48 B model will not run after cleaning idle passages

Kjmarq

Member
hey guys i am having an issue with my 48 b model. after mowing my front field it ran great maybe a little low on power but this was my first time using it for work. it has never idled right since i have had it. it was a non runner at first. had a rebuilt mag from Rudy Calin i did the carb myself but did not do the idle passages at this time. it loped i did lots of reading and it was pulling from the load so i ordered the bits and gaskets and went thru it again. i thought I did a good job this time but now it won’t even run. i tore it apart and re cleaned several times i swear it gets worse each time.

fresh gas from the pumps this week. compression is 110 both sided tried new plugs it has good spark and the same as my d model that runs good. for good measure i tried new points and condenser to rule things out. i had to mess something up readjusted the float level to level with bowl. 38 space 12 space from float to bowl. recheck nozzle and passages. removed oil bath lid no change
any ideas are appreciated. i have done lots of googling but am going cross eyed
 
(quoted from post at 09:52:15 08/12/18) Does it start but not idle?

Actually now it will not start even. That is why I started checking other things like compression, different fuel, plugs and points and condenser. It tries to pop but will not fire. Thank you for the reply. It may be worth mentioning that I also replaced a very hard section of intake hose from the housing to pipe. But since then I have loosened it temporarily to see if the old one was letting air through it enough to let it run from a clogged intake but it made no difference. The timing has not been altered since I installed the mag last year. I could recheck timing to be sure.
 
More than 90% probability that it is carburetor, shoot a little starting fluid in, if starts the other things are OK.
 

I was going to try that today. Thank you if that is the case do you have any idea what I should look for inside it specifically? I am not sure what I did to make it worse it ran well before all this and mowed and bladed the driveway parades and all. I just wanted it to idle better and I seemed to have lost function here.
 
I am not an expert on that carburetor, but would think one of three things, you put it together wrong, you drilled out the passages wrong, or there is crap from the drillings packed somewhere.
 
I assume you removed/cleaned the load nozzle but did you drive it back in all the way? They usually need to be driven a little and should protrude 3/8 - 1/2" into the throat of carb. I just did one for a customer who tried doing his own...put a new nozzle in but did not want to drive on it so it did not even protrude into bore so no fuel for starting. These carbs need full choke for two revolutions and then choke OFF quickly to start. They always pull off the load nozzle to start. If it isn't all the way up...it cannot get start fuel. Make sure and burn clean the spark plug insulators so they are nice and white. Little butane torch works best. Let us know what ya find out. Float level is 3/8" from edge of bowl with bowl inverted. Fuel level is 1/2" down from bowl edge when using the clear tube wet method for actual "fuel" level.
 
Your inquiry is quiet interesting. I would suggest that you seek additional help with your problem. It's not a situation where one can offer an easy explanation of what is going on with your carburetor. Once the parts have been disturbed or modified it could be one problem or combination of several problems.
 

Thanks for the reply with some information. I believe I did have it seated up but with your description it sounds like a culprit I will try to get out there and look tonight and get back.
 
(quoted from post at 21:54:37 08/12/18) I assume you removed/cleaned the load nozzle but did you drive it back in all the way? They usually need to be driven a little and should protrude 3/8 - 1/2" into the throat of carb. I just did one for a customer who tried doing his own...put a new nozzle in but did not want to drive on it so it did not even protrude into bore so no fuel for starting. These carbs need full choke for two revolutions and then choke OFF quickly to start. They always pull off the load nozzle to start. If it isn't all the way up...it cannot get start fuel. Make sure and burn clean the spark plug insulators so they are nice and white. Little butane torch works best. Let us know what ya find out. Float level is 3/8" from edge of bowl with bowl inverted. Fuel level is 1/2" down from bowl edge when using the clear tube wet method for actual "fuel" level.

So I tried again and the nozzle was not as far as it could have been. Tapped it up until it looked like a 1/2 was sticking out and reset float level to 3/8 with bowl upside down. Put it back on and tried again it pops a lot back thru the carb so I opened the needles so more and that is all I could get out of it. Battery is weak and my arms as well. Any more ideas? There is not a lot to these and it’s whipping my butt. Needle settings are about 1 turn idle and 2 turns about for load. Close to where it liked it before but still nothing . Cleaned my first set of plugs and tried my new set again that it never ran on.
 
Sounds like the plug wires are backwards at the magneto cap since it's backfiring through the carb. Try swapping the plug wires around at the cap. You might have the mag 180 deg off.
 
