Possible Carb Problem?

[Richard]

1979 Traveler, new 345, 4 bbl. TQ, 727 TF, p/s, p/b, a/c, cruise, tilt, D44 front and back with 3.54 TruTracs. I have what might be a carb problem?

After getting everything put together and getting the traveler out on the road these past few months, I've developed what I think is a carb issue. The TQ was gone through and rebuilt summer of last year. The Scout starts up just fine, idles smoothly, and when running around town, it is a very nice ride. The engine has about 500 miles on it, so I am taking it slowly re: getting on the freeway. anyway, I've started having this problem:

Starts fine, warms up just fine, goes in gear fine, drives off fine. When I am on the road and have to come to a complete stop (stop sign, red light) the engine starts to die, RPMs go to 200 or so but just for a second or two. Then it comes back to regular idle (650-750 RPMs) and smooths
out. this happens every time I come to a stop. A couple of times the Traveler just died. It starts back up just fine and idles fine - until the next stop I come to. Very weird.

I went to my smog guy (yes, the Traveler smogged just fine) and he looked at the emissions on the machine, all green #'s - very good. At idle, at 1500 RPM's, at 2500 RPM's. He suggested that it might be the EGR not opening or closing quick enough and that might be the cause of the stumble, then back to smooth idle. I went home and over this weekend, disconnected and plugged the EGR. No go - the same issue! I thought it might be a carb flooding issue when I stop, sudden movement would cause fuel to spill over somewhere inside the TQ? I don't know!

Any thoughts or ideas, suggestions would be appreciated, and thanks.

Richard

p.s. - gee - I wish these pictures would load right side up!

 

[1975IH200]

Got a photo of your carb?????

The fuel can NOT slosh over from the float bowl, it is sealed.

Sounds like the dashpot on the left forward corner of the carb is not adjusted properly.

 

[Richard]

ok, I am not understanding the adjustment part. Both the left and right attached hardware ( Vacuum pull off diaphragm, Choke module) are bolted to carb. Other than vacuum, is there another adjustment? All vacuum lines are per the attached service manual page. Gee! this is soooooooooooooooo confusing. Please advise.

 

[1975IH200]

It appears your carb does not have the Dashpot or Solenoid.
The Dashpot (or Solenoid) is a device that holds the throttle open just a bit to keep it at idle speed when your foot is not on the gas.
When you turn off the key (ignition) the Dashpot allows the throttle to close fully to keep the engine from "dieseling" or "run on" after shut down.
Many times these are misadjusted.

Other carbs utilize a DTM device, which accomplishes a similar task, but this unit causes the throttle to close slowly when you let off the gas.
This reduces emissions and prevents the engine from stalling from a quick closure of the throttle.
I do not see this on your carb either.

My suggestion to you: Very carefully check the routing of your vacuum hoses.
Pay particular attention to the routing at the three thermo-vacuum switches.
These are detailed on the drawing. You probably did this, but double check them.

Next:
1. What is your curb idle speed when warmed up?
2. What is your fast idle speed when cold and just started?
3. What adjustments, if any, did you make after the carb was rebuilt and installed?

Follow up:
You may just need to adjust the throttle stop screw if all the above is correct.

 

[Richard]

well:
No dashpot, no solenoid, no DTM. I don't know what a DTM is. OK. The only other items are the two thermo switches, the vacuum pull-off diaphragm, and the choke diaphragm. The driver's side has two ports, the passenger side has three ports. I will double-check these (that would be an easy fix). So, in driving around, it appears this problem only occurs when driving. In my driveway, when "racing" the engine (hand on the throttle and working manually), there is no die-off or stumble when - let's say I go to 2000 RPM's and then let go -back to idle. Is this because the transmission is involved? I don't know. Would it be something with the vacuum pull-off diaphragm?

1 - idle is at 700 RPM's
2 - Cold start fast idle is at 1200 RPM's ( think the book calls for 1600)
3 - no adjustments made after installation. Just straight up install (I'm too afraid to play with this TQ)

will play around with this later today and report back.

 

[FDChappie]

Based on your description of "it only occurs when driving", I'm thinking that means it only occurs when stopping. This may indicate that the float level is marginally high and the slosh in the bowl when stopping causes a momentary flooding condition.

 

[Richard]

I think I found the problem!!!!!! Driving around yesterday and today to confirm. I will report this weekend.

 

[FDChappie]

Oh sure, tease with a cliff hanger will you.

 

[1975IH200]

Good news.

I was going to add since you previous post>

1. Ensure the curb idle is set with the Automatic Transmission in Drive.
2. Check for vacuum leaks along the carb base gasket-to-intake manifold surface, and the intake manifold gasket-to-heads junctions.
3. If all else is good, then a check of the idle mixture adjustment screws adjustment would be next.

 

[Richard]

ok,
problem not solved!. I've checked all vacuum lines to and from carb. What I found was that there was a loose vacuum line on port "E" of the high temp vacuum control. I cinched it up and I thought that it might be the problem. Not. I've checked the Vacuum pull-off diaphragm for vacuum, it holds vacuum. I checked the "choke" diaphragm, it holds a vacuum. I can't tell if the "vacuum valve solenoid" that is mounted to the firewall is functional. This valve is for automatic trans. only, so maybe tomorrow, I'll bypass it and connect the "to and from hoses" together to see what happens.

I have not a clue what this vacuum valve solenoid is for, but it's worth a shot in the dark.
1 - curb idle is at 675-700 in drive.
2- I've checked for vacuum leaks wherever there is a gasket, nothing.
3 - I kinda wanted to leave the idle screws where they are as the Traveler runs really nice at all speeds, and as I mentioned before, on the smog machine, everything is green.

Time for a cold one! or two! or three!.

I know it's gonna be something really simple that I am not looking at, until then................

Richard

 

[Richard]

Wellllllllll? it's been a couple of months. I still have this issue with the engine wanting to die after slowing down. when I slow down from a distance, no problem. It's just when I slow down rather fast to a stop. A suggestion was that I add a dashpot to solve my issue. Well, My 79 Traveler did not come with a dashpot, so I am wondering: what took the place of the dashpot? I mean, the dashpot is for slowing down the speed of the carb to match the speed of deceleration/transmission. So, If that is not on a 79 Scout 345, what took its place to do the same thing? I am really stumped!!

I went to our club IHWR (Western Regionals), did a little off-roading behind Calico Ghost Town, and did not notice anything that would resemble a stuck float, starving for gas, flooding, etc. IT ran just fine.

My 77 Scout has a dashpot, and I see how it works (slowing down the idle), so I am very curious re: the dashpot for a 79 Scout and why it's not there.

Any ideas???

Richard

 

[ihpartsjeff]

I highly suggest cracking open your CTS-2313 factory service manual and reread the Thermoquad section. It is written in there on how to tune this carb so you don't run into drivability problems like you are experiencing. I'll bet you're a little lean in the idle circuit, but if you follow the steps in the manual, you should be able to verify this. As for the previously mentioned DTM(Decel Throttle Modulator), I don't believe auto transmission equipped Scout's came with one, but would have to crack the book open again to refresh my memory on which models did and did not have one.