I need the precision tachometer for, the procedure refers to adjusting the mixture until an rpm change of > 50 is shown. I don't think the stock tach is precise enough.
I did get to confirm that these carbs have stock 115 mains. I couldn't find where they were stamped before the soak, the numbers were full of goo.
I'm going on a bit of vacation this coming weekend so I won't have a day off where I can try and get these swapped and adjusted for a couple weeks.
I do have other good news though. I bought another bike. I got an '04 Honda 750 Shadow Aero. A sweet ride if I do say so myself. My Nighthawk will be on the market soon. Either whole (if this carbs thing works out well) or as parts (if it doesn't). With the new bike payments I can't afford to put anymore money into the Nighthawk.
wish me luck.
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