What is my "engine Vacuum tester" telling me ? RESOLVED !

Fri Jul 04, 2014 1:17 pm

Hello to all,
I usually figure out my Cub " problems ( most of the time ) , but this one is a real headache ! My '57 ran great last winter , and have started it several times since , but now , all of a sudden it is "loping" after a few minutes of "run time" , with the first start-up of the day ! Thought it was electrical , replacing dist. cap , rotor , plugs , and switiched out wires , one by one , problem is still their ! I dug out my engine vacuum tester , and like the loping, the needle on the tester moves down (lower on vacuum scale) with the same frequency as the "loping" . I'm guessing a valve issue , with a "full tank" of gas , I'm slow on doing a compression check and removing the top sheet metal !
Why all of a ssudden now , no problems this Winter with all of the snow plowing , any suggestions would be appreciated, Lee Petrie, Joliet, IL.
Last edited by Lee_Petrie on Mon Jul 07, 2014 6:27 pm, edited 1 time in total.

Re: What is my "engine Vacuum tester" telling me ?

Fri Jul 04, 2014 1:19 pm

what is the gauge readings?

Re: What is my "engine Vacuum tester" telling me ?

Fri Jul 04, 2014 1:24 pm

Loping is usually fuel or carburetion related. Dump a can of carburetor, fuel line cleaner, in the gas tank.

Web search for vacuum gauge testing charts. Compare your gauge results with the chart.

Re: What is my "engine Vacuum tester" telling me ?

Fri Jul 04, 2014 3:00 pm

Thanks for the replies, "Boss" & Eugene,
The guage is an Allstate (Sears) brand , it looks like about 18 1/2 inches of vacuum, then when the "lope" occures, it drops down to 17, with the timing of a "key wound clock" ( tick-tock) . I'm thinking , 1 cylinder is failing ! Also used my Champion "plug scope" , appears to be an even display of the plugs firing ! IF a plug was fouling , would that cause a drop in vacuum ? ///// I'll try the fuel line cleaner, Eugene , I just hate just "tearing things apart" , then it turns out to be something simple ! Thanks , Lee Petrie

Re: What is my "engine Vacuum tester" telling me ?

Fri Jul 04, 2014 3:37 pm

http://www.secondchancegarage.com/public/186.cfm

Re: What is my "engine Vacuum tester" telling me ?

Fri Jul 04, 2014 5:21 pm

Thanks for the link, Eugene ! Noticed when I was working on the Cub, this afternoon, when I "retarded" the engine , the engine smoothed out , but the retarded exhaust , was VERY noticable in sound ! I alway set the timing on the FIRST mark ( as the pulley turns) , figuring it was the NORMAL advanced setting and the second mark, was TOP DEAD CENTER of the piston #1 ! I also added some of that carb./ intake valve cleaner to the tank, probably takes awhile to start working !
Please correct me if I'm wrong, Lee Petrie, Joliet, IL.

Re: What is my "engine Vacuum tester" telling me ?

Fri Jul 04, 2014 7:47 pm

the first mark is 16 degrees before tdc set it on the second mark

Re: What is my "engine Vacuum tester" telling me ?

Fri Jul 04, 2014 8:28 pm

Hi "Boss",
Guess that is my error, always set it on the FIRST mark to pass the pointer ! This is a battery dist. system on this "57, but I guess by that time , they would all have a dist. !
How far advanced is the second mark, I would think you would surely have to produce the spark, well before TDC ! WHY IS THE FIRST MARK EVEN THEIR ? By the way , it did smooth out when it was 2/3 the way to the second mark, but the exhaust had that "retarded" sound to it ! Thanks for all of your help, Lee Petrie

Re: What is my "engine Vacuum tester" telling me ?

Fri Jul 04, 2014 8:35 pm

First mark to pass the pointer is 16* BTDC, second mark is TDC.
Static time the engine to TDC. Once the engine is running at idle, the timing will advance a few degrees. At full throttle with no load, the advance should be at (or very close) the 16* before TDC mark.

