Yayyyy its alive!....and now its dead....AGAIN!!?

[slownugly007]

Well I got my bike back on the road yesterday. This was the first time Ive had it out since I put my new battery, iridium plugs and K&N in it so I was curious if these fixed my problem of my bike dying when I got up to speed. The bike starts right up, you can rev it fast and it stays running. If I hold the throttle open a little, you can hear it sputtering a little in he exhaust and not having a smooth steady tone.

I took it out just to see how it did and the power loos was fairly evident, my thought was my junkyard exhaust that I just threw on it, so I kept going and downshifted into 4th. It sputtered and would not get up to speed like it used to. After a few seconds of stuttering it finally leveled out so I switched into 5th and it wouldnt top out like usual and eventually died. I kept trying to pop the clutch as I was rolling to a stop, it was run for a second then die again.

I finally came to a stop and couldn't get it to fire up. So while I had a nice moment to enjoy the scenery I pondered on what was wrong with it!? Carbs, coils, plugs were brand new so it couldnt be them??, plug wires, my make-shift exhaust..(but it did this same thing pre-exhaust).....Im at a loss. I finally got it started back up and limped it back to the house. Power was terrible and it just didnt sound right.

I get it back home, all header tubes are hot. So all four cylinder are at least firing. I pulled the plug wire off of #4 and it dies?? It should run, not well, but should stay running with a plug wire removed....right? I know cars will but Im still learning about bikes. Could this be an indicator that the coils bad?

On a side note, I find it weird that it ran great 2 days before I moved from florida to tennessee. I took it on an all day sunday cruise and had no problems, 2 days later I move to tennessee and take it out and it dies on me...weird coincidence??

Granted the battery was completely empty when I checked it, so thats why I installed a new one and I thought that was my problem. Apparently I was wrong?  Could a bad battery ruin the coils? Thanks guys for everything! This place is my go to for advice and its helped me tons of times! Thanks!

[LukeM]

If your engine was running well with a fully charged battery, then gradually stumbled, lost RPMs, and then died, those are symptoms of a charging system problem.  Running on battery alone with a headlight, you might get about 10-20 minutes of run time at street speeds.  The more RPMs you have, the quicker the engine will die.

Find the section on Charging System in the FSM, get yourself a good multimeter, and start checking stuff.  In particular, look at the connection for the 3 yellow wires: make sure there's no corrosion or burnt connectors. You can clean them, replace them, or just solder them together (if you don't plan on replacing the reg/rec anytime soon).  At idle, you should have 12-12.5V, at 3000 rpm, it should be between 13-14.5V.

Good luck, and keep us in the loop.
Luke M

[Lucky 1]

IS it a CB750?

What year?

Exhaust type?
Intake type?

You moved from sea level (Florida), to a higher elevation.
Did you take the bike on a trailer?

[slownugly007]

Yep, its an 81 CB750F SS

Exhaust: Mac 4-1 Header w/ a can style muffler
Intake: Stock airbox w/ K&N filter

Brought the bike up in the back of a uhaul

[slownugly007]

Thanks Luke! When I get home Ill check it out and see what I come up with. Would the bad battery screw up the charging system? Like i said the old battery was dry and when hooked to a charger for 3 days straight it never registered fully charged, even after I filled it.

[shinyribs]

The way these charging systems work is the voltage regulator switches on and off. When the battery discharges during normal riding the regulator allows the battery to start charging again. As soon as it reaches max charge it switches off and  waits until it discharges again. Running on a dry battery that will not hold a charge ( or any other battery that will not hold a charge) or even running one of those tiny,little low amp hour batteries is hard on your charging system. It cant hold a charge long enough to provide any real run time, so it leaves your stator running its butt off on max effort to do it best to supply your bike with the juice it needs.

 You need to check your charging system. If it is good,then it sounds like your battery just wont hold a charge and you need to get a good battery in there before your charging system cooks itself. If its bad,well    I dont even wanna say it

[slownugly007]

Thanks shiny! The battery on it now is a brand new Yuasa and I was hoping that my old cheap, dry walmart battery was the culprit in it dying before. But even wit hthe new battery and iridium plugs it still dies once I try to get on it and up to speed. It starts wayyyyyyy better than it did before so Im assuming the battery and plugs have at least helped it in that sense but now Im wondering if the coils gone bad or its not charging??

Anybody ever heard of burning up a coil if you start the bike without a spark plug connected? Also, does anybody know how to check if a coils bad? I have a voltmeter and have checked volts numerous times but never ohms. What ends do I connect to the voltmeter? Thanks guys

[sgtslag]

The coils transform low voltage/high current, to high voltage/low current, which jumps across the spark plug gap, firing the fuel-air mixture.  If you disconnect the spark plug wire, you open the high voltage side of the coil (transformer) -- and, yes, this has the potential to burn through the insulation on the output (spark plug) side.

The OEM Service Manual should give you the resistance reading on a good coil, for both the primary (12 Volt) side, as well as the resistance reading/value expected on the secondary (high voltage/spark plug wire) side.  As to how to connect the leads on your meter, that would depend on the meter you have -- check the user's manual (may be available online, if you no longer have it).  Multi-meters vary by manufacturer.  Cheers!

