Surge problem on new motor.

[Heimedw]

Curious 68 hemi what are you running for timing on your stroke?

 

[Curiousyellow71]

That is a really hot plug for your compression. Imo...it may be part probably of your problem. I think your reading your plug right and your rich. Your vacuum should get better if your solve the rich issue. Imo...run a colder plug and back off the primary jets.

We prefer colder plugs in most of our engines. We have seen some unusual problems do to hot plugs.

I should have been more specific on timing. On a closed chamber heart shape head with a Flat Top piston you should make power at 32-34 degrees. Open chamber or dome piston/closed chamber 36-38.

On one of our 440 engines we have closed chamber stage VI mopar heads but run more timing w/dome piston and 13.4:1 compression. Cam is 276/282 @ .050 solid roller, 850 race holley...set at 38...tried 40 at the drag strip...didn't go any faster. Tried 36 went slower.

We also have a 510 the solid cam is 248/258 @ .05. But its open chamber and 10.5:1. It's closer to what you have.. probably 100hp less then yours.. It's set at 36 total...850 Holley as well.

 

[Heimedw]

The plug is a ngk zfr6f-11g so it's not crazy hot. Its cooler than the temperature recommended plug from trick flow. It is a protruding electrode so it may look like a hotter plug than it is.

 

[Curiousyellow71]

That is colder than I thought... It's not as hot as what it appeared in the picture

On trick flows site they are recommending a really hot plug... you did the right thing not trying that!
I still would try a heat range colder yet if it were mine. A combo that is pushing the envelope is going to be safer on the cold side. Electrode doesn't get as hot..imo less issues. May not last as long but less apt to cause detonation or even a flame out.

If you fattened up your jets earlier..go back to where you were with more timing and try it again...sounds like your widdling away at your problem.

 

[Curiousyellow71]

My guess what's happening is my vacuum at idle is 4.5 and I have to run my low speed jets at 11/8 to idle well.

We aren't running any 4 corner idle carbs like a xp. So can't say if 1 1/8 is normal or not. Maybe someone else knows.

 

[Heimedw]

Yes the idle jets are 1 1/8 out but I have tried 3/4 to 1 1/2 out and it has not effected the issue. I also have gone from a 4.5 power valve to a 2.5 and back to the 4.5 then 85 to a 86 main jet and back to the 85 and you could barely notice a difference. I'm going to try speeding up the timing ramp rate to get all my timing around 2500 and see what that does. Its coming in at 3000 now.

 

[beanhead]

A symptom of not enough idle timing...throttle blades open farther than they should be to get a decent idle, exposes too much transfer slot, and the screws don't do much.

 

[Curiousyellow71]

A symptom of not enough idle timing...throttle blades open farther than they should be to get a decent idle, exposes too much transfer slot, and the screws don't do much.

I think this is right on the money. Until you can make it happy at a idle with more timing...going to be a lot of recreational wrenching.

 

[Heimedw]

The car idles perfect and returns to idle just fine. I took the carb off and check my throttle blades to transition slot and its perfect just a small square showing and I have been able to get it to idle fine with the iac screw in the center.

 

[Curiousyellow71]

Just got to wonder if you advance the initial timing....adjust the iac valve for the new timing...maybe the idle screws will start to actual fine tune like they are suppose too. Idle screws should do something......?

Does your msd dist. have a vac advance on it...or is it a race set up?

 

[Heimedw]

Msd is all mechanical. I took a friend that's a old school 60s car guy for a ride today to see what he though. The first thing he said was its ignition for sure. He did also said is it a ignition problem or the carb causing a ignition problem.

 

[Heimedw]

I'm starting to wonder if my msd box is wired correctly? I did it the way the instructions wanted it done. I did wire it to my original ballast resistor.

 

[steve340]

MSD box is not wired in with the ballast resistor it should get 12 volt direct from the battery.

 

[Heimedw]

I wired it to the top diagram. My positive wire from my coil was the blue wire from my ballast resistor.

 

[Curiousyellow71]

Ballast resistor should not be in the circuit. Need to get power from the wire that supplies 12v to the ballast resistor not after the ballast resistor drops the voltage.

 

[Heimedw]

Then that's my problem. So do I need to buy a non resistor coil as well then.

 

[Curiousyellow71]

Yes

 

[Heimedw]

Well don't I look dumb! Man o man.

 

[beanhead]

Well don't I look dumb! Man o man.

Well, report back if it is the cure, then we'll start the razzin'...
Can't be as bad as that numbnut that started his car with the 1/2" ratchet still hanging on the crank bolt..

 

[Curiousyellow71]

Hope it fixes it!!! It sure a simple fix if it solves it.
Years ago Pulled some high school kids driving a 85 cutlass out of the snow....three of them layed underneath the car and studied where too hook. Thinking we were helping ...We told them don't hook it on the bumper it will pull it off. Well they didn't ...we got them off the snow drift....but gas was pouring out...they hooked it around the gas filler tube.