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> Kinda Interesting Carb Video, FIXED already, odd problem, solution in bold.
McMark
post Dec 23 2013, 01:28 PM
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Trying to trouble shoot an acceleration lean problem on this set of carbs. So we stuck the GoPro on the back and took a quick test drive. Video confirmed that the pump doesn't squirt as readily/quickly as it should. Still working out the solution, but thought I'd share the video since it's mildly interesting.


https://www.youtube.com/watch?v=XYDmTkNTk3w
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rhodyguy
post Dec 23 2013, 01:33 PM
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Chimp Sanctuary NW. Check it out.
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wow. sounds terrible. must be undriveable in that state of tune.
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drgchapman
post Dec 23 2013, 01:44 PM
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Very Clever!
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EdwardBlume
post Dec 23 2013, 01:53 PM
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Very cool. (IMG:style_emoticons/default/beerchug.gif)
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Eric_Shea
post Dec 23 2013, 02:19 PM
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What's up with the emulsion tubes?
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McMark
post Dec 23 2013, 02:28 PM
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QUOTE(Eric_Shea @ Dec 23 2013, 12:19 PM) *

What's up with the emulsion tubes?

What're you referring to? The emulsion tube is buried in the carb. You can't see it. The secondary venturi and how the top is dimpled? These are EMPI HPMXs so there's all kinds of little 'things'. (IMG:style_emoticons/default/icon8.gif)
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McMark
post Dec 23 2013, 02:29 PM
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QUOTE(rhodyguy @ Dec 23 2013, 11:33 AM) *

wow. sounds terrible. must be undriveable in that state of tune.

Pretty much. Total lean on throttle input. Testing out a solution right now.
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ThePaintedMan
post Dec 23 2013, 02:41 PM
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Ouch. I've not really heard anything good about HPMXs. Hard to see from the video Mark, but are both barrels on the same carb doing that? Crappy pump diaphragm?
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Eric_Shea
post Dec 23 2013, 04:29 PM
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QUOTE(McMark @ Dec 23 2013, 01:28 PM) *

QUOTE(Eric_Shea @ Dec 23 2013, 12:19 PM) *

What's up with the emulsion tubes?

What're you referring to? The emulsion tube is buried in the carb. You can't see it. The secondary venturi and how the top is dimpled? These are EMPI HPMXs so there's all kinds of little 'things'. (IMG:style_emoticons/default/icon8.gif)


Sorry... Air correction jets that fit over the e-tubes. Are they offset like that on those carbs? Maybe it's just the angle?
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McMark
post Dec 23 2013, 04:32 PM
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Wide angle lens on the GoPro.
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r_towle
post Dec 23 2013, 04:44 PM
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Very neat idea, really.

Looks like you have your work cut out for you.

Rich
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stugray
post Dec 23 2013, 05:10 PM
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Now if we could put 4X Go Pros and plot Each barrel manifold pressure along with EGTs.....
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tomeric914
post Dec 23 2013, 05:16 PM
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Sounds and looks like you have a plugged idle circuit. Pull all of the jets and make sure they are clean by spraying carb cleaner through them. THEN, carefully remove each idle screw counting the turns so you don't have to set them up again. Take the little extension on the carb cleaner, stick it in the idle screw hole and spray. Then reassemble everything. Be careful not to munge the idle jet o-rings.

I like to spray the jets out on, in or near a white paper towel so I can see what junk comes out. The satisfaction of finding a little piece of junk is akin to popping a zit.

The idle circuit is in play up close to 3000 RPM. When you get beyond that it seems to run better.
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McMark
post Dec 23 2013, 06:20 PM
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Not a plugged idle jet. Runs perfectly at idle and cruise and as long as you don't punch the throttle.

Actually, if you look really close on the HD version in fullscreen you can see the problem. The accell pump squirters don't spray immediately. There is a lag. So when you open the throttle, it goes way lean until the pump finally kicks in and richens things up. There is a tiny check valve in the bottom of the bowl with a ball inside. I compared these 'new' ones with some old IDF pieces and the new ones have a lot more slop. This was also proven by blowing compressed air backwards against the ball. It took half a second for the ball to overcome inertia and move into place, blocking the flow of fuel. This meant that there was half a second of fuel dumping back into the bowl before the ball finally sealed and starting dumping that fuel where it was supposed to go.

Here's how I fixed it - These accel pump check valves have a little plate in them to limit the movement of the check-ball, so I simply tapped the limiting plate closer, moving the ball closer to the seat and reducing the amount of flow necessary to close off the passage. Yes, I thought about making sure not to restrict the flow of fuel overall. But this modification and going one step bigger on the idle jets solved the hesitation.
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Mike Bellis
post Dec 23 2013, 06:32 PM
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Not only do they not squirt right away, they have a limp dribble when they do squirt.

Fix it!



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r_towle
post Dec 23 2013, 06:35 PM
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Amazing use of a go pro camera....
What did we do without all the technology in the past....
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Eric_Shea
post Dec 23 2013, 07:02 PM
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On 40ida3cs you can adjust the cam on the pump and, they wear. Could it be the same here? Worn fulcrum pin or cam itself? Also, on webers the float level plays a big part in acc. pump volume. Yay? Nay?
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McMark
post Dec 23 2013, 07:04 PM
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These are a pin-through-hole design. No adjustment and checked for slop first.
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rhodyguy
post Dec 23 2013, 07:30 PM
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Chimp Sanctuary NW. Check it out.
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faulty diaphragm or an issue with the passageway for the pump jet? how old are those carbs? iirc the early versions had a little plastic wheel on an arm connected to the rod assembly, they go south.

general knowledge picture. the passageway is the round 90* bend that starts behind the accel pump cover and runs to the pump jet. the squirty thing in the video. right behind the top of the cast in passageway inside the bore.


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McMark
post Dec 23 2013, 07:42 PM
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I already knew the diaphragms were pliable and had already cleared the passages before the carbs even went on the engine. But during my troubleshooting I installed a new set of diaphragms and reinspected the passages (no change).

I edited my earlier post for those of you who find my posts a little too wordy to read. (IMG:style_emoticons/default/laugh.gif) I bolded the part where I outlined how I fixed the problem already.
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