Topic: Not running well after carb clean. Please help.

[SkullDanny]

Hi guys I'm new to the forum and just getting my head around it so I apologise if this is already covered.

I bought a 76 CB750 k a few months ago. I was so excited that I changed the oil out, clean up all of the electrical connections. New pugs, bulbs and cables and fired her up. She ran first kick sounded slightly clunky. I tensioned the cam chain and that was that. She ran perfect every time I fired her up. As far as I was aware she had not been run for 2 years prior to my purchase.

So.. I decided to clean the carbs. I pulled them cleaned and checked all jets, floats needles etc. everything seemed fine except a bit of crud in one of the main jets and a pilot jet ( not in the same carb ).

I fixed everything back to gather being as careful as possible.
Now she struggles to start with and without choke. Slightly better with. When she does fire the revs drop and cut out when I apply throttle. I have checked all of the boots for leaks. I can only find one screw in the side of the carbs (not the plug screw).i can't get her running long enough to do any tuning.
Thanks

Dan

[calj737]

You probably need to verify the fuel level in your carbs. And, pull your plugs. What do they look like after repeated attempts to start the bike?

[Phinn]

How did you clean out the crud? Is it possible you pushed some of the crud further up into the circuit where you can't see it?

Is there a divot in the tangs on the floats?  The vibrating float valve will wear a perfect divot into the tang that looks like it belongs there.  It doesn't.  If possible, you can file the divot away, or otherwise you have to replace the float.

Did you change the air-fuel mixture screws? Pull them out and clean out that part of the idle circuit?  There is a very small o-ring and washer under each screw, so be careful when you take the screw out.

[SkullDanny]

Hi Guys thanks for getting back to me. I've had a negative reception in another forum.

The plugs have a layer of sut on them. I'm nowhere near experienced enough to clean the Pistons yet. A single cylinder bike is abouty level. The thought of the overhead cam scares me a little.

When it was running the plugs were a tan colour no sut.

I cleaned the bowls, main jets, pilot jets, air screws, checked that the floats actually still float. I did not remove the needle however. To clean I used carb cleaner all over. I was as gentle as can be with the jets, screws and floats. But more aggressive on the bodies and bowls. I used air to blow everything out .

Regarding the tangs on the floats I am not sure of what they are.

I may have pushed crud deeper into the circuit. I did not completely dismantle the whole unit.

Thanks again
D

[harisuluv]

Picture of your bike please so we know what we're dealing with.

May I ask why you decided to clean the carbs or do anything mechanically considering "She ran perfect every time I fired her up."

[SkullDanny]

I thought because it had been stood for at least 2 years it would only be a matter of time before something clogs up.

My error.

[SkullDanny]

Also.

When I put the carbs back in I also installed the clamps for the exhausts as these were not on the bike when it was delivered.

Could this have caused any issues?

[flybox1]

Interesting that the bike ran well with dirty carbs and possible exhaust leaks
you did the right thing fixing its shortcomings.  It seems thos is just ans air fuel mixture issue.
Answer the following:
Air filter type
new or old
main and pilot jet size
brand
did you install a carb rebuild kit?
Idle mixture screw setting
did you add new exhaust crush washers?

[SkullDanny]

The air filter is a Honda replacement part. Though this was already installed. The owner before me had bought it I put it in.
Main jets are 105, pilot jets are 40 all original i did not use a carb rebuild kit.
Idle mixture screw is around 1-1/4 from seated maybe a tad less.
I did not replace the crush washers.

[Phinn]

Hi Guys thanks for getting back to me. I've had a negative reception in another forum.

The plugs have a layer of sut on them. I'm nowhere near experienced enough to clean the Pistons yet. A single cylinder bike is abouty level. The thought of the overhead cam scares me a little.

When it was running the plugs were a tan colour no sut.

I cleaned the bowls, main jets, pilot jets, air screws, checked that the floats actually still float. I did not remove the needle however. To clean I used carb cleaner all over. I was as gentle as can be with the jets, screws and floats. But more aggressive on the bodies and bowls. I used air to blow everything out .

Regarding the tangs on the floats I am not sure of what they are.

I may have pushed crud deeper into the circuit. I did not completely dismantle the whole unit.

Thanks again
D

Sooty plugs means that the mixture is now too rich.  That could be due to lack of air flow (hence the question about your air filter), or just the need to adjust the idle air-fuel mixture screws. 

I'd also recommend taking the air-fuel mixture screws out, cleaning all the components, and blowing out that circuit, just to be sure the seat you're feeling isn't affected by some blockage. 

The float tang is the little metal tab on the float that makes contact with the float valve.  The float valve has a little spring-loaded pin sticking out of its bottom end, which is what helps the valve push upward when the float's tang pushes it up from below (due to a full fuel level). 

Here's a picture:



Oh, wait, that's not it.  Here's the right one:



The spring-loaded valve pin will wear a divot into the little metal plate (the tang) that it constantly touches.  That divot can cause the valve to get out of alignment and not seat properly, especially if you took the whole thing apart and upset the alignment between valve and float tang even by a tiny bit.

