NEED HELP JETTING CARB

[Mr.curious]

I am running a BBC in a 21 bahner jet. I am having some problems jetting the carb. It rich on low end and lean on cruise at about 4000 rpm and zero psi boost. The secondaryÂ’s are not open yet. Once I get in the secondaryÂ’s it goes rich again. I am running a new holly 850 with 94 jets and a power valve plug in secondaryÂ’s, and right now I have 84 jets and a power valve in primaryÂ’s. I tried plugging the power valve and going to 88 jets but it is hardly drivable down low. I am drawing through the carb. It has ported square port heads with flat top pistons. I am running it on AV 101 low lead with 10 psi boost it only turns 5600 rpms max. The timing is 37 degrees total advance and retards 0.6 degrees per pound of boost so at 10 psi the total advance is 31 deg. Any suggestions on what I should do? I thought I may try to epoxy the power valve vacuum hole then drill the metering plate so I can run the power valve off of manifold pressure after the turbo. Is this a good idea? I also have problems with my spark arrestor being too small. I could not get it to turn over 5200 with spark arrestor on. Take it off and it goes right to 5600 and plugs look slightly lean with it on. So I have been testing it with out any spark arrestor or air filter last couple of days. It is one of those coastguard approved spark arrestor 3 inch tall by about 6 dia. Any suggestions on what I should do for a spark arrestor? Any Help would be greatly appreciated Ken B. Las Vegas NV

[Floored]

try getting ahold of Unchained, he just did a hairdrier project and can probably help more than most. He may see this or just PM him. He also has a recent post here about his project

[Wetter the Better]

sounds like a idle mixture problem and or a power valve issue(i.e) to large,go larger jets on primarys and power valve should be 25 to 35.
,idle mixture and power valve will take care of rich on low end and larger jet will cure the mid range lean out and secondary sound a little large and to big of a spread from the front jetting,try 88 to 90 jets square. just my .02 worth had same problem when i put on a new 750 and K&N makes some real nice flame arrestors
later stan
[ September 06, 2003, 07:24 AM: Message edited by: Wetter the Better ]

[058]

Sounds like the powervalve is closing under boost, very dangerous as you risk detonation and burnt pistons. You will need to boost reference the power valve. Any good carb man can do this for you. It just involves blocking the vacume passage and re locating to where the vac/pressure is taken from, usually at the intake manifold past the turbos.

[Mr.curious]

thanks for the input. I am going to change the power valve to boost refrence and see what happens. thanks for imput and i will let you know the out come on monday evening

[Mr.curious]

thanks for the input. I am going to change the power valve to boost refrence and see what happens. thanks for imput and i will let you know the out come on monday evening

[Mr.curious]

thanks for the input. I am going to change the power valve to boost refrence and see what happens. thanks for imput and i will let you know the out come on monday evening

[Mr.curious]

thanks for the input. I am going to change the power valve to boost refrence and see what happens. thanks for imput and i will let you know the out come on monday evening

[bigkatboat]

Please tell us a little more about the motor, static comp., cam timing, list # of carb, and I might be able to help you. wink

[Mr.curious]

I will get all the specs on engine today i need to dig out specs I am running 470 CID (.070 over JE flat tops) with open chamber square ports the compression ratio is 8 to 1 , donÂ’t have cam specs in head any more but it is a clay smith Hydraulic H9080.o.b from what i can remember it has about 0.310 lift and about 230 dur. I have it advanced 3 degrees so it is on 107 lobe center I am running at 10 psi of boost. Holly 850 list #4781c 88 primary jets and 93 secondary jets the power is a 35. I am modifying the power valve to boost reference today (I hope this my cure my problem) I was running it at 37 degrees timing with it retarding 0.6 degree per pound of boost for a total of 31deg.btdc but the plugs were staring to show a slight bit of pepper so I May try a little bit more retard so it will be at 29 or 30 degree. I am running straight av gas 101 low lead. Any Help is greatly appreciated Ken B

[Mr.curious]

[IMG]http://www.***boat.com/image_center/data/504/1042turbo_engine-med.JPG
[ September 12, 2003, 11:05 PM: Message edited by: Mr.curious ]