help with carb adjustments
 

I'm sure a lot of you guy's remember my build over the winter. I took a factory merc 502 mag carb engine and changed it to a 500hp. Anyways i have the holley 800 off of a 500hp and have the jetting perfect. I am having a problem with base idle. I will set it around 800-900 rpm hot and it will not always hang around there. also during a hot start it doesnt just pop off it will hit a couple and then fire. But when i start it cold and give it one quick throttle snap and let the accelerator pumps pour in some raw fuel it starts right up really snappy. just want to know what is the best way to set my idle mixture and idle and what rpm i should be looking for. and are my mixture screws messing with me when i am trying to start hot?

your starting point on the mixture screws will probably be 1 - 1 1/4 full turn out. with the boat in the water, I set idle first at about 900 rpm. Then put the boat in gear, if it doesnt stumble when put in gear i would start going in with the mixture screws in 1/8 turn increments on all four corners until it stumbles when you put it in gear. put it in gear after every adjustment. Once it stumbles, back it back out about 1/4 turn and you will be set pretty well. That has worked for me as I had to fool with my carbs wuite a bit when they came back from Nickerson in May. That will get you very close. And you may have to fine tune the idle after you get themixture right. If its a dominator type carb, make sure you adjust idle in the front and back, there is 2 adjustment screws for idle on a dominator

It just has 2 adjustment screws in the front metering block and none in the rear circuit. But i wil try what you said.

Another thing to check with the idle screws is if you turn them all the way in it should kill the engine. If it doesn't, you are not running on the idle circuit because the primary throttle plates are open too far. To fix this, you have to open the secondaries a bit to allow the primaries to close enough to run on the idle circuit. Then proceed with adjusting the mix properly.

These are all good pointers...
John

Do you have the electric choke hooked up or is it wired in the open position????

it is wired completely open. and the idle screws can kill the engine

try using a vacuum gauge to set idle speed and mixture. go for max vacuum reading then come out maybe a 1/4 turn on the idle needles

Chances are if it starts and idles well cold with no choke, then its too rich when its warm.

well, it will not start cold unless i give it one quick wide open throttle. so that the accelerator pumps shoot in some raw fuel. but it pops right off. i have done some jetting and my plugs look great. Just want to get it to start like it does cold when it is warm. it has no problem starting but it is not crisp. it is ascending. Oh, yeah 74 mph bravo 1 4 blade!!!!! bblades will make me go faster but she runs so strong. I can cheap shot many bajas out here

Having to pump the throttle once when hot to get to start not abnormal...it's not fuel injected, so yes you need that shot of fuel to lite it off a lot of the time...

sir...what 4 blade are you running ?

i have 500hp and a 1.36 ratio drive and am running a 24p bravo 1. Which was recomended by griff and BBlades. I would consult them for any prop needs. My only problem is that i need to find another one to have labbed by bblades so i am not out a prop.

Check the power vavles.

i do only have one power valve.... the rebuild kit had two power valves in it but they looked different than the on in my carb. so i did not replace it. Is there a spec on what power valve goes in the holley 800 on the 500hp?

Actually your ideal power valve is determined by manifold vacuum. It is loss of vacuum that allows the powervalve to open.

here is some good info http://www.holley.com/data/TechServi...wer_valves.pdf

more good info http://www.holley.com/TechService/Library.asp

he has a 800 he wrote, I had the same thing happen with my nickerson 1050 dom but someone stole it before I got it to idle right:p, and went with CFM DEAN GELLNER said they were very good and the carb is nicer looking but that 670hp motor is sitting now a 572 blower is being finished.

6.5 on stock HP 500 carb