Hello! First timer on the Corvette Forum.

Recently my car has been "hiccupping at WOT", hiccupping might not be the best word for it so let me explain. When WOT happens the car runs perfectly until it is about to shift ( I would say 4500 rpm) the car seems to bog done for a little longer than a second when shifting from 1st to 2nd as well from 2nd to 3rd. Sometimes it hiccups goes for another 100-200 rpm and then hiccups again and then shifts. I first thought maybe my timing was off (I've always been told timing doesnt change, but wanted to check anyway). With my setup the recommend timing is 36 degrees with no vacuum advanced, so just how you would check/ change your timing. I went ahead and backed it done to 34 degrees just to see if anything would change, but nothing, still did it. So my next thought would be the carburetor, which was rebuilt and tuned to my current setup before I did my stall convertor, rear end and shift kit but this problem was still happening before those parts were installed. I think I have a carburetor issue which is not my strong suit so I wanted to see what you guys thought.

I hope I provided enough info, I'll try my best to answer questions/ help provide any info.
I hope you guys and gals can help, I've heard you guys know your stuff!
Thanks, Shyru

My current setup is
1976 C3
Brodix Cylinder Heads, 64 cc, 180cc intake
Cam, 454/454 lift with 268 duration
Side Pipes, no baffles
2101 elder brock intake manifold
stock q jet, i don't remember jet size and all that off the top of my head, but if needed I could figure what the primary and the secondary size are plus any other info
2500 convertor
shift kit
370 gears
th350
Performance DUI distributor
Live wire spark plugs

 

Welcome to the forum!
I personally am so sorry to hear that your car shifts itself.
There are people on here who will know how to deal with this. My only suggestion is of course to install a manual transmission of your choice.
Sorry I'm not much help with this but certainly others will know about your automatic issue.
Just thought I'd welcome you to this fine forum.

 

My '72 also shifts itself.

Do you feel the shifts happen at the appropriate time/rpm range when not pushing it? It's just not very firm in the upper rpm range?
It also sounds like this is a recent change to its past shift characteristics? Any trans service and fluid changes recently? Level is good?

Other than internal shift kits, the shifts are controlled by the modulator on the side of the trans, with manifold vacuum pulling through a hard pipe to the modulator. Each end of the pipe should have a rubber hose connecting to the intake fitting or the modulator. Make sure the rubber tubing is in good condition and seals well.

 

Sounds like you have a fuel starvation problem - very common. If someone "rebuilt" the Q-Jet, I'll bet they put the little .125" seat in it, which will not work at elevated rpm. I'll bet they did not set the rest of the carb up right, too. You also need to check your fuel pressure and make sure you're at over 5 psi when the problem occurs (which will not compensate for the .125" seat that I'll bet they installed)...

 

The “Hiccupp” only happens at WOT. When I took the transmission apart, the fluid was clean and the filter had little to no debris that I could see. I will say when I was taking the transmission out I noticed that vacuum modulator had a rather hard upwards turn/a 45 degree end where the hose goes on. I saw that how the hose was sitting was rather odd, I might see if I can fit a longer hose on the hard end and see if I can make where the hose doesn’t sit so awkward on to the modulator. I will also make sure all the hoses off the intake are good.

Thank you for the info! It is very much appreciated!

 

Hello Lars! I heard you were the carburetor guru when it comes to the Q-Jet. Thank you for the info, I will definitely look into it. Not the best with Q-Jets so this may sound a little silly, if it comes down to fuel starvation do you recommend me going with a bigger seat? If so what size do you believe? If these questions are one of the ones that you can’t answer unless you know every detail I completely understand.

Thank you again! I will get a fuel pressure gauge hooked up and see what I get at WOT.

 

Like our buddy 4-vettes I too would like to welcome you to The Corvette Forum shyru!

This is the place to be if you have questions or issues regarding your Corvette. Getting answers from people like Lars will help solve your cars issues and he is helping you for free. Lars is one of the Quadrajet Experts on this site and he knows a ton about air/fuel issues. We are very fortunate to have his advice and experience with Corvettes!

Take some time and fill out your information in the profile area so we know what year and type of Corvette you have. Otherwise people will ask you the same questions over and over as they try to help you. The more information you provide the easier it is to get accurate answers on your particular model Corvette.

 

and provide at least a generalized geographic location! You never know if a helping hand is nearby.