Engine stumble...
Cargo Master
Joined: Oct 2011
Posts: 2,251
Likes: 306
From: Kenner,La.
stumble
If you have dual exhaust and there is no cross over pipe that can also cause an off idle stumble. Also 1.5 turns on the primary side should be the sweet spot or 1/4 either way. Connect a vacuum gauge with a long hose to the cab and drive it to get an idea when it stumbles. Are the shaft bushings in the distributor worn, that also can cause some stumble.
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Junior User
Joined: Jul 2015
Posts: 51
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Hello guys,
Have looked into it and found that resetting the accelator pump did not make any difference unfortunately. Fuel level in the bowl was OK.
Need to try the mixture screws, as 5 turns out seems to be a lot, although some of you disagree on that.
Will keep you posted !
Martin
Have looked into it and found that resetting the accelator pump did not make any difference unfortunately. Fuel level in the bowl was OK.
Need to try the mixture screws, as 5 turns out seems to be a lot, although some of you disagree on that.
Will keep you posted !
Martin
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Junior User
Joined: Jul 2015
Posts: 51
Likes: 0
Hi guys,
Small update : Hooked up my vacuum gauge to manifold vacuum and increased the vacuum by one point ( from 19 to 20 ) at idle, which took the needles approx. 2 turns in. Also, I tried to suck the vacuum advance hose and it made a vacuum. Also, I sprayed brake-cleaner around the carb and no increase in idle, only a decrease when shot directly into the air-horn of the carb. So, I guess I don't have a vacuum leak. Still, the stumble is there. A carb rebuild kit is on it's way to Holland as we speak, will see if that helps ! Want to try to stay away from ignition timing for now, as the accelerator pump still doesn't seem to work well.
What else could it be ? Any suggestions ?
Small update : Hooked up my vacuum gauge to manifold vacuum and increased the vacuum by one point ( from 19 to 20 ) at idle, which took the needles approx. 2 turns in. Also, I tried to suck the vacuum advance hose and it made a vacuum. Also, I sprayed brake-cleaner around the carb and no increase in idle, only a decrease when shot directly into the air-horn of the carb. So, I guess I don't have a vacuum leak. Still, the stumble is there. A carb rebuild kit is on it's way to Holland as we speak, will see if that helps ! Want to try to stay away from ignition timing for now, as the accelerator pump still doesn't seem to work well.
What else could it be ? Any suggestions ?
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
Yes, with engine OFF, look down throat of carburetor, there should be two squirts of fuel IMMEDIATELY when throttle is blipped. "Normal" accelerator pump rod adjustment is to use the inboard side on the forward holes, and the 2nd hole from the top (for temperatures 40F through 80F)
Are you employing a vacuum gauge for engine tuning and carburetor disgnostics? If not, why not?
Also, setting float height causes some confusion, even with people who speak English. Keep in mind the initial dry "bench setting" for the _float height_ is just an arbitrary baseline setting.
It must be fine tuned, this is done by measuring the actual wet _fuel height_ in the bowl. This distinction is very often conflated or confused. I just repaired my lawnmower for this exact same reason. The technician set the float WAY too high, and this caused flooding and sooty plug. Dang kids!
With the engine fully warmed up, let it idle for two minutes on level surface and then shut the engine OFF.
If you are careful the air horn and gasket can be removed (4 screws) and then observe the height level of the fuel in the bowl.
Most (many) applications specify 29/32nds _fuel_ height from the fuel to the machined flat surface of the top of the fuel bowl carburetor. A U.S. Washington Quarter is pretty close to 29/32" and is handy to have compared to a machinist's rule.
Note that the actual float height is irrelevant at this point, the fuel height is what is important and will affect jetting and idle, transition circuits, everything. If you have to adjust the float arm, it's best to remove float completely and bend the arm carefully.
If you are REALLY careful, and keep an extinguisher handy close by, you can even idle the engine with the 2100 air horn removed and watch the fuel level for a few minutes to check for proper operation. 29/32" fuel height should be maintained. Do this outside, not in the garage, for safety. The float height may have to be set quite low to reach the correct fuel height. This is OK.
Finally, 5 turns out on the mixture screws is not correct. The initial "bench setting" is 1.5 turns out from fully seated. Then they are turned in (clockwise) for maximum RPM consistent with a smooth idle at the same time, and backed out as necessary for smooth idle, though still "lean drop". Typically 1/2 to 1 full turn out (every engine different) is optimum.
