Topic: defeated, depressed, and confused --- UPDATED!

[xfactor]

So as it was a nice day yesterday I decided that I would take a journey on the highway. My 76 cb750f performed beautifully on the way there. However after arriving I started having trouble. Anytime I would go past half throttle she would just bog down and die, while ideling high. I would have to rev it to about 5k rpms even to try and take off in first and still then she would die. I know she has been running rich but I didnt really have any idea where to start.

So after this problem started I decided that i was going to clean the carbs, change out the spark plugs and hope that would work. after pulling the spark plugs and seeing that they were all black I figured hey maybe this could actually be the problem. I spent all of today running around getting everything i need and I finally finshed. So I started her and she fired right up, was ideling a bit high, 2k rpms, but I just let her run and then took her for a spin. Same problem, nothing had changed. so I pushed her back, and tried starting her, she turned over and reved to 5k rpms for a few seconds stayed there then just died. This happend maybe 2 more times, then nothing. She can crank all day but wont start.

I really dont know what to do and I am at my wits end. I really dont want to bring her to a shop because I am very broke, but I honestly dont know what to do from here. I welcome any suggestions comments anything I  just need some guidance about what to do.

Croix

[bistromath]

Well, it's very likely to be either your carbs, a clogged air filter, or an air leak in your carb boots. Probably the carbs. Did you check to see the float heights were set properly? Did you check that you could see light through each of the pinholes in the emulsion jets? Have you checked to make sure gas is getting to the float bowls?

Also, just for grins, check your battery voltage and make sure you have good spark on all four plugs. Bad condensers could also cause that sort of thing.

[sangyo soichiro]

See if it'll run with the gas cap open....

[xfactor]

There is no leak in the boots, and those suckers are on really well. I cleanded the pin holes, pulled them out used an air compressor to blow them out then sprayed them with carb cleaner. The air filter is pretty new and shouldnt be clogged. Fuel is getting to the floats, at least they were before I cleaned them.

What sort of carb problem could it be?


I will have to check the condensors and the sparks maybe this weekend, I had to take  a train back home and cant get out there till then.

How would I go about checking the spark, and condensors?

Thank,
Croix

[mlinder]

Sounds lean to me, not rich

[TwoTired]

How did you clean the soot off the plugs?

[xfactor]

Oh i also forgot that its been back firing and idleing very oddly, it would start and idle correctly at like 1k-1500 then after riding it it would jump to 3k rpms. That is before this happened of course.

[xfactor]

How did you clean the soot off the plugs?

I just bought brand new plugs, they are NGK D8EA, same as was in there.

[Ernie]

I'm thinking more of an electrical problem,try checking plug wires coils points condensors backing plate.sudden rpm increases wouldn't be caused by valve timing, I don't think.oh were all 4 plugs the same color?

[Steve F]

Just remember not to try to fix everything at once.  Do it methodically, one thing at a time until you start to see improvement.  It's easier to keep track of your progress with the certain repairs you have to try.  Everyting works in harmony on these things, and one singer off key ruins the whole effort.  Work on the ONE THING, then move on to the next.

[Spanner 1]

Slow fuel delivery ( rust in petcock) and one or more carb slides too high ( badly need a carb sync. ).... my 2c.

[Ayrity]

I had the same problem the other day, turned out to be a kink in my gas line. Check and make sure fuel is flowing quickly through the petcock and fuel lines. And did you try the tip for running the bike with the gas cap cracked open? could be youre creating a vacuum in the tank

[xfactor]

I'm thinking more of an electrical problem,try checking plug wires coils points condensors backing plate.sudden rpm increases wouldn't be caused by valve timing, I don't think.oh were all 4 plugs the same color?

No all 4 plugs were not the same color. The number 4 plug was definitely blacker then the rest. The other 3 where pretty close to the same color.  Whats the best way to go about checking all the electrical stuff you mentioned?

Just remember not to try to fix everything at once.  Do it methodically, one thing at a time until you start to see improvement.  It's easier to keep track of your progress with the certain repairs you have to try.  Everyting works in harmony on these things, and one singer off key ruins the whole effort.  Work on the ONE THING, then move on to the next.

This is  very good advice, I was just feeling pretty overwhelmed today.

Slow fuel delivery ( rust in petcock) and one or more carb slides too high ( badly need a carb sync. ).... my 2c.

I know I need a sync and this is going to be number 1 on my list, I just want to get it running before I bring it in.

I had the same problem the other day, turned out to be a kink in my gas line. Check and make sure fuel is flowing quickly through the petcock and fuel lines. And did you try the tip for running the bike with the gas cap cracked open? could be youre creating a vacuum in the tank

I will try that trick this weekend, since she didn't run no way I could get home so for now she is living in my friends garage, need to move her this weekend though.



Thanks everyone for giving me suggestions its been a hell of a 2 days and I have been feeling overwhelmed by not being able to figure out this problem.

Croix

[campbmic]

If the plugs are new and black it sounds rich to me. I just rebuilt my bike and carbs with pods and am doing some jetting tweeks at the moment. When I run my bike with the choke closed to 1/2 open it sounds the exact same as what your describing. Are you sure your opening the choke all the way up? Pushing down on the choke lever completely?

