# Miss under 2000rpm. Help!



## steve491 (Nov 20, 2019)

Good afternoon,
I woke up a '67 GTO from a 28 year sleep about a year ago and took the first test drive today. Wahoo! It actually drives very well but I have a miss under 2000rmp, over 2000 it's smooth and pulls very well especially in the secondaries.

Little background and specs:
Original 400 HO (it's the original engine), 4-speed, original 670 heads that were reconditioned in 1991. Unknown cam, previous owner said it was a crane cam but he doesn't remember what it was when he installed it (1991). 
I installed a new "parts store" points distributor, coil, alternator, water pump, carter fuel pump, entire new fuel system, rebuilt Holley 650 double squirter spreadbore, plug wires, and AC Delco plugs.

Car runs right at 180 degrees, 60lbs of oil pressure at idle (10w-40). It idles pretty good but you can loose a cylinder on a HP engine and not really know.

It seems to have a pretty good miss under 2000 that sounds to me like ignition because once you get over that rpm it's like a switch was flipped. I could be wrong, that's why I'm shouting out to the experts! 

Wish I had an original era Quadrajet but it got gone in the 80s. Power valve in the Holley? I have almost 17 inches of vacuum at idle, idle jets are responding well and tuned to max vacuum. DOn't remember which power valve is installed right now. 

Sorry for the rambling post. I walked back and forth several times.

Any input will be appreciated.

Thanks, Steve in NC


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## BLK69JUDGE (Jun 10, 2010)

GM V8 Points & Condenser
#1966294 d112p delco remy & made in USA 
# 1932004 d204​


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## steve491 (Nov 20, 2019)

BLK69JUDGE said:


> GM V8 Points & Condenser
> #1966294 d112p delco remy & made in USA
> # 1932004 d204​


Thanks for the reply. So you think an OEM set of points will fix this issue? What would cause these symptoms only under 2000rpm?
Thanks


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## O52 (Jan 27, 2019)

What is your dwell at idle, 1500, 2000, 3000?


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## steve491 (Nov 20, 2019)

O52 said:


> What is your dwell at idle, 1500, 2000, 3000?


Good question. When I first woke this engine up with a little ATF in the oil to get the lifters working it was idling at 800rpm, base timing at around 8TDC, stock manifolds and a Y-pipe from a '66, and a mixture or 91 octane with an additive for octane and a lead additive it was 30 degrees dwell. Plus, I had the vacuum advance ported. Now I have it running on 110 Renegade with Ram Air manifolds with duals and advance on manifold vacuum, base timing still at around 8, total advance is about 38 and it took a while to get there.
I'm checking the plugs now to see if one cylinder is any different than another, but checking the dwell again is a good point.


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## geeteeohguy (Feb 2, 2008)

Put a vacuum gauge on it and look at the needle. Should be steady at idle. If not, could be a burnt valve. Also, you may want to pull the spark leads one at a time to check for a dead cylinder at idle speed. You could have an open ignition wire. These big V8's will run smooth with a dead hole over 2,000 rpm and run strong. But a miss at idle/cruise indicates an issue. You can also go to the back of the car and listen to each exhaust pipe. If you have a slight popping or hiccup on one side, that's the bank of cylinders to check out for an issue. Could be: burnt/tight valve, bad plug, open plug wire, or vacuum leak. Could also have carbon tracked distributor cap causing arcing, but this would be felt at high speeds as well. Keep us posted.


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## Lemans guy (Oct 14, 2014)

Agree with GeeTeeOhh Guy, Pull those plugs too,.. look at the gaps, look for tracking….loose spark plug wires or bad wire, cracked distributor cap, or one bad cap terminal.


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## ponchonlefty (8 mo ago)

maybe wait till dark and look for misfire. a compression check would be a good idea. had an olds that had a small shake to it.drove it like that for years. i did the tune up,carb, timming adjustments. i finally checked compression had i think it was 3 cylinders that were a little low. turns out it needed the valves seated. they were leaking a little.


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## steve491 (Nov 20, 2019)

Thanks for all the replies. I checked all the plugs and wires and they all seemed to be on the lean side. Points distributor was within spec for dwell, and the coil was a cheap replacement. With this being said I focused a little more on fuel. The carb is a Holley 4165 spreadbore "economy" replacement for a big block chevy in the 70s. I rebuilt it to original a year ago, but original was "economy". Primary jets were 60, which I think is too small. After an inspection there was a piece of shop rag fuzz in the idle circuit (that's HUGE). Cleaned the carb out again and changed the primary jets to 67 (I know that's a jump) and it runs great under 2000! It might be a little rich now, duh, but this old car really likes the road now. Took it out for a test drive today and rolled into the secondaries (83) in second and it broke the tires loose.


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## geeteeohguy (Feb 2, 2008)

Excellent! I learned about 30 years ago NEVER to use shop rags on anything like a carb, auto trans, or engine when a co-worker burnt up a trans he had just rebuilt in a customer car. Pulled the pan and there was nothing but bits of red fuzz everywhere and it plugged up all the oil passages in the valve body and fried the trans. Brake cleaner and compressed air is your friend!


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## steve491 (Nov 20, 2019)

geeteeohguy said:


> Excellent! I learned about 30 years ago NEVER to use shop rags on anything like a carb, auto trans, or engine when a co-worker burnt up a trans he had just rebuilt in a customer car. Pulled the pan and there was nothing but bits of red fuzz everywhere and it plugged up all the oil passages in the valve body and fried the trans. Brake cleaner and compressed air is your friend!


I know. I know. I always use carb cleaner/brake clean and compressed air, small pipe cleaners and wires for the small holes, plus an air nozzle with a rubber tip to blow passages out. You can actually tell from the air sound comparing the left side to the right side if the passages are symmetrical. Smaller carbs like lawnmowers and weed eaters that have limited access to the tiny ports I use an ultrasonic cleaner.
During assembly I always use plenty of WD-40 and I guess, for some reason, I wiped the metering block with a freakin shop rag.
Even though that screwed up half of the idle circuit I think the jet change made a huge difference.
Either way it seems to run very well now.


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