Topic: From the beginning... (spark vs. fuel)

[coffee_brake]

I think your plan is a good one Yoshi, and as soon as I complete making sure spark is unimpeded, then I'll go right back to carbs.

I won't begrudge a 30 year old bike some new plug wires and caps. It looks like these have been trimmed until there isn't enough wire to trim anymore. I've sourced some new 7mm copper core plug wire in bulk.

But the plug caps: do I need resistor or not? Doesn't it just need to be 5 ohms from cap to coil? or to coil lead?
This part confuses me.

[coffee_brake]

I installed new plug wires and caps. The OEM caps were 5k ohms, so I replaced them with the same resistance.

No good.

Adjusted the air gap according to the DOHC forum at .3 mm, no good.

Maybe I'll try swapping the coils from my project '92 Nighthawk 750 into this one, see if that helps.

Any other ideas?

[coffee_brake]

Am I on some kind of shyt list?

[coffee_brake]

Well that makes me feel better at least...

[Yoshimatic]

When you have finally sorted it you will realise that it is not a spark problem. It's a fuel problem, it's starving for fuel.
Either fuel not filling bowls quick enough or float levels too low.

[coffee_brake]

I'm inclined to agree Yoshi, but it's madness to go after all kinds of things at once. Now that I've gone through every component of the ignition system the best I can, it's back to fuel. But I have no idea what else to do. The floats aren't adjustable, and I see no way that the fuel flow is restricted.
I don't know what else to do.

[Yoshimatic]

When something has a problem there's a 90% chance of it being something very simple that is overlooked. Crazy as it sounds but it could even be the fuel cap not venting correctly, that's an example of the basic fault we are looking for. I wish I was there to check it out my self, I love solving probs like this.
Here is like a check list to help find the fault.
1.... With the fuel tap turned on does the fuel flow freely and constantly into a container or jar?
2.... Does the fuel flow increase or decrease when switched from on to reserve?
3.... Does the fuel flow increase with the fuel filler cap removed?
4.... Check the fuel quantity in each bowl to see if they are an even amount in each bowl. This can be done by letting the carbs fill up and then turn the fuel tap off. Get a small glass jar and stick the drain hose from carb#1 into the jar. Open the drain screw on the bowl and let the bowl empty into the jar. Mark the jar with a line at the fuel level, check the other three carb fuel levels this same way and see if they are all at the same line within reason.
5.... Place all carb drain hoses in a jar, have all drain screws open and turn the fuel tap on. See what rate the fuel is coming into the jar.

These are just simple checks to do before looking at further possibilities.
We will get it, it's just a matter of time.

[eigenvector]

one other possibility, do you have good compression?  If you have marginal compression it won't perform well under power because it won't have any power to provide.  That would explain your top-end problems.  Although typically if you have bad compression you won't idle very well.

Never hurts to check compression.

this isn't an electrical issue, either fuel, as Yoshi indicated, or compression.

[Yoshimatic]

I very much doubt that it's a low compression problem, this may sound silly but are the floats fitted the correct way up?

[MiGhost]

I've got to agree with fuel being the problem.
Between here, and the 650 site. Everything electrical has been checked.

Is the vacuum cut off valve still attached? The fuel hose can be routed direct from the tank to the carbs. Bypassing the cutoff valve.
How old is the gas?

[coffee_brake]

I've bypassed the cutoff valve; the fuel is gravity feed now. All good fresh fuel.

I just checked the one and two carb bowls and the floats are installed correctly.

I measured the fuel in each bowl. All were at 50 ml, except #2, that one was at about 65 ml.

Finding a petcock rebuild kit for this bike was no small feat, and it didn't work well at all. The stock petcock is in place, but I have a high-quality in-line shut-off valve in place. It's like this one, but the 3/8 size.

http://www.ebay.com/itm/Motion-Pro-Inline-Fuel-Valve-5-16-Barb-Line-Gas-NEW-12-0036-/291112445522?hash=item43c7a76652&item=291112445522&pt=Motors_Automotive_Tools&vxp=mtr

All that's left is the fuel filter, and it's a honkin' big one. I don't dare run it without one; this is an old tank. There's not a lot of sediment so I don't suspect the in-tank filter, but I'll check it out anyway.

Is there ANYTHING ELSE I CAN CHECK WITH THE BOWLS OFF? I can't express how frustrating it was to remove those screws with the carbs on the bike.

