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Big Block Talk! Everything about swapping a big block engine into your cart! |
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11-27-2022, 01:26 PM | #1 |
Not Yet Wild
Join Date: Nov 2022
Location: Michigan
Posts: 69
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Jetting stock carb on vanguard 18 hp
Quick question on carb jetting. If I am trying to get more rpm out of my motor do I just change the main jet or both the main and idle. I am trying to get the rpm up on a motor with a cam and high rev kit. Currently will run 3800 with no load and 2800 with load. I feel take off is a little sluggish as well. Throttle is directly connected and I have verified that it is opening alll the way and ther is no governor either.
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11-27-2022, 02:24 PM | #2 |
Searching for The Way
Join Date: Oct 2009
Location: Medina, Ohio (NEOHIO)
Posts: 11,421
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Re: Jetting stock carb on vanguard 18 hp
Stock jetting with the rev kit and cam will get you to 5000 rpm no problem. No jetting increase is usually required. If your engine is only reving to 3800 rpm, you have another issue. If it's only reving to 2800 under load then you really have an issue going on. The carb could be dirty. Valves could be loose. Compression could be low. Could be a lot going on there. Especially if it's a used engine we're dealing with. Has this engine ever run properly since you've owned it? What's the history on the engine?
I'd recommend doing a once over on the engine and make sure it's in tip top condition. Check compression. Leakdown test. Adjust valves. Etc. |
11-27-2022, 02:32 PM | #3 |
Not Yet Wild
Join Date: Nov 2022
Location: Michigan
Posts: 69
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Re: Jetting stock carb on vanguard 18 hp
The guy I bought the cart had everything done to it 2 years ago. Everything is brand new. He ran less than a tank ram thru it. Everything looks that way as well. It runs fine up to those rpm.
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11-27-2022, 02:41 PM | #4 |
Not Yet Wild
Join Date: Nov 2022
Location: Michigan
Posts: 69
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Re: Jetting stock carb on vanguard 18 hp
The guy I bought the cart had everything done to it 2 years ago. Everything is brand new. He ran less than a tank ram thru it. Everything looks that way as well. It runs fine up to those rpm. Would the rpm be if it didn’t actually have the rev kit in it?
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11-27-2022, 02:55 PM | #5 |
Not Yet Wild
Join Date: Nov 2022
Location: Michigan
Posts: 69
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Re: Jetting stock carb on vanguard 18 hp
And is there a way to tell if there is a cam in it without too much disassembly.
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11-27-2022, 11:19 PM | #6 | |
Searching for The Way
Join Date: Oct 2009
Location: Medina, Ohio (NEOHIO)
Posts: 11,421
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Re: Jetting stock carb on vanguard 18 hp
Quote:
A stock cam will rev past 4000 rpms if you allow it, but the power is not good up there, and power drops off like a rock past 4000 rpm. Most people will keep revs below 4500 rpm without a rev kit and usually be ok, although I have heard of people getting bent pushrods. The stock pushrods are strange, one is steel and one is aluminum. I think Briggs does that so you can't damage the valvetrain by over rev, the aluminum pushrod usually bends. The rev kits will come with two steel pushrods to replace the aluminum ones, or will replace all the pushrods with stronger billet or chromoly versions. The camshaft is what really wakes these engines up. The stock cam makes decent power and torque down low in the rpm range, up to about 4000 rpm and then falls off. The upgraded cams will increase power throughout, but mostly in the upper rpm range past 4000 rpm. A rev kit is a must to get the most out of the cam. No way to know if an engine has a cam without taking the side cover off. I suppose you could measure valve lift, but you'd have to have stock numbers for that engine, and typically most of us don't have the proper equipment to measure valve lift very accurately. So, my answer is, take the side cover off. Listen, just because "the guy said it's all new and good to go" doesn't mean that it really is. You're taking his word for it. If it were me and I was having trouble with an engine, I will always check the basics like compression, valve lash, pushrods, timing, etc. I don't trust other peoples work. I've found engines built by professional shops had timing off two teeth on the cam. I've found brand new engines out of the box that had too much valve lash. I've found rebuilt engines that had pistons in backwards. My point is, you're having rpm issues, you NEED to check the basic mechanical condition of your engine to make sure it's set up correctly and in good condition. Everything else is secondary. |
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11-28-2022, 09:31 AM | #7 |
maintaining a low profile
Join Date: Oct 2009
Location: SW Virginia USA
Posts: 6,313
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Re: Jetting stock carb on vanguard 18 hp
Are you sure that the engine governor has been eliminated?
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11-28-2022, 09:48 AM | #8 |
VC 460 CLONE GONE WILD
Join Date: Oct 2014
Location: Ray BY The Bay NJ
Posts: 10,593
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Re: Jetting stock carb on vanguard 18 hp
IF it really has the Cheetah camshaft in it the lift at the valve should be right around .40 inches. The cam lift is .310 plus the rocker arm ratio. With the valve cover off measure the top of the valve spring/retainer at no lift. Then rotate the engine until you see the valve spring compressed to the max. This is pretty easy to see. Then measure the valve spring/retainer height again. The difference is going to be the lift of the camshaft. There is about .060" between the 2 cams. IF they used the 23 B&S camshaft and are calling that a cam change that will not show that amount of lift. One other note here is while hand rotating the engine doing this is to note how long the valve is depressed. The stock cams bump thru lift pretty quickly. The performance cams with their longer duration hold the valves open much longer. And again this is real obvious when you are slowly had rotating the engine watching valve operation.
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11-28-2022, 11:06 PM | #9 |
Searching for The Way
Join Date: Oct 2009
Location: Medina, Ohio (NEOHIO)
Posts: 11,421
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Re: Jetting stock carb on vanguard 18 hp
And how is this valve lift measurement to be taken? You'll need a dial indicator for that, or some other specialized tool, if you have one. Duration is subjective unless you can compare one to another side by side. Not a sure thing. The only way to know "for sure" is to take the side cover off.
But before you go and do that, just do some basic testing and inspection first. Do a compression test. Do a leakdown test. Check the valve lash. Those are the basics of the mechanicals of the engine. If those check out then you may not have to "tear into" the engine yet. It sounds like the rpm is getting "held back" so I'm feeling like the engine governor is doing that. However, from the photo you posted in your other thread, it clearly shows no mechanism on the governor shaft. That leads me back to the transaxle governor. Can you show some good, well lit photos of your transaxle governor and an overview of how the cable is run. Try to take some good photos from the top view at a little bit of a distance so we can trace the cable. BTW not sure why you have two threads on this. Might be easier to just keep one thread active. |
11-29-2022, 07:11 AM | #10 |
VC 460 CLONE GONE WILD
Join Date: Oct 2014
Location: Ray BY The Bay NJ
Posts: 10,593
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Re: Jetting stock carb on vanguard 18 hp
It is 1/16 of an inch.With a decent ruler you should be able to see if the lift is less the the .400" the Cheetah cam would give you. I don't disagree the best way is to open the engine up BUT the OP asked if there was some way to get an idea if the engine had the cam or not.P.S. I just looked. You can buy a digital caliper from harbor freight for $20 and know pretty precisely what your lift at the valve is.
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