Regulars here will have already read my series of articles (here and here) about battling the ethanol demon – and casting him out of the fuel tank (and carburetors) of my ’76 Kawasaki Kz900. Well, I’m now in the process of doing the same to my ’83 Honda GL650 Interstate. The carbs are being cleaned – and the tank is being sealed.
But, I’m also doing another thing that was already done to the old Zed. I am re-jetting the Honda’s carburetors to compensate for the leaner E10 (10 percent ethanol) “gas” that I’m forced to feed her.
Here’s the deal on this: Ethanol was originally pushed into the fuel supply back in the ’80s (along with MTBE) as a way to reduce the exhaust emissions of the vehicles then on the roads – most of which were still carbureted and didn’t have computer-controlled fuel management and so could not auto-adjust their air-fuel ratios to accommodate different fuel mixes (and octanes).
Because E10 is 10 percent ethanol – and ethanol is less energy dense than gasoline – the effect (in an older vehicle with a carburetor and “fixed” jets) is a lean-running condition. This tamps down certain emissions, but a negative side effect is that lean-running engines tend to run hotter (and not as well, either). It’s bad for any engine to run lean – and hot – but it’s particularly bad for aluminum/air-cooled motorcycle engines to run lean (and hot).
Now, the ’83 Honda’s engine is water-cooled, but I still prefer it not run lean – or too hot. I’d also like it to run as well as possible on modern fuels. Hence, as part of my ministering to it, I am going to try an experiment. The factory jets – and these GL650s (and, apparently, the related CX series) have Keihin carbs with a main and secondary jet and the expected pilot jet – are numbers 118 (main) and 78 (secondary) respectively. The pilots are – apparently – fixed in place and cannot be messed with, though the air screws are adjustable once you file down the limiter caps.
The usual procedure when up-jetting is to jump two sizes, though the usual rule is to do this only when the bike’s engine has been modified – pod air filters, an aftermarket exhaust, etc. My bike is factory stock. The only difference is the “modified” fuel it’s fed. Remember: Circa 1983, Honda engineers assumed their motorcycles would be fed gasoline. Not gas less 10 percent gas.
The carburetors were jetted accordingly.
But 30-plus years down the road, the fuel is very different. In effect, running the GL650 on ethanol is like running it at high altitude. It is necessary to make some adjustments.
So, I have ordered new (richer) jets, sizes 120 (mains) and 80 (secondaries). I bought ’em here. The prices are very reasonable – and they have a pretty huge selection of both Keihin and Mikuni jets.
While I wait, I de-rusted and sealed the tank and also gave the carburetors a thorough cleaning. Many hard-starting, poor-running issues can be corrected by cleaning (and adjusting) the carbs. If you’re dealing with stuff that’s 30-plus years old, it’s to be expected that varnish/gunk/rust is possibly gunking up the works. Slides get sticky, needles and seats wear out, floats rot and leak. The ethanol in gas accelerates this process. One thing we’re probably all going to have get used to – those of us who dabble with old stuff – is more frequent carb maintenance, including partial/total teardowns to keep them clean internally. It also helps – when you’re doing a rebuild – to use a kit that contains ethanol-compatible parts, especially o-rings and rubber diaphragms/cups (accelerator pumps, etc.).
Oh, yeah – about those air screw limiter caps. Honda installed them to placate the Feds, to make it harder to “tamper” with the factory settings. That is, to richen things up from the factory lean setting. A tab prevents the screw from being turned in either direction more than about half to three-quarters of a turn unless you first remove the fuel bowl. That makes it impossible to do the fine adjustment, which requires that the engine’s running as you turn the screw in (and out) while noting the rise (and fall) of engine RPM.
The fix is easy. You can either file down the tab – or use a grinder to file off the little ridge cast into the fuel bowl that the tab buts up against. Be careful – proceed slowly – whichever path you choose. Just file off enough material to permit the screws to rotate completely with the fuel bowl installed. Now you can adjust the engine to make it run optimally – as opposed to running the way Uncle wants.
Throw it in The Woods?
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