350 engine WOT loses power at top end

[ProStreet83C10]

Hey guys, i noticed this spring after i stored my c10 all winter that when i go WOT and get to the top end of 2nd gear my engine just falls off on power, almost like something has cut fuel or ignition. as son is i get out of the throttle it comes back and i havent kept my foot in it to see if it comes back or not.

what do you guys think the cause of this could be? under normal driving/throttle conditions the truck runs 100% fine and this only happens what at or very close to WOT.

[Dieselholic92]

Not enough fuel at the top of the rpm range? Hard to tell, can you give us some more details about the engine?

[bigwheel15]

Sounds like its not getting enough fuel or needs better spark. I'd like to hear a few more details on your setup as well.
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[ProStreet83C10]

350 block
305 heads
"3/4 race" cam
600cfm Q-jet carb
HEI ignition
700R4 trans (built)

anything else let me know what you need to know

[Firebirdjones]

Type of fuel delivery system would help narrow it down for me but when you listed Q-jet carb that set an alarm off

Q-jets have a very tiny float bowl, and they are notorious for running the bowl dry on long heavy pulls in high gear. May not notice it in 1st, but 2nd or 3rd it will show up.

Best way to diagnose is to install a temporary fuel pressure gauge (4 foot hose and duct taped to the windshield) and go out and duplicate the symptoms. I'm betting just before the truck falls on it's face you'll see that fuel pressure drop to 2-3 lbs, that's not enough to keep the float bowl full.


Q-jets only like 4-5 lbs. of fuel pressure maximum. That usually keeps the float bowl full in most cases with the stock pump. Could be that your fuel pump is a little on the weak side. Fuel pressure gauge would tell the tale.

[cory d]

sounds like a gummed up main jet to me

[gramps]

Had the same issue on my camaro. Orig motor ran fine, put the same qjet on new motor and it did the same thing you describe, fell on its face top of 2nd gear. The new motor was Suckin the bowls dry, the fuel pump couldn't keep up. Replaced the factory 23gph rated pump with one for a 'vette rated at 51gph and it issue solved.

In your case though, if you haven't changed the engines fuel requirements, I'd do as suggested and maybe do a cleanin/overhaul on you carb.
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[frog210]

This just happened to me yesterday
as long as i was going under 30 it was fine,
but when i went over 30 it was loosing power
its a qjet too
i took it to go get rebuilt
When i would press on the gas it would be fine
when i went over there it would loose power and like choke
and it sounded like air escaping when i would press on the gas when it was choking?

[ProStreet83C10]

ok so maybe i should run some fuel system cleaner through it (can of sea foam) and do a tune up on it as well ya spose?

[frog210]

I ran some seafoam
Replaced my fuel pump and filters
And it fixed the issue
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[ProStreet83C10]

filters? the ONLY filter i know of on my truck is the filter on the front of the carb. is there an additional filter somewhere along the frame im unaware of?

if so its NEVER been replaced in the 10 yrs+ the trucks been running

[Firebirdjones]

From the factory there will only be one filter, in the carb.

Now that doesn't mean that someone along the way hasn't installed one somewhere else. Not only is it overkill and not necessary, it makes the fuel pump work harder and in some cases causes a fuel starvation problem at high rpm or under heavy load because the extra filter cuts down the fuel volume and the float bowl goes dry.

I've had this scenario on a couple vehicles. My wifes 71 454 vette (found an extra fuel filter hidden on the frame) and my 79 1 ton 454 had another fuel filter installed right after the solenoid for the dual tanks. Both had fuel starvation issues (fuel pressure would drop like a rock under full throttle) until I found and removed those extra filters.

Keep in mind there is already a "sock" in the gas tank for the fuel line pickup that acts as a very fine filter, and does a good job. There is no need to install another filter in that same line before the pump,,,and then another filter in the carb....if you want to run an inline filter,,,remove the carb filter.

[ProStreet83C10]

well ive never had this problem until now, and this motor has been together for over 10 yrs. so i doubt theres an addtl filter under the truck that ive missed BUT i also havent really looked for just a filter under there.

