I get asked about installation of replacement fuel lines and filters on the KZ750 Twins alot. Such a simple thing, but the topic has many fine points, and I wanted to provide as much detail as possible about my preferred method of installation.
But first, a few points:
- I know many people like clear fuel lines because you can see through them for troubleshooting fuel flow; I even used to like them for the same reason. But now I never use them because over time they get hard and brittle, and easily loose their seal when jostled, sometimes at the side of the road, sometimes just while riding. Even if you take the extra insurance step to use mini clamps, the seal can fail in time. On the other hand, if you use a reputable brand rubber fuel line you will not have these problems, and you won’t need clamps.
- I change my fuel lines and filters every year when I return the bikes to use for the riding season. But even if I lived in a year-round riding climate, I’d still change them yearly. It only costs about $10 to replace it all, and you don’t have to worry about clogged filters, rotting lines, etc.
- Never use paper-element fuel filters. It’s not a lawn mower.
- Plastic inline fuel filters get softened by fuel over time, and can bend to the point of restricting fuel flow if you’re not careful. So be careful.
- 1 early model KZ750 Twin
- 1 package of 1/4″ x 24″ fuel line (Good Year, Prestone, or whatever is at your local auto parts store)
- 2 inline 1/4″ brass-element mini fuel filters (I get them from z1Enterprises.com whenever I’m ordering something else, but you can probably get them at any bike shop)
When the KZ750 was designed, apparently the engineers never thought we’d have to worry about fine rust particles in the tank or inline fuel filters to compensate. Silly engineers. As a result, if you run without inline filters, installing fuel lines is an easy, intuitive breeze.
However, since this is the real world, most of us do have to worry about rust, and we do have to use inline filters. And because of this, we have to do crazy, creative things in order to have room to accommodate the filters… and not cause them to bend and shut down fuel flow as they soften from extended contact with fuel… or melt from contact with the back of the engine.
And this is why I’ve written this post; My goal was to find the best way to run the best fuel lines with the best fuel filters. Oh, and for me, “best” means “best possible at the least reasonable expense”. 😉
So we start with my garage plan chicken-scratch drawing on the back of a dirty envelope to help convey my design layout:
So, we start with one package of reasonable brand fuel line. I’ve always used Good Year line in the past, but this time AutoZone had Prestone. Whatever, it’s 24 inches of 1/4 inch inner-diameter standard fuel line.
As the design drawing above indicates, cut the line into four pieces as follows: 4″, 4.5″, 5″, and 10.5″ (or whatever is left). UPDATE, 2015: For the last couple years, I’ve actually modified the lengths a bit, and have been using 4″, 5″, 5″, and 9″ with great success.
Assemble the parts so that the natural curves in the hose works in your favor, so that when assembled, the filter will be stressed as little as possible. I’m not sure if you can tell from the pic, but the curves are opposite. Here is the assembly order:
Left: Petcock -> 10.5″ hose -> filter -> 4″ hose -> Left Carb
Right: Petcock -> 4.5″ hose -> filter -> 5″ hose -> Right Carb
Assembly Step 1: Connect the right line to the right carb. I hope you have small hands, it’s tight in there. You may have noticed in the pics that I have the tank sitting up on a wooden block for space.
Assembly Step 2: Complete the right line connection to the right output of the petcock.
Assembly Step 3: Now feed the left side line assembly in from the right side, around the throttle cables and connect.
Assembly Step 4: Finally, bring the line around and behind the other right side line, to connect to the left carb.
Here’s a finished view. Note that the filters are spaced offset from each other, they are not bent or stressed, and the lines and filters are not touching the engine. And hey, don’t hassle me about how dirty the engine/carbs are, or that there are old hornets nests that I’ve never cleaned out… It’s a working man’s bike and that’s how I like it to look… 😉
One additional caveat though… If you use the original stock ’76 – ’78 side covers, you will have to cut away a bit of the cover to accommodate the fuel line running where it was not intended to be. But if you do it with a nice, smooth arc, it doesn’t look out of place.
I hope that helps!
This is an excellent Idea I have been trying to figure out how to do this for a while.
I just posted a question asking for this exact information. Thanks, Bique!
