Wits end with new rebuild

JayC · Posted: Mon Mar 16, 2015 2:52 pm Post subject: Wits end with new rebuild

Hi All,

I am at my wits end with a new rebuild and I am hoping someone can give me some ideas on what I am missing.

Background: This is a 1600 DP in a 1973 Thing. I rebuild the motor myself. This is the first VW engine build I have done, but not my first engine build (mostly V8s in the past).

The crank and cam are stock, machined back in to spec. The cylinders are 1915 and the heads are original with new valves and springs. The distributor is a new 009 without the vacuum canister and with Compufire electronic ignition and new Bosch blue coil. It has a stock 34pict-3 carburetor rebuilt by Tim (on the Samba - GREAT WORK).

Everything is back together and back in the car. The motor will start, but that is where everything seems to go wrong.

When the motor starts, it immediately starts backfiring through the carburetor, continuously... pop... pop... pop. If I rev the engine, the backfiring may get worse, or it may go away. However, I did try driving it this weekend and it has no power (that sounds weird, but stepping on the gas barely makes it go).

When I installed the distributor, I confirmed that the motor was at TDC on #1 and the rotor was pointing at #1. I have checked and re-checked the spark plug wires on the cap.

The timing is at 7.5 BTDC according to the timing light. The idle is high (1100 RPMs) and doesn't seem to change while adjusting the volume control screw or the bypass screw. Both screws are set per initial recommendations (volume control 2.5 turns out and bypass at 4 turns out).

So, what else am I missing? What could potentially be causing this? Am i going crazy? The only thing I can think of at this point is that I didn't get the cam and crank gears lined up correctly (tooth off)? Could that account for this?

Is there anything else I am missing? This isn't a request to validate the combination. I know it would be better with dual carbs and maybe should have used a different cam. Right now, i am just trying to get it running smoothly so I can enjoy it on a nice summer day.

Appreciate any thoughts before I pull the engine out and tear it all down again.

jay

SoCalJes · Posted: Mon Mar 16, 2015 3:06 pm Post subject:

Have you double checked your valve settings?
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Q-Dog · Posted: Mon Mar 16, 2015 3:24 pm Post subject:

1,4,3,2
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MacLeod Willy · Posted: Mon Mar 16, 2015 3:36 pm Post subject:

JayC · Posted: Mon Mar 16, 2015 3:41 pm Post subject:

1, 4, 3, 2 - clockwise. I'll have to check it again, but I am sure I have looked at it a a doze times...

Mikedrevguy · Posted: Mon Mar 16, 2015 9:00 pm Post subject:

Did the distributor drive get in 180 (or other) out?
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mark tucker · Posted: Mon Mar 16, 2015 9:07 pm Post subject:

either fireing order,valve adjustmant,pluged up exhaust or.. dead camshaft.

Boolean · Posted: Tue Mar 17, 2015 5:42 am Post subject:

Sounds a bit like cam gear indexed wrong.
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JayC · Posted: Tue Mar 17, 2015 6:23 am Post subject:

Thanks all...

I'm away from the vehicle this week. As soon as I am home, I will double check the firing order. Just to confirm a few things (from my research around here):

If the distributor gear was 180 out, would the car still start? If it was that, it is easy, re-clock the sparkplug wires (he says with confidence).

To check the cam gear alignment, I should be able to pull the oil pump and see the alignment, correct? If so, fairly straight forward to check.

I should have mentioned in my original post that there is exhaust pressure from both sides coming out the rear. It smells very rich (e.g. very gassy if that make sense).

I really do appreciate everyone's thoughts.

jay

sallittjob · Posted: Tue Mar 17, 2015 7:14 am Post subject:

Start with the easy things first.

Pop the cap off the dizzy and rotate the engine so the TDC mark is aligned with the split in the case, then check to make sure the rotor is pointing towards the #1 cylinder's wire. Once you have this right, pop the passenger side valve cover off and checked to see that both the intake and exhaust valves for the #1 cylinder (closest to the front of the car) are closed (you should be able to feel the small amount of lash if they're cold and closed).

