Help!! I screwed up

dave b

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Hello..I recently picked up a 82 750 F with only 4000 miles on her which had sat for the past 20 years. I bought one new back in 1979 when I was 21! It is immaculate, rust free and with about 10 hours of cleaning looks perfect. My problem...It ran really good but was extremely hard to get started. Had to turn it over about 30 times each time before it would finally start. Of course needing to investigate, I pulled the carbs off, took them apart ( they were extremely clean ) used a can of carb cleaner and sprayed and blew out all the jets and everything I could. I put it back together and still the same starting problem. I pulled the carbs again and went with a 38 slow jet to replace the stock 35. I replaced the springs and o rings in the pilot jets. Cylinder 1 was backed out 3 1/2 turns, 2 was 2 1/4, 3 was 2 1/4 and 4 was 3 1/2. I changed them to 3 , 2 1/4, 2 1/4 and 3 to get them a little closer. Started a little bit better but wouldnt idle untill I backed cylinder 1 and 3 another 1/2 turn. Next I started playing with the idle adjustment knob. ( the knob underneath carb 2 and 3) Big mistake. Lost track of how many turns I moved the knob and now I cant even get the bike to run. OK...what to do now.....Does anyone know how to get the Idle adjustment knob back to where it should be without being able to run the bike? And shouldnt those pilot jet be backed out all around the same....maybe around 2 turns. Where would you guys start to fix my mess!!! I really dont usually screw things up like this. Thank goodness for fuel injection.

cb 750F.jpg
 

Old_Crow

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I'm liking the black cylinders and head with the filed edges on the fins. Is that factory, or home done?
 

Davidson750

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Air adjustment for that bike should be approximately one and a half to two turns out. On your idle.. adjust it in until it barely makes contact you can see it actually move, then adjust from there. I never make any adjustments on a carburetor until I read the plugs pretty much tells you the story of lean\rich Etc.
 

Biebs

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if you have an infrared temp gauge and the bike running you can check temperature on each pipe - make sure they are all about the same.

yes all air adjustment screws should be about the same 1 1/2 to 2 1/2 turns out from lightly seated.

pull the air screws all the way out check the tips make sure all four have the same washers.
 

dave b

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Thanks everybody....here is an update. Ive got the bike running really, really good. Replaced all the little o rings on the pilot jets, backed them all out about 2 1/4 and like I said...runs really good! Last thing I want to get right is the way it starts. It takes about 8 -10 pushes on the start button on full choke with some throttle...and finally it kicks in, starts, puts out a little blue smoke and after its warmed up it runs great. Any starting help would be appreatiated.
 

Biebs

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The cb750 is carbureted and cold blooded. Does not have an accelerator pump - engine starts off of vacuum sucking gas into cylinders. if run on a daily bases starting will be easier depending on choke setting and temperature. Sitting for a couple of weeks will make starting harder. Also please shut off the fuel valve as a regular practice.

Good to hereyou solved the problem - Enjoy!!!
 

Davidson750

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Stock Kehein v42's or 43's have an accelerator pump...
 

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Davidson750

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Then you don't have kehein vb42s or 43s... that picture comes right out of the manual and this picture is off of an extra set I have, I have rebuilt at least 20 sets over the years this is what came on his bike in 1980
 

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Davidson750

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If that actually is his bike?, it says you just picked this bike up and that's awesome but something's going on, I've done frame restos that didn't look that good at 42 years old it takes a little more than a buffer wheel to make it look like that that's all I'm saying
 

Biebs

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The carb bank does have an accelerator pump but only on carb #2 so technically you are both correct.

Still point be made is the cb750 in general is very cold blooded and hard to start after sitting idle for periods of 4 weeks or more.
Important to know the beast when warmed up idle and throttle response is comparable to newer fuel injected bikes!!

Carbs are dialed in by Honda try to beat perfection.
 
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