Topic: '79 650 w/ a little problem

[PillaisTrace]

Hi,
  I just recently bought a '79 650.  It looks to be in great shape and the previous owner told me it had been well maintained.  When the weather is cold, <70 F it seems to have a "flat" spot when just starting out.  Also, after the first tank of gas it has started to pop on decel.  It has also died a few times after decelerating to a stop.  I put some fuel stabilizer in the first tank and was just wondering if that prevented the popping or if both of these problems are a carb issue, or if I'll need to replace some exhaust parts to fix the popping and the flat spot is something else.  It has stock exhaust as far as I can tell.

[750goes]

run a small amount of fuel cleaner through the next tank of fuel - it may assist with your issue of backfiring/popping - thats usually a lean issue associated with clogged jets, fuel starvation...but if it is running 99% then ride the bike.

flat spot  - wait till it warms up a bit I suppose.........

I usually splash in 30-40 ml per tank full..

[c_kyle]

1/3 can of Seafoam per tank.

[flatblack]

Yeah, popping on decel indicates a lean condition...

I've got one of these, also.  Haven't had it long, and haven't really had it on the street (it has a few issues...) but these things appear to be set up really lean, for emissions.  Mine also stumbles a bit when cold and revving from idle.  After going through the carbs, rack, cables, etc., it's either normal for this model or there's an accelerator pump issue that eludes me.

You can try adjusting the air screws a bit to see if that helps.  I believe they will work in reverse from normal, since they are on the front of the float bowl; e.g., turn it in for more air, out for less.  My book says 1-5/8 turns out from bottom and that actually seems to be a good spot -- better than 1-3/4 turns, anyway.

YMMV, HTH...

fb

[PillaisTrace]

Thanks for the responses.  I'm going to grab a can of seafoam tomorrow and see if that helps.  After that I'll tinker until I get the mix right. 

Thanks again.

[PillaisTrace]

Update:

I put the seafoam in and ran it for a while.  I let it sit for a day or so and then started it back up again.  It almost seems to be more cold blooded now than before. I still have the same problems and now think I'm going to tinker with the carbs.  Is an air screw the same as the pilot screw?  My manual says 1.5 turns out.  I'm at about 5000 ft.  Do I need to adjust for this?  Which way should I go?

[jesusno2]

that cb 650 to me shoulda had a 38 pilot jet instead of a 35 it clears up alot of them cold blooded issues. i usually drill the dumb things to a 38 one bike i had i drilled the pilot to a 40 with pods and straight 4 into 4 it got a little tad bit to rich when fully warm but i lived with a little soot on the plug for the ease of cold starting and acceleration. every cb 650 owner ive meet has the same issue and i have fixed the problem that way. the mixture screws don't seem to do enough not at a costal sea level which my elevation is 320 feet. 5000 ft elevation ya might have better luck with mixture screws good luck nature of the beast really.

[dusterdude]

what jesus said,them things were seriously lean from the get go,being at 5000 feet aint helping none.

[flatblack]

what jesus said,them things were seriously lean from the get go,being at 5000 feet aint helping none.

Wouldn't being at 5K feet enrichen it?

Anyway, on the air screws, they're at the front of the carbs (although hard to reach at the bottom of the bowl), right?  If so, I believe they work in reverse: turn them in for leaner mixture, out for richer.  I haven't been far enough into mine to know, but can the needles be adjusted?

That's my story and I'm stickin' to it...

fb

[dusterdude]

yea i can agree with that

[nickjtc]

Ditto all of the above. Sophie takes her own sweet time to warm up, whatever the initial starting ambient temperature. And if you rush it she will throw a hissy fit and refuse to pull away cleanly.

I tried the Seafoam-in-the-gas thing and it did not make any difference, either.

Also (off topic, but FWIW) tried the Seafoam-in-the-oil-just-before-an-oilchange thing. The oil that came out didn't seem any dirtier than usual. Perhaps the bike had frequent oil changes before I got it and no sludge built up inside...?

[PillaisTrace]

I went to adjust my pilot screws this afternoon and found that I'm missing one.  My questions now are: does this explain a bit of my problems? is a pilot screw included in a carb rebuild kit? if I need to rebuild one should I rebuild them all?  Any way I suppose it's a good excuse to get a better look at my bike.

[flatblack]

Also (off topic, but FWIW) tried the Seafoam-in-the-oil-just-before-an-oilchange thing. The oil that came out didn't seem any dirtier than usual. Perhaps the bike had frequent oil changes before I got it and no sludge built up inside...?

Next time you change your oil, drop the pan.  Only takes a few minutes.  You'll know right away how dedicated the PO was.

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[nickjtc]

Next time you change your oil, drop the pan.  Only takes a few minutes.  You'll know right away how dedicated the PO was.
fb

Per my "word to the wise" thread today, that's exactly what I did. It's a good idea. By the lack of crud that was in there I'm assuming that the PO did change the oil frequently; unless, that is, my very frequent changes since I've owned the bike have cleaned things out.

[dusterdude]

I went to adjust my pilot screws this afternoon and found that I'm missing one.  My questions now are: does this explain a bit of my problems? is a pilot screw included in a carb rebuild kit? if I need to rebuild one should I rebuild them all?  Any way I suppose it's a good excuse to get a better look at my bike.

1)not good.2)i would think so.3)doubt it.4)i would.good luck

[flatblack]

Somebody around here should have a pilot screw.  So should a junkyard...

But, yeah, that would account for a poorly running bike.

 

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[PillaisTrace]

Thanks to the screw from Soos my bike is up and running again!  I've decided to put superbike bars on and replace the broken tach as well as the speedo.  I'm thinking of getting bar mounted mini tach and speedo.  Anyone have any suggestions?