Stalling When Coming to Stop Downhill Only

[HaggardMelon]

1970 Beetle Sedan / 1600cc SP

A while back I replaced my fuel pump, fuel tank, carburetor (h30/31 PICT) and distributor (Pertronix Flame Thrower 009 type).

I've noticed when coming to a stop when going downhill, when I press the clutch and it lets go of the engine, the RPM drops down to about 500 and it will be chugging a bit like it wants to die. It has only actually died once.

It seems to be much worse when the car is cold. Once warmed up, it's not as much of an issue.

If I just barely blip the throttle, it's straightens up and runs fine again.

I believe the carb is tuned properly. When warmed up and in all other situations it idles nice at 850 RPM without any real issues.

What could be going on here? This is a brand new carb. Is it possible it just had some issues out of the box?

Also, timing is set correctly, I haven't found any vacuum leaks and I believe the choke is set correctly as well.

Thanks!

[mukluk]

Idle mixture is too lean.
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1960 Ragtop w/Semaphores "Inga"

[HaggardMelon]

Is it okay for me to back that screw out like a ¼ of a turn before each drive to see when it improves, or should I reset everything and start over again?

[Cusser]

[airschooled]

I have a secret technique for adjusting stock-style carburetors that isn’t in any manual, ready for it?

1. Ignore everything you’ve read about carburetors.
2. On a warm engine, turn the small screw until the engine is happiest.
3. Turn the big screw until you like the speed.

That’s it. Really.
If you count the number of turns you do, you can always go back to where it was in case you make it worse.

Good luck,
Robbie
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Learn how your vintage VW works. And why it doesn't!
One-on-one tech help for your Volkswagen:
www.airschooled.com

[Pruneman99]

I had that same issue once with a 009. The timing was a bit too retarded. Advanced it like 2 degrees and it was better. Never figured out why it was only on the downhills. Maybe I was lean as well? IDK. That's setup is long gone.

[ashman40]

If the problem is only when facing downhill I'd look to the fuel level in the carb fuel bowl. Warm up the engine allowing time for the engine to stabilize. Rev the engine and hold it at 2500rpm for 10sec to get the greatest output from the fuel mechanical pump. Immediately shutoff the engine w/o letting it idle. Remove the top of the carb and measure the level of the fuel in the bowl. Normally, the float and inlet valve maintain the level at 3/4" from the top of the bowl. If the fuel level is too high you might experience issues with fuel overflowing from the bowl into the carb when tilted (up/downhill).
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[halfassleatherworks]

[Eskamobob1]

There are 3 main things that can cause this (to only happen on down hills, all of which I have stuggled with for months before finding....)

1. Float level too low - If your float level is rather low, the extra retarded timing of the 009 at idle combined with a sudden real lean mixture just causes the engine to cut
2. Intake leak - Pretty self explanitory
3. impropper fuel pressure (low or high) - Over pressurizing will cause some horrendous cold startups and you basicaly just flood the carb. This will typicaly cause the issue regardless of up or down a hill from what i hear, but for me it was only down hill. Low fuel pressure causes the pump to not have enough suction to pull the fuel against the acceleration of breaking. Typicaly though this will also cause a general rough idle and realy exacerbate the deadspot of the 009+pict34
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'74 - front disks/lots more work to do

[borninabus]

given OPs location, i would add intake air preheat to the list.
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88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport

[ashman40]

One other things to check... loose intake center section. I recall a report of someone who had left the heat riser tubes unconnected at the exhaust (because their headers didn't have flanges) so the intake center + carb was only being supported by their connection to the two end castings. In this case the clamps on the boots were loose enough that on hard braking or going downhill caused the intake + carb to rotate towards the fan shroud. This changed the fuel level in the bowl.

The point above about too little fuel in the bowl also makes sense. When the fuel shifts it exposes the main jet and the engine struggles.
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AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[HaggardMelon]

Thanks for the tips, everyone. I'll do some tinkering with it and see if it clears up. I was hoping since the carburetor was brand new I wouldn't have to worry about it too much.

If the float level is incorrect, is there any adjustability with that, or does that just point to fuel pressure issues?

Like I mentioned earlier, there's a new tank, cleaned the metal line out really well, new fuel pump, new filter, new carburetor.

Hopefully I can just adjust the mixture a bit to straighten it out.

Also, someone mentioned intake heat. This may end up being an issue. I have noticed on one side, the heat riser barely gets warm. The other side is too hot to touch within seconds. Can't remember which was which, but it's the side the hot air doesn't go through first that's just barely warm.

[VeeDubWolf]

What brand/model is the new carb?
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Two Bugs-
'70 rust-bucket sunroof sedan
'69 PO hack-job special
-Plus a wide assortment of various parts'n'junk

[HaggardMelon]

It's a new Brosol/Solex that I ordered from JBugs.

https://www.jbugs.com/product/113129029HBR.html

[cbeck]

Take it apart, clean it, set the floats?
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My cut in half and rebuild thread
www.thesamba.com/vw/forum/viewtopic.php?t=647779

[mukluk]

[HaggardMelon]

Okay. Yeah it's just lukewarm on the one side so there's definitely some heat getting through.

[ashman40]

[jarmchairpilot]

When I changed my worn out original 30pict3 for a new, out of the box Brosol H30 I had the same kind of problems on my stock 72 1200.
I added a fuel filter just over the rear drive axle where the clutch lever arm. I use an easily available, cheap, good quality VW rabbit MK1 or 2 fuel filter with 2 jubilee clamps to secure it. Don't forget to check that your fuel pump may have a little built in filter mesh,if so like my one,
it can easily clog causing your problem.
I found my ignition timing needed to be retarded slightly just one or 2 degrees down from near 30degrees all out to near 28 degrees all out.

Then after taking it for a drive, with a hot engine I raised the idle speed by about 50 rpm more than where it was with the original carb.
This just took between a quarter and half a turn clockwise of the Idle Screw.
Try it and see if that helps.😎Worked for me.

[HaggardMelon]

Thanks, armchair. I'll try that too. I've been wanting to move the fuel filter to somewhere safer anyway.