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Blower carb runnin lean

Bertram38

Bertram38

New member
I have a single 800 cfm Holley per engine with 174 B&M under it. Upon spark plug reading I have a lean condition from 3,500 on down. This is not good. So my Question is. If I have 94 jets in rear and 92 jets in front with 6.5 power valve front and rear, how could it be lean. Factory carbs came with like 76 front and 82 rear. WTF.
First thing I did is go to a colder plug, MR41T instead of the MR43T. This should make a change since I read about Blower motors need a colder plug to stay alive without detonation.
Should I go and buy like 98 jets square and try that.
Oh yeah, fuel pressure is 7.5 for both engines with holley blue pumps and reg'.
Or buy a 8.5 power valve for front and rear. I have the gauges under carb now also for true vacuume, but need to go out and test again so what to Buy and try first besides the MR41T plugs is what I need from the SOS Guru forum.
I was born with NA motors in my blood, Blown is a differant world you know.:sifone:
Thanks
B38
 
I just ran a engine on the dyno today 548 cid 250 Blower shop blower 6# pulley 2 holleys 84 on the primarys 92 secondary 4.5 power valve 7# fuel pressure 12.5 A/F ratio if I recall right. How and why did it lean out from before or am I missing some facts? Changing the plug heat range isn't going to correct your fuel air ratio. get back with some more info. fuel pressure, boost timing what was it before this.
 
I don't think I would be tuning a engine on the water by reading plugs, you better get some a/f readings with it unleaded fuel is almost impossible to read, did you just install the blower?
 
I have a several hours one one engine, and about 1.5 on the other, no don't get me wrong here. They run great and strong while TESTING, my boat must be my dyno, no major $.
Ok, 6 Lbs of boost per roller cam 454, read plugs @various 500 rpm increments up to WOT of 5,200 rpm. Load to prefered Rpm , kill it and read with lighted 8 lux glass. Old school is my way and all I can afford. Also my transom and tailtips are clean, hense need more fuel. More fuel = more Hp. base timeing 6 degrees, 28 total on 93 Octane. way safe.

Question, since I am poor, what would be the least costing big change to my carbs to FATTEN HER UP. Jets or power valve, or all. I have no extra parts to swap out on my holleys just laying around. Must buy from local speed shop.
I am haveing a spacer made for exhaust to measure A/F. goal is 13. ratio i belive.
Once again, I am on a limited budget.
Thanks
B38
 
I would try and get the AF down close to 12. I would just increase the jetting. You may just need more carb. For reference, a 525SC with a 177 blower runs a 1050 dominator carb and #98 jets. The MR41T is the stock 525SC plug.

I would also run some more timing. Probably 30-32*.
 
I thought being advanced to 32 degrees would create more detonation. Hmmm
No money for dominators:drool5:, but the jets i can do for now to fatten her up a bit, try the 98 square is my thoughts. that would only be 20.00 in cost for that change. Got to start somewhere.
B38
 
Wait for the a/f adapter to be completed before you spend much time finding nothing out, is the carb boost referenced? if so start with a 6.5 power valve, it will be sure to open when vac drops. I use NGK plugs but, a -8 heat range which is pretty cold, the bad thing about the single carb is fuel distribution from being centered and peak hp and torque # I understand you in cost. I just wouldn't mess around with not knowing a/f ratio plus what percentage of alchol in fuel if any.
 
No MSD, Mallory HEI marine blue. It has 22 degrees built in.
I checked both engines @ idle and 3K = 6 and 28 degrees total.

Yeah , I will have the sniffer spacer built and go from there.

But once again, i need some parts to test with, Wich Ones to Buy since I am lean now.
B38
 
Are you reading the plugs off the porcelain or the base circle color???? Also, where is the burn line on the ground strap???? You want it right at the bend.
 
Porcelain circle color is what I look for, needs to be down close to base, i have no ring at all. Plugs are clean when removed , no ring except at full throttle. So I am lean from 3/4 throttle on down. I removed plugs one day at diferant 500 Rpm increments. Thus found out I was too lean for BOTH engines.
Oh yeah, base for Carb on 174 B&M blower is only 4150, can not install dominator unless I use an adaptor.
B38
P/S, I want to run in the Jacksonvill poker run, but must work out these lean issues before I go.
 
Keep going up on jet sizes until you get the plug color you want. Changing power valves only changes how soon they open. A 6.5 power valve opens at 6.5 inches of vacuum. A 4.5 opens at 4.5 inches of vacuum. They both pass the same amount of fuel. Make sure the float level is set properly. Fuel should just start to run out of the sight plugs when it's right. Good luck.
 
Can you afford to melt your engine before you get a A/F # When I tune my engines on the dyno, I don't make pulls and read plugs or heat rings on the plugs, the heat ring could very from cast iron to alum heads and the heat range of the plug. I could have white plugs with a 12.5 -13.5 a/f ratio and only show color due to idle and pulling the engine down under load , if you were running leaded fuel I would agree with color reading plugs.
 
Merperformance, thanks for the input.
I agree with all on this subject. My only point is commen sense, if lean currently, why go out again to test with a A/F sniffer without some change to fatten her up first. Since I have no parts for testing I felt one up change will not hurt me at all.
Commen sense is telling me this, am I right or wrong.
B38
 
Bertram38 said:
Merperformance, thanks for the input.
I agree with all on this subject. My only point is commen sense, if lean currently, why go out again to test with a A/F sniffer without some change to fatten her up first. Since I have no parts for testing I felt one up change will not hurt me at all.
Commen sense is telling me this, am I right or wrong.
B38
Click to expand...
I don't see that it would hurt changing the jets up in size, I'am just trying to give you good advice, so you don't hurt the engine or waste your time doing it. My point is, if your waitting on the A/F adapter why take a chance, You can richen it up until the plugs do read rich, then you can deal with fuel in the oil and washing the cylinders down. I've been doing this for 20 yrs, and have seen alot of things happen to good engines, until you do it, the right way it only takes that one time, then you end up saying; I shouldn't have done that. If your only 2 jet sizes off thats one thing, more than that you need to know where your at in A/F ratio. Thats my advice.
 
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