The manual says to align the pointer with the BB in the flywheel. When I do this the truck runs and idles ok but short on power.Dropping down the BB below the pointer about a 1/2 inch and she perks up [advance]. The manual doesn't say to dis-connect and block vacuum at the carb and also I'm running a Pertronix system instead of points. Any thoughts?
Is your vaccuum advance working properly? Engine timing must be done at proper idle as well, about 450-500 RPM. Not neccessary to disconnect the vaccuum advance when timing as long as the idle is set low enough. There will not be enough vaccuum at that engine speed to affect the advance mechanism. Andy
Yes But ; What Andy was trying to say is : there _must_ be NO vacuum signal @ idle when you're setting the timing . It is possible there's a vacuum leak between the intake manifold and the cylinder head , get it good and hot and spray some ether at the joints (NOT carby cleaner !) , I had the devil of a time finding my vacuum leak as it's only at the _third_ intake port and only leaks from the underside.... If you can lay hands on a vacuum gauge , connect it to the intake manifold and observe it when the engine is hot and idling , it should be steady (will rise and fall as the engine speed varies) hopefully it'll show over 18" of vacuum . To adjust the timing by vacuum , loop the gauge over the rockerbox where you can see it from the right side and loosen the dizzy's pinch clamp a teense , rotate the dizzy _counterclockwise_ (advancing the timing) and watch the gauge ~ it will rise in vacuum as the engine picks up speed but after a bit the needle will begin to flicker and jump ~ this is bad , so ease it back a little bit until you get the highest , _steady_ vacuum and snug up the pinch clamp . Shut it off and let sit for 2 ~ 5 minutes , then re-start it - if it cranks right up , you're good to go . if it has difficuly turning over , you have another problem and yopu've advanced the timing too far to compensate for it . I hope this helps .
235 timing i checked vacuum at the carb ,where the line to the dizzy goes, and I got a steady 3 inches of vacuum. When I connect the vacuum gauge to the port where the wipers get there vacuum I get a steady 18 inches of vacuum. I realize one port is above the throttle plate and the other is below so which port do I use to adjust timing by vacuum method?
Whoa ! You have a serious problem there ! . Disconnect & plug the dizzy advance line at the carby end , then re - adjust the timing to ball on pointer , you may then need to re - adjust the idle speed screw . (try for 600 RPM's if possible) _Now_ you can connect the vacuum gauge to the lower port on the intake manifold where you got 18" before , and gently and _s l o w l y_ turn the brass mixture screw on the side facing the rockerbox , in and out untill the vacuum read the highest , steady amount . Re - adjust the idle speed as necessary . Now , test to see if the carby port for the dizzy is still pulling -any- vacuum , if so , the carby is JUNK , discard it else it'll never run well . I hope this helps , doing all this in just the correct order will sort out the sheep from the wool and get you going . Chevy Duty has top quality C arter (brand) rebuilt Rochester 'B' series carbys but DO NOT let go of your old , dead carby untill the truck is running well ! . Or , you can always find plenty of cheap , used / mystery Rochesters from other old Chevy owners here , there , pretty much eveywhere , don't pay over $5.00 plus shipping for any carby unless it's gauranteed . I assume you allready adjusted the valves ? if not , STOP and do that first as they're tight , you'll see .
Oh , Yeah : Once you've done all this and there is NO VACUUM SIGNAL to the dizzy @ idle , you can use the vacuum gauge on the lower port to fine tune the ignition timing as described before . O.K. ? .
Thanks for all the help...I'll adjust valves first [hot] then go from there. I'm still running a 6 volt system so I'll find a 12 volt battery to run my timing light. This is about the third carb that Iv'e had on this truck and trying to find a good one is a problem. I guess i hate to part with the bucks for a Chevy Duty rebult but looks like I may have to. Thanks again.. Bob
I found an NOS Carter YF on ebay a while back. Paid $100.00 including shipping. Has auto choke. Popped in on the truck and it is awesome. Wait and you can find the NOS carb you need. There are plenty of them out there. Not NOS rebuilt carbs, but true New Old Stock carbs that have been laying around for a long time. Easy and cheap to get a rebuild kit from that point and pop in a new accelerator pump if it has dried out over the years and you are good to go. May be just as or more expensive than a CP rebuild, but probably miles better. Andy
Cartet YF Series Carby Oh yes ! if you can find one of these , certainly do so ! they're wonderfull carbys and give any Chevy engine much more power and smoother operation too . Take your time and do the things , in the correct order , it may be that a few tight valves slowed the idle speed down so far , you had to open the carby a lot to compensate for it and that's why there was a vacuum signal... Slow & steady wins the race .
As a follow up...Adjusted the valves,they were just about right on, hooked up a timing light and found that the timing was way retarded. Set the timing where it should be {BB] hooked up vaccuum meter and adjusted carb to best vaccuum [19 inches in my case] and she runs great, not burning rubber great but a big improvment.
O.K. Now ; Is it pulling vacuum to the carby @ idle ? . Remember : this truck would barely chirp the tires when it was _new_ , besides ~ doing stupidness like that , will rapidly break extremely expen$ive things you really _don't_ want to get invilved with , trust me .
Vacuum at the carb where it was before the adjustments [3 inches] is now down to 1 inch of vacuum. I guess this is why in the manual it doesn't say to block off carb vacuum to the dizzy because it's just about non existant . Digging thru all my saved info on tune-up I see that at the BB timing is at 2after TC [for a 235] and for what its worth 1954 261 engines BB is 5 degrees before TC. Back to the 235 , seems like a little extra advance works well with these engines. After getting the engine back where it should be I replaced rocker cover gasket, adjusted brakes and lubed the front end so all in all a good day. Bob
Tune Up O.K. Bob ; Sounds good to me , I've not looked in my books for some years but I seem to recall the BB was at either 5° or 7° BTDC . If you care to , you can give it all the advance it'll take , as long as you perform a " Thottle Ping Test " after making the adjustment . these are very low compression engines @ 8.5:1 IIRC . Near the bB you'll faint a faint chevron or triangle stamped into the flywheel , this is the TDC mark and can be used with an advance typ timing light to set the all in timing (that's where it's most important) to 32° ~ 36° BTDC all in , this will really give you a lot of extra power .
