My 75 mav with a 250 recently haveing problems with the idle. Just sitting and running it will increase and decrease in the rpm this started a month ago. I rebuilt the carb about a year ago and no problem. Today I pull the carb off a cleaned it and played with the idle screw and chock nothing. This thing is like a yo-yo with the idle than the engine dies. Its the same way when driving. I did notice that I need to replace the rotor and cap, but that wouldn't be the problem. I'm lost has to the cause. I'm thinking maybe its the distruitor or timing. I don't know right now. Anybody know the problem on what I can do. This thing is hard to drive gotta keep the gas going when its stop. Its a royal pain.
vacuum leak somewhere is the first thing that comes to my mind. might hunt that down just to rule it out.
My '74 with the 250 does the same thing about once a month. Usually if I shut it off and spray some starting fluid down the carb it starts up and runs fine again. Never have been able to figgure it out. Something you may want to check is that your choke is opening all the way. I know thats not the problem in my car though.
you really don't want to use starting fluid! it will wash down your cylinder walls and cause your walls to run "dry" and cause deteriation of your engine rings and gald your cylinder walls. spray carb cleaner on the outside along the intake manifold and carb base gasket and see if your idle goes up and down, you probably have a vaccum leak or a bad gasket.
If your car has an EGR plate under the carb check it for any holes burnt through it due to a stuck EGR valve.
I know all about starting fluid. I only use it as a tool in diagnosing problems and in extreme emergencys like when I'm 100+ miles from home and my car won't idle. It takes a good bit of starting fluid to wash down the cylinder walls. A quick squirt won't hurt anything...
If all else fails If you check all those things posted above and it still doesn't idle right... I would say the next thing to check is the timing chain. I just put a timing chain in my 289 due to some of the same symptoms. I went through the usual things posted above with no solution. I knew it was timing related and replaced the distibutor and even replaced the carb gasket and rebuilt the carb. (again ) I decided to check the cam and valve train, so I re-set my rockers and pulled the timing cover off.. WOW.. stretched chain.. still in line but badly worn. replaced that and no more problems.. Cost me a trip to the meet in owensboro.. but I have good news........ I saved alot of money on my car insurance...
ok if you say so. what you don't seem to realize is that starting fluid is VERY flammable and can and will cause you much pain if it ever ignites, you can't possibly move fast enough to get away from it and its unforgiving, believe it or not you don't have to use alot to wash down your cylinder walls,but its your engine,just trying to help you.
Sorry Wayne, I understand where you are comeing from, but I know starting fluid is very flammable. Thats it's purpose. You don't generally drown a engine in it though. Generally if you try to run a engine off of it, thats when you are going to have problems.
OK thanks for the ideas. I got may work cut out. I'll pull the carb off again and check the EGR. Since I have an extra rebuilt kit I'll do it again. And hope that will help. I'll check the timing and see where its at. I do know I have low compression on 2 cyclinders. Hey the engine has 180,000 miles on it. I hope its not the timing chain. If anybody else has anything let me know.
Hey I just wanted give everyone an update. I fix it. I started to double check all the vaccum hose and when I check the hose that is connect to the pvc value think that hose was cracked. I pulled the pvc value and notice there nothing inside it. All the peices fell out. I took the value cover off and luckly theres a plate over the hole and thats were the peices where. I'm glad they didn't go in the engine nasty. Anyway I replace the pvc value and some minor adjustments with the idle and it runs fine. So you might want to replace the pvc value once in awhile.
Wow....I'm glad you found it before it fell in the engine .....FYI,I would recomend the use of a propane afixed with a length of vac. hose...Hotrod-Daddy
