New carb and distributor

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SPACECOWBOY

SPACECOWBOY

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Well i put a new Quick fuel 950 race carb on the car and a MSD Pro billet dist with timing all in at 2500 total 35. I set the carb with a wide band and its 15 to mid 14 at idle and perfect at cruise and WOT. At WOT at 5800 it breaks up and is done pulling. what would your money be on Dist or carb?

Engine: 414 stroker SB

Short blk: '72 360, torque plate bored & honed .060, sqr decked, align bored, Hard Blok, and fitted with Pro Gram billet 4 bolt mains. 4" MP forged crank, Eagle H beam rods, Ross custom pistons yielding 11.93:1 CR with my heads. Speed Pro moly rings. Comp Cams solid flat tappet cam: 271/279 dur @ .050 with 650" lift and 108 CL. Comp Cams light weight lifters. Roll Master T-chain. Federal Mogal race series mains (Calico coated). Clevite race series rod bearings (Calico coated). Smith Bros push rods. Moroso 7 qt low profile, rear sump pan w/ windage screen, scraper and trap door baffles.
Heads: 308 factory swirl heads, max port & polish and cut to 55cc's. stainless 2.02/1.62 int & exh valves. Crane springs, crane Gold 1.5 roller rockers w/ Smith Bros adjusters on chrome shafts w/ billet hold downs.
Intake: MP M1 thats ported and has had the spread bore top reconfigured to square bore and blended into the runners with the side rails milled to fit the heads.
Headers: Hedman Huslers-1 7/8" w/ 3.5" collectors, Jet Hot coated. For street legal competition I run about 14" of 3" pipe into Flowmaster 3" single chamber muffs w/ hangers.
Carb: Holley 750 DP w/ milled air horn .

Ignition: MP elec dist thats recurved, MSD wires and MSD 6AL box.

Tranny: 727 w/ race clutches, billet servos, Cheetah rev pattern V-body. Freshened up about 60 passes ago. PTC 8" 5000 stall converter 3 years old.
B&M Super Cooler up front. Cooler lines are braided.

Rear: Narrowed 8 3/4, new Moser "489" case with Richmond 4.10 gears, Strange spool, Moser axles. Driveshaft is a custom MS shaft w/ 1350 Spicer joints. The entire 3rd member, case, gears, bearings was new about 100 runs ago.

Fuel system: Harwood 12 gl cell, -10 line from cell to pump, -8 from pump to reg and dual -6 from reg to carb bowls. Mallory 140 pump, Holley reg. Cowl mount press gage.
 
Try switching out the dizzy, put the old on in if it worked ok. That's the easiest and fastest way to go.
 
Also IMO at idle 14-15 is fine, but probably too lean for a load on it.
I bet your plugs are absolutely white if that A/F is correct..
 
Friend of mine says it sounds like it going lean at WOT. The mtx-l says 12 - 13's at 5800
 

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As of now just trying to get high end miss out only thing I changed was carb and dist. I may just put old carb back on because it is easier and see if it goes away. It ran perfect before but Easter bunny brought some stuff.
 

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SPACECOWBOY said:
Friend of mine says it sounds like it going lean at WOT. The mtx-l says 12 - 13's at 5800
Click to expand...

That's what I was thinking, but if it's at 12-13 and the plugs look like that after a WOT run that must not be the case.
Have you tried doing a WOT run and shut it down THEN check the plugs?
Or is that plug after it's been idled back in?
 
No idling till I could get it in the shop, he said I need to lock the dist too but he bet fuel.
 
coil? The MSD is a capacitive discharge so it preloads the coil with 300V. perhaps the coil is not up to it? Sounds like it was running fine with it under the old carb though...? All your ignition grounds good?
 
It's hard to decipher what you wrote.Your opening statement is just too muddy.
"I set the carb with a wide band and its 15 to mid 14 at idle and perfect at cruise and WOT. At WOT at 5800 it breaks up and is done pulling. what would your money be on Dist or carb?"

That is to say; did you set the A/F to be perfect at WOT?.
Or do you interpret 15/14 to be this perfect number for WOT?
When it breaks up, does it just go flat and nothing you do will get it to rev any higher?
Or will it in fact rev higher, just run like crap up there?
See what I mean?
But I'll try;
Your issue is likely one of four things. rev limiter,Valve springs, lean running ,or spark failure.

1)With soft or mismatched springs, the revs go flat in every gear nearly the same.It just revs so high and that's that
2a)When a high rpm miss shows up, not as above,it could be either fuel or spark.
2b)With fuel it gets worse in each successive gear and is principally load related.
2c)With spark it is usually rpm related, but may not just flat quit like valve springs.

But there is considerable overlap of symptoms between fuel and spark.
A high-rpm miss is often load dependant, and controllable with the throttle setting ie if it breaks up at 5800 under full load(say 3rd gear) and WOT, but revs through it ok by backing off the throttle.This is often traceable to;lean running,weak coil or fried plugs.Since it seems possible to interpret your opening statement that you are attempting to run a WOT A/F of 15/14;later amended to 13/12, it seems quite likely, as others have stated, a lean issue.
You may find that after fattening it up, it still has issues, although less severe. In which case a fresh set of plugs would be my next go-to.And finally the coil.
Did I mention Rev-limiter?lol
 
You described it perfect the breaking up gets worse the higher gear it's in , before these two changes it was at 6800 instantly.
 
Never trust the Easter Bunny when it comes to car parts! See what happens? LOL

Being worse in higher gears may be a sign of less fuel being available as time goes one. If it was good before the carb switch, then I'd suspect the carb. Try raising the float's a bit as an experiment; ignore the idle AFR and try a WOT run again and see if the higher floats help or hurt the breakup. I would not be surprised if you have a fair amount of tuning to do on that new carb.

If the prior MSD 6AL system worked to 6800 RPM, then very likely the coil and wires are OK. The new distributor is just a timed trigger for the rest of the ignition system.

As said, idling back to the shop will mask the WOT plug coloration. At the end of the WOT run, back off and immediately shift to neutral, cut the ignition, and drift to a stop and pull plugs for a reading.
 
No way is the carb and ignition curve correct using only the items in the msd box with that camshaft.

Start at the bottom and work up.

May be a fuel delivery issue. Pump swill, it's lean is my guess.
 
Thanks again
I'll put old carb back on and see if it clears up and report in with a update.
 
Is there a built in rev limiter with that dizzy that it set at that rpm level? Seems like there is a dip screw that you can set the rev limit with but I don't know your model number on the distributor.
 
Ok the dist is a pro billet 8534 so pulled it and locked it out set it to 35 degrees and it's scary again .There is still a little miss up top but it will drive through it. So what do you think less timing or carb? Again it ran perfect before these two changes, could it be out of alternator.
 
What is your fuel pressure, and can you watch it thru the run? And by drive thru it. Your hitting a dead spot at 5800rpm but clears up at say 6200rpm?
 
7.5 lbs, I took the fuel pressure guage off the hood but I am going to put it back on till I figure this thing out. Locking out the dist help big time.
 
Listen to crackedback Also you always have to tune a new carb there not plug and play.
 
Yeah i adjusted the idle mixture big time i guess its off to the secondary mains. with the dist adjusted the off idle is nice and crispy again.
 
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