What electronic ignition system did you convert over to? Did you also change the coil? As Groberts mentioned ... is there now a straight 12 volts going to the new coil? Depending on the coil, some of them need to be mounted vertically, too. Some are liquid-filled and need that positioning to properly cool, otherwise you can use one up pretty fast. All this leads to the thought that you are running around on a marginal ignition system ... good enough to cruise on, but falls on its face when you get on it hard.
I don't recall the brand electronic ignition I purchased but it called for a coil that had at least 3 oms or it could damage the EI and therefore void the warranty. Duralast was recommended. That's what's on it. I need to check the voltage to it. CC, the way you described it is exactly how it acts. Cruises perfect, but can't kick into it.
Usually with weak ignition there will be a point where spark starts to "break up" so some misfiring is noticable... Problem will become worse as RPMs increase... Drawing from 50+ years experience, I'm gonna say smooth operation then a sudden bog on WOT probably isn't a ignition problem(at least not totally)... Yeah after "sleeping"on this my opinion has changed... Don't get yourself knocked on your butt, fabricate a holder to position coil wire a inch or so from contact in coil(clothes pins can often be used)... If there's at least 3/4" inch or more spark with engine running 3000+ RPMs, ignition ain't likely the issue... If you have something like 1/2" or less, ignition is suspect...
Not sure if this is relevant or not to my situation but I noticed when first cranking the motor when cold, the fuel pressure is at 6 1/2 to 7 lbs. After driven and motor reaches operating temp, the fuel pressure drops to 3 lbs.
Haven't fixed the problem or found it. I've been searching for someone in my area that knows how to look for the solution. I'm limited as to what I can do. Hopefully I can at least find the issue this coming week. Will post the problem as soon as I get the info.
This stuff isn't as hard as it seems if you have someone coaching you through the basic troubleshooting process. Google has a world of video knowledge at your fingertips too. All the hand tools are basic but you do need a timing light and vacuum gauge to properly baseline the tuneup. Otherwise one could easily assume it is might be ignition related and quite easy to fix if the other carb acted identically when bolted onto this engine. 2-3 psi fuel pressure under load is surely low but still enough to keep this little motor from emptying the bowl as quickly as you've described this bogging issue. Did this engine ever run correctly?.. and then suddenly acted up? Or never run right since its gone together?
I haven't experienced the effect the 4bbl is supposed to show since I installed the motor. It's been that way since day one. It had an over heating issue at first but got that sorted out. Now it's just the stumbling issue. I had one mechanic tell me that it sounds like a couple of the cam lobes could be wore down which could cause the issue when kicking in the 4bbl.
Ok got it. My opinion is still heavily centered around ignition timing. What basic mechanical skills do you have under your belt.. and do you have a vacuum gauge? In all seriousness you really don't even need a timing light to ballpark tune any motor. Simply hooking the gauge up and telling us where you stand with that number(and how steady it is) will shed a lot of light on potential underlying problems going on here. And if any supposedly competent mechanic ever told me that bad cams act up when you "kick in the 4 bbl"?.. I'd find another mechanic. If you are wiping lobes then the oil will be sparkly and clattering rockers/pushrods not too far behind.
I don't know the mechanic that said that. A friend of mine that knows my issue talked to a mechanic and that was his resolution. (Grain of salt). I can get access to a vacuum gauge and check the vacuum and let you know. Then we can go from there. I had the manifold vacuum checked a while back to find out what the vacuum pressure was to determine what metering rod springs to use in my Edelbrock carb. If I remember correctly, the reading was 14.
14 is pretty low for a mild cam. I would tune that motor for upwards of 20+ till you couldn't even do bunny hops because the tires would spin so easily when quickly jabbing the throttle. lol. More important is how quickly vacuum's dropping as lighter to moderate throttle is applied. Major drops at lighter throttle angles would indicate sticky or stuck weights/advance mechanism and/or way too stiff a spring combo being used. Not always one specific cause and could be several cumulative issues. Could still be a bad coil/insufficient voltage too. Also be sure to check your oil for metallic debri if you think the cam could be getting wiped. Best to catch it early before the oil pump, lifters, and bearings are full of metal. Quick and dirty test for you to try. Mark the current location on the base of the distributor and on the block as a reference to its original set point. Then loosen the distributor hold down bolt till you can BARELY twist the distributor by hand. Do NOT grab and twist on the cap.. only grab the vac advance and body of the distributor housing. Now turn the distributor clockwise until the idle speed comes way up. Don't worry about the idle speed set screw adjustment unless it goes sky high and makes going into gear too hard on the transmission(if you want to test drive it).. but you may need to adjust the mixture screws as the extra ignition lead will lean out the idle mixture very quickly. Just a quick n dirty test here, is all. Keep going until the engine speed plateaus and/or starts to misfire and rpm breaks up.. then back off/counterclockwise rotation about 3/8" till it smooths back out. Now quickly wing the throttle. If it improves?.. and it should unless the carb is already WAY lean which will cause it to lean pop/backfire.. then you know what the motor wants. Way more initial timing. If you want to test drive it?.. you can do some quick full throttle blips(about 2 second bunny hops).. but MUST NOT rev past about 3,000 rpm or the mechanical advance will come in to push total advance sky high.. which will cause detonation and could hurt the cast pistons ring lands. Not good at all. All this quick n dirty test does is show you the trends for what the engine likes and possible underlying deficiencies to look at when troubleshooting.
I guess I need to check the voltage at the coil also. Tuning the motor will increase the manifold pressure?
Yes. More manifold vacuum will improve efficiency(actually an indicator of combustion efficiency) and improve throttle response. More manifold vacuum is ALWAYS better.