Topic: Once Again, I'm Stumped. NEED HELP

[SamTheBikerMan]

Hello all. I have a 1978 CB750F. I need some help. I have been working on my bike a lot recently trying to get it to run really nice. The carbs are spotless and the bike starts easily and idles pretty good. But sometimes it doesnt run on all its cylinders. usually after about 10 mins of riding it starts to fire on all 4. So i was thinking electrical. So i cleaned the contacts on the coils, i have a few week old plugs, and such. Another thing i did was replace all the snap connectors with twist caps where all those wires are by the coils. I checked the spark after that and i got a strong looking spark on all 4 plugs,  so it makes me think its no longer and electrical problem. So i took it for a ride and it bogged down after about 10 mins and died. it has done this before in the past but only after i cleaned the tank with vinegar to get any rust out. so my thought is that my problem may be bad gas. meaning that i have gas mixed with a small amount of water or vinegar because after i emptied the tank of the vinegar when i was done cleaning it, i swished it out with water once, then once with gas and slapped it on my bike.
After my bike died today, it was really hard to start, i had to twist the throttle to a very wide open position very fast on and off as i held the starter button in order for it to start and it would only run if i held the throttle open very wide so it was at about 5 or 6 rpm, if i let go it would die immediatley. What i am going to do is swish out the tank a few times with fresh gas and hope that works. But i want to see if you all have any thoughts.
I have a new points plate btw.  PLEASE HELP!

[Don R]

Sounds like it's flooding and it takes a while to get hot to pick-up the wet plugs. Do you need to choke it a lot? Check the float levels, a high float will cause one or more cylinders to run rich and gas foul a plug.  Of course flush the tank and add some of your favorite gas treatment.

[TwoTired]

I'd like to know what the battery voltage is.  Key switch off and later when the key is switched on.  If low, then maybe a dead battery or a charging issue.

[Spanner 1]

1 Spanner 5:7  " Clean out your petcock passages ".

[Terry in Australia]

Hmmnnn. You've said that you've got a good spark, and being that you've got a points ignition, battery voltage doesn't need to be perfect anyway, so I'm wondering if you've flushed some rust crystals into your carbs.

The PD carbs are more prone to slow jets blocking than the early K series carbs, and if your slow (idle) jets are blocked it won't idle (hence the need to hold the throttle open to keep it going) so my advice would be to pull your carbs and (carefully) twist out your slow jets and see if you can see some sky through them. If not, you need to clean 'em out with a fine wire. (guitar string?)

You'll need a pair of vice grips to (carefully) clamp onto your slow jets to twist them out. A cup full of methylated spirits in your gas tank will remove any remaining water. Cheers, Terry.

[martin99]

Sam, don't want to teach you to suck eggs, but those inline filters have to go in the right way - they usually have an arrow on them for direction of flow. Could your carbs have got contaminated because you had it the wrong way round?

[lucky]

There is so many problems with this information.
The thinking jumps all over the place.
I am going to take out all of the useless information from post#1 OP.
This is what is left.


" But sometimes it doesnt run on all its cylinders." Evidence? None given. Evidence would be to check by clipping on a timing light to each spark plug wire one at a time and look for consistant flashes from each plug wire.

"usually after about 10 mins of riding it starts to fire on all 4. So i was thinking electrical."  Why?

"So i cleaned the contacts on the coils, i have a few week old plugs, and such."
And such as? Did you put some new plugs in the bike?

 "Another thing i did was replace all the snap connectors"
What kind of snap connectors?

"with twist caps where all those wires are by the coils."
Twist caps? Like they use on house wiring?  How many wires?
Where do they all go?

"I checked the spark after that and i got a strong looking spark on all 4 plugs,"
How did you do that?

"so it makes me think its no longer and electrical problem."
What about the condition and adjustment of the points and what about the age of the condensers?

 "So i took it for a ride and it bogged down after about 10 mins and died. it has done this before in the past but only after i cleaned the tank with vinegar to get any rust out."
Vinegar mixed with water would make the tank rust quicker.

" so my thought is that my problem may be bad gas."
How would you know if you have bad gas?
Did you recently buy it or has it been sitting all winter?
What makes you think the gas is bad?

 "meaning that i have gas mixed with a small amount of water or vinegar because after i emptied the tank of the vinegar when i was done cleaning it, i swished it out with water once, then once with gas and slapped it on my bike. "

Rinsed with water then you put the gas in it?
It is quite likely that there was water drops in the tank. Did you dry the tank out?


"After my bike died today, it was really hard to start, i had to twist the throttle to a very wide open position very fast on and off as i held the starter button in order for it to start and it would only run if i held the throttle open very wide so it was at about 5 or 6 rpm, if i let go it would die immediatley."

That is what happens when the idle jets get water in them,it prevents gas from going through.

"What i am going to do is swish out the tank a few times with fresh gas and hope that works. But i want to see if you all have any thoughts."

