OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Briggs & Stratton Fuel pump leaking oil

HI all,
Frequent reader but first time poster - can't find any similar problems/solutions on the forum!

I've got a Sentinel ride on mower with a replacement B&S 12HP motor. There is a round black device attached to the engine body, which I believe to be the fuel pump, which operates on vacuum, yes? Three hoses, one from the fuel tank, one to the carby, the third from the oil dip stick shaft.

The fuel pump seems to be spitting oil from the mesh screens on the pump. I've also noticed recently that the engine won't run smoothly. It tends to cycle up and down. Will idle for a second, then revs drop off, until it almost stalls and then revs up again. The speed of the cycle depends on the throttle - low throttle, slow cycle, high throttle, faster cycle. This is more pronounced when the engine is cold, and seems to improve once the engine is warm. Cold start is difficult, unless the throttle is way down.

I'm thinking either there is too much pressure in the sump, pushing oil up and reducing the effectiveness of the pump, hence fuel starvation in spits and spurts.

Does this sound right? Any other thoughts?

Hi Pinelli, welcome to Outdoorking.

Please post the Model, Type and Code numbers for your new Briggs. These numbers have traditionally been stamped on the cooling air cowl, but may be somewhere else on a new Briggs. The whole series of numbers will be together in a group. Some pictures of the engine, including the problem area, would also be very helpful.

If the engine is new, the first port of call for both problems (leaking oil, and hunting) should be the dealer you bought it from, since it should be under warranty.

So far as the oil leak from the fuel pump area is concerned, I won't comment until I see the pictures. I'm used to Briggs 12 hp engines being side-valve with gravity fuel feed. At this point I don't know whether yours is side valve, or a Vanguard, or an Intek.

The cyclic speed variation you have described sounds like "hunting", which is nearly always caused by lean mixture, though it can be due to mechanical friction in the governor mechanism, such as a governor link rubbing against some other part of the engine. However because you obviously have a fuel pump malfunction, I suspect the two problems are linked: the fuel pump may not be delivering enough fuel. Anyway, let's see the pictures and check out the engine model - then we'll talk about it from there.

One reason why we need the model information is that if it turns out your engine is an Intek, there is a good chance that it has a blown head gasket like so many other Inteks. This could be pressurising the crankcase, which is connected to the fuel pump diaphragm by the vacuum pulse hose that operates the fuel pump. With positive pressure on the diaphragm, the pump will not work well, and with pressure in the crankcase, there is likely to be air and oil coming through the pulse hose rather than just air.

Thanks Grumpy,
It is indeed an Intek, 15.5HP, in fact. Not sure about Model type and code numbers. I found this on the cowling:
Family BBSCS.5002VP 278021

Engine isn't really that new, newish compared to the 12 yr old mower body. Engine is probably about 2 yrs old, maybe 3.

Is that any help?

It seems highly likely the engine has the Intek disease, Pinelli (blown head gasket). We need a way to confirm that it is blown. You may be able to check this by removing the oil filler cap with the engine running, and seeing whether it is puffing out air and oil spray with a fair amount of vigour. Note though that the fuel pump won't work with the filler cap removed, so you will have to do this in less time than it takes the carburetor float bowl to empty. If it seems to be puffing, you could probably confirm the problem with a compression test. Also, look at the breather system: if oil is passing through the breather into the carburetor air intake, that is another sign of blow-by, which in the case of an Intek is nearly always due to gasket failure.

Inteks usually blow the head gasket from the combustion chamber into the pushrod cavity. The damage is not always visible by looking at the gasket, cylinder head, or top face of cylinder, unfortunately. There is a good chance that replacing the gasket - carefully - will cure both your problems though, if you find supporting evidence of leakage and/or crankcase pressure.

Cheers, I'm fine to do all those. What sort of pressure should I get on a compression test?

Am I best off getting a replacement gasket from a dealer, or will eBay be alright? How much approx am I looking at?

The Intek has a decompressor (yes, a nasty one that causes tappet adjustment to be extremely sensitive or it doesn't work and many people burn out their starter motor before they figure out what is wrong) so the compression pressure should be something less than 100 psi, but I think more than 80 psi. Listen for leakage if you can.

