1980 kz750 ltd jetting/power issues are sapping my will to live

Hey all,
I’ve been fixing up a 1980 kz750 ltd for the past two years and I finally got my license and decided to bring the motorcycle down to college with me. The previous owner did not treat the bike well and ended up cutting off the airbox mounting points, so I bought UNI pod filters and have been trying to make those work (I know pods are super notorious for causing issues). For reference I have keihin cv34 carbs. I also have a 4-1 exhaust that I packed with fiberglass. With the stock jets, it ran very lean and very hot, and wouldn’t hold an idle below 1.5k rpm. It could rev up to about 5k in every gear, but no higher. So, I did research and it seemed like stepping up my jet sizes was the logical next step. I just finished installing #38 pilots, #70 mains, and #140 secondary mains today. It pulls very nicely at lower speeds, except now I top out at 4k rpm in 5th. I barely have enough power to go main road speeds. It will rev to 7k in 2nd now but I can’t get it any higher there either. It idles way better now (~1100) and I can start from a stop way more easily and the bike doesn’t want to stall as readily. Am I running too rich now? Any ideas on what could be causing this? Anything helps, I’m knocking my head against the wall since I can’t think of anything. Below is a list of everything I’ve checked/tried:

- fuel levels are all within spec 
- rode with gas cap popped to make sure fuel flows
- checked diaphragms for pinholes, they are solid
- I tried taking the ignition advancer cover off but the bolts are seized and stripped out (so now I’m not getting in there until next summer when I’m back home and can drill them out, plus I don’t think it’s a stuck advancer because I wouldn’t have less power running richer?)
- the pod filters do not block the venturi in the carb intakes 
- tried adding the stock airbox back, can’t mount it because of the butchered frame 

I was also getting abysmal fuel economy before rejetting (24mpg) and I thought this was because I had to whack the throttle open to get any power. However, I checked and I’m still only getting 24 mpg currently. 
I have put so much money into this machine and I’m starting to hate it because it breaks down so often. I was thinking that a #130 or #135 secondary main jet might be worth trying instead of the new #140, but I really don’t want to spend more money unless someone can confirm that that is my most likely issue. I unfortunately have limited money and limited time I can spend removing and reinstalling the carbs.

tldr; I run pod filters on my bike so I rejetted and somehow lost even more power. I’m a broke college student. What should I do?

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I have a kz750 E1 with Keihin CV34 carbs like yours. I've had K&N pods for several yaers and that 70  140 jetting was just fine. I got rid of the pods after getting caught in the rain. Cough chug splutter splutter.

Honestly my first thought was that the uni pods had a lip inside blocking or even partially blocking air jet or passage but you say no. It does sound like a restriction  and wondering if the rich condition is because of fuel excess or air deficiency .

Have you tried running without the Uni pods just briefly ?

Perhaps some other carb blockage ? Have you given them a thorough cleaning.?

The bolts on the ignition/advancer cover look like Phillips head bolts but the Japanese but didn't  use Phillips they used JIS heads. A heavy handed Phillips screw driver will strip them. A JIS Iimpact driver the type you hit with a hammer might work if the screw head are not totally destroyed.

Someone else can comment on the fiberglass  packing. I dont know what the effect might be.

If the previous owner neglected the bike he probably never checked the valve clearances. Maybe worth a look.
.

 

JR wrote:

Someone else can comment on the fiberglass  packing. I dont know what the effect might be.

If the previous owner neglected the bike he probably never checked the valve clearances. Maybe worth a look.
.


 

Well, the packing can't be blocking the main flow path or the engine won't rev.  

Here’s a picture of what my baffle looks like before I packed it. Basically, the thing I circled in red inserts into the muffler tube and that’s what kills the sound, but it was crazy loud and obnoxious so I tried to quiet it down by wrapping it with some fiberglass packing sheets. It worked a treat and it’s very quiet now. Unfortunately I’m looking back in my gallery and don’t have a photo of the final setup. 
If I wanted to test for the exhaust as a choke point, could I take the bike out to a back road and unbolt the whole muffler and just let it run straight piped to see if I get power back or will that damage something if it’s that free flowing? It’ll be loud but hopefully nobody will be around to hear. It makes sense that a restrictive exhaust would cause me to run too rich.
I do need to confirm valve specs but unfortunately I can’t do that while I’m at college because I don’t have the place to work or the tools. 
Thanks for the replies,

conrad

Update: 
took the bike out to some cornfields and took the exhaust off… long story short, that’s definitely my issue. 
unfortunately due to the way I packed it I probably can’t redo it at school (and it seems like that type of exhaust isn’t meant to be packed anyways), so now I’m looking at slip-on exhausts. I guess loud is okay, but I still want my exhaust note to be as respectful as possible. Does anyone have any suggestions for decent options under $200? I was looking at those eBay Chineseium exhausts but I haven’t found any good info about whether those would work at all. It doesn’t need to be perfect, I just need something so I’m not straight piping around my campus lol. I was also looking at this remmotorcycle exhaust , could this be any good?

Also, here’s a short video of how it ran while the muffler was off…  
does it sound like it’s running rich still or is popping just a normal straight pipe thing? It’s also a bit wonky around 2-3k so maybe I’ll have to readjust the idle mixture screws or put the old pilots back in—but that’s something to figure out once I get the new exhaust I guess.
 

A little more than $200, but good reputation.

delkevic.com/product-category/mufflers-slip-on/

KZ750specific.

delkevic.com/product-category/motorcycle..._1980-models_kz750/#

Aw man, I’d hate to buy a whole new system when all I really need is the muffler. I guess that will be the move if I keep the bike and start working a job again next summer. Thanks for the links though.
I’m looking at Facebook marketplace for some used slip-ons like arrow exhausts off of gsxr 1ks and s1ks—assuming I can get everything to bolt up, should those flow fine? I’d assume so because it’s for a super sport but I’m not certain

You beat me to the solution- a mechanical baffle like yours doesn’t run packing, in essence what you did was block the exhaust
PS: running it without the exhaust will make it run weak and probably burn a valve or piston 

Any chance I did damage to my engine running it like that for ~300 miles? Or is it pretty much just limited to an immediate performance issue 

If your rides werent too extended you should be fine as long as it didnt heat up too much. you might know if the engine is getting too hot cause you would feel it on your legs when driving and at idle. If you didnt notice any change, your bike is probably fine. Take some measurements of the diameter of the area where the slip-on goes and other dimentions and find any muffler that you think could fit. I also wanted to take my bike to college this year but I did not manage to get a parking pass... Don't give up on your bike though, just take a look at the spark plugs when messing with jetting and do the standard tests for your mid and high rev range for loss of power.