Clone and VC 460 Help

raydhd

We seem to have a number of newbies with clone and DIY 460 questions. As you see we have very few stickies in this section. So if you have a question feel free to ask. Hopefully I or some other clone builder/user can help.

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raydhd

I will be the newbie on this one. The 420 hemi has 1.3 ratio rocker arms versus the wedge 420 with 1.1 ratio rocker arms. Do the leave the factory with the same cam shaft ? That would give the hemi 20% more valve lift plus the larger valves and ports. With these advantages one would expect the hemi to produce a good bit more power with both versions in stock form.

scottykify

I think this subject has sooo many variables depending on the cart your putting it in. For instance my issues may not be issues with a different brand or year... Being new to this "Big Block" swap into golf carts I'll list my biggest hold up's starting out.

Clutch setup.. Used a 780 style primary clutch which came with VC swap kit, but should a stock secondary work with the wider belt, or do you use a narrower belt, or should you just purchase the $250 secondary designed to be used with the 780 and the wide belt. Do most guys use the key start or pedal start, then you have to adjust the belt looser with key start in order to idle in gear without it moving and does this lose top end speed?

Throttle cable setup was another one, its nice to have a "over travel" spring on the cable so your not bottoming out the carb and breaking stuff but alot of the go-kart throttle cable kits and top plate setups do not include those. The swap kit didnt show how to mount the cable either with or without a governor. Maybe some throttle pedals have more throw than others, and if you run a top plate you can adjust the mechanical advantage of the throttle so you get the travel you want but with that style you cant run the governor.

FUEL SYSTEM! I see all kinds of various setups without a consistent answer, and maybe there is not a consistent "use this pump, with this return and add a restriction" answer. From what I've gathered on here some guys are over fueling the carb without a return, some guys are running out of fuel with a return line, some guys just dont have issues at all with either setup, some guys stay with the stock pump, even dudes running a hopper tank mounted up high with a return... So from what I have gathered its mostly trial and error and see what works for you, good luck type of thing.

These are a few of the issues and complicated things I've ran into when doing this for the first time.

raydhd

My first item that I had some hard lessons on is the fuel pump. MAKE sure your fuel pump can keep up so the engine does not get lean at high rpms. I think my head gasket failures were due to lean conditions. AGAIN after trying various fuel pumps the only thing that worked out for me was the B&S Vanguard pump with a return line. Item 2 I run a pretty tight over width belt with a key start. The only time I have to shut the engine down to shift is when both the engine and belt are cold. Item 3 See my thread on clone throttle where I make a bell crank out of the stock throttle arm.

Shepard

I've read a lot over the last few days about high idle - no idle control. I'd like to help to understand the function of the air/fuel adjuster.
#1 == proper air to fuel ratio is 14.7 parts air to 1 part fuel. Doesn't matter if it's idling or under power driving down the road.
At this point in time the EPA requires that the air/fuel mixture screw be sealed in some manner. This has lead to problems in the way we use these little engines. I should say we don't use these little engines as they were intended. The way a governor is set up on a mower or tractor -- it never idles - at least not like a car - starts - idles - revs up on demand. The idle circuit is very lean on a small engine because of this reason. We try to use them like a car and it starts and idles like poo We try to adjust them and sometimes it doesn't go right.
Here goes -- having installed a throttle return spring to the butterfly control on top of the carburetor - this guarantees that the carburetor is closed properly against the IDLE SPEED CONTROL SCREW. If it's not closed properly you can;t adjust the idle mixture. Here's the theory - you are adjusting the air/fuel ratio to a 14.7 to 1 mix for the idle circuit. So you set the idle speed screw to a high idle say 1200 rpm -- then turning the mixture screw slowly to the right till it stumbles and stalls. Back it out a little - enough to restart engine - then turn to the left till it stumbles and stalls. Turn it a little to the right - enough to restart the engine. Now you know the range of the mixture screw at 1200 rpm -- now adjust the mixture screw so the engine will run as fast as it can with the idle locked against the idle speed control screw.
Now the engine is most likely turning a fair rpm -- turn the idle speed control screw on the throttle to slow the engine down to more of an idle like 1000 rpm.
Now you need to re-adjust the mixture screw till it runs faster -- or it doesn't slow -- it's a dance between the idle screw and the idle mixture screw. You may need to do this in 2 or 3 steps to get the idle down under a 1000 rpm.
Your attempting to keep the air/fuel ratio at 14.7 to 1 "at the rpm your idling at".
If it pops out of the exhaust on deceleration open the mixture screw a little at a time till it stops.
The idle and transition circuit controls the engines fuel needs to about 1/4 throttle. After that it's starting to run off of the main jet. Now this is why we run an adjustable main jet kit. So we can tune that 14.7 to 1 air/fuel mixture above 1/4 throttle.

Shepard

One thing I need to add is to clean off the end of the head of the mixture screw and put a magic marker dot on the head of the screw at 12-O'clock position so you can track the turns of the adjustment as you go. Remember = small adjustments - 1/8 turn at a time because radical adjustment = radical changes in the way it will idle.

Shepard

As air races through the carburetor bore you can see that the vacuum is the highest at the smallest part of the bore or venturi. The air is traveling at about 200 mph to lift it up and atomize it into the air stream. That goes the same for the idle port and transfer port. This is why a good sturdy throttle return spring is needed. The throttle must be closed on the adjuster screw to properly adjust the idle.

Attached Images

Venturi.jpg (11.0 KB, 0 views)

raydhd

There you have a ton of tuning tips from the Carb genius that built the 24 mm EXP-S carb on my long rod VC 460

scottykify

Shepard I love the explanation of tuning in the idle circuit, easy to understand! I was just stating the list of problems I encountered as a complete new guy to the swap. And as a new guy I didn't even the throttle was held wide open and used the governor to pull it back down, so step 1 would be to remove the governor or bypass it in order for the butterfly to even close all the way or the engine WILL NOT start without a choke unless your cranking rpm is high enough to overcome the springs, and same as you said it wont idle correctly with governor.. but my issue was trying to figure out if the engine was even meant to idle at all, pedal start engines dont "idle" they just die and start again, but you could still use the same method to tune the "idle", then when its dialed in simply back the idle screw way down so it will die when you let off the pedal.

BUT there is important step missing for the newbies, that is to determine if you want the engine to keep on running at a idle when you let off, or do you want it die and start again like a normal golf cart. THAT imo should be step 1. Then you need to determine proper belt adjustment so it doesnt take off and run over people the first time you fire it up.

And 14.7:1 is the correct AFR for complete combustion, that is not the target AFR for all loads and rpm's. Im sure people familiar with tuning already know this but you can idle and run under light loads at a much leaner AFR. With WOT high load, an engine almost always makes more power with a AFR richer than 14.7:1 and it will stay alive longer due to cooler combustion temps. but I can see where your coming from, it is a great reference point to use when trying to explain tuning to people.

Shepard

I don't deal with machines as golf carts so the pedal start is the first thing to go. Being handicap I'd like my ride running all the time. I wish fuel injection for a cart was easier and cheaper. This way you could have a programmable variable fuel ratio. Carburetors are linear and add a set amount of fuel as they open.