[xfactor]

If the plugs are new and black it sounds rich to me. I just rebuilt my bike and carbs with pods and am doing some jetting tweeks at the moment. When I run my bike with the choke closed to 1/2 open it sounds the exact same as what your describing. Are you sure your opening the choke all the way up? Pushing down on the choke lever completely?

Yeah its completely open I make sure of it every time

[camelman]

How's the intake?  I've seen filters get clogged up bad enough to cause a rich condition.

Camelman

[MickeyX]

Look at your fuel line and make sure it never has a spot that goes up. It should flow downward every bit of the way. The in-tank/in-line filter could be clogged. These two things gave us the same issues you are seeing. We were starving for fuel when revving high. When we shut it off, the bowls had time to fill and we were okay for restart. No sustainable high revs though.

The other things to check closely is the carb boots and the exhaust for leaks. They can make your idle go all over the place. Also, minimum, bench sync your carbs after a cleaning. A good sync tool, like the Morgan, would be a wise investment. It's easy to do and costs about what it does to have someone else do it once for you and it runs so smooth compared to just bench syncing.

(Edit: So, it could be a combination of a few things giving you symptoms in multiple directions.)

Good luck. Lots of good ideas here from everyone. You'll get it eventually. Just do 1 thing at a time, like Steve F said. The you'll know what the culprit was and when you can stop testing and start enjoying again.  

[Old75_ratafe]

Just something I didn't happen to notice anyone mention does your model have the filter in the petcock? If so check it, although I think it was just the earlier models that had that.

[xfactor]

Ive decided what I need to do.

First I of course am going to start with the easy stuff, air filter replacement and checking the fuel lines.

Carb resync, which I am going to do no matter if its running or not ive put it off for too long so I am finally going to do it.

Assuming that isnt going to work, becuase ive come to terms I am not a lucky person, I am going to check the fuel filter, only problem is my clymer guide isnt showing me where it is located.

Does anyone have any ideas about a fuel filter on a 76 cb750f, and where its located?


I am hoping thats it, but assuming it wont be, the electrical system is next, checking points and making sure the plugs are getting spark.

If after all of that nothing has worked, I am going to blow her up with some dynamite!

Croix

[bistromath]

Ive decided what I need to do.

First I of course am going to start with the easy stuff, air filter replacement and checking the fuel lines.

Carb resync, which I am going to do no matter if its running or not ive put it off for too long so I am finally going to do it.

Assuming that isnt going to work, becuase ive come to terms I am not a lucky person, I am going to check the fuel filter, only problem is my clymer guide isnt showing me where it is located.

Does anyone have any ideas about a fuel filter on a 76 cb750f, and where its located?


I am hoping thats it, but assuming it wont be, the electrical system is next, checking points and making sure the plugs are getting spark.

If after all of that nothing has worked, I am going to blow her up with some dynamite!

Croix

Great. The carb resync can only be done by taking the carbs off the bike, unless it's running. I'd wait until it runs. The sync shouldn't keep it from starting and running, just from idling well. Put that off until it runs.

Your comment about #4 being blacker than the rest points to a carb issue. Electrical issues will "follow the coils": 1&4 or 2&3 would show the same symptoms (except in the case of a bad plug wire or cap). But do check the spark, it's easy to do. And check the points gap and static timing. If that doesn't do it, then unfortunately it looks like time to go through those carbs again. Pay particular attention to the float heights (lots of threads here on checking that) and the pilot jet emulsion holes. Also make sure the idle air/fuel screws are set to the proper position -- you can do this with the carbs still on the bike. Check the Clymer for the specifics on your bike, it changed around a lot.

The fuel filter in your bike is a crummy screen located inside the fuel tank. Best way to check it is probably to just let gas drain out the petcock and verify that it flows well.

[xfactor]

Any idea what sort or carb issue it could be? I didnt adjust the float levels nor check them so that is priority number one if i have to pull them. Im thinking I might just rebuild them. but I am gonna wait until I try everything else.

Also I am looking at my clymer but im having trouble finding anything about the timing, as well as the points gap, any ideas where I can look to find something like that?


Croix

[xfactor]

I just realized I forgot to mention that it only dies past half throttle when in gear. I dont know how i forgot to mention an important detail like that.


Croix

[bistromath]

fuel flow from petcock, in-line filters, float levels, gas cap. it will be one of those things.

[Tretnine]

I tried to read everything... but mostly I just scanned. Are you getting spark at all four cylinders? Maybe one of your plug caps came a bit loose or you're just not getting spark somewhere now. I had a bike that after putting new plugs on I forgot to connect one of the plug wires... and it actually idled but wouldn't go unless I revved the nuts off it.

[xfactor]

I tried to read everything... but mostly I just scanned. Are you getting spark at all four cylinders? Maybe one of your plug caps came a bit loose or you're just not getting spark somewhere now. I had a bike that after putting new plugs on I forgot to connect one of the plug wires... and it actually idled but wouldn't go unless I revved the nuts off it.

Yeah im gonna check tomorrow when I go home, becuase shes stranded at my parents place, im hoping its something this easy, but I doubt it.