Will you rinse with acetone then let it dry before putting in gas ?
Will you put on an brand new gas filter?
You will still need to take the carbs off again and take out the idle jets and make sure you can see daylight through them.

"I have a new points plate btw."
Does that mean new points and new condensers?

 PLEASE HELP!


I would slow down and start at the beginning.

Clean your gas tank.
Make sure it is completely dry.
Put on a new filter.

Remove the carbs. Remove the idle jets and clean them.
Put the carbs back on.

Also if you have the accelerator pump system
 make sure it is all working correctly.

Try to start the bike.

[Retro Rocket]

Try cleaning out the breather in the fuel cap, if its blocked or restricted your bike will run for a while then stop, then run for a while and so on... That may not be the whole problem but it will certainly help...

[TwoTired]

and when i said "a few week old plugs" i meant the plugs are actually just a few weeks old.

Here's why, this statement has no functional meaning.
Take a brand new spark plug out of the package and smack the electrodes with hammer.  Technically, it is still a brand new spark plug.  But, it likely won't work like a new one is supposed to.

Similarly, take brand new spark plug and put it in an engine that deposits soot on the spark plugs (carburetor problem).  In short order ,the "new" spark plug will no longer operate.

Time is not the qualitative value for a spark plug.  But, it's treatment and condition, is.

Next scenario:
In the path toward correcting a carb problem, the spark plugs are changed for new.  Carbs still have a problem that corrupt the spark plugs.  Later, even after the carbs are corrected, the "new" spark plug are corrupted than the engine still runs erratically.

Finally, the spark plug deposits are your window into and supply direct information about what is happening in the combustion chamber.  If the engine isn't running like you want, isn't that information help toward finding a correction?


Finally, twist caps on wiring are really crap for motorcycle use that sees the outdoor elements.  Perhaps short term emergency repair after the apocalypse.  But, they WILL fail on your, or the next owner's, time later.

[TwoTired]

The spark plugs look ideal to the picture of a "properly working plug" according to my manual.

Could you tell me the color of the deposits on the center electrode insulator?
Or tell me what they look like in reference to this chart?
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

So what would you do now?

The cylinders need an air fuel mix in a the range of 6:1 and 20:1, compression, and spark properly timed near end of compression stroke.  Get this and the engine runs.
Is it running ok now?  Have you completed the 3K tune up check list?

Get a new filter, Clean the carbs and try again?

I'm wondering why you need an inline filter.  Has the one atop the tank fuel valve been corrupted?
I believe that as long as the particles in the gas are smaller than the smallest fuel orifice in the carbs (pilot jet, about .016"), they will self clean as the particles are blown out the exhaust.

[TwoTired]

A good running bike doesn't need fixing, imo.

Must focus on symptoms/signs when it doesn't.  Does the bike still have these?

Have you decided how many times the fuel must be filtered before the carbs receive it?

[TwoTired]

good news chaps! i thought shooting huge amounts of pressure through my idle jets would be enough to clean them but no. i stuck a paper clip through the tiny hole and some gross gunk was in there. so now i have to find a good way of cleaning them and hopefully i will be good to go!

A paper clip will not (better not) go all the way through the pilot jet.   You will have to yank them out of the carb bodies to clean them properly and then tap them back in afterwards.

[lucky]

so thats how they come out? just pliers and pull? with precautions of course?

No.... twist while pulling. First remove the float so that you do not damage the float.

[lucky]

Thank you for pointing out my problems (tho it seems you answered them all and decided to post about the fact that my message is disorganized anyway) .
Heres what the deal is. My bike doesnt run properly. I dont need a  timing light to tell if my bike is running on all its cylinders. some pipes are hot, others are cold. I check the spark by a tool that plugs into the cap and clips on the motor and you can see a spark in the gap.
The snap connectors are connectors that snap together... The ones i am talking about are the wires by the coils. some are coming out of the coils. they are black blue green and yellow. Yes twist caps. I cut out the snap connectors and used twist caps on the wires by the coils to hopefully get a stronger connection. (perhaps this was a bad idea because I heard small little faint pops while trying to start the bike coming from that area.)
When a new points plate is bought, i doubt anyone would use old condensers. Everything in that area is new. The timing is right, i checked.
I thought the gas was bad because i cleaned it with vinegar, rinsed the vinegar out with water, and put in some gas and then emptied it again. So it made me think the gas was bad...

Today, I cleaned the carbs. I found some rust dust and cleaned everything. One of the jets had gunk in it. I cleaned it. I put the carbs back on, and the bike backfired. I tried turning it over again and it idled nicely and all four pipes were very hot. Though, with a temperature gun i got different temps on all four pipes. I took my bike for a ride and it was performing well. Then after about 20 minutes of riding, the bike died. I pulled over, and tried to start it and it would not start. I pulled the choke up and tried to start it again and it fired and i was able to ride it again. This happened about 4 times on that ride.
I did not change the fuel filter (oops).
My thinking, is that the idle jets are clogged again because the filter is junk. I also may have screwed up some of the electrical connections by using the twist caps. I dont know.

