Good Vc460 Fuel Pump

BrutalSoldier

I have been tearing up the town for a bit now and there finally is an issue. The Vc460 is starving for fuel on the top end. Around 4500 rpm I can tell it is starting to lean out and by 5500 rpm it flat cuts out like hitting that factory 100 mph rev limiter most cars have.(which I bypass on any new vehicle I get lol)
I am still running the stock fuel pump that came with the cart. I also downsized fuel line right after pump to match carb nipple. Might just be the stock pump is old and tired.
Any and all thoughts appreciated

BGW

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Shepard

Where are you getting your pulse signal from? If your using the intake manifold and your leaning out at high rpm? At an idle you have about 27 inches of vacuum --- as you speed up and go to WOT the pulse gets very weak --- maybe to the point it hardly pumps at all.

I'm experimenting using a Mikuni Dual Output pulse pump. I'm using the crankcase pulse to run the pump. It only gets strong the faster you go. In the picture I have the pulse coming off the valve cover. The 2 lines you can see - one goes to the carb and one returns to the fuel tank. The one line in the back is the suction feed line to the pump. In the return line I'm using a restrictor to slow the return so I have a constant fuel supply but not over flowing the carb. I have a line reducer from 1/4 to 3/16 in the feed to the carb. If you do something like this do not use the vent in the valve cover. It doesn't provide a good pulse source because of the valve system in the top of the valve cover. When you pull the cover to adjust the valves you'll see what I mean.

This last summer on a 90 plus degree day my electric pump vapor locked and left my stranded for a half hour and freaked me out. I'm trying out this setup to see if I have any future problems.

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Rooster59

Shepard makes some good points. Some other things to consider:

You reduced the fuel line size to fit the smaller carb inlet. Try maintaining the original diameter fuel line frim the pump and reduce just before the carb. Air compressor experts will tell you to use large lines from the compressor to your hose outlet then you can use 3/8" or 1/4" hoses from the outlet to your air tool. Size doesn't effect static pressure, it effects flow rate.

Keep the length of the pulse signal line as short as possible and the hose as thick/stiff as possible. The longer the line at high rpm the more the vacuum and pressure pulses overlap. At high rpm & wot the intake vacuum reduces making the overlap worse.

Due to higher rpm with the VC460 it may be exposing an inadequacy in the stock pump's flow rate that was fine with the stock motor. You might need to upgrade to a higher capacity pump. When the pulse signal weakens at high rpm you will have more capacity available. At high vacuum/low rpm the overflow will return the excess fuel to the tank. Or your original pump has worn enough to finally show it with the higher demand from the high performance motor.

These are all theories that could apply to your situation. You won't know which one works until you implement them. I would look at pulse line length and stiffness first, then fuel line size, then try the higher capacity pump.

Shepard

I've been working on an idea to use 3/16" steel brake line for my pulse signal. I'm needing a tasteful way to go from steel line to the brass barb on the pump. Its gotta look right. I'm thinking if I got the bump in the brass tube on the pump off -- I could slip a 1/4" brass compression fitting on it. I agree that the pulse line should be as stiff as possible. As it gets hot and softens, it could flex with the pulse. I used urethane fuel line and I'm hoping it will be fine for the winter but like I said earlier -- steel line would be better.

PS The Mikuni pump I'm using is a 36 liter per hour pump.

Rooster59

Making it "look right" could be quite a task Shep. But I applaud the desire. I would end up going the lazy route and use a short section of heavy rubber fuel hose to connect the barb and steel line. Maybe 4" or less.

If anyone else has ideas of using metal line, remember copper line is a no no for fuel. Use steel only just like Shep said.

BrutalSoldier

I was thinking of trying a pump like this....
https://www.amazon.com/Bravex-Univer...wn+mower&psc=1

Would 5-9 lbs pressure be enough or to much? There are other options.

Rooster59

It is hard to say, and your issue may not be a pressure problem. It may be a pulse signal problem causing your engine to starve for fuel at higher rpms.

Shepard

Yes that is way to much pressure. I used a low pressure electric pump 3-5 psi with a return line. It worked fantastic till one 90 plus degree day and it vapor locked. I was stranded out in the middle of nowhere land. After it cooled of all was well. But --- it has lead me to experiment with a pulse pump. Volume is what you need -- not pressure. I'm using a pump capable of 36 liter an hour. Low pressure with high volume pulse pumps are used in jet ski's. Mikuni were I found the one I'm trying. i tried EBay -- Mikuni fuel pump. Deal with a metal model -- less chance breaking a hose barb changing hoses. Here's the listing for the low pressure electric I used. This is my setup with the electric pump. The cool air drawn into the engine fan flows over the fuel pump and it still lost it's able to pump on a hot day.


https://www.ebay.com/itm/New-Univers...dYDgwc&vxp=mtr

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BrutalSoldier

Thanks Shepard. Amazon had a 3-5 psi electric pump for under $10. I will try that for now and let me know how the pulse pump works out. I definitely need more volume. With running the fan right over the air filter it gives it bit of a forced air intake feel. I have to run it super rich (about 2 1/2 turns out) and it burns through gas like crazy. Could also be that I am having so much fun with the Vc460 power and torque (with 6:1 gears) that I am either full throttle or no throttle.

BrutalSoldier

Ordered a electric fuel pump today. Tired of the Vc460 starving for fuel if I want to go over 4500 rpms. The pump is 2.5-4 lbs pressure and 20-30 GPH. I hope this works. Now that I have the engine broke in I would like to see what speeds the cc is capable of.