Firing problem?...Fuel problem?...??

[ole Ed]

OK... I am working on a 250 Nighthawk with what SEEMS to be a firing problem. Doesnt idle, Has SOME midrange, WONT run on topend very well. Cleaned the petcock, floatbowl and the little thingy under the engine... the one with the plug in it. It was FULL. Others were somewhat clean.
Symptoms: While starting you must give it quite a bit of fuel. After starting you must keep working the throttle to keep it running. While riding you must keep it pumped up to keep it running and if you let outa the fuel it will pop beck through the pipes and tries to die. If it does die though, it will start right back up, but once again, only if you give it gas and keep it going.
NOW for the kicker: While running tonight I happened to notice the headlight doing some strange things. It was dimming as I gave it gas and when the engine was winding down it would get bright again but if you gassed on it again it would get dim again and sometimes act as if you were riding down a rough road- it looked to be vibrating even though the bike itself wasnt.
The getting bright and then dim is like its charging system is operating in reverse. The more fuel you put to it the dimmer it gets but returns to normal when it comes back down. Remember now it wont idle so this is at near idle but just a little above. Has anyone seen this before and if so whats doing it?
The owner of the bike bought it this way and has been riding it for some time this way. He rode it with my regular group on a ride Sat. and kept up somewhat. I was asked to see what I could do as I am somewhat of the group bike doc.
I know this is a Rebel group here but the engine is a 250 and appears to be just like my Rebs engine. Thinkin the firing system should be the same also.
Any help would be greatly appreciated.

Thanx guys,
Ole Ed

P.S. The right side exhaust-as you sit on it-pipe is still chrome but the left side-once again, as you sit on it-is very blued which seems to indicate? a rich burn? on that side, CORRECT??

[GearJammer]

Sounds like you've got your hands full there, ole Ed.....

Fuel & electrical problems oftentimes mask themselves one for the other. The blued pipe would indicate a too lean condition. Please check the spark plugs & compare the two different plug reads & let us know how each of those look.

What is the battery voltage reading with the bike off ? Battery voltage with bike running ? Does the battery voltage when running stay constant regardless of different rpm levels ?

The dimming headlight could very well be a regulator/rectifier problem, which could also be sending improper voltage levels to the coils....similar to a funky voltage regulator on a car which can send REALLY erratic voltages to various components.

I'd also check all ground wires you can find to make sure that those are tight & secure.......

The alternator may or may not be compromised and starting to fail, but I'd check out the reg/rect first......

[Duke Bushido]

It's not working in reverse; there _is_ a charging problem. What's going on is that when you make a greater demand for ignition (rolling on the throttle), the headlight is starving for juice.

However, I suspect you may have _two_ problems. It does sound like you _also_ have a fuel problem, but as GJ noted; commonality of symptoms does make it difficult to diagnose them 100 percent of the time.

In this case however, you _know_ you have at least one electrical problem, because no fuel problem on earth will dim your headlight under an electrical load.

[ole Ed]

Thanx guys, I knew there was something in the fire/electrical causing this problem. Now the challenge is to figure out what. I love a good challenge!
Now to the lean condition: Single carb, left side lean... Valve problem?
Intake sticking on the closed side or the exhaust sticking to the open side causing over scavenging of the cylinder? Worn camshaft even? If there was a problem in the valvetrain wouldnt this engine miss considerably?
Its like you said, no fuel problem is ever going to cause the headlight to go dim and so wouldnt that also mean that no electrical problem would make the left cylinder run LEAN? So something is amiss there but what.?
I havent even began to get into this bike yet for lack of time but I want a game plan for when I do and thats why I am askin you guys for input on this. Your thoughts and suggestions are welcomed and added to my thoughts.

Thanx guys
Ole Ed

[GearJammer]

I also agree that you might be dealing with both electrical & possibly fuel problems. Just as a lean condition can cause blueing of the pipes, an OVERLY rich condition can also cause blueing if the "burn" is happening inside of the exhaust pipe rather than fully inside the combustion chamber......possible causes of this could be a malfunctioning coil, burnt valve, exhaust valve staying open longer than it should, improper timing, etc. In these cases, it's also not unusual for the pipe to actually glow red while the bike is running. Depending on the severity of the problem in the valvetrain, the engine may or may not miss noticeably as it might be a subtle valve adjustment that's required (along with the rest of the chasing down of whatever's causing the overall problem(s))

Edit: Please pull the spark plugs to give 'em a look, as that might help with the diagnosis....

