Hi I have 1990 740 2.3 Auto with carburettor. Start fine but recently it idles really slow soon after starting (under 500 rpm). It also stalls at times. I think it should be idling much higher when cold till it warms up? Any ideas what I should be looking for? Thanks in advance. Pete

I'll kick the ball rolling assuming that its a pierburg carb.Starting with the obvious you could adjust the slow running mixture screw. If its got crud on it then thats number 1. Secondly check that your autochoke is functioning ok as this has steps on it which keep revs higher until it gets warmer. Thirdly check your positive crankcase nipple going into the manifold. If blocked it restricts flow of ''fresh air'' which bypasses the butterfly and is commonly blocked up. Then I would move onto the vacuum tube to the distributor which on my mode ran to the control box under the dashboard. Has your carb got an over-run solenoid in which case check that its not gummed up or that the feed wire has not broken due to hardening of the bio degradable insulation. Other obvious points are dirty air filter, crud and gum on the carb where the butterfly is, a simple case of slow running adjustment of the butterfly. Going further is the timing correct. Checking my handbook my engine had a 5 degree BTDC when most were 12 degrees as stated in haynes. . (dont ask me why !!!!) Going further still are plug gaps OK, Is inside of distributor worn..especially as this is very rarely checked these days as it isnt so easy to take off. Hope others will add their pennyworth. Good luck

Hi Sheerwater Took a look at the carb today. Its a Pierburg double barrel carb. The outside of it is so filthy dirty with oil/grease that I could not see any numbers other than on a tag that read: VOLVO 1357108 7 17952 51 I removed the plastic carb cover with the single nut. The choke butterfly valve was seized solid-I could not budge it. I cleaned up the mechanism, oiled it and freed it up. It now opens and closed freely. HOWEVER, the L-shaped rod that comes up from the bottom of the carb (which I think is connected to the bimetal spring and what makes the choke butterfly valve open and close) is not connected to the butterfly valve shaft. The L -shaped rod is connected at the bottom (where I think there is a shaft to the thermal spring mechanism?) but flaps about loose at the L-shaped top end near the choke butterfly valve shaft. Should this L-shaped rod be connected to the choke valve shaft? There IS a red platic piece that sits on the choke shaft at about the right place where the L-shaped connecting rod sits but I can't see how the L-shaped rod connects to it....I think a piece of this red plastic bit (perhaps with a hole for the L-shaped rod?) may have broken off......so the L-shaped rod has nothing to connect to? The L-shaped rod does raise up as the engine warms up so I think the thermal spring part of the choke mechanism is working as it should.) Please can somebody confirm my suspicion about the red plastic piece? Perhaps when the choke mechanism seized, the L-shaped rod tried to pull down and broke off the pastic connector piece? But I can't see the choke thermal spring exerting so much pressure to break a piece of plastic? I did take a picture of the top of the carb if anyone would be kind enough to take a look at it. Also, the top inside of the carb is filthy dirty with a think black oily junk which is what must have caused the choke butterfly valve to seize solid. And the outside of the carb is just as filthy dirty with the same black/grease/oil. Any tips or help from anyone with the Pierburg carb would be appreciated. Thanks Pete, London UK

As my 740 is no more this is from memory!!!! Ive looked at the old haynes manual and I think I can determine the L shaped rod tou are talking bout but from memory this is for the accelarator pump. My email is if you want to send picture. From memory again the choke has a positive coil for pulling on the choke and a negative vacuum control. If there is a lot of gunk about I would suggest you look at the crancase ventilation system. If you dont know where it is....underneath the manifold slightly towards the bulkhead there is an oval shapedcplastic box. black...out of this comes a half inch rubber pipe pipe. This goes to a T piece with a small rubber pipe off. this can have a flame grill insifde which gunges up. this small rubber pipe goes to manifold side of carburetor. the nipple into the manifold can block up resulting in crud oil going up and passing through the carb instead of being sucked into manifold direct. If you send me picture by email I will try and determine your L shaped rod and its connection.

Thanks Sheerwater Another Volvo owner confirmed that myred plastic piece is indeed broken so I won't e-mail you the picture-thanks all the same. But I will take your advice and see if that breather thing is blocked as soon as the weather improves. Thanks for all your help and Happy New Year. Pete

Pleasure, worth checking vent ASAP as any pressure build up can blow seals. Happy New Year

Hi again Sheerwater's posting mentioning the accelerator pump made me look into this further. I seem to recall from another car I had that when you blip the throttle, a neat jet of fuel can be seen being injected from a little nozzle down into the venturi. I can see this nozzle in my Pierburg carb but nothing comes out of it when I blip the throttle. Should I be able to see the jet of fuel? If this is not working as it should, it would explain why the car is really sluggish when I accelerate. (having never driven a 740 before, I thought it was naturally sluggish) Also, does anyone have any pirctures of the top of a Pierburg carb? I am now thinking that the L-shaped rod that is not connected to anything (which I think is the linkage from the choke mechanism to the choke butterfly valve) may not be the choke linkage rod after all....... Cheers Pete