Carb Noob

[Big T]

Thanks, Keith, for the update.

I did spring for a vacuum synch tool and plan to bench synch AND vacuum synch the carbs when I reinstall.

For the main jet situation, I cannot read the numbers on them because the tops are pretty mangled. Stock jets are supposed to be 100.

A friend suggested throwing the stubborn jets into the freezer to see if that will help separate them. Has anyone tried this before? Is it worth a shot?

According to the PO (who, to be fair, is not the villain, the gorilla carb work predates him), the bike was running a bit rich.

Rich is better than lean

If you have the proper sized (8mm?) deep socket for the jet holder, insert the whole thing into the socket so the jet sticks out. Then, apply the proper sized screw driver

 

[MisterCinders]

So here is a funky valve mystery.

Checked my clearances again using the service manual procedure and pairing intakes and exhaust checks. Most of my valves turned up within spec. But 2 were too tight and one was too loose. With my trusty new tappet tool, I checked out the shims. Here are the results

No. 1

Intake - Clearance .076/.102 (i.e., .076 gauge clears, .102 does not) Shim 2.85
Exhaust -Clearance .076/.102 Shim 2.75

No. 2

Intake - Clearance <.038 Shim 2.90
Exhaust - Clearance .038/.051 Shim 2.80

No. 3

Intake - Clearance .038/.051 Shim 2.85
Exhaust - Clearance <.038 Shim unknown (not marked and didn't have calipers to measure)

No. 4

Intake Clearance .063/.076 Shim 2.75x
Exhaust Clearance .127/.152 Shim 2.80

On a hunch, I swapped the Nos. 3 and 4 Exhaust shims. Voila, both clearances went to .076/.102.

That left only the No 2 intake valve out of spec. Since the No. 1 valve had healthy clearance (.076/.102) I wondered if a shim swap there would close this out. ray:

It did not, but the result was weird.

Dropping the 2.90 into the No. 1 intake reduced the clearance from .076/.102) to <.038 - too tight. No surprise. OTOH, the 2.85 in the No. 2 intake was still too tight. That is strange. With the 2.90 in, the shim turns, so there is some clearance. Wouldn't dropping to a 2.85 get above .038 even after zero clearance?

I will pick up a 2.80 and 2.75 shim to be sure, but the math does not seem to work out here.

 

[BassCliff]

Hi,

I'm not sure I understand your procedure, i.e. "pairing the intakes and exhaust checks".

The basic procedure is (although not necessarily in this order):

1) Position #1 exhaust lobe pointing forward (parallel with top of head).
2) Measure exhaust clearances for #1 and #2.
3) Position #1 intake lobe pointing straight up (perpendicular to top of head).
4) Measure intake clearance for #1 and #2.
5) Position #4 exhaust lobe pointing forward.
6) Measure #3 and #4 exhaust clearances.
7) Position #4 intake lobe straight up.
8) Measure #3 and #4 intake clearances.

I would also suggest picking up a real metric feeler gauge set. It will be more accurate and the math will be easier. They usually start at .04mm and increase in size by .01mm increments (.04mm, .05mm, .06mm, etc). If the .04mm doesn't fit I usually swap out the shim for the next smaller size. It's OK to run the clearances just a little bit loose, say .10mm or .11mm, but no larger.

Keep up the good work. Keep us informed.


Thank you for your indulgence,

BassCliff

 

[MisterCinders]

By "pairing the intakes and exhaust checks," I meant checking exhaust and intake clearances in pairs, as you describe.

Before, I was following Clymer's which checks the valves one at a time, rotating the cam to "north" for each check.

I will hunt down a metric feeler set at some point.

 

[MisterCinders]

Update for anyone still suffering through this saga.

GOOD NEWS

While the technical name for this tool is "impact driver," I call mine the MAGIC WAND!! :dancing:

It pulled those damn intake bolts on the first go. The intake boots are still soft and pliable with no cracks. So now I have sporty new O-rings and fasteners in all four intake boots. w00t

MORE GOOD NEWS

My local cycle shop did not carry valve shims, but they let me buy some from their service department. New shims lead to all valves adjusted to spec. Boo-yah! :clap:

I have new slides and clean carb bodies and bits. My new float bowls should be in today or Monday, but I may reassemble with the current bowls to move forward. I fully expect to break down the carbs again this winter because of the mangled main/needle jet issue.

OTHER NEWS

Would that it were all good news. Here are the remaining bumps on my road to recovery.

