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TOPIC: 1976 KZ750B1 with BS38's ran well, now wont start yet will hold a high rev.

1976 KZ750B1 with BS38's ran well, now wont start yet will hold a high rev. 15 May 2019 16:03 #803934

  • Charles 750B
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First, I'm new here. Second, I have read tons of KZrider posts for two years now regarding many different aspects of my bike. I am out of ideas (I restored a 280zx from 16 years of sitting and it was easier than getting this bike running). I will try to describe exactly what I know and I am trying to be as respectful as I possibly can, keeping in mind not to be vague! I know this is the carb field but I'll list the other running stuff for helpful info.

1976 KZ750B1 BS38 Carbs
Gas tank lined with Kreem (as far as it looks, no goo is coming out petcock)
Oiled air filter, new carb holders (fixed vacuum leak)
Strong purple/white spark
good compression ~150psi each side
engine is timed correctly (I drove it 200 mileslast week on highways and backroads) and timed cams to fsm.
MAC exhaust two into one.
Cleaned advancer from 79' 750B and when bike ran a week ago, checked timing and went exactly to 30degree tick marks at 4000rpm

Now for carbs.

About a year ago I bought rebuilt/cleaned BS38 carbs for KZ750 twin.
40 pilot, 125 main, 4-hl12 jet needle
I can not think of anything else to say
I went through carbs cleaning jets and making sure no obstructions exist in all air passeges today, May 15th.
Can gas get to pilot screw but not to carb bore? I ask because the pilot screw was wet with gas when I pulled it after a couple of kicks with petcock open, but no start.

I love my bike so I only appreciate normal people who want to help, not trolls which through my 280zx and 750b, I have seen too many times in the forums...
Im 20 years old so I dont need any sass...

I just know its a great way to travel.

Please help if you can! I will try to post pics if asked for them (what exactly do I need to get pics of in that case?)

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1976 KZ750B1 with BS38's ran well, now wont start yet will hold a high rev. 30 May 2019 22:53 #804922

  • fastfrank
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Hi, Charles:

I, too, have a twin, and am new to this forum.

I’ll have to assume that you meant that it is hard to start, but it will start, since it runs at high revs.

As always in troubleshooting, first be suspicious of whatever you recently changed. Words to live by.

The BS38 carbs are fairly new to me, as well, but having worked on lots of carbs over the years:

My first guess is that you’ve got a stuck choke... but maybe not. Does it return to the off position ok?
My second guess is that you have a stuck float. Sometimes tapping on the bowls will free up a stuck float.
I’d make sure you don’t have a throttle cable issue, too tight or binding or stuck or misadjusted. Are the butterflies closing ok?
I suspect you’ve already figured out how to set the idle, but recheck. I had to adjust mine quite a bit recently, after a choke issue got resolved.
Could be numerous other carb issues... it is worth it to completely go through them, check all jets and orifices, disassemble & dip in Berryman (without gaskets, o-rings), etc. My experience is that pilot jets seem to clog first, but anything will. Most folks don’t check air jets. Use small wire like from a bread loaf twist-tie to poke through the small orifices in the jets.
Drain the carb float bowls, and see if there is no gas, or too much pouring out (stuck float).
You may need to clean your plugs and drain the float bowls each time you start it.
Those are the first thoughts off the top of my head.

BTW, my tank was Kreem’d by the previous owner, and it is starting to peel off, maybe from the 10% ethanol in the gas here.
I use an inline fuel filter, but I’m watching it carefully.

Good luck... sounds like it is well worth fixing.

fastfrank (I’m a newbie here)
(rapidly aging and not so fast anymore)
78 KZ750 Twin
83 GS1100ES
99 ZRX1100
13 GW250

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1976 KZ750B1 with BS38's ran well, now wont start yet will hold a high rev. 31 May 2019 05:13 #804929

  • old_kaw
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A high idle is usually caused by a vacuum leak of some sort. That is assuming everything else is right.

1981 Kawasaki Kz1000K1
Located in the Saint Louis, Missouri Area.

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1976 KZ750B1 with BS38's ran well, now wont start yet will hold a high rev. 31 May 2019 07:21 #804945

  • TexasKZ
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Is it possible that the balance tube that goes between the two carb holders has come loose or cracked? Could the carbs have backed out of the carb holders enough to leak?
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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1976 KZ750B1 with BS38's ran well, now wont start yet will hold a high rev. 31 May 2019 08:34 #804950

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Charles 750B wrote:
First, I'm new here.

<snip>

Gas tank lined with Kreem (as far as it looks, no goo is coming out petcock)
<snip>

Im 20 years old so I dont need any sass...

<snip>

Please help if you can! I will try to post pics if asked for them (what exactly do I need to get pics of in that case?)


At 20 years old you are on the right path to making friends and influencing people. Sometimes certain comments are easily taken out of context, and it is usually best not to jump straight into "attack mode" when someone new is asking for help or while reading the comments. Sometimes the lack of reading comprehension is rampant in this day and age, or the comments was not fully understood. I see this all of the time here, there, EVERYWHERE. Some ego's can be too great to think someone else might have a different opinion. Just sayin.

