Is my 340 Overcarbed? Avg 5-6 MPG
A 770 ultra HP is a vacuum secondary carb, correct? List #86770? You mentioned a DP earlier. If it's not a Vac carb, which list number is the carb?
Cool that the idle and crispness are present, that's the first step.
Idle looks good as long as that's the point of highest vacuum. If it has a higher vacuum at a slightly lower idle number, that's OK. Set it there.
Try turning the float adjuster 1 flat clockwise on both ends and see if the low end numbers clean up below 2500. You will likely need to readjust your idle mixture screws as well. Do this How far out are the screw now? Once you do this and if it cleans up your low speed cruise, then go to the next step.
Take at least 2 jet sizes out of the primary, maybe three and see what it does. The secondary jetting if a vacuum carb won't come into play unless you are really into it.
There is a lot of power buried in the bad tune... No reason at all that you can't get it, BUT, it will take a little work.
My 770 is a vacuum secondary carb listed in the link below:
http://www.summitracing.com/parts/hly-0-86770bl
I may have mislead you by calling it a DP. Sorry, still learning here. It is a double pumper, however, it has mechanical primaries and vacuum secondaries.
I picked up a vacuum gauge and the max vacuum I am seeing right now is 12 which is above the power valve reading of 6.5 which is what is installed C-130. I will rig up some tubing to run that gauge into the cabin and record vacuum at cruising speeds tomorrow.
I will adjust the float levels as discussed above in the morning and let you know how that works. Air mixture screws right now are 3/4 out on all 4 corners. I just pulled the primary float bowl and put in 71 jets from 73 main jets so I will go for a test drive tomorrow to see how things improve. I will leave secondary jetting alone for now.
OK, for those who think its a parts mismatch, I will agree to disagree! I personally think its tuning. I hope my engine builder would not lead me in the wrong direction. Factors in play:
1) Engine was tuned out of the car. A/F ratios were based on turbine on the carb vice my wideband meter sensor mounted in the collectors.
2) Engine was also tuned with a 2" open spacer under the carb. Engine in the car is not currently running a 2" spacer due to hood clearance. Would that affect A/F ratios and jetting?
3) There have been a lot of pms asking is my IFR's are adjustable and what orientation my metering blocks are so here are some pics. It looks to me like the IFR's are staked in and are not adjustable. The PV (only one on the primary metering block) looks fine once I removed it and I vacuum tested it and it works as advertised. Yes, I know my gaskets are bad! I have replacements, but until I get this thing dialed in I am not going to change them! Just trying to answer questions before they are asked!
As always, I am open to suggestions and not trying to piss anyone off. Every motor has different personalities so I am trying to get to best advice for my current setup. Thank you all for the help!
