Does anyone know what could be causing my engine to stutter at high load low to mid RPM? I have a Saginaw 3-speed with O/D but I cannot use the overdrive. It seems to like 2500 to 3500 best. Here is what it does: from 1500 rpm to 2200 under normal driving conditions, the engine stutters. It is not a misfire, but rather like it is intermittently getting fuel. At idle it is fine, and at high rpm it screams like a banshee. Here is what it is: 327 c.i., lumpy cam (bought it this way so not certain, but very healthy), Edlebrock EPS Performer intake, Edlebrock 600 cfm, S-10 rear end (about 3:50), and Excel electronic ignition, all in a 3,000 pound car. I know it could be a million things and this isn't enough information, but without taking the cam out, or pulling the carb apart, I can't tell you more. Anyone have an idea?
Sounds to me like the power circuit on the primary rods / jets isn't doing what it's supposed to do. I'd be checking that the metering rods aren't snarled up in some way and consider changing the springs for a heavier (lighter?) set. Also think about the accelerator pump. Has is ever run properly? Whats' the history on the carb? - they tend to run pretty good out of the box. Chris
Check the easy things first. Make sure your choke plate isn't falling partially closed during operation.
The carb was on my 305 c.i. dog motor before and I don't remember it doing the same on there. I could run that motor (with the same tranny and rear-end) with the overdrive engaged and it would turn around 2,000 rpm on the highway. It may have had the same symptoms but not nearly as noticeable. I can rebuild the carb but wouldn't know how to gauge the springs. Maybe a new Holley is in my future.
have you washed the motor lately? you may have moisture in the cap causing the spark to jump around. is your coil mounted vertically or horizontal? most coils like to be mounted vertical to keep the windings cool. what it is doing is a spark problem or a fuel problem, not the cam. it sounds more like spark than fuel. you may contact phoenix transmissions there in Weatherford, and see if they recommend a motor guy that can help. -Danny
not sure about edelbrock carbs, but i had a simmialr prob with my holley and found that the low vacuum from the cam was too low for the power valve and caused a low speed shutter...I changed powervalves from a 6.5 to 4.5 and it went away so there may be something fuel reated...
1. Is this a new problem or 2. Are you new owner of this problem 3. Has this ever ran well from off idle to 2500 rpm You can check cam specs with two dial indicators one on intake rocker and one on exhaust rocker and a degree wheel on the crank balancer. That may or may not be extremely accurate ( depends on you) but it will give you more info than you have now
@ Hot Rod Pro - How do you know Phoenix Transmissions? One of my fellow Cub Scout leaders has worked there for 18 years. I have never washed the motor and don't think it is a spark problem because it idles great, and runs out at high RPMs just fine. In fact, it will light the tires up (not that I would ever do that, nudge, nudge). It is only at mid-range. Could it be the exhaust? I have headers with 1-5/8" primaries but the rest of the system is 2" because Summit only carried the Smithy's in 2". I do plan on putting 2.5" from the headers back sometime soon. The other thing I should have mentioned is that with the 305, I had a Weiand single plane intake, the Performer is dual plane. With the single plane, I always smelled unburned fuel. I just thought I was overcarbuerated.
Thanks Traditions, both for the spelling correction and the cam lugging information. I bought this motor as is and was told it was an RV grind on the cam but it sounds and feels way too "lumpy" for an RV cam. You sound like you know much more about cams than I do so assuming that you are correct, is there anything you would suggest to make this car more streetable without changing the cam? I really like driving this car like I stole it, but it is my daily driver and I need it to act nice in traffic.
Dump the carb. The fact that it runs well at idle and the accelerator pump works well to make it run well on hard accelration tells me it's go problems with junk in the power metering ckt.
when i was younger and dumber i had a similar problem with a 400 m ford i swapped into a 68 fairlane. it would idle and cruise fine but at full throttle it would spit and shudder like crazy. after much fiddling i finaly took it to a mechanic friend and had him check it out. seems you cant use the old resister wire from the point ignition to power the new breakerless ign. or you will only get @ 7 volts into the module. he rewired it for me with full batt. voltage and then it ran like a raped ape all the way up to 5500 rpm. I would take a good look at the ign. as it seems thats where alot of drivbability probs. come from.
Just last week I changed carbs on my truck took one off one truck that was running fine and put it on mine it ran like shit. Found out when i took off the carb all the settled stuff in the bottom got stired up cloging it up just had to take the top off and clean it.It to was a edelbrock 600.Only took about 15 min to fix.
Check your distributor advance , to much advance or not enough can give you funky results in that rpm range. I have also had a bad ignition coil give a light throttle stutter. Pete
Ok, here is an update: I have put on a new Quick Fuels Technology 650, and a new MSD HEI ignition, and new plugs. Still have the same problem. Is it possible that the cam was installed one tooth off? I ask this because when I put a timing light on it, and backed the dizzy up to see the mark on the balancer, it was so retarded that it would sputter and kick back and backfire. The only way to get it timed was to move the timing mark far off of the timing tab. I now have it timed by ear (which I prefer anyway) to the point that it starts easy enough, but is as advanced as I can get it. Any more ideas? What would it do if the cam were put on a tooth off the mark?
wrong damper and pointer, sbc had multiple dmper timing set ups, in that case you can time by ear or use a piston stop to get ture tdc and re makr the damper to the pointer you have...
Ok, one more try: could a vacuum leak at the intake manifold cause these symptoms? Since putting on the new carb I have noticed that I cannot make it idle low enough. I have the idle set screw all the way out and it still idles high. I tightened all of the screws holding the manifold down and a few were not torqued down enough. I am thinking the manifold, a new Edlebrock may not have sealed completely. What do you think?
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