#6 High Vacuum no firing? (Solved)

[Visseroth]

I know I don't post on here much but I have a Valkyrie, not a Hardly so I usually don't have a lot of problems but I have a question for you Valk gurus, I have a problem with my '98 Valk Standard but let me start with what I've done so it can be considered in the diagnostics...
I have done the following...
Redeye de-smog (to eliminate potential failure points)
Took apart and cleaned carbs with carb cleaner.

Re-jetted to 38 and 100 (was 40 and 105 which was to much)

Replaced petcock with a Pingel no vacuum (was leaking)

Changed timing wheel from stock to 4 degree advance (Out side facing to the front of the back).
Replaced fuel line from carbs to tank and put a 100 micron fuel filter between the tank and carbs (https://www.aircraftspruce.com/ca…/eppages/univinlineff.php…)

Replaced pilot screws with http://carbjetkits.com/fuel-screw-replacement-16016-mas-670… as #6 screw head was stripped and sticking.

Replaced exhaust manifold gaskets.

Now the problem is that #6 is acting like it isn't firing.

When I first noticed it I needed a vacuum cap on #6 so I capped it with what I could find, rode 6 blocks, purchased new vacuum caps and put them on, rode home. #6 was popping and periodically back fired slightly.

I figured there was a problem in #6 so I tried to adjust the pilot screw and the head stripped so I ordered replacements.

I then proceeded to pull the carbs, took them all apart, 3 at a time, cleaned them all with carb cleaner and put them back together and installed the new pilot screws. Each adjusted to 2 turns out.

I then put the carbs back on, air box tank and all, hooked up my gauges and proceeded to sync but #6 is way out of whack. I adjusted the idle screw on 6 until the screw came out and tightened it up and the vacuum went up a little bit but the vacuum needs to come down as it currently shows about 17.5 inches of vacuum vs the 9 on the other gauges.

I tried adjusting the pilot screw but it made little to no difference so I set it back to 2 turns out.

Anyone have any idea why one cylinder would have more vacuum than the others?

Here is a picture of 2 of the vacuum gauges side by side, number 5 and 6...

[WintrSol]

One cylinder with higher vacuum means its throttle is closed more than the rest. The adjustment screw would be turned CW to open it more, which should make the vacuum drop (while increasing rpm).

[longrider]

I think you had best check your vacuum diaphragm in #6 as it may not be opening.

[Visseroth]

One cylinder with higher vacuum means its throttle is closed more than the rest. The adjustment screw would be turned CW to open it more, which should make the vacuum drop (while increasing rpm).

Tried that, idle came up really high while vacuum did come down for a moment but the vacuum on all the rest came down further, If I recall correctly, but it didn't work, I couldn't even get them close.

I think you had best check your vacuum diaphragm in #6 as it may not be opening.

You're thinking the diaphragm isn't getting vacuum or that the diaphragm is stuck?
I did pull the diaphragm and gently blew it off with the air compressor after I sprayed the carbs out with carb cleaner. I also took the air compressor and blew air through all the holes and rails to get out any extra cleaner hiding in there or any debris that may have been there that I didn't know was there or couldn't see but you would think that between the first fire up and the second (after the carb cleaning) that the symptoms would have changed.
Unfortunately I didn't check the vacuum on the first fire up because of the pilot screw. The carbs had to be pulled anyhow to replace the screws but the sound in the exhaust was the same.

[Visseroth]

Just pulled the diaphragm, pulled the needle, replaced the O ring, checked the diaphragm for holes, looked everything over, put it back in, fired it up, same result.
I did notice the needle has 2 washers, one on top and one on the bottom. I didn't know our needles were adjustable! So just learned something new!

