Cb750 what to do project...

cbrianroll

Coast to Coast
A little farther along, got the original battery in until I get the carbs dialed in. Dont want to kickstart it if its way out. Still need paint, bought the wrong color...duh....
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cbrianroll

Coast to Coast
Okie dokie....tuning time, got it ok but needs better. I made a manometer for my goldwing last year and worked great, was thinking I would again for this, but its s but different. On the wing you adjust in pairs then adjust the pairs. How would it work on this? Tube onto each carb from gauge (fluid filled bottlr) then from gauge to gauge? Thanks. I'll prob overthink this...
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irk miller

You've been mostly-dead all day.
DTT BOTM WINNER
That's the way. As long as all four "gauge" sides can find their level being connected, you're good. With the 77-78 750s, you have to tune to #2 because it's not adjustable, so all the matching has to come from 1,3,4 being adjusted.
 

irk miller

You've been mostly-dead all day.
DTT BOTM WINNER
I use ATF, but only because I have a shit ton and it's red. I think either works well.
 

Brodie

Gold Coast, Queensland
DTT SUPPORTER
From what I have read 2T oil is the go as it burns off better if some does accidentally get sucked into the engine.
 

cbrianroll

Coast to Coast
Got some uni filters.. pk-3..coming for this. I use to use pj1? I think along time for dirt bikes, whatcha think would be good for these? Thanks.
 

cbrianroll

Coast to Coast
I think I'm retarded....been reading too much again. Jetting....if my idle won't lean I need new pilots right? Since exhaust is 4 into 1 and carb is open...why is running rich? More air coming in means it would need more fuel right? Shouldn't it be lean unless jets are drilled? It wont lean out. I have it tuned and synced, runs and idles...just stinks and plugs are sooty. I'm working on the math...can someone dbl check me...
A #40 jet sould be approx. A #78 or #79 drill bit..but those are too small, I go down to a #73 then a #72 doesn't fit. Safe to assume they are drilled? I'm ordering jets today...

Or am I chasing the wrong thing? Thanks.
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irk miller

You've been mostly-dead all day.
DTT BOTM WINNER
Which direction are you turning the air mix screw? You aren't adjusting them backwards by chance?
 

cbrianroll

Coast to Coast
I've tried both....in and out. Also...starts with no choke. Blows lots of black smoke when turned out 1/4 at 1/2 and 3/4 throttle. Runs better at 2 to 3 turns out. Not sure if theres much difference after 2 turns out. Is my math wrong about the drill bit size not matching the jet?
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
Your logic sounds good, but ignores a couple of variables:

Float/fuel levels. Set fuel level to 3mm below the gasket surface.

Air passages in the carbs. Clean out the airways to be sure that enough air is getting in to mix with the fuel as it passes through the pilot jets.

Jets: I have no way to convert # sized drill bits to flow rates, but you could do worse than to buy a set of new OEM jets from JetsRus or your local dealer. #78/79 is around about 0.4mm which is what a #40 pilot jet is, so they sound like they are in the ball park for size.
 

cbrianroll

Coast to Coast
Thanks man. Floats are set to service manual specs. I did them. I ultrasonic cleaned and blew 120lbs air throughout...how I've done every other carb with zero issues. Normally have no problems after cleaning...guess I could clean them again. Jetting troubleshooting is new to me. Just trying to make sure my logic is sound lol. I'll be ordering all new stock jets and others to figure it out.
 

irk miller

You've been mostly-dead all day.
DTT BOTM WINNER
The F, with a 4 into 1, ran a 35 pilot vs the 40 for the K . You have to remember that it requires vacuum to suck fuel out of the bowls, so they needed to be leaned out. When you push more air through a venturi, you get more vacuum.
 

cbrianroll

Coast to Coast
Cool man thanks. Got hit in the head with my toolbox when I rolled my jeep...concussion #3....after that I get mixed up with numbers and dyslexic them. Weird.

If I keep it I'll get a better exhaust and air box, but I'd like to get it decent go swap for a dual sport.
 

pidjones

Over 1,000 Posts
I had just one cylinder running way rich on my Hunley GL1000. Finally found that the needle jet was erroded so bad that fuel was always gushingfrom it, even with slides closed. Replaced it (used the same needle) and now it is great.
 

cbrianroll

Coast to Coast
Thanks for that thought..these have been replaced and are in great shape. I have a problem of researching to much instead of just doing it lol. I have what I believe should be stock 40 pilots in route now along with alot of main jets. Should be able to get it...just gotta quit reading and dig in. A color tune also on way.
 

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