he specializes in rochester race carbs....and is very knowledgible on them.... will see if we have his number at the shop.....he's in the national dragster ads...but not on this board....brandon
hot rod pro is correct. Turn the mixture screws clockwise to lightly seat, then back out 1.5 turns. If your buddy had one turned out 2.5 and the other 3 or 4, he doesn't know what he is doing; don't let him "help" you anymore. Disconnect the vacuum line from the engine and plug it. Have the engine warmed up to operating temperature. Turn the mixture screws in (clockwise) until they're lightly seated (not to tight, or you can damage the needles). Back them out (counter-clockwise) 1.5 turns. Then set your idle speed on the throttle linkage screw. After your idle speed is set where you want (e.g. 600-700 rpm), then use a vacuum gauge to adjust idle mixture screws to obtain highest vacuum reading (typically a quarter turn or so). You could also have an accelerator pump problem, where the engine is not getting a good shot of gas off idle when you open the throttle blades...too much air for the amount of gas. I've had that situation a number of times with Rochester carbs over the last 35 years.
cool arkie h.r. will give that a try tonight. I do feel the timing is not the issue..its almost to the book perfect. but i do feel the carb is the issue and its just an adjustment issue..it is possible the accelerator pump is part of the issue too. i am going to take a 1 step at a time aproach to this little bump in the road and see what exactly clears it up. That way i can help the other guys out there with the same problems. There was a guy on this post that mentioned he had the same issue, so i'd like to help him or anyone else who may be expriancing this issue or any one in the future for that matter
I had this exact issue on my 2bbl Rochester. It was the accelerator pump. I had used an NOS kit when rebuilding the carb and the accelerator pump had dried out prior to me installing it. I found the accelerator pump about 500 miles later after dealing with an off-idle stumble. The pump cup was broken into pieces and sitting in the bottom of the well. The car accelerates a lot better, too. It makes sense, the accelerator pump's job is to give you a squirt of gas right off idle to take you from the idle circuit to the low-speed jets. Buy yourself a kit at Oreilly's in case you can't get your gasket to seal back up right, open it up and check it out. You can then do a quicky rebuild if you want or throw the kit in your trunk for a roadside repair later on. I've got half a 371 in my trunk, just like a boy scout - BE PREPARED!
RS i would hope that a NOS carb would be good to go..But your right be prepaired ..you never know..I will try thre screw thing tonight if that doesnt do it i will investigate toward the A pump. Thanks
I'll never use one again. It also started leaking and I noticed that the gaskets were real thin compared to the new Walker kit I got from Oreilly's. The Walker kit also had a real nice accelerator pump. NOS is great for body panels, not so much for things that have gaskets, because gasket technology has come a long ways. I used the Walker kits on my tripower as well, I can't wait to get it installed. They were only $12 a apiece as well...
well i did the screw thing it didnt make a difference in the stumble. although it does idle much better. The stumble is still there. under a load it shows up intermittently. i advanced the timing some and it seemed to clear up a little but is not gone yet. it still could be the dam A pump..i guess but it does squirt fuel when pressed upon, so im not sold yet on taking the carb apart. Checked the cap and rotor they look fine. Think my next step may be to check all my wires and see if one is bad. or any other suggestions out there? Guys?
I just had to read all of this. I have a '68 327 with a 600 Holley. Exact same problem (symptom). I don't drive it that much and so I haven't made a concerted effort to fix it. Although if it didn't have the problem I'd prolly drive it more. I had the carb rebuilt: no good I had it dyno'd: no good Found vac leaks in the intake manifold and fixed 'em: no good I need to try some of the suggestions you guys have made on here. When it goes, it goes good. But off the line it's a dog. I'll watch for your solution. Good luck Pete
Sounds like you tried pretty much everything else suggested here with out getting rid of the stumble. I still have to go back to the accelerator pump, and even though you see it pumping gas when you hit the throttle, remember it only takes a split second of air before fuel starts coming out to give you that stumble. Again, if while playing with the timing, you had a back fire through the carb, you could have damaged the accelerator pump. I'm not going to say 100% that it's the pump (God knows I've been wrong before about things like this before), but I'm really leaning that way. If it were me, I'd throw the roach-chester away and try another carb (personally I prefer the Holley style, because they are a lot simpler to work on...again just my opinion). Good luck and hope you get it sorted out.
ronrob75 i will be definetly chcking out the A pump..but would it stumble thru out the power band? it seems to start stumbling just out of the 1500 rpm range all the way up to where my tires start spinning.(brake torque). would this still be the accel pump? And as for the Holly Carb deal..rochesters are nice street carbs, this is a street car. hollys do a wonderful job of slaming the fuel to an engine but are more designed for strip than street. Fuel economy with my holly on there is friggen lousy to say the least. I have a Holly on my Mopar 440 and its a wild ride but i can pass everything but a gas station.
