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TX19
07-02-2001, 05:44 PM
I'm having trouble getting the mixture rich enough on my new 514. I have run jets as large as .0149" on the 8896 Dominator and am still too lean. The combination includes a Victor Jr. intake, Blue Thunder heads, cam is 258 intake duration / 635 lift, 268 exhaust duration / 645 lift at .050 off with a 112 degree intake center line, Mallory Unilite / MSD 6M and a compression ratio of 9.5 to 1. The short block is an internally balanced SVO 514.
I am picking up horsepower with every carburetor jet change, but something doesn't seem right.

oldphart
07-02-2001, 06:44 PM
sounds like a vacume leak. try spraying some ether around the manifold sealing surfaces. if this doesnt blow you to hell the engine will pick up revs if it finds a leak.

Oldsquirt
07-02-2001, 06:48 PM
Might try carb cleaner for a less explosive reaction.

Squirtcha?
07-03-2001, 07:31 AM
With the carb cleaner you will hear the rpm drop and possibly even stall the engine. Ether is the opposite. Do yourself a favor and use the carb cleaner instead.

okie dave
07-03-2001, 08:09 AM
what fuel pump do you have? i used to run out of fuel even with a mechanical and electric pump running at the same time when i hit the nitrous. sometimes the force of acceleration will cause the rear jets to be uncovered in the float bowl.

TX19
07-03-2001, 12:54 PM
Thanks for the responses! I will try the carb cleaner around the intake. I never thought about something as simple as a vacuum leak.
The engine has not been in my boat yet. I ran into the problems on the dyno and plan to take it back to get it cleared up before I put it in the boat.
The fuel pump on the dyno has handled 800 horsepower on methanol since mine was tested so I don't think I was running out of pump.
I have also been advised to change out the high speed air bleeds on the carburetor to one or two sizes smaller.
I have never changed out air bleeds, and don't know where the high speed air bleeds are located.
I wonder how you tell if you need a smaller air bleed or a larger jet if you want to richen the mixture?

058
07-03-2001, 06:10 PM
Power valve working? PVCR should be .0935" if not you have the wrong metering block. Next step would be to increase the size of the needle/seat assembly, try Holley pt. no.18BP-109AS this is a .120" inlet- steel needle asembly. While you have the bowls off check to see the fittings are not obstructed by inline filters and the I.D. of the fittings are big enough. Make sure you have full pressure at WOT and at all rpms, no pressure drop at all. Even one lb. of pressure drop will drop the float level 1/8" and indicates a lack of fuel to the carb.

TX19
07-04-2001, 07:22 PM
Thanks for the response 058! I really appreciate it!
The carb was purchased new from a carburetor specialty company (and sent back to be checked after our first dyno session)and I think your suggestions have been done, but I will be sure to look before we test again.
I am not sure I have a problem in getting enough fuel to the engine. I don't seem to have any indicators of that. The problem seems to be in getting the air / fuel ratio rich enough to get the exhaust temps down.
I don't have a lot of experience with tuning a 9.5:1 compression ratio engine - maybe exhaust temps with them run a little higher that I am used to seeing?
I would still like to explore the air bleeds and their influence. Any one out there know about air bleed replacement and the effects
of changing them on an 8896 Dominator?
TX

058
07-04-2001, 08:54 PM
TX, Air bleeds are last resort, before you change them make sure the rest of the fuel system is up to snuff. As for the air bleeds they are located between the booster venturuis [one idle bleed and one hi-speed bleed per venturi] you will need to calculate hole diameter/area and change accordingly. You should have your carb set up for screw in replaceable bleeds by one of the carb tuning shops. They can be located by checking out the latest Natl. Dragster, look in the Performance Directory.

TX19
07-05-2001, 04:21 PM
058...thanks for the reply!
I have checked all I know to check on the fuel delivery. The fuel pump is producing 8 rock steady pounds of gasoline between the regulator and the carburetor from idle to 6,500 rpm's through a 1/2" fuel line. The fuel supply system is part of the dyno and is used on a regular basis. They have had no other problems similar to mine on the dyno. In fact one recent test was on an engine with more horsepower than mine and used methanol, so it makes since that if the system will deliver adequate alcohol to about 800 horsepower that the quantity should be sufficient for 660 horsepower on 92 octane gasoline. At least my logic says it's so. What do you think?
The 8896 comes with screw in air bleeds so all I need to do is change them out. There are two bleeds located on the outside end of each venturi, or a total of 8 in the carburetor. I need to know which ones to change and where they are (high speed and / or low) and when to change a bleed instead of a jet when you need to adjust the mixture.
Thanks again for you responses!

058
07-05-2001, 07:00 PM
TX, I think you about covered the supply side ok. I guess its time for the air bleeds, they [hi-speed] are located closes to the bowl vent by themselves. The other two are the idle and the intermediate circuit and are paired together. When run on the dyno what are the BSFC readings and are they equal on all cyls? It could be that you are really rich and burning fuel in the exhaust raising EGT. How about any signs of reversion or excessive draw thru? I'm starting to grab at straws here. I also run a 514 but didn't dyno it. Currently running a pair of 4781 DP and have no lean out with that set-up, I have a 7320 1150 Dom for it when I get a chance to change it. I'm starting to wonder if I'm gonna have a similer prob.

