Cylinders 1&2 colder than 3&4 and lack of power

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Edwin Ek
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Re: Cylinders 1&2 colder than 3&4 and lack of power

#16 Post by Edwin Ek » Sat Oct 13, 2018 8:38 pm

I second Wes's suggestion, which is the easiest to try also. Pull #1 and #2 plug wires and see if running characteristics change. If no change, no spark is reaching those cylinders. That's a big clue and lead to pursue. If change, some spark is reaching those cylinders, so check fuel delivery next.
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Re: Cylinders 1&2 colder than 3&4 and lack of power

#17 Post by Norm Miller » Sun Oct 14, 2018 11:47 am

Perhaps the 3-4 side is lean?
How hot is hot or cool is cool?

The fine art of sliding 7mm hose onto 8mm pipe can shave little chunks of rubber into the carbs.
Consider the hose joining the 1-2 line to the 3-4 line behind the fan housing, actually the front of the engine.
 

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Re: Cylinders 1&2 colder than 3&4 and lack of power

#18 Post by Wes Bender » Sun Oct 14, 2018 2:05 pm

I'm having a bit of difficulty figuring out how lean setting on the #3 & 4 side would cause his symptoms of poor running on the other side, Norm. Could you help me to understand that?
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Re: Cylinders 1&2 colder than 3&4 and lack of power

#19 Post by Miguel Antonetti » Sun Oct 14, 2018 10:04 pm

I really appreciate all the comments and recommendations... have already checked few of them but there are a couple that I haven't. No improvement thus far :(

I just realized that I haven't mentioned the carbs are Weber 40.

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Re: Cylinders 1&2 colder than 3&4 and lack of power

#20 Post by C J Murray » Mon Oct 15, 2018 7:11 am

The only difference with Webers from Zenith or Solex that could be a cause is that the floats have to be set in the full open position as well as the full closed position. Weber floats are not allowed to drop until they hit the wall of the float bowl and this is to eliminate one reason that carbs flood. Google it.

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Re: Cylinders 1&2 colder than 3&4 and lack of power

#21 Post by Norm Miller » Mon Oct 15, 2018 10:08 am

Wes Bender wrote:I'm having a bit of difficulty figuring out how lean setting on the #3 & 4 side would cause his symptoms of poor running on the other side, Norm. Could you help me to understand that?
I guess I was thinking one side warmer than the other and not poor running. I lose the guessing game prize!
If I was working on it I'd start out step by step.

Recently after rebuilding a pr. of Zeniths with Royze kits, I encountered a sticky needle valve which caused flooding.
I put the old valve in and all was good again.
Trouble can come from anywhere but most likely it will be the last thing on which you worked.
 

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Re: Cylinders 1&2 colder than 3&4 and lack of power

#22 Post by Mike Horton » Mon Oct 15, 2018 10:55 am

John Ward wrote:Did you pull the carb or the manifold off on that side when you pulled the fan housing off ?
Sometime, you`ll get an air leak and that would cause that bank to have problems

I'm leaning with John here, I have a 912 friend, who bought a used engine, decades ago, and found a small piece of the manifold to head gasket missing. IIRC, he verified that leak, engine running at idle, by squirting some fluid down there, and it temporarily sealed the vacuum leak, which then, could call for the correct fuel draw from that side carb.

I'm with Vic, C.J., and others on the crossed wire possibility. Any who've not done (admitted) this, haven't worked on enough flat fours...
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Re: Cylinders 1&2 colder than 3&4 and lack of power

#23 Post by Mike Horton » Mon Oct 15, 2018 10:57 am

Norm Miller wrote:
Wes Bender wrote:I'm having a bit of difficulty figuring out how lean setting on the #3 & 4 side would cause his symptoms of poor running on the other side, Norm. Could you help me to understand that?
I guess I was thinking one side warmer than the other and not poor running. I lose the guessing game prize!
If I was working on it I'd start out step by step.

