poor mileage/carb issues

2462 Views 22 Replies 3 Participants Last post by mag, Oct 10, 2005

mag

Discussion Starter · Sep 18, 2005

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I'm still having flooding issues with #1 carb, it seems. However, all the plugs read white now. The bike starts with choke, but seems to not catch easily. I have to start a couple of times, then shut off choke once running, then throttle it and leave the throttle lock at 2000 rpm for a couple of minutes. It idles fine, no smoke, though sometimes the idle drops erratically. There is a constant drop of gas on the float bowl drain screw. I couldn't get the float in #1 to pivot totally free. I changed the pivot pin, float, etc. It seems there might be a casting problem with the pinion, ie alignment, so that it causes a 'wow' in the pin or something. It slides in easily, then at the last 1/3rd of the pin length i have to tap it into place. I don't want to break the aluminum pinions by trial/error tapping on the float pin to 'straighten' it? Also, worried about over-sizing the float pin mount holes in the pinions by burnishing them or reaming with a dremel. Suggestions? I'm only getting 28-35 mpg now. Maybe i set the float too high in an effort to seat the float valve? Before i was having fuel leaks, but at least 40mpg.

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exavid

· #2 · Sep 18, 2005

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Mag, if you have any binding in the float and it's pivot it's not going to be possible to get the carb working right until that's taken care of. Are you sure the pivot pin is straight? If you need to straighten it, do it on a hard flat surface by tapping it with a soft hammer, it should roll smoothly on a flat surface such a a sheet of glass on a very slight incline. You don't want to enlarge the holes in the casting, if the pin can move side to side in the carb the float level will be impossible to set. I would figure out the tight pin and then reset the float level so that it's the same as the other three carbs.The fact that you have to keep the throttle open a bit to idle does sound like the idle circuit is pumping in too much fuel, most likely due to the float level being high or the float valve not quite shutting off.

mag

Discussion Starter · #3 · Sep 19, 2005

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Thanks, Paul. As i said, i have replaced the float pin twice. The current one rolls flat, i checked before. I only have to throttle open at initial startup, a couple of pulls, then it idles fine. The bike accelerates great, and apart from a little choke/throttle at startup, it runs great. But my mileage really sucks now. All other tuneup issues are resolved.

mag

Discussion Starter · #4 · Sep 19, 2005

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If my float level was too high, why wouldn't the plug read black, ie, running rich. With the plugs almost all white, could the bike be running lean, ie not enough fuel delivery in carb 1, and causing higher fuel consumption overall?

axelwik

· #5 · Sep 19, 2005

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mag wrote:

If my float level was too high, why wouldn't the plug read black, ie, running rich. With the plugs almost all white, could the bike be running lean, ie not enough fuel delivery in carb 1, and causing higher fuel consumption overall?

With the additives in today's fuels it's very hard to judge mixture from looking at the spark plugs unless they are completely fouled.

When mine was running too rich all the plugs except one (which was fouled) were almost white. Can't tell anymore.

mag

Discussion Starter · #6 · Sep 19, 2005

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So if my mileage has gone down, and it seems like it's not getting enough fuel at startup, would this still suggest a flooding problem? I assume this is why my float bowl screw is seeping gas, though maybe it is just worn.

axelwik

· #7 · Sep 19, 2005

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mag wrote:

So if my mileage has gone down, and it seems like it's not getting enough fuel at startup, would this still suggest a flooding problem? I assume this is why my float bowl screw is seeping gas, though maybe it is just worn.

If your float bowl screw is seeping gas then I think the fuel level is too high in that carb. The fuel level shouln't be high enough to come out of one of the float bowl screws!

Here are some things to check: Binding or bent float pivotpin, float valve pin not seating inside valve body, foreign object inside float valve, float valve seat or pin damaged, hole in float allowing fuel to fill the float, and float bowl gasket interfering with float action.

mag

Discussion Starter · #8 · Sep 19, 2005

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definitely too high, and definitely binding on the float pivot pin, since i've replaced all the other parts, including swapping out floats/pins/valves. But the pin rolls flat on a table!

axelwik

· #9 · Sep 19, 2005

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Well, you definitely need to find out why its binding. Your bike will never run right with a binding float. There should be absolutely no resistance to the float travelling up and down. Try running a pipe cleaner soaked in carb cleaner through the float pivot hole... there could be some junk in there. Then look through the hole to make sure its perfectly round. If the pivot pin hole is crushed or out of round you might need to replace the float.

