'81 CB750F trying to get it road ready.

[TOOLS1]

What you did was a wet compression test. A leakdown test is a whole different test. Yes I would repeat the test with the throttle wide open.
TOOLS

[Chicago Ted]

Well, I suppose I may have a bit of good news. At least it may be, depending on how you look at it. I did a proper compression test, and the numbers ended up good. 148, 150, 140, and 140. I do worry that the oil I put down the #3 cylinder for the wet compression test last time. I ran it for about five minutes after the last test, and ran it for another five just before this one to warm it up. Ought that to nullify the effects of the oil? How long does it last in the cylinder?

I was a bit lost after that, so, it was recommended that I make sure the torque on the valve cover bolts is per spec. When I brought out my torque wrench, set it to 12 ft*lbs (since I thought they were "camshaft bearing cap bolts", as per my Clymer's manual), and set out to tighten each of them accordingly. When I tightened the cover over the exhaust valve cover over the #4 cylinder (the one that I saw smoke leaking from), I noticed that I couldn't tighten the bolt; it just kept spinning. I pulled out the bolt with my pliers, and it appears to have broken apart. I have added a picture of the broken bolt next to a good one.


So, my question is, could that be causing my loss in power, and additionally, what would be the best way to correct it?

[TOOLS1]

No that would not have anything to do with running. Now you need to find out which cylinder, or cylinders is not running properly. If you can get a laser thermometer (available at Harbor Freight cheap) and take the temperature of the exhaust pipes with the engine running at different RPMs. Or on the real cheap you can use a spray bottle of water to see if there is any difference in the temp of the pipes.  
TOOLS

[Chicago Ted]

When I find the hot cylinder, what next? What would the problem be?

On Sep 15, 2013 7:36 PM, "TOOLS1 [via Honda CB750'S]" <[hidden email]> wrote:

No that would not have anything to do with running. Now you need to find out which cylinder, or cylinders is not running properly. If you can get a laser thermometer (available at Harbor Freight cheap) and take the temperature of the exhaust pipes with the engine running at different RPMs. Or on the real cheap you can use a spray bottle of water to see if there is any difference in the temp of the pipes.  
TOOLS

Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
1976 CB 750-A X 2
1977 CB 750-A X 2
1977 CB 750-K X 2
1976 CB 750 F
1981 CB 750
1995 KZ 1000 P-14
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)

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[TOOLS1]

You want the cold cylinder. That will not tell you what the problem is exactly, but it will start pointing you in the right direction. For instance, if the outside two cylinders are cold, that would lead to an ignition problem since both run on the same coil. If just one cylinder is cold, it would lead to a carb problem.
TOOLS

[Chicago Ted]

Okay, after running the bike for a few minutes, exhaust headers 2-4 flashed some water into steam pretty readily, while header 1 was cool enough to touch. Still warm, but not even close to the others. Whats the next step? (I am glad this points to a carb issue, rather than ignition. It seems slightly less intimidating.) Additionally, from where and how would you recommend I replace that broken bolt I referenced earlier. Thanks for all the help so far!

[motogrady]

I admire your tenacity Ted.
You're doing great.
The cylinder not gettin' hot,
I'd guess a clogged something in that carb also.
If it was electric, I'd think it would not fire at all,
and stay cold.

You can check spark, in a dark place, just get a 5th plug,
put it in the plug wire, hold the metal part of the plug
to a fin or rocker cover, and start it up.
It'll run like crap, but you should see spark.

[TOOLS1]

Now you know where the problem is, but do like Motogrady suggested, and rule out the ignition. As for the broken bolt, try to turn it out with a pick, or some other pointed device. If that does not work try using JB Weld to attach another bolt to the broken one, and screw it out.
TOOLS

[Chicago Ted]

So, do I really need another spark plug? Can't I just leave that plug open and try to start it? Or, alternatively, could I just disconnect all of the tension lines and crank the starter? Do you suspect that there may be an issue with my spark plug, or my ignition unit itself? If the ignition comes back okay, what should I do first with the carb?

Now you know where the problem is, but do like Motogrady suggested, and rule out the ignition. As for the broken bolt, try to turn it out with a pick, or some other pointed device. If that does not work try using JB Weld to attach another bolt to the broken one, and screw it out.
TOOLS

Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
1976 CB 750-A X 2
1977 CB 750-A X 2
1977 CB 750-K X 2
1976 CB 750 F
1981 CB 750
1995 KZ 1000 P-14
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)

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NAML

[TOOLS1]

Worry about the ignition first. No you do not need another plug. You can use the plug that is in the engine. Just take it out. Also when you remove the plug check to see if there is any gas on it. You could also switch the plug, and wire with the ones from the No#4 cylinder. If the No#1 starts working, and the No#4 goes cold, you will know it is an ignition problem. However if the No#1 stays cold, then you will know it is a carb problem.
TOOLS

[Chicago Ted]

Okay, I swapped the plugs, between the #1 and #4 cylinder.  #1 remained colder. I wanted to try switching the cables, but they were not long enough to swap like that. So, I unplugged them all, and took out the plug now in #1, and plugged it into the appropriate cable, and just hit the starter, while grounding the plug. Sure enough, there was a small blue spark, which seemed pretty consistent with the sound of the starter. Does this rule out ignition?

