Engine Surging

[Newtwo6x6]

1999, Max IV, 18HP, Briggs. Engine runs ok at idle, when I give it throttle, the engine surges. I have cleaned the carburetor, ie remove carb cover, float, jet and sprayed with carb. cleaner. With the air cleaner off I did notice the fuel lines were old and cracked, so I replaced them. Max did set for a few months, I added some new gas, it is still surging. Could the fuel line from the fuel tank be the problem.

[Nubs]

I'd drive it for a bit and see if it don't come out of it, does a little choke smooth it out at all? if there is crap in a jet it will need to come apart and blown out with compressed air.

just may be a little water or ice bein' NH and all

[swfleur]

Surge

Hello NH - Im up here in Maine - ( hello neighbor )

I have had some times where my engine surged and I found out it was a case of freezing throttle cable.

Lets make sure we are talking the same language first.

When you say "Surge", You mean it stays revved up longer than you wanted it too or seems to jump forward more than you want?

( Starved or studdering would be if it seems to almost stall and so that would be a different issue)

For my surging problem, I pulled my cable out and coat it with Antifreeze and oil as a lube. Worked much better after. Some guys use the heated throttle cable but I have been ok since I did my redneck lube job.

Mine was not completely frozen, but just got tight and sticky

A kink in the cable will cause a similar problem

You can check by -
1-Putting in Neutral.
2-Getting access to the carb by lifting your top (or however works best for you)
3-Using your hand to activate the throttle lever at the carb. ( This bypasses the cable issue)
4- if it works fine when you bump the throttle lever at the carb by hand, then you probably have a sticking cable.

Or as the other guy said, maybe it will come out of it after you melt the snow and ice by driving it around ( watch out for trees though

[Newtwo6x6]

I've tried operating the throttle by hand at the carb, it seems that at a mid throttle position is when surging is happening. Engine RPM's go up and down and throttle linkage moves and doesn't remain steady. I cleaned the carb already.

[swfleur]

ok - you may have some air leaking in - cracked fuel hoses or bad gaskets at air cleaner attachment will also cause this. Any cracked hoses should be replaced. Thats a cheap and easy fix.

When you say you "throttle linkage moves and doesnt remain steady" - what linkage are you talking about? There are linkage arms can sometimes jump around - especially the governor linkage ( if you have one )

Aside from the cracked hoses and possible air intake leaks, there is another thing you can try. Use some carb cleaner and gently spray quick bursts in a few places around the gaskets or cracked hoses. If you do this and the engine surges, you have found your leaking spot.

Hope this helps

[swfleur]

Governor 101

Not sure on the model but here is a quick explanation of the governor. You may already know this but just incase.

The governor is a basically designed with some counter weights that will spin out faster and further - when you increase RPM. Its a mechanical safety to prevent over rev of the engine.
When the weights spin out and cause movement by centrifugal force ( spinning faster causes them to move outward like whipping a ball in a circle on a rubber band the faster you go, the further out that ball will get stretched ) Ofcourse there is no rubber band in the engine but there is mechanical device that acts similar

The weights move outward and are usually attached to a lever or mechanism that forces the carb throttle lever to back off and therefore reducing the throttle and so the RPM goes down and the engine wont blow apart by over revving. I had one engine that needed this adjusted but it's rare. The weights are usually internal somewhere and mated to the output crankshaft but you wont see them, unless you pull the engine apart ( not suggested at this point )

Does your surging happen when you are driving ? ( load on the engine )
or
Does it only happen when you are idling in Neutral? If the answer is only in neutral, I would look at the governor

but I think you have some leaks from cracked hoses or gaskets as discussed earlier.

Also worth checking is that your choke mechanism and cable is ok. A loose choke or broken choke return spring can allow the choke plate to get sucked closed when you give it throttle

[Newtwo6x6]

Hi swfleur, thanks for the info. The surging happens both while driving and in Neutral. I did replace the fuel hose from inline fuel filter to fuel pump, fuel pump to crab. I will keep looking for a leak as you mentioned. As a side note I grew up in Hartford, Maine.

[JohnF]

This is my guess:

Your carburetor isn't clean. Some internal port is still varnished over.

Most carburetors in the engines we use have two main circuits - an idle circuit and a main circuit. (In some diagrams called a low idle and high idle circuits giving hints to their intended use) They will have some sort of compensation to get the engine over the hump of switching from low to high that will, in one way or another, give the engine a rich moment for the cut-over. You are jumping across that gap over and over because your main circuit isn't working properly and once the rich moment is over it swings to low idle and then tries to go back - getting a rich moment again.

You may be able to fix this by running some SeaFoam. For this you may want to shine a flashlight down the throat of the carburetor looking for the tiny ports and poking a teeny wire to make sure the ends of the ports are open. You will be able to fix it by doing a thorough cleaning.

Anyway, that's my guess.

[Newtwo6x6]

Ok, thanks, Seafoam, I will give that a try. Do you add that to the fuel tank, or straight down the carburetor.

[JohnF]

It needs to run through the high idle/main circuit of the carburetor with the fuel. I would add enough to make the cleaning concentration from bottle, clamp the throttle on high, and walk away for 15-20 minutes. If the surging doesn't improve a little I would just remove and clean the carburetor. Oh, I would still make a tiny L shaped fine wire and poke it into all of the ports inside the barrel first.

I'm assuming that your engine is governed to its design high idle. If not, make sure you clamp the throttle at a position that the carburetor would be in the main circuit but not so high that it will head for fly apart RPM. High enough to surge at the start.

Crossing fingers...

Some ports are air ports and they won't benefit from this process. These will be holes/jets above the float level. You might look for them and poke the little L shaped wire just into them. If you are careful you can run small bits of carb cleaner through these while it is running.

[garretttpe]

Carb Cleaning

I have found that 50/50 solution of hot water and pinesol will work wonders for cleaning a carb if you let it soak overnight. worked great on my Vette carb and it is cheap

side note, I am also in Maine, Presque Isle area

Larry

[lunnex]

I was having the same problem with my 16 twin. I removed the breather housing and reved the engine. then chokedout the carb with my hand. this created enough suction in the card to loosen up the blockage. oh ya, don't forget to remove your hand from the carb before it stalls out. this is just a trick that has worked a couple of times for me.

[Newtwo6x6]

I seemed to have improved the surging, (sea-foam treatment), but now Engine is bogging down when throttle is advanced quickly. It also sometimes backfires both from carb and exhaust, not at some time. Could it need adjustment, I see the idle adjustment screw. The only other adjustment I can see is a small knob with a spring behind it. Could it be the valves need adjusting. If so where can I find the clearances and how to adjust them.