I think getting a genuine Briggs gasket would be the best bet, just because even genuine ones frequently don't work, so an el cheapo would be adding insult to injury.

Okay, haven't done a compression test yet, but did the dipstick thing and got a little puff of smoke when I pulled it out. Also a clear positive pressure coming out of the dipstick, and finger covered in oil when putting it in the tube. I'll check compression in the morning.

Head gasket I can deal with. Rings and valves are a little more complex.

Do you know if these engines are sleeved?

The Intek arose as a Briggs redesign of the Vanguard (which was a Daihatsu design) to make it cheaper and easier to make. The Vanguard was a successful design, and I believe it is sleeved, but what Briggs did to the Intek I don't know (most likely it's sleeved like the Vanguard). Aside from its remarkable propensity to blow head gaskets, there are two other main distinguishing features of the Intek. First, their air filter doesn't work, and they frequently become dusted early in life. The problem was that the plastic filter box didn't clip together properly, so the filter element was bypassed. Recently Briggs redesigned the filter box. The second problem was the decompressor, as I mentioned in an earlier post in this thread. The tappets need to be adjusted to minimum specified clearance: just 0.0005" more than that is likely to disable the decompressor, with disastrous results (it is a race between the wiring harness and the starter motor for which burns out first, but most tenants don't stop when the first fails, and soldier on until the other burns out as well - a few diehards burn out several starters). So, before you pull the head off, take a close look at the air filter box. It would be worth checking whether you can fit the new revised type. Then, when you put the head back on, adjust the tappets very carefully to minimum spec, then retorque the head and readjust them after a couple of hours running. After that adjust them at least once a year forever, if you want to avoid burned out starter motors.

You may find this previous Outdoorking thread of interest:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=39266

In addition to redesigning the air filter box, you will see that Briggs also switched to an electric fuel pump instead of the crankcase-pulse-operated one. I suspect that the pulse one would be fairly satisfactory on an engine with an intact head gasket, but perhaps Briggs' dealers and customers lost patience with the issue (especially if the head gaskets are continuing to fail anyway).

Thanks - very detailed! I'll read the other thread in a moment.
Compression tests at 130psi, so I'm assuming the head gasket is ok then?

Next step would be the leak down test, then to see if its rings or valves, yes?

I have had problems with the air filter too, dodgy thing that it is. Electric fuel pump too would be most satisfactory, but obviously won't fix the existing problem.

The leak-down test is not to see if there is a ring or valve problem, it was just intended as an additional check on the head gasket. You are not likely to have a ring or valve problem unless the engine has been dusted due to the air cleaner problem. Also, if your compression pressure tests at 130 psi, it sounds as if your decompressor is probably not working. Does the starter motor have a tough time getting the engine past compression, so it cranks in a series of fast-slow cycles rather than steadily?

An electric fuel pump will not fix either a blown head gasket or a dusted engine, but it will fix the oil spraying out of the fuel pump, and there is a good chance it will stop the engine from hunting when it is idling.

I can offer two alternative approaches you might consider. The first is to aim to make your engine run properly without changing from the original Briggs design. That would mean replacing the head gasket, and inspecting the cylinder bore while you are doing it, to see if there are signs of longitudinal scratches in the bore due to dust entry. If the only cause of the fuel pump oil problem was a leaky head gasket, that might fix the problem.

The second alternative is to replace the crankcase-pulse-operated fuel pump with the current electric one, so both the oil spray and the possibly erratic fuel delivery are eliminated without addressing the head gasket issue. This amounts to saying that the compression is good enough, so the gasket isn't leaking enough to matter, if it is leaking at all.

I suspect Briggs would recommend the second approach - they may even have a service bulletin issued to their dealers on the subject.

Whichever of those approaches you choose, I think you need to look very carefully at the tappet adjustment: I can't believe the decompressor is working properly, with 130 psi cylinder pressure at cranking speed.

