BCDD Solenoid on 1980 720 Hitachi California carb

[720LA]

Hi all,

My L20B engine runs awful, and I'm not sure if the problem is electrical or if it's fuel. I'm leaning toward carburetor issues though, because it also gets less then 10 mpg. The only reason I was even thinking that it might be electrical is that sometimes it cuts out like the spark gets interrupted. But from reading up on this site about how the carb works I think maybe the BCDD Solenoid is stuck and is constantly enriching the air and fuel. Does that make sense? But for the price of that solenoid I could buy real estate in NYC! What the hell!

Anyone know any way to solve it that is more affordable? Or better yet - how do I test it so that if I"m wrong about it being stuck I don't waste time and money? 

I really don't want to give up on this truck but I just can't get it to run decent. Any help would be really appreciated.

Thanks,

Scott

[datzenmike]

Take the rubber cap off the center and turn the screw inside counter clockwise. The increases the manifold vacuum needed to turn it on and keep it on.

 

Seriously I doubt it's that causing 10MPG.

CARB:

Choke stuck on or part on? Take the air filter top of and look when warmed up. Yes... no?

Flooding. When running look at the round sight glass on the front of the carb. Fuel level in middle? Yes or no???

 

Dirty air filter?

 

Timing at 12 degrees? Yes or no? Retarded ignition wastes gas.

 

Vacuum advance working? Take distributor cap off and suck on hose going to the distributor vacuum advance can. Rotor should turn clockwise and hold until released. Yes or no???

 

Plugs and wires in good shape???Yes or no??

 

Valves set??? Tight valves will affect performance and economy

 

Do you smell gas???? Could there be a leak in the lines or tank??????? Puddle under truck???

[720LA]

Thanks a lot for taking the time to try to help. I'm still baffled though. New plugs, wires, cap and rotor. Fuel level looks good when running (maybe even slightly low,) choke is open when warm, timing could be retarded by at most 1 or 2 degrees but I'm sure it wouldn't be enough to make it run this bad. Vacuum advance works.

I can smell gas but not raw gas - it just smells like it's running really rich, and it's probably just because I've got some exhaust leak and rusted out floorboards so I'm just getting exhaust smell. (I haven't wanted to spend money on the exhaust until I can be sure I can get it running better) No fuel leaks - no puddles.

Valve clearance is a good question, but the problem seems like it gets a little worse and then a little better, so that doesn't seem like a valve clearance issue to me, but I could be wrong. Maybe one evening this week I'll go through them and see if that gets me anywhere. Even when it's a little better though, it's bad. It has barely any power and I really have to avoid hills. 

If the matchbox is bad it wouldn't be intermittent like this - right? Isn't it the case that it's either bad or not bad? Another thought I had was that maybe I should start replacing wiring. Maybe there's a bad ground someplace or a bad connection somewhere.

Anyway, again, I appreciate your help.

Scott

[datzenmike]

If it's getting 10MPG the plugs will be black dry and sooty.... are they? Knowing this will definitely point to over fueling... possibly a carb problem. 

[720LA]

Another good point. The plugs have been in long enough now so that I should be able to check that out. I'll check that tonight and maybe adjust the valve clearance and take a good look at the ignition circuit wiring to look for iffy connections.

Thanks for staying in touch on this.

[datzenmike]

Are you really getting 10MPG or was that good natured exaggeration? A 5 speed 720 2wd should get mid 20s on the highway even high 20s. 10 is so low it's hard to imagine. Ignition alone wouldn't explain it but a combination of things like timing, choke, fuel leak or flooding, Stuck open thermostat, brake dragging could add up.

[720LA]

Yes it really is getting about ten, and it's entirely possible that its a combination of things. You mentioned stuck open thermostat? Its got no thermostat in it. Would that impact gas mileage? Very interesting. I also read somewhere that an exhaust leak before the catalytic convertor can have an impact similar to a vacuum leak which is interesting. Maybe I better start fixing things one at a time and see what effects the way it runs and the gas mileage. I'll post each time I get some stuff done and let you know what the results are just for posterity.

[datzenmike]

The L20B is designed for maximum efficiency, power, economy and lack of emissions when running at about 185-190F. Always run a proper thermostat.

 

Can't see an exhaust leak affecting the mileage to any great amount.

 

Timing is important to get the rapidly expanding hot gasses pushing down on the piston tops at just the right time.. .