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Discussion Starter #1
Ok thanks so much for all of the help to get this car going. I've nearly got it where I want it. Got the new heads and new carb on it. Runs great except at WOT and high rims it has a flutter with a noticeable hesitation. Part throttle all the way until the secondaries start to open its perfect, good power.
I've been playing with the timing and I believe it is good.
So is this a lean secondary jetting or is the stock mechanical fuel pump not keeping up? Or is it plug gap? Or what do you guys think? Thanks again
 

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Just curious where do you have your timing set, and when does full advance come in?
 

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Discussion Starter #3
Well initial is set to 16 (it likes it there). I don't know where it's all it because my HB only has timing marks to 16deg.... it is advancing to more than that when I Rev it. I guess I should look into this further.
 

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Ok thanks so much for all of the help to get this car going. I've nearly got it where I want it. Got the new heads and new carb on it. Runs great except at WOT and high rims it has a flutter with a noticeable hesitation. Part throttle all the way until the secondaries start to open its perfect, good power.
I've been playing with the timing and I believe it is good.
So is this a lean secondary jetting or is the stock mechanical fuel pump not keeping up? Or is it plug gap? Or what do you guys think? Thanks again
I would be inclined to enrich the secondary jets by one step at a time, first. So, what carb are you running?
Are you feeling the misses(seat-o-meter) at WOT or watching the tach? Perform your WOT test, then immediately shut down the engine coast to stop and pull a couple plugs from each side. Might give an indication of the AFR. An alternative is to seek out a chassis Dyno and have them tap into an 02 bung (collector) to read your AFR from approx. 2500 to 6000 RPMs.
 

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There is no way to know if it is running lean (or rich) in the secondaries unless you have a wideband air/fuel sensor... any idea what your air/fuel ratio is? What's your vacuum when you feel the hesitation and what's your power valve? If it is stock from Summit then it is 6.5 inches. Did you adjust your primary/secondary jets already? Old timers would adjust the carb based on the spark plugs/headers but running at WOT is only a small part of an overall run so you can't easily see what is going on using this method.

david
 

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A 600 cfm carb is just right for the old HiPo 289, but your heads can flow considerably more air, and need at least a 650, or more. With all due respect, the Summit carb is not a high performance carb. A Holley Street HP carb is much better suited to your heads.

https://www.summitracing.com/parts/hly-0-82651

From your description it sounds like your carb cannot keep up with the engines cfm needs. A little richer main jets may be helpful, but not a comprehensive solution.

My favorite wideband
https://www.summitracing.com/parts/avm-30-5130




Z
 

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Discussion Starter #9
I haven't adjusted anything as far as the Jets or springs go in the summit carb. I'll have to look into how to do that. Thanks
 

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Discussion Starter #11
Filter is the canister at the bottom of the pump. I noticed one time it fluttered at WOT at lower RPMS's after it changed gear. No question that if you let off the throttle ever so slightly (maybe to 90%) it stops fluttering and runs stronger. Thanks.
Where is your fuel filter located? Does it run fine at WOT at lower rpms? Does it run fine at part throttle at high rpms?
 

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I'm doubtful its your fuel pump or your filter... The carb only needs 6-7 psi and when diaphragm fuel pumps go bad or filters get clogged things get worse and worse until the engine doesn't run at all. However if you'd like to check get your wife to run the engine at high revs for a short period while you watch your float glass. If the fuel level goes down then your fuel pressure is not high enough.

Given what you've told us about your build I'd suspect your power valve needs to be increased or your vacuum secondary spring is too light. However without some numbers it's hard to know anything for sure.

David
 

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im running a 289 with afr 165 heads and the same summit 600 cfm carb and I never had problems with it the way it came out of the box. Im running around 18 initial 36 total
 

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Discussion Starter #14
Hmmmmm. I better check for a vacuum leak I think... I'll change out the fuel filter too ...it's time.anyway....
 

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Unless you're spinning some crazy rpms, I would be surprised if symptoms are a result of your carb being too small. I have AFR 165s on a 302 with a 500cfm carb and it rips really nicely under full throttle all the way up to the cams upper threshold which is about 5,800rpm. I'm also a big fan of the onboard A/F wideband gauges when comes to dialing in a carb - feels like I'm flying blind w/o them.

