Help, I'm stumped!

[snakebittexan]

I have a strange intermittent problem that I’ll do my best to describe by recounting the last several occurrences;

Engine, Keith Craft 408, QuikFuel carb, manual fuel pump

Sunday (yesterday) she was running good, stopped and sat for fifteen minutes, started easily, went two hundred feet in first, changed into second and died, one and a half pumps restarted, smoothed out and ran ok.

Sunday running good, stopped for fifteen minutes, normal start, while pulling out after 50 feet it cut out like it's out of gas, stopped one and a half pumps, restart spitting, sputtering, smoothed out then ran normally.

Saturday afternoon, running good, kicked it in second, same sputter, pop, died, pop clutch restarts, never in all these occurrences do I smell fuel.

Last weekend while at our Cobra rally in San Marcos a number of us got some bad gas and the problem was even worse, popping, missing, usually at higher RPM. She would die, leave it in gear to restart.The sooner I could get it into the higher gears the sooner she smoothed out. Sometimes while pulling back up a hill after a sharp curve adn lower speeds whe would spit, stutter, adn die, I would kick it down into a lower gear or leave it and she would restart and run just fine.

While in San Marcos and driving the hill Country I could kick it in third or fourth and she would start spitting and sputtering sometimes completely shutting down. NOTE, Saturday in San Marcos was hot, high 80’s—90. Coming home Sunday it was cold and damp, she performed perfectly all the way home (200 plus miles). Yesterday and Saturday were hot and problem pops up again. On one occasion after stopping for lunch she would start, die, start, die and after the last restart smelled flooded but that was the one time I could smell fuel.She usually starts easily, idles good and only the one time have I smelled fuel.

I tracked at Harris Hill Friday on "Dallas" fuel and she ran great.

I have a new coil and MSD box. After our Saturday cruise in San Marcos we cleaned the float bowls, front fuel filter and replaced the rear filter.

Any ideas?

[Tom Wells]

snakebittexan,

Sounds like percolation or vapor lock. This happens when the fuel gets too warm and boils, which can happen at 140*F temp or even slightly below. Today's gasoline is cr*p.

The result is that one or both floats sink (frothy gas is not as dense as the liquid) and the carb pukes through its vents into the intake.

If it's severe the engine will flood and die.

The cause of the high fluid temp can be discovered by detective work. A gas line near a header somewhere, heat climbing into the carb from the intake manifold or any of several other places.

Take a look at your gasoline path from the tank to the carb and see if anything looks like it may be causing this.

If it's not the line, then a phenolic spacer and an aluminum heat shield both under the carb may help.

You need to do some looking and report what you find.

I'm fighting this on a hot rod here: http://www.firstcoastcobraclub.com/v....php?f=8&t=743

Being an extremist , I've opted to replace the whole system tank to reg, add a return line and relocate the reg too.

I doubt you'll need to go anywhere near that far!

Tom

[Voyager]

snakebittexan,

Not sure it’s related to your issue…

I have the same setup. Mine doesn’t like restarting when hot. Doesn’t want to run clean down low until I can “clear out the junk”. I assume the fuel is not too happy sitting in the hot carb during the shutdown period and until I can pull in some fresh fuel, it sputters, stalls, etc. In town, it usually takes a mile or two to clear out. Doesn’t bother me. Figure that’s the nature of the beast.

Bob

[G_Edmonds]

New needle and seats will probably solve your problem. The Viton N&S doesn't handle alcohol well. They end up sticking and flooding the carb.
-Greg

[snakebittexan]

Good ideas all. I have almost 7000 miles on her and I've have driven in 100++ heat here in Dallas with no heat issues.I totally understand "cleaning out the junk" that's exactly what happens after one of these episodes but again why now and not over the past years and miles? I've had same set up over the last three thousand miles. What would be a good alternative to the Viton N&S?

[G_Edmonds]

With the gas you get at home, Viton N&S should be fine. You could go to stainless steel N&S which are for alcohol but will work fine with gas.
-Greg

[vector1]

still burning winter fuel blend in warmer weather?

[jwoodard]

My guess is it's the fuel. Probably winter gas from recent fill up.

[snakebittexan]

"My guess is it's the fuel. Probably winter gas from recent fill up.
__________________
Jim Woodard"

Step one change plugs out, step two double check heat sources relative to fuel lines, step three go crusing.

I'll be back with update soon, thanks everyone.

[Joe Wicked]

I had a similar problem with an old Trans AM I had years ago. Turned out to be a clogged fuel filter, but even after changing it, it helped but didn't go away completely. Turns out that the pump was having to work a lot harder to get past the clogged filter and it was beginning to fail. It would only happen when it was over 80° outside. If the other ideas don't work, it at least gives you something else to check.

[madmaxx]

is it possible your floats are 2 high

[snakebittexan]

I'll double check, thanks!

[wideglidejoe]

I've been making gasoline for over 33 yrs, so I'll take a couple of guesses......

first, someone commented that our gasoline is crap, and I'll agree, but its not because we want to make it that way, our federal gov't requires it. Don't you just love the feds? I would love to blend with more toluene, TEL, etc., like the good ole days.

OK, first thing, if it was warmer than usual (for this time of year) in San Marcos, the refiners (in San Antonio) are still blending to spring RVP (Reid Vapor Psig), which means there are more "light ends" (butanes,etc) blended into gasoline for cool weather starting, warm-up, etc. Regardless of what part of the country you are in, if you have warmer than normal seasonal weather, any carb'ed vehicle is going to be more prone to vapor lock. Mechanical fuel pumps only pressurize gasoline to 6-7 psig, EFI systems run at much higher psig's, keeping the fuel in liquid state instead of vapor.

Add methanol to the mix, and it is much, much worse. Methanol will boil off at much lower temps, and carb'ed vehicles will suffer. Not to mention all of the other issues with methanol!!

Your vehicle may be fine in July in Dallas, but July gasoline RVP is 9.0#'s (or 7.8#'s, or even 6.8#'s if you are in an EPA high profile area), you are burning gasoline blended with July temps in mind. Mar/Apr RVP gasoline may be 11.5 or 13.5 RVP in your area, so if you get a 90+ degree day, you'll get vapor lock.

I hope I explained this well enough to make sense. Just drive out the high RVP/methanol blend, and you'll probably be OK. Obviously, it won't hurt to check out everything else that has been suggested.

Good luck!

[bobcowan]

I had a similar problem with a previous carbed car. All of a sudden it started to run bad. It ran, but not nearly like it did 10 minutes before.

Most diagnosticians will tell you that a carb is a very simple device. EWven when it has a lot of neglected years and miles, the carb will still continue to perform reasonably well. If the engine suddenly changes, it's probably not the carb. Look at fuel delivery and ign ition first.

So, that's what I did. Checked fuel prssure and flow. Took the ignition apart, inspected everything, replaced a few things. Bypassed the CD ignition box. Did everyt hing I could think.

Finally, I said, "OK, time to look at the carb". I pulled the front bowl off, and found a small chunk of FOD stuck in one of the primary jets. No idea what it was, or how it got past the filter. Maybe it was stuck in the bowl out of the box? Anyway, removed that, put the bowl back on, and it ran like a champ. Problem solved.

[WardL]

Wideglidejoe, you are right on with your comments, but you don't really mean Methanol. Don't you mean Ethanol? Good old Corn Ethanol? Sorry to be nit picky.....

[scott cooper]

i had the same problem san marcos gas melted my fuel filter and melted my fuel lines replaced everything perfect fix in my case i figure bad mixture of toluene buy who knows

[Wbulk]

Just buy gas from stations that don't mix it.

http://pure-gas.org/

[G_Edmonds]

This site is good but has to be updated by users. I know that there aren't any stations in my area that sell unmixed gas unfortunately.
- Greg
Wish there was.

[wideglidejoe]

WardL,

Yes, I meant ethanol...............thanks for the catch!

I avoid it like the plague. Not because I work for a refinery either. Even if I didn't work in a refinery or make/blend gasoline, I don't like the stuff! It's OK if you run it 100% pure, and have all of your equipment set up to handle it, but I don't like it mixed. Even in a stock daily driver w/EFI, your mileage suffers when running 10% ethanol. So much, that I'll gladly pay up to 15 or 20 cents per gal for 100% gasoline.

Then, from the economic and political side, it just isn't sustainable! There's not enough land to grow enough corn to make this sustainable. Corn to ethanol has driven the farmers to substitue other grains to feed their livestock, which drove up the price of those grains too. Corn to ethanol has taken food off of our table, and driven food prices up. Just look at how many of our foods have high fructose corn syrup in them. If/when they can make ethanol from switch grass or algae or ??, then maybe it is sustainable and it might make economic sense.

OK, I'll get off my soap box now, on the economics and politics. Thanks for letting me vent.

Any kind of alcohol, methanol, ethanol is a "cleaner". If you normally buy 100% gasoline, then you buy a tank or two of 10% ethanol blend, it will clean your gas tank, fuel lines, etc. and foul your fuel filter. So, be prepared to change them too.

[lnfletcher]

Originally Posted by G_Edmonds

This site is good but has to be updated by users. I know that there aren't any stations in my area that sell unmixed gas unfortunately.
- Greg
Wish there was.

I use an additive if there is not any pure gas around.