Losing my mind trying to get this 360 to run right

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gtmopar

gtmopar

Phuckin A!
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First off sorry for my rant but I'm just discouraged and fed up tring to get this motor running right. So here's what's going on. Motor fires up but won't idle at all. Motor is new still barely broken in. Its a 360 LA roller, custom cut cam( nothing huge very mild) M1 intake heads mildly ported and polished with bigger valves, roller rockers 9-1 roughly.
When it runs and I rev it slightly it pops. The full exhaust is not on it yet because the front end is not on it to get it to the exhaust shop. I'll admit I cheaped out on the distributor and to be honest I don't like it, think its a proform so that could be one issue. The carb is an older 750 DP that I rebuilt but either I'm losing my touch or this carb is ready for retirement. I am at a loss on why this thing will not idle AT ALL! I'm guessing idle circuit on the carb is screwed up or that distributor is crap which I'm leaning really hard towards that. I really don't have the cash right now close to Christmas to drop on an MSD and new 750. I know there are a million variables but could there be something I'm missing? At part throttle it revs real quickly but under 1500 rpm it flat just peters out and dies. Again I know there are a ton of things that could be wrong but if anything rings a bell that I need to check please let me know I'm all ears. Or else this beautiful car is going to get crushed!! Lol. The other dart is getting FAST EFI 2.0 I don't give a **** how much it costs.
 
Where is your initial timing set at, have you checked for vacuum leaks, vacuum ports plugged, did you degree the cam in, did you check your float height with the sight screws on the side of the bowls? You need to give more details I understand your venting but that won't help.
 
wow like you said variables when its never been run right yet , it could be from vacuum leak to timing, to carb good luck trouble shooting that 1 sorry to hear
 
I think a lot of your frustration is coming from running open exhaust and a rich mixture. If it's scavenging cold air from the lack of exhaust, it can cause the popping, you're talking about.

I wouldn't blame the distributor, just yet. Have you checked total timing?

The second you put pipes on that thing, it's going to need tuned again, anyway, so that's the first thing I'd be checking. Depending on the overlap of your cam and vacuum needs of the engine, it may not idle well without tubes.

I know when I fired up a Toyota 22R that I was putting a glass pack on, it would not idle at all on the factory timing, with a short exhaust system.

Those double pumpers are also sensitive to float flooding. The screws on the float bowls that adjust fuel level usually need tinkering with them.

That could also explain the rich condition/ popping with short exhaust. The carb may be flooding from high float level. You could try that, before exhaust to get it to idle.
 
Did a shop do the engine?
Have you compression tested this thing?

The reason I ask is because this could be caused by valves not closing all the way.
(popping)
Just trying to think of something that could cause it that has not been mentioned yet.

A video of it running would probably help a lot if you can.
 
Pop out of the exhaust or out of the carb?
How is your fuel pump?
Just to set up the engine to get it running , if you think the distributor is bad get one from the parts store and try it
 
Check your plug wire sequence you might have it off a wire,chk plugs,chk timing,chk carb and if you have another one known to be good put it on and see if prob is better or worse,coil backwards it wouldnt run but may be cracked and bad,chk vacuum lines and intake gasket seal,rockers/pushrods,check for a bent pushrod,good ground to engine,dist chk gap.08-.010..cracked cap or loose rotorbug..bad gasket between carb and manifold..stuck valve maybe?If you have another dist try it after setting gap and chkg reluctor for consistantcy[shaft]...pull engine timing up to tdc and chk it against your timing marks versus piston being tdc on #1 cylinder,just some things I would chk on and run down 1 at a time and as a process of elimination,you'll figure it out I'm sure,prob something stupid we've all been there before,pipes would def help as in mufflers,open pipes will pop and crackle...just my 2 cents
 
gt I have to tell you that it sounds as if you've created your own problems. Since I'm a "flat tappet" guy, and have broken in a few cams, I ALWAYS do my very best to insure that an engine is "ready to run." That means learning to set the timing so that it RUNS. If you can't insure the entire fuel system is up to snuff, run fuel out of a safe container, siphon from above. Make CERTAIN you have a good working carb, even if you have to borrow or buy one.

1.....Very first order of business is to figure out what timing and ignition is doing..........What is your initial advance, how much total (mechanical) do you have, and leave the vacuum unhooked until you get this sorted.

2.....I you suspect, and it sounds as if you do, that the carb has a problem, then the solution is easy.......find a friend. try the carb on his car. Or borrow or buy a used/ good working carb.