Well,don't quit yet. I was just getting started and you fixed one item, now for some more info. Popping and backfiring is also caused by worn throttle shaft and bushing. If you can feel any slack sideways on shaft , it's too much. Also, I'm 90% sure your throttle blade is worn out also. Take it out and look at bottom. you will see a pronounced "step" worn on bottom and that lets the whole blade sit down lower and leak air all around the top. Unmetered air causes lean mixture because engine will not suck fuel up the 6" it has to to get fuel from bowl through idle circuit. I've heard them sound like a shotgun out exhaust sporadically just from worn shaft/bushings sucking air. You can usually feel a step worn on shaft by running a fingernail over it. Most re-builds need Throttle shaft , upper bushing , throttle plate and BOTH bushings need pushed all the way in so they protrude into the bore a little and then ground back to bore contour with a die grinder. This will keep air from leaking under the plate right at the bushing itself. You will need a 3/8 reamer ( or file it) to ream the bushing back to size after install . Also, I have yet to build one that idles great with anything less than 1 1/4 to 11/34 open on idle needle. You also have to realize that to set idle needle on these you have to have the tractor wide open throttle which is "fast idle" and is still using just idle circuit. Going down the road in 6th wide open is still JUST using idle circuit so wide open is where you set needle. Here is the drill...open idle needle 2 turns , load needle 1 turn...start tractor and warm for few minutes and then thew throttle wide open...while at that speed, close load needle all way, it should not even falter..if it does or quits..your carb needs drilled out and or the above mentioned wear parts replaced. Assuming that you have those parts replaced and the tractor stays running at fast idle with load shut , now slowly , a few clicks at a time, start closing idle. 1/8 turn and wait 5 seconds, 1/8 turn and wait and so on UNTIL you sense the slightest change in sound or smoothness or if tractor stops. At that point, open idle up 1/4 turn from where it faltered or stopped. Idle is now SET. Leave it alone. Open load back up 1 turn and start tractor back up. From idle, thow open throttle lever quickly. It should accelerate right up to fast idle with out hesitation and with just a whif of dark in exhaust. if it hesitates, open load 1/4 turn until it accelerates cleanly. Now they are both set correctly. leave them alone. Another note..the start procedure on these is as follows..cold or warm , close choke all way , from idle position, move throttle lever slowly until the wide open stop on top of carb just sits on the stop pin. Now hit starter and after two turns, open choke all the way quickly. Don't let off starter until it starts it will start the quickest this way. It has to have choke to pull start fuel from main nozzle to get it going. I have built hundreds and tested every one of them and this is how they start best every time.
 

Thanks so much for all your help. When I originally rescued this tractor the carb was a complete ball of rust. So after scraping and cleaning and days in the electrosis bath I cleaned the passages besides the idle ones with the bits from Roberts carb the other day. I ordered a complete rebuild kit with new bushings, shafts and throttle blade. I cleaned and reused the original nozzle and needles as they survived well. I also replaced the float and needle and seat. It ran and started well the whole year until I messed with it the other day. I will closely look at the blades again and shaft as well as try the needle settings you suggested. the gasket kit I got had new felts as well that I used on throttle shaft to hopefully take up the space that could go around the blade itself.

Thanks again. I just don’t understand what I’ve done when it ran so well. I will try to get the fittings and hose to do the fue level check you suggested.
 

It’s worth mentioning that I did have to reuse the choke plate when I repaired/rebuilt the carb a year ago. It seems to fit very tight and will slow the engine down while cranking marginally but enough you can hear it labor more. I did move the bushings to the inside for the throttle a lot and used a felt to help give it a more airtight around the blade with the new kit so that is different from my original repair when it ran. To clarify I cleaned and repaired it intially but it wouldn’t idle so I got the bits and a new gasket set and that is where the story here begins. I will try it again tonight with the new info.
 
worn bushing/misaligned choke plate/etc will not keep the tractor from running...however clocked primary circuits will as fuel will not feed from the well to the idle passage. Your tractor has one idle passage and is a tiny hole behind the throttle plate. Actually most light use only requires the tractor to run on the idle passage then when carb opens significantly the fuel comes up the main jet...I would suggest you look at diagrams of the jetting....get you some fine wire ...torch out the brass plugs...there a video on this and clean out all those passages...cleaning up a clogged carburetor is not easy...I've cleaned then several times before getting all the debrie out....
 

I will double check these. I found some diagrams as well as repair reference deal on the marvel shebler carbs with a few different models, lots of info. Thanks
 

Update, I rechecked the shafts again and plates. Very tight and no real slop to speak of. I also checked the float level as well as installed a fitting a clear hose to represent the gas level in the bowl as I have seen in some pictures and videos. It was very low so I adjusted it again to a little less than 3/8 and the gas level rose to maybe a little over 1/2 inch and tried to start it seems to have stopped backfiring and has several pops In a row but will not quite take off. I think we are on to something here. New question what is considered normal for the gas level to fluctuate in the tube as it’s trying to start it moves up and down and when it’s higher it tries to fire it seems but then drops to low and quits until the process starts over. Will not quite go. I have good flow from the metal tube to the bowl and I can blow thru the inlet fitting in the bowl and raise and lower the float and stop the air flow and let it go as I move it. Is there something else I need to look at or adjust the float more to raise the fuel level. Seems simple enough but I don’t want to overdue it and flood
It or break the float. Again thanks to all those who have taken interest in this and I have enjoyed learning about this.
 
Just another note...when you check fuel level with the claer tube...you cannot get an accurate read with tractor running! Same as trying to drain fuel bowl with tractor running...it will just dribble and when tractor is shut down..it will run out twice as fast. There is slight suction on bowl when running. You must check fuel level with engine off.
 
(quoted from post at 22:11:00 08/15/18) Just another note...when you check fuel level with the claer tube...you cannot get an accurate read with tractor running! Same as trying to drain fuel bowl with tractor running...it will just dribble and when tractor is shut down..it will run out twice as fast. There is slight suction on bowl when running. You must check fuel level with engine off.

So I have the fuel level 1/2 from the mount gasket. Rechecked passages and tried suggested needle settings. Still no changes. Another question for Randy. There is a hole in the top of the nozzle larger than the others and there is a hole in the carb body in the front that looks like it should line up with that hole. Is that a suction hole and my issue ? I am going to try to see if I can line it up when I reinstall it and see if it helps any. Thanks.
 

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