Thank you for the advice. It worked and my bike is running better than ever. Please keep it up. If at all possible I would like to learn how to inspect my jets on the carb. Thanks again.
Lets discuss air filters: K & N produces an air filter, and UNI produces an air filter for the KZ750 B1-B4. I also see an air filter on e-bay that is a copy cat to K & N. What’s good and bad about any of them?
@ Doug –
That’s good fodder for a post, thanks for the suggestion.
In the meantime, here’s my $0.02 about air filters for the B series.
The bikes were jetted lean to start with. The stock Kawasaki filters are still available all over the place, since they were used with a few models. The K&N is a great near-stock replacement, that breathes a tad better (so you probably need to reject from stock) but lasts longer. The UNI breathes VERY well, and MUST be oiled to maintain its functionality, otherwise it is mostly decorative…
Thanks, I thought I knew everything about these 750 Bs . How could something so simple get by me ? Use the fuel outlet that one would think goes to the left side carb and put it on the right side ! I’m feeling kind of stupid right now.lol
Hello Sir, I heard you have a method for cleaning carbs with seafoam.. I looked and could not find your method in posts. Could you please send me a link or a brief discription? I have a 440 LTD I am getting tuned with UNI pods since the airbox was missing. May not need farther cleaning of the carbs this time – but I would love the information of your method. Thanks -James
Hi James –
Really, I don’t use Seafoam to manually clean carbs, but Seafoam does wonders if you just introduce it to your regular fuel.
Here’s what I mean – If you recently got a bike that is running, and are unsure of it’s origin; after doing the standard stuff (fresh gas, oil/filter change, etc), just add 1/2 of a small can of Seafoam to a full tank of fuel. In my experience, the bike will start to run poorly/rich in a day or two, since the previous owner likely was making carb adjustments to compensate for years of carbs clogging slowly… The Seafoam will eat away the gummed up fuel from the tiniest passages that you can’t get to without professional cleaning, and can get you by until then, if not completely cure problems.
Then, what I do, is run about 1/3 can (I have 3 running bikes) through the tank every couple months or so. At $10 per can, it’s cheap insurance, really. Especially for bikes that sit a week or so, and the fuel dissolves in the carb passages and gums them up…
I hope that helps!
Good presentation. I do basically the same.
My 2 cents:
I learned the first time I did it that it is a good idea to “flush” some fuel from the “on” and “reserve” petcock positions in the tank into a container before hooking up the lines to the carbs. The first time I replaced the lines I noticed some rust particles and debris flowing into the new filters. So, flush before hooking up to the new lines. Good day.
So I bought a 1976 750 and I need a carburetor. I cannot find one anywhere BS38, right? Anyone know where I can get one re-built or new?
BS38 is correct, but none lying around here…
I just got an old 78 KZ750, I had it running when I picked it up but only with a jump. I’ve replaced the Battery but now it won’t start. Every time I try to start it I end up flooding the carb. It has this really “Mickey Mouse’d” Petcock on it that is leaking. The carb wells leak too; in fact if the petcock is on it all leaks nonstop and when it off it only leaks a little. So, I’ve determined to start with replacing the Petcock and fuel lines like you’ve posted.
I’ve never worked on a bike fuel sys before. Where do I get a new Petcock? The only ones I see online don’t look like the one here, or one I can even mount, or they only have one outlet. How do I get one like the one you’ve pictured here? Salvage?
@ Rich –
There’s a lot to reply to here, I hope I can hit some of the big points…
First, as with all old bikes, the carb is probably gummed up with old evaporated fuel.. If it won’t run *at all*, then you likely have no choice but to clean the carbs in some way. You can have a pro do it, or you can grab the service manual, research a bit, and try it out yourself. Who knows… if you’re anything like me, you’ll get it close at first, then better with each re-try… 😉
As for a new petcock… I’m not sure you actually need one, because it sounds like you haven’t disassembled this one and looked into it… But the good news is that the “screw-on” type on our early KZ750s is exactly the same as on many Harleys and custom bikes, so you might be able to use one of them with a splitter or something. I might even try that myself some day, as I’ve already bought some of the parts needed.
Other than that, take a good look at some of my favorite resources listed herein.. especially z1Enterprises.com and a few others…
That should get you started…
Thanks, for the advice. So far I’ve used your forum for a lot of helpful direction.
