Explosions in carb!

[stuartrubin]

First thing for those who have been reading my posts: maybe I'm not a car guy...

Second, I have an even more "interesting" problem with setting up my new Chinese ADF 34. For background, I installed the carb, had a small air leak at the base. I also had a loose set screw which was keeping the secondary throttle open. Otherwise things seems OK.

Today, reinstalled the carb with a new paper-backed spacer which I oiled. I put some permatex on the loose set screw. I got the car running and warmed up to tune the idle mix and speed. After some time, I noticed that the choke was still mostly closed, and had previously observed that the choke was rotated 90 degrees from the typical install. Because of the way the water tubes connected, I had to disconnect the tubes before I twisted the choke base back. I forgot that this would cause a good bit of coolant to spray (luckily I did not get burned) and some coolant got on, and maybe a few drops IN the carb.

Restarted the car, let it warm up, and now whenever I open the throttle I get an explosions (visible, loud, kind of scary!) coming out of the top of the carb!

What's with this? I assume that anti-freeze is not explosive or flammable. Could the little bit of oil on the gasket be exploding? Again, I doubt that, too.

I also would have expected to get burned from the coolant. Maybe the engine wasn't really warmed up, even though the thermostat was right in the middle of the dial, and I should not have twisted the choke. Even still, I would not expect that to cause explosions, just a hard time getting the idle, throttles, etc. correct.

I have read that explosions (for lack of a better word) may be from overly rich mixes, but I don't see what I could have changed mix wise. The only adjustment was the idle mix screw and speed, but that shouldn't really affect the mix when you open the throttle.

All advice and sympathy welcome! Thanks.

[bradartigue]

Usually a timing issue. Now that your car is working a bit better have you checked the ignition timing? Make sure it is right before you start diagnosing the carb.

[sptcoupe]

You also need to check the jetting since the carb wasn't a stock carb for the TC. Who knows what jets are in there. A backfires or cough in the carb is also a symptom of a lean condition.

And coolant in the carb will cause the same, but it should clear up after a bit of running.

[stuartrubin]

sptcoupe, since it was "sort of" working (with just a minor air leak and loose set screw), I'm hoping that it's not a jetting problem. Others have reported that their Chinese carbs worked with the jets as-is (but some have not). I AM hoping that the issue is coolant! That stuff does NOT want to evaporate... I don't know much about antifreeze, but I'm assuming it's expanding and boiling and just throwing gas/air mixture out as it expands. Maybe not.

Should I be SCARED of these "backfires" (for lack of a better term)? Is there any kind of fire hazard? Honestly, I was very skittish in the hours when I was fooling with the car today and only pulled the throttle back hard once and got one backfire. I did take it around the neighborhood for about a mile, but only got up to about 25 MPH.

Brad, the timing was professionally adjusted when I had the engine apart to fix all the oil leaks. Would the timing change with a carb change?

As for the choke, I took the cap off and saw that the nut which holds the spring/cam/choke assembly was not attached. It's possible that since the nut wasn't attached that the whole choke mechanism was just sort of jammed up. I got that in place, including a nice plastic insert which guides/limits the turning of the fork to the spring. Finally today I was having trouble keeping it idling AT ALL when cool and I believe that the fast idle screw (which butts against the cam inside of the choke) is not set correctly. I can't look or adjust it easily until everything is cooled off. Hopefully tomorrow.

Does anyone have a guide for setting the fast idle screw? The shop manual shows doing it with the carb removed and taking some pretty fine measurements of the secondary throttle opening. I'm hoping there's an easier, if not perfect, way to do it.

Thanks!

Stuart