No pulling power

[Chuffer]

Over the last two days the C3 has decided to run like a dog under acceleration and engine load . This has scuppered plans for a run out with Gus our regional rep tomorrow on Drive It Day . It fires up fine and revs well whilst standing but under moderate or hard acceleration there is a big loss of power . I have carried out the usual checks of plug leads and connections , had the HEI distributor cap off and cleaned the contacts . I run a small block with 750 cfm Holley with vacuum secondaries and am wondering if it is a vacuum problem on either the ignition advance or the secondaries . The sparks plugs are new having replaced them when I serviced it about 5 months ago and hardly driven since . Really fed up as was looking forward to a fun day out .

 

[Oneball]

A big power loss doesn’t strike me as being related to secondaries or ignition advance. If it’s not misfiring I reckon you’ve got a blockage in the carb or the throttle cable has slipped.

 

[Chuffer]

The throttle cable is ok . The loss of power is more like a rapid stuttering and to achieve 50 / 60 mph up hill requires dropping auto box down to second . Down hill on a fast stretch of dual carriageway it runs much better but it is still not as it should be .

 

[Oneball]

That sounds more like a proper misfire to me, I’d go back to the ignition system. Have you got any spare bits you can swop, cap, leads, plug, coil.

Is it still on points? Check them too

 

[Chuffer]

No spares unfortunately . The distributor is a HEI Street / Strip unit with no points . Thanks for the suggestions anyway .

 

[Oneball]

Check the HEI unit is seated. Clean the inside of the dissy cap and rotor arm. Check the rotor arm to cap spring clearance.

 

[Daytona Vette]

Possible Fuel Filter blockage - take it off and reverse blow it, on to a white piece of paper to see what you get

 

[Roscobbc]

Brainstorming
Myself, if you've first established the issue isn't electrial (like a coil breaking down) - and you may not want to do this but if you have exhausted all other things I'd be kinda inclined to remove the hood and air filter assembly, take a drive and whilst looking at the carb linkage (and specifically the vacumn pot to secondaries linkage) to see if there is a clue there. Unfortunately revving the engine at rest won't put enough load on the carb to enable the secondaries to open properly.
Question. Under normal driving conditions you should be able to drive for ages applying part throttle without sufficient load being put on the engine to activate the secondaries - that would include going up inclines etc.
Perhaps check for blocked fuel filter - do you have an in-line filter - is there one that fits in the fuel pipe entry. Holley carb gaskets are sometimes subject to breaking down, the bits from the gaskets can jam the float needles (not your problem seemingly) or create other issues. Have you checked when the 'stuttering' is occuring that it nor actually running too rich and trying to flood-up?

 

[Chuffer]

Check the HEI unit is seated. Clean the inside of the dissy cap and rotor arm. Check the rotor arm to cap spring clearance.

That was the first thing I did matey but thanks anyway .

 

[Chuffer]

Thanks for the brain storming Ross . Do you fancy coming over and riding on the fender whilst I take it for a blast ? I know just what you are saying though and am seriously considering getting the car booked in for a rolling road test and have the carb set up properly by a specialist that knows what they are doing as I am sure it could do with it what ever else may or may not be going on . There is not an in- line filter in the fuel entry pipe to the Holley . Running rich is a possibility as it does smell a bit fumey at the exhaust .

 

[Oneball]

Stuff you may want to look at but they’re all guesses.

Check both the advance mechanisms. You should be able to rotate the rotor arm(mechanical) and the baseplate where the magnetic pick up is (vacuum). Suck the vac tube to see if it moves.


There’s at least three vac ports maybe four on the carb/inlet. Check they’re all piped or capped.

Looking down the carb with the engine running, blip the throttle and you should be able to see fuel entering both barrels.


Check that all the ignition leads are separate from each other and not wrapped around themselves

Assuming it’s a Holley check there’s fuel in there by removing the sight ports.

Check magnetic sensor clearance in the distributor.

Check distributor hasn’t moved.

Try it without the fuel cap on.

