KZR's Bikes of the Month for 2024

Kz750 twin

More
10 Jul 2022 05:11 #870119 by Dan77kz750
Kz750 twin was created by Dan77kz750
I am beyond frustration with my bike. 1977 kz750b twin. Running the stock carbs, stock jets, stock airbox, stock rubbers in good shape. Only thing not stock are some open slip on mufflers that came on the bike. Bike generally starts good and run goods, well not anymore. Bike will not restart when hot, will not reliably start when I want it to, has stranded me twice in two days. I'm about to go grab a trailer to bring it home again and it's only 20miles away. 

I'm fed up with these carbs, no matter how much I clean them, adjust them, mess with them, I can not get this bike to run reliable and it's all in the fuel delivery. I'm almost ready to scrap the thing and say good riddance. Spark, compression, valve clearance, etc are all within factory specs. 

Seems to me the only option for replacement carbs are through speedmotoco, has anyone used them on a kz750b and was it worth the investment? I generally love how this bike rides but if I can't take a 30min trip without fear of being stranded by a carb issue this thing is dead to me.

Any suggestions, experiences, or ideas? 

Please Log in or Create an account to join the conversation.

More
10 Jul 2022 06:06 #870122 by TexasKZ
Replied by TexasKZ on topic Kz750 twin
Not starting when hot is almost always an electrical issue. I would first suspect the battery. A dead cell will cause this problem. It may show proper voltage at rest, but under load will show a dramatic drop.
Next I would suspect the coil. When coils reach the end of life, they will often overheat and fail to provide strong reliable spark.

1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

www.kzrider.com/11-projects/620336-anoth...uild-thread?start=24
The following user(s) said Thank You: Dan77kz750

Please Log in or Create an account to join the conversation.

More
10 Jul 2022 06:19 #870123 by Dan77kz750
Replied by Dan77kz750 on topic Kz750 twin
My bike is kick start only due to a dead starter, not sure if that would still make the battery suspect but I will check for sure.

Next, I will go through the manual and see what checks are available for the coil and do that too, wouldn't surprise me i guess, looks original. 

As a New issue, it has always started when cold, now this morning after sitting overnight it won't start and that's new, so once home in gonna check through the battery and coil. Any other ideas? Keep them coming, anything to help get past this frustration block 

Please Log in or Create an account to join the conversation.

  • Scirocco
  • Offline
  • Premium Member
  • Never change a running system
More
10 Jul 2022 07:27 #870127 by Scirocco
Replied by Scirocco on topic Kz750 twin
A clogged tank cap vent can create a vaccum and disturb the fuel flow. 

Please Log in or Create an account to join the conversation.

More
10 Jul 2022 08:40 - 10 Jul 2022 08:40 #870133 by F64
Replied by F64 on topic Kz750 twin
What do your spark plugs look like?
Do they smell like gas?

81-KZ440-D2.
Louis Dudzik's GM HEI ignitor conversion installed 2015 s3.amazonaws.com/gpzweb/Ignition/GPZgmHEImod.html
Motogadget m-unit blue installed 2017.
LIC, NY
Last edit: 10 Jul 2022 08:40 by F64.

Please Log in or Create an account to join the conversation.

More
10 Jul 2022 11:48 #870143 by TexasKZ
Replied by TexasKZ on topic Kz750 twin
A truly dead KZ starter is pretty rare, which makes me think something else is afoot.

1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

www.kzrider.com/11-projects/620336-anoth...uild-thread?start=24

Please Log in or Create an account to join the conversation.

More
10 Jul 2022 13:01 - 10 Jul 2022 13:02 #870153 by Dan77kz750
Replied by Dan77kz750 on topic Kz750 twin
I will be checking everything out tomorrow, I decided to step back from the bike today and start fresh tomorrow calmly instead of today while I'm frustrated.

Thanks for all the ideas so far, I will be updating with what I find along the way. 

I already tried with the gas tank cap open to see if the problem is cured and that was not the case, vent seems clear. 

And my starter is not the bad part even though I state the starter is bad. The starter  spins with power directly applied but some previous owner removed the chain between starter and starter clutch so it really doesn't do anything, just spins freely. I really don't mind the kick start so I'm not gonna approach that issue till much later down the road when doing other work inside the covers.

When the bike is running well and starting like I want it usually starts first or second kick so not an issue for me with the starter. 
Last edit: 10 Jul 2022 13:02 by Dan77kz750.

Please Log in or Create an account to join the conversation.

More
10 Jul 2022 13:12 #870154 by TexasKZ
Replied by TexasKZ on topic Kz750 twin
So the starter motor problem is previous owner inflicted, not electrical. Many previous owners should have their toolboxes welded shut.

Stepping away when frustrated is always a money saver and sometimes prevents gushing blood and broken bones.

1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

www.kzrider.com/11-projects/620336-anoth...uild-thread?start=24
The following user(s) said Thank You: Wookie58

Please Log in or Create an account to join the conversation.

More
10 Jul 2022 13:20 #870156 by Dan77kz750
Replied by Dan77kz750 on topic Kz750 twin
TexasKZ - thanks for the help so far, the previous owner was somewhat of a hack, happily would have his toolbox welded if I could have lol. 

I'll start fresh tomorrow morning and go through this methoidcally. looking forward to getting some testing done and reporting back so i can solve this. Thanks again. 

Please Log in or Create an account to join the conversation.

More
11 Jul 2022 09:06 - 11 Jul 2022 09:52 #870193 by Dan77kz750
Replied by Dan77kz750 on topic Kz750 twin
Alright so, I started by checking voltage and load testing my battery, the battery checks out fine.

Spark plugs didn't look great, so i put a fresher set in for the continued testing. Plugs I pulled out .....
 

I then moved onto testing the coil per my sevice manual. The manual says to set my meter to rx100 for the primary but my meter only goes to 2k ohm. When I tested that I got .002 for my range
 

I then tested across the secondary using the plug leads and my reader didn't seem to show anything.....

 


So should I assume the coil is bad even though it started a few times before i began my testing. It still wasnt a reliable start and shut off at idle a few times and still struggled to restart when hot 


Now for a twist, after reassembly the bike starts easy. Gonna go out in a few and run it till the motor is hot and park it and try the restart
Last edit: 11 Jul 2022 09:52 by Dan77kz750.

Please Log in or Create an account to join the conversation.

More
11 Jul 2022 11:11 #870195 by Wookie58
Replied by Wookie58 on topic Kz750 twin
Your primary reading is 2 Ohms ( it's on the 2k scale so you need to move the decimal point) as the meter only has a 2k scale it can't measure he secondary at 10k

Please Log in or Create an account to join the conversation.

More
11 Jul 2022 12:03 #870204 by Dan77kz750
Replied by Dan77kz750 on topic Kz750 twin
Awesome, thank you for clearing that up, I will look for another meter for the secondary, I was getting between .003 and .004 after I checked again, so I'll assume that's OK now that I understand the meter better 

Please Log in or Create an account to join the conversation.

Powered by Kunena Forum

If you like KZR Please consider making a donation. Thank you.

KZRider is free, but not without cost.

Please consider chipping in a few bucks to help cover the cost of running the KZR servers.