Rochester Carb

[CliftonRover]

I have a rochester carb on a rover 2.25L. the engine is 9.5:1 compression with a 2.5l cam with a petronix ignition. The truck seems to be running rich, and it is not idling as smoothly as I would like. any suggestions? how will the compression affect the timing, should I advance it more?
the engine also runs a little hot, and diesels when I turn it off.
thanks

[badvibes]

CliftonRover-

What do the spark plugs look like? Any carbon build up? When you mention dieseling after shut down I'd check the plugs. Is your cooling system OK? Running hot can contribute to this, do you notice the problem if you run the truck briefly and then shut it down before it warms up? I have a Rochester on a rebuilt, stock, 2.25. You can tune with a vacum gauge if you have one. Set for maximum vacum reading at idle, fuel mix and timing, with the vacum disconnected from the distributor. From there I adjust higher RPMs, slightly if needed, by feel/sound with the vacum re-attached to the distributor. My buddy Scott and I have also been known to set timing by the beer method. Set your bottle of beer on the wing as you're timing and adjust things so that you have the fewest ripples on the surface of the beer in the bottle at idle. Sounds strange but it seems to work fairly well.

Jeff

[CliftonRover]

the truck only diesels for me, when my father drove it it did not happen. I just guessed that I was putting extra fuel in the system.

[BellaCoola]

Dieseling is usually a result of unburnt gas in the carb.

You can try letting the beastie idle for a couple of seconds prior to shut down. I've heard that flooring it just after you turn the key sometimes works.

The best solution that I came across is a solenoid shut off attached to my carb (weber)...works every time.

Don't let it diesel though...pop the clutch if possible as dieseling is very nasty for your engine.

[CliftonRover]

I still can't help to think that it is running too rich, but if I lean it out anymore it won't idle with a reasonable adjustment on the idle screw.

[greenmeanie]

What jet size do you have and where/what altitude are you at? IIRC most overhaul kits come with a 52 jet while I found my truck ran/tuned much better with a 50 and I may have even tried a 48 at one time. THe 2 1/4 is on the small side of engines that used the BV.

[shortbutslow]

GM - I have a 51 in the one I'm rebuilding and I'm in Indy (715 ASL). What do you recommend, and how do you know when its right?

Thanks

[greenmeanie]

I'm sure there is a scientific method but in my case I set the float height and then tried tuning it. I couldn't get the engine speed to vary with mixture over the normal range of the screw so I bumped down a jet size. After that it brought the idle into what I consider normal behaviour, I tuned it and I've aced emissions ever since.

[CliftonRover]

I should have the correct jet size as the carb came from British pacific, but then again who knows, I will call them to find out what size jet they ship them with. I can get my engine speed to change with the mixture screw. I guess I can get it running right, so not I need to figure out why its running hot, my past rovers always ran cold, but this thing runs 3/4 of the way to hot or higher. the water pump is new, the radiator was just fixed, and the engine is new, so I figure the only other option is timing. with 9.5:1 compression should I advance or retard the timing? I would guess that for the increased compression it should be more advanced, but with it running hot I am going to retard it some and see what happens.

[gassner]

I just rebuilt mine a month ago and rejetted it to a 51. It had a 58 and would carbon foul the plugs. It would blow blackish smoke under heavy acceleration. What I found was that the power valve was stuck open causing if to over fuel. I completly took it apart and soaked all metal parts it carb dip then blew all ports out with compressed air. When I reassembled it I made sure that the power valve would cycle up and down and had to reset the the float height. This is a real simple task, reassembly took less than a 45 min. Now is starts with minimal choke and does not smoke at all during any acceleration. Also, after pulling the plugs, they are a light tan color. I may lean it out a touch more after a desert trip.

[JimCT]

timing and carbon

The timing is only important with the ignition on and the plugs firing. I would try the old method of taking the air cleaner off and holding the throttle open and slowly pouring water into the carb, giving it enough throttle to keep it running. Works well at cleaning out the carbon, which is probably what is igniting the remaining fuel after you shut off the ignition. Jim

[CliftonRover]

the engine is freshly rebuilt so I would home carbon hasn't built up in the short time I have run it.

thanks for the advice, I can see a little black soot on the rear fender where the exhaust leaves, so maybe this is a similar problem to the one discussed.