[ProStreet83C10]

so i went on a car cruise yesterday and on th e way back into town i dropped it down to 1st and held it out through 1, 2 and half of 3 manually shifting up and i had NO power loss at top end of any gear....i filled with 89 octane (E10 ethanol) before the cruise as my normal station was across town and i normally fill with 91+ premium octane which this station didnt have. Do you guys spose that added alcohol cleaned out my carb or whatever the issue was and fixed my power loss problem i had (clogged jet etc?) OR do you guys think it was just coincidence that it didnt fall on its face on the top end of the gears

[74 shortbed 406]

You may have been lucky and had a little dirt or emething clog a jet and get blown out on the second go around. I would definately check fuel pressure, and if i remember correctly there's a screen on the inlet of the carb, it can get corroded and clogged as well.

[motornut]

may want to check all the metal tubes sticking out of the carb
the ones the hoses go onto...
tap them in a little,make sure they are all seated tight
solves some bogs,vac leaks

[ProStreet83C10]

Well, after all this time, it ran fine BUT today i went to a car show and scored a top 50 award. Came home and truck was BADLY missing on the top end of 2nd gear (completely losing power when 3/4 throttle or more was applied, letting back out of it to have it coughing, farting, hiccuping etc) so i went to my Oreillys and picked up some tune up parts......pics of parts to follow, first of all, heres some pics of old plugs (been in truck 10-12 yrs, 25k miles on them) plug wires were horrible, looked like burnt insulation etc on them


Out with the old












In with the new






















Mind you, the plug wires were a cut n make your own kit.....never done that before, complete mess and confusion, BUT i got them done and they work. Fuel system cleaner is to hopefully help with that loss of power issue, if its not the filter, hopefully its not a weak pump, if so, their cheap! Cap, rotor and coil are all self explanatory as well as fuel filter. Took about 3-4 hrs till it was all done, longest part of it was fighting those dang plug wires!

[Firebirdjones]

Originally Posted by ProStreet83C10

Fuel system cleaner is to hopefully help with that loss of power issue, if its not the filter, hopefully its not a weak pump, if so, their cheap! Cap, rotor and coil are all self explanatory as well as fuel filter. Took about 3-4 hrs till it was all done, longest part of it was fighting those dang plug wires!

A quick road test with a fuel pressure gauge taped to the window will answer that question for you pretty quickly, then you'll know precisely if it's fuel related or not

[ProStreet83C10]

well i took it out tonight, and it didnt act up. that being said, still not sure if it solved the prob. or not as it didnt do it for 2-3 mos then came back.

Anyway, you spose there will be any performance gains noticed with the new coil and plug wires?

[motornut]

Originally Posted by ProStreet83C10

well i took it out tonight, and it didnt act up. that being said, still not sure if it solved the prob. or not as it didnt do it for 2-3 mos then came back.

Anyway, you spose there will be any performance gains noticed with the new coil and plug wires?

sure i've always noticed an inprovement after a tune up
hows your sending unit? fuel line?

[INSIDIOUS '86]

You may have gained a few hp down low and some mpg
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[INSIDIOUS '86]

I think your q-jet might be suspect. I remember playing with the rods on mine and it did something similar. It was to rich up top and was "two stroking" basicly i couldnt get any more rpm.
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[NorthwestGrudgeRacer]

If you can get a fuel readin at wot and a pic of the plugs after a wot run. this will tell us more to whats happen.

[mMad Dawg]

Pro Street. You said something that sent up a possible red flag for me. You said the truck ran better when you filled up at a different station. Got me to thinking that maybe you regular station might have some water in their tanks. If it does it again after you fill there again try some gas line antifreeze(methyl hydrate) I there is water in your tank it will help your motor burn it off. OLD SCHOOL Gord

[ProStreet83C10]

its doing this mid tank though, its doesnt do it constantly through a tank of fuel, it just did it randomely when it wanted to