I am happy to at least attempt to start working on my carb, but I should first share some reservations. First, When I initially noticed this issue, I would have sworn the problem was somewhere on the right side of my block, either #3 or #4. There was white smoke coming out of the right side exhaust, and the burbling noise that I would hear, accompanied by a rush in acceleration from time to time, came from the right side exhaust. Additionally, white smoke is still coming out of my right side from time to time. Could that be left over from the wet compression test? How long does that take to work its way out of the system? Alternatively, could the broken bolt be allowing oil to leak somewhere it ought not to go?

The second reservation to working on my carb is that I literally JUST got this back from the shop to do a full cleaning and repair on it. Now, I have no love left for the shop that did the work (Honda Powersports of Crofton, MD), but I like to think that their work would have lasted more than a week. I paid $300 in parts and $600 in labor to get the thing cleaned out (ultrasonic cleaner too), and I got new air cut off valves, screws, and gaskets. So, this is at least why I didn't assume the carbs to be the issue in the first place.

All that said, if you guys can hold my hand through the process, I am happy to get my hands dirty and figure this stuff out.

[shinyribs]

Man, I hate to hear when guys pay hard earned money for repairs and end up with stuff like this.

IMO,if you dont mind getting dirty (and you say you're not afraid of that)you're better off investing in tools than shop labor.

Harbor Freight sells a sonic cleaner that you can get for about $55-60 when they go on sale. It's just big enough to hold one of our carbs. My buddy has one and we've been using it with a 1:1 mix of 409 and tap water. It works great.

Anyway...that blue spark you saw is a real good sign. Blue is strong. A yellow spark is weak. Will all four spark like that?

Oil residue from a wet compression test should burn away pretty quick. Not sure exactly how long,but it should all be gone by the time the engine is at full operating temperature.

[TOOLS1]

The broken bolt will not have anything to do with the operation of the engine, but it should be repaired. Now you need to do a search for DOHC carbs with the search feature here. There are several really good write ups on them here.
TOOLS

[motogrady]

Wow, Crofton Md.  I used to live in Glen Burnie.

Do you have an inline fuel filter installed?

The guys that did the carb may have done a good job, only to have a speck of rust
in the tank find it's way to the carb in question.

Inline fuel filter at Lowes, in the lawnmower section, every bit of 10 bucks.

The smoking, ya, till you get it out and run it for a bit, don't let it bother you.

[Chicago Ted]

I do have an inline filter, but my track is not in too great a shape on the inside, so I can believe that something may have gotten through. Also, I tested all the plugs. Sparks all around. So, once last thing, before I busy open my carbs. Could I mitigate my issues by just adjusting the idle set screw below the carb? If something is blocking my jet, causing leanness, then enriching it should make it run better, yes? It could at least be a disgusting tool.

On Sep 19, 2013 11:08 AM, "motogrady [via Honda CB750'S]" <[hidden email]> wrote:

Wow, Crofton Md.  I used to live in Glen Burnie.

Do you have an inline fuel filter installed?

The guys that did the carb may have done a good job, only to have a speck of rust
in the tank find it's way to the carb in question.

Inline fuel filter at Lowes, in the lawnmower section, every bit of 10 bucks.

The smoking, ya, till you get it out and run it for a bit, don't let it bother you.

www.cyclebytes.com

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[TOOLS1]

Umm  NO!
TOOLS

[Chicago Ted]

Sorry, I was using my phone. I meant a "diagnostic" tool.

On Sep 19, 2013 8:59 PM, "TOOLS1 [via Honda CB750'S]" <[hidden email]> wrote:

Umm  NO!
TOOLS

Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
1976 CB 750-A X 2
1977 CB 750-A X 2
1977 CB 750-K X 2
1976 CB 750 F
1981 CB 750
1995 KZ 1000 P-14
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)

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NAML

[shinyribs]

LOL.  I know all about phone typos.

Well, you KNOW that you have ignition on all four cylinders, so you can move past that. And you also KNOW that you have compression. The only thing lacking would be fuel. Since you have that one cold cylinder you're just gonna hafta go in to those carbs. You could try to diagnose it some other way, but until you go through the carbs you'll never have a truly dependable bike.

Once you go through them and keep a good quality inline filter on the bike you'll be golden. IMO, use a filter with a paper element. They are all I will ever use. They just filter better.

[Chicago Ted]

I installed this filter, right after I got my bike back from the shop, mostly because I thought it looked cool. In my defense, I am a dumbass. Is it any good? Which one would you recommend?

[TOOLS1]

"If something is blocking my jet, causing leanness, then enriching it should make it run better, yes? It could at least be a disgusting tool. "
Umm  NO!
TOOLS