Jump to content

Newbie- Carb Flooding


Recommended Posts

Hi. I've just recently got a GT6. It seems to start reasonably well on most occasions from cold. But I have found on one or two starts that it doesn't get going. I probably turn over the engine in 3-4 second bursts with no luck. After 3 or 4 goes with 10-20 seconds in between there's petrol pouring out of the air filters. Is this likely to be the floats and petrol shut off not working properly? The other thing I've noted is that the petrol feed goes over the top of the rocker cover so there's a downhill route into the carbs. Just wondering if that's causing some sort of capiliary action.

Any advice greatly received.

Link to comment
Share on other sites



This is a common bugbear caused (usually) by slivers of rubber from the fuel pipe getting trapped in the float needle valve. Take a look at the fuel thread from 28th February 2016 and you'll find that Euan Douglas had similar problems. There's plenty of advice there. From bitter experience I know it can take a number of goes before you get rid of all the little b*ggers because every time you disturb the carbs you make more slivers. Try dropping the float bowls in situ to get at the float needle valve to avoid this problem. Regarding your fuel line route it shouldn't be going over the top of the rocker cover. The correct route is around the front of the thermostat housing in brass "bundy" tube but I don't think that this will be causing your problem.


Good luck



Link to comment
Share on other sites

there loads of Tee shirts for this , the problem  debris will be lodged in the back of the float valve so wont be visible in the float bowl  unless its passed through the valve


with the pipes off the carbs let some fuel pump through into a jar , see what you catch,


 Waynes right every time you refit a hose you make more  they breed like rabbits 


R9 is a harder rubber and worth changing all fuel to this,

even replace the thermo hsg route with rubber  not bundy ,, less joins = less problems 

Link to comment
Share on other sites

Make sure there are no sharp burrs on the metal ends of fuel line to carve the slivers. I also put a bit of vaseline around the ends of the metal fuel lines to help and get the rubber hoses aligned as much as pos and gently fit them.


Also could be sticking needle valves or there not seating properly. I had a flooding problem with worn or very gummed up needles not seating on both carbs, thought they might have been gummed up as car not used much when I bought it and soaked them in cellulose thinners and then flushed them through, still no good. Bought new ones in the end and this cured it. Wished I had just replaced in the first place to save the hassle. 


Floats heights set wildy out though these wouldn't alter if it's been ok before.


Float/s punctured.


Also had a flooding/very bad running problem after fitting an air filter upside down, so blanking off the cut out  for air intake at top of carb body intake, though it would run ok for a few miles.


Can you see if it's flooding from both carbs. If you take the air filter box off you can some times see fuel sitting above the jets and or fuel coming from the breather channel that is an oval shaped orifice around the top, right hand side of carb front face (from memory).


This is for Strombergs, though others have some of the same.



Link to comment
Share on other sites

Thanks for all the recommendations so far. I ultrasonically cleaned the float valves. Everything else looks good. Put it all back together and having primed the float bowls with petrol it started first time. I ran it for a minute at most and then turned it off. No sign of petrol. Having put the air filters back on, I tried to restart it. Choke and no choke it didn't want to start. Having turned it over a good few times I got petrol dropping out of the air filters. I pulled off the filters and there was petrol on the inlet on both carbs. Looks like the fuel was coming from the float chamber breather. I dried it off, left it for about 10 mins and then retried to start it with no choke but some throttle and after a couple of turns it started. Sorry for the long winded explanation. Am I just seeing the evidence of flooding or something else?

Link to comment
Share on other sites

Have a read of buckeye theres good detailabout strombergs





float needles dont last for ever and some floats have two needle arms they can be fitted upside down

and you get wrong float levels


stroms are pretty reliable floats are unsinkable , I would invest in new valves and double check the supply lines for floating debris, did you pump some fuel into a jar ....??


Make sure the filters do not cover any ports in the front face its easy to fit the filter elements or the air box upside down and you block the vents

Link to comment
Share on other sites

  • 3 weeks later...

So the latest on this is that I think I set up the choke wrong. I set the fast idle screw without the spacer behind the cam which I guess meant that the choke was opening the throttle very wide for starting. Whilst I haven't managed to get the choke set up properly yet (as I don't have a working tacho) I've not had a recurrence of the flooding since. Thanks for all the advice.

Link to comment
Share on other sites

just set the small tappet screw to have a minimal gap (books give various gaps but 1-2 mm is ok) between its head and the choke cam


do this after you have the idles top set to a steady idle speed of around 650/700   or what ever you are happy with

if there is no gap the choke cam will try to control the  idle ,and  not the idle screw  .

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...