Has anyone had any problems with stalling when choke opens? My 1600 Dual Port won't run when the choke opens. It's a new carb and I've had it apart, flushed it out several times with carb/choke cleaner and compressed air. I've checked vacuum (18~20 hg) at idle, i've replaced manifold gaskets and boots, new caps on the vac ports on carb, have adjusted timing, bypass and idle screws, but no change. The PICT manifold gets pretty cold under the carb if thats any clue. We wanted to try to keep the stock setup, but I'll try anything at this point...
If the manifolds are cold, then I'd suspect a clogged heat riser.
The risers direct warm air to the manifolds to prevent icing. It sounds as if that's your problem.
When the engine is warmed up, touch the risers. If they are cool or just barely warm, then they're clogged. They should be very hot to the touch. They can burn skin, so be careful when you're checking them.
If the rubber hose won't work, try a length of old clutch cable or other sturdy wire, chocked into a hand drill. Run the wire up into the risers and drill away till they're clean.
Tip-o-da-week: run the drill in reverse so the covering on thet clutch cable deesn't unravel.
Is your carb a 34mm or 30mm. I had a 34mm that I had rebuilt and was cautioned about this because apperently for some reason the 34's don't refurbish very well. I was told that if he sent out 10 carbs, if he was lucky 3 might work properly when he got them back. All I did to solve this problem was buy an adapter and ran the 30mm carb with the 34mm jets. I didn't notice any power differance. It does sound like your heat risers are plugged like BoatCop suggested. It may be icing up after the choke comes off.
I'm not sure I understand the operation of the heat riser. I can say for sure that the mounts on the muffler side of the heat riser connections are completely closed, they look like theyve been welded shut... I assume the exhaust is supposed to circulate through the riser tubing in order to heat the manifold area under the carb.
The manifold does feel cold to the touch, although it hardly feels like it's iced up. I will try to heat the area under the carb with a heat gun while the engine heats up and the choke opens. If this works, I'll be buying a new manifold as both heat riser tubes have been cut off of this one.
I'm a little unclear as to what exactly could be icing up, the manifold, or the lower section of the carb?
The heat riser mounts on the muffler side are supposed to be like you described. However, if the actual heat risers are missing from the intake I would definately recomend getting an intake with them intact. These ones should not be welded though. It isn't meant to circulate the actual exhaust through the heat riser, where it mounts to the muffler is just meant to heat up the air inside the heat riser and well as the name says heat rises and boom. Your carb or intake might not be icing up but if it is cold then the fuel doesn't have a chance to vaporize and well liquid gas doesn't burn.
Personally I would just do what I did. Save up some money and buy dual kadrons. I never had another problem after that!
30/31 PICT carb tuning problems
