Hard Starting

March 21, 2007 Update: A weak starter can cause hard starting in a perfectly tuned bike if does not spin fast enough. Details here

Is your GL1000 hard to start after sitting idle for only a week or so? This is a very common complaint … even for specimens that are perfect in every mechanical, ignition and carburetion respect. My own bike does this too. Here's why.

The consensus of opinion on this (a common problem that plagues all bike of this vintage) is that the low "head pressure" of fuel combined with the vacuum effect of a barely vented tank and the "stickiness" of the float valves contributes to the problem. Often, the vibration of a running engine is required to get the float valves to move enough to flow fuel. If fuel has evaporated from a short lay-up, this will require quite a bit of grinding on the starter.

Modern unleaded gasoline is not your father's petrol! Unleaded fuel is a real "witches brew" which contains many volatile, lighter components. These evaporate readily. This is why you need to keep the cap tight on your supply of gasoline for the lawn mower! Rapid evaporation can cause fresh fuel to develop a type of "staleness" which makes starting difficult in just a few days. I'm no chemist, but I'm told that smooth running in carbureted engines is way down the priority list for oil conglomerates since most autos are fuel injected these days.

(Please note that I'm not talking about long-term fuel staleness which leads to residue and gum formation after several months. Using products like "Sta-bil" can abate long term "bad fuel".)

The GL1000 has four carburetors which feed individual cylinders of 250 cc displacement. The fuel bowls are on the smallish size even for a 250 cc cylinder. The fuel bowls are necessarily vented to the atmosphere. The surface area-to-volume ratio for these small, shallow fuel bowls is high. Combine these factors with the characteristics of modern fuel, and you have rapid evaporation of fuel components in the bowls. Hard starting is the result for two reasons:

Compounding all this is the fact that the GL1000 relies on a mechanical fuel pump which operates only when the engine is spinning. On most bikes, you can simply turn the petcock to "on" and gravity will cause fuel to flow and refill the bowls after a short lay-up. Not so, for the GL1000. Fuel will not flow without the aid of the fuel pump unless the tank is ¾ full or higher.

At cranking speeds, the fuel pressure is trivial (2.4 psi), so it takes quite a bit of "grinding" to refill the bowls via the fuel pump. Further, the way the four carbs are plumbed together through the plenum complicates matters when re-filling of the carb bowls in this manner. The bowls will fill sequentially starting with the two rear cylinders, then in turn the front two. What generally happens is the rear cylinders will fire before the front, so you will invariably have an extended period where the bike is only running on one, then two, then three before all cylinders are firing. Owners usually panic during this process and fear catastrophe. It's really only a matter of (partial) fuel starvation.

Incidentally, extended cranking is a good way to fry your starter. Always crank in bursts - no longer than about 10 seconds at a time. Allow a break between tries for the starter to cool.

Here are my recommendations: