14 hp Briggs, performance parts or replace?

[james8719]

So far so good! My top speed was 19 mph Now it will hit 31 mph at 5000 rpm. It gets to 30 mph in less than half the distance it used to get to 20mph. It pulls hills much better also. I might add that the pre build speeds were with a bare machine and the post build speeds were with a roll cage and a winch mounted, so the machine is heavier but performs much better.
I am a little disapointed with the rpm range. I was hoping to be able to run at 6500 rpm. The engine is capable, we ran it up to 7500 rpm on the bench but with the clutch attached and in the machine it will only hit 5000. I contacted comet clutches and they said to replace the spring in the clutch with a red one. They said that would allow the engine to rev higher, quicker. I got the spring in the mail today and will install it tomorrow.
I still need to build a set of headers and might go with a different carb.

[Roger S]

Your stock exhaust may not be as lousy as mine was. It crippled all the gains from a modified engine. Really hurt mid and upper end. I'd say 5 hp difference for me with a header and straight through muffler. Our cams have some overlap so volumetric efficiency is sensitive to vacuum or pressure in the exhaust system. And that 14 hp carb is a limit too. I'd look at Whipper's header and maybe use the glasspack he found. I'd wouldn't use as big primary tubing as his though. I think a good exhaust and a rejetted one barrel would make you happy.

Now, forget about turning over 5 or 6000 rpm. Set your clutches up so it runs around 4000 as the cvt runs out. Our cams make good power at 3 or 4000. The compession is what pushes the pedals. Make sure you run good gas. Either AV gas or I'll tell you where to get a real octane booster, not the gimmick stuff at the parts house. A header and rejetting was a huge improvement for me.

I have my 18 hp rejetted carb I could sell.. have to ask George if the manifolds are the same on 14-18. Glad to hear it's running! We have stock flywheels, so I don't want to be near it at 7500 Also when George runs 8-10,000, it's on a couple hundred lb mower, with a $350 lightweight, ARC safety flywheel, and a modified 2 barrel with a bored venturi that flows 23% more. That's a $700 modified carb. And while he may turn those high rpms, that's just because his gearing was too low, and he pitted and re geared.

I think exhaust, carb, and fuel will get you what you want.

[Meinfield]

12 mph is a stout increase! Congrats on the build, it is really a lot of fun when you finally get to take out the machine and test it.
A red spring will keep the rpms higher for longer at slower speeds, but will do nothing on the top end. Check out JEGS for exhaust parts. I ordered some
1 5/8" mandrel bends and a 2" collector for my 31hp briggs, and I think they have smaller pipe (measure the diameter of your exhaust port and try to get as close to that as possible) for your 14 but you might have to fabricate some type of collector. Try and make the pipes from the head to the collector as close to the same length as possible, and probably around 14"-16" but check with the briggs guys to be sure.
Thanks for sharing the build info with us!
Roger, tell us about that lead octane booster you are using? I am going to need something to boost up my pump gas!
Chris

[Roger S]

Kemco is the company in Utah that makes a product called Octane Supreme 130. A year ago when I bought it, I ended up getting it directly from them. You can add increasing amounts of it to pump gas to up the octane. It is cheaper in bulk, like 1/2 price. Basically a quart is $20, a case of 12 quarts is $125 and free shipping (from Kemco). You can google it and see who else handles it. I saw a site that sold 6 quarts for $60. At $10 a quart, it costs 50 cents a gallon to raise 90 octane pump gas into 95. A dollar a gallon to raise 90 to 100 octane. It's cheaper to buy and treat 91 rather than 87.. It doesn't do any good to run more octane than you need.. although I tend to err on the high side due to the briggs doesn't have any spark advance.. it's fixed. So I have full 36* advance at idle! It's easy to get spark knock if you wick the throttle from low idle. For that reason, I try to bring it up off idle to 2000 rpm (get the belt engaged) before I cram it.

Kemco Oil & Chemical Inc

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Headers for James.. Herrin would suggest 12 to 15" of 1" ID primary pipe for the 14-20 engines. You'd need the port adapters like Whipper has from Al Hodge to allow larger flanges. No need for them on the small briggs though. Too big will kill low and mid range anyway. When you bring two primary pipes together in a collector, the gas pressure and sonic waves from one cylinder affect the other cylinder. IE, the vacuum signal in the collector from the end of one cylinder's exhaust pulse can travel up all other primary tubes. The vanguard twin, like Harleys, doesn't have evenly spaced power strokes. What I'm saying is Harley header builders run a longer rear primary tube. That delays the vacuum signal in the collector that affects the front cylinder. There's a longer delay from when the rear fires till the front fires, as compared to elapsed time from when the front fires till the rear fires. My point is, making the rear primary tube a few inches longer may be a good thing. A straight through muffler lets these pulses all the way through uninterupted. Problem is, free flowing and straight through = louder. If that is a problem. More of a problem for the guy behind me.

[Meinfield]

Thanks for the info.

[james8719]

Ditto on the thanks for the info! The red spring I got was the wrong one! It was not large enough in diameter.
As far as a carb goes, at what point is bigger too big? I would hate to buy a carb that was too big and would dump too much fuel too quick! I would assume that a carb from an 18 hp would work on my 14 hp, given the modifications I have made to it. Any thoughts?

[Roger S]

I can't imagine an 18 carb being too big. The difference between the 14 and 16 is the carb. I would guess the 16 and 18 carb could be the same. George could tell us..

You could start with the exhaust, and go up in jet size at the same time with your existing carb. They are borderline lean when stock, and with the cam and header, it perked up a lot when richened up. Not a sooty tailpipe or anything, just giving it what it needs.