Slight miss when cruising

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dustya_383

dustya_383

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Not sure if this is a misfire but when cruising on freeway roughly 60-70 mph 2700 rpm I feel a slight hesitation not major just enough to annoy me where should I look first?? ... Now mind you this is a 410 stroker 4 speed 3:23 gear .. Holley 850 dp and dizzy is locked out no mechanical advance locked at 35 degrees ... Now when I floor it ... It goes hard ..no knocking or anything when I punch it just cruising I can feel a mis and hear it in the exhaust ...running 91 octane

Would the 5/16 fuel line be part of that issue?? Have yet switched to my 3/8 line

Thanks guys
 
did this just start? like around the beginning of October? if so i think its the gas, my dart and 46 truck started doing the same thing on part throttle and high vacuum cruize...

i backed off the vacuum advance with a little luck but am going to try up jetting a couple.
 
I have noticed the same issue at 60-70 mph, I also have the small fuel lines but they are only feeding a 318. I only run premium fuel.

Hopefully someone has dealt with this before.
 
to me, it sounds similar to "lean tip-in", except that you're crusing. But if it goes away when you mat it, you might have a temporary lean problem in your part throttle cruise/acceleration circuit. I think 805 might be on to something...many places use different blends of fuel in the colder seasons to enable easier starting (oxygenated blends). If memory serves, those additives alter the mixture requirements a little bit...do you have a vacuum gage to find out where it starts acting funky?
 
txstang84 said:
to me, it sounds similar to "lean tip-in", except that you're crusing. But if it goes away when you mat it, you might have a temporary lean problem in your part throttle cruise/acceleration circuit. I think 805 might be on to something...many places use different blends of fuel in the colder seasons to enable easier starting (oxygenated blends). If memory serves, those additives alter the mixture requirements a little bit...do you have a vacuum gage to find out where it starts acting funky?
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yea mine starts at about 13" of vacuum and gets worse with more and even to the point your almost off the throttle completly (20" vac). so what im thinking is in those times were getting the most adv out of the vacuum advance canister. Im going to disconnect it and see if it goes away, if it does we either need to up jet and retry with vac advance or have the can come in later. By later i mean instead of 10" of vacuum maybe 15".
 
so i undid the vacuum advance canister and the miss went away. i can only figure the blend of fuel is leaning the mixture out OR the octane level is not as labeled.
 
Advance is pulling the timing ahead to far . Disconnect the vacuum and you'll see it goes away. 2 bbl an 4bbl have different ratios. 2 bbl are 11.0 4 bbl are 8.5 marked on the vacuum rod. They are also adjustable with a allen inside the vacuum port on the dist. The more open your exhaust is the less timing you need. One reason many go with a mechanical advance.
 
Oldmanmopar said:
Advance is pulling the timing ahead to far . Disconnect the vacuum and you'll see it goes away. 2 bbl an 4bbl have different ratios. 2 bbl are 11.0 4 bbl are 8.5 marked on the vacuum rod. They are also adjustable with a allen inside the vacuum port on the dist. The more open your exhaust is the less timing you need. One reason many go with a mechanical advance.
Click to expand...

way ahead of you... my slant is at 16 intial, 30 total by 2500, and 52 vac (11R)(starting at 10")

i ran this just fine when it was 110* out, second week in october it started...

and your vacuum rod part isn't true. depending on the year and app there are about 6 or 7 different cans. all with different total timing and adv rates
 
I am running straight pipes from my headers, so I should check the vacuum and back it off from 8.5 and see if the stutter leaves? This is on a 73' vacuum can, if that matters.
 
The fuel change will cause performance change. I run my cars 16 int. 36 total anything more is for economy on a cruise. I figure if I want performance I will have to sacrifice the economy. My orange duster is locked at 35 . It has a retard built in for start up. I shift it at 8000-8500 its sounds as smooth as a well tuned two stroke. The more total you put in a motor the quicker it takes out the rod bearings. Remember The more advance you have the sooner it fires before the piston reaches the top. Causing it to try and reverse the motor. The ping you hear is piston wobble. It will hurt the motor if its missing a high rpms. Cheap fuel burns hotter so it ignites faster and causes pre-ignition. Meaning its firing way before it reaches the top. The slower it burns the more advance you can have. The faster it burns the less advance you can have. Its not when it sparks. its when it ignites.
 
