I have '79 Scout terra 345, and I need help with a carb choice I should go with and what other steps I should take to get it running good.? Right now my problem is the truck is dieseling out pretty bad... So much so that I have been walking away and it fires back up and idles...my main goal/use for the truck is daily driver in town and highway cruising (once in a while with a car trailer not often). The carb on it now is a 2bb motorcraft d3tf hc a 2l 20 and has stock manifolds with single exhaust.
Carb help ?
- Thread starter Sean7379
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FDChappie
Well-known member
That's not a bad carb and one of the easiest in the world to rebuild. Looking at all those throttle return springs, I'd say getting the idle speed down has been an issue with that carb. How does it run except for the dieseling?
We should start with the basics here first. Have you done a tune up recently? What's the timing set to? How often to you drive this truck and is the gas fresh?
We should start with the basics here first. Have you done a tune up recently? What's the timing set to? How often to you drive this truck and is the gas fresh?
Scoutboy74
Moderator
Engine run-on is often the result of the engine racing when the ignition is switched off. It looks like your Scout May also have an auto trans. High rev drops into gear from park can be potentially destructive to the auto trans. You also can't accurately adjust your ignition timing when the engine speed is too high. So for multiple reasons, you need to get your idle speed down below 1000 rpms. 7 to 800 is a good range to shoot for. Does the choke work on this carb? In the picture, the plate is closed, which is what you want for a cold engine start, but it needs to open up as the engine warms.
I'd replace that carb with a Holley 2300, 350cfm. That Ford carb has a plastic-like concoction for a float that is so bad a local parts store had a dozen hanging at the counter.
The 'deiseling' is caused by lean fuel mostly, timing plays a sigificant role as well. When an engine deisels it literally runs backwards, any loose fitting vacuum caps will be blown off the carb/intake due to the pressure and it can hurt the power valve & distr vacuum pot in some cases.
The engine will want more idle fuel - slightly, maybe 1/2turn, and put a timing light on the engine. I suspect you'll find the real problem in your distr, maybe the advance weights are not returning or the vacuum advance is hung up.
The short term is to shut engine off while in gear to keep a 'load' on it, if a clutch then let the clutch out slighly when turning the key.
The 'deiseling' is caused by lean fuel mostly, timing plays a sigificant role as well. When an engine deisels it literally runs backwards, any loose fitting vacuum caps will be blown off the carb/intake due to the pressure and it can hurt the power valve & distr vacuum pot in some cases.
The engine will want more idle fuel - slightly, maybe 1/2turn, and put a timing light on the engine. I suspect you'll find the real problem in your distr, maybe the advance weights are not returning or the vacuum advance is hung up.
The short term is to shut engine off while in gear to keep a 'load' on it, if a clutch then let the clutch out slighly when turning the key.
Robert Kenney
Super Moderator
Going to have to echo scoutboy here.. Idle speed it the foremost cause of run-on.
Slow and lean will be the least likely to diesel/run on if you will..
Basically the incoming af mixture is ignited by something glowing in the combustion chamber. The slower the engine is running the cooler the hot spots. The leaner the idle mixture the harder it is to ignite. On the other side of the spectrum a Rich idle mixture tends to be cooler.
Poor fuel is more likely to burn under these conditions also.
So correct ignition timing so you need the smallest throttle opening to idle. Slow idle speed eg 600-700 rpm. Correct idle mixture. Eg best vacuum.
The carb choice is going to be one that runs right. The engine won't care what it is. If you need a two barrel the 350 cfm 2300 is a good choice. If your motorcraft carb runs ok keep it and dial it in..
In the short term. Although we don't know what trans type you have for an auto stop the engine in gear while holding the brake or for a manual, turn the key off while the clutch is dragging and release the clutch completely as you turn the key to off..
Slow and lean will be the least likely to diesel/run on if you will..
Basically the incoming af mixture is ignited by something glowing in the combustion chamber. The slower the engine is running the cooler the hot spots. The leaner the idle mixture the harder it is to ignite. On the other side of the spectrum a Rich idle mixture tends to be cooler.
