Stromberg and car gas
Posted: Sat May 21, 2022 12:44 pm
OK long story short I’ve been burning 100LL for a long time due it storing well and availability and car gas just stinks. I have a 280 gl tank in my hangar now for 100LL.
I have run straight no ETH car gas before and it ran beautifully.
Due to the insanity of fuel prices I’ve decided to put up with the hassle to save some bucks, initially everything was fine with a blend of the two, but once I ran the port tank down to 1/4 and filled up with car gas at mid range 1500 to 1800 or so it hesitated and even seemed to have a slight miss. So I thought somethings wrong with the carb, it’s after firing slightly just in that range, runs fine WOT, so I spent yesterday going through the carb to not find anything, it has been almost 15 years since I was there before repairing a leaking float and I was sort of happy but disappointed to find everything clean and no throttle shaft wear etc. However I did blow out the mixture assy with carb cleaner and got some what looked like dirt out, so I thought great that’s it, slightly clogged mixture bleed hole would make it go lean.
Also read the thread where car gas will cause a Stromberg to stumble and thought maybe it’s normal, almost convinced myself of that.
Went out and ran it just now, some mid range stumbling and even some slight missing, but ran fine at idle and WOT, ran it awhile thinking maybe getting hot it would get better and playing with the ultra sensitive mixture to see if it helped, it didn’t and it didn’t improve when fully warmed either. Switching mags didn’t point to either mag being an issue.
So I started looking, with my finger and calibrated spit I determined 1,2 and 4 cylinder head would fry spit, but number 3 wouldn’t, it was too hot to touch, but not fry spit hot. So I did have a weak cylinder, further looking and you could see the inner rubber out near the head on the intake tube had slipped down, getting a screwdriver further confirmed the intake leak hypothesis as the clamp wasn’t real tight. I loosened the outer rubber slid it down, repositioned the inner and reinstalled the outer and tightened the clamps.
Engine runs beautifully now, no stumble. I can even open the throttle very fast from a high idle to wide open with no stumble and no miss.
So I don’t think a stumble on car gas is normal, mine didn’t use to, and apparently once I fixed the vacuum leak it still doesn’t.
So if your engine stumbles on acceleration you may have something wrong, she just might be trying to tell you something, do some looking
I have run straight no ETH car gas before and it ran beautifully.
Due to the insanity of fuel prices I’ve decided to put up with the hassle to save some bucks, initially everything was fine with a blend of the two, but once I ran the port tank down to 1/4 and filled up with car gas at mid range 1500 to 1800 or so it hesitated and even seemed to have a slight miss. So I thought somethings wrong with the carb, it’s after firing slightly just in that range, runs fine WOT, so I spent yesterday going through the carb to not find anything, it has been almost 15 years since I was there before repairing a leaking float and I was sort of happy but disappointed to find everything clean and no throttle shaft wear etc. However I did blow out the mixture assy with carb cleaner and got some what looked like dirt out, so I thought great that’s it, slightly clogged mixture bleed hole would make it go lean.
Also read the thread where car gas will cause a Stromberg to stumble and thought maybe it’s normal, almost convinced myself of that.
Went out and ran it just now, some mid range stumbling and even some slight missing, but ran fine at idle and WOT, ran it awhile thinking maybe getting hot it would get better and playing with the ultra sensitive mixture to see if it helped, it didn’t and it didn’t improve when fully warmed either. Switching mags didn’t point to either mag being an issue.
So I started looking, with my finger and calibrated spit I determined 1,2 and 4 cylinder head would fry spit, but number 3 wouldn’t, it was too hot to touch, but not fry spit hot. So I did have a weak cylinder, further looking and you could see the inner rubber out near the head on the intake tube had slipped down, getting a screwdriver further confirmed the intake leak hypothesis as the clamp wasn’t real tight. I loosened the outer rubber slid it down, repositioned the inner and reinstalled the outer and tightened the clamps.
Engine runs beautifully now, no stumble. I can even open the throttle very fast from a high idle to wide open with no stumble and no miss.
So I don’t think a stumble on car gas is normal, mine didn’t use to, and apparently once I fixed the vacuum leak it still doesn’t.
So if your engine stumbles on acceleration you may have something wrong, she just might be trying to tell you something, do some looking
, Harbor Freight has their laser thermometer on sale this weekend for nominal $20. Yeah, I know it's not to NTSB standards, but ok for troubleshooting and comparison among cylinders, etc.