I finally got a replacement carb (Holley reman carter yf) for the 70 Mav and I'm having problems getting it to idle right. Can someone give me some tips or a systematic way of getting the air/fuel ratio mixture and choke setting right? Thanks
Idling problems are usually of a mistune, or a vacuum problem. A little more history of your total problem might help us help you. Dan
Ok here goes. I can get it to start and idle, but at very high RPM. When I try to adjust it to the proper RPMs for the curb idle, it dies when put in gear. I know its something simple, but I can't quite figure it out. All the vacuum lines have been replaced and I'm certain that there are not any leaks. I checked the advance and retard, and both are working. I guess what I'm looking for is a start point. Thanks
JB, it is a bit difficult to know your specific circumstance but here is some things to look at. As you know a cold engine will idle. There may be an electric choke on your carb. It's cap is adjustable for choke plate position vs temp. This is an element that you have to adjust into for what you consider best average operation over cold temp ranges you have. The high idle can be choke setting related because it also operates a fast idle cam on the throttle side by not allowing the throttle to set against it's stop where there could also be an electric throttle position controller. (in effect, two throttle stops) There is a spec idle speed for when the idle is on the hard stop and when it's on the electric stop as well and in or out of gear for an auto trans. You can see by all this that a combination of settings could be a problem when not near correct. Then, the idle mix adjustment on top of all this. I would start with a hot engine and adjust in the idle making sure the choke is not interfereing by adjusting the cap to fully open the choke plate. Proceed to set the hard idle stop screw and mix screw to get you smooth idle. Then add in the electric positioner adjustment. After this then the Choke circuit can be worked on along with the electric solenoid positioner. This electric posititioner has a lot to do with keeping the ide when in gear. It's a lot to digest and there is still more to get informed on. Best to try to get a copy of the Haynes book on the MAV and refer to page 140/141 for more info because the overall adjustments are somewhat interdependent so all this can still present a problem. Trying to bring togather cold start, hot idle, in gear loading needs some understanding that few today would even have a feel for with everything being fuel injection. Hope this gives you at least a better understanding of what you have to do. Hang in there and make is a learning challange.
The holley reman carb is "stripped" in comparison to the Carter that it replaced. There is no adjustment screws for the choke on the opposite side where the throttle linkage connects. Also, there is no electric choke. Being this car has a semi-auto trans, there is no kick down linkage either. I can get it to idle ok when hot, but now when you give it gas, there is a "popping" sound that comes from the carb. Still dies or runs extremely rough when you put it in gear. All plugs are firing (replaced points, rotor, condenser, cap, wires. Points are gapped correctly and dwell is ok) and timing set per manual. Rechecked again for vacuum leaks and all is good. This is really frustrating as I can't get it running to even get it up on the ramps. Gonna start from square one today and go through EVERYTHING again. Thanks for the insight and ideas. JB
Sorry not to be able to help more. This is what happens when the replacment is not the same. Do I detect you saying you have a C4S transmission? If so it's one with a manuel valve body. Not that many ever used.
The tranny is a C4S, which is foriegn to me at this point. Shifting w/o a clutch, reminds me of a Honda 90 I had once. But like I said before, as soon as I can find a suitable 302/C4 trans I plan on doing the swap. Thanks again for your help.
I have purchased faulty remanufactured carbs before. In fact, I had to go through 4 of them one time before I got one that worked correctly, and it was a Holley. Just something to think about.
I called Holley and they said it sounds like a problem in the carb, so I'll take it back and try one more time.
I bought a remanufactured holley about 20 years ago for a Dodge van with 440 ci. Big carb, but it had a plastic body. I had all kinds of problems getting one that wasn't warped, didn't immediately flood, etc. We had to take it back and swap it many times. The one we ended up with worked well, but on hot days, it would not start, so we had to take the engine cover off and hit it with a screwdriver, then it would start right up and run fine the rest of the day. We decided to live with that one until we sold the van. I hope your Holley experience works out better than mine. Now, I always buy new. Not worth my time to save a little money and have to install and take out multiple times, and try to adjust it to work when it is a malfunction, not an adjustment issue.
This might be a crazy one but we are not talking about an engine with a larger than stock cam in it, right. Sounds like the problem I have before I got a stall.
To offer info on your trans C4S, it is close to a regular C4 but with a manual valve body such that it dosn't shift automatic. The 'S' means semiautomatic, a combination of using a torque converter and manuel shifting. It has no modulator, no kick down lever,and no internal governor to effect the auto shifting. If it works ok and your not ready to relace it then it's fine but not a real heavy duty unit. Only offered in 1970. Those who have a Haynes Manuel refer to page 185 under Automatic Transmissions.
I've always had the best luck adjusting the idle with the car in gear. Go ahead and replace the carb though. Them Carter YF's can be strange sometimes. I would have put a Carter RBS on it if it were my car. But thats just me. I've ran both a YF and a RBS on my car, and have had alot better luck with the RBS. The pop when you give it gas almost sounds like a timeing issue to me. On these old loose engines, you can't always follow the book to a T.
