question about carbs.

[jgreg53]

My P15 has the carter b and b.  I have rebuilt it twice, the second time with a kit from Mikes carbs with video instructions.  I have a skip at idle. While it's not bad it still grinds on me.  It's not on one particular cylinder.  I can adjust the idle mixture and make it better or worse but it doesn't go away completely.  I have changed points and plugs a couple of times.  any ideas?

[Dave72dt]

Compression readings?  What's been done internally on the engine and how many miles ago?   Vacuum readings?  Distributor shaft wear?

[jgreg53]

I have checked all that, Dave. The motor has never been opened up from what I can tell.  Compression is good.  Vacuum readings are good.  Distributor wear is minimal. I'm thinking a vacuum leak somewhere.

 

Edited October 10, 2018 by jgreg53

[Dave72dt]

 Have you tried using a timing light  on each plug wire and the coil wire to help determine if it's an ignition problem?  How about a cylinder leakdown test?  As you look down the carb, do you see drops of fuel happening.  Having not been opened up, as far as you know, you could have broken rings, valves hanging on an intermittent basis and the closer to the lower end of the "good compression range" it is, the more likely you are to get a random misfire.

[jgreg53]

Didn't know you could do that with a timing light.

[Dave72dt]

Hook it onto each wire in turn and watch the flashes.  It's just a strobe that picks up the magnetic impulses as the high voltage goes through.  Wire doesn't fire, it doesn't flash.  You don't even have to aim it at the timing marks.  You can of course , if you want and you should get the same timing reading off of plug wire #6 as you did off #1

[Dave72dt]

Any test results?

[P15-D24]

Disconnect the distributor vacuum advance at the carb and plug the carb side. Test to see if the skip is gone. 

[jgreg53]

ok, thanks. I will try that.  I tried the timing light on each plug wire.  No skip in the strobe. 

 

[Dave72dt]

How steady are the timing marks?  Since you've pretty much verified the ignition system is working efficiently, the intermittent miss is either mechanical or fuel related.  Pick either and test to prove what is right.  compression reading, cylinder leakdown and vacuum readings, some visual inspections to pinpoint,and it may be a combination of several items that's causing the situation.

[torqczar]

 A can of carb. cleaner  w/tube , lightly spray  carb and anything that touches the intake.  If  spray finds  any sorts of spark, it will burn , and that's always exciting . .. my guess is a worn throttle shaft.  Or the less flammable  way,  fingers over the carb. to slowly  richen   mixture.  if its a vacuum problem it should smooth up  just before  trying to stall...this way doesn't pin point the location, but just verify  a leak ....... I want to see pics. of the plugs.

[jgreg53]

I have tried the things suggested.  I really think it's fuel and air related.  I can change the fuel air mixture and change the nature of the skip but not get rid of it altogether.  I did find a bad hose going to the vac. operated wiper motor. changed it and that helped smooth it out.  I took the air cleaner and soaked the horse hair in green cleaner and blew it out real good . that helped. I'm going to drive it this way for a while and see what happens.  Should the clamp holding the air cleaner on the top of the carb be tight enough to create an air tight seal?  I tighten it up as much as I can but the air cleaner will still spin around.

[Merle Coggins]

11 hours ago, jgreg53 said:

  Should the clamp holding the air cleaner on the top of the carb be tight enough to create an air tight seal?  I tighten it up as much as I can but the air cleaner will still spin around.

 

Yes, the air filter should clamp down tight against the carburetor. Are you missing the gasket? There should be a rubber gasket at the carb flange to aid in the sealing. Without it you probably won’t be able to tighten down the clamp enough to be tight against the flange. 

[johnsartain]

Mine doesn't have the gasket but it would be nice to have. Does anyone you know carry that item for sale?

[jgreg53]

I'm not finding one in my sources.  Should be able to make something.  I believe air getting in the carb around the clamp would be screwing with the air fuel mixture.

Edited October 30, 2018 by jgreg53

[jgreg53]

So I made a gasket from a piece of weather stripping. seems to help. Gonna keep looking for the correct gasket.

[Los_Control]

so here is a photo of what my original gasket looks like, I did not make this it was on the carb.

And if I needed to make another one, I have this handy little package of gasket material, is a variety of different thickness, cork and rubber. I bought it at local parts store.

 

[Dave72dt]

7 hours ago, jgreg53 said:

I believe air getting in the carb around the clamp would be screwing with the air fuel mixture.

Air coming through the clamp area of the filter is before all the A/F metering parts of the carb so it wouldn't affect the mixture.

[Dodgeb4ya]

9 hours ago, jgreg53 said:

I'm not finding one in my sources.  Should be able to make something.  I believe air getting in the carb around the clamp would be screwing with the air fuel mixture.

https://www.amazon.com/MAHLE-Original-G25936-Cleaner-Mounting/dp/B000CLKEXU

 Carb to air cleaner gasket..RockAuto has it too .MAHLE G25936 {Click Info Button for Alternate/OEM Part Numbers} Paper Info

[jgreg53]

can't tell from the pics how thick the gasket is from amazon

[jgreg53]

I made a gasket for tha air cleaner and carb. Still idling rough. I reshafted the choke rod. It was wallowed out. It's a mystery to me that i have to turn the mixture screw to almost bottoming out to get the vaccuum up th 19 lbs. How does the screw work? Turing it in makes more air and less gas?

[plymouthcranbrook]

Is it possible that the end of the screw or seat is damaged by someone previously turning the screw to tight into the seat?  A damaged seat or screw will let more fuel in and at a certain point you cannot lower the amount by adjusting it. 1 1/2 to 2/12 turns usually is about right.