Hey guys, I rebuilt my carb over the weekend and now I'm having some strange results. I have adjusted the carb for max vacuum (around 19Hg). 1 - The car is a little slow to start up and runs a little rough until the engine warms up. Nothing too bad, but different than before. Maybe need to adjust the idle mix (used to be at 4-1/2 turns out) or choke setting. 2 - When first hitting the accelerator after setting for a while, it stumbles pretty bad and acts like it wants to die. Much better after engine warms up. 3 - The engine will sometimes surge at very low RPMs (idle set to around 650). The RPMs will jump around to between 350-750 and eventually settle back to normal idle, but sometimes it dips low enough that the engine dies (but fires right back up). This usually after accelerating at low speeds while in 1st gear. 4 - I'm also getting some very light throttle surging that I can feel when just barely pushing the accelerator. Throttle plates not open enough/too much? 5 - The engine every so often (no pattern, not touching accelerator, in drive w/ brakes on or in park) kind of jumps, almost like a misfire. Shouldn't be an ignition problem since I just replaced mine and it has been working fantastic and I haven't touched it after getting it set up. 6 - While in gear, I disconnected a line from my manifold tree (vacuum canister), the RPMs went up along with my vacuum reading, but the motor ran more rough. Running rough I get, due to the vacuum leak and sudden lean condition, but why the higher RPMs? 7 - The fuel bowl was almost dry this morning after sitting overnight. Maybe I didn't tighten the power valve enough and it's leaking down into the manifold? Ideas?
when a carb is properly adjusted to run when warmed up, it will be too lean for when the motor is cold that gas that is traveling through the intake and heads on a cold motor will have a tendency to pool on the walls. that is why the choke exists, to put more fuel into the motor while its warming up. so to fix your first problem you need to work on the choke adjustments. the stumble when cold could be the same problem it sounds like your float level adjustment could be off. the random "jump" could be a drop being pulled out of the boosters from too high of a float level. the bowl being low is weird. it could be leaking through the power valve like you said and this could also be responsible for the "jump" and the random surging.
I've looked down the throat of the carb when it's acting up but haven't seen any drips. If it's coming from the power valve, would I still be able to see it?
Some people adjust the chock all the way closed when rebuilding the carb. This is not good. A 1/8" drill bit or dial pin should be held down the throat. Adjust the carb to just touch the drill bit or dial pin. This will be the correct setting, providing the rest of the settings are correct. Blue Brick X2.
I do have mine almost all the way closed, but when firing up cold, the choke pull-off opens it up a little more. Being that it's getting warmer here in Texas, I have it set so the choke opens fairly quickly due to the higher ambient temperature here.
First things first, Ditch the choke altogether. You don't need it.(wire it open, or remove it altogether like I do) Next, set the initial timing before tuning the carb. It sounds like you're timing is retarded. Set the initial at about 12*BTC. adjust the throttle blades all the way closed, then crack them open slightly, like about 1/2 to 1 full turn of the throttle screw (not the mixture screws) Now, set the mixture screws, turn all the way in, then 1-1/2 turns out. Now make sure there's no slack in the accellerator pump linkage, you should see fuel squirt the instant you open the throttle blades. With all this done, the engine should start and run when hot, then fine tune the mixture screws and the idle speed. Also set the float level (on a Holley, preset it on an Autolite)
How many turns out are all of you on your 2100's? I think mines set rich, but I'm looking for ideas where everyone else is at. Also, for us southern states guys, where do you all have your choke setting (if using a choke at all)? How many turns out from a closed throttle plate are you for the idle speed screw? I'm not looking for right or wrong answers...just what you've got going on.
not to start a debate or anything.. but why does that really matter? baddad gives good advice above to properly baseline the settings. having the choke settings in the way only compounds issues and will have you chasing your tail even longer here, IMO. It's like this.. timing changes affect mixture qualities(advance leans out the idle mixture and retard richens it) and therefpre requires a different "tune" in the carb. You have to work back and forth between the two(fueling and ignition lead) to sneak up on the optimum setting for your car. BUT.. proper baseline setting of both would be required to even start the process. So, if others are well more than 2 turns out like yours is.. their tune would be off too and nothing can be learned from their examples.. well.. other than "you're not alone here".
Ok, I did some more testing today and I found that when my car is all warmed up, when I hold RPMs at around 1500 where it runs most rough, that if I close the choke plate by maybe 2/3 that it smooths out very nice. This make it so the car wont start when it cools down though. Lean misfire, right? Ok, so I reset the choke and get back to the problem RPM and disconnect my vacuum advance from the carb and plug the hole....again, it gets better, but now low RPM power is noticeably lower. Again, sounds like lean misfire. How can I tune this out and keep my vacuum advance connected? Timing is at 12º at idle and 36º total w/ no vacuum advance connected. Power above around 2000 RPMs is very good, as is 650-1400....its just that one spot giving me fits between 1500-2000. My distributor allows vacuum advance adjustments if that is what is needed.
So do you guys think this is a timing issue or carburetor related, or both. My power valve is good, float/fuel levels are also good. It seems that adjusting the timing may be easier, but I don't know if that is the best choice.
Check very carefully for any vacuum leaks! Check all your vacuum hoses for damage and that they are connected. Your mixture is too lean. Closing the choke somewhat richens the mixture. Also, if you have power brakes, squeeze the vacuum hose shut with the engine running. If it smooths out, the booster is leaking internally.
No, I dont have power brakes, so that isnt it. I've tried disconnecting all my vac lines and plugged them, but the results are the same. I can't find any vac leaks by listening or spraying carb cleaner around. If i had a leak, wouldnt it affect me all the time, not just at this particular rpm? If my vacuum advance is set to advance too far at that rpm, would it burn lean? I've watched the timing advance with my light going up in rpms, and nothing LOOKS wrong, but obviously something is.