[coffee_brake]

When something has a problem there's a 90% chance of it being something very simple that is overlooked. Crazy as it sounds but it could even be the fuel cap not venting correctly, that's an example of the basic fault we are looking for. I wish I was there to check it out my self, I love solving probs like this.
Here is like a check list to help find the fault.
1.... With the fuel tap turned on does the fuel flow freely and constantly into a container or jar?
Yep, good strong flow from the downstream side of that in-line fuel valve.
2.... Does the fuel flow increase or decrease when switched from on to reserve?
Always on reserve.
3.... Does the fuel flow increase with the fuel filler cap removed?
Nope, didn't change at all.
4.... Check the fuel quantity in each bowl to see if they are an even amount in each bowl. This can be done by letting the carbs fill up and then turn the fuel tap off. Get a small glass jar and stick the drain hose from carb#1 into the jar. Open the drain screw on the bowl and let the bowl empty into the jar. Mark the jar with a line at the fuel level, check the other three carb fuel levels this same way and see if they are all at the same line within reason.
I already posted the results of this test, looked pretty good.
5.... Place all carb drain hoses in a jar, have all drain screws open and turn the fuel tap on. See what rate the fuel is coming into the jar.
Not set up to do that yet, but I CAN set up for two at a time into a shallow dish.

These are just simple checks to do before looking at further possibilities.
We will get it, it's just a matter of time.

Thanks again for the suggestions.

I took off the tank to put the stock coils back on (I actually DID run the '92 Nighthawk 750 coils with a jumpered ground and it didn't change anything) and I took off the fuel filter. It's not completely gunked up but it does have very fine sediment in it. So did the two carb bowls I removed. I never tried to run the clean carbs without a filter, so this tells me the filter isn't doing a very good job. And I DO have to use a bit of pressure to blow air through it.

I'm going to try the same filter from NAPA that is common for my big Concours, which cannot run a small filter. It's the NAPA Gold  3006, it has an "L" bend on one end that makes it fit pretty well.

If it's in stock, I'll try to get it installed tomorrow.

I also pulled the main jets from carbs 1 and 2, since the bowls were off, and they were clear.
I also made a cork gasket for the air filter. I've never seen the proper part, I don't know if mine is thick enough or not.

[MiGhost]

Thanks again for the suggestions.

I took off the tank to put the stock coils back on (I actually DID run the '92 Nighthawk 750 coils with a jumpered ground and it didn't change anything) and I took off the fuel filter. It's not completely gunked up but it does have very fine sediment in it. So did the two carb bowls I removed. I never tried to run the clean carbs without a filter, so this tells me the filter isn't doing a very good job. And I DO have to use a bit of pressure to blow air through it.

I'm going to try the same filter from NAPA that is common for my big Concours, which cannot run a small filter. It's the NAPA Gold  3006, it has an "L" bend on one end that makes it fit pretty well.

If it's in stock, I'll try to get it installed tomorrow.

I also pulled the main jets from carbs 1 and 2, since the bowls were off, and they were clear.
I also made a cork gasket for the air filter. I've never seen the proper part, I don't know if mine is thick enough or not.

That fine sediment is more than enough to foul the tiny passages in the carbs. I dealt with it for a couple years until the tank gave out. You need to get the tank cleaned out to get rid of that rust sediment.

The gasket on the air filter is not that thick. Maybe 1\8" at the most. All it does is seal the cover. Not highly critical.

[Yoshimatic]

I'm hoping the new fuel filter will fix it.
If you still have the bowls off I would remove the floats and the float needle valves. Then let fuel flow through the carbs with the needle valves removed and see if any debri comes through. Possibly blow back the opposite way with air blower or even some hose held up again it and blow with your mouth. Just to check that the fuel supply gallery is clear.

[coffee_brake]

OK good call on flowing some fuel through the needle valves.

I don't think I can get all four bowls off but I'll try.

In the light of a new day (after getting mouthful of fuel testing the accelerator pump last night), it's obvious that the fuel filter has been installed since the first run, while everything else including fuel source has been swapped out with the problem remaining.

Gosh I hope this thing is up to freeway speeds soon.

[coffee_brake]

Crap. Got the better fuel filter on there, still the same problem. 

Can y'all confirm how many turns on the air mixture screws?

[MiGhost]

OK good call on flowing some fuel through the needle valves.

I don't think I can get all four bowls off but I'll try.

In the light of a new day (after getting mouthful of fuel testing the accelerator pump last night), it's obvious that the fuel filter has been installed since the first run, while everything else including fuel source has been swapped out with the problem remaining.

Gosh I hope this thing is up to freeway speeds soon.

We will get you through the entire 3k check up sooner, or later.

Generally 1.5-2 turns from lightly seated on the idle mixture screws.
You caught me in the middle of posting in the last response.

[harisuluv]

Are there tears in your diaphragms??

I'll try to be clearer about this.  Those carbs are bad, crap design, and not rebuild friendly with the rubber diaphragms.  If they are torn it will not run right.  If they are too hard, it will not right right.  Imagine the piston moving up as you open the throttle but meanwhile hard diaphragms are essentially not allowing it to move all the way up. 

If you have an air leak, cause of torn diaphragms, air is going to escape and hence your "cutting out."

