Topic: Leaking needle jet?

[shortside750]

This is my first post. I've got a lot of good advice from this forum over the last year. So thanks to all of you who post here and help the less mechanically inclined like myself. I'll give you a little background on the problem I'm having.

I've recently rebuilt a '74 CB750. I've gone through the entire bike and fixed all of the previous owner's mistakes. The last big problem that I'm having is with the carbs. I'm running an open exhaust and pod filters. I switched the main jets to 120s. They had 105s in them stock.

I started the bike up yesterday and it was idling hard. I tried giving it a little throttle, but if I give it the slightest bit of gas, it will die. It won't start with the choke in either. It's giving all of the symptoms of getting way too much gas.

I pulled the filters off and tried running it after I noticed what looked like fuel squirting out of the filter elements. Sure enough, the inside of the carb bodies were all wet with fuel. The thing that confuses me is why it's happening to all 4 carbs.

I started it back up again and watched the needle jet. It looks like there is fuel gushing out. I pushed one out and checked it, and everything looked fine. Is there supposed to be an o-ring or washer that goes with them when you press them in?

The last thing I tried was removing the fuel lines to see if it would run better as the fuel went down, and it didn't make a difference. I did notice that fuel would still gush out of the needle jet though.

I inspected the float level and float valve sets and they are all fine.

Any advice you could give would greatly appreciated.  

[Flying J]

your float needle might  is leaking. Fuel is supposed to come through the needle jet but if your floats are not shutting off the fuel when it gets to high then its going to keep filling until it reaches a way out

[shortside750]

your float needle might be leaking.

When I pulled them they were pretty clean. One had a ring faint ring around the tip, but when I scratched it with my finger nail it was smooth. So I know it's not pitted.

I've been pouring over my manual and I can't see anything that would indicate that I'm missing parts. Washers or o-rings. I wish I had another set of carbs to test with.

[shortside750]

your float needle might  is leaking. Fuel is supposed to come through the needle jet but if your floats are not shutting off the fuel when it gets to high then its going to keep filling until it reaches a way out

I thought that might be a possibility, so I pulled the fuel lines to see if it would help any. I figured if it was getting too much fuel in the carbs, then eventually as it used up fuel it would start to run normal. As of yet, it hasn't made a difference. I guess it will have to double check them in the morning. Thanks.

[Flying J]

YOUR FLOATS ARE NOT STOPPING THE FUEL! when you set the float height it is to shut off the fuel at a specific height. If the fuel is going above that height its because its not being shut off by your floats. You may need to clean the seats of the float needle with a q-tip, you may have a float that is getting stuck or hung up. There are a few possibilities, but you are probably not missing anything, your 30+ year old carbs just need a little more attention.

[Flying J]

Has it ever run right with that jetting? All you did is replace the the main jet and put on pods and an open exhaust? Did you adjust the points and the valves and the timing and the plug gap? As much as i hate to say it, When you start getting away from the stock setup it getts harder and harder to make the bikes run correct.

[shortside750]

Has it ever run right with that jetting? All you did is replace the the main jet and put on pods and an open exhaust? Did you adjust the points and the valves and the timing and the plug gap? As much as i hate to say it, When you start getting away from the stock setup it getts harder and harder to make the bikes run correct.

I started on the valve clearances after I noticed the fuel problems, but it was the last thing I did before I called it a night. I'm going to double check the points tomorrow. I did it when I put the motor back in the frame and first started it. It wouldn't hurt to do it again.

When I first got the bike it already had drag pipes and pod filters. It ran, but it ran poorly.

[Flying J]

You may want to go back to the original jetting and sort out your problems first. Jetting is not as easy as just trowing in a set and then it runs better. The main jet really only controls the wide open range. If you just change the main you are neglecting the mid and low jetting. That being controlled needle, cutaway and pilot. So my suggestion is to start with your carb problems. If you know the bike ran on stock setup then go back to it. Make it run as best you can by adjusting timing, valves....ect. then at that point if its not running right determine if it is running lean due to the jetting and then change the jets and check again. From my past experience re jetting is the easiest way to solve a problem but is hardly ever the solution. It usaly ends up being something totally different. SO what im saying is dont assume that the jetting is your problem until you have proved that it could not be anything else.

[shortside750]

Update: I went back over the valve clearances, point gap and timing. I quadruple checked my work. The engine is running pretty damn good now. I must have don't something wrong along the way.

I know that the carbs are one of the last things you want to change when tuning your bike. I guess I'll serve as a lesson to the rest of you. Thanks for your help