My finicky 360

tbm3fan

Old Man with a Hat
Joined
Jan 22, 2012
Messages
5,254
Reaction score
2,805
Location
Pleasant Hill, CA
Things cannot be that hard when it comes to tuning a Mopar 360 could they? I have no trouble with all the Ford engines but the 360 denies me.

Today I went to take it out for a drive. Noticed that the engine had a subtle surge and at times a subtle stumble. Felt the slight surge when on the freeway at 65mph. Felt surge and stumble when at a stop light which had me keep my foot on the gas. Did get home ok.

Pulled out my tools to take a look. Checked all vacuum lines as first order in case any off. No, they were all on and being replaced two years ago all good. Hook up vacuum gauge and timing light. First thing I notice is the vacuum is at 15mm and bouncing about 2mm. You can see, hear and feel the engine surge and then stumble back before starting it all over again. Checking timing and don't see a damn thing. The marks had been detailed out every 10 degrees and they were nowhere to found. Whatever.

So I loosened the distributor and moved it to tune by vacuum. Highest vacuum was reached at 20mm. Still no timing marks and the vacuum gauge bounced between 19-21. Still could see the engine bounce back and forth, feel it in the body, and hear it via the fan speed as rpm varied. The idle mixture screws were already at highest vacuum while idle speed close to 900-1000. If at 750, as called for, the engine died when in drive eventually. Anyway called it a day to think on it for awhile.
 
I do not know which year 360 you have or the model of carburetor. I have a 1973 Monaco with the 360 2 bbl Holley 2210 on it. I have had a bear of a time making that thing run right - I have had it apart and back together several times now, and had to give up on it. I looked at all the service manual diagrams of fuel flow, and can't figure out why this Holley won't idle right and also stumbles and sags on launch from a stop (and I made sure the accelerator pump was functioning just fine). Some of the 1971 - 72 Holley 2 bbls had the air cleaner stud fastened only to the top part of the carburetor (fixed in 73 and later carburetors by screwing the stud into the main body as well), and after some years of operation with the air cleaner screwed down too tight, the top part would bow upward, causing it to run lean. There is a service bulletin on a fix for this issue if that might possibly be the model year of your car/carburetor. The service bulletin can be found on the Hamtramck Registry website. I had another 360 with that actual problem, and I fixed it per the service bulletin, and when I rebuilt it, it ran fine.

I ordered a rebuilt carburetor from NAPA for my Monaco though, thinking there must be some warping of the carburetor causing an internal leak, and decided to just get a rebuilt one . But it was just as bad as the one I rebuilt. Then I put the Holley 2 bbl that I fixed and ran well, on the Monaco, and it ran fine. So something in these Holleys is a systematic problem that is not easy to find. I am pretty much done with original Holley carburetors - they are all warped pieces of junk. Never had a problem rebuilding a Carter. I feel your pain........ When these 360s have a good carburetor, they run awesomely smooth and reasonably quick.
 
Yep, 73 Polara with the 2bbl Holley. When I first got the car I toyed with the idea if I could get a Autolite 2100 to fit. Might be time to try out that Carter 2bbl. I have sitting in the garage. I have the same stumble from a dead stop also and always have had it. Stumbles and then boom off it goes.
 
If it is a Carter that also stumbles, it is likely an accelerator pump problem. I had a 70 Newport with the old big Carter 2 bbl and it was flawless. You might want to be sure your vacuum advance can on the distributor is not leaking as well.
 
The carb is a Holley 6486 that was stock. As for the advance can on the distributor it was plugged while I was trying to tune the engine.
 
Actually the 6486 is the Holley part number while the designation 2210 is the Holley model number. Sorry for the confusion. I was thinking having vacuum advance operational when accelerating at least fairly lightly tends to help minimize any stumble problem. There is usually no vacuum to the distributor advance at idle, unless the idle speed screw is adjusted out a lot more than normal, but plugging it off while adjusting is good.
 
The more I read on the BBD the more I see owners complaining about them also being a crappy *** carb. Stalling, stumbling and hard to tune. Will have to see how it works out. While looking online I saw some info about using a MC2100 or 2150 on Jeep engines and some AMC engines. That still intrigues me as I have never had a problem with those carbs. Easy to adjust and never let you down. It would be nice to enjoy driving the Polara if I didn't have to worry about moving from stop, feathering the gas and the terrible gas mileage of 10 mpg. Even my big 410 FE, known for poor mileage, gets 12 mpg.
 
Last edited:
Best thing I ever did for my built 360 was replacing the carb with a Holley 4412. I also tried a GM Rochester 2 BBL that ran like a champ.

Are you absolutely sure you don't have a vacuum leak somewhere? Did you sniff around with some spray while it was running? Or some propane?
 
Best thing I ever did for my built 360 was replacing the carb with a Holley 4412. I also tried a GM Rochester 2 BBL that ran like a champ.

Are you absolutely sure you don't have a vacuum leak somewhere? Did you sniff around with some spray while it was running? Or some propane?


Vacuum leaks were highly unlikely given that the engine wasn't doing this two months ago. Nonetheless, that is the first thing I did check while it was running. Yet the tendency to pick up rpm and then bleed off rpm and on and on would argue against a steady vacuum leak.
 
