89 Gas mileage improvement

[frankd]

Last fall, just before we went on our 4,500 mile trip out west, I changed my carb. diaphrams. The bike ran a lot smoother under load, but my gas mileage went from about 40-42 MPG overall, down to 35-38 MPG. When I was above 5000 feet, you could tell that it was rich. When I got home, I checked carb. fuel levels and all 4 were high, so I adjusted them. I had problems with the carb floats and finally changed the needles, float gaskets, and the O rings on the float bowl drain screws to cure fuel leaks that developed when they were disturbed. Now the bike ran fine, but the gas mileage didn't improve much. I still was getting just shy of 40 MPG. I decided that I wanted to adjust the slide needles to lean out the mid-throttle mixture, so I moved them into the jet by about .075". When I started it, it was too lean. Unless I opened the throttle very slow, it would die. I then moved the needles back out so that the change was .045" Now the bike ran OK in the garage so I took it for a short ride. It felt OK. Today my wife and I had a chance to take a longer ride. Before I changed the needle adjustment, you could start my bike cold without the choke unless the temperature was below 50 degrees. Today it was almost 80, and it would start without the choke, but then die. I used the choke to get moving, then I turned it off. It ran OK. On my side streets, I hardly used any throttle. When I pulled onto a 40 MPH road, I cracked the throttle in 1st, and it bogged slightly and then pulled good. After that, no problem with throttle response. The motor sounded a lot happier. I filled it with gas and drove 98.2 miles on state highways. I ran about 65 MPH, (GPS---68MPH indicated---my odometer is accurate) and I did pass some cars in 5th gear while running the speed up to 75-80 briefly. It took 2.22 gallons to fill it again, which figures out to 44.24 MPG.

[Big Lou]

GOT TO TRY THAT

 

THANKS FOR THE POST

 

NOW TO GO PLAY:cool10::cool10:

[cimmer]

Hey Frank, have you ever replaced the sparkplug wires and caps on your bike. I wonder if that might not help you out some also.

Just asking.

Rick F.

[pmelah]

ok im intrigued how do you move the slide needle out .045 do you add washer or somthing i have never don it so dont know

[frankd]

I moved the needle IN so that I'd lean the mixture out. The MK I bikes have a clip on the needle that you can just raise or lower. The MK II's have a non-adjustable needle. I removed the spacer that raises (or moves out) the needle and measured it. It's a round nylon type spacer that has a locating pin and a nub on the end that rides on the bottom of the plunger. I measured the thickness of the shim (including the nub) and it was about .125" thick. I removed the spacer and replaced it with 3 brass washers I bought at Ace Hardware. I also found that the washers I bought weren't all the same thickness. Some were about .024" and some were as thick as .029. I picked a combination that measured about .080". That indicates that my needles are .045" further in. When I said that I'd moved the needles out some in one step, that was because I moved them too far in initially.

 

Frank

[frankd]

Rick,

 

I have checked and replaced 1 defective plug cap on the 89. You can verify the condition of the caps, and also if the coil wire connections are OK by measuring with an ohmeter from the plug end of the cap to ground. You will read the resistance of the cap and the coil. All 4 should measure almost identical, and if memory serves to total resistance you will measure us about 28 Kohms. Also, as I remember MK I and MK II bikes measure slightly different. The plug wires themselves will not add any measurable resistance to this test because they are solid core wire, not resistance wires. Of course this doesn't test the condition of the plug wire insulation. My bike has always run perfectly on all 4 cylinders, but was a little rich.

 

Frank

[Keemez]

Hey Frank, mind if I jump in and lowjack this thread? Thanks!

 

I've got a related tale of woe. Some of you may remember my ongoing troubles with the OEM fuel pump last fall. ( http://www.venturerider.org/forum/showthread.php?t=68861 ) I did eventually snag up a Mr. Gasket pump and installed it...and promptly noticed a considerable increase in fuel consumption.

 

Recently I had the carbs off (man, what a colossal pain. I am NOT doing that again as long as I own this thing), mostly disassembled, and ran each one individually through my ultrasonic cleaner. Probably more for peace of mind than anything else- I did not see anything specific that led me to believe anything is seriously awry in there. My assumption was that the 3psi of the MRG being higher than the OEM might have been causing the float needles not to seat properly. Carbs back in and a fresh tank of eth-free gas through it yields approximately the same mileage as before, but still down from where I used to be with the OEM pump.

 

I recently ordered a new set of diaphragms because mine are indeed pinholed (and el-cheapoed in the form of multiple RTV blobs). I suspect that like Frank, once I get around to installing the new phragms, my mileage will decrease even further. A very simplistic view of the sitch going on in there tells us that the diaphragms' purpose is to pull the slider and thus the needle up out of the jet and let more gas be pulled through. Common sense dictates that if the diaphragms can't pull as hard (because they leak, due to pinholes), the needle will stay in the jet longer and less gas is consumed.

 

So in chasing my mileage, I've gone back to the idea of reducing the thickness of the nylon spacers on each of the needles. I measured them (I've "modified" on them before) as follows:

LF: 1.53mm RF: 1.49mm

LR: 1.65mm RR: 1.52mm

 

You might have noticed that my LR nylon was thicker than the rest. I went to work on all 4 of them again and even though I got them slightly lopsided they all measure pretty close to 1.49-1.50 now.

 

Then when re-reading this thread ( http://www.venturerider.org/forum/showthread.php?t=28432&highlight=needle+shim ) and particularly post #13 ( http://www.venturerider.org/forum/showpost.php?p=302298&postcount=13 ) I've got myself all confused up on what the proper stackup is. Mine is as follows (image attached at bottom): nylon spacer, steel washer, e clip, steel washer, spring, plastic screw. To make a long post/story short, my question is: is it JUST supposed to be the nylon spacer underneath the e clip, or is there a steel washer between the spacer and the e clip as well? I was kind of thinking that the washer being under there makes a nice flat surface for the spring to perch against. But those washers range in thickness from .38mm-.42mm, which since they're currently under the e clip, that brings the needle up out of the jet by that additional amount as well. The thing is though: that's how it's been since 2010 and there were numerous times I got over 40mpg with it. Now I'm lucky to hit 35. I will also include that I noticed that really rich smelling gassy smell after the fuel pump had been replaced, and the tailpipes are indeed fairly sooty. Plugs kinda dark but not black. Everything points to a rich burn condition. I'm just tryin to lean er out some.

 

K, I said too much as usual. Here's the needle stackup pic.

[campfire12]

Skydock at one time had machined shims he made that were just the right thickness. We used them on my 84 and milage is constant 43-44 mpg. With 2 up and pulling the trailor me and the wife got 40-41 mpg up and back to freebirds md.

[frankd]

It's just the nylon spacer. The washer goes underneath the spring.

 

If your spacers are about 1.49mm thick (.059") your needles are in about .020" (.5mm) more than mine. When I had mine about the same as yours, my bike ran real lean. I never rode it like this, because I could tell in the garage. As I said above, I'm using brass washers for a spacer, but mine measure about .080" (2mm). Did you check the fuel level in your carbs?

 

Frank

[Keemez]

Weird. I wonder how/why I wound up with one washer tucked under the clip all that time. Well, since my nylons are marginally thin at this point I better leave it the way it is. It seems to run fine like this, although I think I'm borderline lean what with the latest modification to the stackup thickness. Since I rarely ride at that load/RPM I'm not going to worry about it too much.

Thanks!