[shinyribs]

Some coils will burn out if not grounded like you say (connected to the plug) . Would have to find about your specific ones. Also the irridium plugs are resistor type plugs. Not sure if they jive with your coils.  Seems like it ran OK before, so I guess so. Have you checked charging output yet? That's square one really

[Hellbilly429]

It is the same problem I am having, it is most likely a charging system problem. These bikes do not like to run with one spark plug wire off for some reason, mine will die if I do the same thing, am not sure if it is a safety thing or if it is because these bikes are so dependent on the timing of all 4 cylinders to keep the motor turning. Sorry man, that really sucks! Also if you need a cheap rotor (if your charging rotor is bad) Billman (I think it was him) has bought this one and is working for him perfectly so far http://www.ricksmotorsportelectrics.com/proddetail.php?prod=41-101&pmc=ODFIb25DQjc1MEs=
And for $180 you aren't gonna find another rotor unless it's on Ebay.

Good Luck!

[slownugly007]

I checked my charging system, and it got up to 14.90v in neutral. So it seems like thats normal, right? I also checked the continuity of the coils and checked the spark units according to the FSM I downloaded. Everything checked out good. Tested the spark with a gap tool and all wires fired accross the 1/4" gap...Checked my plugs and they were black, these are brand ne! I installed them a couple weeks ago when I got my new battery but yesterday was the first time Ive ridden with these plugs. I was curious so I swapped back to the stock D8EA plugs that were a little discolored but still good. I took it out again and it was running smoother, then suddenly started spitting and sputtering again? I pulled over and it idled very low and almost died, so I pulled the choke out and limped back home....is this an indication of the fuel ratio being too rich?

[Hellbilly429]

Yes, where are the screws set now? If the plugs are coming back black with carbon build up it's running rich, if they are covered in oil you have a whole different problem

[shinyribs]

Good point HB. I thought about Slow's oil in the pipe issue when I saw that,too. But oil in just one pipe shouldn't be that big of a deal.Def shouldn't affect all 4 cyl's. Slow,any chance your crank breather is hooked up funky and sucking excess oil vapor into the engine? Just pulling at straws really. I guess the next thing to do is find out where your jetting is and see what you're working with. Might just be a case of fouling plugs.

[slownugly007]

They were a flat black. As for my screws....well I have no idea? Ive always been told I have a screw loose, so maybe thats my problem??  Im curious, how to you adjust fuel richness? Also, does the octane of gas matter? Im running 93 no ethanol in it and to be honest I cant remember what I ran in florida? All I know is that it was ethanol gas.

Another thing I noticed last night was there was a clear oil like substance in my fuel filter? It was heavier than the gas and you could see the seperation. Could this be the old sea foam still in my tank? I wonder if this could be messing with my gas? Thanks guys!

[shinyribs]

Aaaaah,water in the fuel. Put some gas out of your tank in a bottle and shake it up. If it is water in your fuel it will look mirky/cloudy after you shake it up.If you watch it for a little while the cloudiness will settle into bubbles,then eventually into one big bubble in the bottom.

[slownugly007]

OH NOOOO!!!! What does this mean if it is? How will I remove it?

Im gonna try some 87 octane no ethanol in it later just to see if I can keep from fouling out the plugs? The brand new iridium are completely black! I ran th ehotter D7EAs last night and it fouled out again and sounded like it was only running on 2 cylinders after about 10 minutes.

[shinyribs]

Not a big deal. Just drain it. If your real worried you cam swab some tampons around I.side the tank. Also, I hate to be the bearer of bad new, but it may make life easy on you : just buy whatever gas is close and cheap. I was talking to some guys at the local truck stop that just pulled out of the oil terminal next door. We were discussing ethanol. I told them that Id never seen a difference in it. They how long I've been driving and I told them 16 years. They I.formed me that we have had ethanol gas in my draw longer than that. Its all ethanol bro. They just ain't telling us. Imagine that,  Government keeping secrets????

[Piute]

  Thought I'd add this while talking gas :
High octane gasoline does not outperform regular octane gasoline in preventing engine deposits from forming, in removing them, or in cleaning the engine. Consumers should select the lowest octane grade at which the car's engine runs without knocking. Occasional light knocking or pinging won't harm the engine, and doesn't indicate a need for higher octane. On the other hand, a heavy or persistent knock may result in engine damage.

   I believe there are 3 ways to make octain , so your boost would need to be made the same,

[Hellbilly429]

Lol, think we all got a screw loose bud, otherwise we would blend in with the "hip" crowd and all ride crotch rockets and HD's. Here is a link that will tell you pretty much everything you need to know about these carbs.
http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revD.pdf

There is a small brass screw on the bottom of each carb, turning them in will reduce the fuel/air ratio (leaning it out) and turning the screws out will increase the fuel/air ratio (richening it up). Not sure where your screws should be set since you are running aftermarket exhaust now, but sounds like you need to turn the screws in. Probably the best idea would be to turn all the screws all the way in, then back them out a 1/4 turn only each time until the bike idles and runs right. The FSM also describes what to do in better detail with pics.

Could be anything that caused the problem really, you moved, so the air pressure might be different, you put a 4-1 exhaust on the bike (had 4-2 exhaust before right?) and that water in your gas can definately make the bike run like shit. I would drain all the fuel out of the tank and turn the drain screws on each of the carbs and get out as much of that old fuel as possible, then refill the bike with fresh fuel.

[slownugly007]

Cool! thanks guys, Im gonna drain the tank and dry to dry it out as best I can then fill it up with new gas and see if that will fix the problem. I drained the carbs and there was quite a bit of water in the bowls, the picture below shows just how much. That white bubble to the right is all water!? Im hoping just a quick drain and refill will fix my problems? Ill repost tonight when I find out. Thanks again guys!