Importance of cross-pipe on Exhaust...XJ650 Need Advice

How important is it to incorporate a cross-pipe from cyl 1 to cyl 4 on a 4-2 exhaust setup? I just finished making a custom 4-2 tubular exhaust that pretty much mimics the stock exhaust minus the cross-pipe. Now there is a significant loss of power. It feels like it's only firing on 2 cyclinders, power-wise. Also, cylinder 2 and 3 only get warm post cyl head(I can hold my hand on the pipes while it's running). coils have been tested for resistance. 2.8 and 12.9k ohms. The bike 'sounds' like it's firing on all four. Plugs are not foul. Leak down test was performed and has healthy compression. Valves were professionally adjusted. Carbs have been COMPLETELY gone through by my mechanic, three times. Pilots are #45 and i do not recall what was put in the mains but they are bigger. The bikes idles fine and runs very smooth, there's just a massive loss of power. I mean, it literally struggles to get up to 50mph. I am at my wit's end with this.. It does not run lean. Maybe a slightly rich but not enough to make it idle bad, smell gas out the pipe, or smoke black. This literally all started after the exhaust, which is why I want to point to it, but is there any possibility my Ignitor is going out??

Thanks to anyone who can help. Also, if anyone is willing to drive to Carmel, IN, I will cook you a steak, feed you a few beers, and throw you some gas money+an extra $40 to come give me some help with it.

 

I changed from a 4-1 to a 4-2 custom with no crossover on my 81. I had to rejet the main fuel jet and shim the needle to make it happy.

You may not have enough back pressure depending on your exhaust. Are you running mufflers or straight pipes? Pictures of the exhaust?

You're into trial and error now. I'd try to shim the needle first. I bought some washers at the home depot (#4 I think they were), several packs and mic'd them to find 4 of the same thickness. Installed them in the slide above the needle. Was better but still not good. Then upped the jets. To what I do not recall. Bike runs fine since.

 

Keep in mind I am no expert but offering opinion.

Couple of things I noticed from the pictures.

1. The wrap will help speed the gases down the pipe as they retain heat. Making the cylinders leaner than they were with no wrap. Mine are also wrapped.

2. That merge looks to be an awefully sharp angle which will alter the back pressure on the two inner cylinders and may require different jets for the proper mix in those two.

When I did mine the merge was more of a >- and about 6 inches long. Little angle to the merge.

 

Yea, that's why I think I'm either going to have to incorporate a cross-pipe or revisit the angle of the collector. When I originally thought about the design process, I noticed the sharp angles of the stock collector. I figured it would be fine but it doesn't seem that way.

 

With the collector the pulses can expand out. The way it looks in the picture they are running straight out the bend and into the sidewall of the other pipe.

A cross over may fix it. A straigher merge may fix it. A rejet may fix it. Or most likely some combination of the three.

 

Yamaha was always way out in front as far as doing cutting edge work with exhaust design's effect on throttle response and midrange power....

In general, removing a crossover or collector will make most small engines just completely fall on their face as far as those two items go, unless specifically tuned for the new setup. It wouldn't surprise me that a Yamaha suffers even more extremely.

What you've done is not only created a need for a much freer flowing intake tract and richer jetting, but also eliminated any low end throttle response benefit from exhaust scavenging effect on intake charging...so it's a double whammy. I can imagine it's really suffering.

 

I have no comment on the exhaust, but that is a SHARP looking bike. I like it!