Not firing on 3&4

[Mysp1]

Hi, I have a problem after fitting new after marked coils. Tried to start her but only firing on 1&2, which doesn’t add up as coil 1 sparks 1&4 and coil 2 2&3. No spark at the end of HT lead on both problem cylinders, any advice much appreciated.

 

[brettp]

Have to ask: sure your plug wires are connected to the correct plugs?

 

[MisterCB750SCMoto]

Have to ask: sure your plug wires are connected to the correct plugs?

Well they have to be I would think, when I first replaced the spark plugs, that was right after I did oil change n cleaned gas tank, she started right up & I rode her all day & for a couple days after that. Right after I cleaned & rebuilt carbs is when I started having this problem. So it’s gotta be an issue with that. Either I didn’t do the carbs correctly like I thought I did or which I’m pretty sure this is the case, she isn’t getting fuel. That’s why I manually put fuel in fuel bowls and she stared & then I bypassed the vacuum thingy altogether, like I’ve seen many people say to do on here!

 

[brettp]

Verify spark on 3 and 4 by pulling the plugs and putting them against the block. Check to see if they are wet, too.
If they're wet, you have a spark issue for sure.
If you have spark, look for an air leak around the boots on the carbs.
If no air leaks, you have a fuel delivery problem to, or from, carbs 3 and 4.

 

[Mysp1]

Thanks guys, I will investigate further, got her firing on all four on Saturday took her out for a 30 mile ride, but started her yesterday and the problem is back! Plugs were wet, cleaned and good spark, as soon as I tried starting again both down pipes were cold.

 

[93trident]

Thanks guys, I will investigate further, got her firing on all four on Saturday took her out for a 30 mile ride, but started her yesterday and the problem is back! Plugs were wet, cleaned and good spark, as soon as I tried starting again both down pipes were cold.

Did you sort the problem out mate?

 

[Mysp1]

I did thanks, intermittent fueling, carbs cleaned, old fuel cleaned out and new higher octane fuel used. All good!

 

[Stan C]

You did not mention that you fitted NEW PLUG WIRES, only new plugs. Had a similar issue and as soon as I put new wires on, it would pull 9500 RPM without any hesitation. Hondas like this one only like nice clean fuel and nice new electronics.

 

[plantguy]

You did not mention that you fitted NEW PLUG WIRES, only new plugs. Had a similar issue and as soon as I put new wires on, it would pull 9500 RPM without any hesitation. Hondas like this one only like nice clean fuel and nice new electronics.

^^^^
What he said.

Check my post in this thread.

https://www.cb750.com/threads/cdi-ignition-module.9296/

 

[93trident]

^^^^
What he said.

Check my post in this thread.

https://www.cb750.com/threads/cdi-ignition-module.9296/

All the plugs, coils and leads were all new. Removed them and put the old ones back on as the bike hated them . All units are firing now but I still have cylinders 1 and 2 cold or cool. I think it's the pilots. Number 1 will get hot after I heat it up with a blow tourch ,2 stays cooler no matter what
It gets wet and sort of fires but neither are as hot as 3 and 4. Can't get the pilots out with 2-56 tap and socket head allen screws they just won't budge.