Carb question. 850 vs 800
 

My motor was rebuilt late last summer. 509 with promax aluminum heads. The builder says i need a bigger carb. Its currently got a 800 (think it was from a hp500 motor). He says i need a 850. He rebuilt the 800 for me just so i could get the motor back in the boat and running. Got to take the boat out once before it got to cold and it ran good. I was taking it easy so didnt really pish it hard.

Is there a big difference between a 850 and 800? I dont know chit about carbs. Seen some quick fuel brand new ones for about $650-700. Is that a good option? Only wanna do this once. Past 2 summers have not been great boating wise so i am trying to get everything fixed befor summer.

I know a particular build that picked up right at 75 horsepower on the dyno from switching from a HP 500 800 to a Quick Fuel 1050. Back to back, no other changes and the 1050's were not tuned ideal.

Mark

I could see a difference between a 800 and a 1050. But 800 bs 850?

Should i be look for something bigger then a 850.

Run you engine with a vacuum gauge hooked up. At WOT there should be very little vacuum. Approx. 1.5. If there is much more than that then there is a restriction. Either the carb is to small or current flame arrestor is to restrictive. Once this is done you will have an idea as far as how to proceed. Just my opinion. In theory the 800 "should" be ample for a 509 up to about 5450 rpm.

GM recommends a 750 with their 500hp 502, fwiw.

The 800's will work but you will make more power with bigger carb. Don't feel bad. My builds went from 1050 doms that I already had new and now need 1250's. Will the 1050's work yes but leaving power on the table the way the intakes and heads are ported. Btw same heads as you just more CI.

You can always run with 800's and borrow an 850 for one side and see if you go in circles.

Another thing. If indeed you find high vacuum see if you can borrow a larger carb to try. This was the case if was referring to earlier. Had a 1050 lined up to try in the event the 800 was not enough. There are numerous similar builds I am aware of using 950-1050.

yes..... buy the 850..... smokin gun had 1 for sale on here

Is the guy telling you that you need the extra 50 CFM selling you the bigger carb?