mag

Discussion Starter · #10 · Sep 19, 2005

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Thanks, Marco. Both the pin and the float pin hole are clear and smooth. The problem actually seems to be with the carb casting. The pin slides in smoothly, and when it reaches the last 1/4 of the way, i have to tap it in. I think it causes a 'wow' in the pivot pin at this point?

exavid

· #11 · Sep 19, 2005

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It would be difficult to correct the alignment of the bores in the carb casting without a straight reamer of the appropriate size, however if you could find a drill bit of the right diameter and push and twist it through, by hand, it's unlikely you'd do any damage and might be able to line things up. You'd need to run the bit through both holes to keep it in line. Other than that, a jeweler's file and a bit of judicious filing in the float's pivot might do the job. I'd try a little bit of both until I got the bind out. Unless you can get the float moving freely it isn't gonna work dependably. Any bind at all is going to change how high the float rides above or below the fuel level.

As for the spark plug readings, it take quite a few miles for any definiteshow in color unless the carbs are really way off, soot and white from over leaning can show up pretty fast, but a little bit off is going to take some time to show.

axelwik

· #12 · Sep 19, 2005

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mag wrote:

Thanks, Marco. Both the pin and the float pin hole are clear and smooth. The problem actually seems to be with the carb casting. The pin slides in smoothly, and when it reaches the last 1/4 of the way, i have to tap it in. I think it causes a 'wow' in the pivot pin at this point?

Try installing the pin from the other side.

mag

Discussion Starter · #13 · Sep 19, 2005

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ok. I realize now i was adjusting the float from the valve tang, and not the float arm tang. I had assumed it was the smaller pin valve tang since this is what makes contact with the valve assembly. Wrong, i guess. THis is possibly why the valve isn't seating? off-angle, not plumb float action.

exavid

· #14 · Sep 20, 2005

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Sure could be. The other three carbs are okay?

mag

Discussion Starter · #15 · Sep 20, 2005

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#1 is the only one leaking out the float bowl drain screw, and the only one i adjusted, from memory.

mag

Discussion Starter · #16 · Sep 21, 2005

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i took off the carbs, put the OEM fuel screen on the #1 float valve that i had from my other carb set, and adjusted the float to 21mm with the float arm tang. This seems to have stopped the leakage/flooding. The bike idles perfect now. Still needs a little choking at startup, but warms up quick. Not sure on the mileage thing, will report back. The bike seems to accelerate smoother at low rpm now. I still noticed 'hiccuping' from the carbs at startup, though. I think maybe my vacuum pistons are hanging up (i was in a rush to ride, so didn't take off the carb tops -- doh!).

axelwik

· #17 · Sep 21, 2005

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Sounds like you got it fixed. Let us know how it goes...

mag

Discussion Starter · #18 · Sep 22, 2005

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Hey Guys -- just went out for a ride, topped up and checked the mileage -- 41mpg city!! Not a drop of gas leaking anywhere, the bike idles perfect and runs smooth as silk.

Still a little choppy at first startup of the day, though i wonder if that is because i am starting it right after turning the petcock on. I would think there's enough gas in the float bowls. Once it catches, it holds idle without choke, but it sputters for a little while with choke on full at first. If i take it off choke briefly, crack the throttle a couple of times, then re-choke for 30 seconds, it holds fine.

Anyway, the bike runs like a hot damn now!!!!

mag

Discussion Starter · #19 · Oct 8, 2005

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Ok, so float drain screw was still leaking, and over the course of 1/2 a tank, mileage dropped. Also, backfiring. So, off came the carbs, again. I decided to have a closer inspection of the air-cut valve, and discovered i had installed it upsidedown /forums/images/emoticons/shock.gif So, i put it in properly, pin side up, and proceeded to readjust all the float heights in the carbs. Turns out some of the float heights were out a few mm, when measured on the inside set of the floats. Back together, whammo, runs great. So far, fuel consumption looks excellent. No backfiring, no leak so far. Crossing fingers.

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exavid

· #20 · Oct 10, 2005

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Glad to hear you cured your problem. :clapper::clapper::clapper:

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