Gettin' Frustrated!!!

[Anonymous]

Ok guys, bear with me for a sec.

Here is where I stand: I got a professionally rebuilt M0 head and put it on my car. The theory was, was to get better breathing from the valves and larger log and carb hole. Now I switched from a 1.5" Autolite to a 1.75" Carter YF off of a 300. When I got everything assembled, it started up but real rough. It did not want to idle for the life of it. So after a little exploring, I found a vac leak under the carb. I fixed that and it ran a little better but still was surging at idle. I noticed that if i gave it more choke, it would idle better. After this I took everyting apart and went over the diagrams for this carb and found that there was a seccond idle screw right over the bottom one. Mine did not have this but it appeard to have a hole for it with a little plug shoved in the hole. So took the base and tried to blow air through the idle screw hole but nothing was blowing through. This made me think that the plug had gotten pushed in too far and was choking the idle screw off. So I drilled the plug out and then I could blow air through the idle screw hole now. I went back and reassembled everything and started the car. The idle screw now actually did something and I could get the surging to settle out too a point. I tried rejetting it with little success and the vaccume is right around 20". This brings me to today...

I still cannot figure out how to get the darn thing to stop surging and idle correctly. I can open the choke all the way open but it still surges. If the choke is open and I cut off the airflow from the pcv valve, it will idle a little better and not surge as much. I have the pcv valve pulling vaccume from the port on the log directly under the carb. Is this correct? Another thing that is making me think is that the seccond idle screw port. How should this thing work? Should I go in there and drill out more and then plug off the top of the hole?

I reinstalled the origional Autolite and I runs well. I don't want to use this carb thought. Do you think I should get my hands on a YF from a different engine? Say, a 250 maybe? I don't see how the carb could be too big given my setup (stated in my sig.). It pulls enough vaccume but...I DON'T KNOW!!!!!!!


Anyone have a 1.75" carb that is NOT from a 300?


HELP ME PLEASE!!!!
I'M GOING OUT OF MY MIND!

Thanks,
Paul

 

[Anonymous]

Try putting the old carb back on and verify that the carb is indeed the problem.

 

[Anonymous]

I did just that. It didn't do the surging but it was a lot harder to start cold than with the 300 YF.

-Paul

 

[Anonymous]

What about a Holley 2bbl? It takes a little work to put it on, ubt the tunability of it is unmatched.

 

[rbohm]

8) sound slike the same problem a friend of mine had. he rebuilt his card to no avail. we then replaced some bad vacuum lines, added timing, replaced a bad vacuum advance unit, and a couple of other things, all helped a bit, but it wasnt untill he picked a good rebuilt carb that the problem was solved.

 

[Lazy JW]

When I rebuilt my YF the spec sheet had several different float settings depending on the various engine applications it was to be used on. I wonder if a float setting change could help? A 300-6 has a pretty strong vacuum pull, a smaller engine may need a higher float? Just speculating.
Joe

 

[Anonymous]

After much tinkering, I decided to drill out the idle speed screw hole (the top one with the plug in it). I went to the dia of the hole and but it all back together. Guess what? IT IDLES NOW!!!

But...

at about 1/4 throttle it starts to buck and hesitate. What could this be a symptom of. I havn't gotten this far before so I did not know of this hidden problem. It runs good now but it has a slight hesitation at half throttle. Acc pump? jet size?

Thanks all for the help on the idle problem!

Later,
Paul

 

[Anonymous]

I got it!!! Everything runs fine now. Took me all day but I guess that is the way it goes. It runs great and screams up to 5500rpm and pulls all the way through. It lost some low end torque though.

Later,
Paul