I’m going ahead with a quasi-rebuild/cleaning of the carb I’m ordering 2 Carburetor Kits (KZ750 2-cylinder 1976-1979 KL18-2464) from z1enterprises.com. Is this the right kit? Also I’m ordering a Petcock from them (SU009-334 Petcock Pingel Fuel Valve DOUBLE OUTLET) since my tank has a screw-on petcock. The reason I’m pushing the Petcock is that the one on there right now is bad; really bad, threaded on all cady-wampus and rusted out; oh and did I mention leaky… I’m going to remove the tank and clean it out to repaint it/fix it if there are any issues
Additionally I’m replacing the air box with two K&N clip-on air filters (K&N RC-0982) and removing the plastic and chrome fenders. I’m thinking I’ll just put them out on Craigs list unless you know someone who wants them…?
Glad to help. By the way thanks for the questions, because they might make good subjects for tip pages some day.
I’ve bought those carb kits in the past too. They should be fine. I wish they had the rubberized tips on the floats like many modern ones do (for a good seal), but they don’t. Other than that, I can’t complain.
I actually bought a petcock like that one from somewhere, but it was single-outlet (to use with a splitter). I stayed away from the double, because it looked like all the double ones were either going to hit the carb, or send the fuel line off in some goofy direction. I should install mine someday too, I’m also kinda’ sick of the stock ones…
Regarding the pod filters… well, I’ll admit, I’m biased and I hate those things. So now that I warned you about my bias 😉 I’ll also tell you that you’ll probably need to run the floats a half millimeter to a millimeter high, and definitely get larger pilots and maybe mains. Heck, you pretty much need larger pilots just because the stock ones are too small outta the box, but there you go… And just be careful when balancing them, and you should be fine.
I already have a mountain of parts, and I don’t know anyone who needs ’em, thanks though. You’re probably best served listing those things on eBay or Craigslist.
Got a problem, there is a jet on the float well/bowl that I was extracting but it broke. I drilled and was using a makeshift extractor and it broke in it. Now I’m having that kind of trouble extracting whats left I a way would destroy the bowl itself. So, I figured I’d call a local Cycle Salvage guy and see what he could do. He offered to sell me the same kind for $200(no idea if it is rebuild or not). I’m thinking that I might take him up on it but I’d hate to have to spend money on something I already have not even knowing if it is in good condition. however, if I did then I’d have a carb to pull parts off if necessary and possibly a set of rebuild kits for the future… should I take the plunge in to that dark abyss of part hording or continue to press on the bowl in the vain hope that it will work out?
Holy cow, don’t pay $200 for *anything* on these bikes! Except paint, I suppose. First, I don’t know why it broke while you were removing it, that’s a bummer. But you should just watch eBay for a replacement piece. Or post on the KZRider.com or Kawasaki Twins Owners Group forum. Post a picture of the part that broke. See if someone has one, etc. And be patient! Impatience costs lots of money….
Don’t worry I didn’t, I was way to put out about the cocky mater-o-fact attitude the salvage guy had. It made me not want to do business with him. I took the bowls to a motor-head friend who saved the day with his masterful skills of mechanics. It took him about 3 hours but he got it out without damaging the bowl; now I owe him a case of beer.
Hi I have a kz750 1980 model just wanting to know if anyone out their has set of carbys . The ones on here are in bits and pieces some missing . Also wanting to know if any other carbys fit this bike
Toast, hello, I have a quick question for you. what is the stock postion for the pilot screw on a 79 twin? I just rebuilt carbs but no where in the manual does it give this setting. Thank you for your time, Kevin.
@ kevin a
Actually, it *is* in the manual… I just checked and in page 14 of my older-style manual, under the “Adjustment” section, subsection “Idling Adjustment”, it explains to start by setting them a 1 1/2 turns from seated. It goes on to say that normally the final result will be within a half-turn from the specified setting.
I run mine at 1 1/2 to 1 5/8 turns out from seated.
I hope that helps!
