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Engine skip "miss"
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drawkvw
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PostPosted: Sat May 27, 2017 7:23 pm    Post subject: Engine skip "miss" Reply with quote

So here is the deal folks, I bought a 1971 bus with 1600 dual port engine. Old owner abused it and did a tune up and it never ran again. He got mad at it and hit it with a bat. Anyway I saved it. I pulled the motor because it had oil leaks everywhere. Anyway I dropped in a pertronix flamethrower distributor SVDA. And rebuilt the carb while I was at it. So with valves adjusted and everything looking good I put the motor back in. I get it started and the dizzy timed at 7.5 btdc as a baseline. But the motor does this weird thing where it seems like it skips. I can send a video to who ever wants it. It will be running fine then skip and keep going. It doesn't go away when I mess with the carb and it seems to get worse when I mess with the timing. I'm kind of at a loss here. Any help will be greatly appreciated thank you all in advance
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PostPosted: Sat May 27, 2017 7:44 pm    Post subject: Re: Engine skip "miss" Reply with quote

the BTDC timing is for later type IV powered bus, I don't know if it fits '71,
think 0 degress (TDC) is the idle spec, then 009 adds advance from there.
other than that I'd check the wires at the distributor posts for corrosion,
and the intake boots love to tear & feed unmetered air to the cylinders,
leading to the mystery drop you describe.
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drawkvw
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PostPosted: Sat May 27, 2017 8:19 pm    Post subject: Re: Engine skip "miss" Reply with quote

Wires look good and I replaced the intake since the last one was trashed and got new intake boots. Wires seem to be ok. I'm thinking I need to double check the valve lash, check the spark plug wires, and maybe put the old 009 distributor back in to see if that helps. Maybe do the carb settings again and see if that helps
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drawkvw
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PostPosted: Sat May 27, 2017 8:33 pm    Post subject: Re: Engine skip "miss" Reply with quote

Forgot to add that it is a ak code block
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PostPosted: Sat May 27, 2017 10:07 pm    Post subject: Re: Engine skip "miss" Reply with quote

I've got a 71 too but have dual carbs on mine but have a similar miss. It's comes and goes and seems to clear up if I richen the mixture. Yours is probably a Stock Up-Right Type 1 engine with the PIC 34-3 carb which has had the retard vac line disconnected and is timed wrong to compensate for a worn out carb that has a bad air leak around the throttle shaft. It kind of sounds like a vacuum leak to me though.
How well do the power brakes hold without the engine running turning? (You know, shut the engine off in neutral on a slope to test how long the vacuum boost holds.)
The original DVDA distributor is the best to run with a stock set-up Dual Port retard vac line connected or not.
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PostPosted: Sat May 27, 2017 11:43 pm    Post subject: Re: Engine skip "miss" Reply with quote

Post the video to YouTube and link it back here. Your timing should be set at 28 degrees full advance at 3500 rpm with the hoses plugged if it is vac advance. If you are high altitude you can run one or two more degrees of advance. Your idle timing will probably end up around 12 or so. Doesn't matter. Set valves first, then dwell and timing and then mess with the carb if you feel you have to. The vacuum brake system has a strong effect on the engine if it has leaks. To negate its effect, remove the brake vac hose from your manifold and plug the port with the appropriate size rubber stopper (available at most good hardware stores). If you drive it this way beware that the brakes will require massive force to apply them. If your engine smooths out then report back and we can work on troubleshooting the brake vac system.
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PostPosted: Sun May 28, 2017 5:27 am    Post subject: Re: Engine skip "miss" Reply with quote

Sometimes a little stumble can happen when it is running over rich when the float chamber is dripping into the inlet manifold.

But I would suspect the ignition circuit - loose crimp connectors on spade terminals, flashovers down to bad leads or not clipping leads properly on plugs or even a bad electronic unit even though its new.
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PostPosted: Sun May 28, 2017 5:55 am    Post subject: Re: Engine skip "miss" Reply with quote

You set your timing based on the specs of the dizzy you are running. An svda (or a dvda with retards plugged and you should plug them) its basically 7.5 btdc. If you set it at TDC, it will have 7.5 too little total advance (assuming its functioning properly).

A 009, who knows? Ive seen them need to be timed 10 btdc or even higher to get to the 28-32 total advance.

ANYTHING you have to time at 10-15 btdc will have a stumble and may miss.

DVDA? If always capped the retard and ran it just like an svda. The retard is an American market emssions thing designed to make it run hotter at idle. I dont need mine running even hotter amd the engine doesnt really like running w retarded timing.

