Got the MC2150 dialed in real good about a month ago... great idle, great response, no surging or stutter.
Last night while out driving with the wife, I notice a stutter that starts getting worse. Shut it off at a store, 15 mins later, come out and starts fine, however, it falls flat on its face when trying to accelerate. Carb has new power valve, new jets, getting, good pump shot, no new changes, since last month, and has been running perfect.
Double checked pump shot (good) checked timing (good), checked mixture (good). No backfire since new PV, and no fuel in PV cover. Really, as far as I can tell carb is un-changed. This happened while driving, then sitting for about 15 mins.
Pulled filter, dumped out gas, through cheese cloth, its clean. Blew compressed air from where fuel line connects to pump, back to tank, fuel blew out open tank fill.
I'm thinking bad fuel pump, (replaced about 6 months ago with NAPA pump) or bad gas, or obstructed pickup.
Idles perfect, revs perfect sitting in driveway, try to drive...bog.
Power valve nozzles? Do you mean the accelerator nozzles??
Edit... they are the Pullover discharge nozzles.
Maybe I'm wrong on what they are...above the accelerator nozzles, are 2 nozzle looking things. I assumed they had something to do with the PV. When I rev the motor by hand, I see the acc pump squirt a good shot from the pump nozzles, then a momentary misty spray out of these other nozzles.
Getting good shots from acc pump. With motor off...I get 3-4 good shots as well, when working the carb by hand.
Checked the vac advance on DUI dizzy, unplug the line, rpm drops, plug back in, rpm rises, hit the throttle, watching timing mark with a timing light, the mark moves to where it has always moved to before this all started. Let off the gas, mark returns to set point.
Like stated this happened to a well running motor and carb, in a matter of minutes without any previous changes or tinkering that I can tie back to it. one minute its running perfectly, and the next, its a bogger. Idle and revs fine in the driveway.
So today, I put in a new power valve, still bogs, new acc pump, still bogs, re-check timing, spot on. Electric choke is working correctly. Re-check for vacuum leaks, can't find any, vacuum gauge is nice and smooth, no erratic movements. No audible misses or sputters while at idle, or when reving in the driveway. Have good voltage on volts gauge. DUI is getting voltage direct from battery through a relay. Re-checked all plugs for fouling, they are nice and tan, and clean. Re-check gap @ .50
Only rubber fuel lines are the one's right at the tank, a short 4" piece up front, from the steel line end, to the pump, and from the pump to the filter. I don't see any leaks or moist spots on any fuel lines, and other than the rubber lines at the tank, which I can't see by myself while trying the re-create the symptom, no signs of collapsed hoses. Filter is a brand new WIX, correct position with return nipple at 12 o'clock. Fuel pump is brand new, and working.
I did recently fill up with about 12 gallons of gas from a high volume station. Yesterday, I plumbed a 5 gallon gas can with fresh gas from a different station, into the newly installed pump, with clear hose, and tried to run it. It started, idled, and reved fine, bogged under load.
This carb was a new MC2150 from the eBay guy, and after getting it dialed in, has run very well. It is not dirty and worn out, no junk in the bowl. It's less than a year old.
I'm going back out to re-check float level, if that does not help, I am at the end of my abilities to diagnose this.