Toast, thank you for your response. I don’t have my manual with me right now, its at work, but I will check page 14 for sure, but thank you for the info. Got another “situation” for you to ponder. I can’t get engine to start, but by what you just told me, I think I might ne flooding it, I have it set to 2.5 out from seating. Engine turns over, got spark, got New contactors and condensor, adjusted to specs as per manual, but engine will not fire. Any thoughts? Thank you very much for your time.
Toast, by it, I mean pilot screw is 2.5 turns from s bottoming out, 1 full turn past manual prescribed setting. Thank you for your time.
Clear fuel lines are good, but you need to buy the right material, not just any clear ‘fuel’ line. Visu brass cintered in line filters are good to put inline. ITW Fastex produces them in the USA. K&N filters are for racing applications, they do not filter very well in a street enviroment, avoid them like the plague. The best is the OEM paper stye units for prolonged engine life. my 2 cents, mc mech 20+ years…Came across your site looking for a rear master cylinder replacement….Viton is the company that makes the rubber tips on the fuel needles, the line should be the same material, the name escapes me at the moment…Todays fuel kills yesterdays rubber bits in the carbs, ethanol is the culprit.
Thanks for the comments and for stopping by… I definitely appreciate your two cents… Hell, this whole site is my two cents and maybe together we make about three cents after inflation… 😉
The fuel line thing… I remove my fuel lines and filters each year as part of winterization, and you just can’t go wrong with complete replacement when re-installing during winter thaw. So in the end, I don’t have to worry too much about it I guess. Oh, and man I wish I could find rubber tipped Viton fuel needles for the 750, make sure to let me know if you ever find ’em…
Hey thanks so much for going to the trouble to middle this. I just bought a 76 and this is extremely helpful!
Thanks so much! I just did this to mine, super easy and well worth it. On a side note the 1980 kz750 twin I bought, the carbs didn’t have any vacuum lines…can anyone post a few pics of the lines on their carbs so I know where each line goes to and from? Thanks!
Thanks for the info! I’m just getting into a KZ750-h that’s been sitting for years. I’ve cleaned the old fuel out of the very rusty tank and also disassembled the petcock. I can’t seem to find any part listing for the inner-tank fuel filter – do people just leave this part off and run inline filters instead?
That’s what I do. An “H” model, eh…? I’m afraid I won’t be much help with the four-cylinder bikes, I’ve never had one… But thanks, and welcome to the KZ world!
I was wondering if you could help me. My kz750b was running great then all of a sudden started puking fuel out the vent tube on the right carb . Ive tried everything. I adjusted the float both up and down, still the same, I replaced the float needle and seat, no change. What did I miss ? Any ideas? Thanks for any and all help.
I need to know if the “puking fuel” occurs while running or parked. Or both.
Either way, given what you’ve changed, here’s my quick thoughts.. When fuel comes out of the overflow tubes, it means that the fuel is flowing un-regulated. This usually means the petcock seal is not sealing off the tank flow, and/or the float needle is not seating in the float jet for a clear seal. If the problem is happening while parked, it could be a few different reasons, especially if it hasn’t run for a while. This has happened to me for two reasons: 1.) the petcock was not touching fuel as the tank was stored for winter, and every spring the petcock valve needs to “re-expand” after making contact with fuel for a few days or more. It’s a ritual that in spring there is kitty litter below my bikes for the first days/weeks. 2.) if there’s “grit” in your fuel, either from sand in the air, or rust in your tank, that may be too fine for you to see or really feel. You need to run brass-element inline fuel filters to make sure that nearly-invisible grit doesn’t get in your lines and stop the float needle and jet from mating up.
I hope that helps…
Mr. Toast, I have a question about the carbs for the twin. Well, first off let me say I have a kz750 b1 and I was doing a carb rebuild on it and when I went to check and replace (if necessary) the pilot screws, I noticed one was broken. Not sure if from myself or previous owner (as I just bought the bike). I’m not sure if there is a solution other than trying to buy a single carb for the bike or buying a replacement? Thanks for your time!