Have you got a choke? Is it opening?

 

[Roscobbc]

Chuffer - I have been 'F' ing around (F being fiddling) around with American cars for the last 45 years. The first thing we would do with any any when we bought it (not knowing the service history) was 1. new plugs, points and rotor arm (if applicable) 2. Oil and filter change 3. Jiffy/rebuild kit for the carb. Problem with irregularly used cars is the degrading of gaskets, seals and 'o' rings within the carb. Today's fuel accelerates these issues.
In your case a carb re-build is a good preventative measure (even if it isn't your current issue) - and not a complex job. Setting-up float levels again isn't a difficult job.

 

[Daytona Vette]

"Looking down the carb with the engine running, blip the throttle and you should be able to see fuel entering both barrels"

That could well Singe your Eye Brows

 

[Daytona Vette]

No inline filter, oh dear! - take the Holley off and blow out the orifices with an air line

 

[Corvette]

Car been standing, drain float bowls and get busy with carb cleaner aerosol. It works for my holley,s, lawnmower and boat engine.

 

[Chuffer]

Stuff you may want to look at but they’re all guesses.

Check both the advance mechanisms. You should be able to rotate the rotor arm(mechanical) and the baseplate where the magnetic pick up is (vacuum). Suck the vac tube to see if it moves.


There’s at least three vac ports maybe four on the carb/inlet. Check they’re all piped or capped.

Looking down the carb with the engine running, blip the throttle and you should be able to see fuel entering both barrels.


Check that all the ignition leads are separate from each other and not wrapped around themselves

Assuming it’s a Holley check there’s fuel in there by removing the sight ports.

Check magnetic sensor clearance in the distributor.

Check distributor hasn’t moved.

Try it without the fuel cap on.

Have you got a choke? Is it opening?

Hi Oneball . I need to get over to my rental place and get my vac test kit as car is at home now 9 miles away and just decided to play up once I got it home ! The vac advance was the next thing on my list . I do not have a choke by the way .
Ignition leads are all straight through with separators and and not twisted together .
Vac ports are all as should be and nothing changed since I bought the car .

 

[Chuffer]

Chuffer - I have been 'F' ing around (F being fiddling) around with American cars for the last 45 years. The first thing we would do with any any when we bought it (not knowing the service history) was 1. new plugs, points and rotor arm (if applicable) 2. Oil and filter change 3. Jiffy/rebuild kit for the carb. Problem with irregularly used cars is the degrading of gaskets, seals and 'o' rings within the carb. Today's fuel accelerates these issues.
In your case a carb re-build is a good preventative measure (even if it isn't your current issue) - and not a complex job. Setting-up float levels again isn't a difficult job.

Thanks Ross , I have been toying with the idea of a carb refurb and proper set up for some time as have no history for it but have often felt that the with the Holley and Edelbrock Inlet manifold it should have more to offer in the power stakes for a while now . I did use carb cleaner only a week ago before finally getting her out on the road again . I am thinking of booking in for a rolling road road test and a proper carb set up to hopefully get it on `the button `.
Also thanks to all the other guys too and for the record it has only run a few miles since I did a service with new plugs , oil and filter change and hydraulic lifters out for checking for oil bore blockages and resetting pre loads .

 

[Roscobbc]

With 305 cubes and perhaps an oversized carb (650 cfm would be more than adequate for this engine) - and possibly an auto transmission with maybe a lock-up torque converter and an ultra low rear axle ratio (2.78 ?) and you'll have a recipe for perhaps performance that'll be a great cruiser but will be a little sluggish off the line and at lower road speeds.

 

[sublimemike]

Check choke still open

 

[Chuffer]

With 305 cubes and perhaps an oversized carb (650 cfm would be more than adequate for this engine) - and possibly an auto transmission with maybe a lock-up torque converter and an ultra low rear axle ratio (2.78 ?) and you'll have a recipe for perhaps performance that'll be a great cruiser but will be a little sluggish off the line and at lower road speeds.

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 .