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| Carter YF 938SC; Going through the Carter carburetor | |
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| Tweet Topic Started: Aug 11 2011, 09:35 AM (3,880 Views) | |
| skiprocks | Aug 11 2011, 09:35 AM Post #1 |
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New to the group. My current project is a 61 CJ5, F134, Carter YF 938SC. No, it's not a 3B, but if I'm not mistaken everything under the hood is similar. Modifications are a 6V to 12V upgrade and solid state ignition distributor. I've had the CJ for three years, and it has taken nearly that long to get it home to FL. It runs too rich. The exhaust burns my eyes. When it coasts without a load (e.g. rolling up to a stop sign or stop light) I get multiple small backfires. The worst thing is that they scare my dog and she won't ride with me anymore. I have a new, remanufactured carburetor - same model - that came with the vehicle when I bought it. It's still in the box. The previous owner purchased it through Walck's about five years ago, couldn't get it to run right and put the original Carter back on (which is what's on it now). I tried the remanufactured one as well with similar results. I've read through multiple postings on this site, the early CJ5 page and willys tech. What seems to be a common thread is that some of the remanufactured carburetors just weren't set correctly and sometimes had incorrect components installed. I've searched for just about everything I can about the Carter YF and if there's a common theme, it's this. When everything is "JUST RIGHT" it's an awesome carb, but there are a myriad of things that prevent everything from being "JUST RIGHT" I've downloaded just about everything I can find which includes: 1) Carter Carburetor 1949 Service procedure for the YF downdraft carburetor 2) Carter Carburetor Corp document for the CJ3B YF down-draft carburetor 938S that includes specs, adjustments, etc. 3) A really good period article for International trucks with the Carter YF - yes, a different model, noticeable differences are in linkage (but I'm sure there are more) - I like this one because there are some good explanations, not just a schematic. 4) last but not least a very helpful article found on this website that Ken appears to have written - it's "in process" but seems pretty comprehensive and detailed to me. My plan. I'm going to take the remanufactured carburetor completely apart, inspect each component, clean if necessary (it looks brand new but has had fuel in it twice), and put it back together and try it out. If anyone has any other suggestions and by that I mean a step-by-step tear down & rebuild manual, I'm game. Or any other suggestions for that matter. Perhaps I should have mentioned, my Willys rebuilding persona better fits a cutting torch, crow bar, ball peen hammer, grinder and welder than the teeny tiny parts in this carb. Thanks in advance Skip |
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Skip Owens 1961 Willys CJ5 - F134, older restoration 1961 Willys Pickup - L226, 2006-8 frame off restoration 1930 Ford Model A Coupe NE Florida | |
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| jyotin | Aug 11 2011, 04:44 PM Post #2 |
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More than likely you have a freshly remanufactured YF carburetor with the wrong float valve. If you get the correct float valve, my guess is that it'll run fine. The YF that is 'rebuilt' by a rebuilder has been rebuilt as a generic YF, but the jeep version of the YF takes a special float valve. The aperture is smaller as well as the construction of the valve. Only place I know of to get the correct valve is www.thecarburetorshop.com good luck j |
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It's just my luck that something good is going to happen to me today. 54 - 3B - down on the farm 67 - cj6 - former state of Alabama vehicle ?? - cj5 T98a - made from spare parts - Ford tractor blue ?? - cj5 T98a - made from spare parts - Jeep green | |
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| skiprocks | Aug 11 2011, 05:34 PM Post #3 |
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Thanks, that's one of the issues I'd noticed that pops up the most in threads - the wrong parts are used in the rebuild. This one was remanufactured per the invoice - don't know where - and sold through Walck's, but that's just what the invoice says. - Skip |
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Skip Owens 1961 Willys CJ5 - F134, older restoration 1961 Willys Pickup - L226, 2006-8 frame off restoration 1930 Ford Model A Coupe NE Florida | |
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| oldtime | Aug 11 2011, 08:10 PM Post #4 |