@jake – Ah, the carbs. In this case, you have yourself quite a pickle. But getting a replacement carb only leads to other issues you might run into, such as stripped screws, damaged passageways, gas-scummy insides, etc., and then assembling & re-balancing, etc. If I were you… I’d try *really* hard to gently.. patiently.. extract that screw. How? I dunno. I’m stumped. But I think I’d try to find a way to drill it out with a jeweler’s drill and get a reverse thread into it and back it out. Or some way to get a small groove cut to get a tiny driver in there to work it out. All that depending on how deep the break line is, and all without damaging the threads. Check out this video: https://youtu.be/dJfkCj3FWBs That’s all I can think of, sorry… – ‘Toast
Update, I tried several things including screw extraction and was unsuccessful. I ended up just buying another used set and one of the bowls had a stripped screw (luck-fully) it was the opposite one I needed. Thus I was able to combine the two good ones quite nicely.
Though, I’ve found a new issue (of course) I’m dealing with now. I’ve just re-installed the airbox and like a novice bought the uni filter because it was the only alternative I could find other than the k&n for triple the price. (Not sure where to find the paper filters, if you know let me know!) or if I should just re-jet the carbs (I later read the comments about how they breath VERY well). I know you said they ran small to begin with anyways. But the issue I’m having (at last lol) is the idle seems to want to stay at 2-2.5k (after fully warming up ~5-10 minutes). If I switch the enrichment cycle on (choke up slightly) I notice the idle drops. Assuming due to the fact that it’s creating a better air/fuel ratio. I’d rather not re-jet the carbs (1 cause I’m tired of pulling the carbs off and 2. Cause I have no clue what sizes I would need). Some more preface too, I know the throttle cables are routed correctly and have enough slack. Butterfly valves are on the first hole of the three at the top of the carb inlet (could be too closed I suppose as well). No vacuums leaks that I can detect using starter fluid while the bike is running. Just installed your fuel line idea as well. Pilot screws are at factory specs (1.5 turns out from seated).
Again, thanks for your time!
@Jake – Gotcha. In a normal situation, turning on the “choke” during idle should make it want to stall. So, like you suspect, you are running lean at idle, which means either too much air (your new filter, or rubber boots not seated, some other leak, etc.), or mis-adjusted pilot screws, or gummed-up fuel passages. Here’s my advice to troubleshoot in this order, for what it’s worth: Make sure your pilot screws are turned all the way in to gently seated, then backed-out 1.75 to 2 turns out. If you have to back the screws out more than that to get it to idle at all…. then… Second, do what I call a “treatment” of Seafoam… get a 16-oz can, dump about 3/4 of it into a full tank of gas (or something like that ratio, if you are using a temp tank)… run it for a few minutes and it won’t do anything. Run it the next day for a few minutes and it might still not have done anything. But as you run it for a few minutes each day, the idle should get lower and lower each day (until it doesn’t do any more good), allowing you to set the screws at the correct level. I’m a “believer” in the Seafoam miracle cure in this way, it’s worked for me on all my bikes. If you do the Seafoam treatment, days have gone by, and you still aren’t at 1.75-2 turns out, then something else needs to be looked at, like the filter or leaks. Oh, and I don’t know anything about that filter, but don’t go rejetting until you have done all that. I suspect that the filter *might* need a different jet size, you you want to establish “normal” baseline first. I actually run stock filters in my 750’s, and have just watched ebay and found them to pop up. Then I just clean them with air from a compressor, and it’s served me well. I’m tempted to build new ones out of paper elements of new filters with the old filter frames, but I haven’t had to do that yet…. Good luck! – ‘Toast Edit: I want to ebay and found this stock used/dirty filter, probably can be cleaned, for $8 (no affiliation to seller!): https://www.ebay.com/itm/Kawasaki-750-KZ-KZ750B-TWIN-KZ750-B-Used-Air-Filter-1978-KB95/402318939147?hash=item5dac13d40b:g:A9oAAOSwRE5aXpnk
Sorry for taking so long to get back to you. I was actually in the process of moving all last month and didn’t have daily access to my bike and it was just a crazy time. Anyways, I’m at the new place with the bike. I made sure the pilot screws (from slightly seated) are now 2.0 turns out. The bike starts off low in idle (right where it should be ~1.2-1.5k) stays there for 1-3 minutes then when the bike fully warms up it slowly works the idle up to 2.2-2.5k. Also, turns out I have the stock filter, I wasn’t sure if I tossed it or not. I swapped the filters out and had the same outcome. So I started the sea foam treatment as suggested, today marks the first day. Also, I completely forgot about this but the previous owner had a two into one exhaust on it (which I hated)…I was able to find to headers and slip on mufflers but the dummies that cut the oem exhaust cut it before the connecting pipe so thus my exhaust is missing the connecting pipe, not entirely sure if that matters in terms of idle (I know I should lose some power though, not that big of a deal at the moment, just want to be able to safely ride the dang thing lol). I’m going to continue with the seafoam and report back in a couple of days. Hopefully by then it will be solid (fingers crossed).
