Author Topic: Clear tube method failure (Read 7925 times)

DaveBarbier · « **Reply #25 on:** September 20, 2016, 07:48:18 AM »

Dude, just tell me that the vent hose that's connected to your vent nipple that's right by the fuel inlet is clear. Snap a picture of that.

SamP · « **Reply #26 on:** September 20, 2016, 07:57:12 AM »

Quote from: DaveBarbier on September 20, 2016, 07:48:18 AM

Dude, just tell me that the vent hose that's connected to your vent nipple that's right by the fuel inlet is clear. Snap a picture of that.

I'll try and do that this week, but I'm either blind or an idiot (or some combination of the two) but I have not seen a vent nipple on these carbs. I'm gonna scour my photos from my rebuild to see, but I do not recall ever seeing this. Otherwise the pinholes bring clogged aren't doing what they need to.

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flybox1 · « **Reply #27 on:** September 20, 2016, 07:57:39 AM »

Quote from: SamP on September 20, 2016, 07:43:15 AM

But when I have the clear tube full of gas, it cuts that off, creating pressure from the full bowl, which then backs up and causes it to overflow. Since that tube is open to atmosphere, it will rise up to the height of the gas in the tank, overfilling the bowl in the process. Right?

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If gas continues to rise up the clear tubes, you have a malfunction of your floats/float valves. Period.

SamP · « **Reply #28 on:** September 20, 2016, 08:03:53 AM »

Quote from: flybox1 on September 20, 2016, 07:57:39 AM

Quote from: SamP on September 20, 2016, 07:43:15 AM
But when I have the clear tube full of gas, it cuts that off, creating pressure from the full bowl, which then backs up and causes it to overflow. Since that tube is open to atmosphere, it will rise up to the height of the gas in the tank, overfilling the bowl in the process. Right?

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If gas continues to rise up the clear tubes, you have a malfunction of your floats/float valves. Period.

Unless the air cannot escape the bowls because the only functional vent is filled with gas. Then the floats are floating but the valve is stuck open because gas is climbing up through the clear tube and the jets, and air cannot escape to lift the float higher. I've already established that the bowls do not overflow when the drain screws are closed, so valves and floats are functioning normally when the clear tube is not applied and full of gas.

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DaveBarbier · « **Reply #29 on:** September 20, 2016, 08:32:19 AM »

Yes, it requires a lot of things to line up properly so the fuel keeps rising and it not being the needle valve. Seems unlikely and it's more likely that the needles aren't shutting off the fuel, but I'm still convinced that if the air can't escape then it'll cause this scenario even when the needles work as they're supposed to.

Are these PD46A carbs? It'll say on the #4 carb above the bowl. On PD46C carbs that "pin hole vent" you're talking about is a little nipple.

Since it's the outside carb, they aren't drilled out from the factory, only the other carbs are (they use the same body for multiple carbs and only finish machining if required). The other carbs have this nipple too and it's drilled out all the way for venting. There's a rubber hose connected to it linking it to the neighbor carb as I explained in my earlier post. Where the fuel hose from the petcock connects there is another nipple that vents all carbs to the outside air. Usually has a hose on it. It must be unobstructed because this along with the overflow tubes are the only way air escapes.

The hose can be seen in this picture. It's the one that wraps around to the left.

scottly · « **Reply #30 on:** September 20, 2016, 08:38:05 AM »

With the drain screws closed, can you blow air through the clear tubes? You might also try opening the gas cap on the tank before doing the clear tube test.

flybox1 · « **Reply #31 on:** September 20, 2016, 08:39:52 AM »

Sam, Please post some closeups of your carbs. Inside and out. And of the vents.
Use photobucket and attach the URL's

SamP · « **Reply #32 on:** September 20, 2016, 10:39:21 AM »

Not home, busy for the next few days. Will take and post photos of outside, and check for vent opening. If that doesn't solve the problem, uninstall and inside photos.
Thanks everyone, this has been really helpful.

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SamP · « **Reply #33 on:** September 21, 2016, 02:48:15 PM »

Here are some pics just to show my carb bowl vents.

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DaveBarbier · « **Reply #34 on:** September 21, 2016, 04:24:35 PM »

Well I'll be damned, I guess PD46A's are more different than PD46C's than I thought. I bet these clogged often so they went to the other design. Harisuluv could have probably told us that, haha.

Anyway still, these have to be clean. I bet you could clean them with carb cleaner while they're still on the bike.