[ole Ed]

Update: I pulled the left side plug-out of curiosity-and found it to be slightly reddish with a touch of blackening to it also. Which says its ok. Didnt pull the right side plug yet-the phone rang and of course it was for me-but I suspect it will look the same.
The bike is showing 12,500 miles and probably never had new plugs in it, so thats my next move. Then pull the carb and do a complete go-through on it. As for the charging problem I am leaning towards a ground fault somewhere as the battery seems to keep a good charge. Then pull the valve cover and look in there. All this will have to wait til tomorrow though.

Good Night

[GearJammer]

Sounds good ole Ed........new plugs, a good carb cleaning & valve adjustments are good places to start.

If the battery is holding good charge before, during & after running, then your alternator & reg/rect are probably good. It may be as you're thinking....a ground fault....or possbily a questionable coil. Is the timing a factory pre-set the same as the Rebs ?

[ole Ed]

Got the carb. apart and soaking. As suspected, its got some trash and dried fuel additives..?-all the red stuff- but the diaphram and squirter look almost new. There is some wear on the throttle piston itself but I dont think its enough to cause problems. The needle on the bottom looks very clean and shows no wear or scuffing.
After taking the valve cover off this morning I now know there are no rocker-arm or cam problems but there may still be some valve issues. Thought I'd get the carb right first and go from there.
Now to the charging system: OK, there is a problem here. I have a digital Greenlee meter and not an analog so its shows all fluctuations-and there were fluctuations. Shows a good 12.47 with the key on and headlight burning. Drops to 9.6 when starting the engine. Down to 12.01 at somewhere near half throttle-thats as low as it will idle- and as you rev it, it will drop even further-down to less than 11.83. Let it return to idle and the voltage returns to normal all the way til it dies completely-remember it doesnt idle.
Any suggestions? Dont hold back, let me hear 'em. I can really use the input on the voltage problems.

Thanx guys,
Ole Ed

[ole Ed]

Oh, sorry. YES the engine is exactly the same as the 250 Rebs. I can see no difference. They even mount to the frame the same way.

[GearJammer]

You're goin' for it, which is cool, ole Ed..........real quick as I've got to get in motion & will check back later........the carb cleaning may solve the idle problem........On the battery, you might wanna pull the battery & put it on a trickle charger after topping off the cells with distilled water. A fully charged battery should actually read closer to 13.5V......the battery might be weak/old......if the battery is able to take & HOLD it's desired charge, then I'd be suspecting a funky reg/rect..........or as previously agreed upon, checking for a ground fault somewhere's in the charging system.

[ole Ed]

IT LIVES!!!
Got it back together and running today. Runs fair but still has issues.
Starts right up and after oiling the choke cable-it was sticking-it idles ok.
Pulls good through midrange and right up to topend but just before it gets to w.o.t. it does something strange. It acts like it has a rev-limiter and actually does the rrr-rrr-rrr til you let off the throttle a bit then picks back up and goes on. HMM.
The charging systems fine now-loose ground strap and several other loose wires. All tightened and now the headlight is actually brightening up when I open the throttle. Didnt pull the voltages again as it seems fine.
Now back to the firing. Instead of a rev-limiter, could this be the ignition breaking down or something else? Is there a way to test the ignition-other than pulling it and putting it on my Reb-to see if and/or which?


Once again, thanx
Ole Ed

[Duke Bushido]

Ignition breakdown is my thought, yes.

I don't know any back-yard type tests, however.

[GearJammer]

Other than just before WOT, is the power band smooth & strong (normal) ?

I'm wondering if the linkage for the throttle cable is binding at the carb end.....

You're getting into areas where I have to stretch now, LOL! Should the headlight brighten with added throttle or should it stay constant ? What I'm wondering is......could it still be a bad reg/rect ?

As regards ignition breakdown......could this be a coil getting ready to bite the dust or would a bad reg/rect be having an adverse effect on the coil ? The juice in the primary coil windings build, then the field collapses which pushes the voltage into the ignition system with a rush of high voltage, each build/field collapse being accelerated or decelerated in relation to the rpms......

What year is this Nighthawk ?

[GearJammer]

Thought of this after posting last time.......Depending on the age of the bike, am wondering if a new CDI is a possble.......After the experience of the 450 Reb CDI scare, it seemed like 20 yrs. give or take was the magic number for replacement........