One last question, what do you recommend for starter motors that are going bad. I bought a rebuild kit (that was wrong…..) so I wasn’t even sure if it would be worth my time in getting another or not.
@Jake – Between my two bikes, one is 1.75 turns out, and the other is 2 turns out from seated, in order to run optimally. I’ve never really known why, but I chalk it up to the slight variations between them, and I do mean slight. But like you say, the connecting pipe shouldn’t affect the idle or any of that, just optimal performance under load. But you’ll be fine. Glad to hear about the Seafoam treatment. Remember, if your bike starts to run rough now, it will be because the Seafoam is working and it’s running richer, so go in to 1.75 turns out. If it has not effect, then that wasn’t the problem. And, I hate to say it but I don’t know much about start rebuilds… I had so much difficulty with starter clutches (see my articles about it on this blog) that I ripped those suckers out before they became a death trap, and now I’m kickstart-only.
So to update. I’ve got it idling at 1.1-1.3k now. The only caveat is that I have to hold the throttle forward. As in if I allow the throttle to be left alone the bike likes to idle up to 2.2-2.5k, I’ve chalked it up as throttle cable play (more so because the cable has never been replaced, though I am skeptical that it could be from being adjusted incorrectly as well.) Though, I’ve not gotten it to idle where it does when I hold it closed versus not holding it after adjusting the cable multiple times. Definitely running slightly richer due to the seafoam treatment which is great. I’ll dial the pilot screw back in some. I’m currently at 2.0 turns out from slightly seated. I figured too that I should run the bike slightly “harder” to really get the gunk out. I may look into deleting the electric starter then this winter (planning on doing a complete refresh from the ground up, she needs it). I’ve also developed an oil leak. The leak is coming from the plastic plug and group of wiring behind the clutch lever adjustment panel on the left side of the bike down at the bottom. I’ve tried high temp rtv but since it’s leaking from the ports the cords run through I’m not having any luck. Wondering if you’ve encountered anything like that and if so how in the world did you fix it??? It’s the only thing stopping me from daily-ing it currently. Another quick question too, kick start works for me but it can take up to 5 or more kicks sometimes. Any reasoning as to why? Also, sorry for all the questions again lol.
@Jake – Lots of great stuff there, let me try to hit them one-by-one. That idle is perfect, but yeah, about the cable… You might want to temporarily disconnect your “push” cable and get the adjustment correct without it. I dunno, try to look down there while you twist the throttle and see if the “pull” cable is keeping it open, and if it’s really the “push” cable putting it into position. The springs and pull cable should all snap back to rest at proper idle. And hey, if I haven’t mentioned it, have you “balanced” your carbs? Especially after replacing carb parts? It’s essential to proper smooth running, or you’ll get weird adjustment irregularities. I wouldn’t think you have to run it “harder” as you mention, I personally think the Seafoam really works mostly just due to time. Like sitting overnight after having made good contact in running through. Regarding the oil leak… not to be the bearer of bad news, but you’re gonna have to get in there and replace the gasket, likely. Get a roll of gasket paper from an auto parts store (my advice is to avoid ancient OEM gaskets), and spend an afternoon (beer, cigar, etc) tracing out the sidecover and gently cutting new gaskets. I actually enjoy doing it. And never use metal on mating gasket surfaces! You’ll make a nick, and then you’ll *have* to use RTV. I really, really, really try to avoid RTV… but I don’t blame you if you have to. Yeah, my bike takes like 4-5 kicks after sitting for a week… or a pandemic… 😉 but usually starts first kick after just days. You just gotta dial it in. Carbs cleaned, balanced, and adjusted, and timing set… we’ll get you there… Read the Service Manual, it really is your friend. -‘Toast