Add to that the amount of passages and jets, some of those jets are pressed in and not even able to removed.

Also they are CV carbs, which are much less forgiving than our SOHC "pulse" type carbs.  Catching up on where your at, it seems you are just guessing at random problems, and whether you know the condition of your carb internals is perhaps still unknown, although it is perhaps the most likely offender.

With a CV carb, a simple bench sync may not cut it, a vacuum sync will give you actual information you can use to diagnose your problem. 

[coffee_brake]

No diaphragms.

And yes, I'm guessing, because I've addressed every issue I can think of that would cause the problem.

That's why I'm so glad folks who know more than I do are willing to offer their experience. I'm learning here, I've never faced this before.

I assume I have to pull the carbs again, but I don't know what I'm going to do once they're off. I've done everything I know how to do to clean carbs, including the ulstrasonic. Hence my questions.

[harisuluv]

Ok, so you don't have the diaphragm type, yours are much like the the typical DOHC variety carbs.

So with that out of the way, I would check your caps for dents.  Those big soda can caps on the tops aren't just caps like on SOHC models.  That is the actual cylinder that the slide travels up and down.  One small ding, one small dent that is only visible under close scrutiny means that the slide travels up, hits that point of the dent and stops. 

Something like this would be consistent with hitting a throttle or rpm "ceiling." 

Ultrasonics have their uses but they are not magic.  There are a million different solutions out there, and that's because different contaminants require specific solutions.  Unless you have some special solution that will address lacquer or gummed up gas, you are going to have limited results with household solutions and probably mostly superficial. 

Have you checked all connections for air leaks?  ACTUALLY checked all connections?  carb cleaner spray, propane, whatever.

[coffee_brake]

I thought I polished the caps very well. I made sure each stayed with its carb and that they could all slide freely.

I polished everywhere they touch, just aluminum polish on a cloth, no aggressive grit or anything like that.

I DID have air leaks, and I found the suspect place(s) with aerosol low-flashpoint stuff. I pulled the carbs, cleaned every rubber sealing surface, polished where they go onto the engine, and used Honda Bond all over to ensure a good seal. Now the idle doesn't change at all when I spray starter fluid around the sealing surfaces, yet the problem remains the same.

I just use Pine-sol with distilled water until it stays clear. Then I use CLR (calcium, lime, rust remover) until no more funk comes out. Then I use lots of carb cleaner through everything, followed by compressed air. I've brought back several "won't start/won't run off of choke" bikes this way.
But I never had one that wouldn't run at higher RPMs except a CX500 that had burned out its CDI.

I've run every possible configuration on the paper Emgo air filter. Right now I've got it with the cover on, problem is the same.

Gone through every component of the ignition system one by one with no change.

Next I'll bite the bullet and test compression, after I make sure the idle mixture screws aren't adjusted wrong.

THEN I suppose I'll pull the carbs, unless someone here has a suggestion. 'Cause I have no idea what to do once they're off, that I haven't already done.

[Don R]

Exhaust plugged?

[Yoshimatic]

I would love to have a live cam looking up the carbs to see if the slides are fully open when it is limited to rev. Looking up there would let you know definitely what the problem is. If the slides are fully open and it is struggling revs then the fuel supply is not good enough. If the slides are only half way up then there is a problem with the slides or the vacuum to lift them.

[coffee_brake]

At idle I can feel the exhaust pulse and it feels the same on all four. No trash came out of the pipes when I first started it.
I'm not sure how else to tell if something's in there plugging the exhaust.

My idle mixture screws were at 1.5 turns out. I've put them at 1.75 for a test run. Does that sound about right? A quarter turn at a time?

[Rufus2010]

I had a bike (different brand) where the charging system quit on me. As the battery got weaker and weaker, my top speed got lower and lower. This is because it takes more electrical energy for a spark to jump across a denser combustion chamber environment than a less dense one.

Remember those old horror movies where the "mad scientist" was in his lab? Somewhere in the lab there always was an open spark travelling up between two vertical electrodes. The spark always started on the bottom and traveled up. This is because the spark heats up the air it travels through. This heated air naturally rises because it is less dense. The spark "floats" upward with the hot air. Why? Because it is easier for the spark to jump across to the other electrode through the less dense warm air than the more dense cooler air below it.

The greater the throttle opening, the more air and fuel gets in, the denser it is when compressed and the spark is triggered, the stronger the spark needs to be and therefore the greater the load on the battery.

You mentioned that you checked the charging system and it was OK. Have you replaced the battery or replaced the grounding cable? I know this means going back to the electrical side of things, but I don't think your getting enough spark. Reving to redline under no load and then topping out at 50 mph under load could very well be a bad battery. My problem was kind of in reverse of yours, good battery, bad charging system, but it sounds like the same problem to me. Like someone else said, it's usually something simple. Even if a battery is new, it could be bad, or you have a bad ground.