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Skip, Welcome to the CJ-3B Bulletin Board ! Backfiring is not specifically a carburetion issue. Yet malfunctioning carburation can certainly help to induce backfiring. Backfiring normally but not always manifests from an incorrect timing issue. This can be either the ignition timing and or the valve timing. Not to put you or anyone else down... Yet many frequently find fault with the Carter YF. Perhaps this is simply besause they do not fully comprehend its myriad of seemingly complex functions. Not to worry... carburetion is mearly the physical science of metering fuel to control the charge. If you have not done so... I suggest that you follow the factory specified tune-up sequence. The carburetor is generally the final issue of the complete tune-up sequence. |
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Currently building my final F-134 powered 3B . Rock Crawler using factory parts from the Willys Motors era (1953-1963) http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new | |
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| skiprocks | Aug 12 2011, 07:33 AM Post #5 |
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Oldtime Youv'e certainly nailed that one on the head - I ABSOLUTELY don't fully comprehend the myriad of seemingly complex functions on the F-134. What I do know about the F-134 (and L-226) has been gleaned from the various tech sites, books, manuals and then - of course - actually working on them myself. I completely rebuilt the Flathead L-226 in my Willys pickup, but I've only changed the oil and cleaned the F-134 to date. I'll provide some more info for everyone. This F-134 has an electronic ignition comprised of a Street Fire multi-spark ignition unit & coil (ignition unit mounted on the firewall) as well as a solid state ignition distributor. The Street Fire was mounted on the vehicle when acquired, the distributor is new - acquired from Kaiser Willys by me (don't ask what happened to the distributor that was on the F-134 when I bought it) :-( I may be oversimplifying things here, but the specs that came with the distributor state that there is no timing necessary once installed correctly - which I'm pretty sure I did. As for the valves, I'm absolutely unsure. I do know that the previous owner had the engine gone through by a shop in 2005. The paperwork includes valve replacement and there are less than 700 miles on the odometer since the engine work was done. What I do know is that when the F134 runs with the existing Carter YF 938SC, the engine runs well with no missing, but the exhaust smells of unburned fuel, burns my eyes and backfires in the muffler when not under a load. When I pull that carburetor and install the "new" remanufactured Carter YF 938SC it hardly runs at all. The previous owner had the same issue with both carburetors - that's why he reinstalled the original after purchasing the remanufactured unit. Following my own albeit circuitous deductive cycle, I'm fairly certain that there is a problem with the remanufactured carburetor and that's what I've set my sights on now and will tackle this coming weekend. One of my concerns there is that I won't be able to tell if one/any of the components that were installed when it was rebuilt are correct or not. I hope it's a setting that is off. In the end I may end up pruchasing a rebuild kit for the remanufactured carburetor if I can't identify the issue. |
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Skip Owens 1961 Willys CJ5 - F134, older restoration 1961 Willys Pickup - L226, 2006-8 frame off restoration 1930 Ford Model A Coupe NE Florida | |
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| jyotin | Aug 12 2011, 08:22 AM Post #6 |
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If the jeep is running too rich, then it is carburetion. If the jeep is backfiring it could be timing. Is it backfiring through the tail pipe or the carburetor? If it is through the tail pipe it could trace back to carburetion. A backfire is created when fuel is burning where it isn't supposed to burn. Now, if the spark causes the backfire it is timing, but if the heat from the exhaust system causes excess fuel to burn that is not necessarily timing. I'd start with the carburetor and make sure it is working properly. Once done, then you could check timing. Doing it the other way 'round would be adjusting timing with excess fuel floating/bouncing around. Another option is to borrow a known good YF and install it. See how it runs and which problems disappear after install. |
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It's just my luck that something good is going to happen to me today. 54 - 3B - down on the farm 67 - cj6 - former state of Alabama vehicle ?? - cj5 T98a - made from spare parts - Ford tractor blue ?? - cj5 T98a - made from spare parts - Jeep green | |
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| oldtime | Aug 12 2011, 08:44 AM Post #7 |
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Skip, What specific article did you find by "oldtime" ? I can possibly answer all your questions concerning the YF 938 SC but my guess is that it may not correct the described condition. I still encorage you to procede with a strategized tune up sequence. "Knowing" the Jeeps condition is paramount to diagnostic repair. A strategized tune-up sequence can be specifically oriented toward the condition of backfiring combustion. Information gleened from the tune-up will assist in detecting the source of the backfire. So I ask what do you presently prefer ? Strategized tune-up or carburetor rebuild ? |
