2004 Venture runs poor and vibrates esp in 4th and 5th

[Sam]

I bought a 2004 Venture that had sat for 6 months and carbs were plugged. Guy I bought it from told me he started it on ether a few times but was done with the bike and wanted it gone. Mileage was 13,200.

Im a mechanic but regretfully didn't have time to clean the carbs so I ended up paying a local shop to clean them and they changed the air filters. Since getting it back it doesn't seem like it runs right in 4th and 5th gear. Feels like a vibration and like I'm hitting a strong headwind or like the cylinders are fighting each other. Power not great either, especially in 4th & 5th gear. I'm assuming it's a dead cylinder?

Read many posts including those talking about these engines need to rev; they have enough power they can run on 3 cylinders, 4th and 5th are overdrive, etc. Plus, I've had a couple of these a few years back and don't recall them running this way.

Ran a tank of seafoam, then checked spark on all 4 cylinders (visually strong spark and pulled each plug wire which killed each cylinder). All but 1 plug looked good. Left front plug looked gas fouled but still had good spark.

Drained tank and put fresh premium gas, fuel filter & fuel lines and new petcock. Also replaced plugs and rechecked shops work. Found 2 carb/intake boots and all plugs real loose. Tightened everything (poor shop work which causes me to question what they did to my carbs?) I also synced the carbs. 

Put 150 miles on it and seemed better at start yet shortly thereafter ran the same as before. 

I just pulled the plugs to do a compression test and now see all plugs running rich and looking into the plug hole I see heavy carbon buildup on top of the pistons. Will do my compression test tomorrow, change plugs again and run full can of seafoam thru a full tank of regular as I also read its not good to run premium then recheck my plugs again.

 

At this time, assuming it's a dead or dropping out cylinder and the compression is OK, im thinking carbs werent done right or possibly coil weakens or plug wire is shorting  out after it warms up.

Anyway, I'd love to get this sorted out and appreciate anyones advise.

Thanks!

 

New member, Sam in San Antonio.

[Marcarl]

Start with the carbs. After all they have been through and the story you shared, I bet something isn't right in there. Take them off, open them up, throughly clean them and make sure the right jets are in the proper ports, then set the floats and check all linkages and connections. Don't go by what you see when you take them apart, go by the specs.

[Sam]

Thanks. Regretfully I'm expecting that's where I'll end up after the compression test.

[Marcarl]

5 hours ago, Sam said:

Thanks. Regretfully I'm expecting that's where I'll end up after the compression test.

Having good compression may not have anything to do with a noisy rod, but sometimes it might, in other words: inconclusive. But a compression test is always interesting enough to do.

[Carlos Paez]

Hello Sam, I would like to know if you managed to find a solution, I am in the same fault that you describe, only that sometimes it is restored for a few seconds and the fault returns, the sound it generates is like that of a WWII plane when they failed in the air, a sound of ignition failure, i change spark plugs, coils, and the ignitor unit and it still fails the same.