Cheers. I've played with decompression units on other mowers. Can you tell me where to find it on this engine? Starter has no problem in turning the motor over. The motor does have trouble starting unless the throttle is almost off, and then I can only raise it slowly - needs time to warm up.

Replacing the fuel pump is easy enough. Is there one you recommend from another model?

Tappets I will check.

First, some clarification. The decompression system uses an extra cam lobe, right behind the timing gear on the camshaft, adjacent to the exhaust lobe. The mechanism is centrifugally operated. If you crank the engine with the rocker cover removed, you should be able to see the rocker arm "bump" during the compression stroke, long after it has opened and closed the valve fully during the exhaust stroke. I suggest you watch the valve movements. If the "bump" is clearly happening, all is well. If it isn't, the probable cause is too much tappet clearance.

The compression pressure you have measured, 130 psi, is only slightly below the 140 or so I would expect as the nominal reading for an 8:1 compression ratio, and normally a range of plus or minus 20 to 30 psi could be accepted. Hence there does not appear to be any major level of leakage through gasket, or past rings or valves. Hence I cannot sustain my initial suggestion that you had a problem in that area. I was overly sensitive to the bad reputation your engine has rather than waiting for the evidence.

Given that you do not seem to have an exceptional level of blow-by, the cold start and idle quality erratic running issues you have reported are probably due to a combination of two causes: an emissions carburetor, which intentionally runs as lean as possible, and some gum formation inside the carburetor making it substantially leaner even than that. Cleaning out the carburetor with carburetor cleaner will probably make it noticeably better with regard to easy starting and smooth idling. I tolerated having to wait about one minute after cold start with an emissions Honda I have before it would run perfectly without choke for several months once. Then I cleaned the main jet. It now runs perfectly without choke the moment it starts. Emissions carburetors tend to be blamed unfairly at times.

This leaves you with only the oil spray from the fuel pump. There is a thriving industry selling replacement pulse-type fuel pumps for Intek engines, which suggests that your pump may be defective rather than the base engine having a significant problem. If you search "briggs fuel pump" on ebay, you will see plenty of alternatives, many of them genuine Briggs parts.

Because we now have no evidence to suggest a base engine malfunction, the simplest and cheapest way to proceed seems to be to clean out the carburetor, and replace the fuel pump with another pulse type unit. If you are near a Briggs dealer, I suggest you consult him about the fuel pump though, since he will have experience with how long they last and how easy it is to substitute the electric one from the new Intek engines. A new genuine Briggs pulse pump will cost you about $35 including shipping on ebay, so replacing it occasionally is not a huge expense.

Aaargh. I hate playing around with carburettors.

I'll check the tappet first, and then have a crack at the carby. What sort of tappet clearance should I have?

I can't find any record of the model number you have quoted, on the internet Pinelli, so I can't tell you the specified tappet clearance, or direct you to an owner manual (which contains the information). In principle you can get it by going here:

http://www.briggsandstratton.com/support/frequently-asked-questions/Engine%20Valve%20Clearance/
and selecting Engine Specifications Chart.

I have found in various internet reports that many people are using 0.004" clearance on both inlet and exhaust tappets. I am fairly sure this is wrong, but they have an understandable reason. My brother has a 16.5 hp 500 cc Intek, for which the specified clearances are inlet 0.003-0.005", exhaust 0.005-0.007" according to the owner manual. By experimenting he found that the decompressor stopped working when the exhaust tappet clearance was 0.008" or greater. He now sets it to mean specification (0.006") and has no problems - but he knows he will when that clearance increases just slightly. Internet reports say that the tappet clearances continually increase on that engine, hence Briggs insisting that tappet clearances must be checked once per year.

The problem with the popular practice of setting the exhaust to 0.004" is that it is below minimum specification and might therefore lead to a burned exhaust valve.

Thanks. The numbers I gave you arent the proper numbers! Not sure what they are, but will track down the proper numbers to get a replacement pump.

Thanks for all your help. Will probably take me about a week to get to these things as hols are just about over - I'll get back to you with news of success.

Feel free to come back regarding the carburetor if you want to, Pinelli. You said you have issues working on them, so going through it in this thread might make it easier - it's your choice of course.