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

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

Very Clever!

Very cool.

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'.

Pretty much. Total lean on throttle input. Testing out a solution right now.

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?

Sorry... Air correction jets that fit over the e-tubes. Are they offset like that on those carbs? Maybe it's just the angle?

Wide angle lens on the GoPro.

Very neat idea, really.

Looks like you have your work cut out for you.

Rich

Now if we could put 4X Go Pros and plot Each barrel manifold pressure along with EGTs.....

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.

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.

Not only do they not squirt right away, they have a limp dribble when they do squirt.

Fix it!

Amazing use of a go pro camera....
What did we do without all the technology in the past....

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?

These are a pin-through-hole design. No adjustment and checked for slop first.

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.

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. I bolded the part where I outlined how I fixed the problem already.

What causes this is replacement pilot valves with a differing ball weight and needing the travel modified to accommodate that.

The way Mark fixed it is the best way.

Yah, but the camera thing was cool

Hey Mark... were you ever able to get this fixed?