If that's all right and you're sure the wires are in the correct sequence, then maybe you have a bigger problem.
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PumaVW79 · Posted: Tue Mar 17, 2015 7:56 am Post subject:

[email protected] · Posted: Tue Mar 17, 2015 11:41 am Post subject:

Have you rejetted the carb for the extra displacement? A 1915 most likely would not idle at all, and pop when given throttle if the jetting is the same from when the engine was a 1600. I would say you would need a 60-65 idle, and possibly a 130 main to make up for the added displacement.

JayC · Posted: Tue Mar 17, 2015 12:07 pm Post subject:

Thank you again all. I am making a list of things to go through on Saturday.

On the jettinng issue, I wish I could remember for sure, but when Tim rebuilt it, he asked me about cam, distributor and displacement.

Is there a simple way to tell what jets are in a carb?

Jay

Dougy Dee · Posted: Tue Mar 17, 2015 1:30 pm Post subject:

Less than 12V at the dizzy will cause the problems you are having.

JayC · Posted: Tue Mar 17, 2015 1:49 pm Post subject:

That is a new one I will add to my list... the battery is newish and I fully charged it before trying to start. The car cranks fine...

jfats808 · Posted: Tue Mar 17, 2015 1:55 pm Post subject:

Start with basics. Check and set timing statically. Go where u think #1 tdc is on the pulley. If its numbered, better. Pop 1/2 valve cover. Note position of #1 E & I position. They should be closed. Now rock the pulley back and forth. Confirm #2 EXHAUST is rocking with the motion. Compare position on dist body with where #1 should be. This is tdc # 1 .Now recheck valve lash. Check # 3-4 also.
Turn ignition on and rotate dist body to note spark intensity across points.. Orange bad, white or blue is good. Now set static timing to more than 7.5 mark by a degree or two.
Reset af mixture and idle screw to baseline settings. 1.5 turns idle, 2-2.5 af mix screw.
Start engine. Allow to warm and set idle to stable 900 or so. Report back with results. Im trying to eliminate the basics. If u suspect you put the cam timing marks off, then youll have little choice.
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CHUBB805 · Posted: Tue Mar 17, 2015 2:05 pm Post subject:

"The idle is high (1100 RPMs) and doesn't seem to change while adjusting the volume control screw or the bypass screw."

Get some carb cleaner and check for vacuum leaks.

JayC · Posted: Wed Mar 18, 2015 2:32 pm Post subject:

Thank you all. This gives me a good list of things to check out this weekend. A lot of them I knew... and a few new ideas. Hopefully I can get it straightened out. Attack plan:
1. Validate firing order on distributor
2. Validate distributor at #1 when on TDC. Validate TDC by checking valves.
3. Check alignment of crank gear and cam gear (I believe I can see this through the oil pump).
4 Check for vacuum leaks around the carb
5. Check jets on carb

Hopefully one of those gets it Smile

Again, thank you for your thoughts and insight.

JayC · Posted: Mon Mar 23, 2015 7:44 am Post subject:

Just thought I would pass along my thanks to everyone on a successful weekend. Followed down the checklist and resolved the issue. Verified the firing order and then took the valve cover off the 1-2 side. With a buddy, rotated the engine completely through the firing order and guess what? Yea, I was an idiot and the distributor gear was 180 out. Rotated the plug wires around 180 degrees and tried again. Fired right up and purred like a kitten...

So now, back to figuring out the high idle. It appears that something is preventing the throttle from returning all the way to closed? I can push on the throttle arm (arm that the throttle cable connects too) and push it all the way down and the idle drops down to the 650. However, if I just let it return by itself, it sops and leaves the idle around 1200.

A few things to investigate:
1. Throttle cable sticking? It doesn't seem too and is brand new and greased.
2. There is a damper on the left side (as you look at it) that appears to slow the return. This could be binding? Not sure how to set this as I can't find anything about it in the book.
3. Return spring not strong enough?

But hey, at least I got to drive it a bit this weekend!

Thanks again all!

jay

[email protected] · Posted: Mon Mar 23, 2015 8:15 am Post subject:

a common error is connecting the throttle cable when the carb is closed with the choke activated. This creates a cable that is too tight when the choke is open. Make sure the cable is tightened after manually dropping the carb to the smallest choke-step.
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