When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hello everyone this is my first post . I have just had a c3 5.7 ltr engine and auto box fitted to my 1958 Volvo tp21 sugga . It has a holly double pumper carburettor fitted that looks new . It starts fine will run for about 5 mile or 15 to 20 minutes. Then it looses power and stops unless I pull the choke out then it will run rough for a minute or two then I can drive another half mile it will do it again . It has the original mechanical fuel pump fitted and a fuel regulator tap that is set on the highest setting ie 5 . Anybody have any idea what the problem could be . Ps it smells of petrol when it’s running rough . Many thanks in advance for any help . Thanks ivor
You need 7 PSI at idle, if you have a stock fuel pump remove the regulator.
Can't tell clearly from the picture but that does not look like a double pumper, looks like a vacuum secondary.
Do the float bowls have sight plugs, if so check float level.
Have you adjusted idle mixture screws?
Have you checked timimg?
Obviously the carb is starving for fuel. But why? Doesn't sound like a float adjustment issue because those bad effects would show up sooner than 5 miles.
Like Melwff said, suspect the regulator. Its not doing its job.
I see mechanical linkage from primary to secondary throttle shaft, but do not see a secondary accelerator pump. Huge transition slots.
Are you using the front vacuum port for the distributor? Back port goes to some type of power brakes?
And lastly, do not re-use that base gasket. Its showing cracks and maybe heat damage.
You can purchase an inexpensive fuel pressure test gauge to verify fuel pressure before the fuel enters the carb.....or you can remove the fuel line from the carb inlet/secure it in a clear gallon container/crank the engine to see how much fuel is pumped into the container.
Obviously the carb is starving for fuel. But why? Doesn't sound like a float adjustment issue because those bad effects would show up sooner than 5 miles.
Like Melwff said, suspect the regulator. Its not doing its job.
I see mechanical linkage from primary to secondary throttle shaft, but do not see a secondary accelerator pump. Huge transition slots.
Are you using the front vacuum port for the distributor? Back port goes to some type of power brakes?
And lastly, do not re-use that base gasket. Its showing cracks and maybe heat damage.
Hi thanks for the information the front port is the distributor vacuum pipe . I have no brake booster fitted . I will try the fuel flow test after removing the regulator. Many thanks ivor
I'm confused. Front vacuum ports are yellow & black capped off. One of those is full manifold Vac. The other is "timed" Vac. Which you don't want.
The Vac port off the back of the carb goes . . . . . . .?
And, are you using a fuel line filter? If so, where? Has it been changed recently?
I am 99% sure that is not a "Double Pumper". Not seeing an additional pump.
Does it have a Inline fuel filter between the tank but before the fuel pump? If the gas tank has a bunch of rust the filter clogs and then when you shut down the filter opens back up. Change your filter or filters cheap attempt to eliminate the possibility.
Hi yes I have a filter each side of the pump . My next attempt will be a separate fuel supply and an electric pump . A new condenser is on its way just in case it’s breaking down . Thanks for your input ivor
Hi there I have put a separate fuel system in via jerrycan / electric fuel pump etc . In ran for about 1/4 mile . So can anyone tell me if inside the carb there are any spring valves etc that could shut the fuel off . Then I start the engine it will run again . The carb is a holly twin choke twin float chambers . Any idea would be helpfull. is it worth my time to get a complete carb overhaul kit . Thanks in advance
Is the gas tank vented? Loosen the gas tank cap, see if it makes a difference. Make sure your fuel filters are mounted in the proper direction of fuel flow.
Last edited by Cooter Tech; Mar 15, 2020 at 02:40 PM.
Hi it here the filter is the correct way round .when I run it on a Jerry can I had a pipe from the fuel from the engine fuel pump I run a long pipe to the filler cap which was open . Thanks anyway ivor
Hi if I had to change the carb I think I would ditch the twin choke and go for a single choke. I have no idea if I could get an adapter for the four stud inlet . ?
Hi what would be the best thing to do regards venting the valve covers ? . The car is positive earth as the vehicle is a radio command car . there are a lot of radio suppression devices . So we thought best to keep it positive earth .itd 12 volt
It looks like the gas filter is sitting on or close to the radiator hose. That could be causing the gas to vaporize as it will vaporize at about 140 degrees F. Engine runs at about 200 degrees F.
Last edited by Cooter Tech; Mar 15, 2020 at 07:04 PM.
C3 engine running problem
