Modern Buddy

Ever since day 1 my Blur's had a problem with cold starts. Never went into high idle and, on especially cold days, the throttle had to be constantly cycled until the engine was warmed-up.

I'd had the carb off at least 3 times looking for such things as clogged ports, improper float height, bad autochoke, etc., and was on the verge of just learning to live with it. This last time however, I decided to take a closer look at the fuel feed to the enricher.

The main portion of the enricher circuit resides in the top half of the carb (as opposed to the float bowl). Specifically, there's a long brass pickup tube that fits into a cylindrical reservoir cast into the bowl. The reservoir itself is fed via an inlet in the bowl. On a hunch, I hooked a hose into the reservoir and tried to blow out the inlet. Nothing doing, so I took a close look at the brass fitting on the inlet and it seemed OK. Then I took a closer look at the pinhole passage between the fitting and reservoir. Voila, there wasn't any. A closer look revealed that this wasn't a casting error, rather, the Einsteins who originally prepped the scooter had apparently attempted to clean out the passage with a sledge hammer and railroad spike, and thus sealed it altogether. (These are the same guys who overfilled the tranny, underfilled the tires, and loused up almost every piece of paperwork that came with the scooter.)

I drilled the passage out with the smallest bit I could find and further restricted it with some tiny brass tubing I had lying around. The result was that I could now get a reliable cold start by cracking the throttle a tiny bit to add more air into the mix (the tubing I used was too large and provided a way-too-rich cold-start mixture).

Got a new float bowl from Scooterworks a couple of weeks ago and finally had the chance to install it this past weekend. Night and day difference!

Now I need to find something else upon which to fixate.

A most excellent find/fix. Thanks a lot for sharing your detective work - it may help others with a simular problem.

Thanks for sharing.

My Blur has always started great cold, but I've noticed with this warmer weather, it doesn't seem to be going to the cold map (or using the choke as much). It hasn't died yet, but it just hasn't revved as high when starting.

I think its normal, just haven't been used to it since it was winter time when I got my Blur.

Well, what's referred to as the choke is really a thermostatically-controlled plunger with a built-in electric heater. When cold, the plunger is retracted, allowing extra fuel to enter the carb via the cold start circuit. As the "choke" heats up, the plunger pinches off the circuit.

So, I'd would imagine that the initial boost you get from this arrangement would vary with the ambient temperature, i.e., super cold = plunger fully retracted; not so cold = plunger partially retracted, etc, etc. In other words, I'd guess that the behavior you're seeing is normal. Since I never had the thing working during the coldest part of the year, I don't have a basis for comparison. With temps in the 40/50s, I'm getting about 2500 - 2800 RPM cold, then dropping down to about 1750 - 1800 when warmed up.

Personally, I think it's kind of a lame system for three reasons:

1) The usual failure mode is for the choke's heating element to fail, which pretty much leaves you running too rich. Better than too lean, but still not great.

2) It's not feedback-based. Once the choke is hot, the assumption is that the engine is warmed up, and that's certainly not true in all cases.

3) It needs to draw power from your electrical system in order to keep the choke disabled and the cold start circuit closed. With a typical resistance of 5 to 10 ohms, that's 1.2 to 2.4 amps that could be better used elsewhere.

As time allows, I think I'm gonna dust off the old lathe and see if I can build a manual plunger arrangement to replace this.

I'll see if I can find it again (just did a quick look around with no luck) but in the past, I've been able to find a manual choke extension that would allow you to relocate the manual choke on an aftermarket carb to elsewhere on the bike. I'll throw up a link if I run across it again.

I would frequently encounter this when I just purchased my vino.

thanks for sharing!