new motor.... need help....

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11-15-2003, 12:20 PM
GlennL

new motor.... need help....

I just finished replacing my 350 with the new Vortec 350 (330 hp) Everything went well I thought. The new motor is missing a beat, sounds like a popping from exhaust. Timing is about 12 degrees ahead,new high rise intake,750 TBI. The truck is a 93 GMC Z-71.. After market chip to match motor. EGR is all hooked up,replaced mod in dist.,replaced fuel filter,performance chip and its fastttttt BUT if I just touch the gas a little there is a big hesatation but if I nail it to the floor, the hesatation is there but only for a fraction of a second. ohhhhh yeaaaaa I had the intake bored out to match the 750TBI. Im running out of ideas. (and money) I also have it about 10 degrees ahead on timing. Seems to be the best there. Any more ideas? Thanks !

Oh Yeaaaaa What should the spark plug gap be? Remember its 330 hp crate engine.
Any Ideas ?????? The first 1/2 inch is when it seems to bog down. after that,its smooth sailing from then on. It also seems to burning alot of gas. (going by the gauge) No smoke or bad fumes though. Thanks !
11-15-2003, 12:39 PM
RSpurlock

Just a guess, try leaning out your idle mixture.
11-15-2003, 07:41 PM
len

it could be your fuel pump or screen pluged not delivering the right fuel pressure.or one of your injectors.or your coil is getting bad.or that high rise intake.
11-19-2003, 09:54 PM
CD667

and it could be your timing is a tooth off on the cam

Cd
11-20-2003, 09:19 PM
4speedTerror

I just got done with this same problem

i just tackeled this prob with my 454.....but mine turned out to be a bad valve guide......but the main problem was timing....bad gas mileage?.....hesitaion?....but higher RPM's she is all there right?....
but what kind of ignition are you running?
vaccum advance dist.?, coil,?.....MSD?

pull the plugs and see if there are signs of detonation (small black spots on porcelain)

and if they are fouled that is fairly obvious

but i had my initial set to 10....and i thought that was to advanced.....so i went to 12 and it cleaned up right away.....

check the timing advance as well....i had a bad diaphram and that would make the car run really crappy off idol.

you have already thought of all this.....but it got be back running.....hopefully it can help you
11-20-2003, 11:42 PM
76GMC1500

You said you had this problem when you nailed the pedal to the floor? Maybe you shouldn't nail the pedal to the floor. This is a big problem on 4 stroke motorcycles and is only magnified by the single cylinder, small intake, and lack of accelerator pump. It's usually refered to as the 4 stroke hiccup. The only way to prevent the hesitation is to roll on the throttle instead of rip it wide open from idle. The hesitation is caused by a momentary loss of vacuum in the intake because you allow more air to enter the intake, but the cylinder is still drawing the same volume. The speed of air moving across the jets slows considerably, and fuel can't be drawn into the incoming air as efficiently. Most car carburetors and some newer dirtbike carbs have accelerator pumps which inject fuel into the incoming air during this low vacuum period. Dirtbikes also have a pilot circuit to help the carburetor move from the idle to the main cicuit and you have to tune and tune and tune to get it perfect. Even slight changes in weather can throw it off. In conclusion, it sounds like you're hitting a lean spot coming off idle. Or, your TBI setup is too large for the engine and the engine cannot maintain vacuum while the butterflies open.
12-21-2003, 08:11 PM
Need4Speed

Re: new motor.... need help....

hey bro..i think i have had this problem befor, i believe that the spark plugs wires aren't in the right order..try to re orgnize them and start it.. it will work fine with god's help.

Quote:

Originally posted by GlennL
I just finished replacing my 350 with the new Vortec 350 (330 hp) Everything went well I thought. The new motor is missing a beat, sounds like a popping from exhaust. Timing is about 12 degrees ahead,new high rise intake,750 TBI. The truck is a 93 GMC Z-71.. After market chip to match motor. EGR is all hooked up,replaced mod in dist.,replaced fuel filter,performance chip and its fastttttt BUT if I just touch the gas a little there is a big hesatation but if I nail it to the floor, the hesatation is there but only for a fraction of a second. ohhhhh yeaaaaa I had the intake bored out to match the 750TBI. Im running out of ideas. (and money) I also have it about 10 degrees ahead on timing. Seems to be the best there. Any more ideas? Thanks !

Oh Yeaaaaa What should the spark plug gap be? Remember its 330 hp crate engine.
Any Ideas ?????? The first 1/2 inch is when it seems to bog down. after that,its smooth sailing from then on. It also seems to burning alot of gas. (going by the gauge) No smoke or bad fumes though. Thanks !