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Started it up, let it warm up a bit, idled down to around 750-800 then picked it up to 3000, pulled the plug cap on 4 and could not tell any difference. ???

Easter wrote:snip................. I am using a timing light/tach/dwell meter clipped to number 4 wire so I think I am getting a pretty good rpm count and am positive that it is getting spark. .

That's not an accurate way to check for spark at the plug.


Pull the wire, install a plug and lay it on the head to ground it. Then see if you have spark at higher rpm.
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Easter wrote:Started it up, let it warm up a bit, idled down to around 750-800 then picked it up to 3000, pulled the plug cap on 4 and could not tell any difference. ???

That doesn't sound carb related. At least not the idle circuit.

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I have used a spark plug and a screw driver shaft to ground. Strong spark. You can actually see the spark go to the plug when I start to reattach the cap. I switched plugs between #2 and #4 to verify that it wasn't a bad plug. I even pulled the screw out of the intake runner to verify that I had vacuum (running out of ideas).

Have you tried a new plug?

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They are new and I switched 2 and 4 to be sure.

Be very careful doing this but maybe try a shot of starting fluid in the hole for sync screw while it is running.
Both at idle and at higher rpm.
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Out of curiosity and for lack of anything else to try, I decided to see if I could sync the carbs. Especially since number 4 is from a different set. I am not sure what it says if anything but I was able to get quite a close match at 1000 rpm.

I did squirt a little starting fluid and the engine would pick up very briefly in both situations. Just to be sure nothing had changed, after I replaced the screw and let it idle down, I pulled the cap from the plug and still no change to engine speed.

If the squirt of starter fluid kicked up the engine, it's almost certainly a carb issue, I would think...

quote:"Out of curiosity and for lack of anything else to try,"

Did you try opening the fuel bowl drain screw? Does any fuel come out?

gltriker wrote:quote:"Out of curiosity and for lack of anything else to try,"

Did you try opening the fuel bowl drain screw? Does any fuel come out?

Yes, covered somewhere above.

You've tried two different carbs and had the same issue correct?

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Well maybe, the idle circuit is definitely plugged solid on the first carb but clear on this one. I have ordered a third carb but won't see it till sometime next week.

Erichheath wrote "Back to Easter’s issue with 1200 carbs. The needles on the end of the starter valves (choke) and the air/fuel screws can break off. Maybe you looked for sure but you could check that they each have their needles in tact and that one isn’t broken off in the respective holes for them in the carb body. PO snafu. Another possibility is a PO substituting a mixture screw from a different model which could be a different length. Kind of a pain in the butt, but maybe."

Haven't looked closely at the starter valves except to see they move smoothly and are as a group functioning to start when cold. Mixture screws have their tips and springs and o ring. Seem to be identical in both carbs. On the carb presently on the engine adjusting the screw in or out makes no difference. But then it wouldn't if that cylinder wasn't functioning (i.e. no spark or fuel or just away on vacation)

Even if the starter valve on #4 was broken wouldn't it still run at higher rpms?