tunning question

aliensecretion · Apr 4, 2012

Been having problems getting my new set up dialed in just right. Here's what I've got: Newly built 302, mild cam, 4 bbl quickfuel HR 580, c-4, 3.50 gears. Here's how I'm set right now: 6º advance, idle adjustment screws are less than 3/4 of a turn out, float level right on the middle line in the windows. Like this i get really good power all around but when pulling out I have to go easy on the throttle or I loose power and get a small backfire. I'm also only getting 6-7 mpg and it still smells like it's running rich. If I turn out the idle mix screws any further, It get's rough. If I go in, it starves. I've tried advancing through the range up to 12º but the further up I go, the smoother on the hgwy but no power down low. Not sure what to do next. Jetting that came in it is 66 for primary and 72 for secondary. Never messed with jets before... Do I need to go down a size?

broncnaz · Apr 4, 2012

What tire size are you running? What are the specs on your cam?
Might want to check to make sure all the fuel bowl screws on the carb are tight. if they are loose you may have internal fuel leaks and that could cause a lot of your issues. Also make sure the choke is fully opening.
I'd say you should probably be able to go down in jet size on the primary side. Check your spark plugs what color are they? If they are black I'd get some 62 and 60 jets and try them out.
As for your idle mixture well sounds like thats kinda jacked up as well. maybe the airbleeds or idle feed restrictions are to big dont really know. QF has some good features on there carbs but it may take a good bit of knowledge/tinkering to get it dialed in.

You may also need a larger acclerator pump squirter or pump cam to cover the lean condition when you step on the throttle. Also what power valve is in the carb?

aliensecretion · Apr 5, 2012

Tires are 31's. Don't have the specs on the cam handy but it's mild. Bowl screws are tight and choke opens fully.

Going to check the plugs when I get home and try again advancing a little more. Looks like my mechanical advance in the distributer is 21. Total advance should be low-mid 30's right?

360 4V · Apr 5, 2012

Could your camshaft be too too big for your torque converter stall speed?

What size carburator are you running? a 600 cfm is the largest I would put on a 302.

broncnaz · Apr 5, 2012

You might have to much or to fast of a advance. 21 at the dizzy means 42 at the crank not counting your current 6 degrees initial and any vacuum. usually you want no more than 34-38 degrees total advance.

aliensecretion · Apr 5, 2012

Don't seem to have the cam specs... would have to call the builder but it was built around what I already had. My trans has a low stall converter (that builder said 1500-1700 depending on engine torque).

Found the carb specs... 580 cfm, jets: 66 pri, 70 sec., idle air bleed:70, High speed Bleed:31, Power valve: 6.5.

Did the math on the MSD and am getting 21° @ 2500 rpm. I can change the stop bushings and get 18@2100 or change bushings and springs for 18@2900 if one of those is better.

Broncaz, why do you double that number? I'm was going off the MSD directions that shows the formula initial+adv=total... I haven't seen anything about doubling that. Always happy to learn something new!

aliensecretion · Apr 5, 2012

Ok, just found an article that talked about it a little... not quite sure i fully understand why but I think I get how to figure it. Going go outside and set my initial at 0 and see how it does.

So found around 2º initial gave me a total of 32°. Could feel there's more power there but it runs too rough. Adjusting the idle leads to either too much fuel or not enough. I'm thinking of trying either smaller jets or larger idle air bleeds.

broncnaz · Apr 6, 2012

The Dizzy turns at 1/2 speed of the crank so timing at the dizzy is doubled at the crank. i think MSD already figures this for you so there 21 degree bushing actaully means 21 degrees at the crank.
If you have vacuum advance unhook it while testing the advance at RPM see what your readings are there. Kinda sounds like your advance may be a little to slow as by 2500 RPM you should have closer to 32-38 degrees with vacuum advance unhooked. You may want to swap to lighter springs so all your advance is in by about 3000 RPM.
Every engine is a bit different so you kinda have to play around with the timing to find what yours likes best.

ransil · Apr 6, 2012

my $.02
Timing looks Ok low 30 total is what I have found works
idle screws only affect idle, adjust them to get the best idle
power valve & accelerator pump affect acceleration put a lower vac power valve in and play with the accelerator pump adjustment .

aliensecretion · Apr 6, 2012

Been thinking about this... why would my total advance be 32 when I started with initial 2 and 21 mechanical? Shouldn't my total be 23 not 32? The vac advance was unhooked when I did this.

ransil · Apr 6, 2012

I was talking about total advance
Total =initial +mechanical +vacuum

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bad 68 · Apr 6, 2012

timing needs to be checked with vacuum disconnected because vacuum advance only advances timing under light throttle, high vacuum situations. its there to help with fuel mileage under cruising down the hi way. It should not effect your low rpm, higher throttle condition where your experiencing hesitation on take off. It should not effect engine idle either.

broncnaz · Apr 7, 2012

aliensecretion said:
Been thinking about this... why would my total advance be 32 when I started with initial 2 and 21 mechanical? Shouldn't my total be 23 not 32? The vac advance was unhooked when I did this.