**The above only applies to battery ignition distributors. Cub Magnetos are pegged to 13* advance at all throttle settings.

Re: What is my "engine Vacuum tester" telling me ?

Fri Jul 04, 2014 9:23 pm

what Raymond said.

Re: What is my "engine Vacuum tester" telling me ?

Fri Jul 04, 2014 9:56 pm

A very large thanks for all that helped, with my problem !!
Frankly I got so excited to adjust the timing the correct way, I put my shoes and pants, back ON , went out to the garage , and set the timing the correct way ! Sounds different, but still it has the consent up and down , searching ( very quickly) , but the governor linkage IS NOT MOVING ! I thought someone once said their was a carb "vent hole" that plugs, I'll have to check that out tomorrow ! Again, a big thanks to all on the forum, Lee Petrie, Joliet , IL.

Re: What is my "engine Vacuum tester" telling me ?

Sat Jul 05, 2014 12:54 pm

Add some seafoam to the gas and crankcase. By the time you run some gas through it the upper part of the crankcase will be lubed. The rpms should pick up and smooth out too.

I use seafoam in everything it stabilizes this newer blend of gas too.

Lube the brackets that hold the governor rod with PB Blaster. Make sure the governor rod moves free so it's not frozen.

Using a engine vaccumne tester will show if you have any intake manifold or carb leaks.

Re: What is my "engine Vacuum tester" telling me ?

Sat Jul 05, 2014 2:20 pm

Thanks for the "tips", BigBill ,
That will be my next direction, I usually can figure out my problems , but this issue did me "IN" ! That SECOND timing mark help a lot on the "loping" issues, I think in the past I have set it to the FIRST mark, alway ran like a "sewing maqchine" , smooth and very quiet , at the second mark , the engine is LOUDER with the retarded exhaust "bark" ( and exhaust SMELL), BUT THAT IS WHAT THE BOOK SAID, SECOND MARK !
My second thought , does the inside of the air-cheaner ever plug up ? I replaced the oil in it the CUP , at the bottom , but when I connect the air cleaner hose to the carb., RPM's drop, and it appears to be a LITTLE roughter ( occasional miss at times ) , maybe that filter unit can be taken apart, and washed with gas or solvent !
Thanks for your help, Lee Petrie, Joliet,IL.

Re: What is my "engine Vacuum tester" telling me ?

Mon Jul 07, 2014 1:29 pm

After several days of "trial and error" , my LOPING problem is still their , Carb. cleaner added , plugs , points, cap., rotor , and the wires changed with a subsitute , one at a time , then retimed to the "second mark" ( as the operator manual states), NO BETTER ! I removed the air cleaner hose , at the carb. ( having replaced the oil in the cup, prior ), the engine smoothed out ! I presume the "air adjusting screw" on the carb has to be changed , to off set the air going through the oil in the aircleaner cup ? " IN " is less air , and it does miss more, "out" would give MORE air flow to off set the oil restriction , MAYBE I'm not being able to give that EXTRA air, that is causing in "loping" , and "running RICH "( bad exhaust smell) ?? I thought for a long time , "IN" with the adjusting screw meant less fuel , but appears it means less "air" , to the mixture ! Anymore ideas out their ? Lee Petrie, Joliet, IL.
Last edited by Lee_Petrie on Tue Jul 08, 2014 6:35 am, edited 1 time in total.

Re: What is my "engine Vacuum tester" telling me ?

Mon Jul 07, 2014 3:11 pm

Lee_Petrie wrote:does the inside of the air-cheaner ever plug up ?
Yes

Remove the entire air cleaner. Sit in solvent, parts washer or bucket of kerosene. Periodically shake the air cleaner up and down. Do this for several days. Then remove from solvent, let drip dry, add some oil to mesh to keep from rusting.

Basically, you can not take the air cleaner apart.