What carb ya running? Maybe it's getting to large a shot from the accelerator pump?

 

It’s a Brawler Diecast 650 Mech. sec. It’s #67276.

I did overlook the accelerator pump but I did set it up to where it was adjusted properly when the vac advance was hooked to ported vacuum. With it now on manifold vacuum it idles a lot higher so I had to turn the idle screw back quite a bit and it has an off idle stumble now so I feel like if anything the accel pump is too loose.

Would it be a good idea to start turning up the timing until I hear pinging then back it off? I feel like 13 initial may be too low for this particular engine as before I changed the jets when it was on the 68s it was at around 16-20 degrees and it seemed happier and of course got better mpg even with the larger jets

 

Won't hurt to try it. Push it until you get spark knock under hard acceleration, then back it off a bit.

 

Update after driving about 20 miles or so, and it’s still running super rich. The timing is at about 14 right now on manifold vacuum advance. It is colder out but I feel like once the carb warms up that doesn’t matter, the idle mixture screws are almost all the way lean too and it still runs so maybe fuel is getting in somewhere else?

EDIT: Just did some more research. I have had a couple of intake backfires, primarily when I try to revmatch while the engine is still cold (my fault obviously). Could it have blown out the power valve?

 

Do you have adjustable main jets? Or do you have to replace them to change 'em? What are you running for a fuel pump?

 

Theyre not adjustable they’re just screw in replacements though. 4 bolts to take off the bowls and they’re right there, just need a flat head screwdriver. Stock the carb came with #71 primaries which were way too rich so I went down to #68s. While making it run more lean it was still super rich and you could smell it. Switched over to #66s and now it’s even more rich than it was with the original jets which makes me think maybe I blew up the power valve and it’s just gulping fuel.

I googled the symptoms of the engine running with the idle mixture screws all the way in and a blown power valve is one of the symptoms.

 

What's your inlet fuel pressure at the carb? I have seen electric pumps overpower the floats, and literally DUMP gas into the engine.....

 

It’s a cheap pump but it bounces around between 5.5 and 6.5psi, the carb wants 6.5. Bowls are set just below halfway on the sight class from what Uncle Tony recommended for daily drivers.

 

Maybe try lowering float level to just barely into the sight glass..... I seem to remember way back when...... before it was GLASS.... that we adjusted the floats until gas just started barely dribbling out the hole.

 

Small update, I replaced the power valve. I drove home for Thanksgiving and decided to stop halfway between school and home to measure my mpg (my chinese autozone fuel pump float sender is garbage so my gauge doesn't work), about 140 miles and I averaged 15.6mpg. It appears that I did somehow rip the diaphragm in the original power valve but its nice to be getting better mpg. I'm tempted to drop down one more jet size from the current #66 to a #64 to see if I can squeeze out any more mileage but 15.6 is better than 6 which is what I started with my last drive on the highway. I do plan on getting a wideband to really nail in the AFR in a more accurate way as well.

Next up on my list for toying around will be to lower the floats slightly, and move around the all in timing rpm with the kit I bought. I'm not entirely sure if changing my initial timing will really do anything as I'm pretty sure its as good as it will get in terms of efficiency. Surprisingly while I was readjusting the idle mixture after replacing the valve I was able to get 20 inches of vacuum at about 750rpm which is from what I've hard A LOT for an engine, let alone one with a small cam. I do want to get one of those "economy gauges" aka one of those vacuum gauges with like green, yellow, and red ranges for "economy" "power" and "idle" lol.