Post by: Grimpala on June 27, 2019, 07:55:06 AM
I'm running a Mallory ign. module in an old points dist. The ignition seems strong, strong enough that I backfired and blew the top plate gasket out of the TR.
The motor is a '78 454 out of a truck, stock cam. I put 781 heads on it at the same time, those are good to go. I'm also running OT Bassetts.
My question is: Am I over carb'd? The plugs are a little wet, but I attribute that to pumping the carbs to get it to fire and then it not running long enough to burn everything off. I can't get this thing to idle at all, it revs to ~2500 then coughs and sputters a bit and dies. I can fiddle with the throttle and keep it half-assed alive, but it's not happy. A little poppy through the pipes, The timing isn't perfect, but I've gotten it kind of in the middle of too advanced/too retarded.
I'm thinking that I might have a vaccuum leak causing this, the mid piece on the TR isn't as flat as I think it should be where it mates to the top plate. I can see light under a straight edge on one side of the TR. I'm going to sand the plate this weekend and see if I can true it up. The way the gasket blew out of it makes me think that it isn't sealing as well as it should.
Also, how flat does the carb base plate have to be? The perimeter is flat/true, but on an angle there is ~.005 gap at the middle of the carb. It's like the ears have been a little too tight, but like I say, the perimeter isn't leaking, so I figure this little bit of gap shouldn't matter on a squarebore.
Long story short, engines revs high real quickly, then dies out and won't idle even when fiddling with the throttles. Too much carb or a massive vaccuum leak?
Thanks in advance.
Post by: angermgmt on June 27, 2019, 08:23:57 AM
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Post by: Grimpala on June 27, 2019, 09:58:58 AM
Spray WD around the bottom of the intake and carbs. If it revs up there’s your leak.
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I can't get it to run long enough to check this. I got it to run extremely roughly for about 30 seconds last night by monkeying back and forth with the throttle .
Post by: bobjthomson on June 27, 2019, 12:17:40 PM
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Post by: Grimpala on June 28, 2019, 11:43:28 AM
Get some brake clean and prime the front carb , when it fires keep spraying the carb to keep it running . Sounds like it’s running lean and that’s why it’s backfiring through the carb . Set ur idle screws down to closed the back off 1 1/4 turn out .
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It's not lean, if anything it's pig rich. I was futzing with the timing during all this and retarded it too much.
Going to sand the TR mating faces this weekend and get them nice and true to definitly eliminate vaccuum leaks, then try again.
Post by: bobjthomson on June 28, 2019, 11:49:35 AM
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Post by: Grimpala on June 28, 2019, 01:42:14 PM
Good luck bro
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Thanks. I'm getting tired of working blind on this thing. Might have to go back to the Performer RPM and a single 750. :(
Post by: mash on it on June 28, 2019, 02:07:16 PM
It's not lean, if anything it's pig rich. I was futzing with the timing during all this and retarded it too much.
Going to sand the TR mating faces this weekend and get them nice and true to definitly eliminate vaccuum leaks, then try again.
With any fresh GM build, or manifold change, I static time the engine at 10° and lock it down, it may not be perfect, but it's damn close.
This eliminates 'futzing' with the distributor. Never fun with over transom headers.
Simple to static time the engine.
GM HEI, points, msd or others.
Dan'l
Post by: nordicjet on June 28, 2019, 03:35:43 PM
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Post by: Grimpala on June 29, 2019, 05:29:27 PM
With any fresh GM build, or manifold change, I static time the engine at 10° and lock it down, it may not be perfect, but it's damn close.Yeah, I set it back to 10-11, after I realized it was a vaccuum leak and not the timing.
This eliminates 'futzing' with the distributor. Never fun with over transom headers.
Simple to static time the engine.
GM HEI, points, msd or others.
Dan'l
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Post by: Grimpala on June 29, 2019, 05:30:24 PM
Put a cam in it. Around 540/550 lift with 280/286 duration. Too much carb for stock cam.Ive got a 630 lift with ~270 duration solid flat tappet, but I'm thinking that's too damn big. Plus I'll have to cut the heads.
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Post by: Grimpala on June 29, 2019, 05:32:01 PM
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Post by: Grimpala on June 30, 2019, 10:53:48 AM
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Post by: mash on it on June 30, 2019, 12:18:19 PM
It runs!!!!! But it idles at like 1800. Still tuning it a bit. What's a good idle speed? 1000 - 1200?
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I have mine at 900 rpm or so, for more maneuverability around the docks. But that's on a heavy azz day cruiser.
On a lil boat, 700-750 should be appropriate.
Dan'l
Post by: Grimpala on January 07, 2020, 10:28:58 AM
Evidently when you use a rect port intake on oval port heads you need rect port gaskets... I read this somewhere on the web before I did the install, but failed to remember it when the time came for install.
Post by: tunnels on January 07, 2020, 08:01:10 PM