Keep in mind that most who do reply to your questioning > actually are trying to help<, it's up to you to be able to decipher and actually use the info that others take their time to share while passing on their own experiences. It's all a big guessing game, especially with no pics. We have yet to see ANY pics of this bike. In case you haven't notice yet.. A pic is worth 1000 words. It helps put things into the proper perspective.

That said a few overall pics would show what WE are dealing with and some closeups of the carbs / holders, etc. Also be sure to insert the pics into your topics, so that they show in your comments, not a thumbnail. Some moderators will fix it for you a few times, but want you to learn how to do it yourself. I googled the BS38 carbs high idle and and got 13,000 results in .055 seconds. They were also used on the Yamaha XS-650 and there is a ton of info and video's on them at your disposal.

This is my 81 Kz1000M1. I sold this bike years ago. The pic shows the carbs well.


Why Kreme? Tank liners IMHO are meant to fix pinholes after the tank is cleaned of iron oxide (rust). I spent a lot of time / money removing the kreme in my tank, then I used $100.00 worth of metal rescue to remove the rust that was under it.

1981 Kawasaki Kz1000K1
Located in the Saint Louis, Missouri Area.
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Last edit: by old_kaw. Reason: hmmmmm

1976 KZ750B1 with BS38's ran well, now wont start yet will hold a high rev. 31 May 2019 10:55 #804960

  • loudhvx
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Kreme tank with a bike that won't hold an idle. That is exactly what I'm fighting.

The Kreme seems to dissolve, then somehow re-solidifies in the pilot jets. To run the bike you just have to rev it beyond normal idle. I've just been searching for a new tank that doesn't cost more than the bike.

If you blast through the jets and ports it will usually run ok for a few days. Eventually one or more pilots will stop functioning. Eventually the intermediate circuits will clog if your carbs have them. Then you basically only run on the main so you have to rev it pretty hard to keep it running.

I really hope it's something simpler for you, but I fear you may be fighting the same problem I have.

Vac leaks can cause similar, but much less pronounced symptoms. It's hard to check for vac leaks if you can't get the bike to idle at all.

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Last edit: by loudhvx.

1976 KZ750B1 with BS38's ran well, now wont start yet will hold a high rev. 31 May 2019 16:02 #804966

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Vacuum leak? Yup, been there a few times, too. I started with choke, since that was what I was fighting just a week ago with the same carbs, and the symptoms were pretty similar.

I don’t doubt the Kreem angle at all... I keep having similar issues. I can see the stuff peeling loose in the tank... suspect I’ll have to remove it all and redo the tank. Right now I have two separate inline filters going, but they won’t stop liquified suspended gooey Kreem, I suspect. I had everything running well for a while, after tearing into the carbs (yes, found a clogged pilot), but then the same issues started again.

fastfrank (I’m a newbie here)
(rapidly aging and not so fast anymore)
78 KZ750 Twin
83 GS1100ES
99 ZRX1100
13 GW250
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1976 KZ750B1 with BS38's ran well, now wont start yet will hold a high rev. 31 May 2019 16:20 #804970

  • Scirocco
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I am not a Kreem fan, I use only POR15 de-rust and seal kits for a fuel tank.
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Last edit: by Scirocco.

1976 KZ750B1 with BS38's ran well, now wont start yet will hold a high rev. 01 Jun 2019 09:11 #804990

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Scirocco wrote: I am not a Kreem fan, I use only POR15 de-rust and seal kits for a fuel tank.


I'm not a big fan of any tank liner, except in the cases that a tank leaks. The liners seal in the crud while filling small leaks, except in the real world, the crud needs to be removed. A totally clean bare metal tank is best, with no chemicals / coatings to interact with whatever fuel is put into them. Spend whatever money and clean it out properly, then there is nothing to plug up anything.

I had also been having repeated problems with contaminated carbs, flooding, intermittent fuel related performance issues, etc. My main reason for removing it was not because ot the carbs plugging, it was because it just looked like crap every time I fueled my bike. I didn't connect the dots at the time, mainly because it was in the tank when I bought Kz1000 #2. It was at least 10-15 years old at the time. (assumed it was well cured and hard). It may have been the main reason it sat as long as it did. It's always easier to toss in a tank coating, rather than actually cleaning the tank and fixing it right.

>If< I were ever to ever use a liner in a tank, I would also prefer the POR-15 kit. I have used POR-15 to paint certain things, and lemme tell ya, you better be wearing rubber gloves, because if it gets on your skin, it will need to wear off. It sticks just that well. It will not just wipe off with lacquer thinner or mineral spirits.

POR-15, the worlds worst frame paint. It's almost impossible to do a nice job with the stuff. :woohoo:
1981 Kawasaki Kz1000K1
Located in the Saint Louis, Missouri Area.
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