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Cb750 carb adjustment help

Odmckee

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HI new to the site have a question I can't find the answer to I got my first Honda a 1981 cb750 I have been building. after getting it alltogether I tried to start it and it would start back fire out of cylinder 3 and die. I have good spark so I assumed the carbs were out of sync but after looking they are at least bench synced. My question is what is the next step in tuning the carbs without being able to get the bike running. other than that I'm not sure where to go next. Any help would be appreciated.
 
Compression test first as most of them never get the valves set, then the owners tear apart carbs all day long for nothing. The valves don't get set because it requires shims to do it and even the service departments skipped most of that back in the day.

Backfire is either no compression or plug wetted out to foul. Maybe plug wires mixed up.

Next step without running it? You need to be sure any carb work is correct, most of the time it's not.

Don't overlook the importance of compression, can't count the number who discard the idea then go crazy to only find out the big mistake. Putting a finger over a plug hole to check it is NOT a test, the numbers have to be there or junk the bike, it will NOT run right. Should be done on 100% of the early DOHCs before lifting a finger doing anything else as it is such a major problem.
 
Compression will be my next step then. How should the pilot mixture sews be set to begin with just by looking at them they are all set different wasn't sure if it could be part of My problem.
 
Never in the universe will you find all 4 pilot screws in the same place as by simply looking at them.

Take all 4 in until they seat LIGHTLY with no force and then bring them all out 2 turns each. Or try 2 1/2. The idle limiter caps if still in place may limit that and can be removed with a soldering iron and heat, they are loctited on. Force will break the stems and designed to do so, be careful. You can also grind the fuel bowl tab off to clear the caps, and what I commonly do.

If bike has sat for any long period and/or ethanol laced fuel used in your local area you can just about bet the carbs are clogged if you haven't cleaned them. The pilots clog at the drop of a hat.
 
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