Common Problems and Troubleshooting

Bob Evans

In this chapter we will list some of the common problem you may encounter with the Briggs motor on Methanol and the most typical solutions. Some of these can be very frustrating at times but if you check everything completely you’ll find the problem.

NO COMPRESSION - This problem exhibits itself when you try and turn the motor over by the cranker and cannot feel it build resistance as it comes up to TDC.

. Blown Head gasket - Replace gasket and double check the head bolt torque after running the motor once. The area around the bolt on the exhaust side of the cylinder is where 90% of all failures occur.

. Stuck Exhaust valve in the open position -This is most often from a close fit of a new exhaust valve guide. At the track you can see the valve stuck open by removing the plug. Try and push the valve down with a screwdriver and then shoot some penetrating oil on the stem. Once the motor cools down you have a shot at making it run and wear in the needed clearance. The best way is to go back and hone the guide for proper fit(.002-.0025). A loose guide will also lose compression.

. Bent valve - On rare occasion either valve can get bent by hitting the cylinder head and thus loose seal. Simply replace the valve if it will not seal after attempting to re-lap it.

. Bad Seat - this one will drive you crazy!. If the seat is loose it will loose seal as the motor heats up and you motor will exhibit many symptoms such as skipping or no real power. Sometimes the engine will cut off after it gets up to temp with a loose seat. Drive the seat back down in it’s pocket first. If this does not fix the problem replace the seat with a new one or use a high temperature seat locking sealant that you can find at automotive stores.

SKIPPING - With a methanol motor where the motor skips is of importance in isolating the root cause and fix.

. Skipping at the end of the straight or max RPMs. - lower your jet size. Normally shows up when the weather changes from winter to summer and the air gets thinner(worse). Go down at least two jet sizes(.002). A bad coil can also cause the problem(especially when hot) or a fouled plug. Change the plug first then start looking at the other solutions.

. Skipping in the turns - This is most often a problem with the fuel being thrown out of the small pick tube’s pocket in the tank. Most newer tanks from Briggs have rather large slots built into the small pickup tube area to let excess fuel flow back into the main tank portion. These large slots can contribute to the fuel being tossed out in high G turns. The solution is to find Briggs part # 555520 which is a small spring like piece of steel that goes into the small pickup area and decreases the slot size.

. Low/medium speed skipping - Timing is off. Check you timing again to insure the flywheel has not slipped. If it did then re-lap the flywheel to the crankshaft and torque to 70 Ft. .Lbs.

EXCESSIVE OIL IN CATCH TANK - This problem can also show up as oil being blown out of the crankcase through the seals or gaskets.

. Worn or non sealed rings - If the motor has quite a few races then worn rings may well be the issue allowing excessive blow-by into the crankcase causing pressure to blow the oil out the vent tube or seals. A good motor will throw very little oil into the catch tank. On a new motor the rings may not be sealing properly. A hard run on a warm motor will often fix this problem.

. Worn Valve guides - Here pressure is being pushed down into the crankcase through the guides if they are worn. Simply replace the guides.

. Worn seals - Replace the seal in question either on the PTO or Flywheel side.

. Blocked catch can - Check the catch can to make sure the hose is not plugged or free to dump oil into the bottle.

HOT CYLINDER HEAD TEMPERATURES - Opinions will vary here but anything over 410 CHT is too much to my thinking.

. Kart TOO Tight - This is a big one. If your kart is tight or pushing then you are putting strain on the engine and it will get hot. Fix your handling.

. Too hot a plug range - Changing to a colder heat range plug can lower this CHT a bit. Generally one heat range will lower the temps by 10 degrees. Moving from a ND 24Fs to a 27 or 31 will help a bit.

. Move to a larger jet size - Move up in jet size by .002 increments. If .004 increase does not help any, then the problem is most likely elsewhere.

. Clogged Pickup tubes - Check you carb pickup tube screens to insure they are not clogged. Also if changing the jet size does not fix the problem on a new carb check to insure that the body of the high speed screw is not blocking the small pickup tube passage into the jet area. A thicker gasket will help this problem.

. Excessive Timing - Double check you timing and make sure it has not slipped. Also moving down a few degrees in timing may help.

. Blocked air screen - Make sure you have all the holes open on your flywheel screen. On some screens you may want to open the hole sizes up a bit to allow more air into the motor. Also make sure all your shrouds are in place. They are there to direct air flow.

. Bad Exhaust guide or seat - Check you exhaust seat for looseness or the guide sticking out into the exhaust port excessively.

COLD HEAD TEMPERATURES - An engine must obtain enough heat to produce its maximum horsepower. Changing weather can affect the heat of your engine. maintain at least 375

. Put a piece or two of duct tape on the blower housing. By taping the holes us you block air flow and build heat in the engine. Make tabs on tape accessible to the driver just in case a piece needs removed.

. Too cold plug range- Just like cooling an engine, the plug range can be adjusted to add heat. Move to a hotter range of plug.

. Smaller jet- once again I recommend moving in .002 increments.

. Advance Timing- I recommend only attempting this in the luxury of your shop. Adding just a touch of timing will give it a few degrees.

ENGINE LACKS TOPEND - The engine is running fine just seems to lack a little top-end.

. Reduce jet- simple and easy to do at the track.

. Open intake valve quicker- closing lash on intake will open valve quicker and add to top-end. "SEE CAM THEORY"

. Reduce Timing- Subtracting a few degrees of timing will add top-end

REMEMBER! Generally it's a given that you have to give to get so when hunting top-end don't be surprised with a loss of bottom end.

ENGINE LACKS BOTTOM END - In most situations you will find by doing the opposite of adding top-end will increase bottom end.

. Add jet- This will add to your fuel therefore adding to the bottom end torque of your engine.

. Shut exhaust valve quicker- add lash to your exhaust valve for added bottom end. "SEE CAM THEORY"

. Add Timing- this causes the piston to be deeper into the hole during ignition adding to the bottom end of the engine.

. Change pipes- headers are one of the most underrated aspects of a good stocker. I have had "good" motors all of a sudden become "great" by changing 2" on the pipe length or moving to a different initial diameter. A smaller initial diameter pipe will help you bottom end torque as will a longer pipe.

ENGINE LOSES FIRE - The engine is getting fuel but wont start.

. Change plugs- spark plug has fouled. From personal experience I can tell you that this could make the Pope mad!! I promised myself that a $5 plug would never cost me a race. Although I will admit that this is excessive, I change my plug weekly before the mains begin.

. Bad coil- This is usually very simple to recognize. In most situations the coil will overheat before losing fire. With this I mean that the engine will run briefly and shut off.

Troubleshooting a stock Briggs is fairly simple in most situations. Above we have discussed a few of the problems faced and the most common solutions for each. Although the problems faced on the Briggs are generally very easily diagnosed, I guarantee that these simple engines have caused the greatest and most knowledgeable engine builders to lose a few hairs. I've had them as finicky as Morris the cat but that’s what makes them fun to build.

We also discussed a few ways to change your "power band" on your engine. For those of you who enjoy running at different tracks this can be some very important information. For example, a short tight track may need more jet than a long wide open track for the added pull up off of the corners. Pipes and jets can be quickly changed at the track to change the "power band" of the engine. We also made a few suggestions on changing the "pull" of the motor when we are playing in the shop. These are just a few of my preferences that I generally go to first, when I'm hunting a little horsepower for that certain part of the track. Best of luck to you all at the track but if you are reading this chapter my well wishes may be too late.