My car is hesitating at high speeds. 70mph if I punch it to 80+ and really put the peddle down. it seems to stutter. but it pushes through. it also seems to stutter when I'm about to shit from 4th to 5th if I hammering on it. the car has a carbed 3.5 m90 engine it. Any Ideas?

I'm not super experienced with carbs, but is your accelerator pump working properly?

Is your fuel pump able to keep the bowl full with a sudden throttle stomp at those speeds? hmm, if that were the case it doesn't make sense why it would happen at 80 and not at the same rpm in a lower gear as well. Unless it does it then too, but the car just accelerates fast enough you can't feel it.

it does at sometimes at lower speeds only when I really dump it. not if I take it easy on it.

The WOT stumble sounds to me like an accelator pump not being adjusted properly, but I'm no carb expert.

I'm sure there are some carb guys here.

I just messed with it. a spring snapped around the accel. pump so lets see . keep the ideas comming. though.

A properly adjust accel. pump is crucial to WOT response. Adjust the lever so that the pump diaphram begins to move just when the throttle moves, but not before.

yea that whole spring thing wasn't it. close though..What lever are we talking about here.

you could either have a problem with the accelerator pump or maybe your jets. a lot of carberators have these jets on the top of the carb that spit fuel so when you do go WOT the jets make up for that time it takes for the accelerator pump to kick in. sometimes they get clogged.

yea that whole spring thing wasn't it. close though..What lever are we talking about here.
I only have experience with the dual webbers on my dad's '02 and a 2 barrel holley I had on an old truck. On the Holley there was an adjusting screw to adjust the postion of the accel pump lever in relation to the throttle position.

What kind of carb you running? Do a google search and find info on how to tune and trouble shoot your carb, you'll be glad you did. That's how I learned to tune my Holley and the Webbers. I'm sure there is a wealth of info at your finger tips.

I am running a holley 390 4bbl with a JAM intake. i was going to switch back to tripple webbers, But my mechanic says that this is the best route......that and webbers arn't much different then holleys. so there is a srew on the side? i need a valve adjustment. And I have powder coating project. so i will probably rebuild the carb and drive the skyeline. i think i need a winter beater. anybody want to buy a skyeline?

http://www.holley.com/data/TechService/Technical/Carburetor%20Tech%20Info.pdf

just a thought... easy stuff.Are you sure you're not running too rich?
Cause if it runs rich it would hesitate just like you're describing. Choke is off, right?

Max

yes I have checked the choke. its electric so maybe. thanks for the link