Are you employing a vacuum gauge for engine tuning and carburetor disgnostics? If not, why not?
Also, setting float height causes some confusion, even with people who speak English. Keep in mind the initial dry "bench setting" for the _float height_ is just an arbitrary baseline setting.
It must be fine tuned, this is done by measuring the actual wet _fuel height_ in the bowl. This distinction is very often conflated or confused. I just repaired my lawnmower for this exact same reason. The technician set the float WAY too high, and this caused flooding and sooty plug. Dang kids!
With the engine fully warmed up, let it idle for two minutes on level surface and then shut the engine OFF.
If you are careful the air horn and gasket can be removed (4 screws) and then observe the height level of the fuel in the bowl.
Most (many) applications specify 29/32nds _fuel_ height from the fuel to the machined flat surface of the top of the fuel bowl carburetor. A U.S. Washington Quarter is pretty close to 29/32" and is handy to have compared to a machinist's rule.
Note that the actual float height is irrelevant at this point, the fuel height is what is important and will affect jetting and idle, transition circuits, everything. If you have to adjust the float arm, it's best to remove float completely and bend the arm carefully.
If you are REALLY careful, and keep an extinguisher handy close by, you can even idle the engine with the 2100 air horn removed and watch the fuel level for a few minutes to check for proper operation. 29/32" fuel height should be maintained. Do this outside, not in the garage, for safety. The float height may have to be set quite low to reach the correct fuel height. This is OK.
Finally, 5 turns out on the mixture screws is not correct. The initial "bench setting" is 1.5 turns out from fully seated. Then they are turned in (clockwise) for maximum RPM consistent with a smooth idle at the same time, and backed out as necessary for smooth idle, though still "lean drop". Typically 1/2 to 1 full turn out (every engine different) is optimum.
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Junior User
Joined: Jul 2015
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Hi guys,
And again, one step closer to the solution. Rebuild the carb and set the new float to the prescribed dry setting. Put the carb back and fired the engine...NO stumble ! Very pleased, smiled for about 5 minutes and wanted to take a picture of my beloved stumblefree Bump... But...carb flooded big time, gas was boiling and only started after 10 minutes of rest and a lot of throttle. Visited a friend and when engine cooled off, it started without any issues.
So, tonight I set the wet float to 29/32", as proposed. Damn, the stumble came back ! Now, my next question would be : if I set the wet float a little higher, would that solve the problem, or is it a truly and official number.
Thanks guys, going to bed now...smellin' of gas....
And again, one step closer to the solution. Rebuild the carb and set the new float to the prescribed dry setting. Put the carb back and fired the engine...NO stumble ! Very pleased, smiled for about 5 minutes and wanted to take a picture of my beloved stumblefree Bump... But...carb flooded big time, gas was boiling and only started after 10 minutes of rest and a lot of throttle. Visited a friend and when engine cooled off, it started without any issues.
So, tonight I set the wet float to 29/32", as proposed. Damn, the stumble came back ! Now, my next question would be : if I set the wet float a little higher, would that solve the problem, or is it a truly and official number.
Thanks guys, going to bed now...smellin' of gas....
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
For purposes of clarification are you setting float height to 29/32" or fuel height to 29/32"; the terms and what is being measured are not interchangeable even if it sounds like we know what you mean, not trying to beat up on you here but this is a common error to conflate these.
The fuel height in the bowl, is ultimately what matters, the dry float or bench setting is just the starting point. Let the warmed up engine idle for a couple minutes on level ground, shut the engine OFF, and then measure the _fuel height_ from the machined surface at top of carb to the fuel surface in the bowl. Raise or lower the float to achieve this as required. A US Washington quarter works perfect for measuring as it is very close to 29/32". The float height and fuel level specifications for any particular application is listed in the shop manual by year, it varies somewhat by engine, it's not absolutely super critical but it has to be close. I'd think the 29/32" fuel height level would be fine for about any 2100 carburetor for stock applications and good enough to eliminate it as a source of the trouble here.
The fuel height in the bowl, is ultimately what matters, the dry float or bench setting is just the starting point. Let the warmed up engine idle for a couple minutes on level ground, shut the engine OFF, and then measure the _fuel height_ from the machined surface at top of carb to the fuel surface in the bowl. Raise or lower the float to achieve this as required. A US Washington quarter works perfect for measuring as it is very close to 29/32". The float height and fuel level specifications for any particular application is listed in the shop manual by year, it varies somewhat by engine, it's not absolutely super critical but it has to be close. I'd think the 29/32" fuel height level would be fine for about any 2100 carburetor for stock applications and good enough to eliminate it as a source of the trouble here.
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Junior User
Joined: Jul 2015
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Hi Tedster,
I've set the fuel height to 29/32" and the float pivot pin is clipped. Last time, I left the fuel height a touch higher and I'm about to take a cruise today ( sun's out !! ). Will report later today with my findings.
Thanks,
Martin
I've set the fuel height to 29/32" and the float pivot pin is clipped. Last time, I left the fuel height a touch higher and I'm about to take a cruise today ( sun's out !! ). Will report later today with my findings.
Thanks,
Martin
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Junior User
Joined: Jul 2015
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OK, that didn't work either... idles fine, but runs far too rich during driving and cuts out during idling after driving. Need to start with full throttle and a lot of black smoke from the exhaust.
Checked the power valve and the one that came with the rebuild kit, has bigger orifices I noticed. Would that be a possible source of serious flooding ??
Thanks,
Martin
Checked the power valve and the one that came with the rebuild kit, has bigger orifices I noticed. Would that be a possible source of serious flooding ??
Thanks,
Martin
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
I think we need to go back to the beginning and get this rig to square one. What is the timing set at? Is there still points in the Dizzy or have you put in a pertronix kit? If there is still points and the gap is set wrong you may not get good coil saturation and therefore a weak spark. Which can't burn all the fuel and looks like a rich mixture. What grade of gas do you have there in Holland? What octane and which additives do they add there?
Ford had a gazzion jets and power valves back in the day. Depending on your gas and altitude there I can try to figure out the part numbers of the ones that would work better for you. By chance is the carb's original tag with it's number still on it? Next time you take the lid of the carb off please remove BOTH jets and look for their numbers on the sides. Example "58F". I've seen aftermarket rebuilt carbs with two different sized jets! And the ones in there may be too big. An over rich mixture can wash raw fuel over the spark plugs. Will stall at idle and sometimes restart after that gas has evaporated enough to allow the spark plugs to spark.
I have an old instruction sheet out of a carb rebuild kit. It doesn't list 70/71 truck for some reason but it does list this:
70/71 ford and Mercury cars...390 A/t...Dry float level 7/16" and #3 pump over travel hole.
72 Truck 360/390 engine... A/T...7/16" and #4 hole.
72 Truck 360/390 engine... S/T...1/2 " and #4 hole.
72 truck 360-390 engine...S/t with carb tag number D2TF-FC...1/2" AND #2 HOLE.
Ford had a gazzion jets and power valves back in the day. Depending on your gas and altitude there I can try to figure out the part numbers of the ones that would work better for you. By chance is the carb's original tag with it's number still on it? Next time you take the lid of the carb off please remove BOTH jets and look for their numbers on the sides. Example "58F". I've seen aftermarket rebuilt carbs with two different sized jets! And the ones in there may be too big. An over rich mixture can wash raw fuel over the spark plugs. Will stall at idle and sometimes restart after that gas has evaporated enough to allow the spark plugs to spark.
I have an old instruction sheet out of a carb rebuild kit. It doesn't list 70/71 truck for some reason but it does list this:
70/71 ford and Mercury cars...390 A/t...Dry float level 7/16" and #3 pump over travel hole.
72 Truck 360/390 engine... A/T...7/16" and #4 hole.
72 Truck 360/390 engine... S/T...1/2 " and #4 hole.
72 truck 360-390 engine...S/t with carb tag number D2TF-FC...1/2" AND #2 HOLE.
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Junior User
Joined: Jul 2015
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Thanks Jefffafa,
Just a quick one before I turn to your plans. Does anybody happen to know what the main difference is between these two seats ?
Autolite 4100 Carburetor Needle & Seat
Motorcraft 2100 2150 Needle & Seat
I pulled the bottom one out, but my rebuild kit came with the top one.
Thanks a lot !
Martin
Just a quick one before I turn to your plans. Does anybody happen to know what the main difference is between these two seats ?
Autolite 4100 Carburetor Needle & Seat
Motorcraft 2100 2150 Needle & Seat
I pulled the bottom one out, but my rebuild kit came with the top one.
Thanks a lot !
Martin