Carby starving after 80kph

[commy vk]

I have dual fuel with varajet standard carb black 3.3 engine
I have recently replaced the fuel pump to be able to run petrol in case the gas system fails.
Everything was going fine until I switched over to petrol on the highway and after 80 kph when the carb seemed to be starving and jerking and at times stalling until I changed back to gas which the car will run fine.Any ideas where to look?
I have had the butterfly shafts rebushed recently and renewed gaskets.
I can drive around the city and it's only when I get up around the 80 kph where the problem occurs.I have also checked the throttle position sensor and the anti dieseling thing.

[VK SL 3800]

Will the engine sound like its starved at high revs in lower gears? Or is it just in top over 80?
You could have a clogged up jet or something, especially if you've only been running gas for a while.

[commy vk]

Thanks for that and from what I can gather is that the secondary butterfly only opens at a certain speed and I'll strip the carb and have a look at the jet/s.
Probably just go to Sprint Carbs and get a rebuilt one off the shelf...Cheers.

[red_vb]

Thanks for that and from what I can gather is that the secondary butterfly only opens at a certain speed and I'll strip the carb and have a look at the jet/s.
Probably just go to Sprint Carbs and get a rebuilt one off the shelf...Cheers.

i have one of those carbies on my red 202 and i run dual fuel, the only problem with mine is (puff)of black smoke when i overtake. my mister has put carbie cleaner down it and its running better now. i was told its single barrel with secondary when u put your foot down/punch it then the secondary opens. i have heard alot of people dont like these carbies, turning reasons given.

[ari666]

check/change your fuel filter. then check your timing, gas can run far more advance than petrol without pinging, so you may be way over your mark.

[VK SL 3800]

check/change your fuel filter. then check your timing, gas can run far more advance than petrol without pinging, so you may be way over your mark.

Have you put on a HEI dizzy? otherwise you cant touch your timing.

[ari666]

lol, i keep forgetting about that stupid est thing.. so yeah, what VK SL 202 just said...

[scozz76]

My old VK developed a cough and fart syndrome. I narrowed it down to the dizzy had moved from the correct timing marks.
From memory, you set your timing mark to 6 degrees BTDC, then line up your rotor button notch to the notch on the dizzy housing (should be pointing to #1 lead).

Although it's EST, if the timing marks are out, there will be a problem.

Please correct me if I've got my numbers screwed up - it was approx 15 years ago when I fixed it.
Anyway, that solved my problem. I did not have a gas system, only petrol.
This may not have anything to do with your problem, but it's worth having a look.

[commy vk]

Just an update on the carb problem so I went down and bought a new fuel filter before christmas and fitted it and after christmas went away to the country and along the way I switched over to petrol and then the car was running intermittantly and at times even dying so I had to restart on gas.
This was going on every time I switched over to petrol so I left it on gas until I got home and lifted the bonnet and I looked at the fuel filter and it had fallen apart inside.As it was a none Ryco I just assumed because of the age of the car they were no longer available so make do with the inferior one.As I was running under a quarter tank of fuel the crap from the tank must have come thru and ended up perforating the small filter inside the inlet of the carb.I stripped down the carb and put a rebuild kit thru it but it mad no difference and after doing a comp test thinking a bent valve but they were fine (good consistant readings)I was getting ready to have it towed to the mechanic shop when I thought to just test the ignition timing and blow me down she was off the bloody radar....Somehow as I was mucking around installing the fuel filter I must have moved the dizzy about 10 mins on a clock dial and all I had to do was line up the timing marks on the harmonic balancer and the dizzy with #1 piston at TDC.Now I have a perfectly running dual fuel.

[ari666]

check/change your fuel filter. then check your timing, gas can run far more advance than petrol without pinging, so you may be way over your mark.

*clears throat*

ummm. yay me! Lol