Without going to deeply into the math, they will all get you to about 28-32 total mechanical advance. The vacuum/mechanical combos go higher than that bc there is no threat of leaning it when you have your foot in it. 009 has no way of knowing throttle position, only RPM so it cant handle as much advance.
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Last edited by nemobuscaptain on Thu Jun 01, 2017 2:10 pm; edited 1 time in total
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drawkvw
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PostPosted: Sun May 28, 2017 1:53 pm    Post subject: Re: Engine skip "miss" Reply with quote

I put the old 009 back in and went to start it, alas the battery was dead. It would rotate for a couple turns then catch and stop. I check all my connections and the bolts holding down the manifolds. Once this battery charges I will give a update.[/youtube][/vimeo]
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drawkvw
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PostPosted: Sun May 28, 2017 1:57 pm    Post subject: Re: Engine skip "miss" Reply with quote

https://youtu.be/_yS8gNWO8-8

You can see the engine shaking miss toward the end
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lil-jinx
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PostPosted: Sun May 28, 2017 4:19 pm    Post subject: Re: Engine skip "miss" Reply with quote

Is the alternator getting warm.
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PostPosted: Sun May 28, 2017 5:26 pm    Post subject: Re: Engine skip "miss" Reply with quote

Whatever distributor you have in there, the goal it to have it timed to about 28º +/- 2º when all of the centrifical advance the distributor has to offer is all in at about 3500 RPMs or so (vacuum hoses removed and plugged).

I am not a big fan of the "hot spark" distributors as people who own them seem to walk a lot. Tough to beat a well rebuilt original Bosch "034".
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drawkvw
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PostPosted: Tue May 30, 2017 9:21 pm    Post subject: Re: Engine skip "miss" Reply with quote

The 009 is back in and it fired up like a champion. Now I have a vac leak which I believe is coming from the vacuum brake booster line and perhaps too much fuel. I can't get it to idle below 1200 rpm even with the big screw on my 34-3 pict turned all the way in. I replaced the manifold gaskets on the end and the manifold boots so I shouldn't have a vacuum leak there. I rebuilt the carb and replaced the float and everything I could. My only thought is maybe the float valve is stuck or the gasket with the kit was too thin and it's not hitting anything. Smells rich. I pumped the brakes and the rpm climbed by 100 or so rpm with rapid pumping
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PostPosted: Tue May 30, 2017 10:00 pm    Post subject: Re: Engine skip "miss" Reply with quote

drawkvw wrote:
I can't get it to idle below 1200 rpm even with the big screw on my 34-3 pict turned all the way in.

What's the base number on the carb?, some PICT3's require a rivet in the throttle plate when used with a mechanical only distributor to get the idle down to where the screw does some good and the progression ports make a difference.
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PostPosted: Thu Jun 01, 2017 12:30 pm    Post subject: Re: Engine skip "miss" Reply with quote

drawkvw wrote:
https://youtu.be/_yS8gNWO8-8

You can see the engine shaking miss toward the end


This looks to me like it's just running on 3 cylinders. If you remove one plug wire at a time at idle you should be able to figure out which cylinder it is not hitting on. Probably the Spark Plug or the wire!
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PostPosted: Thu Jun 01, 2017 1:46 pm    Post subject: Re: Engine skip "miss" Reply with quote

drawkvw wrote:
The 009 is back in and it fired up like a champion. Now I have a vac leak which I believe is coming from the vacuum brake booster line and perhaps too much fuel. I can't get it to idle below 1200 rpm even with the big screw on my 34-3 pict turned all the way in. i

You have to disconnect and plug or fix that power brake leak before anything else.

After that use a vacuum gauge to make sure you have no others. Most arent obvious at least to me.

From vwresource


Note: If you find it difficult or impossible to make these settings, it is possible that you could have stripped threads on any of these adjusters, a damaged hole for the tapered screw, or a damaged needle valve or O-ring.

It is also possible that you have a vacuum leak (i.e., leaking of air into the intake manifold). If there are any holes/gaps in the manifold or at any of the connection points, then air can be sucked into the manifold, causing the fuel-to-air mixture to become too lean. This can cause (among other things) adjustment of the carburetor impossible. See our Discussion of Air Inleakage, which includes diagnosis and repair.

http://www.vw-resource.com/34pict3.html
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drawkvw
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PostPosted: Sat Jun 10, 2017 8:41 pm    Post subject: Re: Engine skip "miss" Reply with quote

So here is the update, sorry it took so long I'm a commercial plumber and I have been super busy. I changed the float needle valve gasket and valve back to the old one that was in the carb. Problems went away. I have full adjustment now. All I have left is to figure out why I get no brake fluid to both rear wheel cylinders. I am assuming the proportion valve or old rubber lines.
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