Looking for advice please!

[Mching07]

Hello all, I just recently purchased a 1908 cb750c. Me and my friend are currently trying to figure out why cylinder number two isn't firing. We cleaned the carbs, and replaced the spark plugs. I'm fairly green to all of this but really interested in learning more. We took compression tests and they were as follow: cylinder one:125 cylinder two:(problem cylinder) 125 cylinder three: 125 cylinder four:120. Please any advice would really help. Thank you much!

[TOOLS1]

"1908"? You must have the first one produced.
It takes 3 things for an engine to run.
1. Fuel
2. Spark
3. Compression.
Since you have compression, you need to start checking the other two. Start with switching spark plugs, or pull the plug, and attach the plug wire, and ground the threaded part to the engine, and crank it over. Look for spark. If that does not do it, switch the #2 plug wire with the #3 (they both fire at the same time).
If you have spark, then it will be a carb problem.
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[Mching07]

Lol1980! Thank you I do have spark with the plugs we did check them. What more about carbs could you tell me?

[TOOLS1]

I would check the pilot jets, and their passages.
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[bnag0]

Here is a break down on what we did so far....

The bike has 26k on it.
Bought new plugs
Bought new air filter
Pulled the bowls off the carbs and all the jets are clear (Couldn't get the tops off though) can smell gas on plugs
First compression test (Battery low, engine cold, carbs off) 1-100 2-75 3-90 4-60 (My first compression test ever haha)
We charged the battery and did another comp test and came up with 1-115 2-115 3-115 4-100
put the bike back to running form and ran it for a few minutes #2 still not hitting
another comp test right after it was running 1-120 2-120 3-120 4-115


We have nice blue spark on #2 but maybe while running its not good enough?
What are your thoughts?

[bnag0]

We will try switching the #2 and #3 wire first and if that doesn't work I was told to check the jets again to make sure they are not over sized and flooding #2

[TOOLS1]

Just because the jet is clear, does not mean the passage is.
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