I am trying a second rebuilt carburetor, this time by United. I would like to know what it is about these Holleys that is so problematic. It isn't obvious, that is for sure. I never even try to rebuild a 4 bbl original Holley, a complete piece of junk with castings that warp with time internally and outwardly. Just replace them. I see Holley offers their own rebuilt 2 bbl 2210 model but they want $450 for it. I will go with a Motorcraft carb before I give Holley any more of my $$.
 
Hey TBM I have had the stumbling problem with a number of holleys regardless of 2 or 4 barrel, the problem has always turned out to be the accelerator pump diaphragm which while not perforated, becomes worn.
 
Surging is almost always a lean condition especially at speed/cruising. A stock carb is usually never lean, sounds like a vacuum leak or a fuel supply problem does it run okay at w.o.t.?
 
Hey TBM I have had the stumbling problem with a number of holleys regardless of 2 or 4 barrel, the problem has always turned out to be the accelerator pump diaphragm which while not perforated, becomes worn.

I have had only one other Holley in my cars and that was a 4bbl from the Ford Performance book in 1970. Had it modified by Fuel Curve Engineering back then and it always ran well. Have had several Autolite 2100, 4100 and 4300 carbs handled by the late Jon Englert, of Pony Carbs, and they ran beautifully. The 4300 would make you think it is fuel injected in that it is that smooth.

I am going to throw a few others on and see how they run. Still don't think it is a vacuum leak given at the vacuum hoses check out like always. Yet even at highway speed there is still a sense that the engine has a very subtle hiccup at 65. More a feel in the foot than in something you hear.
 
The 2 bbl Holley 2210 models do not use an accelerator pump diaphragm as do the 4 bbls. It is a conventional plunger and cup pump design like the Carters have. But they have more adjustability than the Carters. Just the mention of this issue though, reminds me that my 2 bbl Holley that ran well also had a stumble on launch from a stop - and I really didn't think it was the accelerator pump because it had a good discharge of fuel when looking at it. But it turned out to be that despite having the accelerator pump rod in the specified slot for my application, I moved it up to the next notch to extend the pump shot duration, and the stumble went completely away. Apparently despite the healthy shot of fuel visually, it wasn't continuing quite long enough to prevent the stumble. I was quite surprised at the fact that just adjusting it one slot completely cured the stumble problem. Sorry I didn't remember this earlier.

As far as surge, since yours is a 1973 vehicle, you very well might have an EGR (exhaust gas recirculation) valve (mine does). Sometimes you can feel surge at light acceleration and steady cruising from it especially if the carburetor is calibrated on the lean side. You might disconnect the EGR to test if that might be the cause, and maybe enrich the metering system a little to cover it up if keeping the EGR (which actually allows a little more vacuum advance since it suppresses pinging, increasing your gas mileage). The EGR valves in 1973 were pretty small, so they were not so bad as the later cars such as in 1977 that really made for driveability problems.
 
My '79 New Yorker did the same surging. I tried Sea Foam etc several times. I suspected the accelerator pump. The mechanic said there was alot of gunk inside of it from sitting with ethanyl gas inside and the accelerator pump was chewed up. Now with the new kit in it fuel milege went up from 16 to 19 mpg for mixed driving.
 
Just wanted to provide an update on my own Holley 2 bbl problems. As I said before, I tried multiple times to rebuild one of my Holley 2bbls with no success, while another one I rebuilt worked just fine. After essentially giving up on the bad one, I ordered a rebuilt one from NAPA based on the claim that their Balkamp brand of rebuild was "engine tested by certified technicians" - so it had to work, right? Well, after a lot of $$ and a long wait, I got the carburetor and it was just as bad as the one I tried to rebuild with no success. So I returned the NAPA rebuilt one and went over to Autozone and talked with one of the counter guys that I know since I go in there all the time and just asked him if any rebuilds have a good reputation, and he suggested I order a rebuilt one from United. Well I received it today and installed it in just a few minutes (I am fast at it now!) and it started right up, idled very smooth and drove as nicely as my other good one. The car now runs flawlessly, like I couldn't complain about anything it was that nice. I didn't even have to adjust the idle speed screw or the idle mixture screws. Unbelievable.
So if you get frustrated like I did, then this is a source that at least for me this time, worked great! And it was about $20 cheaper than NAPA. I am finding that unlike the past, NAPA has fewer and fewer parts for the old vehicles, and actually Autozone has more parts available now. And in the past, NAPA has usually had very good rebuilt products, but not so any more it seems. The counter guy at Autozone who I know well (he is also a Mopar guy) says that Autozone is quick to cancel suppliers/rebuilders that do not achieve a good record with them. Good luck on your project.
 
The reason I stayed with Holley was to preserve the EGR and to keep the canister purge working correctly. I didn't think any other carburetor would have the right signals. Good luck with either course.
 
I've been reading some bad reviews online about Carter carbs too. :( I've always found the Autolite 2100 to be a basically troublefree carb. I've never had a 2150.
A lot of people seem to dislike the Edelbrock AFB and AVS based carbs as well. Seems they either love them or hate them.

Since your timing marks aren't visible, I was wondering if there's a possibility that your distributor may be 180 degrees out? Just a thought. :)
 
Last edited:
Back
Top