Trying to get truck to run right

[Dm1pfoy1]

I have 72 c10 with 383 with lage cam dont know specs demon carb w vac advance 625 cfm. 350 trans will run about 3000 rpm at 70 mph. What would make it feel like I "lost" my secondaries? Its while driving that I notice it when I go wot its like there is nothing I will feel same amount of acceleration as just going mid throttle no pop backfire nothing. It did seem a bit lean when driving on hwy yesterday...smelled lean if that makes any sense.....temp didnt change again no poping adding fuel helps but as it is car has strong fuel oder and before when throttle was ok truck ran so rich it burned eyes never smoked though now it seems to run alotbetter but afraid I am leaning out on big end

[GASoline71]

Not sure how "lean" smells... except for a really hot engine cooking the paint.

What is your timing set at?

Gary

[Dm1pfoy1]

I have truck set currently off of ear. Yeah I know its not correct way to do so but issue I am having is im not even sure what timing I need. I know w vac advance dist like I got I know total time needs to be set...that im not sure how to do also how can a truck run rich at idle and lean at top?
I made short vid of truck running if anyone wants and in 15 min of running truck in garage my clothes smelled of rich exhaust. float bowls at lowest line and mixture screws at about 1 1/4 th turns. I am going to check vacuum and timing soon..another question is I have batter in cab how should I get power to timing gun? Also what is good vacuum ive herd from 8-16 depends on cam. Is there a way I can check time with voltmeter?

[hugger6933]

Welcome to the site first off, you'll find a lot of help here. What about your vac diaphram for the secondaries and see if it is working, check the timing, fuel pressure. What has been done recently to make this change possible? has anything been taken off the motor or has it been torn down? maybe a intake change or something like that? That would lend it self to think about a vac leak. You said the cam was large have you had a vac gauge on it before to see how much it makes? all of the questions may seem uneeded but in them may lie the answer to your problem. Jim

[Dm1pfoy1]

How do I check diaphragms is that spring in carb? I now under idle secondaries opening. Only changes are timing and carb Thats not to rule out vac leak just I have not changed anything where should I check fuel press at? I have clear filter and I have noticed it will nearly empty (bearly enough to keep engine going) at times.

[oklalawnboy]

Large cams don't make much vacuum. Do you have power brakes and if so do they have enough vacuum to work properly. Maybe not enough vacuum to pull secondary's open. Float levels too low and running out of fuel as the demand is quite a bit higher at 3000 rpm. Is your fuel filter one of those crappy little glass ones? I have seen them come unscrewed on the inside (if that makes sense) covering up the holes for fuel to flow through it. Just my thoughts.

[Dm1pfoy1]

Breaks seem to be working ok... I do notice a surge whwn putting it in a drive gear that seems to overcome brake power so more vacuum is prolly needed didnt think to relate them. Would it be better to time based off vacuum or timing light? I do have one of the crappy glass type filters ill look that over and increase my float levels should I change my mixture settings? Idle ?

[Dm1pfoy1]

How does not having a choke effect everything I am trying to tune......my experience with carbs is all book based and read and apply so not knowing my choke plate is not there. I have no manual choke nothing. So can this alter all I am trying to tune and adjust. Thinking of going with manual choke. Should I wait to time and tune till I do this also another question is it best to time when hot or cold should I take trial runs. Sorry to ask so much my experience in this is low. Only second carb vehicle I ever owned and wasn't taught much on this in auto class.

[18436572GMC]

You might need different pressure springs on the secondary metering rods to match the carb to the cam. look on demon carbs website for the carb owners manual. lots of good information there. As for getting power to the timing gun just use a separate 12 volt car battery that you can place near the engine bay, or some jumper cables

[magwakeenercew2jh]

I'm not an expert. That's my *always* disclaimer.

I'd use your truck's battery. Just run a longer + good size gage wire from the light to wherever the positive pole is.

I have a 600CFM Street Demon. Set the mix(es) to the initial set up rec. from Demon. No choke? Hummmm! What Demon is that?
No matter.

Buy a decent in-line fuel pressure gage. Over the years, it saves soooo much time. Answers a ton of questions. Put it close to the carb.
Upstream (toward the tank), make sure you dump that ass wiping filter for a decent one.

What else...???? Why does the truck smell of gas? Or is it your clothes? Was it the 15 minutes of running it in the garage...I'm just happy you can still type.