3....Along the way, how do you KNOW, and I don't mean guessing and assuming, that the valve gear is in proper shape. "Usual" scenario is either a reground cam with reduced circle, and or milled heads/ block which adds up to improper valve clearance. Add in screwups by "Chivvy" machine shops who've not properly set up the valves and springs. There's numerous threads on here where guys have ended up with mis-matched parts problems with valve gear
 
Thamk You for saying valve adjustment, so many threads with the same symptoms and everybody always goes for the carburetor and the distributor and everything but the first place that should be checked Thank You!!!!!!!!!
TrailBeast said:
Did a shop do the engine?
Have you compression tested this thing?

The reason I ask is because this could be caused by valves not closing all the way.
(popping)
Just trying to think of something that could cause it that has not been mentioned yet.

A video of it running would probably help a lot if you can.
Click to expand...
 
valve adj. on a magnum roller could be the issue, but I don't know that it would get rid of it without a full exhaust system.
 
1) Adjust the valves
2) set fuel pressure to 6 psi
3) start with the idle mix screws 2 turns out from completely closed
4) set base timing to 10-14* btdc with no vacuum advance hooked up


Start with those things, and report back.
 
rnaz said:
1) Adjust the valves
2) set fuel pressure to 6 psi
3) start with the idle mix screws 2 turns out from completely closed
4) set base timing to 10-14* btdc with no vacuum advance hooked up


Start with those things, and report back.
Click to expand...

Great place to start. It is hard for us to tune over the computer. Most of the guys on this thread could have it running like a champ in an hour if they could
lay their hands on it instead of guessing over the net. tmm
 
Ok so here's some more info. The motor fires right up first rotation. It's not backfiring through the carb its popping through the exhaust and it could be the scavenging and hot headers. I can't really get a good timing gauge because it won't idle and when it gets the rpms low enough it dies. I reran the valves the other day to make sure all was good so I checked that off the list. I've made sure all vacuume leaks have been checked and so far everything seems good. Heads have been completely rebuilt with all new parts. I'm thinking I should get the exhaust back on because tuning is going to change vastly after the exhaust is on. I built the motor so I know everything that has been done to it. Float levels and fuel pressure is good. I scored a new carb this evening as a test mule to rule out the 750 that's on there. Thanks for all the suggestions guys ill do a compression test on it tomorrow just to be on the safe side. If I can get her to idle then I can really narrow down the timing and hopefully get this sucker somewhat running right. I'm thinking seriously I need to get the exhaust on. Ill post a video of it running tomorrow.
 
Normally I'm really good about troubleshooting and getting things running top notch but it always helps to call in the troops instead of pulling out your hair. Even seasoned mechanics get stumped now and then. I appreciate the help that's the reason I ask the guys that share the same hobby. Some guys on here try to make you feel incompetent and that's just bullshit. I'd say the majority genuinely want to help and those are the guys I give my gratitude to. I'm hoping that the carb swap will help.
 
toolmanmike said:
Great place to start. It is hard for us to tune over the computer. Most of the guys on this thread could have it running like a champ in an hour if they could
lay their hands on it instead of guessing over the net. tmm
Click to expand...

Thanks!
That should at least get it somewhere in the ballpark.


Not my first rodeo with these beasts. LOL!!
 
Anything to help GT , hey we all get lost from time to with problems. Not sure what balancer you have on the engine, but I had an engine with one from professional products and I could not get that engine to idle either and later I found out the balancer marks where way off.
 
dwire67 said:
Anything to help GT , hey we all get lost from time to with problems. Not sure what balancer you have on the engine, but I had an engine with one from professional products and I could not get that engine to idle either and later I found out the balancer marks where way off.
Click to expand...

Very good point, well all them in this thread are. Dad n I had an issue with his 273 and the balancer TDC was wayyyyy different then true TDC.
 
Wondering if you have a blown power valve on the 750. Throwing on the other carb should eliminate that
 
I'd rather see him take a look at the existing power valve instead of just swapping carbs. There could be a bunch of things that are off on the carb, and he would never know what it was if the different one works right.
 
Will the power valve effect the idling? It's been a long time since I've messed with a Holley, all my last carbs were Eddys which were pretty straight forward yet not very tunable. I'm wondering if the idle circuit on the metering block is plugged? I rebuilt that carb about a year ago and I ran it on another motor for a short period then pulled it off and it sat. It may have gotten some crap in it so I'll pull it apart and inspect it before I buy a new one.
 
There a way to test those power valves or can you just tell the diaphragm is shot. What size would you suggest. Also the primary jets are 67's haven't checked the secondaries. Seem a tad small to me.
 
Put a vaccum gauge on it. If needles jumping erratic its valves.If its really low, vaccum leak. Put a timing light on it. If it jumps around i,d say distributor. Pull the plugs. If they are black bad idle circuit in the carb. Idle slot probably uncovered too much.
 
PV. Has no affect on idle, unless your throttle is open past the idle circuit. If you have the carb off the idle transfer slots should be square if they are not turn the idle screw
To close it up to square.
 
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