Engine power

[Mike V. Florida]

It has to be electrical. everything else seems right, but what would cause the engine to quit when shorting plugs 3 or 4. We see display engines running on one plug and compressors running of two.

If you turn off the lights in the garage or do this test in the dark what do you see? Place the plug wire approx 1/8" from the plug and run the engine.

Can you cut an old cap into a thin strip so you can see into the distributor when it is running. How does this look as well.

[jfreddie]

I agree with the idea that #1&2 cyls are the culprits.
As Tom said before, what is the vacuum reading?
If it's not steady you may have sticking valve guides in those cyls.
Try taking out the plugs in those two and squirt some penetrating oil down the open intake valves and see if that doesn't make a change.

[Dollar Bill]

I am running out of places to look. Why are 1-2 not as strong as 3-4?

Vacuum leak on front runner at manifold/block connection.

[Mike V. Florida]

Originally Posted by Dollar Bill

I am running out of places to look. Why are 1-2 not as strong as 3-4?

Vacuum leak on front runner at manifold/block connection.

In post number 9 he states; "I checked no leak at manifold."

[George Miller]

Originally Posted by Dollar Bill

I am running out of places to look. Why are 1-2 not as strong as 3-4?

Vacuum leak on front runner at manifold/block connection.

Plus1 It has all the signs.

[Mitch//pa]

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Model A vacuum leak tester

[Tom Wesenberg]

Originally Posted by Dollar Bill

I am running out of places to look. Why are 1-2 not as strong as 3-4?

Vacuum leak on front runner at manifold/block connection.

I agree and that's why I suggested the propane check. If the propane or other flammable liquid doesn't show the problem, then I'm back to thinking it could have slow to close valves, and that's where the vacuum gauge should show a good flicker of the needle.

A scope check could eliminate the electrical, but the wire swap Bob did pretty well also eliminated the spark. It's just nice to see what's actually happening on the scope. At the least I would check the top distributor plate for side play, and remove the cap and rotor, hand crank the engine, and make sure each lobe opens the points exactly .020" and make sure the points have good spring action. I have seen where the copper points strap touched the cam, so make sure this isn't a problem also.

[Dollar Bill]

Originally Posted by Mike V. Florida

In post number 9 he states; "I checked no leak at manifold."

Using a shop vac?

[Benson]

Originally Posted by Tom Wesenberg

I agree and that's why I suggested the propane check. If the propane or other flammable liquid doesn't show the problem, then I'm back to thinking it could have slow to close valves, and that's where the vacuum gauge should show a good flicker of the needle.

A scope check could eliminate the electrical, but the wire swap Bob did pretty well also eliminated the spark. It's just nice to see what's actually happening on the scope. At the least I would check the top distributor plate for side play, and remove the cap and rotor, hand crank the engine, and make sure each lobe opens the points exactly .020" and make sure the points have good spring action. I have seen where the copper points strap touched the cam, so make sure this isn't a problem also.

I am leaning toward slow or not closing valves at warm engine conditions also.

0.011 on intakes and .013 on exhaust sounds a little tight but I believe it depends upon how the camshaft was ground.

For instance Model B clearances were .015 and .022. (yes 0.022 on exhaust). Different cam, lifters and maybe valve materials than model A.

I know that SB Page 231 changed clearances from 0.013/0.015 to 0.011/0.013. BUT that is for the valve materials, lifters and camshafts used when the SB was written not with newer camshaft profiles and valve train parts.


As engine heats up the clearance can decrease. Thus valves that are right on the border of being too tight will remain SLIGHTLY open with lost compression then go back to being closed when engine cools and you run compression check after engine is cooled down.

Bob have you asked cam grinder as to what clearances are for HIS reground camshaft?

As an example of engine missing under high loads.

I know VWs are air cooled but principle still applies.

I had a new 69 VW fastback with the factory Electronic Fuel Injection.

Engine was fine in all conditions EXCEPT when running up a long steep hill, in third gear, with a dirt bike trailer on the back, the engine started to miss. Missing went away when I let off the gas at top of the hill and it cooled down.

When pushed hard again the missing returned again.

Factory valve clearances at the time were specified at 0.004 for intake and exhaust.

I tried 0.006 on both. Guess what? The missing problem went away.

I told my friend who was a Service Manager at the VW store about what I found.

Six months later the factory issued a Service Bulletin changing the clearances to 0.006 !

[Bob Johnson]

Vacuum test. See link below.

http://www.modelahouse.com/images/vac01.mp4

[George Miller]

Originally Posted by Tom Wesenberg

I agree and that's why I suggested the propane check. If the propane or other flammable liquid doesn't show the problem, then I'm back to thinking it could have slow to close valves, and that's where the vacuum gauge should show a good flicker of the needle.

A scope check could eliminate the electrical, but the wire swap Bob did pretty well also eliminated the spark. It's just nice to see what's actually happening on the scope. At the least I would check the top distributor plate for side play, and remove the cap and rotor, hand crank the engine, and make sure each lobe opens the points exactly .020" and make sure the points have good spring action. I have seen where the copper points strap touched the cam, so make sure this isn't a problem also.

Yes it could be a slow closing valve also.

[Jacksonlll]

Guys, it sure sounds to me like an intake manifold or gasket leak. They can be very hard to find.

[1crosscut]

Earlier I suggested swapping #1 & #2 plugs to #3 & #4 locations. Have you tried that?
I know it would be unusual for two plugs to fail simultaneously but... an easy one to check.

[Simonpie]

That 25 Ft-LB to rotate the crank equates to 7 HP at 1500 RPM. That might be pretty noticeable in a 40 HP motor. I noticed in my new motor that the rope gasket in the front really choked thing down. My pulley got hot from just minutes of running. I'd lean toward putting a few hundred miles on it before getting too worried.

[aonemarine]

Might be time for a high speed pass down the interstate and a plug reading.......Im thinking vacuum leak also...

[Bob Johnson]

Tom you were right. I sprayed starter fluid around the intake and I got a speedup. I found a crack in the intake manifold. This did not show up with my first leak test because I was only looking at the gasket, my bad. Now I have to find another B manifold, open up an A manifold, just use an A manifold or ....

Bob

[CarlG]

I bought a propane torch just to do this type of test (unlit torch obviously).

[aonemarine]

Originally Posted by bob johnson

tom you were right. I sprayed starter fluid around the intake and i got a speedup. I found a crack in the intake manifold. This did not show up with my first leak test because i was only looking at the gasket, my bad. Now i have to find another b manifold, open up an a manifold, just use an a manifold or ....

Bob

bingo!

[tinkirk]

why not just repair what you have

[Bob Johnson]

I do not think I have the talent to repair it.