Oldmanmopar said:
The fuel change will cause performance change. I run my cars 16 int. 36 total anything more is for economy on a cruise. I figure if I want performance I will have to sacrifice the economy. My orange duster is locked at 35 . It has a retard built in for start up. I shift it at 8000-8500 its sounds as smooth as a well tuned two stroke. The more total you put in a motor the quicker it takes out the rod bearings. Remember The more advance you have the sooner it fires before the piston reaches the top. Causing it to try and reverse the motor. The ping you hear is piston wobble. It will hurt the motor if its missing a high rpms. Cheap fuel burns hotter so it ignites faster and causes pre-ignition. Meaning its firing way before it reaches the top. The slower it burns the more advance you can have. The faster it burns the less advance you can have. Its not when it sparks. its when it ignites.
Click to expand...

So I should bring down the total timing a bit ? For cruising ?
 
Oldmanmopar said:
The fuel change will cause performance change. I run my cars 16 int. 36 total anything more is for economy on a cruise.

I figured thats what we were talking about.

I figure if I want performance I will have to sacrifice the economy. My orange duster is locked at 35 . It has a retard built in for start up. I shift it at 8000-8500 its sounds as smooth as a well tuned two stroke.

To a certain point. you could put a little vac advance in for your high vacuum situations and get better econ, of course to much and you'll have our current issue or as you described bearing issues.

The more total you put in a motor the quicker it takes out the rod bearings. Remember The more advance you have the sooner it fires before the piston reaches the top. Causing it to try and reverse the motor. The ping you hear is piston wobble. It will hurt the motor if its missing a high rpms. Cheap fuel burns hotter so it ignites faster and causes pre-ignition. Meaning its firing way before it reaches the top. The slower it burns the more advance you can have. The faster it burns the less advance you can have. Its not when it sparks. its when it ignites.
Click to expand...

Yes your right about advance and igntion, but you have to think about bore sizes, quench pads, and all the other variables. Also again your going to the extreme, under light loads/high vacuum situations you can add more timing and gain econ with no draw backs. When you throttle in that timing goes away and your back into the "safe zone" on timing.

dustya_383 said:
So I should bring down the total timing a bit ? For cruising ?
Click to expand...

depends what your curve right now? what is the number on the vacuum advance canister? at what vacuum is the can coming in at?
 
805moparkid said:
Yes your right about advance and igntion, but you have to think about bore sizes, quench pads, and all the other variables. Also again your going to the extreme, under light loads/high vacuum situations you can add more timing and gain econ with no draw backs. When you throttle in that timing goes away and your back into the "safe zone" on timing.



depends what your curve right now? what is the number on the vacuum advance canister? at what vacuum is the can coming in at?
Click to expand...

He has no curve.... He's locked out with msd at 35. No canister.
 
Back it down to 32 and see if that makes a difference.im still not liking locked out timing on a street car though....
 
bad440 said:
Back it down to 32 and see if that makes a difference.im still not liking locked out timing on a street car though....
Click to expand...

if its what it likes its what it likes. my slant like 30 locked, so i just have it all in at 500 rpm, soon as it kicks it full advance.
 
This all started happening when I filled up last .. It has to be the fuel mixed with weather this week it's been the coldest it's been in a long time ... I'm hoping I didn't accidentally put 87 octane instead if 91 .. I'm gonna try backing total timing down a bit and see what happens .. Maybe throw some 100 octane in there
 
dustya_383 said:
This all started happening when I filled up last .. It has to be the fuel mixed with weather this week it's been the coldest it's been in a long time ... I'm hoping I didn't accidentally put 87 octane instead if 91 .. I'm gonna try backing total timing down a bit and see what happens .. Maybe throw some 100 octane in there
Click to expand...

if you could just put a little in there and get the octane up to at least 96 see what it does, that would help us both out as far as if its octane or lean, or both. if its octane im going to be rasing some hell at the gas station!
 
dustya_383 said:
This all started happening when I filled up last .. It has to be the fuel mixed with weather this week it's been the coldest it's been in a long time ... I'm hoping I didn't accidentally put 87 octane instead if 91 .. I'm gonna try backing total timing down a bit and see what happens .. Maybe throw some 100 octane in there
Click to expand...