Recently after rebuilding a pr. of Zeniths with Royze kits, I encountered a sticky needle valve which caused flooding.
I put the old valve in and all was good again.
Trouble can come from anywhere but most likely it will be the last thing on which you worked.
Amen! +1
Mike

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Re: Cylinders 1&2 colder than 3&4 and lack of power

#24 Post by Mike Horton » Mon Oct 15, 2018 11:06 am

C J Murray wrote:The only difference with Webers from Zenith or Solex that could be a cause is that the floats have to be set in the full open position as well as the full closed position. Weber floats are not allowed to drop until they hit the wall of the float bowl and this is to eliminate one reason that carbs flood. Google it.

http://forums.pelicanparts.com/porsche- ... ectly.html
I've helped others set the Weber float heights before, one set the original Italian, and as delivered, the other Spanish, and rejetted by a VW shop, when they "rebuilt the carbs". Of the 4 float heights, NONE were correct, and after the corrrection, ran well. just my $.02 worth of experience.

C.J., is right on this, and IIRC, runs Webers on his street car.
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Re: Cylinders 1&2 colder than 3&4 and lack of power

#25 Post by Dave Wildrick » Mon Oct 15, 2018 11:41 am

So far, no one has mentioned the most frequent problem I have had with Weber IDF40s--the idle jet clog, which can produce the symptoms described.
The easiest way to check for this is to fit the leads loosely on the distributor so you can lift one without having the cap come up with it.
At idle, lift the #1 lead from the cap and see if the idle drops. If not, you have an idle jet clog on #1. Do the same with the #2 lead; no idle drop, no clogged idle jet.
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Re: Cylinders 1&2 colder than 3&4 and lack of power

#26 Post by Miguel Antonetti » Mon Oct 15, 2018 5:52 pm

Well well well surprising to me, but hey, it happens and I'm definitely getting old sooooo... the issue was cylinder 2 plug was shot, as in "no gap". I could swear I calibrated them all - brand new - setting the right gap before putting them on last week while the engine was out - so easy then, almost impossible to damage the tip. But I guess I did. Otherwise, how could that happen?

Many thanks for all the assistance, as always, extremely helpful...

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Re: Cylinders 1&2 colder than 3&4 and lack of power

#27 Post by C J Murray » Mon Oct 15, 2018 6:09 pm

If your engine has the piston closer to the spark plug than stock, which is often the case, you can not use extended tip plugs used in stock engines. What plugs did you have before vs now?
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Re: Cylinders 1&2 colder than 3&4 and lack of power

#28 Post by Miguel Antonetti » Mon Oct 15, 2018 8:47 pm

Same plug before and after CJ, Bosch WR6BC these ones made in Russia.

I went for a spirited drive, the car was feeling real good, after 30' or so it started to miss a little at mid throttle good at WOT, when I got home, let it cool and pulled the same plug #2 - easy one :-) not completely shot this time but the gap was reduced from .55mm to .25mm. Why would this happen all of the sudden? What's changing, piston, head, connecting road, shaft/bearings… or just an out of spec spark plug? I know, stay tuned...

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Re: Cylinders 1&2 colder than 3&4 and lack of power

#29 Post by C J Murray » Tue Oct 16, 2018 6:44 am

Oh no! Not Russia again!

I don't use Bosch but I am pretty sure that is a projected tip plug. Change to "regular" plugs and the problem is solved. NGK is a much better plug. B6HS, B7HS

If the porcelain is chipped by the impact from the piston you could have BIG problems. The porcelain is very much harder than pistons, cylinders, and valves and even small pieces will "machine" your engine into death mode unless it miraculously flies out the exhaust without hitting anything.
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Re: Cylinders 1&2 colder than 3&4 and lack of power

#30 Post by C J Murray » Tue Oct 16, 2018 6:53 am

The reason this didn't happen before is that the ground electrode was facing another direction when installed or maybe the new plug was a few thousandths larger. When things are this close it is normal for higher rpm to close the plug further so at first it runs ok and then it doesn't which doesn't really point to a spark plug.
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