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150 is probably close to stock new. 120 is low and needs to be looked at. Could be a valve too tight, could be a leaky head gasket, which might also explain the white smoke.
The bang is probably coming from the cylinder that is trying to fire. That might usually be a lack of gas getting to it, or a plugged air filter. First I would check for fuel flow to the cylinder that is not warming up.
My 41 Ford tractor pumps out 110 pounds, which is about 7.5 to compression. Old motors like that will just run with 90 pounds. Engines need a few horsepower, just to keep running.
140 and up for most modern bikes seems reasonable. 120 is too low, and needs fixing IMO.
UK
 

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Discussion Starter #42
150 is probably close to stock new. 120 is low and needs to be looked at. Could be a valve too tight, could be a leaky head gasket, which might also explain the white smoke.
The bang is probably coming from the cylinder that is trying to fire. That might usually be a lack of gas getting to it, or a plugged air filter. First I would check for fuel flow to the cylinder that is not warming up.
My 41 Ford tractor pumps out 110 pounds, which is about 7.5 to compression. Old motors like that will just run with 90 pounds. Engines need a few horsepower, just to keep running.
140 and up for most modern bikes seems reasonable. 120 is too low, and needs fixing IMO.
UK
okay thanks man. Big help. I notice my throttle cable was frayed and pulling out so I got another from Ebay itll be here in a month . I'll get back to you
 

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I see where you cleaned out ONE carb in that thread. Did you do the other? How did you clean it? Just popping the bowl off and spraying around with cleaner isn't enough. This bike has been sitting long enough they need pulled out and completely torn down to be cleaned properly.

I lucked out with mine (I have the same bike) and haven't had to do that yet; but I have for several others. Any carbed bike that's been sitting for more than a year I basically just automatically tear the carbs down.

The smoke is probably just some grease/dirt/bug burning off. Give it a bit of a wash and see if it doesn't get better.

I've had excellent luck with Berryman's Chem Dip to really get them good. Pull the carbs out, disassemble and put all the metal bits (jets too) in overnight. Rinse with water the next morning and reassemble. Preferably with new bowl gaskets and other rubber bits (Should be able to reuse the diaphragm as long as its not torn). Afterward you should be able to see daylight through the jets; and it should be a nearly perfectly round hole. Not just a pinprick either. If there is still some blockage I've used a bit of copper "thread" by stripping the end of a smaller gauge speaker wire (like 16/18) and poking it through. The copper is soft and thin enough to not hurt the brass in the jet and usually stiff enough to break loose whatever crud is in there. Usually it will be the idle/low speed jet (smaller one(s)) that would need that treatment.

These bikes also have an automatic compression release when starting, so make sure you find out for sure how to check compression before trusting a dial reading.
 

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Can't be any worse (and doesn't look to be) than the 4-carb rack setup on the 80s honda Magna. Of which I had out 3 more times that I wanted to.... More cables but more straightforward access. And can be done one at a time.

Honestly doesn't matter. It needs done before doing anything else. The compression numbers aren't great if they're accurate but it should at least fire up and rev reasonably.
 

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Ace Tuner
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Can't be any worse (and doesn't look to be) than the 4-carb rack setup on the 80s honda Magna.
I don't know... I've done both.
The phrase "what genus engineered this" comes to mind when dealing with two totally different carburetors, not even close to each other, operated by a fist full of cables that are mounted in delicate brackets, and all for that Special Look.
My opinion may be biased toward serviceability, so there is that.

S F
 
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