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Currently building my final F-134 powered 3B . Rock Crawler using factory parts from the Willys Motors era (1953-1963) http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new | |
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| skiprocks | Aug 12 2011, 10:01 AM Post #8 |
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Oldtime Thanks for your quick reply - I may make progress this weekend yet! The article is titled "How to Rebuild your Carter YF". To answer your second question - BOTH! :rolleyes: 1) first, a strategized tune-up is obviously in order - (Willys must run) and 2) I've got a remanufactured carburetor that doesn't work and needs to. Based on your comments I recognize now that a comprehensive tune-up sequence should be given priority. Suggestions? |
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Skip Owens 1961 Willys CJ5 - F134, older restoration 1961 Willys Pickup - L226, 2006-8 frame off restoration 1930 Ford Model A Coupe NE Florida | |
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| oldtime | Aug 13 2011, 04:42 PM Post #9 |
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NOTE: The following is not a complete tune up but rather it is oriented toward detection of a backfiring condition. The first thing is to pull each spark plug for visual inspection. Post pics of each one if possible or be able to detail the observed condition of each one. Specify plug make, number and gap.... Specify the exact condition of each spark plug ... Wet, dry, carbon soot, oil film, porcelin cracks, porelin blistering, porcelin coloration, electrode burned etc.? Secondly perform a compression test on all cylinders with all spark plugs removed. By using the starter motor cycle the pistons 4 strokes for each cylinder. Record the pressure of the 1st and the 4th stroke for each cylinder bore. QUOTE: A] When pressure quickly comes up to specified pressure and is uniform between all cylinders within 10 psi; it indicates that the engine is operating normally with satisfactory seating of the rings, valves, valve timing, etc. B] When pressure is low on the first stroke and builds up to less than specified pressure (120 to 130 psi); it indicates compression leakage usually attributed to rings or valves. To determine which is responsible, pour 1/2 oz. of tune-up oil into each cylinder. Allow a few minutes for the oil to leak down past the rings and then again test compression. If compression pressures improve over the first test, the trouble is probably worn piston rings and bores. If compression pressures do not improve, the trouble is probably caused by improper valve seating. If this condition is noticed on only two cylinders that are adjacent, it indicates that there is a possible gasket leak between those cylinders. If inspection of the spark plugs from these cylinders disclose fouling or surface cracking of electrodes, gasket leakage is probable. C] When pressure is higher than normal it indicates that carbon deposits in the combustion chamber have reduced the size of the chamber enough to give the effect of raised compression ratio. This will usually cause pinging under load that cannot be satisfactorily corrected by timing. The carbon must be cleaned out of the engine to correct this trouble. The third tune up item concerns adjusting the valve tappets. Adjust all valves with the engine cold. Intake = .018" Exhaust = .016" I suggest you use a flat feeler gauge and the gauge should be a snug fit with the cam lobe setting on its heel. (lowest point) Realize that you cannot see the camshaft to determine its exact position. So how do you know if the tappet is on the exact center of the lobe heel ? I use a technique that I call "the opposing valve technique". The techique can determine when any particular valve is fully closed and the tappet on dead center of the camshaft heel. The #1 and #4 cylinders are exact opposites, also the #2 and #3 cylinders are exact opposites. You cannot see exactly when a valve is fully closed but you can definately see when any valve is fully open. You can look at the #1 exhust to deternine the position of the #4 exhaust and so on and so forth. If 1# exhaust valve is fully open then you deduce that the #4 exhaust must be fully closed. Please record the existing tappet clearances for all 8 tappets. More to follow........ |
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Currently building my final F-134 powered 3B . Rock Crawler using factory parts from the Willys Motors era (1953-1963) http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new | |
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| Ian's AC 3b | Aug 13 2011, 10:03 PM Post #10 |
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Keep coming with the responses Ken, you are excellent and I am learning more from this than the service manual.