Yeah your probably correct there. maybe you have other issues like a slipping balancer ring thats giving you bad readings.

aliensecretion · Apr 7, 2012

broncnaz said:
Yeah your probably correct there. maybe you have other issues like a slipping balancer ring thats giving you bad readings.

Good timing broncaz! Was just checking this before I head out into the garage. Going to check the balancer and also install my lokar throttle cable and get rid of the old solid linkage. See if maybe that makes it a little more accurate.

Update to the original question... set the timing yesterday at (what should be) 29 total and that seems to be the sweet spot for the power. (actually had tons of power available at 65mph!) Improved vacuum too judging by break feel. But i still can't get it really smooth because it's either too rich or not enough fuel for take off. If I'm understanding things correctly, would that be the accelerator pump being too small?

broncnaz · Apr 7, 2012

Too small or to large of a accelerator pump squirt will cause stmbling on take off. you might be avble to fix it with acclerator pump cam maybe even change the position of your current one they usually have 2 screw holes which will give a different fuel shot.
you can check to see if your getting to much of a squirt by watching the exhuast when you open the throttle quickly if you have some black smoke come out then your pump squirter is to big. If no smoke then it may be to small.
But your rough idle is something else. Kinda have a feeling that with your carb something in the idle system is off maybe air bleeds or idle feed restriction might need smaller idle feeds. as with your idle mixture screws at around 3/4 out well that kinda says its to rich at idle. Does that carb have 4 corner idle adjustment?

Broncobowsher · Apr 7, 2012

This will sound odd, but check you plug firing order.

I have had a couple of V8 engines that had a couple of plug wires swapped around. Sometimes it would pop out the intake like you describe. Or just run perfectly smooth without issues. That is the scary thing, they ran smooth. Started right up. The boat I ran for a couple of years, had several gearhead friends ride along and none of them ever commented that it ran bad. Just lacking a bit of power. Loose a spark plug, yes they ran rough. Even the plugs read good across all 8 of them.

Just yank all the plug wires off and put them on again one by one. Takes 15 minutes and costs nothing. And my boat would have run a lot better for those couple of years when I first got it.

mcknight77 · Apr 7, 2012

broncnaz said:
Too small or to large of a accelerator pump squirt will cause stmbling on take off. you might be avble to fix it with acclerator pump cam maybe even change the position of your current one they usually have 2 screw holes which will give a different fuel shot.
you can check to see if your getting to much of a squirt by watching the exhuast when you open the throttle quickly if you have some black smoke come out then your pump squirter is to big. If no smoke then it may be to small.
But your rough idle is something else. Kinda have a feeling that with your carb something in the idle system is off maybe air bleeds or idle feed restriction might need smaller idle feeds. as with your idle mixture screws at around 3/4 out well that kinda says its to rich at idle. Does that carb have 4 corner idle adjustment?

+1 Sounds to me like accelerator pump problems. First check that it isn't blown out. That will cause a vacuum leak. If it is OK, go to a larger size or a faster pump cam.

aliensecretion · Apr 9, 2012

Had a little bit of time to mess with this over the weekend in between projects in the house. Here's what i've found. No black smoke on accel. Balancer pully is good to go. Plug wires are correct. 3 initial gives me 35 total and puts a huge smile on face with how much power is there! Seriously, I had no idea a bronco could accel and run like that!

Still have the stumbling on take off and still only pulling 6-7 mpg. The initial and mech still doesn't add up properly. Also, plugs show rich and i'm getting a lot of varnish building up in the carb. (used a whole can of carb cleaner on it) I called quickfuel's tech line but they said they can't really diagnose and reccomend the right stuff until I know why the advance doesn't add up. the only thing I can think off that might have something to do with that is the idle where i'm measuring initial. I'm measuring idle with the throttle as low as it goes (3). when I rev the engine, it wants to idle around 9-10 for a few before it settles back down to 3. I was blaming that on the old mech accel linkage (didn't get to install the new lokar linkage yet).

I'm sure the accel pump is wrong like everyone is saying but then there's the mpg issues as well. Since it seems I have to order whatever i need (accel pumps, jets, bleeds), i want to have the best info possible so I can call and determine what to order. I guess if nothing else, i'm learning quite a bit from all this and it will be cool when it's all done knowing I did it and not paid somebody!

aliensecretion · Apr 9, 2012

Broncaz, yes it does have 4-corner idle adjustment screws.

aliensecretion · Apr 9, 2012

Just put in a fuel regulator to ensure I didn't have too much pressure... set it for 5 but it doesn't seem to make any noticeable change.
Should have mentioned the farting. That's the best way I can think of to describe it. When I take off from a start and don't feather the pedal, I also get a little pop out the exhaust before it lags and also a few seconds after i shut down.
Found this video to explain the accel pump stuff. http://www.youtube.com/watch?v=k-Nx5HEzvlY&feature=related Now that I understand what it does, I'm going to get the pump cam on the way so I can hopefully cure the hesitation and go from there I guess.

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