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Good morning !
First of all, I'm a beginner in mechanics ^^
I am the proud owner of a windsor 351 v8 5.8L with a carburetor and a 3 speed automatic transmission. This is a 21 foot Class C motorhome.
The engine runs perfectly except for the first 3 minutes when the engine is cold.
There are backfire that bother my neighbor ^^ and I can see grey smoke from the exhaust.
The RPM during this backfire moment (2-3 minutes) is around 1400 and when the engine is warm the RPM drops to 800 in parking mode or 650 in drive mode (and no exhaust smoke)
How can I avoid these backfire ?
Thanks a lof for your help !
Depending on the carburetor, there may be cold adjustments you can make. If it's just a simple electric choke, you should adjust it when the engine is cold. You loosen the 3 screws that hold the electric choke housing and turn the housing until the plate almost closes. There should be a hard stop to prevent the plate from completely closing, and that may also be adjustable.
Other carbs may have a vacuum controlled stop on the choke plate that may also be adjustable. You can manually pull that vacuum lever and push the choke plate against it to check and adjust the gap with your third hand.
thank you so much for your answer !
My carburetor is a Holley 4180c and I see I cannot turn the housing like you said but I found (I think) the hard stop you said. Pictures for show you this.
I m not able to turn this hex head (too rusty I suppose) but when I checked this hard stop I think it wasn t in a good position. Now it s seem better because the choke plate is not completely closed.
I will test tomorow again.
Other thing, I don t understand totally how the choke works despite many videos on that... I understand when ignition is on, 12v heat the coil of the choke for open slowly the plate and like that have a rich mixture at the begining
and then balance mixture. But is there a real link between the temperature of the engine ? If we don t heat with the 12v, the temperature of the engine should heat the coil ?
The round housing that has the electric connection on it is what you turn, by loosening the 3 screws holding the retaining ring. It looks like one of those screws has a stripped head.
You have the concept of operation correct; the choke helps enrich the A/F mixture when the engine is cold. As the engine warms up, it needs less enriching, so less choke is needed. In most cases, as the engine warms up, the automatic choke needs a heat source to slowly deactivate it. Older chokes ran a heater hose next to the choke housing to help it warm up. The idea is that by the time the coolant warms up enough to affect the choke, the engine should be warmed up as well. Later automatic chokes used the electric heating element inside the housing to warm up the choke. But they all need some kind of stop to keep from completely closing off the air supply when the engine is cold.
I can't tell for sure from your picture, but I think what you circled may be the high idle cam setting. One of the other things that most chokes did was to increase the engine idle when activated. This keeps the cold engine from stalling.
