Well. I will try and see what you guys have as advice. Just recently started getting a weird almost “dieseling while giving gas” very very lightly. While driving. It also king feels like it a trying to go into low or passing gear but I know that is not the case. The engine was relatively cool. Or running temp. I am mostly using high octane gas. Cadillac 500 engine, AVS2 650 Edelbrock electronic ignition. Fuel Pressure valve with a return. Set about 2-3lbs. while I’m giving gas it seems to drop into this effect. If I let of the gas and roll a bit it goes back to normal and I can drive on. I thought it might be vapor lock but I don’t think that is the case. I ended up adding heat shield to the inlet lines. The coils is new and runs nice in the early mornings. We were running at about 70 all the way to car and coffee this morning. Any thoughts or suggestions would help.
Not sure actually it’s pretty much a stock engine. No funny cam or domed pistons. Just stock. Let me know how that would help anyhow? Thanks.
You know. I don’t ever think I have experienced surging. I will have to check into that. If anything it might be rich. I believe I set the initial time per the Edelbrock guides. I do have a clear plastic filter and don’t see any sediment and the fuel is moving as needed. it was running without any hiccups a few months ago, I went back and forth to work for a car show and a later dinner. In different weather conditions. Even as hot as it was when it first did this. Stop and go traffic a few mile then the freeway and back again. I will take a look at the Edelbrock manual on this one. I kind of suspect something got past the filter and is plugging some place or an accelerator pump issue. I checked the Edelbrock videos. It seems to be more like hesitation initially. I may try the different setting on the accelerator pump. But like I said. I didn’t seems to be an issue before. BAd Gas??
Stock compression on the first year (1970) of the 500 was 10 to 1, and it dropped to 8.5 to 1 in 1971 when everything built in Detroit went to shit. If you have an engine with 10 to 1 compression you may well be hearing detonation, which is quite likely to occur when you lightly touch the throttle. The reason is that when you are cruising down the road at a steady pace, the vacuum is high and so the distributor is at maximum advance. Touching the throttle a bit adds just enough combustible mix to cause some knocking. Push the throttle a little more and the advance will back off a bit and the knocking may subside. My old '64 Olds with the "Ultra High Compression" 394 did that. I could be rolling down the road with the engine just running nice and smooth, and touching the throttle a bit would cause it to knock for a bit until the advance backed off a ways and the engine accelerated a bit.
The stock Y-pipes were well known to collapse inside. It's a double wall pipe. That fooled many mechanics back in the day.
I was kind of thinking along that line. If it is a high compression 1970, it could be detonation. You could test by backing off the timing about 5 degrees and see if it has an effect.
If you are on the throttle and it stumbles and falls on it's face and then picks up and goes after you let off the gas for a second (about like letting off the gas to shift a stick) it may be running the bowls dry in the carb and the engine is running out of gas. That 650 is pretty small for a 500 Cad that came with a Qjet rated at 850. I'm thinking that you are just starving the engine for fuel on acceleration both with the little carb and low fuel pressure.
The stumble wasn't there before and recently developed. What changed? Go over the fuel system and replace rubber line and filters. Alcohol in fuel breaks down old rubber lines and swells them shut or causes then to flake off and clog up filters and get into carbs. Test the fuel pump, if the diaphragm is breaking down with ethanol fuel. Clean carb out, best you're able. If that isn't making a change, drop the tank and ensure the fuel sock isn't disintegrating and clogging the pickup.
I Know I Know Listen very Carefully to the.................................................! Monkey in the Trunk.! and if that Dosent work Did You Change the Fuel I Run High Test Gas in my Merc. 327/300 hp. Stock engine! Just my 3.5 Cents Live Learn & Die a Fool
Before you do anything, set your fuel pressure to 5.5psi, and your timing to 8º BTDC at idle. Test it. Then, pull the vacuum advance hose and cap it at the suction end, and test again. These are free and easy things to do.
And replace the plastic fuel filter with metal one. Only you can prevent engine compartment fires. vic
I know you said it just recently started, but as @indyjps asked, was anything changed beforehand? John
Depending where and how long it sat, mice or chipmunks can pack exhaust and mufflers full causing drivability problems.
Bumping this back up for an update. I went ahead and checked my fuel lines in the front. I did notice on the last run that the pressure gauge did read zero while in idle somehow. Anyhow I took the advice and got new regulator. the 6.5 and higher. Set at 6.5. And now it seems to be working ok. I need to do a few drives to see if that did the trick. I using the Quick Fuel branded one. I didn’t know a regulator can go fault to the point it closes up. The Jury's still out. also changed out the plastic fuel filter to metal one. Timing is good.
Just seems to be running ok. We were thinking the low pressure to no pressure was effecting the fuel delivery. I have a AVS2. So if it has the full pressure from the mechanical pump without a reg it really messing things up.
My 500 was stumbling while driving/accelerating. Had a big or running out of gas feel. It was. I found a mistake I’m my hastily built fuel line just before the carb. It was blocking fuel flow. Made a new line and it fixed itself. Recently, it did it again. Stopped up fuel filter. I’m running a stock pump with return. No regulator. Stock a-jet.
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