Not much power...

meanstreakmark

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Hi- I have a concern that I'm starting to research and was wondering if anyone can point me in a direction - to save a little time.

The issue is that I don't seem to have very much 'get up and go'. Certainly nothing near like some of the You Tube videos wherein they're burning out or popping wheelies. If I get on it, I'd better pack a lunch!

The specs: '81 xs650 (of course), Hugh's pma swap-out with Pamco ignition (the kit from Mike's), timing between the firing marks, air pods with stock exhaust, carbs have been separated and cleaned 3 times or so using an ultrasound tank, rejetted to 142.5 main, 45 pilot, idles really well, however an occasional pop coming from the RH carb... valve clearances set per Mike's.

Electric start (currently) does not work, but still tried a compression test by kicking: about 135 -140 LH and 150 RH. Also tried a leakdown test (using a Harbor Freight unit- instructions not quite clear) and LH side was about 10% ? , whereas RH was 20% ? - the biggie though, was that I could hear air expelling through the RH exhaust.

BTW, I'm very confident about finding TDC for adjusting valves and doing the leakdown test.

This bike has not been ridden hardly any in many years, by the prev owner, nor me, as I'm trying to get it to the point of being rideable/reliable.

Any idea? Thanks!
 
All this is a semi educated guess. Depending the condition of the valves and their seats, a lapping in of the valves to a full valve job is in order. Perhaps a slightly bent valve on the right side? A free-er flowing exhaust will help with power.
 
Azman- I guess that's something I need to do: to tear into the engine and check the valves, pistons and rings.

Grinder- I'm very mechanically inclined, but I've not much experience in dealing with timing... never had to. I understand the basics though. Yes, the timing 'mark' moves when I rev the engine. With a timing light, the line on the rotor 'moves' toward the front of the bike--clockwise-- as I rev it. At an idle, it strobes perfectly between the firing marks.

The PO had this bike sitting in an out-building for many years, unridden. There are some minor oil leaks as to be expected, so I knew I needed to open up the top end for new gaskets, seals, etc.

I guess it's either a carb situation or a compression/top end thing, right? And btw, the charging system is spot-on with the PMA swap and Pamco ign. Love it!!!
 
Your motor can't be in that bad a shape with those compression readings. Maybe it is a carb/jetting thing. What do your plugs look like? Some types of pod filters don't work well with the xs carbs...just a thought. Maybe those 142.5's are too big. Thats 4 sizes up from stock.
 
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That's what I thought about the compression readings... that they weren't that bad. But the hissing coming thru the RH exhaust when attempting the leakdown test did concern me. The pods I'm using came from Mike's. I have a pair of 140 main jets I can try as well. I thought about buying new carbs at some point as the originals are a little restrictive from what I've read, but the budget doesn't permit that yet after the PMA conversion.

Riding the bike today, it seemed like I could have the throttle wide open in fourth gear(for example) and it would never any faster to the point I needed to shift into 5th. Also, today I had the instrument cluster off, so I don't know the tach, or the speed. It just seemed "tapped out".
 
Hello.

I agree.....you may have a bit large jetting setup. Both main and pilot. But if it idles fine but don´t quiet have the "punch" I would start with the mains.

Have you checked your diaphragms in the carbs?? Small holes will interupt the lifting mechanism and you´ll never go full throttle.
Small holes can be fixed (at least for a moment) with permatex etc.

/BigBoreSwede
 
BigBore- yes, I have inspected the diaphrams previously, and no pin holes. But perhaps will check them again. Thanks for the tip as well on the jetting. I will drop the mains down to the 140's I have, and perhaps order up some smaller ones to see what happens.

Just a thought: I have not yet investigated thoroughly a potential blockage in the original exhaust... but it does seem as if they are expelling gasses?!..
 
you can do a quick diaphragm test by lifting them to the top of their stroke manually with your finger and covering the oblong hole at the top of the carb throat. If they have a puncture they will drop to the bottom instantly or rather quickly. If they are good it will take much longer. Mine take about 20-25 seconds to fall
I switched my carbs on my '80 over to a pair of 1976 38's ...the difference in speed and power was dramatic......no comparison !!! Mine was a dog with 34's
 
Hi- thought I would close out this thread. My bike now runs like a scalded dog! ;-) And this is the first time it has done so since I've owned it.

The cause for the problem: apparently the RH exhaust valve was badly out of adjustment and was not closing fully at TDC. So basically it was running on 1 cylinder. I don't know how I missed this one the first time around; so it pays to DOUBLE-CHECK everything!

Thanks for all the help!
 
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