Carburettor adjustment
- Thread starter LolHare
- Start date
Chuffer
CCCUK regional rep
If it has the original Rochester Quadrajet carb the mixture screws are on the front lower edge I think . As for MOT time , I very much doubt a testing station will have the data set up for a 40 year old Corvettes emissions . They would probably tap in a `fudge factor` figure into the machine . My friendly local MOT guy doesn`t even bother with my 1980 C3 so far as emissions are concerned . It passed again only yesterday .
Chuffer
CCCUK regional rep
Good luck .
Derek Nicol
Well-known user
They did but 81's that are still original seem to be rare. Mines got an older Quadrajunk fitted.
LolHare
Regular user
Looks like this could be it,a countersunk screw? However on start up it sometimes struggles, fluffs up and emits a lot of smut out the back like the choke isn't working properly,any advice on how to adjust them and would this contribute to the problems?
Edit, not sure if files uploading
Edit, not sure if files uploading
Chuffer
CCCUK regional rep
Have you had the spark plugs out to see what condition they are in ?
There could well be a cap over each of the idle mixture screws to deter meddling making them look recessed. These need to be removed before you start any adjustments. I would google idle mixture adjustment on Rochester 4 bbl carb , from memory there are quite a few good explanations of what to do. A remote tachometer and a vacuum gauge should take the guesswork out of any changes if you follow the process carefully. Best of luck!
LolHare
Regular user
Yes they're fouled up, ive renewed them but they foul again because this richness
Roscobbc
Moderator
Unless you can be assured that a recent carb re-build has been carried-out I would suggest irrespective of anything to source the correct re-build kit and do the job. The re-build kits are simply a kit of gaskets, seals, float needle valves and other consumable parts. The effects of petrol (especially with Ethanol) being left for long periods will make some of the internal parts corrode, others deteriate and generally gum things up.
Chuffer
CCCUK regional rep
As Roscbbc said , I rebuild kit might be the best option if you have no history of the work carried out . I would also consider a replacement new carb as it might be more cost effective in the long run . Afterall , a 40 year old carb will have plenty of warn components and a brand new recently manufactured after market one should be ethanol compliant . I have recently had a new Edelbrock fitted and it has transformed the cars performance .
johng
CCCUK Member
I suggest you read this thread from the US forum. Looks like an 81 has a one year only carb with electronic mixture control.
Where are the air/fuel mix screws on the '81 - CorvetteForum - Chevrolet Corvette Forum Discussion
Where are the air/fuel mix screws on the '81 - CorvetteForum - Chevrolet Corvette Forum Discussion
Chuffer
CCCUK regional rep
I always cringe when I hear " one year only " ! Hope it turns out be an easy fix .
LolHare
Regular user
Thank you, i played around with the choke mechanism and sprayed it and it fired up and ran great, it drives fine, just smells rich,looking at the plugs again, yes they're fouled but when i say that they're well within usable realms, the thing is that the car doesn't run for months at a time,
Thank you, the do sell a tool for these carbs that seems to be for it, maybe it will work, I'll try it, I cant load pictures up for some reason,
I played with the choke and it firea up and idles a treat, always drives great but just
CaptainK
CCCUK Member
I cringe a lot as I own a '68.....