SamP · « **Reply #35 on:** September 21, 2016, 05:02:27 PM »

Quote from: DaveBarbier on September 21, 2016, 04:24:35 PM

Well I'll be damned, I guess PD46A's are more different than PD46C's than I thought. I bet these clogged often so they went to the other design. Harisuluv could have probably told us that, haha.

Anyway still, these have to be clean. I bet you could clean them with carb cleaner while they're still on the bike.

Just good to get confirmation that I'm not a complete idiot

I'll remove the bowls and floats, spray down the outside with carb cleaner, run a wire through the holes and then do some compressed air. Reinstall and try and get my float heights correct. Maybe then I can get a proper synch and plug chop.

Will report back if this doesn't do it.

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DaveBarbier · « **Reply #36 on:** September 21, 2016, 05:10:14 PM »

While you have the bowls off clean the overflow tubes out too. Or, like Scottly said, try to blow through the tubes with the drain screw closed at least just to see if they're clogged. Hopefully they are so it's more likely that's the issue.

Gene · « **Reply #37 on:** September 21, 2016, 05:54:15 PM »

I had this exact same issue. turned out it was 2 things - float needle stuck open from schtuff making it to the carbs (they needed cleaning and re-setting - replaced float needles) and a clogged overflow tube. I may not have noticed for a LOT longer if the overflow wasn't clogged since the fuel would have just poured itself out under the bike as designed.

SamP · « **Reply #38 on:** September 23, 2016, 12:53:11 PM »

For anyone wondering what these pinhole vents look like clean :

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SamP · « **Reply #39 on:** September 24, 2016, 09:29:24 AM »

Well, cleaned the vent holes on all 4, checked float height via the clear tube method and I got all 4 right below the seam. Had to change one float valve, the spring was too soft and not creating a good seal. But after all this I think we're good. Thanks everyone.

Quick question for the old timers - why does float height being even so crucial? I checked where this height would fall inside the bowl, and it would submerge both idles and mains at this height, or down 2cm or up 1cm. Seems to me that so long as both jets were submerged in gas across all 4, they should have the same vacuum. I know real world experience says differently, just wondering why this is so important.

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DaveBarbier · « **Reply #40 on:** September 24, 2016, 05:34:06 PM »

Nice! Those levels look good to me.

As far as fuel height translating into rich or lean conditions: I take it as the higher the level, the easier it is for fuel to be delivered because fuel isn't fighting against gravity as much and the weight of the fuel in the bowl is helping push the fluid up the jets.

NobleHops · « **Reply #41 on:** September 24, 2016, 10:38:54 PM »

Way to go. And great detective work, all you diagnosticians.

I will be very interested to hear how it runs tomorrow.

N.

Bailgang · « **Reply #42 on:** September 25, 2016, 03:18:50 AM »

I hope I'm explaining this correctly but the fuel has weight, the more of it in the bowl the more likely it is willing to be drawn up through the jets with a given amount of vacuum so what ever fuel level your bowls have does have an effect on the over all air/fuel ratio that carb is delivering. It wouldn't be that big of a deal if it was just 1 carb feeding all 4 cyls but we've got 4 carbs and that's why it's important because your goal is to try to balance all 4 carbs to flow the same, if all 4 are jetted the same then getting all 4 to have the same fuel level in their bowls helps to insure they actually meter the fuel the same. I know it may not seem all that critical but consider how well our bikes idle after being synchronized, well the same holds true with getting the float height the same. It's basically another step taken to insure all the carbs are flowing and metering the fuel the same as best as you can get them.

It all sounds picky I know but doing your best to address all these tuning details does add up and can make a difference between your bike running OK compared to running really good.

flybox1 · « **Reply #43 on:** September 25, 2016, 04:20:03 PM »

SamP · « **Reply #44 on:** September 25, 2016, 05:37:26 PM »

Quote from: NobleHops on September 24, 2016, 10:38:54 PM

Way to go. And great detective work, all you diagnosticians.

I will be very interested to hear how it runs tomorrow.

N.

Yeah, very grateful to this forum. Started to sync, but the battery died. Damn anemic charging system!

Will try again next weekend. Was running well towards the end, but really wanna nail this sync.

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SamP · « **Reply #45 on:** September 25, 2016, 08:02:39 PM »

I've got an LED headlight and a killswitch for it. Problem was I hadn't ridden in a while and the prolonged running under 4k was draining the already weak battery. It's since been trickle charged, so if the weather is good next weekend I'll try again.

I keep a box fan on it when I sync. Definitely don't need any seized pistons.

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Author Topic: Clear tube method failure (Read 7925 times)