Rough running at low revs, No.2 exhaust downpipe not as hot.

Kozak · Derestricted Danger Joined: 16 May 2013 Karma :

As in the title been rough running at start up and low revs as if only running on 3, but once revs up higher beyond 5,000 seems to improve, plenty of power and cruises no problem 70+. I was convinced the valve clearances would be way out on No 2 but no, all still in spec. Pulled the cap off and with a spare spark plug fitted there are plenty of sparks getting through. The No2. sparkplug looks similar tan coloured like the rest.

What to check next? - I just stripped and cleaned the carbs this last winter and don't want to do that again. Should I check if carbs are out of balance? Would that explain having one cylinder No2 not getting enough fuel/air getting through. Or should I check the fuel level in each carb? Suggestions welcomed.

1987 Kawa GPz550 91,400 miles. Regularly serviced.

MCN · Super Spammer Joined: 22 Jul 2015 Karma :

If electrics ar eall good then carb balance is next thing. If out as much as you say then the gauges will show what's what.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

jaffa90 · World Chat Champion Joined: 06 Apr 2016 Karma :

Sounds like No2 pilot jet is blocked.

temeluchus · World Chat Champion Joined: 01 Oct 2008 Karma :

blocked pilot jet, stuck float, float needle stuck, carbs wildly out of sync, idle mixture screw not set correctly.
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Some shite cruiser. Now with guns and FREEDOM!

mentalboy · World Chat Champion Joined: 05 May 2012 Karma :

andym · World Chat Champion Joined: 16 Nov 2010 Karma :

I had the same problem on the CBR, when I connected up the (homemade) manometer and started the bike all the 2 stroke oil was instantly sucked up by by the no. 4 carb.

If the GPZ 500 is anything like the 750, it should be a simple enough job to balance them.

Kozak · Derestricted Danger Joined: 16 May 2013 Karma :

Just removed the carbs - taken out the battery overflow tube that sits between the battery and rear of airbox, removed the 2 bolts each side holding the air box in the frame which allows the box to move back a little and came off without too much trouble - found that the rubber flange connecting carbs to the engine was loose on No 2 - ? don't know if that was causing the problem (except an air/vacume leak I thought should make the mixture lean and run hot not cold?) - also remembered that I have some spare carbs and found 3 lots that look clean so will swap with one of these after a quick check and clean this one at my leisure.

Kozak · Derestricted Danger Joined: 16 May 2013 Karma :

Sorted (for now) Thumbs Up

Combination of problems - the carb flange between engine and carbs was loose on No 2. Stripped and cleaned No 2 carb - the pilot jet was clean. Checked fuel level ans No 2 was too low, 11mm instead of 7mm like the rest so adjusted the float, and when all back on balanced the carbs and No 2 was way off, took almost a whole turn of the screw to balance. Short test run and runing smoother than ever, and No 2 pipe as hot as the rest.