When did Chevy start using the 'new' hokey cam blanks that were prone to go flat (cheaper hardening process)? I have read it was a problem in the early 70's but, could it have started in the late 60's? Seeing Sriper's post about a different (serial #) engine of the same vintage giving the same problem with a different carb makes me wonder if there isn't some other problem that coincidentally cropped up with VRF's ride when the work was performed (and the cam is the thing that came to mind especially with today's oils)? Maybe nothing, maybe something.
hey that a possibility..Im also going to look at all my chassis ground straps to be sure they are good and tight and not grounding correctly. The cam thing is a possiblity..it does seem to become more pronounced as the engine gets warmer.
any suggestions on a nice cam set up for a mild 327? 1.6 rockers, rollers too? I was planning on doing this to the engine this winter anyway, maybe get an early start on it. Just would like to be sure this isnt some other problem
I've got a 327/325HP Comp Cams grind in the 350 in my beater parts chaser. It has been in there since I did the overhaul 4 years ago. It sits alot, then we drive the crap out of it, then it sits more, pretty much the worst thing I can think of for a flat tappet cam. Of course it doesn't wind very tight so it has stock type springs (355, overhauled stock heads, 9.25:1, performer, Edelbrock smog legal Rochester repop, O.E. iron manifolds). I'm sure there must be a cam grinder here that can get you a cam that is exactly what you need. But if you don't find one you like, I have had good luck with Comp. Oh, and I'm not using any special oil in it, whatever low zinc formula was in the bottle. I didn't know about that back then. But for a hi po application, the springs will probably have to be heavier, so I would be more careful about that.
Had the same hesitiation problem with a buddies Blazer in college years ago. I must have gone through the carb 3 times before we brought it home for the old man to look at it. He pulled one plug and told they needed to be changed. I looked at the plug and argued with him that he was crazy because they appeared to be fine. He told me again to get plugs and that he would pay for them if it did not clear up the problem. Nothing to lose, right. Bolted in the damn plugs and the stumble was gone. I went back to look at the old plugs and sure enough the electrode was burnt. It appeared to be porous and rounded on the edges. Probably the trickiest read I ever had, including the nitrous motors I have worked on. My experience is that the HEI is really hard on conventional plugs especially in lean carbureted applications with really wide gaps (0.060 and up). Check your plugs again looking for the signs mentioned above and if your gap is wide, close it up to 0.035 or 0.040 and give it a shot. Good luck.
ok matt i did gap them at .040 i believe..and they were new accell plugs..shorties for my headers..that would suck to have to go buy all new ones when these dont even have 3,000 miles on them.
Well I think ive got it//..the very expensive toy my friend used to set up my timing and curves and all that were way off thrie mark..my timing was very late.. as i bumped it up in timing the engine started to smooth out.I took it for some slow driving with a few times clearing the engine..I tuned it be ear and seat of the pants as to how much timing to give to the engine and kept doing that slowly advancing until it was too early, than backed it off to where it ran best under a load..Runs like it did before it was screwed with..So much to say for my buddy who thought he knew what he was doing. He mis, calculated..(in my judgment)..didnt know how to work this sofisticated timing tool he had and had my timing way out there..and not tomention he forgot to get the idle screws right also..so it was a combination of errors no doubt,,but the stumble did com from the dizzy
I have a '76 Chevy PU with the same type of problem. Was fine, and now stumbles at idle. Everything is new/rebuilt/etc. Striper-for part of your problem, about being a dog off the line. For several Chevy V8's I have used a Trans-Dapt 1" aluminum spacer with swirls in runners under carb and gain a lot of bottom end performance.
yeah no doubt it never happens like that for me so im jacked!..now i can feel good about moving on with other things that need attention on the car,,Like a nice cam and some 1.6 rollers for it..maybe this winter
You'll also have real world experience to offer later to someone who comes along with the same problem. Like I said in my earlier post, don't let your friend "help" you anymore!
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