Proform 750 CFM DP carburetor tuning?

[BSB67]

I'm having technical issues (self induced) on my last couple of posts..

On the subject of air bleeds, I think we'll just need to disagree.

[justcruisin]

I can't see how changing mains will have an effect on idle AFR as all the fuel will be through the IFR jets. As far as WOT is concerned I get my idle cruise an moderate throttle right and tune WOT with secondaries, power valve and PVCR jets. Although I am tuning for the street and not the track. I agree with BSB67 on the air bleed effect. I guess there is more than one way to get the job done and we all do what works for us, good discussion though.

[NHCharger]

Still playing with the carb. I have actually driven the car about 16 miles. After a 12 mile run on Sunday I pulled three plugs (easiest ones to access). They look a little too white?? Not the greatest at reading plugs but I thought they show it running lean. Currently all four corner idle screws are set at 3/4 turn out. I reset them all at 1 complete turn out and went for a 3 mile drive. The idle speed dropped a bit after the adjustment and I could notice a stronger gassy smell when I pulled into the shop and let it idle for a moment.The car ran fine but with only 16 mile on the engine I'm still babying it.

Below are two pics of the plugs, front left to right, # 8,2,1.
tomorrow night I will pull the same plugs and also check the timing.

[firefighter3931]

Still playing with the carb. I have actually driven the car about 16 miles. After a 12 mile run on Sunday I pulled three plugs (easiest ones to access). They look a little too white?? Not the greatest at reading plugs but I thought they show it running lean. Currently all four corner idle screws are set at 3/4 turn out. I reset them all at 1 complete turn out and went for a 3 mile drive. The idle speed dropped a bit after the adjustment and I could notice a stronger gassy smell when I pulled into the shop and let it idle for a moment.The car ran fine but with only 16 mile on the engine I'm still babying it.

Below are two pics of the plugs, front left to right, # 8,2,1.
tomorrow night I will pull the same plugs and also check the timing.

Brian,

The idle dropped when you richened the mixture....that makes sense and shows that the idle circuit is now functional/responsive.  I would go back the 3/4 turn to eliminate the rich idle which will keep the plugs clean. Under no-load conditions it's OK to be lean. Idle AFR of 14-14.5:1 is fine.

Take it out for a 20 min run and keep the rpms steady at say 2000-2500 rpm then shut down right away and pull a plug. Don't let it idle at all. This should give you an accurate cruise (light load) reading on the plugs. 


We can revisit the wide open jetting once you get some more break-in miles on the engine 

Looking at the plugs it doesn't look too lean to me. 



Ron

[NHCharger]

Ron, Plugs after todays cruise. (Thursday nights cruise did not end well )I live on a dirt road so there is 2-3 minutes of engine idle driving until i get from the paved road to my shop.
The plugs from L to R  1-2-4-5.  They still look a little too white compared to my other cars. Would it help if I backed the timing down a couple degrees?

[firefighter3931]

Ron, Plugs after todays cruise. (Thursday nights cruise did not end well )I live on a dirt road so there is 2-3 minutes of engine idle driving until i get from the paved road to my shop.
The plugs from L to R  1-2-4-5.  They still look a little too white compared to my other cars. Would it help if I backed the timing down a couple degrees?

Brian, try richening up the idle mixture a small amount. It doesn't take much so go slowly....maybe 1/4 turn at a time 


Ron

[ottawamerc]

Nh that's how my plugs look too and according to my A/F gauge I'm running a little rich

Scott

[Nickrc3]

Firefighter3931 - yes, I have planned to continue the route with increasing the IAB's. Like you said, one more round of larger sizes and see what that does.

Well, I installed new #78 IAB's - no difference. Engine still runs best with the idle-mixture screws 1/2 turn from base. Plugs were pulled and though not clean, definitely not carboned-over & sooty. Exhaust smell has improved.
I'm now at the point where I feel generally satisfied with the results, therefore, may leave well-enough alone. She start good, idle is @ 835RPM, and has very impressive acceleration. Drilling the primary throttle blades is my next option, however, my focus is now switching over to my teenage car:



circa-1977. Those side window stickers were worth another 15HP 

Starting a new thread over in the body forum

[BSB67]

Firefighter3931 - yes, I have planned to continue the route with increasing the IAB's. Like you said, one more round of larger sizes and see what that does.

Well, I installed new #78 IAB's - no difference. Engine still runs best with the idle-mixture screws 1/2 turn from base. Plugs were pulled and though not clean, definitely not carboned-over & sooty. Exhaust smell has improved.
I'm now at the point where I feel generally satisfied with the results, therefore, may leave well-enough alone. She start good, idle is @ 835RPM, and has very impressive acceleration. Drilling the primary throttle blades is my next option, however, my focus is now switching over to my teenage car:



circa-1977. Those side window stickers were worth another 15HP 

Starting a new thread over in the body forum

Or you could do what was suggested on the second post of this thread and likely actually fix the problem.   

[Nickrc3]

BSB67,
          Yes, I suppose reducing those four IFR's would be the next logical choice. Their size is not specified on the 750DP spec card. Does anyone know what size may be installed on this particular carburetor? I had the fuel bowls off the carb this weekend, but never bothered to observe their size.

Thanks Guys!