sluggish 550

[mickwinf]

z1100r i agree, if you want a job doing.....

[z1100r]

 Get yourself a nice evening with an early start and get the head off again. Turn it upside down and pour petrol into the combustion chambers, the level will go down fairly quick on the bad ones and fuel will be in the inlet or exhaust tracts of the dodgy valves. 50psi is awful and definately signifies a major problem, I'm not going to speculate what the problem is anymore, firstly you need to satisfy yourself that the base engine is sound.

 Personally I would get all the valves out and roll them on something flat - surface plate,  kitchen worktop. Once satisfied they were al straight I would put them back in 1 at a time turning them and watching the head for wobble. Then give them  a light lapping in with paste just until i could  see complete grey rings on valve and seat. I would then be happy with the head.

 So moving on, this previous engine builder bloke sounds like he aint got a clue. I would definately at this stage whip off the barrel and make sure I had a full complement of rings and that their end gaps were roughly correct.

Its upto you how far you go but I think you need to get certain things straight like...RIGHT THE BASIC BLOODY ENGINE IS NOW OK.......!!!! Thats the bores the pistons, the rings , the valves, the head gasket, the cam timing.

[mickwinf]

well... good news and bad, i had a spare hour this am so rechecked the compressions, i had not screwed the tester in properly!! now all 4 cyls are showing  140-150 psi.hmm take rocker cover off and check cam timing,it is spot on.So i am sure basic engine is ok. plan now is to re-assemble and check and recheck clearances clean and check carbs.I am thinking which jets would be operating at 5000 rpm, could it be wrong size main jet or needles set wrong?? will keep trying!

[z1100r]

 well if your happy thats good. To get the lack of revs/power that your getting something has to be not working, not be just out of tune. You've swapped too much stuff for 2 sets of everything to be that wrong and have the same thing wrong it. I'm lost, willing you to find the problem quickly.

[mickwinf]

i am stumped also,but i checked pistons etc when i replaced valve so am sure its not a big mechanical problem, but what the hell is it?!!

[K2-K6]

Well that is good news that the motor seems ok.

At that revs and with throttle wide open it's mostly pure main jet running as I understand it with the height of the needle controlling when it gets to max flow as you open the slides more, i.e. if you raise the needles then it gets to max flow a little earlier but doesn't increase the total. If you raised the needles (and this was the fault) you'd expect to see some increase in the faltering revs, if it gets better then you'd have to consider going up in main jet size and bringing the needles back to the central position.

One thing we haven't gone over is the breathers into the float chambers, if these are blocked at all then it will run lean at high demand as you need free air to get in for the venturi vacuum to draw fuel out at
the correct rate.

[mickwinf]

k2-k6 this is one thing i had not considered where are the breathers?

[z1100r]

 You are setting the carbs up to the right manual aren't you...not the Haynes manual with the 500 carbs in.

http://data.sohc4.net/SM500/HSM500550_16.pdf

[mickwinf]

well guys i have found the problem and sorted it!! Believe it or not all it was was a float needle! the little sprung rod that contacts the float was stuck in place on no 2 cyl, all that trouble for that!! now it revs like a good un, thanks for help everyone.

[K2-K6]

Sometimes it's something small like that that's missed, it just shows when discussing jetting etc how such an insignificant looking device can have a huge effect.

Good you found it though, should get some decent time out on it during the summer now.

[z1100r]

I'm glad its sorted but still a little dubious that thats what was causing it to only rev to 5000rpm and be as sluggish as you say. I would of expected fuel to be leaking out all over the place and the plug on that cylinder to at least have been very black if the problem was that power sapping.

[K2-K6]

I think what you're saying is that the needle valve was stuck closed, is that correct? if so then that cylinder would not have been running at all in that case.

If so you could have found it when you started it by putting your hand or a wet rag (before it got too hot) onto each header pipe as that tells you if one isn't firing.

[mickwinf]

yes k2-k6 i think it was sticking shut.thats why it felt like it was running on three cyls,exhaust didnt get as hot.Iam sure this was the problem all along,will go for a blast at weekend.

[K2-K6]

Hope it goes well anyway as it's nice to get a decent runout on a bike.

The question you made about breathers, they are just the tubes that come ot of the bottom af the carbs and dangle down the back of the engine. They obviously direct fuel away from the motor if the float sticks so neat petrol just goes to the floor but they also keep the pressure equal to normal so that the jetting is not unduly affected as the main jet demand rises during max throttle demand so that the carbs work as designed (obviously not the case here but we were cluthching at straws to help out).