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.
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.
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.
Might try carb cleaner for a less explosive reaction.
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.
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.
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?
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.
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
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.
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!