Recently read an article about something that I always felt was true based on more of a feel than science but recent trends, where all emphasis is placed on dyno #s, are causing some confusion out there. Just because a larger carb produces more hp on a dyno does not necessarily mean it will run faster in say a 1/4 mile or on a road course and in fact, tests prove there's a point where HP increases when adding CFM yet at diminishing returns when pavement and stop watch are applied. There's a point where the dyno can begin to mislead you -- when data doesn't translate effectively in the real world.
 

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Discussion Starter #16
Ok, I think I need some help with the timing... with the dizzy vacuum line attached to timed vacuum on carb (and the dizzy end plugged) I can set the advance to 16deg and it will advance to near 40 when revved... Runs good(still have a flutter at high rpm so) idles good, but I notice the temp will try to creep up at idle...

Or

With the dizzy vacuum line attached to full vacuum on the carb, plugged, I can set the advance to 16, plug the vacuum back in the dizzy(the rpms rise) but when I lower the carb idle screw to normal idle speed, it really starts to miss... Barely idles...and it's showing around 40 deg advance at idle(with everything connected)

What am I doing wrong?
 

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The Summit 600 vacuum carb looks decent. Comes out of the box with 67 and 73 jets which should be pretty close. The .035 shooter looks a bit big to me though. If you flog that from a stop it will dump all the pump shot and you may not be up on the carb yet. I would expect to see a .031 or even a .028 pump nozzle but the key to all this is what ever the engine likes. Have you checked for vacuum leaks?

On a vacuum advance distributor, you disconnect the distributor vaccum and plug the hose to set initial timing. Unless you have a wonky kind of an engine, the stock vacuum advance curve in the distributor should be ok. It also sounds like your distributor vacuum should be plugged into the timed vacuum port at the carburator once you get the initial timing set.

Oops, forgot one question. What is your idle vacuum, in gear if it is an automatic.

Depending on what rpms the flutter comes in at, it could be that the secondary jets are too lean. It could also be that the secondaries are just on the verge of coming in and not coming in which will make the engine feel like it is surging and falling back or fluttering. How does it run if you go from light throttle to WOT?

You can check to see if your secondaries are too lean the old way without an A/FR gauge. Put in a couple of fresh plugs and immediately go out and create the problem on the highway. Pull off the road and quickly shut it down and check your plugs. If they are whitey white its too lean. Look up some of the photos of too lean plugs to see how to determine if that is the issue. Unleaded fuel doesn't color up the plugs much unless you are way fat and then it turns them black.

Only make one change at a time. If you decide to jet up the back side, go up 2 to 3 jet numbers and see how it does. TYhat would be like 75 or 76 which I have had to run with a Holley 600 on my engine so it may need it or it may be something else.
 

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Discussion Starter #18
Update:
I got a tach connected and ran some timing vs rpm numbers with vacuum hose disconnected and plugged...

Idle: 16deg
1500: 18
2000: 24
2500: 26
3000: 27
3500: 28
4000: 30
4500: 32
5000: 34
5500: 36
6000: 38
6500: 40deg

Didn't go any further, but looks like it doesnt ever stop?
Is this correct?
 

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That is strange. Running on the mechanical advance only with 16 at idle it should go up to 36 total by around 3000 rpms or so and then stop advancing.

The mechanical advance curve is also just that, a curve. It adances a bit faster initially and then flattens out to total advance. YThis is just a typical example. Happens to be a vette engine.


Yours is almost a linear plot. I don't recall ever seeing anything like this except when somebody is monkeying with a computer controlled engine.

What kind of a distributor is this?
 

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Discussion Starter #20
This is a Motorcraft reman (cordone)I bought from Dallas Mustang...
That is strange. Running on the mechanical advance only with 16 at idle it should go up to 36 total by around 3000 rpms or so and then stop advancing.

The mechanical advance curve is also just that, a curve. It adances a bit faster initially and then flattens out to total advance. YThis is just a typical example. Happens to be a vette engine.


Yours is almost a linear plot. I don't recall ever seeing anything like this except when somebody is monkeying with a computer controlled engine.

What kind of a distributor is this?
 
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