CB750K Help continued

[stevenolts]

I got it running but now it is pouring gas out of the overflow tubes. Not when turned off as before I cleaned the carbs but when running. The more throttle I give it the faster it pours out.

I posted about this last week / thank you for the comments.

I guess it was flooded last week when I posted because when I tried it today the bike fired up. I warmed it up and then slowly backed the choke off until completely closed as it warmed up. I adjusted the main idle knob under the carbs until it idled correctly. It will shut down and can be started back up. Fair throttle response for now until I can sink the carbs.

I just emptied the gas out last week and filled a gallon of fresh gas. Petcock is on the low fuel setting. Do you think maybe there is shit in the tank that clogged the carbs? I just bought an in line filter but have not installed yet.

[Bill1584]

It's been many years since my Suzuki GS750 days, so please forgive me if the following has no bearing on your carbs. If the carbs have fuel bowls, they will have a float and a needle valve to regulate flow. Excess flow would overflow through the tubes. If this is the case for your carbs, have you checked the floats and valves? Just a tiny bit of crud on the valve will cause it to stay slightly open. Also, your floats need to float in gasolene.... Again, I do not recall whether this even applies to the mikuni or mikuni style carbs of the day.

[stevenolts]

That is what I think is the problem and most likely caused by the tank being mixed around when emptying the stale gas. I just did a quick clean of the carbs since I had them off for another reason. The main problem was the overflow tubes leaked when the engine was shut off. I think now there is crud in there holding them open or a stuck or bad float.

[Bill1584]

Keep me posted please, and good luck! I have a feeling that sooner than later I will search out a metric 4-banger from the 70's. Knowledge is power. If I can make it safe and reliable to ride, then it would be fun to cat around on it sometimes.

[DMAGOLDRDR]

An easy task to perform to flush the needle valves is,,,

Fire the engine and as it is running shut the petcock off. Keep the engine running until it starts to die from fuel starvation. Then open the petcock and sometimes the rush of fuel into the bowls will wash out fine debris around the needle valves and seats.

Sometimes it works and sometimes it doesn't but it is easy to do.

[Dirtstiff's F6B]

It's been many years since my Suzuki GS750 days, so please forgive me if the following has no bearing on your carbs. If the carbs have fuel bowls, they will have a float and a needle valve to regulate flow. Excess flow would overflow through the tubes. If this is the case for your carbs, have you checked the floats and valves? Just a tiny bit of crud on the valve will cause it to stay slightly open. Also, your floats need to float in gasolene.... Again, I do not recall whether this even applies to the mikuni or mikuni style carbs of the day.

+1

[Bill1584]

An easy task to perform to flush the needle valves is,,,

Fire the engine and as it is running shut the petcock off. Keep the engine running until it starts to die from fuel starvation. Then open the petcock and sometimes the rush of fuel into the bowls will wash out fine debris around the needle valves and seats.

Sometimes it works and sometimes it doesn't but it is easy to do.


That is an excellent suggestion. My memory is not what it once was, but that reminds me: Alternatively, if you remove the air filter[s] and run the motor, you can rev it up a bit and quickly cup your hand over the air intake for each carb, one at a time. Listen for the motor to bog, and remove your hand. This will cause vacuum to rapidly suck most of the gas from the bowl and really swirling things around in there. All the fuel has to go rapidly through the valve, so it could knock the crud on through. Used to work with single barrel automotive carbs, too. Instant tuneup!

Note: If you leave the intake covered too long, you could also just flood that cylinder, so not too long. ALso, use a rag, not just your hand. That much fuel and you could backfire that cyl, which hurts like hell.

[Old Ryder]

One of the big problems from bikes of the 70s-80s that sat for a long period of time, was that the inside of the gasoline tank would rust and clog up the fuel system. I remember reading and buying a chemical that would paint your tank from the inside. Prep work included putting a bunch of BBs in the tank and swirling them around to clean the rust.

I also dealt with carb floats not sealing. Also, if one of the floats has a hole in it, that will cause the same problem. Or it may be---with the ethanol in the gasoline, the rubber seals have eaten away. Seen that, too.

[stevenolts]

I started the bike again today and the overflow tubes were not leaking when the bike was running. I took it for a test ride and it is running real strong. Once I sink the carbs and make a few adjustments to the idle it should be running great.

When I got back and put it away I saw gas on the ground. It may be only when the engine is off now like before I started. It is freezing today / yesterday was 68 degrees. So that will be all for today.

I will pick it back up again in a few days / hopefully it will be warmer then. I will pull the carbs again and do a little better job of cleaning. I plan to clean out the low speed jet with an e-string (I have one ready) / I will also polish the float valve seat and check the tubes for leaks to stop the pissing fuel out of the overflow tubes.

A few questions:

1. Do I just polish the seat? Do I do anything to the float valve rubber tip. When I lapped the valves on my lawn mower I put compound on the valve and spun it with the suction cup rod to match the valve to the seat.

2. Should the floats / float valve be springy once installed? I see videos with a different version where there is a spring in the assembly / I have a 81 CB750K which has no spring or adjustment as far as I can tell.

3. Where would you buy replacement O-ring clamps for tor the carburetor engine side boots. The ones I have don't seem to get tight enough and the carbs seem to slip out if moved a little. I see that Randak's has them but they are very expensive. I replaced the air box side boots / I ordered through Honda parts.

I am learning a lot along the way.

Thank you for your help. You guys are great!!!
Steve

[stevenolts]

One thing I already knew but has been driven into my head again is how great fuel injection is.
I use fuel conditioner in my tanks for the motorcycles, lawn mower, and trimmer.

[Old Ryder]

I started the bike again today and the overflow tubes were not leaking when the bike was running. I took it for a test ride and it is running real strong. Once I sink the carbs and make a few adjustments to the idle it should be running great.

When I got back and put it away I saw gas on the ground. It may be only when the engine is off now like before I started. It is freezing today / yesterday was 68 degrees. So that will be all for today.

I will pick it back up again in a few days / hopefully it will be warmer then. I will pull the carbs again and do a little better job of cleaning. I plan to clean out the low speed jet with an e-string (I have one ready) / I will also polish the float valve seat and check the tubes for leaks to stop the pissing fuel out of the overflow tubes.

A few questions:

1. Do I just polish the seat? Do I do anything to the float valve rubber tip. When I lapped the valves on my lawn mower I put compound on the valve and spun it with the suction cup rod to match the valve to the seat.

2. Should the floats / float valve be springy once installed? I see videos with a different version where there is a spring in the assembly / I have a 81 CB750K which has no spring or adjustment as far as I can tell.

3. Where would you buy replacement O-ring clamps for tor the carburetor engine side boots. The ones I have don't seem to get tight enough and the carbs seem to slip out if moved a little. I see that Randak's has them but they are very expensive. I replaced the air box side boots / I ordered through Honda parts.

I am learning a lot along the way.

Thank you for your help. You guys are great!!!
Steve

http://www.partzilla.com/parts/search/Honda/Motorcycle/parts.html?gclid=CJnsrc-UvtECFRGHswodxrsIiA

[DMAGOLDRDR]

Check out Randakk Cycle Shack. He is a 70s Honda Motorcycle restorer and supplies hard to find parts. I have used him a few times for my 1978 and 1979 GL1000s

http://randakks.com/collections/honda-dohc4

As you can see from the pic's I like my old Honda.