Allan Gorneault
07-06-2001, 08:21 AM
Just a stupid question but is there any chance the dyno you tested on was still pumping methenol ?? That will lean out an engine .

058
07-06-2001, 09:39 AM
Damn....I never thought of that, Thats so dumb its probibally true. Even a mix of 10-20% is enough to screw thing up. Good point!

TX19
07-06-2001, 02:46 PM
A.G.- Good thought about the alky in the mix, but the methanol was after me. I supplied my own fuel for the session and it went into a completely dry system. We ran through nearly 10 gallons of gas, so I am sure the residuals from previous runs were gone. I do appreciate your comments! I am really stumped on this one!
I am beginning to think it has something to do with the lower compression???

TX19
07-06-2001, 03:18 PM
058...the brake specifics were within .02 per cylinder all day. First pull with 4 Holley #92 jets showed BSFC's from .41 @ 3700
rpm to .45 @ 6000 rpm. There is a slight dip downward at mid-range, and that stayed there all day. Exhaust temps ran from 1200 deg, @ 3700 rpm to 1400 deg. @ 6000. The A/F ratio was between 15 and 16.9:1. We changed jets all day until we ran out at .149 inch in all four holes. The BSFC's were then between .43 and .51, exh @ 1100 to 1300 degrees and A/F @ 12 to 13.9:1 .... but horsepower was up nearly 100 from the first pull.
I have not seen any sign of reversion. A leakdown before and after the tests show 2 to 3% loss.
I have now reloaded on jets, have a full set (170.00 damn $ worth)of air bleeds and am ready to go back to the dyno, I just don't know what I'm going to do when I get there!
Whatcha' think now?

058
07-06-2001, 03:49 PM
TX, I am at a loss. I tried to think of everything and thats about it. I still think something has been overlooked but what do I know? The 9.5 to 1 compresson shouldn't have anything to do with it unless the cam is really mis-matched for the low compresson. I don't have much experence with Hi-performance/low compresson engines [except boosted engines] My 514 is 12.75 to 1 comp. with a cam from Comp's dyno shop ground for this combo, so far no fuel probs with that one. One last thought....are you running any carb spacers? How about trying a 1" or even a 2" and try both open and 4 hole...or how about a "Turtle" insert? Just a thought.

TX19
07-08-2001, 10:51 AM
058...thanks for the responses. I appreciate your suggestions. I too do not have experince with the 9.5:1 engines. I have heard one discussion about them on an MRN radio broadcast at Daytona and exhaust temperatures were mentioned - something about the fuel burn rate being different and doing things inside the combustion chamber that didn't happen at 12:1 and higher. I also read an article in a magazine about a dyno test on a 514 similar to mine that said they chased exhaust temperatures all day.. I know that feeling.
I am running a 1 inch spacer that came with the manifold, and will try a 2" and a "turtle" the next time out. I also plan to try a "cloverleaf" spacer. With all the suggestions I have from this forum, I have enough to take up another day on the dyno, so I guess I will get to work.
Thanks again to everyone!

TinMan57
07-08-2001, 11:22 AM
Just another thought to throw into the blender. Have you checked, changed cam timing? I've changed egt's from high 1300's to 1650 with a cam change on a gas burning drag boat. With 36 lbs of boost. I've never done a natually aspirated engine by egt but you should be able to change something by moving the cam.

Racing Ray
07-08-2001, 12:41 PM
Using a taller spacer will kill more carb signal. This means more air less fuel opposite of what you want.
You might try a 4 hole spacer if you have not. This will also help pull more signal.
The air bleeds do not work like jets, you must change at least 10 sizes to even notice a differance. Want less air more fuel use a smaller jet. Maybe this little diagrahm will help.
o idle air bleed
o intermediate air bleed
o high speed air bleed
-- squirter/vent
o high speed
o intermediate
o idle

TX19
07-08-2001, 06:43 PM
Tin Man....the cam was installed at +4 degrees at the cam grinder's recommendation.
Cam timing is something we will try on the next dyno pull. We tried different valve lashes on our last outing and picked up a bit by tightening up both intake and exhaust-but not very much.
Thanks for the suggestions!

TX19
07-08-2001, 06:45 PM
Ray...Man was I glad to see your diagram telling me what hole the high speed air bleeds were in. Now I can try out my new air bleeds I paid $170 for and at least know what hole to change out to change the top end mixture. Thanks also for the heads up on changing in 10 number increments - that will save a lot of time.
I hadn't thought about the one inch open spacer I am using versus a 4 hole for carb signal improvement. I have always run an open spacer with higher compression engines before and I guess never really needed more carb signal -anyway, I could always get good exhaust temps and air fuel ratios with higher compression combinations.
I am callings Jeg's tonight!
[This message has been edited by TX19 (edited July 08, 2001).]