[Chrisj CMA]

The carburetor can still be clogged if you didn't insurre all the passages were clear

[WintrSol]

The carburetor can still be clogged if you didn't insurre all the passages were clear

Especially if those passages don't let the CV piston rise. There are passages in the CV piston between the throat end and the vacuum chamber above the diaphragm. As the air flow increases, the velocity of the air creates a vacuum under the piston, proportional to the velocity; that vacuum causes the diaphragm to lift the piston, keeping the vacuum created in the venturi nearly constant, hence 'Constant Velocity'. If something is blocking that vacuum passage, of the spring is too strong, piston binding, etc., the piston won't rise, creating excessive vacuum drops. When you assemble the carbs, you should ensure the pistons will rise easily, by lifting them with a soft probe. If not aligned properly, they may bind.

[gordonv]

I have very little experience on carbs. I kind of shy away from them. But if they need work, I'll do it.

Why did you do all the work that you did? What was the problem?

The fuel filter. Most don't like it. Some say there is no issue. Those that have had problems, and removed the filter, problem went away.

Have you drained fuel from each carb, to insure fuel is in the carb?

Is the bike drive able, and have you taken it out for a ride? How does it behave at lower rpm (1.5K) and higher rpm (3K)?

Me, I'd drive it with fresh fuel, 1/2 tank and 1/2 can of Berryman B-12. I suspect a carb with clogged port. Give the cleaner fresh fuel a chance to do it's job, and see if any change.

[Visseroth]

Well I decided that I needed to rejet the bike a while back because a prior owner put the 6 shooters on it and according to what I read 6 shooters would likely need to be rejetted or it would likely run lean. I couldn't afford it for a while, then I rejetted to 40 and 105.
Things seemed to be fine except when I tried to pull a hill, it would spit and sputter and act like it was dying until I either opened it up all the way or let off, then it was fine.

So... I figured the high jet was way to much. Mind you I was and still am learning about carbs.

So, I decided before riding season I'd do any and all maintenance I could think of, including re-jetting.

The desmog was to eliminate a 20 year old point of potential failure.

The 4 degree advance was to take advantage of premium non-ethanol fuel and a bit more pep it it's step.

Anyhow, I agree with you. I do find it sad that we don't have nor can handle a fuel filter. It seems to me that's just asking for trouble as most of our US fuel is dirty stuff.

At 1500 to 3K under load it seems ok but you can definitely feel the power is gone and still hear that it does not sound healthy.

Simple cruising at about 25mph causes a occasional back fire. Not a big one, but it obviously shouldn't do that.

Draining the fuel bowl on #6 does drop fuel, so it is getting fuel.

I fear it might be a valve seat that has been eaten away.

I plan to do a compression and bleed down test as soon as I can. I don't have the tools but I have a buddy that does. Problem is he's out of town for a bit, so I'll have to ask around and may need to take it in to a shop that does or wait tell he gets back. I just want to be sure it's not a valve.

Also bear in mind that prior to me this bike was not treated kindly. When I purchased it had obviously been laid down and I'm not sure if the prior owner was the one that did it or purchased it to fix it up.
The handle bars were bent on the right. The exhaust has some road rash and dents on both sides, the crash bars were dinged up, oxidation was everywhere and I still find bits of rust that I have to clean off.
Basically this thing has been a clean-her-up project bike since I purchased it but has run well for the most part up until now.

The other option is to buy another one and use this one for parts. I've wanted a interstate for quite some time, just hasn't been on the radar and I don't like wasting things, specially classics like these beasts, though fuel injection would have been nice, lol!

[Visseroth]

Well just ran a compression test on a cold engine, ended up with 80 lbs all the way around except #6 which was 40 lbs.
Since the bike does not have a history of burning oil and/or smoking while being ridden I believe it's safe to assume fried valve seats.
Seems I will be doing heads as soon as I gather all the parts together.

[gordonv]

Well just ran a compression test on a cold engine, ended up with 80 lbs all the way around except #6 which was 40 lbs.
Since the bike does not have a history of burning oil and/or smoking while being ridden I believe it's safe to assume fried valve seats.
Seems I will be doing heads as soon as I gather all the parts together.

Could it also be the valve lash? There is that, a bent rod, valve stem, but all things that the head needs fixing.

