1982 CB750F...Better Devil

20 or so hours in and this stuff is already tough as nails. There’s a little flexibility which is a good thing, but I can’t mark it with a fingernail. As long as it’s bonded to the steel then all will be well. I’ll leave it another day, give it a rinse out with some gas and then try it out.

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36hrs in and this stuff is rock solid. Gave the tank quick rinse out with some gas, hooked it up on the bike and rode it up and down the alley a few times, damn it’s good to be back in the saddle.

Tomorrow I’ll get it around the block and see what gives.

Definitely roadworthy! I’ll get some more pics up too, show her off a bit.


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Whoa now, steady there Winston. Maybe “roadworthy” was a little over-ambitious.

Bike is idling well, right around 1100rpms no drama. Starts with a bit of a choke then settles down nicely. ColourTune’d the cylinders again - all burning Bunsen blue so the mixture is right on the money. Problems start when I take it out for a ride - after about 5 minutes the engine starts to labour, and will cut out at a stop light. Limp mode home.

Feels like gas starvation. Bike idles well on either auxiliary tank or gas tank (so I don’t think it’s the cap not venting) and from what I can tell (by looking at the inline filter) there’s gas pulling into the carbs. So I don’t think it’s the vacuum diaphragm on the carb rack itself (emphasis on think). It just seems that under load something’s not right - either gas starvation, spark or something else.

I’ve checked for spark - good on all 4. Unless something is happening when the bike is riding, spark seems ok. Could it have something to do with timing? Once I reassembled the engine I never checked the timing - truth is I don’t know how.


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Take it out until it acts up, go home and redo the colour tune and see if its still the same or if its gone rich.
 
I tuned my first cb cold and it did the same thing. I then did the same, road it till it acted up then went home and re-did the idle screws etc and then it was better
 
Oh yeah? That's good to know Mike. So just to be sure, it's just the mixture screws and idle screw I'll be adjusting?
 
Bunson blue just means lean- but it doesn’t tell you how lean. When I use the color tune I find the neutral flame and then turn it ever so slightly lean.
 
Yeah. You have to set idle at full warm or it will go rich when fully warmed up and stumble and run like crap off idle. Just like you have to check and set valves stone cold or they get tighter as it heats up and screw things.
 
And remember it takes forever (well, seems that way) to get a CB750 warmed up. You really should set timing before messing with carbs, too.
 
How do I set the timing? That seems like a small question for what’s probably a big answer.


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I was just reading through the FSM manual Maritime (slightly different one tho, for the 750). Learning more about something I knew little about before. Static and dynamic timing. I don’t have a strobe timing light - would static timing give the same degree of accuracy?


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Static has to be done first and then you can use dynamic to verify and fine tune. I never bother dynamic timing as I have no light and I set static and ride and if it runs good, I'm good.
 
Nice. What works for you will work for me.

Here’s the engine (warm, but not ridden) at idle -



Does it sound like it’s stumbling or misfiring at all?


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I skipped ahead a bit but it seems to be idling just fine, so you need to look at off idle issues. Is the advancer plate free and moving as it shoud?
 
See, that’s where my ambition exceeds my current skill set . Is the advancer plate the same thing as the “pulser base plate”? A disc with two black box things on either side, with a small window up top where you can read the timing marks on the crank? And if so how should it be moving?


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I dont know exactly as Ive not qorked on that exact bike but yes it would be there. It could be an electronic advance or mechanical. My plate is weights and sprincs and you can twist it to see it is moving freely. This is where a timing light might be good for you as you can use it, rev up and see if the timing is advancing. I know mine is by watching the plate. Yours may advance by an electronic means. My 81 CM had a CDI and it controlled the advance based on pick ups in the stator.
 
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