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Thought the Dellorto's had come out of synch due to sudden backfire through carb and exhaust.

Hooked up the Carbtune manometer and found cylinder number 1 just sucking air.

Checked for spark and found a wet spark plug but, spark was sparking.

Ran with #1 plug out and found compression (don't know how much without a comp. tester.) but, good suck through the carb.

 

Any thoughts?

Mike_

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i know little about your setup but it sounds like it dumped a bunch of gas and flooded the cylinder...dry out the cylinder and plug and try to start it then check your fuel delivery

 

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A cylinder only needs three things to fire: Fuel/air mixture, compression, and spark. Wet plug indicates you're *probably* getting proper fuel, but on sidedrafts since each cylinder gets its own jets can't hurt to pull them to check.  Compression yeah is best checked with a compression tester, but I think those are pretty easy to rent from Autozone if you don't have one.  Spark is usually the culprit, I'd guess maybe 7 times out of 10 anyway.  And since the other 3 cylinders are good you can rule out the points, condenser, coil, rotor, and timing.  Quick visual of the cap will tell you whether that's the problem or not, and then it's just down to swapping around wires and plugs.

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Yes, swap the plug wire first.  Then drive it a little ways. (around the block).

 

Compression test first, then leakdown if you care to know where the

failure is before you take it apart.

 

You have checked valve lash, haven't you?

 

t

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Gotta assume you guys mean change out the wire with another one and not pull

the number 2, 3 or 4 wire from the distro and put on the number 1 cylinder.

This adventure would prove the plug wire is bad? It was "tested" with another

spark plug on the wire with the motor running.

 

Yes, very few hours since the valves were adjusted.

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5 hours ago, TVeye said:

Gotta assume you guys mean change out the wire with another one and not pull

the number 2, 3 or 4 wire from the distro and put on the number 1 cylinder.

This adventure would prove the plug wire is bad? It was "tested" with another

spark plug on the wire with the motor running.

 

Yes, very few hours since the valves were adjusted.

We mean move #1 wire and plug to #2 and see if the problem moves. Then figure out which it is. My old snowblower taught me that just because a plug test fires against the cyl head, it may not give enough spark under compression installed. I also spent hours fiddling with DCOE when problem turned out to be a failing plug wire with intermittent miss. So when you say tested, how did you test?

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Yes, very few hours since the valves were adjusted.

 

But take the valve cover off and check them now. 

If something's gone wrong under there,

from a wiped lobe to a slack adjuster to a dropped seat 

to an exhaust that can't close all the way-

well, there's your problem.

 

You don't need to lash them- just get #1 to TDC

and see if both rockers have a bit of clearance.

 

Easy to rule out.

 

t

 

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