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10T502 Leakdown question

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10T502 Leakdown question

Postby KE4AVB » Mon Oct 15, 2018 3:01 pm

I know I should know this but just got a leakdown tester. What is a normal % of leakdown considered to be max leakage that still indicate a good cylinder? The 10T502 I working has been eating dust for a while and has a 35% leakage rate pass the rings.. It seem that I remember reading that 20% was considered the max allowable. Of the SM is setup using the Briggs tester and and the one I got only needs 12 psi instead of the high pressure that the Briggs unit uses to set the gauge.

Now when I pull the head the piston is covered in wet oil on the carbon and the cylinder has quite a bit wear. Now it might just might be that diaphragm on the carburetor may be sucking excess fuel too as it emmitting black exhaust. Its diaphragm is pull in at the one of the fuel pump flaps so that may that source of the problem.

Just looking a for some thoughts as it has about 5 yrs since I work on a L head push mower
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Re: 10T502 Leakdown question

Postby bgsengine » Mon Oct 15, 2018 3:32 pm

nice thing about those L-heads , they are so robust - it can probably run for a couple more years even in that condition, long as oil is kept full and carburetor maintained... but it gonna be a skeeter smoker... probably won't have full power either.. But yeah 20% is about the max for a "passes as good" test .. 35% would put it in the "yellow" (warning) zone as a bit excessive,but they can still run pretty good.. Wouldn't fly quite as well on an OHV with emissions carb though..
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Re: 10T502 Leakdown question

Postby KE4AVB » Mon Oct 15, 2018 5:21 pm

Well I got it back together and it is definitely running rich. I didn't see anything internally wrong with the carburetor that is on it but may have been switched recently. I think I order a new carburetor for the engine hopefully no one has changed the tin out and give it a try. It more blackish puffs out of the exhaust but takes a keen eye to see it. It definitely not oil smoke.

A kinda strange I never had one these engines to ever run rich. It got an all plastic nozzle and not one those that has the metal jet that gets lost.
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Re: 10T502 Leakdown question

Postby bluemower » Mon Oct 15, 2018 6:02 pm

After reading your comments, I watched the briggs training on the power portal.

The acceptable leakage per B&S is 10 - 40%.
With 100 psi applied, the leakage would drop pressure to a range between 60 - 90psi.
the briggs tester has a .040 orfice.

Previously, I examined a 2 month old DR roto tiller in which the owner removed the air filter. Definitely turned this into a smoker.
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Re: 10T502 Leakdown question

Postby bgsengine » Mon Oct 15, 2018 9:47 pm

KE4AVB wrote:Well I got it back together and it is definitely running rich. I didn't see anything internally wrong with the carburetor that is on it but may have been switched recently..

Pulsa-Prime carburetor right? awfully common to find them with warp (like the air cleaner bases - overtightening screws , and tightening them in wrong sequence) You are familiar with the gas tank repair kit for the older style pulsa-jets right? about the same spot you may find the carb, the tank , sometimes both, may get a bit warped - have had a 75% - 85% success rate using a double gasket to solve that issue - fuel leaks up and seeps past the throttle shaft - worse when the air filter is "cloggy" (too much oil, filter failing, or just plain dirty) have also had - just once - one where it was actually somehow feeding extra fuel through the primer circuit.. never did figure out that one - it didnt make sense, gas capo was clear so tank couldnt be pressurized, should not be any sort of vacuum before the venturi (but a "weeks later" theory came to mind that maybe just a bit of damage to the primer port where fuel squirts in , might have caused it to get a low pressure point effect much like blowing across a straw in your water glass) Then there are the ones where gasket and diaphragm are incorrectly assembled..
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Re: 10T502 Leakdown question

Postby KE4AVB » Tue Oct 16, 2018 9:20 am

Tnx for tips.

