Cruzn620 Posted October 14, 2007 Report Share Posted October 14, 2007 I have been having trouble with my L20b running rough since i got it back together. it takes a small shot of ether to get it going, then once going, it will not hold an idle. i rebuilt the stock carb today, put it back on, same deal only now the electric choke actually functions! LOL! on the drivers side of the carb there is a plate there with like 6 or 8 screws in it and on the side there is a small spigot on there that has nothing hooked to it. is this the source of my problem? if so, does it need to go to the canister or what? since i can't keep the truck at a constant idle, what is a good base setting for the air screw? i have it at 3 turns out right now (i'm like 300ft. above sea level if that matters) can somebody post pictures of how they have their dash pot adjusted? thanks for all the help guys! Quote Link to comment
datzenmike Posted October 14, 2007 Report Share Posted October 14, 2007 I have been having trouble with my L20b running rough since i got it back together. it takes a small shot of ether to get it going, then once going, it will not hold an idle. i rebuilt the stock carb today, put it back on, same deal only now the electric choke actually functions! LOL! on the drivers side of the carb there is a plate there with like 6 or 8 screws in it and on the side there is a small spigot on there that has nothing hooked to it. is this the source of my problem? if so, does it need to go to the canister or what? since i can't keep the truck at a constant idle, what is a good base setting for the air screw? i have it at 3 turns out right now (i'm like 300ft. above sea level if that matters) can somebody post pictures of how they have their dash pot adjusted? thanks for all the help guys! The thing on the carb is likely the BCCD boost controlled deceleration device. From at least '75, all L20Bs had them. The California models had a vacuum line from them to a driver's side, fender mounted control and solenoid valve. The BCDDs purpose is to monitor manifold vacuum and open and close to keep it at a predetermined level when decelerating. It should not be on at idle. It would cause a vacuum leak and make the idle rough. First, check the idle cut solenoid is working. On the 620 there are two wires at the back of the carb a Red and a Blue (I think) one goes to the electric choke and the other to the idle cut solenoid. Have someone turn the ignition to on, (not start) several times. You should hear a click sound if it is working. If it is not working there will be no fuel for the idle circuit. Quote Link to comment
Cruzn620 Posted October 14, 2007 Author Report Share Posted October 14, 2007 ok, if that idle circuit is bad, what do i need to replace? can i just buy the parts to replace or...what am i looking at for that. thanks for all the help mike!!! Quote Link to comment
datzenmike Posted October 14, 2007 Report Share Posted October 14, 2007 Check all intake manifold bolts are tight. Check that the carb mounting bolts are tight. Inspect the finger size hose from the intake to the brake booster behind the m/c for leaks and that any other hoses are connected or capped off. Another source for a vacuum leak is an EGR that hasn't closed properly possibly due to carbon deposits: http://i138.photobucket.com/albums/q251/datzenmike/EGRandPCV.jpg[/img]"] In the above picture there are two light colored, flat round objects. The one on the right and slightly higher than the other is the EGR valve. If you feel around yours just under the round flat part, (doesn't show very well in my picture) you'll find a tiny shaft that you can lift with your fingernail. Normally at idle this valve should be closed. With the engine running this will cause a huge vacuum leak and may run rough or stall. Sometimes just letting the valve snap shut will help it seal the vacuum leak and it will idle much better. If you suspect a leak here remove the two 12mm nuts and lift off. The valve and the manifold can be wire brushed clean. Quote Link to comment
Cruzn620 Posted October 15, 2007 Author Report Share Posted October 15, 2007 what motor is this out of? mine has neither of those vacuum bulb looking things! also, coming off the carb towards the firewall, that almost white colored larger hose...mine is capped off. now you have to realize that my truck belonged to a diesel mechanic/truck driver/hill billy, and it has a LOT of jerry rigged stuff on it (mostly wiring...lucky me) so it wouldnt surprise me if he just ripped most of the emisions stuff off of mine. on the other hand, i haven't changed the set up since i did the tear down/rebuild and if i remember right (its been 2 years) it idled fine when i took it apart. next time i am at the garage to work on it, i'll try the old trick i use on my motorcycles to trace a leak. get the motor running, then spray carb cleaner around potential leaking points. usually finds the leak pretty quickly and hey...cleans gunk too!! Quote Link to comment
datzenmike Posted October 15, 2007 Report Share Posted October 15, 2007 http://i138.photobucket.com/albums/q251/datzenmike/STP80217.jpg[/img]"] This is from above and behind the driver's side of a '78 620. That large hose is for the PCV Positive Crankcase Ventilation valve. It's very important to have it working as it uses manifold vacuum to remove unburnt blow by gases, and oil and water vapors that condense inside the block when it cools. These deposits dilute the oil and contribute to corrosion and wear. Even if all the emissions stuff is removed this is the one thing that shouldn't be. It is a totally passive system and has absolutely NO effect on performance and actually does good. If the p/o removed the EGR then the PCV valve will be missing as well and there will be a block off plate to prevent vacuum leaks. Take a good look around this area for any leaks. Pisses me off when people do this, it just causes problems for others. It's easier to deactivate the EGR by pulling one hose and plugging the end. Quote Link to comment
Cruzn620 Posted October 15, 2007 Author Report Share Posted October 15, 2007 yeah, on my truck, that hose is capped for sure! pisses me off! i will try to snap pictures of mine when i am back down at the shop next weekend so you know what i am dealing with! THANKS Quote Link to comment
Cruzn620 Posted October 21, 2007 Author Report Share Posted October 21, 2007 found the intake leak...intake gasket...easy fix! thanks for the advice!! Quote Link to comment
copacetickid Posted October 21, 2007 Report Share Posted October 21, 2007 Just gotta say I second that. I'm replacing my entire manifold with one from a yard because someone ripped out the pcv hose and plugged the manifold with jb weld. At least they left you the hose! Just took off both manifolds today, and they are going back on tomorrow. What a pain in the ass!! Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.