fuel pressure question

[jakepup]

hey guys, few questions.
I have a 871 blower on a 440 with 2 quickfuel 750 blower carbs running on e85, the car seemed to run fine early this spring and now for some reason she sputters and shakes a quite a bit when your first take off from a stop light and once you get up and going it seems to even out and run just fine. the only thing that has changed is the following, I changed plugs and opened up the gap a little bit, they were at .018 and I went to about .028, and the fuel has went from e73 to e77 which should mean its a little leaner than when it was on e73, the engine was tuned on e85 but we just don't have it at the pumps yet. could the spark plug gap be causing this or did something maby wear in on the carb side that needs to be adjusted? I have an a/f gauge and it doesn't look like that has changed much and should only run better with higher ethanol content, so Im leaning more towards something with the plugs or timming or carbs? forgot to add, fuel pressure is adjusted at the regulator so the gauge reads 5psi, when you hammer on it the gauge shoots up to 8-9psi so fuel delivery is not the issue

 

[67 coronet]

if it sat for any amount of time i would check your accel pumps to make sure they are giving an immediate squirt and not slow responding.gap should not effect it that much.normally just a minor horse power change with gap mods.

 

[Budnicks]

Is the fuel old in the car ?

newer fuels especially with ethanol
"Usually" only have maybe a shelf life of 3 months,
is there a bunch of moisture in it ?

I'd thing just the plug gap should change it that much,
unless your ignition spark is weak as hell...

IMO 8-9 PSI is too much for the needles & seats,
7-7.5 PSI max usually "operating/flowing rate"
even on the best types of "Vinton" needle seats in a Holley style carb
unless;
maybe that the flow rate is before it hits the carb,
on the inlet side of a reg. dead headed, then using a bypass regulator
& some fuel bypasses/flows back to the tank...

 

[jakepup]

it is brand new fuel that I have filled up about 4 days ago, it was doing this before I filled up to so im pretty sure its not a bad fuel issue, its had 10 new gallons through it that haven't changed anything.
I spoke with the guy who built the e85 carbs and he explained that at 14psi "im only running 8psi" that the spark gap actually "doubles" on a boosted engine , so a plug gap of .020 becomes .040 at 14psi so my gap is probably .035 or better actually but like you said I don't think that would make it really fall on its face, and I only does it under a load so that adds a bit of question to it.
well I have the aeromotive a1000/aeromotive regulator combo, not sure how the return works. the gauge is plugged right into the side of the regulator so im not sure where its actually measuring the pressure. so your saying I should adjust my fuel pressure so its about 2-3 psi at idle and shoots up to 7psi when I get on it?

tonight I will go home and put my old plugs back in to verify that the gap is not the issue. I guess a guy needs to start double checking timing and carbs if that doesn't change anything hugh?

 

[hangn0ut]

Something funny here. Pressure normally drops under hard acceleration with a rear mounted electric fuel pump. And viton tipped needles dont play well with alcohol based fuels. Steel needle and seat like holley sells should be used. And a small gap is needed as a denser charge is harder for a spark to jump. Your spark will find another path to ground. More boost needs less gap or an ignition that keeps the spark contained better.

 

[hangn0ut]

I think your old plugs will solve your problem. But that doesnt mean those other issues should be forgotten....

 

[cdr]

spray carb cleaner through all the air bleeds.

 

[jakepup]

okay,, so I got ahold of a very nice gentleman at aeromotive last night and he told me that I should see if there is a vacuum line attached to the regulator which there was, he said to remove it and plug the line and just let the regulator suck from atmosphere, removed the line and pressure shot up to 9psi at idle, turned the screw out about 15 turns "a lot" and now I have a steady pressure of 6psi at idle and under hard acceleration it drops to maby 4psi, no jumping up like before so that problem is solved!!! as far as the carbs they were built buy a guy "e85carbs.com" specificly for alcohol so i'm guessing/hoping he has the correct needles in there?? I never got a chance to do the plugs but I will this weekend and report back if that solved the stumbling issue but like stated before im a bit leary because I could notice it before I swapped plugs, anyways thanks guys and ill let ya know

 

[hangn0ut]

So,was the stumble still there after you adjusted the fuel pressure? Not as bad as before? Did you reset the floats? Keep an eye on those needle and seats as they will need changing if they are viton. And as you run higher boost, less gap. Pro-mods run around .012 gap and their mags can arc weld!

 

[jakepup]

ya know, i sure think it runs a little better but the stumble is still there for sure, i will do the plugs this weekend and set the gap at .020 or so and see what happens then, it really feels/sounds to me that it may be something in the carbs but i guess i will start with the plugs and see what happens. i will also try and pull the scoop off and check everything there and spray some cleaner through the bleeeds. havent touched the floats or anything yet

 

[Budnicks]

Maybe some
Contaminants, corrosion, left from condensation or debris left in passages
from the using Ethanol in the fuel, "if it dries out at all, it will leave a residue",
in the tank, lines, fittings, squirters, accel. pumps, carb bowls, any & all of the
little passages {especially on/in alum., but can/will do damage to steel too}

earlier post; your question, I was referring to free flowing pressure
or "while running"
{or take the fittings off the carburetor & put a line into a bucket & make sure it's flowing pressure "not dead headed pressure", especially if your not using a "By-Pass style fuel regulator system, that allows the unused fuel to flow back to the pump or back to the tank}
should be about 7-7.5 psi flowing max
or it will overcome the needles & seats

 

[Budnicks]

Just spit-balling here;
Does your ignition pull out timing as boost comes in ?
I hope so or don't run as much initial timing...

it could be a form of detonation,
weak or spark distortion, {bad coil?} especially when boost it up
air or fuel distribution too, a bunch of variables...

more spit-balling
have you read the plugs ? {what heat range are the plugs ?}
what do you see ?
you need to know what to look for ?

IMO to much ignition at wide open throttle it will fall off,
it'll run better if you pull out timing at the big end...

a bunch of timing off the line won't hurt as much,
but will kill MPH/HP & possibly detonate
{&/or lean out, neither is ideal with boost}
on the big end, wide open throttle...

good luck

 

[jakepup]

yes i pulled the plugs and they look good, they are not perfect "a little rich" but not fouling or anything, I will try and snap a pic of em and put em on here, I believe they are 10's for the heat range, it does pull timming, its a 6btm with msd coil as well, not sure what initial timing is set at. the knob is set to pull 1.5 out per lb of boost, I know the engine builder said he was going really conservative on the timming so im wondering if it could be the combination of rich mixture due to only e76 now vs e85 when dynod and that? I did swap plugs back to the .020 gap and it doesn't seem much different if any. I did not pull the blower hat off to look down the carbs so I will work on doing that this week.

 

[Bigal75]

Why are you pulling timing with e85? What compression/boost?

Yes plug gap can cause these issues. Also you may want to clean out your carbs and blow out the passages in the metering blocks.

 

[jakepup]

Why are you pulling timing with e85? What compression/boost?

Yes plug gap can cause these issues. Also you may want to clean out your carbs and blow out the passages in the metering blocks.

I will have to check with the engine guy on what the initial timming is set at, or go get a timming light, its 9.3:1 static compression making 8.2psi of boost. should a person not be puling timming?

 

[jakepup]

I have a car sow this weekend and maby after that I will tear into the carbs and make sure everything is cleaned and good to go, im sure there was a little $hit going thorugh them the first 800 miles of the car getting drivin from assembly