I pulled the carburetor/tank again this morning as I found a core carburetor to work with. Quite obvious it was warpage when I look at the new gasket impression. It was between the two mounting screws under the outlet of the carburetor, just about .003. warpage was not from over tightening but appears to be from plastic shrinkage over the last 9 years.

So I change the venturi and nozzle out and install the replacement carburetor then I did a test start and the over richness is resolved but still had a slight governor hunting. Considering the 35% leakdown it is to be expected. That might be resolved when I install a new air filter as the old filter has crumble away as it is that rotten.

Looks like instead of the fuel going though the throttle shaft it was going up through the vacuum port for the pump section of the diaphragm.
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Re: 10T502 Leakdown question

Postby creia » Tue Oct 16, 2018 6:41 pm

bgsengine wrote: You are familiar with the gas tank repair kit for the older style pulsa-jets right?

Brian,
Can you please tell me about this? :o On almost every old Pulsa-Jet carb/tank that we take apart and restore on these 1960's and 1970's engines the CARB is warped at the 3 projections where the screw holes are. I have been truing the base of the carbs at those locations using a Dremel tool with a tiny grinding wheel and a straight edge (feeler gauge). If I DO this I have a 100% success rate that it will NOT leak. If I do NOT it is about a 75% that it WILL leak.
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Re: 10T502 Leakdown question

Postby bgsengine » Tue Oct 16, 2018 8:33 pm

creia wrote:
bgsengine wrote: You are familiar with the gas tank repair kit for the older style pulsa-jets right?

Brian,
Can you please tell me about this? :o On almost every old Pulsa-Jet carb/tank that we take apart and restore on these 1960's and 1970's engines the CARB is warped at the 3 projections where the screw holes are. I have been truing the base of the carbs at those locations using a Dremel tool with a tiny grinding wheel and a straight edge (feeler gauge). If I DO this I have a 100% success rate that it will NOT leak. If I do NOT it is about a 75% that it WILL leak.
Michael

grab a copy of the antique engine service manual from briggs.. page 35 of section 3 near the bottom..
Briggs service manual wrote:Repair kit #391413 may be used to repair Pulsa-Jet
fuel tanks which are not flat. Install roll pin and Teflon
washer as shown in Fig. 235.


Pays to read the manual, eh? :)
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Re: 10T502 Leakdown question

Postby creia » Tue Oct 16, 2018 9:05 pm

Thanks Brian - I just read it. That addresses a different problem than I have experienced. On our engines, the TANK top surface HAS been flat. It is the base of the CARB that is always warped. The 3 perimeter "ears" that protrude from the carb base are always bent down slightly so those areas make contact (and seal), however, the middle area between the 3 ears of the carb base where the screw holes are does not.Even with 2 gaskets it would still generally leak.
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Re: 10T502 Leakdown question

Postby bgsengine » Tue Oct 16, 2018 9:54 pm

creia wrote:Thanks Brian - I just read it. That addresses a different problem than I have experienced. On our engines, the TANK top surface HAS been flat. It is the base of the CARB that is always warped. The 3 perimeter "ears" that protrude from the carb base are always bent down slightly so those areas make contact (and seal), however, the middle area between the 3 ears of the carb base where the screw holes are does not.Even with 2 gaskets it would still generally leak.
Michael
Yeah and it is more common on the horizontal shaft engines, which I assume you work with mostly.. that happens primarily from people being a little too ambitious with their screwdrivers - really outta be an inch-pounds torque screwdriver handy , you'd be amazed at the "feel" for those low torque specs compared to how tight you can get them by "guesswork".. I experimented with that long ago just to see, and with some of those ergonomic grip torx screwdrivers, I can actually achieve a little over 200 inch-pounds of torque through hand/wrist/forearm strength... and just what might normally "feel" tight , usually comes in at around 50 inch-pounds (compare to the common spec of around 15-20 inch-pounds) so it is kind of understandable at *why* so many of those things get over-torqued causing warpage... but it is still no excuse.. :)
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