No pulling power

Forrest Gump

Forrest Gump

CCCUK regional rep
It sounds like fuel starvation to me, and if you’ve not got a fuel filter, I’d suspect a partially blocked float needle valve. The car will run okay ish until the fuel level in the bowls can’t keep up with demand and then power will totally drop off. Start at the primary end.
 
Chuffer

Chuffer

CCCUK Member
Thanks Forrest , further investigation and a process of elimination over the next few days me thinks .
 
Roscobbc

Roscobbc

Moderator
Chuffer said:
The 750 carb sits on an Edelbrock Torker 2 single plane inlet manifold . A 3 speed auto , lock up torque converter and 3.08 : 1 diff ratio . You are right Ross that it does pull much better in the mid range rev band once on the move ( prior to this current problem developing ) and I regularly manually shift down to 2nd at low road speeds to keep revs up and prevent bogging down .
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750 cfm Carb is really too big for size of engine - being a vac secondary it'll work, and work OK (if jet sizes on primaries are OK - unlikely to be too small) a smaller carb should improve lower rpm pick-up. Torker inlet (being a single plane) is generally acknowledged to be a poor choice nowadays as compared with newer and more efficient dual plane designs. With a comparitively small capacity engine you really need the improved inlet port velocity and efficiency that the smaller inlet runners of a dual plane inlet give you. An Edelbrock Performer or Performer RPM or similar could be a good choice (if the additional height fits under your hood). Has the engine got an aftermarket performance 'cam' installed? - irrespectively the other thing to do to perk things-up a little (and this does have a down-side) is to swap-out that 3.08 diff for a higher numerical one, like a 3.55 or 3.89 - but then things will get all 'revvy' and noisy when cruising...........
 
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Forrest Gump

Forrest Gump

CCCUK regional rep
Carb CFM Calculation:
Engine capacity x max rpm x efficiency /3456

For my car
383 x 6000 x 0.9 /3456 = 598Cfm
I'm running a 600Cfm holley double pumper and it goes very well (circa 400bhp)

For a 305cu in
305 x 6000 x 0.9 /3456 = 477cfm !!!

The 90% efficiency value might be optimistic too, maybe 85% is more likely - so even smaller carb requirement.

Being of the male variety, we all tend to fit a bigger carb than we really need. Having said that I'd still like to try a 750 on my car.
 
Roscobbc

Roscobbc

Moderator
Andy is correct - so for you Chuffer a 500 cfm (and for me the 750 cfm that you have!!!!!) - seriously though I know the 950 cfm on mine is too big - it was used for dyno time on a race engine. I needed a fully adjustable and jetable double pumper. Reality is that on most engines the secondary choke should rarely be operational in normal use - unless doing a 'pedal to the metal' overtaking manoever.........o_O
 
Chuffer

Chuffer

CCCUK Member
Thanks for all the advice guys . A lot of it sounds a tad drastic and expense I could do without to be honest , especially an engine rebuild . Everything on the car is as I bought , big carb , Torker 2 etc. Having no history on the car I have no idea if the cam is standard or a hotter aftermarket . All I know was the engine is originally a 1985 Camaro IROC - Z with 9.5 : 1 compression ratio and the standard IROC - Z tuned port injection replaced with the Holley set up .
I do not want to replace the diff as I had a brand new replacement fitted barely three years ago and stuck with the standard 3.08 : 1 for more relaxed cruising .
I am thinking maybe a professional carb re - set up and a rolling road test might be a starting point .
 
Daytona Vette

Daytona Vette

Well-known user
IMO likely to be fuel starvation - quick easy and cost free remove the Carb and clean it out - you have been running without a filter - that is where I would start - been there got the T shirt
 
Mad4slalom

Mad4slalom

Well-known user
Chuffer said:
Thanks Forrest , further investigation and a process of elimination over the next few days me thinks .
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Hi chuffed, remember my similar issue turned out to be a bit of blue float chamber gasket partially blocking one of the two jets. 👍 good luck with the search
 
Chuffer

Chuffer

CCCUK Member
Cheers Mad4 . I wanted to get a rolling road test at Northampton Motor Sport and get everything set up properly but earliest they can book me in is 19th July !!! :eek: Looks like I will be doing more investigation work myself .
 
Chuffer

Chuffer

CCCUK Member
Not on mine Oneball :( This is a trouble with a car that has been fuffed about with in its past life . You never know what is right , wrong , good , bad , or indifferent . :unsure:
 
Chuffer

Chuffer

CCCUK Member
Thanks for the vote of confidence Ross . I have been swatting up on Holley carbs on internet until my brain bulged ! If I had not lost out on so much driving of it over this past year and more , I might well have pitched in and had the whole thing apart but I have decided to leave to the pro`s who will no doubt do it in a fraction of the time . By a bit of Googling I was amazed to find Williams Brothers Speed Shop that are units on what was a farm only 6 miles from me yet never knew they existed . Very hidden and discreet and secure . They have had write ups in Classic American magazine . I called round this morning and met the guys , really friendly and helpful and gave me a conducted tour of all their separate workshops . It was an Aladin`s cave of resto`s , rebuilds , up grades on all sorts of muscle cars and hot rods . They have a clinically clean engine build workshop plus dyno room and are into Chevy`s in a BIG way . They have body shop and spray shop too .There are doing a resto on a 1968 C3 and putting a totally rebuilt big block in it . They grew up around building drag racing cars and engines with their dad so lots of experience . It`s amazing what can be on your doorstep without even knowing . Got me booked in next week and will even drive me home after I drop the Vette off . :) (y) Will keep you all posted .
 
Mad4slalom

Mad4slalom

Well-known user
Chuffer said:
Thanks for the vote of confidence Ross . I have been swatting up on Holley carbs on internet until my brain bulged ! If I had not lost out on so much driving of it over this past year and more , I might well have pitched in and had the whole thing apart but I have decided to leave to the pro`s who will no doubt do it in a fraction of the time . By a bit of Googling I was amazed to find Williams Brothers Speed Shop that are units on what was a farm only 6 miles from me yet never knew they existed . Very hidden and discreet and secure . They have had write ups in Classic American magazine . I called round this morning and met the guys , really friendly and helpful and gave me a conducted tour of all their separate workshops . It was an Aladin`s cave of resto`s , rebuilds , up grades on all sorts of muscle cars and hot rods . They have a clinically clean engine build workshop plus dyno room and are into Chevy`s in a BIG way . They have body shop and spray shop too .There are doing a resto on a 1968 C3 and putting a totally rebuilt big block in it . They grew up around building drag racing cars and engines with their dad so lots of experience . It`s amazing what can be on your doorstep without even knowing . Got me booked in next week and will even drive me home after I drop the Vette off . :) (y) Will keep you all posted .
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More pulling power required? ... I can feel a steam engine conversion coming on ! we would see you arriving at the meetings then !!😂😂👍
 
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