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J.I. Fraser, Nova Scotia, Canada 1956 Cj-3b originally a airport belt loader, second owner 2008 Patriot ltd. daily drive Selling as soon as new muffler installed 2016 Cherokee North uptrim 1952 Dunbar Kapple trailer with a 2013 frame Past: 1952 M38 Canadian ( basket case) | |
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| skiprocks | Aug 14 2011, 08:00 AM Post #11 |
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Oldtime First and Second suggestions completed. Will post results later after cleaning up. |
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Skip Owens 1961 Willys CJ5 - F134, older restoration 1961 Willys Pickup - L226, 2006-8 frame off restoration 1930 Ford Model A Coupe NE Florida | |
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| skiprocks | Aug 14 2011, 12:28 PM Post #12 |
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FIRST Pulled the spark plugs![]() All four NGK R BR6S plugs look good. Gap on all four plugs is .030 Note: these plugs are new and have less than 3 hours (100 miles???) on them. SECOND Compression test Warm engine, FIRST compression strokes #1 70 #2 70 #3 70 #4 72 Warm engine, FOURTH compression stroke #1 125 #2 125 #3 123 #4 125 So far so good it would appear. Need a cool engine to check the valves. ... So you want me to pull the exhaust manifold eh? ... please say it ain't so Shane |
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Skip Owens 1961 Willys CJ5 - F134, older restoration 1961 Willys Pickup - L226, 2006-8 frame off restoration 1930 Ford Model A Coupe NE Florida | |
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| skiprocks | Aug 14 2011, 04:21 PM Post #13 |
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As I had time on my hands today I played battleing carburetors. I removed the original carb (again) and replaced with the remanufactured carb (again). Definite differences. Original carb: Runs rich, exhaust smells, burns eyes, etc. Note: I read in one of the posts on here that when you turn the idle adjusting screw all the way in, the engine sputters (it does), and when you turn the idle adjusting screw all the way out, the engine sputters (it does not). Which suggests according to that post that there is some form of internal fuel leak. Also, the original carb has been on the engine for a long time. Remanufactured carb: Runs decidedly worse than the original. Appears to be a miss just about all the time (engine ran smooth with the original carb). Never took it over 35mph because I was afraid to leave the neighborhood with it, but it ran better under a load than when idling or coasting. Regardless of the tuneup outcome on the engine, I know I still have a carburetor issue. Attaching a photo of my "dual" carb setup
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Skip Owens 1961 Willys CJ5 - F134, older restoration 1961 Willys Pickup - L226, 2006-8 frame off restoration 1930 Ford Model A Coupe NE Florida | |
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| oldtime | Aug 15 2011, 10:21 AM Post #14 |
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Those are resistor plugs of the correct standard heat range. I cannot see the color but they look to have a light coating of black soot on all 4 of them ? I suppose they all look the same ? Yes / No ? Yes your compression tests indicate the rings and the valves to be in very good condition. Those numbers appear to indicate a standard 6.9 compression ratio head. Excepting the tappet adjustment you have ruled out valve issues as a possible cause of the backfiring. Do not remove the exhaust manifold to check the tappets. Remove the side valve cover to access the exhaust and remove the rocker cover to access the intake valves. While your in there retorque the head bolts to specs. (60 to 70 ft. lbs.) We will address the carburetor issues as need be following proper sequence. |
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Currently building my final F-134 powered 3B . Rock Crawler using factory parts from the Willys Motors era (1953-1963) http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new | |
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| skiprocks | Aug 16 2011, 07:47 AM Post #15 |
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The valves are adjusted. The were actually all set properly with the intakes at .018" and the exhaust at .016". In the CJ-3b Specs and Tech Tips section - "More Engine Tech Tips - Valves & Camshafts" was very helpful. It's worth a read and having a copy with next to the manual on the fender as you go along. It actually took longer than I anticipated last night and I didn't get things battened up until the wee hours of the morning, but it was a simple and straight forward job. Having done it once I could do it again in 1/3 the time. If anyone has been following along here, Oldtime is correct in an earlier submission on this stream - you don't have to take the exhaust manifold off to adjust the exhaust valves. Having said that, if you're like me and have never adjusted the exhaust valves on an F-134 before, it might be worth your time to do so. Given limited access I was progressing by touch more than sight and as both the evening and my frustration level progressed I finally decided to remove the manifold. (Note: I was lucky, while this engine was rebuilt 6 or 7 years ago, it hasn't seen much use and the manifold nuts backed off easily enough. The parts box that came with the Willys included a full gasket set which has been an added benefit). I also suggest you take note of the throttle linkage before removing from the access panel. I did and still managed to put it back incorrectly. There is a suggestion to run a compression test after adjusting the valves. I didn't do that last night. Primarily because it was very late and I'd have heard about it if I'd started the Willys up, but also because the valves didn't need adjusting. |
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Skip Owens 1961 Willys CJ5 - F134, older restoration 1961 Willys Pickup - L226, 2006-8 frame off restoration 1930 Ford Model A Coupe NE Florida | |
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Keep coming with the responses Ken, you are excellent and I am learning more from this than the service manual.

7:39 PM Jul 10