Poor fuel is more likely to burn under these conditions also.
So correct ignition timing so you need the smallest throttle opening to idle. Slow idle speed eg 600-700 rpm. Correct idle mixture. Eg best vacuum.
The carb choice is going to be one that runs right. The engine won't care what it is. If you need a two barrel the 350 cfm 2300 is a good choice. If your motorcraft carb runs ok keep it and dial it in..
In the short term. Although we don't know what trans type you have for an auto stop the engine in gear while holding the brake or for a manual, turn the key off while the clutch is dragging and release the clutch completely as you turn the key to off..
Thanks guys, sorry its been a while since I checked back. I ended up rebuilding the motorcraft carb for now.. Also it is an auto/trans. I have had it running maybe twice since, with the same issues (just to run to work and back) and leaving it in gear did stop the dieseling not a permanent fix obviously. I'm not sure if I said this last time but if I do get it started, it climbs in rpm's as it warms up. Messing with the throttle adjustment screw (which if I understand also isn't a permanent fix) will get it running good but eventually, but not always gets to a point where it will want to die. And still in park an neutral it idles fast, which causes the dieseling correct? Tonight I plan on installing a tach and running a timing light, that is if I can get it running at all. One auto shop I talked to mentioned new points and condenser, other wise they didn't know...? Am I heading in the right direction?
Again thanks for the replys! Any other suggestions are great thanks for baring with me.. I'm mostly baffled by the fact that I drove it three years with ease and now problems hot,cold,freezing snow ?
Again thanks for the replys! Any other suggestions are great thanks for baring with me.. I'm mostly baffled by the fact that I drove it three years with ease and now problems hot,cold,freezing snow ?
Hondo
Member
Could use some help myself on this carb. Looks like thats whats on my 72 345 Scout II. Mine runs fine, but have been fighting a poed choke. Someone tried to convert it to manual choke as the picture shows. It was attached with self tapping sheet metal screws. Spent a few hours chasing the threads and remounting and adjusting it, then tried it the next morning and it now hits the air cleaner, which was off to work on it. Does anyone know if they make an electric choke kit for this carb?
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Scoutboy74
Moderator
How extensive/meticulous was your rebuild process? I ask because I believe the root of your issue was and still is the carb. Don't mess with the timing until you can achieve a proper curb idle speed on a consistent basis without any macguyver-style gimmicks. New points and condenser are relatively inexpensive, so you May as well replace them as a matter of course. Do pony up your dough for a top shelf condenser, instead of the el cheapo chai-knee item. They're known to be crap right out of the box more often than not. Don't toss the old points/condenser away, unless the replacement items alone suddenly make the engine start up and run just as perfectly as the day it rolled off the assembly line...or you can plainly see that the old points are severely pitted, burned and/or the rubbing block is worn down. Otherwise, toss them in the glove box for trail spares.
I suspect your throttle plates aren't fully closing. If that is the case, it is impossible to correctly adjust the carb. I didn't notice where you are located, but you'll never pass a smog check like that - if it matters to you.
Try this. A lot of scouts have gummy throttle cables. First don your safety glasses to protect your eyes. Take some wd-40 and spray it on the metal cable where it enters the plastic sheething. With the engine not running open the throttle fully by hand and spray some more. Don't be cheap, wd-40 doesn't cost much. Then give it a try. You'll probably note the idle can now be adjusted.
Because wd-40 evaporates, you will likely have to repeat the treatment every few months or so (or get a new throttle cable). Give it a shot! Good luck.
Try this. A lot of scouts have gummy throttle cables. First don your safety glasses to protect your eyes. Take some wd-40 and spray it on the metal cable where it enters the plastic sheething. With the engine not running open the throttle fully by hand and spray some more. Don't be cheap, wd-40 doesn't cost much. Then give it a try. You'll probably note the idle can now be adjusted.
Because wd-40 evaporates, you will likely have to repeat the treatment every few months or so (or get a new throttle cable). Give it a shot! Good luck.