Hesitation

[Johnny69]

I know this has probably been asked before but here goes.

Standard 1600 twinport, solex 34 carb, vac dizzy, timed at 7.5 btdc, new plugs, new points.

When it's cold it drives really well, no hesitation.

When it's warmed up and I try to accelerate its as if there is something holding it back before the power comes in. If I back off the throttle it seems to pick up? Does this in every gear.

Any ideas what to check?

Johnny

 

[aircoolsteve]

Hard to guess without seeing it but it may be "icing" in the carb throat due to a blocked heat riser. It may not be getting enough fuel after the choke flap closes. Check out the float level in the carb and the float valve. Best to give that carb a service before you get onto the icing check as its a lot more work to get the inlet manifold off. Good luck.

 

[bluenose]

could it be accelerator pump needs replacing or adjusting?

http://www.vw-resource.com/accelerator_pump.html

 

[Johnny69]

Hard to guess without seeing it but it may be "icing" in the carb throat due to a blocked heat riser. It may not be getting enough fuel after the choke flap closes. Check out the float level in the carb and the float valve. Best to give that carb a service before you get onto the icing check as its a lot more work to get the inlet manifold off. Good luck.

Carb has been cleaned out.

How do I know if the heat risers Are blocked?

 

[aircoolsteve]

You really need to know that your carb is working properly before you get onto the icing issue. Take the carb off but don't pour the fuel out of it. hold it the right way up and work the throttle. Watch for the jet of fuel from the pump jet. If the jet is weak, that may be your problem. There is a diaphram in the service kit that will cure it. The heat risers are part of the inlet manifold. They are the small pipes that are cast into the manifold just under the main inlet tract that the fuel/air mixture is carried to the cylinder heads. They bolt onto the heat exchangers. Hot air passes through this pipe and warms up the manifold. If it becomes blocked then the manifold stays cold. The air passing through the carb, into the manifolds creates ice just under the carb and stops the fuel/air getting atomized, thus the break in power.
If you have a hot air pipe coming from the rear tin to the air filter box, take it off its connection on the air filter and gaffer tape it to the air box inlet. Run the engine till the choke is open (engine at working temp), If the problem goes away, then its icing up due to those heat risers being blocked. If they are blocked, you will need to pull the engine, remove the fan shroud and generator to remove the inlet manifold. You will need to replace that manifold as personally, I've never found a way to unblock them. Good luck. if it turns out to be something else, let the forum know. we never stop learning!

 

[Bluesnailman]

id check your valve gaps and timing, might be firing a little too early once the cylinders are hot?

Personally, I go to the carbs last when I have a problem with running. 95% of the time its something else

 

[crede999]

my mate had similar problem turned out it was the coil (brand new flame thrower :shock: )_ so if you have one kicking about chuck it on and give it a try

chris

 

[aircoolsteve]

Try everything before you start on that inlet manifold!

 

[Dave.P]

Set timing to 30degrees btdc at 3500 rpm vac pipe disconnected and plugged carb end.
Set mixture correctly on carb ( have a search, tricky gave a good explanation on set up recently somewhere or at rob and daves site) I'd wager it's one of those two..
Are you running a stock air filter btw ?
If your manifold is icing below the carb you don't need to drop the engine to clear the heat risers, I've cleared two using the same clutch cable in a drill, it can usually be done by removing exhaust and up you go hehe single carbs do need a warm air feed to intake though to avoid all that icing shit
Have a look here.. http://www.vw-resource.com/hestate4.html" onclick="window.open(this.href);return false;

 

[Johnny69]

Thanks - will have a look tomorrow - I think the heat risers are working okay so it must be something else. I've just done the tappets so I'll see where I get to tomorrow.