[ole Ed]

Thought of the cdi also, but it hasnt stopped running, not even when hot, so I kinda put that on the bottom of the list-for now-anyway. But after reading a little more about cdi troubleshooting and symptoms, I may have to place it further up the list again. It is very possible the cdi is working fine at lower to near full throttle and then breaking down. Guess I will have to replace it and see-if it doesnt fix it then I will have a spare for my Reb-what happens. The bikes a 95 model which does put it over that 20 yr mark---so.
Now back to the headlight again. It has reverted to its old ways. When you let it idle, the lights kinda dim-as it should be-but when you give it a little fuel it brightens up. BUT only to a certain point and then it starts to dim, even as you give it more gas. But as you slowly let outa the gas and bring it back to almost idle, it brightens up again but only for a split second then as you get to idle it goes dim again. In other words, it seems to have only a small span there where it is charging. Has me stumped.
Oh and yes the power is smooth and what I would call normal until just before w.o.t. and then when it hits w.o.t. it seems like it has a rev-limiter in it. It doesnt have the power my 05 Reb has but it seems close. My Reb will clock in at 85 but this bike wont reach 75 unless your going downhill so the speeds definitly not there.
Thanx for all you have done guys. Keep the suggestions coming. They are helping.

Ole Ed

[GearJammer]

When at near full throttle & you say "starts breaking down", do you mean that it starts to cut out & then catch again ? If so, that could be symptomatic of a CDI problem. Mine did that as well as a variety of other interesting, frustrating things, LMAO!

Thought of another thing you can try in regards to the lighting prob. Both of the control switch housings on each handlebar end might need to be opened up & given a good cleaning. Cans of spray electrical contact cleaner can be scored at places like Radio Shack for around $10 per can. Just please be careful to not get any on any paint surfaces.

Both of those switches have contacts that definitely are in the continuity line for the lighting system. There might be dust particles interfering with the continuity of the electrical flow. It may or may not solve the problem, but it's something that should be done periodically as a part of routine maintainence anyways & there's always a chance that it may yield positive results. If not, at least you'll have eliminated that as one of the potential sources of the prob.....

[Duke Bushido]

So far, I'm leaning toward the CDI box. As it breaks down, it will draw more and more and more current, much like a short. That can account for your 'narrow charging span.'

[GearJammer]

At this point, I'd be leaning towards CDI as well.......the CDI probs on mine ran me ragged trying to chase it down and things only got progressively worse....

Bike would cut out & then catch again
Bike would shut down completely for no apparent reason
Bike wouldn't fire until it was good 'n ready to, which always made me wonder if the battery was gonna give it up before I got it started again
The CDI finally gave it up to where it would fire, idle for about 6 seconds & then quit. That was the end of the show for mine until getting the replacement from Jack.

It's very possible that a bad CDI is messing with the lighting system as it seems like all of the electricals are run thru that "CDI central"......hehehe.....BUT....IF the lighting problem can be chased down to some other cause & remedied, it also sounds like the CDI has enough life to keep running as is for however long it will. Other than the "possible" CDI-related lighting problem, it sounds like it's in better shape than mine was.

[Duke Bushido]

The bikes a 95 model which does put it over that 20 yr mark---



My _goodness_ how time has flown! :shock:

[ole Ed]

LOL.........I didnt even notice that. Very observant of you.
At least Duke was nice about it and didnt say something like,"Hey stupid old man, its only 12 yrs old" and make me feel really dumb. LOL. Like I need help for that....
OK. I did the voltage check and it went as follows- At idle it reads only 11.93 volts and as I gently give it more fuel it does climb to 14.12 just before reaching half throttle. As I open her up a little more it drops back to 12.25. Runs fine now. No spittin or sputterin. And no more sluggishness, but still has the splatter just at w.o.t.. Still has me wondering about the rev-limiter thing because thats exactly what it sounds like, A splatter-box.

[GearJammer]

No worries, ole Ed......I noticed it when you originally posted, but thought that you either meant to type an 8 for 85 or hadn't typed the n't for "doesn't".....no matter at all, we don't have spellchek police on this board..........

Have you tried re-charging the battery yet to see if it'll take 'n hold a charge of 12.5V-13.5V on the bench ? At idle, it should read better than 12V & the erratic voltage ratings make the battery, reg/rect or CDI suspect.....Do you know how old the battery is ? One thing these Rebs seem to require is a good, strong battery at all times.....

Edit: In this case the Nighthawk, not the Reb......same/same.....

[Duke Bushido]

Everything sounds great till you get to that voltage drop. A charging system in good condition should never, ever-- with only factory draws (no electrical add-ons) drop below 13v once the idle revs up.

_could_ be CDI-- breaking down under a load and drawing excess amps.
_could_ be a regulator/rectifier. A bad diode in the rectifier can cause similar issues. So can a single burnt winding in the stator.

At this point, it's process of elimination, I think.
I believe the Clymers has the listed readings for testing the stator and the rectifier with a meter.