JETS

First, those needle jets. I tried using an 8mm deep socket, but the main jet screw heads are stripped like security screws at this point. Before any Dremel work or other aggressive attacks on those mains, I prefer to have some new needle jets for back up. The current assemblies are clean and clear, so I plan to use (with fresh o-rings, natch) those in the rebuild for now.

VALVE COVER

Second, the valve cover gasket is still an issue. I ordered a new gasket, but don't know how long it will take to get it. If it has not arrived today, can I close it up with "liquid gasket" (the toothpaste type) in the short term? Or is my weekend blown?

BREATHER GASKET

Third, the breather cover gasket and mesh are a problem. That gasket also perished in removal. I have not found a replacement (other than the spendy Real Gasket version). I can order one of those, but will the "liquid gasket" approach work in the short term?

BREATHER MESH

Fourth, the breather came off with only one of the two wire mesh inserts. The other must have wandered off in a PO's custody. Where can I find new mesh to replace that? It looks like heavy steel wool. Can I fashion a replacement from steel wool or a scrubber? If not, will reassembling the breather with only one pad be a disaster in the near term?

The theme to all this is the waning riding season. I bought the bike as a starter and need to get some riding time in before winter. Even if I can do that with some of these "scotch-tape" options, my plan is to dive back into the bike overhaul in the fast-approaching off-season.

Thanks again.

 

[KEITH KRAUSE]

I'm no expert on crankcase ventilation but I doubt there will be any ill effects from some of the screening being gone. I would NOT put steel wool in there. It will quickly rust. The crankcase hose attaches to the airbox and all I can see is maybe a bit more discharge draining into the airbox? The box allows for that. There's a drain hole and hose at the bottom of the box.
As for the valve cover gasket, I wouldn't use anything but the new gasket you have coming. Trying to rush things and use a sealant could cause a lot of leaking and maybe even get bits of sealant swimming around in your oil. Who knows what the sealant does as you tighten the bolts and things are oozing everywhere? Same opinion on the breather cover. I know you want to ride but that's my suggestion.
Too bad about the stuck mains. Considering how bad you want to get to riding the mains aren't a real issue at this time. We all like to wind it up here and there but we don't spend THAT much time at 3/4 to full throttle so you shouldn't have any issues with running lean for brief amounts of time. Long term of course they need to be changed if they are factory 100 or too small.
Interesting that you said if anything the bike seems to run rich. Could be a lot of things. Since you can't see the size of the jets they could be larger than 100?? If actually 112.5 or larger I could see a richness problem. But who knows? Maybe your carb cleaning/rebuild will fix something that could be causing richness. Floats set too rich...air jets dirty...inner o-rings in poor condition...even a dirty air filter...
Hopefully your work will fix any rich issues. If you still have a rich problem then you'll know it's either the jetting or weak spark/voltage (assuming compression is good). If spark/timing is good then you need to double check the jetting. That would mean inspecting the jet needle e-clip position is factory and figuring out what size mains you have. Also, verifying you have the stock #15 pilot jets in there and you have the pilot fuel screws (underneath) and the side air screws set correctly.
Keep in mind that a good vacuum synch relies on correct valve clearances (you're good there) and ignition timing being correct.

 

[Steve]

... So I get to wait for the tool to come in and then figure out what shims to order and wait for those to come in.

I have read through to the (current) end and saw that you have your clearances set, finally, but thought I would say "good luck" with "the tool" and extend a personal invite to get my valve adjust spreadsheet. (It was mentioned in your "Welcome" from BassCliff.) It will help you figure out what shims you will need and will keep track of previous work. It also does not care whether you use inch or metric measurements.

Positioning the cam for measurement is a bit confusing, though. Clymers says to point the cam straight up and measure the gap. Others say to point the cam away from the valve/shim and measure that gap.

I don't have my manuals with me to verify, but I do remember that the whole procedure is confusing. The correct (rather simple) procedure is explained by BassCliff, below.

The Clymer method says check the valves with the cams pointing north.

The service manual is consistent with this:

The "A" position is the same as Clymers. If my measurements are consistent after double checking from the due north position, can I work from those?

Is the problem with Clymers the "due north" position or the greater amount of hand-turning?

Again, I don't have my Clymer manual here with me, but the idea is to position one lobe UP, the other FORWARD or BACKWARD (depending on whether you are doing exhaust or intake), then measuring BOTH valves on that side of that cam without moving anything.

