Cylinders 1 and 2 wont run!

[Honda7503747743674]

Drug out my grandpas 1978 750 after 20 years sitting in his garage. , cleaned the carbs, put fresh gas in, changed the oil, new plugs. Fired right up but it will only run with the choke on and cylinders 1 and 2 are not firing. Ive checked the compression and its fine , im getting a spark from the plug. And after ive ran it for awhile i can pull out one if the plugs and it will have black gas like liquid on it. What could be my problem?!

[shinyribs]

My first thought was the pilot jets were plugged and not allowing it to get fuel at idle. Black on the plugs could be oil form stuck rings causing it to foul a plug. Can you determine if the plugs are fuel-fouled or oil-fouled?

[TOOLS1]

I'm going to say no matter what the plugs are telling you about the condition of the rings, your pilot jets are still plugged!
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[Honda7503747743674]

 i pulled out the pilot jets soaked them in carb cleaner, conpletely cleaned them to where i could see day light through them. Put it all back together and it still wont run cylinders 1 and 2, and it still wont run unless the choke is on!

[shultz_1978]

Just a though. With the air box off. Try chocking # 1 cylinder by hand. You will know if ti picks up and runs by the sound of the bike.

If so look into the cfarbs more. The fuel may not be getting to those carbs like it should. Floats, Float valves, even the port and lines.

If I remember right ! coil run #1 and 3 and the other runs #2 and 4. I think Most of the time if a coil is not firing it will not be 1-2 or 3-4 missing.

You could even open the drain over flow screws on 1 & 2 to see if they are getting fuel. Just put the over flow lines in a bucket or jug.

[TOOLS1]

Shultz is on the right track. Since No#1-2 are fed from the same fuel line/rail check to make sure that the are getting gas. Also since the coils fire 1-4, and 2-3 you can pretty much rule out ignition.
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[Honda7503747743674]

I opened the drains on the carbs and they are all getting fuel. I havent tried chocking the carb with the airbox off yet.

[TOOLS1]

Next step is to check to see if the idle passages in the carbs are plugged. Just because the pilots are clean does not mean that the passages are.
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[Honda7503747743674]

Did that too tools , i sprayed carb cleaner down the passages and they were clear too. Could cylinders 1 and 2 be getting to much gas??

[TOOLS1]

No that wouldn't cause it not to fire. Have you run a compression check?
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[Honda7503747743674]

Yes is around 115 on all 4 cylinders

[TOOLS1]

You have spark, air, gas. Are the 1, and 2 plug wires switched?
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[Honda7503747743674]

Nope , the #2 wire wont reach the #1 plug

[TOOLS1]

Are they switched at the coils?
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[Honda7503747743674]

Ill have to check, i never knew they could be switched at the coils.

[shultz_1978]

Did you try to chock it by hand?

If so what did it do?

[Jimboslice]

Gotta bump this. I've had the exact problem for the past few weeks on my 82 cb 750 dohc.  All cylinders are at 120 psi compression. Had the carbs in and out and rebuilt many many times. (I could do it blind folded) the p.o of the bike had destroyed the stock carbs with a drill and tap and ive replaced it with the vb42f model. (Non removable pilot jet)I've confirmed spark on all 4 cylinders. Im absolutely stumped.   Ive also tried to carb sync and checked for vacume leaks. There are none that i can tell and the sync is good.

[TOOLS1]

Will they fire if you give them a shot of starting fluid?
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[Jimboslice]

They will when i bring rpm up to around 3000. I just finished cleaning the pilot  jets again still nothing.  

[TOOLS1]

So, even with a shot of starting fluid, you have two cylinders that will fire only above 3000 rpm? With starting fluid, it should fire at any rpm as long as the ignition is working.
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