I am sorry my previous messages are not organzied and are confusing. Let me know if you need more help clarifying anything.

Your post and thinking IS disorganized and that is why you are having these problems.
I did not go through all of that for nothing.
I am trying to help you get organized in your thinking and your efforts to have a nice running bike.

[Terry in Australia]

Ignore Lucky mate, he's our pet Troll. I told you to carefully twist out the idle jets and make sure you could see daylight through them, to save me repeating myself, just go back and read my previous post. Cheers, Terry.

[TwoTired]

so thats how they come out? just pliers and pull? with precautions of course?

Yes.  I use one of these (soft jaw parallel pliers).   Gotta use two hands sometimes, and bench vise (wood padded jaws) the carbs.

 No need (or desire) to twist while pulling, as that just creates grinding of the metal (or corrosion) in the body and the jet similar to twist drill action.  Eventually and with enough remove and install cycles, jet retention will become a problem.

[lucky]

Thank you for pointing out my problems (tho it seems you answered them all and decided to post about the fact that my message is disorganized anyway) .
Shortened.

Ok I understand more now that you have made those explanations and they all seem like good ways to check on things and to repair possible electrical problems.

Acetone is 4 times more effective to absorb the water out of a gas tank than MEK.

[lucky]

so thats how they come out? just pliers and pull? with precautions of course?

Yes.  I use one of these (soft jaw parallel pliers).   Gotta use two hands sometimes, and bench vise (wood padded jaws) the carbs.

 No need (or desire) to twist while pulling, as that just creates grinding of the metal (or corrosion) in the body and the jet similar to twist drill action.  Eventually and with enough remove and install cycles, jet retention will become a problem.

I should have said slight twist in one direction.

[lucky]

Ignore Lucky mate, he's our pet Troll. I told you to carefully twist out the idle jets and make sure you could see daylight through them, to save me repeating myself, just go back and read my previous post. Cheers, Terry.

Troll???    What about you?

I do not call other forum members names.

[Terry in Australia]

If you're gonna try to pull them straight out as Lloyd suggests, be careful you don't bend them, that's what usually happens if you try to pull them straight out from the top. By twisting them, you'll get a straighter pull lower down on the jet. The jets are made out of brass, so they won't "grind" the pot metal carb body either

[TwoTired]

Okay I got a really really shallow bend in one of them. Do you think it will be fine? The rest are straight.

Probably ok.  But, shallow is a subjective term.  Can you post a picture?
I have never bent any pilots with the tool I use for extraction.  Bending them is probably likely if you choose channel locks for the task, though.

I disagree with "twisting doesn't grind the metal bits".  It is a friction interference fit between jet body and casting hole.  The more they rub, the more metal is disturbed on both.  Twisting makes more metal rub.  I'm just concerned about maximum preservation the parts.  I'll admit it is a minor difference.  But, it takes so little effort to minimize the wear, I simply must recommend it that way.

[Black 750K8]

so thats how they come out? just pliers and pull? with precautions of course?

Yes. I use one of these (soft jaw parallel pliers).   Gotta use two hands sometimes, and bench vise (wood padded jaws) the carbs.

 No need (or desire) to twist while pulling, as that just creates grinding of the metal (or corrosion) in the body and the jet similar to twist drill action.  Eventually and with enough remove and install cycles, jet retention will become a problem.

@ TT I have a set of pliers like those they are smooth no teeth. My question is do yours adjust? Mine do not they are only parallel when closed 

[754]

I am thinking, warming the carb body, would make it grow..more than the brass jet.. And aid in removal..
 Let me be clearer.. Very careful warming..

[thomellis]

Sam, don't want to teach you to suck eggs, but those inline filters have to go in the right way - they usually have an arrow on them for direction of flow. Could your carbs have got contaminated because you had it the wrong way round?

I was riding a buddies bike once, and experienced exactly what you're describing.  After staring at it for a few minutes, and thinking how much it was going to suck to have to push his bike back, I was sitting on the curb and noticed one filter was pointed a different direction than the other.  Doh! Flipped it around and she was good as gold.  I was tempted to put it backwards again when I got it back though so he could deal with it ;P

[TwoTired]

Yes. I use one of these (soft jaw parallel pliers).   

@ TT I have a set of pliers like those they are smooth no teeth. My question is do yours adjust? Mine do not they are only parallel when closed 

No, mine don't "adjust", the jaws don't have teeth, and the jaws remain parallel in any position open or closed.  I assumed that's why they were called parallel jawed pliers.    LOL

If yours are similarly constructed, the jaws mount in two pivot points per jaw.  I'm wondering if yours were simply assembled wrong or perhaps of a slightly different design.