I was running my 68 Camaro V8 350 with Holly 600 at hi alltitude (5500 ft) and it was using 63 size jets. I am now back around see level (0 to 1000) feet. I noticed that on acceleration it was a little choppy so I changed back to the stock 66 jets. Earlier today my friend was following me and he said he could see gas mist from the mufflers and said it looked rich. I also notice that on initial acceleration the engine almost chokes out. Seems like it is getting to much gas now.

I know the 66 jets are factory stock on this carb and rated for sea level driving. Is there another adjustment I should make now that I changed the jets? This was my first time changing jets on a carb and I made sure I was careful with the transfer tube O ring and the gasket. I have read that over tightening the front bowl can warp the carb, however, I do not feel that I really over strained when tightening the bowl screws.

Any suggestions?

Since you mention changing only one set of jets have to assume this carb has metering block on the secondaries which remained in place in both the high and low alt. scenarios?

Did you also readjust your idle mixture screws for the lower altitude? Should make a big difference down there.

Consider buying a wideband air fuel gauge. I just got mine and can't wait to install and better tune my carb with this awesome tool ($200 from Jegs).

Also - pull one of your spark plugs and post a picture if possible.

Hope this helps.

p.s. - Once you tune that baby in it should feel like a totally different car at sea lvl vs. 5,500ft. Enjoy!!

Gas mist out the tail pipes? Usually, if a car is running super rich, it is black smoke. How is the gas getting thru the combustion chamber without burning?

alan

I am surprised to hear the 66's are making it that fat over the 63's, might want to drop a step and try it. Also if you now have a big bog off the line it sounds like you might not have got the accelerator pump hooked back up, or if so, may just need to up the squirter size.

Since you mention changing only one set of jets have to assume this carb has metering block on the secondaries which remained in place in both the high and low alt. scenarios?



Hope this helps.

The carb is just a 1850 Holley 600 vacume secondarys.


I hadn't thought about the idle mixture screws, might be worth while to put a vacume gauge on it and readjust them now you have dropped 4500' or so.

I am still troubled by the notion of "gas mist". If what your friend is saying is a whittish or greyish color, is it possible you have a coolant leak into the combustion chamber? Did the smoke smell sweet? If so, it is coolant.

alan

I am surprised to hear the 66's are making it that fat over the 63's, might want to drop a step and try it. Also if you now have a big bog off the line it sounds like you might not have got the accelerator pump hooked back up, or if so, may just need to up the squirter size.

I have been reading online and you are right, I think I need to adjust the idle mixture. And yeah, when I initially put the bowl back on I had the accelerator pump arm in the wrong place. However, I looked online and saw how to connect it so I removed bowl again and connected it ok.

Anyway, I think adjusting the idle mixture and dropping the jet size to 65 will do the trick.

Adjusted the idle mixer and problem solved. Turns out one of the mixture screws had vibrated loose and was 2 1/2 turns open and the other was 1 turn. Set them both at 1/2and it runs great.

... I mean 1 and a 1/2

[QUOTE=68RS-SS;1244536]

Consider buying a wideband air fuel gauge. I just got mine and can't wait to install and better tune my carb with this awesome tool

This is excellant advice ^.:thumbsup:
Why struggle reading plugs with todays fuel when you can dial in the perfect a/f ratio utilizing a wideband o2 sensor that reads on the fly in real time ratios.
My AEM wide band cost a tad over $200.I fully expect to recoup the initial purchase price in fuel savings alone..not to mention how i was able to modify internal ckts for driveability and safe wot runs.