My advice is to take the carbs off again, check the float tangs for divot wear, and either file the divots out, or replace if necessary. 

Also, it's not possible to see the circuits completely, even if you take it all apart 100%.  Look at a cutaway diagram of your particular carb model to see what the fuel-flow paths look like.  You can blow air and carb cleaner through them, and some people use little copper wires or plastic cleaning picks to get them really clean.  A soak in an ultrasonic bath is the only way to be 100% sure. 

[harisuluv]

Really hard to make any educated guesses.  Could be dozens of different things.  Something changed, unfortunately only you know exactly what changed.

[ekpent]

 Next time you can get it started and warmed up a bit check the temps on the exhaust head pipes to see if any are colder than the rest so you can start narrowing down your problem. Might only be running on 2 or 3 cylinders, always nice to know when troubleshooting. If for instance 1 & 4 or 2&3 were colder it could be dirty points. If maybe one is out it could be that carb is not right. Hopefully floats etc were all put back together correctly. Were all 4 plugs sooty ?

[SkullDanny]

Hi guys.
When I can get some idle all 4 headers are hot. I would say about the same ( burnt fingertips ).

All 4 plugs are sutty and at the moment all four carbs are set at the same air screw adjustment. I noticed some popping when I got down near the pipes. Like subtle misfire.

I will pull the carbs and give them a thorough clean. I'm just looking up places that will do ultrasonic cleaning near me. I will also take pics of the parts.

Just ordered some new crush gaskets. (Just in case)

I'm also going through my shop manual to see if I get an epiphany.

[SkullDanny]

Hold on a second.
My fuel tank is away for painting at the moment.
I have been using an old mower tank that doesn't have a vent.( I think it did at some point but it is severely banged up)

The fuel may not be draining in to the carbs properly.

If I open the cap it should change the pressure in the tank and allow it to flow.
I can't do it now as much neighbours are not a fan on motorcycles or any noise in general.

Honestly I have the subtitles on my TV all the time, it's ridiculous.

[harisuluv]

Let me point out that I disagree when someone said that the only way to be 100% sure is ultrasonic.

Ultrasonic isn't magic, it can be effective in some cases, and in others does next to nothing.  Now an ultrasonic's cleaning is highly dependent on what kind of solution you use.  If you want to get rid of lacquer/varnish, you need some harsh detergent.

Ultrasonic also does poorly with the hardened crusty stuff.

I use ultrasonic cleaning as a compliment to soda blasting.  It removes some of what the blasting might have missed and whatever is left in crevices for the most part.  That and any residual baking soda dissolves.

There are plenty of jets that I could throw in my industrial ultrasonic cleaner and they won't be any better than when they went in.  If you want to make sure a jet is clean, you can verify that VISUALLY.  Spraying it with carb cleaner and then compressed air is worthless as far as verification unless you confirm that the hole is cleared visually, just by holding it up to the light.

[harisuluv]

Hold on a second.
My fuel tank is away for painting at the moment.
I have been using an old mower tank that doesn't have a vent.( I think it did at some point but it is severely banged up)

The fuel may not be draining in to the carbs properly.

If I open the cap it should change the pressure in the tank and allow it to flow.
I can't do it now as much neighbours are not a fan on motorcycles or any noise in general.

Honestly I have the subtitles on my TV all the time, it's ridiculous.

Probably not, if that were the case you would be initially ok and as the bowls were drained the mower tank supposedly wouldn't refill the bowls fast enough cause they were restricted.  You are having problems initially though.

More likely that there is a bunch of crap in an "old mower tank" and that contaminated something or introduced debris.

I'm not confident of the mower tank being your problem though.

[Phinn]

Let me point out that I disagree when someone said that the only way to be 100% sure is ultrasonic.

Listen to Harisuluv. I am proud to have precisely one (1) bike's worth of hard-earned experience, but he's one of our bona fide experts.

[mrbreeze]

Shot in the dark...........are the choke plates fully opening when you turn off the choke?

[SkullDanny]

Thanks for all of the help so far. You are right it's not the mower tank. I'm going to spend a few days cleaning and checking and checking again.

The air box boots look a bit stiff so it may be worth replacing those as well.

Danny

[SkullDanny]

So I popped the cb fuel cap over the mower tank hole and the bike started and idled. Also took the choke off and it stayed on.

I noticed leaking fumes from header#2 and the revs appears to be sticking on. Having said that I removed the air box and just attached the velocity stack boots to stop any fuel from spitting back.
 
All headers are still heating up.

[flybox1]

So I popped the cb fuel cap over the mower tank hole and the bike started and idled. Also took the choke off and it stayed on.

I noticed leaking fumes from header#2 and the revs appears to be sticking on. Having said that I removed the air box and just attached the velocity stack boots to stop any fuel from spitting back.

why not nip up the exhaust clamp bolt/nut to stop the leak?
...instead, you just made the cylinders run lean 

[SkullDanny]

I will nip it up and see if the revs settle down.

[flybox1]

I will nip it up and see if the revs settle down.

please put the complete airbox assembly back on as well.