Topic: Changed exhaust cb750. What do I do now? Cr29 carbs.

[zstoldt]

Hey guys, I just bought a 75 cb750k. The bike was running great with the CR29 carbs and 4 into 2 exhaust. I rode it home and was really impressed. The only problem was, on one side the baffling was busted out, so the bike sounded terrible! I already had a nice 4 into 1 exhaust, so I put that on the bike and it is running terribly. I'm not surprised by this, but I'm really not sure what the next step is. Will syncing take care of my problem? do I need to rejett? I'm going to include pictures and a short video of the bike running.

The bike starts right up and idles, but boggs down when I give more than just a little bit of gas. After running for a few minutes, the bike dies and wont start for a few minutes.

Treat me like a kid with you explanations, I'm really new to working on bikes. Thanks in advance for your help. You guys rock!

-Zak

video of the bike running and dying when I give it gas:

[flybox1]

Im not the expert on CR's, but they are a pretty free-flowing carb, especially with velocity stacks.
If the CR's were jetted properly to match the 4:2 exhaust, and you swapped on a more restrictive/increased back-pressure 4:1 (MAC) style exhaust, it'd be my guess you are running rich.
this will be confirmed by wet black plugs....

[zstoldt]

That brings me to another question. Should I change my air filtration method before I try to get the carbs synced or jetted? I know K&N has big pods that fit over the cr29s. I don't know if the velocity stacks are safe for daily use, considering they are wide open!

And obviously they suck in a #$%* ton of air.

[flybox1]

some of the CR carb guys will chime in soon with what you need 

[zstoldt]

Sounds good. Thanks Flybox!

[scottly]

Zac, just changing exhaust shouldn't have created a major tuning issue. Got enough gas in the tank?

[zstoldt]

Valid question! Wouldn't be the first time...

I've decided to wait on doing any syncing or adjusting until I get the k&n pods. I didn't realize the velocity stacks are not recommended for daily use.

The exhaust that I installed is much different than the previous one. I've been told this can really throw off the gas/air ratio.

Thanks!

[flybox1]

what do your plug insulator tips look like?

[zstoldt]

Flybox, sorry for my ignorance, but the plug insulator tips are the end of the spark plug that goes into the engine, correct? I changed the spark plugs today and the old ones where black and a little bit oily.

The bike was running rich before I bought it, so I'm not sure if the fouled plugs are from the new exhaust or the old one.


Also, it's blowing out some white smoke since changing the plugs.

[flybox1]

if you switched to the 4:1 it'll be MORE rich, and, if you then add K&N pods to your CR's, you'll be even MORE rich.
the insulator is the ceramic covering in the center.
how do your plugs compare?


what i really think you should do is open up your CR's and find out what main and pilot jet sizes you have in there.
Its pretty easy.  just 3-4 screws will give you access inside the carb bowl, and you can see.  It will also give you a chance to turn in your mixture screws to see what (baseline) they are set at now.
you need to know where you are first, anyway, before you can decide how to proceed (after your K&N's go on) with jetting

[zstoldt]

I think carbon fouled is probably the closest. The insulators are black, but not very oily.

I'll check out my jets asap! Good call. I'm not sure how to get the gas out of the bowls before taking them off, though.

I figured out the white smoke. The previous guy put WAY too much oil in the bike.

Thanks again for your help!