74 400 missing

[sleddinskeeter]

74 400 with .20 off of heads stk valves no porting.eddy performer rpm intake and cam. with eddy 750 carb bored .40 over headers. in a 84 chev pkup.

timing is at 12 advance

Symptoms:

1. bouncy vacuum gauge at idle/ give it throttle and it smooths out
2.air/fuel screws seem to make little to no difference on gauge.
3.high rpm miss starting at 3800 and going up very noticable

Other than this it idles very nice lopy at about 650 or so and runs real strong out of the hole to 3800 or so Itriple checked all plug wires for proper routing the dist cap is pretty old I havent checked advance module on dist yet. any thoughts this thing is gonna rip if i can get ride of this thanks

[sleddinskeeter]

OH forgot to mention also that it holds about 7lbs vacum at idle but eradically? you throttle it and it smooths out

[MT-2500]

Run a good compression test dry and wet on all cylinders and post back readings.
Also note cylinder leak down.

[777stickman]

What distributor do you have?

The vacuum readings are ok for the Performer RPM cam as it is a cam with big lifts and overlaps.

The 750 carb is a big ??. When I built "R57 3CAR" with all the RPM stuff the 1st thing I did was get rid of the 750 carb and replace it with a Holley 650 double pumper. A world of difference. And then replaced that with the Edlebrock Pro-Flow fuel injection system and another world of difference.

So, again, what distributor?

[2000CAYukon]

So there is no miss until 3800 RPM? Like 777stickman said, that is a lot of carb; however, I have also seen valves adjusted too tight cause a miss at higher RPMs.

So how did you adjust the valves? 0 lash plus 1 turn? 1/2 turn? 0 lash is not when you feel resistance while rotating the push rod. 0 lash is when you can no longer move the push rod up and down.

//2000CAYukon

[sleddinskeeter]

OK so many ?s

first what I did
to correct bouncy vac needle backed off the rockers 1/2 turn needle now sits solid at 7.5 lbs or so.

Cam was also in retard according to eddy is now at 17 degrees initial.

Changed carb metering rods from stock (not sure of the #) to 1455 and changed springs to lavender

Now Ive got solid needle and the air fuel screws work.

took it for a drive pulls real hard to around 4800 smooth but then just and i mean just a studder (maybe just a bit lean?)

Its got .110 stock from eddy thinkin about .113 but gonna run for awhile
and check the plugs.

Now ya think maybe back off the rockers 1/4 more maybe ? I usually adjust them running but wanted to try the other way since I had never done it (Note to self they dont need to be that tight He He

Keep the ideas comin Dist is also stock hei unit cap and rotor wires new.
Thnks

[2000CAYukon]

Sounds like the valves were too tight. At this point, I would adjust them with the engine running to get them set correctly. Back a valve off until it makes noise, them 1/4 to 1/2 turn after the noise stops.

//2000CAYukon

[sleddinskeeter]

ok so valves are good mis is still there. Thinkin now maybe f/u plug so another set of plugs.

Also gonna check float level its kinda surgin on the freeway.

Anything else im missing?

[sleddinskeeter]

ok starting to look at the control module on the HEI. will this thing deliver spark above 4500 RPM? sTARTING TO THINK THIS IS A SPARK DLIVERY PROBLEM. Cause there is no miss to 4000 then starts dropping cylinders?

STUMPED!

[sleddinskeeter]

Got it !! fouled plugs 4 out of 8 done rolls at about 6400
thanks