Engine stumbles and dies at 4500 RPM, HELP

[Neo71]

Hi! I came across this website and wow! What a learning experience!
I'm having issues with my 79 xs650 special. I bought this bike a few months ago, done some work on it and I'm now hoping to find a solution here to my problem.
I removed the stock air filters and installed pods, changed the old muffler with a new slip on muffler found on e-bay, changed the main jets to 145 and pilot jets, lowered the needle... I actually tried several jets and needle positions but nothing!
The bike wont go over 4500 RPM when riding it and a lot of popping/backfiring/stumbling. I was able to have it idle decently with the new jets and setting the mix screw accordingly. If I give gas while it's still on the kickstand it sounds pretty good and the RPM will go up as I would expect (still some popping though) but there is no way to ride it.
I thought that the coils may be the issue here and checked the spark. I Didn't find that nice fat blue spark I read about but I might be wrong. Can it be the valves? the CDI? The coils? All of the above? I'm a little confused here...
Any help would be very much appreciated... Thanks

 

[littlebill31]

First, check your cam chain tensioner, then the valve lash, then the timing, then go to the carbs. You have a '79? Did you add a TCI (not a CDI)? '79 should have points. Read this 'til your eyes bleed-http://www.amckayltd.com/carbguide.pdf
How did it run before you started changing things? Air leaks?
I suggest going thru the tech section, especially "maintenance and trouble shooting" first.

Before you start changing stuff, make sure you have an undestanding of how everything works together. Example: I have open exhaust and pods, but only run a 142.5 main.

 

[MrBillohnooo]

Check your voltage with engine off at battery. then running at idle and at higher rpm. it should be over 12 volts and no more than about 14.5 volts as the rpm go up.

 

[johnnymac]

I have a 75 and had similar problems when I switched to cheap pods- the rubber blocked air flow to the carbs. I switched back to my stock air boxes and all was good until a similar thing happened again which turned out to be rust in the gas tank that clogged passages in the petcock and leaned things out greatly. I suspected electrical problems every time so now I finally got a pamco system with higher output coils from mikes (which ended up being a really cheap way to get electrical peace of mind)- I hope you solve your problem.

 

[5twins]

If you have '79 carbs then 145s are probably too big for the typical "pipes and pods" mod you have. Try 140s. If your pods are the cheap K&N copies, they could be part of the problem. Pull them off and try a test run.

 

[Neo71]

Thanks for all the advice. Tomorrow I'll start out checking the battery, it's brand new but not the original type... right after that I guess an easy test without the pods would be a good idea just to see if anything changes. I haven't checked cam chain tensioner, valve lash, and timing yet so I might need to dig deeper into that. I've never done it before and this might be the right time to start. I did find some info on how to adjust the cam chain tensioner and valve lash (looks easy enough) but don't feel confident messing with the timing. Is it something I can do by myself? Any references? Thanks for link to the carb guide, I already had that and did read a few times before changing stuff. I also test ran the bike with the original jets before changing them to 142.5 and eventually to 145 without any improvement.
Sounds like before touching the carbs again I need to first check all the other points just mentioned. I Hope to figure out what's going on, it's been a while now since I haven't been riding and I just can't wait to get it going!
Thanks again

 

[5twins]

Yes, you must make sure all the other settings are right before doing the carbs. You can't properly tune them if the other stuff is off.

 

[littlebill31]

Just remember that the carbs work on throttle position. So the mains will be in question when the throttle is 3/4 to full open. Jet needle at 1/4 to 3/4 and the pilot from idle to 1/2. I say this 'cuz some people, including myself, when new to carbs, adjusted jets that didn't need to be changed.
I will commend you on noting that you will be taking the advice given. I wanted to point this out due to other threads I have read that people don't listen and keep chasing the problem instead of doing what was advised. Good on ya!! All this info is tested and used, not theory.
Good luck and you'll be fine doing the valves and tensioner. Once you do it a couple times, you'll do it all the time.

 

[Neo71]

I found out what was going on, it was the damn pods! Thanks for all the info guys. Great help

 

[pa23driver]

just curious, what kind of pods were you running?

 

[Neo71]

they were some cheaper pods bought off from ebay. they look cool but the rubber plugs the ports and doesn't let the slide work properly. I should be able to modify them or add an extension...

 

[XSLeo]

A sharp knife works wonders on the lip that blocks the air.