..., but the math does not seem to work out here.

Get the spreadsheet. See my sig.

The basic procedure is (although not necessarily in this order):

1) Position #1 exhaust lobe pointing forward (parallel with top of head).
2) Measure exhaust clearances for #1 and #2.
3) Position #1 intake lobe pointing straight up (perpendicular to top of head).
4) Measure intake clearance for #1 and #2.
5) Position #4 exhaust lobe pointing forward.
6) Measure #3 and #4 exhaust clearances.
7) Position #4 intake lobe straight up.
8) Measure #3 and #4 intake clearances.

I would also suggest picking up a real metric feeler gauge set. It will be more accurate and the math will be easier.

That is exactly the order I use. Once you line up the first cam position, you measure (and record) two clearance numbers, rotate the crank 180 degrees, measure another two valves, rotate another 180, repeat as necessary. This can actually be done in just a couple of minutes.

As far as the metric feelers go, suit yourself. The bikes were built using metric tools and specifications, anything with "inch" measurements will be an approximation. Luckily, we know what approximate measurements are close enough, so if that is what you have now, it will still work. One last time, the spreadsheet does not care which you use.

.

 

[BassCliff]

Hi,

If you can find the right thickness of gasket paper, you could make your own gaskets.

Gasket Fabrication
(by Mr. Suzuki_Don)


Just a suggestion.


Thank you for your indulgence,

BassCliff

 

[MisterCinders]

Thanks for the info on gaskets. I thought about making one, but could not find a template. I may try using the method in that PDF sometime.

Update on the mains/needles - after soaking them in chem-dip, a deep 8mm socket and channel-grip pliers were enough to divorce those brass lovers. HUZZAH! I will change them out with the rebuild kit mains for now. Over the winter, I will probably look into new jets and pod filters. My airbox is OK, but lacks the snorkel and seems sub-optimal for the job.

As for the liquid gasket advice, I suppose Keith is correct :-(. Just FYI the product I have and was considering is this stuff:

http://www.bikebandit.com/threebond-liquid-gasket-1194

 

[raistian77]

Mistercinders, not trying to give you more work but feel you should know.
If you have a V&H megaphone, it flows better than stock, enough that it will change the air/fuel ratio. In my opinion, the jet needles MAY need richening about 1/2 position but I don't feel it's necessary. Yes, the pipe will lean that circuit out some but I feel the A/F ratio will still be OK. Testing is always best to determine.
But as for the main jets, the main circuit will be effected more. The mains only effect performance from 3/4 to full throttle position so keep that in mind. I realize your mains are stuck solid.
Again, it's my opinion that your bike won't run dangerously lean while on the mains but performance will be compromised. You may not feel it but the bike will be lean at those throttle positions. Generally, a quality pipe/stock intake combo requires at least one full size (5) increase to two full sizes(10).
Also, if you can't do a vacuum tool synch, then you must do a careful bench synch before re-installing the carbs. I don't know how much VM info you are aware of but a bench synch is mandatory. I have a post around here that details it if you need it. It was in Hoomgar's thread titled something like: "GS1K rejet/bad fuel economy attn Keith Krause"? Reply #36.
Look at the mains and there should be a number stamped into them. The 750's should be 100 I believe or 102.5. If they are, then try to separate the mains if you can without creating worse problems.

my '79 850 VM stock mains are 102.5 not sure about the 750s

 

[KEITH KRAUSE]

Update on the mains/needles - after soaking them in chem-dip, a deep 8mm socket and channel-grip pliers were enough to divorce those brass lovers. HUZZAH! I will change them out with the rebuild kit mains for now. Over the winter, I will probably look into new jets and pod filters. My airbox is OK, but lacks the snorkel and seems sub-optimal for the job.

I suggest using genuine Mikuni jets. Up to you but many have found aftermarket jets to be sized wrong. If you have them apart I'd get some 110's as a compromise for now and work on the jetting later when you go for the pods. 110's in your case would be a 1 and 1/2 size increase (total 7.5) which figures to work well enough for a pipe only change and certainly better than leaving stock mains in. But it appears whatever you do that it's only temporary so do what best suites you now. If you are for whatever reason actually running rich then the larger 110 mains would figure to worsen the problem.
So your stock airbox uses a snorkel but it's missing?? That could at least partly explain why you believe the bike is running rich.