Pump the old gas out and use it in your wife's car. Fill it up with fresh pump premium. My 410 is 23* initial, 34* all in at 2200 rpm. 9:1 compression. 91 pump premium. 850 DP, No hesitation or miss, does not miss a beat temp runs at 170* no matter how I thrash on it. 904 RMVB with a continental converter about 4000 Stall. RHS heads from IMM & Small Solid Roller. 242@50 634 lift..
 
Curious if this is happening right away or after you been driving a bit? What fuel pump are you using and does it have a return? Reason I ask is you could be heating up the fuel?
 
"Not sure if this is a misfire but when cruising on freeway roughly 60-70 mph 2700 rpm I feel a slight hesitation not major just enough to annoy me where should I look first??"


Are you saying that the engine misfires when you're cruising at a constant speed and when you start to accelerate you get a slight hesitation. Or are you saying that the car is misfiring as you cruise at a constant speed. I ask because my car would hesitate (when I would try and accelerate) when I was cruising at a constant speed. Once I got past the hesitation it ran great.
Turned out it was running lean, had to change the metering rods (Edelbrock) until the hesitation went away. In your case it would be the power valve (Holley) I believe.

But I guess it could also be the gas blend or octane?? Do they sell octane booster, that would be an easy trouble shooting method without having to drain the gas.

Treblig
 
Mad Dart said:
Curious if this is happening right away or after you been driving a bit? What fuel pump are you using and does it have a return? Reason I ask is you could be heating up the fuel?
Click to expand...

This happens right off the bat ... I'm running a holley mechanical fuel pump.. It does have the original fuel lines so the return is still there..
 
Treblig said:
"Not sure if this is a misfire but when cruising on freeway roughly 60-70 mph 2700 rpm I feel a slight hesitation not major just enough to annoy me where should I look first??"


Are you saying that the engine misfires when you're cruising at a constant speed and when you start to accelerate you get a slight hesitation. Or are you saying that the car is misfiring as you cruise at a constant speed. I ask because my car would hesitate (when I would try and accelerate) when I was cruising at a constant speed. Once I got past the hesitation it ran great.
Turned out it was running lean, had to change the metering rods (Edelbrock) until the hesitation went away. In your case it would be the power valve (Holley) I believe.

But I guess it could also be the gas blend or octane?? Do they sell octane booster, that would be an easy trouble shooting method without having to drain the gas.

Treblig
Click to expand...

There is no hesitation upon acceleration .only when cruising ant constant speed. Unless I'm in 3rd or 4th gear it will kind of hesitate cause it's at a lower rpm but if I down shift and get rpms back up it'll pull like a frieght train .. I've changed power valves before forget which ones I put in Ithink it was a bigger valve... They sell octane boosters here I will try that first... See what happens
 
If your float levels are a bit low, it changes the Sg of the fluid in the bowl, because there is less of it on top of the jet and can cause a lean condition.

The reason you aren't experiencing this when you stomp on it from idle, is because your fuel level is higher and you have accelerator pump.

I'm wondering if you aren't running enough fuel into the bowls under cruising conditions.

Big lines would help, but what is your fuel pressure at right now? Can you monitor your pressure under cruising?
 
If it's happening under light throttle with heavy load/ 3/4 gear, it could also be too much advance. The engine is already fighting your rear tires under that condition, so if you've got more advance, like the old man says, you've got a situation where everything starts to try and slow the crank down on both ends, from the tires/ gear its in with leverage against crank and from the piston coming back on itself a little.

Back it off about two degrees and see what happens. If it still messes with you, start looking at fuel pressure and fuel levels in the carb.
 
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