You can tell if the bogging down is due to too much fuel from the rolling laps by having someone watch your exhaust as you 'start' the race (hit the throttle) if you produce a SUBSTANTIAL cloud of smoke, specifically as much as everyone else if not more, then you are flooding on the rolling lap.... easily done and easily cured, too.
Firstly, this solution only works if you are Direct Drive (have no clutch).... yet another reason not to have a clutch!!!
Basically, the vile Walbro can't be set properly to give you good race performance AND good rolling lap performance.... neither can the Tillotson for that matter... During the race, you can get pretty busy and might not want to play with the carb settings so..... set the carb for how you want to race, not for how you want to rolling-lap.
The concept is that the carb delivers too much fuel while on the rolling lap; this leads to a build up of oil and sometimes fuel in the crank case. When you hit the throttle to start the race, this excess is 'washed' into the cylinder and causes the 'bogging down' as there is too much fuel/oil for the engine revs.
So.... we need to REDUCE the fuel on the rolling lap. The approach is simple but the technique REQUIRES PRACTICE to get it RIGHT!
Basically, run the fuel pipe (near the engine so you can rest your hand on something) through you RIGHT hand so that it goes UNDER your thumb, OVER your index finger and UNDER your middle finger. Now bring you thumb and index finger together. That will have made a loop over you index finger that can be SHUT TIGHT with ZERO FUEL passing simply by squeezing your index finger and thumb together!
You MIGHT be able to judge your grip enough to reduce the fuel flow without stopping it (mentioned elsewhere in this thread).... but that's not easy as you don't know how efficient you fuel pump is. I’d argue, it's better to STOP the flow as required.
Basically, once the engine is WARM to running temp (not HOT!!!!!), you can SAFELY shut off the fuel supply so long as you rolling along. When the supply runs out, the engine will CUT. All you need to do is to release the grip, the fuel will re-flow and, so long as you are rolling fast enough.... it'll re-start. Even if it doesn't (and it WILL) you can always LIGHTLY choke to bring the fuel through but that is only RARELY required if your pump is working properly.
Now, you need to practice this, firstly at quite a pace so that you KNOW it's going to restart! Then, practice getting slower and slower as you shut off the fuel. In the old days, (with 100 National) we could get the pace to the point where your mechanic could EASILY TROT alongside and STILL you could re-start the motor just by opening fuel line again!
Now...... fuel/oil build up happens during the 2 or 3 rolling laps. It does take a good 'length of a straight' to build up too much fuel/oil so.... the ideal is to ensure that you have run the engine OUT of fuel/oil by 'pinching' BEFORE the start straight! This will 'dry' the engine, allow you to restart it and STILL have it comfortably running, damned nigh 'smoke free' as you need it for the 'start'.
The effect is ELECTRIC..... done well.... the problem is that you are SERIOUS danger of running into the bloke in front who is producing CLOUDS of smoke while YOU are accelerating just as you would on (for example) your second lap! You WILL need to re-learn how fast your kart comes off the line!
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Taken to its logical conclusion.... what happens if you get GOOD at this technique and are on POLE.....? You slow the pack to damned nigh WALKING pace during the final rolling lap: this floods ALL the karts who don't use the 'technique' and delivers YOU to the start with a clean motor.... My record on this from pole was to be the length of the straight at KIMBOLTON on the second lap because P2, P3 andP 4 had almost STALLED on the line and held all the others up! It's not kind..... but we are RACERS aren't we?
Taking pole for the final on that day, I was PUNCHED about 5 times on the rolling lap by the P2 driver (when we were out of sight of the start line and other marshals) who knew what I was doing but couldn't repeat it! You know who you are Chris, don't you! (None of the regular contributors here, I might add!)
In my day, you 'nipped' the fuel line next to the carb with your hand appearing to be about to CHOKE the carb! Others, who didn't know what you were doing, thought you WERE choking: they then tried copying that at this ultra slow pace..... and promptly stalled their engines! Tee hee!!
Believe me or not..... just TRY it. It’s another technique that you SHOULD be able to master...... in my opinion.... of course.
Ian
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Bogging down by 'ExtremeTkmDriver' (05 Feb 2013 @ 22:28)
