Flat Spot

[lil_mickey]

I have a pretty bad flat spot in a vh 253 blue motor.

All I want to know is what i should start looking at in the morning...

the flat spot is from around 1500 - 3000 RPM

As far as i know it is a standard 4brl carb.

Also if anyone has the diagram for the vacuum hoses on a VH V8 that would be great,

I would like to have this fixed tomorrow (today)

[vkberlina]

I have VK v8 ones on my site which are close

[lil_mickey]

Hey thanks man,
Just Bookmarked you site

[v8commy]

as far as i know 253's had a 2brl carby

[lil_mickey]

Not the Blue 253's, I thought the same thing before any research

[vk.jonno]

i dont know much about mechanical problems.. like i know about engines and stuff but whats a flat spot
sorry about the noooooooobbbb question :P

[lil_mickey]

i dont know much about mechanical problems.. like i know about engines and stuff but whats a flat spot
sorry about the noooooooobbbb question :P

Its like a "dead" spot on accelaration, when i was taking off the motor got to 1500 revs then just died and sputtered for a bit, then out of nowhere It just takes off like a rocket,

can be caused by timeing being to far retard,

Worn shaft in throttle housing/throttle plate,

Vacuum leak,

Or incorrect mixture from a faulty o2 sensor

Mine turned out to be a vacuum leak inside the carby, I put a kit through it and hooked up the necessary hoses redone the timing and it has been fine since...

[vsl67]

Is your vacuum advance on the dizzy working ? and what sort of carby are you running Rochester or Holley? & is it set up right ? if you give it a boot full and it bogs down its getting to much fuel & if you get a flat spot/pause its not getting enough ,this can be fixed by playing around with different quirters and pump cams on the holley but the Rochester is a bit harder to adjust and also getting the parts for it can be a pain aswell ,I just want to point out this problem has nothing to do with jets like most people seem to think before its suggested

[lil_mickey]

I haven't checked it yet but at the moment the car was running fine, I took it to NSW over the weekend and averaged 13 liters to 100Km without any flat spot.

The Vacuum Advance is hooked up but i don't think its working

[ari666]

if its a quaddy, well, then theres your answer on the secondary butterfly flap at the top of the carb is an adjusting screw. a real prick to get to and the culprit for flat spottting on quaddy's which is really common.

basically on the drivers side of the carb at the back there is an alley key which is hidden away under everything and an adjusting screw. you need to hold that screw and undo the allen key, turn the screw 1/8th of a turn clockwise then tighten up the allen key. if you let go of the screw the spring behind it will unravel then ya gotta start from scratch.

take it for a drive and see if it flat spots. if it does, pull over and repeat till it goes away.

f this, im getting some pics

this is the side of a quaddy if you look through the throttle flap linkage there is a screw


then the locking allen key us underneath. you ant see it when the carb is fitted, you just have to believe that its there.

[ari666]

Mine turned out to be a vacuum leak inside the carby, I put a kit through it and hooked up the necessary hoses redone the timing and it has been fine since...

sorry, didnt read this bit

[lil_mickey]

sorry, didnt read this bit

Nah thats ok, even after doing the carb kit i still didn't know that screw was there

[ari666]

well, even if your car is running sweet, it still is a good idea to play with that screw cos' it may just free up a few more horses. what you are meant to do is turn the screw counter clockwise in 1/8th increments untill you hit the flat spot, then take it back 1/8th.

it basically determines how much vacuum it takes to open you secondary flap (the bit at the top) and your secondary needles and hanger are connected to that via a cam. so if it is not opening fast enough or far enough then you are robbing yourself of power.

mate, i just rebuilt that son-of-a-bitch in the pic. how did you go getting the the primary needles back in their jets?!?! worst prick of a job i have done for a while.

[lil_mickey]

mate, i just rebuilt that son-of-a-bitch in the pic. how did you go getting the the primary needles back in their jets?!?! worst prick of a job i have done for a while.

With one eye closed and the tongue in just the right spot

First time i ever did a quaddy and glad it worked, Because as you said "prick of a job".