[Visseroth]

That is a possibility and I will post back when I know more. I suspect burnt valve seats as I don't think the mixture has been right for a while. Something I've been working towards fixing.

Hind site being 20/20 or there about, I'm wishing the previous owner would have left the stock stuff on it instead of the Cobra 6 shooters.

Anyhow, I'll let you know what I find.

[Visseroth]

I had a hard time finding my own post, lol!

Well after a lot of work, pulling heads, replacing head gaskets, cam seals, lapping the valves, setting valve lash, ect, the problem still persisted, I was starting to think I had bad rings!

Then a friend came over and helped me do some of stuff and I realized I was being a ID10T!!!!  
I was checking compression with the throttle CLOSED! Why? Because I didn't know any better.

Later I ran some tests and found I was right at about 135# on all cylinders with the throttle open and about 80 to 90 with the throttle closed except on number 6, I was only 50# with the throttle closed, which left my scratching my head wondering what in the tarnation was going on!

Valve lash is good, compression is good with the throttle open, timing is good, blah blah blah....

So, I pulled the tank, looked in the air box, all clear!
Looked down number 6 tube, all clear!

Sigh!

I pulled the carbs and checked for plugged jets on number 6, all clean!

I figured at this point since I couldn't sync the carbs while on the bike I'll try and sync them on the bench visually and wouldn't you know number 6 was more closed off than the rest and that's why I was getting low compression with the throttle closed! Number 6 couldn't breath!!! 
Come to find out this was all because of a weak spring and a bent tine that kept number 6 out of alignment with the rest of the carbs!!!
Good grief, sure I'm a back yard amateur mechanic but I learned a lot during this last cycle of maintenance and/or screw ups, or whatever you want to call it.

Bottom line is the fat lady is running and she's running well and I know now that the valve seats, valve seals, cam seals, ect are all good and new!
So thank you everyone for your input, and now you know if anyone is getting 80 or 90# of compression they are likely checking compression with the throttle closed! 

Oh, learned something else too! Too tight of a timing belt causes chirping up front at between 1600 and 2000 RPM. Don't put your timing belt on tight. Let the springs set the tension!

Edit: Oh and one more thing, no fuel in a cylinder because of a closed off carb = no firing, duh!!!  

Anyhow, problem solved, now to setup a O2 sensor for fine tuning of the air/fuel mixture, but that's at a later date, I'm just going to enjoy riding her around for now. She sounds good, runs good and smooth and I have a lot of hours into her. I'm taking a break for a while and moving on to other projects like the valve cover gaskets on my truck 

[The emperor has no clothes]

Thanks for the follow up report. 

[Visseroth]

No problem. I don't like finding forum threads without answers to questions, so I make it a point to post a answer to a question I posted for others to reference and to look back on if I forgot what the answer was. 
And thank you guys for the replies. I very much appreciate the input and any help given! 

[9Ball]

Congrats on all the maintenance and rebuilding that you completed.  You should have a sense of satisfaction that the engine is now in spec.  It’s tough buying someone else’s bike not having a complete history of what was (or wasn’t) properly maintained.

Just curious, did you split the carb banks and replace the fuel and air rail o-rings too?  Also, did you replace the o-rings and tubing on the air cut valves?

[Longlivedixie]

No problem. I don't like finding forum threads without answers to questions, so I make it a point to post a answer to a question I posted for others to reference and to look back on if I forgot what the answer was.  
And thank you guys for the replies. I very much appreciate the input and any help given!  

WOW!! Quite the ordeal you went though! You sound like ya know what you are doing around a Valk engine.....especially the carbs. Good luck with getting her completely squared away.

If you live near NW Arkansas, I would like to hire ya to do my carbs!!

One question though......you said your #6 carb issue turned out to be a spring and a tine (whatever a tine is). Scuse my ignorance........but are you referring to the long main spring in the carb?? Doesn't it fit in the diaphragm & slide somehow?? That spring?? The part number would be  16050-MBY-671.

Thanks!!