 

[MisterCinders]

This weekend I reassembled the carbs. Despite their poor reviews ITT, I used many of the jets from the rebuild kits because the originals were in pretty rough shape. Never could figure out the old main sizes, but the replacements are 102s. The stock jets are supposed to be 100s, so we'll see how these play out.

I kept and will soak the old jets and clean them up if performance suffers. I did make sure to change the o-rings with goods ones from www.cycleorings.com.

I tried to make a valve cover gasket, but the cutting was too finicky. So I am waiting for my gasket to arrive.

I reassembled the bike. Three times.

First, got the carbs together and bench synched. Wrestled them into place and then the airbox, only to notice I had neglected to put to the two spacers in between carbs 1/2 and 3/4 (not the fuel lines, the rubber bumpers). Not sure if these were critical, I tore it back down, re-synched the carbs, and reassembled the bike.

Then I noticed that I had not properly routed the clutch cable. So, once again, off with the air box to sort that out.

Then I had a devil of a time connecting a new fuel line. The old one would slip into place, but a fresh line would not attach without more leverage than the assembled bike permitted. Pulled the air box again to get to the fuel connection.

Now, I just need that damn gasket to proceed to vacuum synch and, God forbid, actually riding the damn thing.

If I have to wait for the parts again, I may tear it down once more. I saw the note to use anti-seize compound on the intake fasteners only after all this assembly. If I have to wait another day, I may dive back in to re-do those fasteners.

At this rate, I can strip the thing blind-folded.

Couple follow up questions.

There are four drain hoses on the bottom of the carbs. I get that these connect to nowhere (i.e., open air), but where do you route them? They seem to dangle all over, but I can figure out a good place for them.

Also, the fuel line that I picked up fits the fuel connections well, but not the vacuum port. What size line should I get to replace that? The old one is OK, but I'd like to get some fresh tubing in place anyway.

Stay tuned.

 

[Big T]

The fuel drain hoses go down thru the rectangular opening at the back of the main case, on the brake pedal side

Sorry, I can't remember the vacuum hose size.

Did you buy metric or Std size hoses? Metric, from NAPA, will fit better. Always put the fuel and vacuum lines on the carbs before installing the carbs on the bike.

 

[MisterCinders]

The only fuel line I found at Z1 was 1/4"

http://www.z1enterprises.com/detail.aspx?ID=297

It fits snugly on the fuel connection, but is too large for the vacuum port.

I will look into some metric tubing for the future.

BTW, I see a lot of folks rig up a separate fuel tank for testing by using an old oil jug and tubing. What connector do you use to attach the line to the jug?

 

[BassCliff]

Hi,

Here's my CHEAP temporary tank setup...

Thank you for your indulgence,

BassCliff

 

[cowboyup3371]

Basscliff,
I'm looking at building one of those myself; is yours strictly gravity fed or do you have to do anything to prep it when you hook it up to the bike?

 

[MisterCinders]

BassCliff:

Does that bottle come with a cap that accepts a fuel line connection? If not, how did you fashion that part of the rig?

 

[Dave8338]

BassCliff:

Does that bottle come with a cap that accepts a fuel line connection? If not, how did you fashion that part of the rig?

The Gear Lube (all that I've ever used) comes with a tapered pour spout that the hose just slips over, rather tightly, and then you can use a barbed nipple like the brass one Cliff shows, to either step up or down on the final fuel line fitting size.

Also notice the use of a golf tee, to block off the vacuum port on the #2 carb. YOU NEED A GOLF TEE, no other device will work. lol

 

[MisterCinders]

The Gear Lube (all that I've ever used) comes with a tapered pour spout that the hose just slips over, rather tightly, and then you can use a barbed nipple like the brass one Cliff shows, to either step up or down on the final fuel line fitting size.

Also notice the use of a golf tee, to block off the vacuum port on the #2 carb. YOU NEED A GOLF TEE, no other device will work. lol

What is the part no. for that golf tee? I cannot find it in any of the fiches.

 

[BassCliff]

The Gear Lube (all that I've ever used) comes with a tapered pour spout that the hose just slips over, rather tightly, and then you can use a barbed nipple like the brass one Cliff shows, to either step up or down on the final fuel line fitting size.

Also notice the use of a golf tee, to block off the vacuum port on the #2 carb. YOU NEED A GOLF TEE, no other device will work. lol

Very observant Dave, thanks. A golf tee works best but other objects will suffice.


Thank you for your indulgence,

BassCliff