440 misfire when hot curising

[nigel]

So my 440 started to suffer with a misfire after it gets hot at cruising speed. Picked the car up today and it started first tip of the key. Took it for a drive and it pulled like a train all the way up to 95mph. The throttle response is great but after a drive on the interstate at 70mph for 15mins traffic got a bit busy so ended up slowing down to 50mph which is when I noticed a slight misfire. The slower I got the worse the misfire got. When I had a chance I gave it WOT and it dow nshifted and screamed right up 80mph without hesitation but as soon as I got back down in speed to 50mph it started to misfire again. When I got in around city driving it ran like a bag of spanners. Constantly misfires but if I hit the throttle it pulls like a train again until I get back down in the speed. Checked the #5 and #7 leads and they are not touching.

Motor is a fresh build with a whiplash cam, 452 heads, torker 2 intake, MSD pro billet with 6AL and MSD leads, accel 23 peanut plugs and a quickfuel slayer 760cfm vacuum secondary.

This has me scratching my head as it has run perfect for the cam breakin, drove 250 miles without any issue and the last drive I had was 2 weeks ago doing a round trip of 120 miles without issue. Anyone any ideas?

 

[Don Frelier]

Could be a rotor phasing problem.

How much compression?

 

[nigel]

Don't have a compression gauge on me so I can't check it at the moment. Have to wait till I get mine back from my buddy next week. As per hughes engines instructions it has 16 degree initial with 18 degree mechanical all coming in around 2400 rpm. The car pulls strong and hard when your on it but at cruise when hot it's just jumping due to a bad misfire. Checked all the plugs and wires. Everything seems fine with them.

 

[Don Frelier]

I meant the calculated ratio when it was built. Not from a compression test.

 

[Darter6]

Just a thought. Does it miss at idle ? if not you may have a part throttle primary lean condition.
May have to re-jet.

 

[nigel]

I meant the calculated ratio when it was built. Not from a compression test.

My bad. It was 8.75:1 which I checked with hughes before ordering the cam and they said it will work fine with that. For a 67 block the compression is pretty low but the 452 heads are open chamber

 

[nigel]

Just a thought. Does it miss at idle ? if not you may have a part throttle primary lean condition.
May have to re-jet.

It only misses at idle when it initially starts as it doesn't have a working choke. I've never had any joy with electric chokes ever. Once it warms up after 2 mins it runs perfect. Even after the drive today when it misfired badly it idled perfectly

 

[Darter6]

Does it miss at idle ?

Ok, I should have asked at idle after it is completely warmed up.
Static cruise( not driving )rpm say 2400 will it miss or surge ? if so you can partly cover the carb air horn with a rag and hand, see if it smoothes out. If so it means a lean condition. Just shooting in the dark for ideas.

 

[Cranky]

It only misses at idle when it initially starts as it doesn't have a working choke. I've never had any joy with electric chokes ever. Once it warms up after 2 mins it runs perfect. Even after the drive today when it misfired badly it idled perfectly

I'm with Darter6 in post #5......

 

[nigel]

Shooting in the dark is good for me. I'm open to all ideas. Only thing I haven't checked was the voltage regulator. I installed a 130 amp alternator due to running electronic ignition and electric fans. I'm wondering could it be an ignition issue. It's a bit late to have a look at the car right now and I just introduced my neighbours to a 440 open header for the first time. Set off every cars alarm as I drove past so I'm a bit unpopular with them at the moment. I'll have a check tomorrow with it idling at 2400 and cover the horn

 

[Don Frelier]

Well open headers is going to make it more lean.
8.75:1 should be good. Thanks

 

[Cranky]

Shooting in the dark is good for me. I'm open to all ideas. Only thing I haven't checked was the voltage regulator. I installed a 130 amp alternator due to running electronic ignition and electric fans. I'm wondering could it be an ignition issue. It's a bit late to have a look at the car right now and I just introduced my neighbours to a 440 open header for the first time. Set off every cars alarm as I drove past so I'm a bit unpopular with them at the moment. I'll have a check tomorrow with it idling at 2400 and cover the horn

If you live in a neighborhood that's a bit tightly spaced, yeah, that'll piss em off lol. Used to have a 9 second race car and my neighbors/neighborhood didn't care for it much and it even had mufflers lol

 

[nigel]

I'm only living in this neighbourhood for 3 months and I haven't met any neighbours yet but I'm sitting in my house and all I can see is my my neighbours going up to the car and taking pictures so I'm guessing they like it apart from the alarms I set off.
Recently here in ireland we made the move from e5 fuel to e10. I'm wondering if that has anything to do with it

 

[Cranky]

I'm only living in this neighbourhood for 3 months and I haven't met any neighbours yet but I'm sitting in my house and all I can see is my my neighbours going up to the car and taking pictures so I'm guessing they like it apart from the alarms I set off.
Recently here in ireland we made the move from e5 fuel to e10. I'm wondering if that has anything to do with it

Had E10 for several years now and the talk awhile back was for going to E15 soon but so far, that hasn't happened thank God! Has your car been sitting for a period of time and is it out on the street where people can get close enough to take pics?

 

[nigel]

Normally it's in a super secret location aka my workshop which is away from my house but for the night it's parked outside my house with street parking. The only people that are around it are neighbours. There's no way or need for the normal public to be down around my car.

The car was sitting for 2 weeks. It has a new fuel tank, 3/8 fuel line with a 3/8 return. Mechanical fuel pump and any rubber hose is R9 hose rated for e85 so that should be good.

 

[Darter6]

Sounds like you did a fine job putting a Mopar together in Ireland.

 

[blue69runner]

This sounds like a jetting problem in the carb. Mine did the same thing and found that I had to lower my primary jets a few numbers. I was watching the tv show where they went to Australia. The fuel was different than here in the USA so had to run a richer mixture so their car would run on it. This something you have to consider. Don't do too much only one thing at a time or you will have more trouble than you started with. Good luck an enjoy the car.

 

[1967coronet]

Just me but I would pull the plugs and have a look.

 

[Geoff 2]

What ign system? You could have a bad spark plug.

 

[lewtot184]

Dead miss or surging? They're are different and can have different causes and cures.