Author Topic: No start - troubleshooting help  (Read 2500 times)

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Offline ekpent

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Re: No start - troubleshooting help
« Reply #50 on: July 01, 2022, 09:24:07 PM »
I see you mentioned that after your ride on the K4 750 the whole back of your bike was covered with oil. That happened to a bike I got running for the first time in many years that I had bought. The leak was severe and dangerous and for me it was a plugged up long rubber breather hose that runs off the backside of the valve cover nipple. Check yours if its attached and still there or the nipple fitting.. In my case an insect/paper wasp had built a nest of some type in it plugging it up making pressure and making oil come out the oil tank vent and all over the back of the bike.
  Here's a pic of some of the chud that was in the vent hose causing the problem, hopefully yours also.  ;)
« Last Edit: July 01, 2022, 09:26:43 PM by ekpent »

Offline Bigmant

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Re: No start - troubleshooting help
« Reply #51 on: July 03, 2022, 07:40:46 AM »
I see you mentioned that after your ride on the K4 750 the whole back of your bike was covered with oil. That happened to a bike I got running for the first time in many years that I had bought. The leak was severe and dangerous and for me it was a plugged up long rubber breather hose that runs off the backside of the valve cover nipple. Check yours if its attached and still there or the nipple fitting.. In my case an insect/paper wasp had built a nest of some type in it plugging it up making pressure and making oil come out the oil tank vent and all over the back of the bike.
  Here's a pic of some of the chud that was in the vent hose causing the problem, hopefully yours also.  ;)

I actually haven’t had the vent on at all, which maybe is another problem… you’ve actually just reminded me that I need to put it back on haha.

Today is the leak check day though! This leak is the only thing stopping me from getting it out on the road for a long ride, so I need to figure it out!
‘74 CB750 K4 Owned by my father and now me

Offline Bigmant

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Re: No start - troubleshooting help
« Reply #52 on: July 03, 2022, 01:42:32 PM »
Good news! Found the leak, or I guess I should say, the second leak. There is a nipple, on the back of the crank case, that goes to the back of the oil tank. I forgot to attach the e old oil line when I reassembled everything, probably because I just assumed it was a vent line. But in fact it will leak if you don’t have the two nipples connected!

I went ahead and took the carbs apart and moved the needle two clicks up and rebalanced the carbs. So second from the top, and somehow I have made the bike worse. I used to be able to give the bike more throttle and push past the 3000rpm flat spot, but now it just gurgles/whooshes like it’s sucking air and will not get above 3000 in any gear. 1/4 throttle works fine, but anything more than that doesn’t work.

For reference to those that want to help, I have:
4-1 Carpy Yoshimura exhaust
Air filter pods
120 main
40 idle
2nd ring from top of the needle
1 turn on air adjustments

Since I made the bike leaner by putting the needle farther down (moved clip up), I now assume that perhaps I was lean to begin with and need to go the opposite direction. Before I messed with it today, the needle was 4 down from the top. Does anyone believe that being at the very bottom ring of the needle will help?
‘74 CB750 K4 Owned by my father and now me

Offline Bigmant

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Re: No start - troubleshooting help
« Reply #53 on: July 04, 2022, 10:42:02 AM »
Update:

Oil leak is fixed! Took the carbs apart again and moved the needle all the way down and re-synced, so full rich and it made a very noticeable improvement, but there is still a flat spot more around 3500-4k rpm range now.

So the bike is officially semi-ridable, I think the next step is to go up in main jet size, maybe like a 125 and start with the needle back in the middle. Any thoughts?


‘74 CB750 K4 Owned by my father and now me