Otherwise, what's the smell from?

Get a good timing light. One with a digital display that shows RPM. Not BIG $$$$, really. The only thing wrong with those is that all your buds will keep borrowing it.

And, oh, yeah...One thing at a time.

[Zeke's Garage]

First off, don't worry about the choke just yet. And second off, Let's verify your ignition and timing first. So many carb and fuel issues turn out to be ignition issues.

1. Check your initial timing. Unhook and plug the vacuum advance from the carb to dist. If you're battery is in the cab, connect the positive lead of the light to the hot lug on the back of the alternator, or the terminal on the inside of the passenger fender. Set your initial timing to, oh let's say 12*.. see what the engine is at now, I'm not sure what a 383 likes, but I think 12 is pretty safe. After you're done with initial, hook the vacuum advance up and proceed to the next step.

2. You'll need a vacuum gauge hooked up to a constant source, either on the manifold, or a vacuum port below the throttle plates on the carb. Look at the gauge reading and make note of it. I'm not familiar with the Barry Grant carbs, but it should have at least two idle circuit adjustment screws in the front, and it might have two more in the rear if it's a four corner idle model. Slowly turn in one of the adjusters, until you notice the engine begin to change speed, or quality of idle. Note the vacuum reading. Adjust the screw slowly to get the best vacuum reading on the gauge. Do the same for any of the other idle screws. Again do this slowly, about 1/4 turn at a time and let the engine settle. Once you get the highest vacuum reading, re-adjust your idle speed (it may have changed), then adjust the idle screws again to see if you can make it better. Once this is done, you're done with the idle circuit.

3. If you can get your hands on a 'dial back' timing light, then you can check your total timing at say 3000 RPM to ensure you're getting full advance from the weights in the distributor.

Give some of these a try and let us know what you run across.

Shawn

[GASoline71]

First and foremost... you need the proper tools to maintain an old rig. First things first... go buy a timing light. They are not expensive, and it will save you a lot of headache by setting the timing correctly.

Timing needs to be set first before you start fiddling with the carb.

Gary

[msgdsrf]

Actualy you should not be able to feel the secondaries. If you do, then there's a problem, especially with a Demon. Perhaps what your looking for the tranny to kick down...

[Dm1pfoy1]

First thank you so much for all the replies. I finally got timing dialed in took last 24 hrs to research cam and proper timing with modified engine and i got in at 15* total advance on dist. and timed at 21* ,from a MSD posted youtube video (thank you MR. Fryberger from HotRod Mag.) this is not to unheard of, for total of 36* at 3k. My biggest mistake was not pulling vac line for advance. Truck runs fantastic now.So thank you to all of you. I still need to adjust for idle circuits, just found out about that while i was away, demon stresses 4 corner tuning but not until i dug that I found that.

Also all made sense when I sat and thought about it the th350 is vac operated (for kick-down) so my trans and vac secondaries were not getting appropriate vac to open secondaries (partially or fully) and kick-down trans also think that not pulling vac cause a lot of "rich smell" at idle and "hot" smell at top end was due to curve being so far off that was some how acting as if at 0*(or something like it) at idle making a rich smell due to incomplete burn and hot at top end due to vac advance and lack of fuel due to lack of vac. I hope I have thought this though properly please correct me if wrong.

the demon had elec choke on side but no choke flap no axis or whatever you call bar that holds flap...no choke leg nothing.....so found manual kit will eventually get.

haven't looked on barry grant but does anyone know a good filter and fuel gauge i can get? Will it be filter then gauge or gauge then filter?

The hot and ground lead on alt worked great for timing. going to adjust vac and recheck timing soon.Its getting cold and don't want to fine tune till spring since fair weather/summer only truck. Its a 204/214 @.050 .420/.440 112 lsa (rv, 3/4 cam)

To find timing I used the take total time of 12* minus initial time to get dist advance than recommended total time is between 34* and 38* so i took dead center and subtracted total time to get timing needed on engine.

Again thank you all i really appreciate the responses and I was kind of taken back in all performance crap I have owned this is best forum I have been on and you all were so helpful and very knowledgeable makes it a lot easier to know i can trust info I am getting.. I will have pic's of truck up tonight if anyone would like. Going to make a build thread (more like fix it list and question list).

Anything to add please do tell....