Cold starting the bike (@ 50* or so) took a few minutes of warm up time. Took about 3 tries to get the bike running, then had to hold throttle at 2k RPM for a full minute before idle could be achieved.
Once warmed up, things were fine and idle consistent at 1100 RPM. Re-starts were instantaneous with a touch of the switch. What really amazes me is the amount of acceleration when the Weber carb secondary opened up. ....65 MPH to 100 MPH happens VERY quickly. Engine ran smooth and consistent at highway speeds with no issues.
Occasionally experiences some throttle "lag" when starting out from a stop. I was pre-warned of this trait without the plenum preheating in place. Only experienced that at a few start outs from a standstill. When sitting stationary in neutral and hitting the throttle, zero lag is present....it only occurs when starting out, under load, when "lugging" the engine.
I monitored fuel usage for today's ride and was at 42 MPG for the highway riding, varying from 50 MPH to 80 MPH. That was exactly the same fuel mileage I was seeing prior to the conversion. The plenum heating will be next on the list to hopefully eliminate the occasional throttle "lag" I'm experiencing. Thinking about routing some exhaust heat via tubing up to the plenum. Not sure if that is a good idea but it would definitely be the simplest way. Still sorting out options:
1) Cooling System Heating
2) Electrical Heating
3) Exhaust System Heating
Saw where one aftermarket VW single barrel conversion used scavenged exhaust heat (EGR) for their preheating. Not sure how they achieved that but I'm going to think it through.
starting update:
I've "cold started" the bike a few times now and have a routine down to start it with one attempt. About 8 throttle twists, then hit the starter...... feathering the throttle for a few seconds will keep it running. Then lock the throttle at about 2k RPM for 60 - 90 seconds, after that point the engine will idle.
3 comments:
This really is a pretty nice mod and getting rid of the individual carbs should really simplify things. Interesting problem on heating the plenum. I thought that it was only a problem with a cold engine. Once the engine is started, I thought that there might be enough heat from the engine to keep it warm.
That's what I would think also, but at operating temperature, you can feel the lower plenum body and it is cool to the touch. The Carb Vendor was a former GM Engineer, specializing in intake systems. He utilizes the same Weber/Carter Carbs on older 6 cylinder dual carb Hot Rod set ups. He's found that to provide the proper enviroment in the intake system, preheating is a requirement for proper fuel / air mixture atomization. He warned me in advance that "lag" would be present without proper pre-heating of the plenum.
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