Topic: I still need help... PLEASE!

[Scout]

I'm really getting tired of working on my 78 CB750K8 without any appreciable results. You guys have been a ton of help, but I need more!... But let me start from the begining - here's what I've done so far:

1. Valve adjustment
2. Cleaned and gaped the points, and set the point gap, and dynamic timing
3. Took the carbs off, removed the slow jets, cleaned them well, and cleaned whatever else I could while I had them off, replaced float needles, set float level, and synced them
4. new D8EA plugs and air filter

The bike currently has the following mechnical issues:

1. The idle is a bit rough, and it wont idle below 1,200RPMs. It sounds like it just works on 2 cyl. below that, and dies.
2. It takes a long time to warm up, about 10 minutes of riding. Before that, it will die if I don't keep the revs up.
3. When cold starting, I first pull the choke all the way, and start it. It starts on the first try, and will go up to 3 - 4,000 RPMs, then after 10-20 seconds, it will drop down to 1,200 - 1,600, and sometimes die. I have to keep reving it to let it warm up.
4. The vibrations... I thought I finally got rid of them, but after my ride at lunch, they are back. Sometimes, when I ride it harder, then slow down to 50 MPH, it will be fine. Other times, the bike vibrates annoyingly...
5. Last night, I spent 3 hours with Blue Away and Chrome Polish to clean the exhaust pipes. I got them to look beautiful. After my 12 mile ride to work, 2 - 4 are yellow at the top, 1 is fine. Assuming that the 2 - 4 are running hotter, but why...

I'm not a mechanic, I've really spent a lot of time that I don't have trying to learn everything, and do it right, but it's just so damn frustrating... Can somebody please help me here... I just want to have a street bike that I can ride and not have to worry about 20 different things every time... It has left me stranded twice now, once because of the ignition switch, once because of a blown main fuse...

Of course, if there is anybody that would be willing to help me in person (I live in Aurora, IL, west Chicago burb), I would be greatly indebted too

Scout

[Bob Wessner]

3. Took the carbs off, removed the slow jets, cleaned them well, and cleaned whatever else I could while I had them off, replaced float needles, set float level, and synced them

Not that you want to hear this, but it sounds like carb issues. When you took them off to "clean" them, what exactly did you do? You mentioned pulling and cleaning the slow jets, but what about the passages in the carb body? Did you soak the carbs and then blow compressed air though passages, etc?

If it is any comfort, carbs are the single most troublesome and often discussed maint. issue here.

[eldar]

Well this certainly sounds fuel related. Pull your plugs and clean them. Start the bike and see if it runs good for a couple of minutes. If it does then goes to crap, most likely fuel then. Pull the plugs and see if they are fouled from fuel or whatever. When the bike is running, put you hand by the exhaust and feel if it is warm or cold. 2 and 4 are probably just fine. You issue is probably 1 and 3. since it is different coils, you can probably el;iminate ignition or spark as 1 & 4 are the same coil and 2 & 3 are the same.

I would say to pull the bank again. You do not need to pull the bodies apart though. pull of the bowls and clean your float seats VERY well. Crud builds up on them and causes the float to not work right.

Make sure your low speed screws are set to, should be a start of 1.5 turns out. Now here is the thing. earlier carbs were AIR screws, ours are FUEL screws. So if you turn them out, your mix will get richer. In makes the air mix leaner.

1 thing you could do is to switch 1 & 4 and 2 & 3 and see if hte problem moves. You could have bad wires or boots. It would be somewhat odd but could happen.

These are the places to start. I had this issue on my 78k and it was my #2 float not maintaining fuel flow correctly.

[Dusthawk]

I had a kinda similar problem with my 750F many years ago and felt real stupid when I realised I hooked the coil wires up wrong. One coil was on one and two, the other was on three and four. Needless to say it didn't run real well and about three hours later I finally fiured it out. And what made it worse is that I've been a mechanic for 20 odd years, mostly back yard stuff but I did it for a living for 11 years. Imagine my chagrine.

Hope this helps a bit,

Peace and Long Rides,

Jeff

[Scout]

Well, when I had the carbs out, I didn't take them apart and soak them, I just used a can of spray carb cleaner and compressed air. I tried cleaning everything I could. Now bear in mind, the carbs were really clean to begin with. Also, I took the accel pump apart and cleaned that. Finally, I took the floats off and clean them, and like I said earlier, I replaced the float needles, because one of the old ones was broken (the "springy" part didn't work). Everything seemed to be moving freely, no binding anywhere. The one problem I had was that they were supposed to be adjusted right at where the floats just touch the needles. I had a hard time determining when that happens exactly, so I just eyeballed it. But I think they are pretty accurate...

One thing I didn't mention was that when the 4-into-2 exhaust what put on the bike in '98, the dealer's work order stated that they rejetted the bike. They have also put in D7EA plugs in it at some point, because that's what was in there when I got it. The bike has been serviced at the same dealer all it's life... I'm not sure if they have adjusted something for the hotter plug, but I replaced them with the correct D8EA plug...

As far as the plugs, after my lunch ride I pulled out #1 and #4. #4 was a little darker on the rim, but both had white ceramic part, and looked very clean.

I haven't played with the speed screws at all, but I will do that next when I get home tonight, see if that does anything...

What I would love to see is a perfectly running 750, to have a refference point

Scout

[Scout]

OH, one more thing. When decelerating, I get some mild poping through the right exhaust. After riding for 20-30 minutes, it disappears almost completely...

Scout

[Scout]

Jeff, I didn't touch the coil wires yet (trying not to touch anything that I don't have to

Scout

[Scout]

Ok, I took the carbs off again, and the speed screws were set at a little over 2 turns out...

Scout