MC2100 leaking venturi question

[80GoldenEagle]

So in the process of getting the AMC 304 tuned, I noticed I had a rough idle issue that I could not seem to eliminate. Upon looking into the carb at idle, I heard & saw that the left venturi had a very steady leak. Almost to the point of being constant. In the picture below, the one on the left looks a bit wetter than the other.
View attachment 14923
My plan is to pull the top of the carb off, verify the wet float level. Is there anything else anyone can think I should look for? I also plan to pull the venturi booster assembly to verify that it is as it should be. I have seen the copper sleeves around the needles split down the seam & want to make sure these aren't. Anyone else have this issue? Thanks in advance for any & all help.

 

[80GoldenEagle]

Just to give some background, it's a stock AMC 304 with carb rebuilt within last 6 months. I rebuilt it myself as one of the first steps in resurrecting it from "barn status".

 

[Fastatv]

I had a very similar problem with my MC2100 on my 360, was running very rich and idling poorly. Your problem could be as simple as a float that is adjusted too high. That was the first thing I tried on mine....made no difference. I soaked and rebuilt the carb, problem went away. I found that the accelerator pump weight was missing ( but ball was there ), no gasket between the Acc pump screw and venturies ( the hollow screw that holds the venturies in ), the needle valve seat was missing the shroud, the power valve had the wrong gasket on it, and there was no gasket under the plate that the carb bolted to. I hope this helps in some way. Let us know what you find and good luck!

 

[80GoldenEagle]

Thanks for the reply, I'll keep an eye out for all that. Here's what I found with the venturi booster. View attachment 14924
View attachment 14925
These tubes are cracked & may be letting the flow of the idle circuit cross with the main metering circuit. Not sure if that is my exact problem, but can't be very good none the less. So I guess I'm on to finding another venturi booster or another complete carb. Well see what happens once I move forward from there. Thanks again for the input.

 

[Fastatv]

You know you mentioned that...good catch! I have built carbs for over 30 years, and I have never seen that. I just learned something.....thanks

 

[80GoldenEagle]

Just to update, have not had much luck locating any parts for the carb, so I just ordered a carb from National Carburetor. I was really hoping to be able to troubleshoot this one as it was an opportunity to learn something but that's how it goes I guess.

 

[GRONK Performance]

Wish I would have seen this earlier. I have thousands of 2100's in stock and have bins full of venturis clusters. The cracks are caused by water getting in your fuel system and freezing.

If you want to sell the core, let me know or if your new carb needs anything, I can help. I'm assuming your 2100 has a 1.08 venturis casting. I would have recommended going to a 1.21 if buying a new carb (350 CFM) It's a little more carb and the AMC 304 's love it.

 

[Fastatv]

Wish I would have seen this earlier. I have thousands of 2100's in stock and have bins full of venturis clusters. The cracks are caused by water getting in your fuel system and freezing.

If you want to sell the core, let me know or if your new carb needs anything, I can help. I'm assuming your 2100 has a 1.08 venturis casting. I would have recommended going to a 1.21 if buying a new carb (350 CFM) It's a little more carb and the AMC 304 's love it.

Question for you. What's the venturi size for an AMC 360? Thanks

 

[80GoldenEagle]

Thanks for the reply Gronk, I just now saw it after I already got a new carb. I may take you up on the parts as I plan to keep the original carb as a spare. I installed the new 2100 from National Carburetor & that fixed it. It's amazing how easy these are to tune when the RPM's aren't jumping 200-300 RPM. Runs awesome now, comparatively anyway. Thanks again for all the replies. Here's a pic of the carb.
View attachment 15009